Fatigue performance of thermal spray coatings on carbon steel: a review

Chia sẻ: Nguyễn Thảo | Ngày: | Loại File: PDF | Số trang:16

Thêm vào BST

Báo xấu

18
lượt xem 1
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

This paper contributes to a review of the research of the fatigue behaviour of thermal spray coatings on carbon steel. Previous studies provide the experimental characterization of the fatigue resistance of coated carbon steel.

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Fatigue performance of thermal spray coatings on carbon steel: a review

International Journal of Mechanical Engineering and Technology (IJMET) Volume 10, Issue 03, March 2019, pp. 1285–1300, Article ID: IJMET_10_03_131 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=10&IType=3 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed FATIGUE PERFORMANCE OF THERMAL SPRAY COATINGS ON CARBON STEEL: A REVIEW M. A. M. Halmi Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Johor, Malaysia M. A. Harimon Faculty of Mechanical and Manufacturing Engineering, Centre for Technology Oil & Gas, Teaching Factory, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Johor, Malaysia L. Mohd Tobi Centre for Technology Oil & Gas, Teaching Factory, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Johor, Malaysia M. F. Mahmod Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Johor, Malaysia ABSTRACT This paper contributes to a review of the research of the fatigue behaviour of thermal spray coatings on carbon steel. Previous studies provide the experimental characterization of the fatigue resistance of coated carbon steel. Different coating powders were deposited to a different type of carbon steels. Also, S-N curves were drawn from axial- and rotating bending fatigue test to determine the fatigue strength or fatigue limit of the samples. Thermal spray coatings showed great improvement to the work hardening effect but worsen the fatigue life due to the inclusion of oxide and pores, the presence of stress concentrators, and high microcrack density. Moreover, the effects of the surrounding environment have also resulted in pros and cons towards the fatigue strength. An improvement, however, can be done with the shot peening treatment, which significantly increases the compressive residual stress at interfaces of coating/substrate. The high compressive residual stress could delay the crack nucleation, thus increasing the fatigue life of the coated part. Key words: Carbon steel, Coating, Fatigue, Thermal spray http://www.iaeme.com/IJMET/index.asp 1285 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review Cite this Article: M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod, Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review, International Journal of Mechanical Engineering and Technology 10(3), 2019, pp. 1285–1300. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=10&IType=3 1. INTRODUCTION Application of thin film of functional material to an object (usually referred to as the substrate) is known as a coating process. The functional material may be solid, liquid or gas; organic or inorganic; metallic or non-metallic. In many cases, coatings are applied to improve the surface properties of the substrate [1]. Composite coating innovation primarily has been created to satisfy the mechanical requests for coatings whose details surpass the capabilities of customary coating innovations, which are able of working in extreme environments and within the confront of challenges postured by temperature, corrosion, abrasion, fatigue, friction, and erosion [2]–[4]. Nowadays thermal spray coatings have been broadly applied to improve functions such as wear resistance, corrosion resistance, bioactivity and dielectric properties to light metals. The characteristics of the deposition process, including splat cooling and successive stacking of splats, create coatings of unique microstructure which are different from conventional materials [5]. The common processes of thermal spray are arc spray, flame spray, high-velocity oxy-fuel spray, and plasma spray. High-velocity oxygen fuel (HVOF) spraying is widely utilized in groups of thermal spraying and it has been extensively used for tungsten carbide (WC) feedstock powder in order to obtain good bond strength, higher density, and less decarburization. This is because of the lower temperature and higher velocities experienced by the powder particles as compared to other thermal spray technique like vacuum/low-pressure plasma (VPS/LPPS), and atmospheric plasma (APS) with a higher temperature around with lower velocities [6]–[11]. However, the effect of the coating on the fatigue performance influenced the acceptance of thermal spray coatings in many applications. When a structure is loaded, a crack will be nucleated (crack nucleation) on a microscopically small scale, this crack then grows (crack growth), then finally complete failure of the specimen [12]–[17]. The factors causing fatigue failure can be divided into basic factors and additional factors. For the basic factors are a high maximum tensile stress value, a large amount of variation or fluctuation in the applied stress, and a sufficiently large number of cycles of the applied stress. While for the additional factors are stress concentration (geometry), corrosion (environment), temperature (environment), overload (loading), metallurgical structure (material), residual stress (manufacturing) and combined stress (loading). One of the factors that influence the fatigue life of thermal spray-coated components is the residual stress in the coating. It was found that there is a direct relation between the residual stress in the coating and the fatigue life of the coated part. Fatigue life can be changed by a factor of ten due to the level of compressive residual stress in the coating [18]–[21]. On the other hand, surface defects (such as roughness or scratches and notches or shoulders), corrosion and galling (due to rubbing of mating surfaces) may reduce the fatigue strength of the coated part [12]. This work focuses on the main results available in the literature on the fatigue behaviour of thermally sprayed carbon steel. In actual fact, the current development of coating technique rises significantly to fulfil industrial demands in the best possible ways. Also, the possibility to withstand in extreme environments and in the challenges posed by fatigue, temperature, corrosion and abrasive is expected to become more and more dominant. From these perspectives, the utilization of thermal spray coating having a better performance than those of http://www.iaeme.com/IJMET/index.asp 1286 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod traditional coating would be recommended for a number of applications. Therefore, to achieve significant results, numbers of research studies would be necessary. 2. THERMAL SPRAY COATINGS PREPARATION 2.1. Material selection Material selection is very significant due to their benefits and limitations. In this paper, carbon steel will be reviewed as a fixed substrate with different coating powder characteristics functioned to protect the metal substrate. Every coating powder has its own benefits toward improving the substrate's characteristics. In [22], [23] the coating powder comprised of cobalt element, which acts to provide a ductile metallic binder for hard carbide particles. Besides that, cobalt can also help the coating powder to achieve a high density of deposition as its wetting or capillary action during liquid phase sintering. In the study [9], [24]–[30], the coating powder comprised of nickel element, which acts to improve the corrosion and oxidation resistance of the substrate. However, nickel does not wet the WC particles as effectively as cobalt, resulting in low strength, hardness and wear resistance. 2.2. Substrate and specimen preparation For material preparation, metal substrate was first grounded and polished using SiC sandpaper with 60 to 200 grit range [22], [23], [27], [30]. Then the substrate will be quenched from 815 ℃ - 845 ℃ for 45 minutes and cooled in oil (20 ℃). After that, the substrate was tempered in the range of 220 ℃ to 260 ℃ for 2 hours and then it will be cooled in the air [22]–[25], [28]. Fatigue specimens were then machined and sectioned according to the ASTM-E466 [9], [22]– [30]. To reduce residual stress induced by machining, the specimen underwent stress relieving heat treatment at 190 ℃ for four hours [22]–[25]. Before coating deposition, the substrate underwent a grit blasting process, which main purposed to generates surface roughness ensuring mechanical anchoring between coating and substrate surface. Grit blasting process can be inputted with different alumina size, pressure and distance, which produce variable significant surface roughness. Also, this process will help to remove any contaminants on the surface of the substrate before coating deposition taking place [26], [27]. Optionally, the surface roughness of the substrate will be kept constant to prevent any cause on the fatigue strength due to low/high bonding between substrate and coating. 2.3. Coating deposition Nowadays there is plenty type of coating guns/ machines used to thermally spray the coating powder to the substrate. For instance, Jet Kote thermal spray system [22], [23], JP-5000 HP/HVOF spray system [22], [23], JP-5000 TAFA 1310 VM Technologies [24], [25], [28], and Praxair-TAFA JP-5000 gun [26], [27]. Furthermore, the coating parameter such as powder feeding rate, the distance of the spray, number of coating's layer, oxygen pressure, fuel pressure, air flow, fuel flux, oxygen flux, etc. play important roles for the result of coating deposition. The change of the parameter could possibly affect the properties of the specimens. On the other hand, the coating thickness and surface roughness of the specimens must be kept constant. The coating thickness was kept constant at 100-150 µm in [22], [23], [28], and at 170 µm in [24]. In [22], [23], surface roughness of the specimens was 4 µm, and 6.4 µm in [26]. 2.4. Fatigue test http://www.iaeme.com/IJMET/index.asp 1287 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review Fatigue tests can be conducted under different types such as axial fatigue test, rotating bending tests, etc. Figure 1 (a) and (b) show examples of fatigue specimens that have been used in fatigue testing. In [22]–[25], [27], [28] axial fatigue test was conducted with a sinusoidal load type and a load ratio of R = 0.1 while in [22], [23], [26] rotating bending test was conducted with a sinusoidal load type and a load ratio of R = -1.0. The load frequency used was varied in the range of 10 - 50 Hz [22]–[28]. The fatigue test underwent commonly under room temperature but it can be varied depending on the aim of the test. The result of the test will produce a set number of cycles from each different variables in the same stress. As a result of that, an S-N curve was produced which provided the fatigue strength data at 106 to 107 load cycles. After fatigue tests, fractographic analysis of the fractured surface of the specimens was taken place using a scanning electron microscope (SEM) machine. The aims of the fractographic analysis were to characterize the failure mechanisms that took place during fatigue tests. In particular, they were to identify the fatigue crack nucleation sites and determine the mechanisms of crack propagation. (a) (b) Figure 1 The specimen of fatigue tests, (a) Rotating bending fatigue testing specimen, and (b) Axial fatigue testing specimen [23]. 