Summary of Materiasls science doctoral thesis: Study on fabrication and properties of nitride coatings on WC-Co hard alloys by magnetron sputtering

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Scope of thesis: Fabrication and characteristics of single-layer nitride hard coating with multi-components (TiAlXN (X: Si, B, V)) and multi-layer nitride hard coating with multi-components TiAlXN/CrN (X: Si, B) with high hardness and low friction coefficient; to determine the influence of main parameters on the properties of coatings.

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Nội dung Text: Summary of Materiasls science doctoral thesis: Study on fabrication and properties of nitride coatings on WC-Co hard alloys by magnetron sputtering

MINISTRY OF EDUCATION VIETNAM ACADEMY OF AND TRAINING SCIENCE AND TECHNOLOGY GRADUEATE UNIVERSITY SCIENCE AND TECHNOLOGY ----------------------------------- LUONG VAN DUONG FABRICATION AND CHARACTERIZATION OF NITRIDE COATINGS ON WC-Co HARD ALLOY BY MAGNETRON SPUTTERING Major: Metal Science Code: 9.44.01.29 SUMMARY OF MATERIASLS SCIENCE DOCTORAL THESIS HANOI – 2019
PREFACE 1. Urgency of the thesis The abrasion and corrosion are the cause of energy loss and material loss, which reduced performace and lifetime of cutting tools and machine parts in industry. In industrialized countries some 30 % of all energy generated is ultimately lost through friction. In the highly industrialized countries losses due to friction and wear are put at between 1 and 2 % of gross national product. Therefore, research on fabrication and devolope the coatings with excellent properties such as high hardness, low friction coeficience, high corrosion resistance, and thermal stability are in great demand in moderm industry [1]. Over the past several decades, the coatings with different features, from single-layer films with single element such as TiN [2- 3], TiC [4-6], CrN [7 -9] to single-layer films with multi-element such as TiAlN [10-11], TiAlSiN [12], TiAlBN have been studied. In addition, the fabrication of TiN/CrN and TiAlN/CrN multilayer films to combine the good characteristics of each monolayer is also studied and developed simultaneously [14-15]. For fabrication of the coatings, some methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and physical chemistry have been used. However, the PVD method is commonly used because it has high performance, good adhesion, high density and can deposite on large tools and parts. In Vietnam, the study on fabrication of nitride coatings have been attracted the attention of many research groups in both fabrication technology and applications at Universities and Institutes such as: Hanoi university of Science and Technology, University of 1
Science, Vietnam National University Ho Chi Minh City, The National Research Institute of Mechanical Engineering ...etc. The single-layer films TiN, Cr [16-17] and muti-layer films TiN/TiCN [18], TiN/CrN [19] are focused on studing. It can be seen that the most of studies only focused on single-element nitride films (commercial targets), which have not been fabricated multi-element nitride films yet because a target with multi-component is not still fabricated yet. Therefore, the application of these studies is very limited. From 2013 up to now, Institute of Materials Science in conjunction with Korea Institute of Industrial Technology has performed the join projects of nitride coatings with multi- components on WC-Co hard alloys. Moreover, the targets of multi- components are also fabricated. As mention above, it is a desire to form the nitride hard coatings with high hardness and low friction coefficient and expand the applicability of these coatings in industries. In my thesis, the title is selected as: "Study on fabrication and properties of nitride coatings on WC-Co hard alloys by magnetron sputtering". 2. Scope of thesis - Fabrication and characteristics of single-layer nitride hard coating with multi-components (TiAlXN (X: Si, B, V)) and multi-layer nitride hard coating with multi-components TiAlXN/CrN (X: Si, B) with high hardness and low friction coefficient. - To determine the influence of main parameters on the properties of coatings. 3. Main contents of thesis 2
- Introduction of single-layer and multi-layer nitride coatings in Vietnam and the world. - Introduction of fabricated method of coatings and devolopment mechanism of coatings. - Research on fabrication of single-layer nitride coatings TiAlXN (X: Si, B, V) by magnetron sputtering, consist of: + Research on effect of basis parameters as power, pressure, distance of target and substrate on hardness of the coatings. + Research on effect of nitrogen gas flow rate on the properties of single-layer nitride coatings. - Research on fabrication of multi-layer nitride coatings by magnetron sputtering and characteristics of the coatings. Main results of thesis - Single-layer nitride hard coating with multi-components (TiAlXN (X: Si, B, V)) and multi-layer nitride hard coating with multi- components TiAlXN/CrN (X: Si, B) have been fabricated successfully by magnetron sputtering on the WC-Co hard alloys. - With regard to single-layer hard coatings, research on effect of N2 gas low rate on the properties of 03 coatings (TiAlXN) using by Ti50Al40X10 (X: Si, B, V) target. Namely, the optimal N2 gas flow rate is determined at 6 sccm for TiAlSiN and TiAlVN coating, at 4 sccm for TiAlBN coating. - With regard to multi-layer hard coating of TiAlSiN/CrN and TiAlBN/CrN, research on effect of bi-layer thickness and the pairs number of coatings on the hardness of multi-layer coatings. Namely, TiAlSiN/CrN coating has highest hardness at bi-layer thickness of 245 nm (thickness of TiAlSiN is 127 nm and thickness of CrN is 118 nm) and pairs total of coating is 6 (12 layers). With regard to 3