3. FATIGUE BEHAVIOUR OF THERMALLY SPRAYED CARBON STEEL A thorough collection of recent experimental results for fatigue tests on coated samples is outlined in this section. These works have been focused on fatigue behaviour of thermal spraying coating on carbon steel. The main results are summarized in Table 1, 2, 3, 4, 5 and 6. 3.1. Fatigue behaviour of WC-Co thermal spray coating Souza, Nascimento, Voorwald and Pigation [22] studied the effect of WC-17Co thermal spray coating by HVOF and hard chrome electroplating on the fatigue life and abrasive wear resistance of AISI 4340 high strength steel. Analysis of the experiment showed that both coating process (HVOF and electroplating) decreased the fatigue life of AISI 4340 steel. However, a significant fall in fatigue strength associated with the steel coated by chromium electroplating compared to the WC-Co thermal spray. The reasons are due to the high tensile residual stresses, high microcrack density and strong adhesion coating/substrate interface, which allows the passage of fatigue cracks from coating to the substrate. Table 1 Some results from fatigue tests of WC-Co thermal spray coatings on carbon steel. http://www.iaeme.com/IJMET/index.asp 1288 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod Base Coating Test condition Test Stress ratio Fatigue strength Ref. material temperature AISI 4340 Uncoated Rotating RT R = -1.0 ≈ 650 MPa at 107 [22] bending test cycles AISI 4340 HVOF WC- Rotating RT R = -1.0 ≈ 550 MPa at 107 [22] 17Co bending test cycles AISI 4340 Uncoated Axial test RT R = 0.1 ≈ 825 MPa at 107 [22] cycles AISI 4340 HVOF WC- Axial test RT R = 0.1 ≈ 600 MPa at 107 [22] 17Co cycles AISI 4340 Uncoated Rotating RT R = -1.0 ≈ 615 MPa at 107 [23] bending test cycles AISI 4340 HVOF Rotating RT R = -1.0 ≈ 531 MPa at 107 [23] Treated WC- bending test cycles 12Co AISI 4340 HVOF WC- Rotating RT R = -1.0 ≈ 531 MPa at 107 [23] 12Co bending test cycles AISI 4340 Uncoated Axial test RT R = 0.1 ≈ 850 MPa at 107 [23] cycles AISI 4340 HVOF WC- Axial test RT R = 0.1 ≈ 750 MPa at 107 [23] 12Co cycles (a) (b) Figure 2 (a) Residual internal stress distribution for WC-17Co by HP/HVOF TAFA thermal spray coating, and (b) Residual internal stress distribution for WC- 17Co by HVOF Jet Kote thermal spray coating [22]. Moreover, there is no significant contrast in fatigue strength of AISI 4340 steel covered by HVOF TAFA and Jet Kote processes were observed, despite the spraying parameters are different, however, the coating thickness was kept constant for both tools. Figure 2 (a) and (b) demonstrate the residual internal stresses profile from WC-17Co thermal spray covered by the HP/HVOF TAFA and the Jet Kote. As indicated by the Figure 2 (a) and (b), the residual stress change form tensile near coating surface to compressive stress throughout the coating thickness and the maximum compressive residual stress was seen at the interface of coating-substrate. The residual stress then changes from compressive to tensile stress corresponding to the increase of depth inside base material. On the other hand, the influence of tungsten carbide thermal spray coating by HP/HVOF and hard Cr electroplating on fatigue behaviour, abrasive behaviour and corrosion behaviour of AISI 4340 high strength steel were studied [23]. For the tungsten carbide inorganic compound coating, WC-12Co powder was deposited on the substrate using the HVOF spray method at a http://www.iaeme.com/IJMET/index.asp 1289 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review thickness of 100 µm. The commonly allowed roughness of the specimens was Ra ≈ 4 µm within the as-deposited condition. The result of the tests produced S-N curves, which provided the fatigue strength data at 107 load cycles. The S-N curves show, that the decrease of the fatigue strength of AISI 4340 steel due to the effect of tungsten carbide thermal spray coating applied by HP/HVOF process and hard chromium electroplating. The influence is more outstanding in high cycle fatigue tests than in low cycle fatigue tests. The decrease of the fatigue strength of AISI 4340 steel influenced by the tungsten carbide specimens was analyzed. This can be due to the high density of pores and oxide inclusions in the coating that commonly form during the thermal spray process, despite the compressive residual stresses induced by the process. This inclusion in coating subsurface may be the main factor of crack nucleation. Contrarily, a small improvement in rotating fatigue strength was obtained for tungsten carbide thermal spray coated specimens blasted with aluminium oxide compared to samples without superficial treatment. This is due to the induction of the compressive residual stresses by the blasting, besides the particle impact would also cause this induction. Similarly, the negative influence of coating on the rotating bending strength has the same tendency towards the axial fatigue strength. This performance can also be described by high tensile residual internal stresses on the coating surface, oxide inclusions, pores, and microcracks inherent from each process. Microcracks form when the high tensile residual internal stresses exceed the cohesive strength of the tungsten carbide deposits and affect the fatigue behaviour of a coated part. Therefore, microcrack density arises as a relief of the tensile residual internal stresses, which increase when the coating thickness increases. It showed that the microcrack density changes along the thickness, being higher at the core and lower at the surface of the coating and in the substrate/coating interface due to the balance between the residual stresses. Therefore, in general, the higher the microcrack density, the higher the tensile residual internal stresses and/or their relief. 3.2. Fatigue behaviour of WC-Ni thermal spray coating Table 2 Some results from fatigue tests of WC-Ni thermal spray coatings on carbon steel. Base Coating Test Test Stress Fatigue Ref material condition temperature ratio strength AISI 4340 Uncoated Axial test RT R = 0.1 935 MPa at [24] steel 106 cycles AISI 4340 Uncoated Axial test RT R = 0.1 1100 MPa at [24] steel (shot 106 cycles peened) AISI 4340 HVOF WC- Axial test RT R = 0.1 750 MPa at [24] steel 10Ni 106 cycles AISI 4340 HVOF WC- Axial test RT R = 0.1 850 MPa at [24] steel (shot 10Ni 106 cycles peened) AISI 4340 HVOF WC- Axial test RT R = -1.0 750 MPa at [25] steel 10Ni 106 cycles AISI 4340 HVOF WC- Axial test RT R = -1.0 850 MPa at [25] steel (shot 10Ni 106 cycles peened) The evaluation of WC-10Ni thermal spraying coating by HVOF on the fatigue and corrosion AISI 4340 steel was studied [24]. The aim of this research was to evaluate the effects of shot peening on the axial fatigue strength of high strength steel HVOF thermal spray coated. The coating investigated was WC-10Ni, thermally sprayed on AISI 4340 steel substrate using HVOF. The spraying parameters used for WC-10Ni are spray distance of 150-300 mm, density http://www.iaeme.com/IJMET/index.asp 1290 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod of 4.8 g/cm3, deposition velocity of 900 m/s, and deposition rate of 50 μm/min, according to ASTM B 212. Before the spraying process was taken place, material machined into dimensioned specimen, heat treated, shot peened, and grit blasting with aluminium oxide were conducted subsequently. The shot peening parameters used were the intensity of 0.006 - 0.010 A, S230 steel shot, output flux of 3 kg, velocity of 250 mm/min, a shot’s distance of 200 mm, and rotation of 30 rpm 120% covering. Vickers diamond indenter was used to determine the coating microhardness system on the top surface of the polished cross-section. The results indicated lower values near to the coating surface, increasing until a maximum close to the interface, decreasing again at the interface coating substrate. The possibility for such cause is the fact that the thermal spray coated specimens were blasted to enhance adhesion, give rise to such work hardening effects. The residual stress field induced by the thermal spray coatings was determined with the X-ray diffraction method. Layers of specimens were removed by electrolytic polishing with a non- acid solution, in order to obtain the stress distribution by depth. For AISI 4340 steel, tensile residual stresses were obtained at surface and 0.10 mm depth. On the specimen surface for shot peened AISI 4340 steel, high compressive residual stresses were observed (– 630 MPa resulted in 0.10 mm surface measurements). On the other hand, a reduction of tensile residual stresses on base metal specimen surface due to the HVOF thermal spray process was observed. For shot peened AISI 4340 steel WC-10Ni thermal spray coated, the through thickness residual stresses changed from compressive to tensile inside coating, with maximum compressive stresses at 0.02 mm depth. This can be concluded that shot penning and HVOF thermal sprayed, due to the impact of coating powder onto the substrate, decreased the tensile residual stress, at the same time increased the compressive residual stress. From the drawn S-N curve, an increment of fatigue limit for the shot peening base metal from 935 MPa to 1100 MPa. Similarly to the coated specimens, the fatigue limit of the shot peening WC-10Ni HVOF coated specimens (850 MPa) is higher than the normal WC-10Ni HVOF coated specimens (750 MPa). This point out that the compressive residual stress field delayed or arrested the fatigue process. Conversely, a drop of axial fatigue strength and fatigue limit of WC-10Ni HVOF coated specimens, from 935 MPa to 750 MPa, due to the presence of oxide inclusions and pores into the coating. Similarly, the case is equivalent to the comparisons of shot peening WC-10Ni HVOF coated specimens (850 MPa) and non-shot-peening uncoated specimens (935 MPa). Despite the lower tensile residual stress value of shot peening and coating, the presence of oxide inclusions and pores into the coating overcome the reduction factor of the fatigue strength of the metal. From the results, the fatigue strength flow of the specimens can be shown as; shot-peened uncoated specimen > uncoated specimen > shot- peened coated specimen > coated specimen. Junior et al. [25] studied the evaluation of WC-10Ni thermal spray coating with shot peening on the fatigue strength of AISI 4340 steel. The base metal was machined from hot- rolled, quenched and tempered bars, according to ASTM E466. Using an HVOF torch, model JP-5000, HOBART-TAFA Technologies, coatings were deposited. The spraying parameter was kept constant for all of the specimens. The shot peening process was the manipulated variable, which the parameter was constant. The process was performed before blasting with aluminium oxide, according to standard SAE-AMS-S-13165. The axial fatigue strength of AISI 4340 steel WC-10Ni thermal spray coated specimens increased due to the shot peening process. The fatigue limit also increased by 13.3% from 750 MPa to 850 MPa. Shot peening affected the delay of the crack nucleation and propagation. Compressive residual stresses at the interface between the coating and the substrate were effective in delaying the nucleation and growth of fatigue crack. http://www.iaeme.com/IJMET/index.asp 1291 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review On the other hand, Fig. 3 (a) and (b) shows the fracture surfaces from axial fatigue specimens WC-10Ni thermal spray coated. It is possible to observe the coating homogeneity, strong interface substrate/coating and microcracks density distributed along thickness in a radial shape, and show fatigue cracks initiation and propagation at interface coating /substrate. (a) (b) Figure 3 Fracture surface of axial fatigue specimen coated by WC-10Ni, with magnification of (a) 200X, and (b) 500X [25]. In summary, thermal spray coating decreases the fatigue strength of the base metal due to the resulted microcracks during deposition. Eventually, the shot-peened helped recovered the fatigue strength by induced the compressive residual stress at the coating/substrate interface. As a conclusion, the increase in microhardness near the interface WC-10Ni coating/AISI 4340 steel substrate were related to these work-hardening effects by shot peening treatment, thus increasing the fatigue strength of the coated material. 3.3. Fatigue behaviour of Colomony 88 thermal spray coating Table 3 Some results from fatigue tests of Colomonoy 88 thermal spray coatings on carbon steel. Base Coating Test Test Stress Fatigue Ref material condition temperature ratio strength SAE 4340 Uncoated Rotating RT R = -1.0 ≈ 600 MPa at [31] bending 106 cycles test SAE 4340 HVOF 50% Rotating RT R = -1.0 ≈ 410 MPa at [31] WC–10Co–4Cr bending 106 cycles + 50% test NiWCrSiFeB alloy (Colmonoy 88) SAE 1045 Uncoated Axial test RT R = 0.1 ≈ 471 MPa at [27] steel 106 cycles (polished) SAE 1045 Uncoated Axial test RT R = 0.1 ≈ 380 MPa at [27] steel (grit 106 cycles blasted) SAE 1045 HVOF Axial test RT R = 0.1 ≈ 391 MPa at [27] steel (grit NiWCrSiFeB 106 cycles blasted) alloy (Colmonoy 88) http://www.iaeme.com/IJMET/index.asp 1292 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod Barbera-Sosa et al. investigated the fatigue performance of an SAE 4340 structural steel coated with a WC-10Co-4Cr/Colmonoy 88 deposit by the HVOF method [31]. The existence of stress concentrators at the substrate-coating interface and the properties of the coating decreased the fatigue strength of the coated substrate (≈ 30%), in comparison with the uncoated substrate. Also, the fatigue limit of the coated substrate was found at ≈ 390 MPa, which is 32% lower than the uncoated substrate (≈ 575 MPa). Indeed, the analysis of fracture surface shows that nucleation of fatigue cracks could occur at both the substrate-coating interface and the outer surface of the coating at the same time. The nucleation of the cracks would be related to the irregularities that exist at the interface and the existence of alumina particles, which act as stress concentrators. Moreover, the presence of craters and the high roughness of the coating would also be the cause of the crack nucleation. Nonetheless, crack propagation through the coating thickness occurs preferentially along the particle boundaries that comprise the coating, specifically through the Ni-rich particles. Besides, Puchi-Cabrera et al. [27] studied the fatigue behaviour of an SAE 1045 steel coated with Colmonoy 88 alloy deposited by HVOF. The experimental result shows that both coating process and grit blasted method were not changing the substrate’s tensile properties, instead of lowering the substrate’s fatigue strength in the range 10-20%, similar to fatigue limit, which had a reduction of ≈11–13%. Also, analysis from the S-N curve as shown in Fig. 4, showed the S-N curve between ‘grit blasted + uncoated specimen’ and ‘grit blasted + coated specimens’ had no significant difference, however a clear visible difference between the ‘not grit blasted + uncoated specimen’, the ‘grit blasted + uncoated specimen’, and ‘grit blasted and coated specimen’. This can be concluded, that grit blasting treatment do play a big role in the fatigue strength. Figure 4 S-N curves for ‘not grit blasted + uncoated specimen’, ‘grit blasted + uncoated specimen’ and ‘grit blasted and coated specimens’ [27]. The findings from the fractographic analysis [27] can be concluded as:  Crack initiation has been observed occurred both at the substrate-coating interface and free surface of the coating. http://www.iaeme.com/IJMET/index.asp 1293 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review  At the substrate–coating interface, cracks initiate mainly at alumina particles embedded on the substrate (cause high-stress concentration) and sharp notches produced by plastic deformation during grit blasting.  At higher maximum stress applied to the material, the cracks formed at the free surface of the coating can traverse the entire coating thickness and bifurcate along the interface, leading to the delamination of the coating from the substrate. Such cracks can also activate sharp notches on the interface and continue their propagation into the substrate.  The characteristic heterogeneous nature of the coating, especially regarding some of its mechanical properties, such as fracture toughness lead to distinctive tortuous fatigue crack paths which follow those phases where crack propagation is easier. 3.4. Fatigue behaviour of WC-CrC-Ni thermal spray coating In [28], Barbera-Sosa et al. investigated fatigue in AISI 4340 steel thermal spray coating by HVOF for the aeronautic application. Before the coating deposition, the AISI 4340 steel was hardened by heat treatment to 815 ºC for 45 minutes with cooling in oil between 20 and 60 °C, followed by double tempering at 220 °C for two hours with cooling in air. The mechanical properties obtained were: the hardness of 50 – 53 HRc, the yield strength of 1500 MPa and tensile strength of 2000 MPa. Then, the WC-CrC-Ni powder was deposited onto the metal substrate with the model JP 5000, TAFA1310VM Technologies, at a density of 4.8 g/cm3 according to ASTM B-212, with a deposition rate of 900 m/s, and rate of 50 µm per minute. To obtain the S-N curve, axial fatigue test was conducted. Specimens were divided into few groups: a base material without shot peening, a base material with shot peening, coated base material without shot peening and coated base material with shot peening. Experiment’s result shows that generally uncoated AISI 4340 steel is a better fatigue resistance compared to the WC-CrC- Ni HVOF coated AISI 4340 steel. This behaviour is due to the high number of microcracks formed at AISI 4340 steel’s surface during undergoing the HVOF spray process. These microcracks are formed by inclusions, both oxides and particulates not rendered, and porosity also affect the initiation and propagation of these microcracks. Besides that, the microhardness test result showed that the substrate has a lower mechanical strength compared to the coating. Because of that, the crack that usually formed at the interface propagates easily into the substrate. On top of that, the fracture specimens were put under SEM after the fatigue test to analyze the fracture surface. It proved that the crack propagated in the core and interface coating-substrate due to microcracks generated by the process of the thermal spray coating. On the contrary, a shot peening helped in improving the fatigue strength of the uncoated/coated AISI 4340 steel. This is due to the presence of compression residual stresses, delaying crack nucleation. Table 4 Some results from fatigue tests of WC-CrC-Ni thermal spray coatings on carbon steel. Base material Coating Test Test Stress Fatigue strength Ref condition temperature ratio AISI 4340 Uncoated Axial test RT R = 0.1 ≈ 950 MPa at 107 [28] steel cycles AISI 4340 Uncoated Axial test RT R = 0.1 ≈ 1100 MPa at [28] steel (shot- 107 cycles peened) AISI 4340 HVOF WC- Axial test RT R = 0.1 ≈ 800 MPa at 107 [28] steel CrC-Ni cycles AISI 4340 HVOF WC- Axial test RT R = 0.1 ≈ 850 MPa at 107 [28] steel (shot- CrC-Ni cycles peened) http://www.iaeme.com/IJMET/index.asp 1294 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod S235JR carbon HVOF WC- Axial test RT (air) R = 0.053 ≈ 250 MPa at 107 [9] steel CrC-Ni cycles S235JR carbon HVOF WC- Axial test RT (3% NaCl R = 0.053 ≈ 200 MPa at 107 [9] steel CrC-Ni solution) cycles Meanwhile, Murariu, Cernescu, and Periau [9] investigated the effect of saline environment on the fatigue behaviour of HVOF-sprayed WC–CrC–Ni coatings. Nickel-contain powder was recommended because of the high corrosion and wear-resistant properties. Experimentally, 6 loading levels were established for each testing environment, in air and saline water, to obtain the fatigue curves. To achieve the saline environment, a solution with a concentration of 3% NaCl in water was prepared. The tested specimens were mounted on a sealed tank filled with salt water (in this case NaCl water) to perform the tests in a saline environment. Contrarily in an air environment, the tested specimens were tested under a normal condition in the lab with a room temperature kept constant for both tests. As a result, a reduction of about 30% of the fatigue life due to the 3% of the saline environment in comparisons to tests in the air. The main possibility for this reduction is because of the saline environment speedup the crack propagation rate. Such an environment acts as a wedge, opening the imperfection of the coating and advocating crack propagation through coating thickness and eventually resulting in a straight attack of the substrate by the corrosion environment. 3.5. Fatigue behaviour of Y2O3-ZrO2 thermal spray coating Table 5 Results from fatigue tests of Y2O3-ZrO2 thermal spray coatings on carbon steel. Base Coating Test condition Test Stress Fatigue Ref material temperature ratio strength A low-carbon 8% Y2O3-ZrO2, Tension RT R = 0.1 10.4 MPa at [29] steel powder 106 cycles A low-carbon 8% Y2O3-ZrO2, Compression RT R = 0.1 200 MPa at 106 [29] steel powder cycles A low-carbon 8% Y2O3-ZrO2, Compression 800 ℃ R = 0.1 375 MPa at 106 [29] steel powder cycles The fatigue behaviour of a plasma-sprayed 8%Y2O3-ZrO2 thermal barrier coating was studied by Rejda, Socie and Beardsley [29]. In this study, two tests were performed to simulate the thermal barrier coatings for diesel engines development. The first test was a cyclic compression fatigue test at room and high temperature (800 ℃). The different temperature settings were to imitate the loading environment. As a result, shown in Table 5, fatigue strength of coated specimens in 800 ℃ was higher than the coated specimens in room temperature. It was suggested that the deformation behaviour of coating material can influence the fatigue strength related to the changing of temperature. According to [29], the increase in temperature will increase the compressive modulus, where the compressive modulus is a ratio of compressive stress applied to a material compared to the resulting compression. The increase in compressive modulus will reduce the resulting compression, thus reduce the strain range of the coated material during the loading cycle. Therefore, it was proposed that fatigue strength was dependent on strain range related to a different temperature. The second test was the fatigue test in tension and combined tension/compression stress at room temperature. These tests were applied to evaluate the effect of mean stress. Results from SEM observations and fatigue tests showed that the damage accumulated during the tensile and compressive portions of fatigue cycles were independent of each other. To support this hypothesis, Rejda, Socie and Beardsley [29] stated that cracks caused by tensile loading propagate on planes perpendicular to the axis of loading, while cracks caused by compressive loading tended to propagate on planes parallel to the axis of loading. http://www.iaeme.com/IJMET/index.asp 1295 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review 3.6. Fatigue behaviour of Ni-based self-fluxing alloy thermal spray coating Table 6 Results from fatigue tests of Ni-based self-fluxing alloy thermal spray coatings on carbon steel. Base Coating Test Test Stress Fatigue Ref material condition temperature ratio strength Medium Ni-based self- Rotating RT R = -1.0 267 MPa at [30] carbon steel fluxing alloy (1.0 bending 107 cycles mm) test Medium Ni-based self- Rotating RT R = -1.0 318 MPa at [30] carbon steel fluxing alloy (0.5 bending 107 cycles mm) test Medium Ni-based self- Rotating RT R = -1.0 402 MPa at [30] carbon steel fluxing alloy (0.2 bending 107 cycles mm) test In [30], H. Akebono, J. Komotori, and H. Suzuki studied the effect of the coating thickness on the fatigue strength of steel thermally sprayed with Nickel-based self-fluxing alloy. Experimental result in Table 6 proved that coating thickness influence the fatigue properties. The data from Table 6 shows that the thinner the coating, the higher the fatigue strength. Further evaluation was required to analyze the results. Firstly, the fracture surface was observed using the SEM and analysis from the observation was made. It shows that crack nucleation was initiated due to the defects at the coating surface. Contrarily, the crack nucleation was not possible to happen at the substrate-coating interface due to a cleavage surface was found at the fracture specimen. The cleavage fracture at substrate indicates that the adhesive strength between coating and substrate is strong. Fig. 5 shows an S-N graph, which was calculated by using finite element method analysis, including the difference of Young’s Modulus between the substrate and the coating and the difference of coating thickness. From this analysis, it shows that coating thickness influence fatigue properties; the thinner the coating, the higher the fatigue strength. Behaviours of fatigue crack propagation also have been observed. The cracks of fatigue propagated on the coated surface through many defects accordingly. Coating thickness was used to determine the sizes and number of coating defects; the thicker the coating thickness, the greater the defect and number. Hence, the sprayed specimens with thinner coatings showed higher strength of fatigue [30]. http://www.iaeme.com/IJMET/index.asp 1296 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod Figure 5 Result of fatigue strength by finite element analysis method [30]. 3.7. Prediction of fatigue strength In addition, estimates of fatigue strength of coated substrate can be made using the equation of Murakami (Eq. 1) [30], [32]. Three parameters have been used to estimate the fatigue strengths of thermal spray-coated specimens; (i) maximum coating defect size estimated by extreme value statistics, (ii) matrix hardness and (iii) coating defect fraction volume. 1.43(𝐻𝑉+120) 𝜎𝑤 = 1/6 (1) (√𝑎𝑟𝑒𝑎) According to Murakami’s equation, σw is fatigue limit, √𝑎𝑟𝑒𝑎 indicated as maximum defect size to be expected in the coating and HV indicated as the material Vickers hardness. 4. SUMMARY A review of literature findings on the fatigue performance of thermal spray coatings on carbon steel is reported in this paper. The influence factors, which decreased the fatigue strength of carbon steel were observed. The inclusion of oxide and pores, the presence of alumina particles which act as stress concentrators, and high microcrack density, high tensile residual stress were the main factors that contribute to the lower fatigue strength of coated steel. Additional factors such as surrounding temperatures, and corrosion environment, coating thickness also affected the fatigue strength of thermally sprayed carbon steel. Therefore, ways to improve the fatigue strength of carbon steel is by shot peening and grit blasting. In respect of the review presented, the following issues are remarked:  Generally, the thermal spray process decreased the fatigue strength of the carbon steel even though it increases their microhardness ability.  One of the other factors that caused a decrease in fatigue strength is the high porosity and high oxidation content.  Besides that, the presence of residual stress is also one of the factors that can decrease the fatigue strength of the coated carbon steel. This is because a high tensile residual stress at the coating’s surface initiate crack nucleation faster than compressive residual stress.  Others factor that promotes crack nucleation is the existing of microcracks at the carbon steel surface during particle impact of thermal spray process.  Grit blasting, however, increased the fatigue strength of coated carbon steel as the process creates a strong adhesion coating/substrate interface and also induced a high compressive residual stress at the interface. However, the presence of alumina particles (from grit blasting) which embedded on the carbon steel surface can cause crack nucleation due to high-stress concentration.  Shot peening process will increase the fatigue strength due to the increase of compressive residual stress.  A saline environment accelerates crack propagation, resulted a shorter fatigue life.  The higher the surrounding temperature during the loading cycle, the higher the fatigue strength. Related to the changing of temperature, fatigue strength was affected by deformation behaviour of coating material.  The increase of coating thickness results in a lower fatigue strength due increase size, number, and volume fraction of defects on coating surface per unit area. http://www.iaeme.com/IJMET/index.asp 1297 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review ACKNOWLEDGEMENTS The authors acknowledge the financial support by the Ministry of Education Malaysia and Universiti Tun Hussein Onn Malaysia. This research is supported by the TIER 1 Research Grant Scheme (H181). REFERENCES [1] A. Wadnerkar and G. S. Zamre, “Preparation And Analysis of High Temperature Protective Coating,” Int. Res. J. Eng. Technol., vol. 3, no. 2, pp. 456–462, 2016. [2] A. S. H. Makhlouf, “Current and advanced coating technologies for industrial applications,” in Nanocoatings and Ultra-Thin Films: Technologies and Applications, Germany: Woodhead Publishing, 2011, pp. 3–23. [3] A. S. H. Makhlouf, V. Herrera, and E. Muñoz, “Corrosion and protection of the metallic structures in the petroleum industry due to corrosion and the techniques for protection,” in Handbook of Materials Failure Analysis, Elsevier Ltd, 2018, pp. 107–122. [4] A. A. Olajire, “Recent advances on organic coating system technologies for corrosion protection of offshore metallic structures,” J. Mol. Liq., vol. 269, pp. 572–606, 2018. [5] C. J. Li, “Thermal spraying of light alloys,” in Surface Engineering of Light Alloys, China: Woodhead Publishing, 2010, pp. 184–241. [6] J. R. Davis, “Introduction to Thermal Spray Processing,” in Handbook of Thermal Spray Technology, ASM International, 2004, pp. 3–13. [7] N. Espallargas, “Introduction to thermal spray coatings,” in Future Development of Thermal Spray Coatings, Elsevier, 2015, pp. 1–13. [8] X. Liu et al., “Performance evaluation of HVOF sprayed WC-10Co4Cr coatings under slurry erosion,” Surf. Eng., vol. 0, no. 0, pp. 1–10, 2019. [9] A. C. Murariu, A. V. Cernescu, and I. A. Perianu, “The effect of saline environment on the fatigue behaviour of HVOF-sprayed WC–CrC–Ni coatings,” Surf. Eng., vol. 34, no. 10, pp. 755–761, 2018. [10] A. P. Krelling, M. M. de Souza, C. E. da Costa, and J. C. G. Milan, “HVOF-sprayed Coating Over AISI 4140 Steel for Hard Chromium Replacement,” Mater. Res., vol. 21, no. 4, pp. 3– 12, 2018. [11] L. F. S. Vieira, H. J. C. Voorwald, and M. O. H. Cioffi, “Fatigue Performance Of AISI 4340 Steel Ni-Cr-B-Si-Fe HVOF Thermal Spray Coated,” Procedia Eng., vol. 114, pp. 606–612, 2015. [12] A. A. Azeez, “Fatigue Failure and Testing Methods,” HAMK University of Applied Sciences, 2013. [13] R. C. Souza et al., “Fatigue behavior prediction and analysis of shot peened mild carbon steels,” Surf. Coatings Technol., vol. 5, no. 2, pp. 95–100, 2017. http://www.iaeme.com/IJMET/index.asp 1298 editor@iaeme.com
M.A.M. Halmi, M.A. Harimon, A.L. Mohd Tobi, M.F. Mahmod [14] E. Maleki and K. R. Kashyzadeh, “Effects of the hardened nickel coating on the fatigue behavior of CK45 steel: experimental, finite element method, and artificial neural network modeling,” Iran. J. Mater. Sci. Eng., vol. 14, no. 4, pp. 81–99, 2017. [15] A. Vackel and S. Sampath, “Fatigue behavior of thermal sprayed WC-CoCr- steel systems: Role of process and deposition parameters,” Surf. Coatings Technol., vol. 315, pp. 408– 416, 2017. [16] M. Senthil Kumar, S. Ragunathan, and M. Suresh, “Fatigue behavior of Ni-Zn Composite coating on EN8 steel by pulse electroplating,” ARPN J. Eng. Appl. Sci., vol. 11, no. 2, pp. 1376–1383, 2016. [17] S. Guarino, M. Barletta, and A. Afilal, “High Power Diode Laser (HPDL) surface hardening of low carbon steel: Fatigue life improvement analysis,” J. Manuf. Process., vol. 28, pp. 266–271, 2017. [18] R. T. R. McGrann, D. J. Greving, J. R. Shadley, E. F. Rybicki, T. L. Kruecke, and B. E. Bodger, “The effect of coating residual stress on the fatigue life of thermal spray-coated steel and aluminum,” Surf. Coatings Technol., vol. 108–109, pp. 59–64, 1998. [19] K. Pang and H. Yuan, “Mechanical Behavior and Fatigue Performance of Carburized Steel Specimens,” vol. 853, pp. 72–76, 2017. [20] S. Baragetti and F. Villa, “An Updated Review of the Fatigue Behavior of Components Coated with Thin Hard Corrosion-Resistant Coatings,” Open Mater. Sci. J., vol. 8, pp. 87– 98, 2014. [21] A. Ibrahim and C. C. Berndt, “Fatigue and deformation of HVOF sprayed WC – Co coatings and hard chrome plating,” vol. 456, pp. 114–119, 2007. [22] R. C. Souza, M. P. Nascimento, H. J. C. Voorwald, and W. L. Pigatin, “The Effect of WC- 17Co Thermal Spray Coating By HVOF and Hard Chromium Electroplating on the Fatigue Life and Abrasive Wear Resistance of AISI 4340 High Strength Steel,” Corros. Rev., vol. 21, no. 1, pp. 75–96, 2003. [23] M. P. Nascimento, R. C. Souza, I. M. Miguel, W. L. Pigatin, and H. J. C. Voorwald, “Effects of tungsten carbide thermal spray coating by HP/HVOF and hard chromium electroplating on AISI 4340 high strength steel,” Surf. Coatings Technol., vol. 138, no. 2–3, pp. 113–124, 2001. [24] H. J. C. Voorwald, L. F. S. Vieira, and M. O. H. Cioffi, “Evaluation of WC-10Ni thermal spraying coating by HVOF on the fatigue and corrosion AISI 4340 steel,” Procedia Eng., vol. 2, no. 1, pp. 331–340, 2010. [25] G. S. Junior, H. J. C. Voorwald, L. F. S. Vieira, M. O. H. Cioffi, and R. G. Bonora, “Evaluation of WC-10Ni thermal spray coating with shot peening on the fatigue strength of AISI 4340 steel,” Procedia Eng., vol. 2, no. 1, pp. 649–656, 2010. [26] J. G. La Barbera-Sosa et al., “Fatigue behavior of a structural steel coated with a WC-10Co- 4Cr/Colmonoy 88 deposit by HVOF thermal spraying,” Surf. Coatings Technol., vol. 220, pp. 248–256, 2013. [27] E. S. Puchi-Cabrera et al., “Fatigue behavior of a SAE 1045 steel coated with Colmonoy 88 alloy deposited by HVOF thermal spray,” Surf. Coatings Technol., vol. 205, no. 4, pp. 1119–1126, 2010. http://www.iaeme.com/IJMET/index.asp 1299 editor@iaeme.com
Fatigue Performance of Thermal Spray Coatings on Carbon Steel: A Review [28] R. G. Bonora, H. J. C. Voorwald, M. O. H. Cioffi, G. S. Junior, and L. F. V. Santos, “Fatigue in AISI 4340 steel thermal spray coating by HVOF for aeronautic application,” Procedia Eng., vol. 2, no. 1, pp. 1617–1623, 2010. [29] E. F. Rejda, D. F. Socie, and B. Beardsley, “Fatigue behavior of a plasma-sprayed 8%Y2O3-ZrO2thermal barrier coating,” Fatigue Fract. Eng. Mater. Struct., vol. 20, no. 7, pp. 1043–1050, 1997. [30] H. Akebono, J. Komotori, and H. Suzuki, “The Effect of Coating Thickness on Fatigue Properties of Steel Thermally Sprayed with Ni-Based Self-Fluxing Alloy,” Int. J. Mod. Phys. B, vol. 20, no. 25, 26, 27, pp. 3599–3604, 2006. [31] J. G. La Barbera-Sosa et al., “Fatigue behavior of a structural steel coated with a WC-10Co- 4Cr/Colmonoy 88 deposit by HVOF thermal spraying,” Surf. Coatings Technol., vol. 220, pp. 248–256, 2013. [32] Y. Murakami, Metal fatigue: effects of small defects and nonmetallic inclusions. Elsevier, 2002. http://www.iaeme.com/IJMET/index.asp 1300 editor@iaeme.com