TiAlBN/CrN coating, the highest hardness is obtained at the bi-layer thickness of 232 nm and pairs total of coating is 7 (14 layers). CHAPTER 1. INTRODUCTION - Introduction of concepts and devolopment history of coating - Introduction of single-layer nitride coatings and multi-layer nitride coating in the world. - Introduction of structure of TiN, AlN, TiAlN, CrN. - Introduction of fabricated methods, including: chemiscal vapor deposition (CVD), physical vapor deposition (PVD). In this thesis, the PVD method is used for deposited single layer coatings and multi layer coatings. This is also a common method to be used in the manufacturing industry because it is a simple, easy-to-control, and automated method. - Formation process of coating by sputtering method and applications of nitride coating as well as research situation in Vietnam. CHƯƠNG 2. EXPERIMENTAL AND RESEARCH APPROCHES 2.1. Fabrication of nitride coatings By reference, analyze publishing papers on component coatings based on Ti-Al alloys in the world [31-34, 45-47], the results of target components are inherited from Korea Institute of Industrial Technology [31]. In this thesis, the coatings are deposited by magnetron sputtering using 02 targets, including: - 01 target systerm with TiAl-X (X: V, B, Si) for depositing of single – layer coatings - 02 targets consist of TiAl-X (X: V, B, Si) target and Cr target ( > 99,9%) for depositing of multi-layer coatings. 4
The chemical composition of these targets is shown in table 2.1. Table 2.1. Chemical composition of 02 targets. Elements (% at.) Ti Al X ( V, B, Si) Cr Size Target systerm 1 50 40 10 ɸ75 x 8 mm Target systerm 2 100 ɸ75 x 8 mm 2.1.1. Fabrication of targets In this thesis, the targets are fabricated from 03 metal elements (Ti, Al, X (Si, B, V)) by using powder metallugy technology. Size of the fabricated target is ɸ75 x 8 mm. 2.1.2. Fabrication of coatings 2.1.2.1. Preparation of surface substrates WC-Co substrates are ground and polished by SiC paper and diamond solution, and then the substrate samples are continually cleaned by ultrasonicvibrators in an alcohol or acetone environment for 10 minutes to remove dirt from the surface of the samples. 2.1.2.2. Fabrication of single-layer TiAlXN coatings After polishing and cleaning the surface of WC-Co and Si (100) substrates, which introduced into vacuum chamber (1.5x10-3 Pa) of magnetron sputtering. The samples were subsequently fixed in the substrate holder and continuously cleaned by Ar+ ion bombardment for 30 minutes using the dc pulse discharge (Us = 600 V, PAr = 1.2 Pa, Is = 0.02 A) to further remove adsorbents and residual oxides on the substrate surfaces. Polished samples are deposited by DC magnetron sputtering in the gas mixture of Ar/N2. The buffer layer of Cr or Ti metal is 5
deposited on the subtrate before deposition to increase the ahesion strength between coating and substrate. The deposited conditions of single-layer hard coatings The parametters of magnetron sputtering processes deposited coatings as follows: o Deposition power: 200-350W o Deposition pressure: 2.5; 5; 7; 10 mtorr o Flow rate of N2 gas: 2; 4; 6; 8; 10 sccm (TiAlSiN coatings, TiAlBN coatings); 4; 6; 8; 10 sccm (TiAlVN coatings), flow rate of Ar gas: 36 sccm is fixed in during the magnetron sputtering. o Distance of target and WC-Co substrate: 30-60 mm o Deposition time: 30 minute o Temperature of the substrate: Roon temperature (25oC) o Target composition: Ti50Al40X10 After the deposition process, the coated samples were cooled down in the chamber for 15 minute before venting to the atmospheric pressure. All coated sample are analyzed and evaluated. 2.1.2.3. Fabrication of multi-layer TiAlX (Si, B)N/CrN coatings Base on the optimal parameters in the fabrication of single- layer coatings, the multi-layer coatings are depostited at the condition as follows: - Deposition power: 300 W - Deposition pressure: 5 mtorr - Distance of target and WC-Co (Si wafer) substrate: 50 mm - Flow rate of working Ar gas: 36 sccm, flow rate of N2 gas: 6 sccm (TiAlSiN/CrN) và 4 sccm (TiAlBN/CrN) - Deposition time: TiAlX (Si, B)N: 5-15 minute, CrN: 2-6 minute - Temperature of the substrate: Roon temperature (25oC) 6
CHAPTER 3. FABRICATION OF SINGLE-LAYER TiAlXN (X: Si, B, V) COATINGS 3.1. Optinal parameters of magnetron sputtering processes The basic parameteres consist of depostion power, pressure and distance of target and WC-Co substrate are determined through affects hardness of the coatings. The basic parameters are determined as follows: o Deposition time: 300 W o Deposition pressure: 5 mtorr Distance of target and WC-Co (Si wafer) substrate: 50 mm 3.2. Fabrication of single-layer TiAlSiN, TiAlBN and TiAlVN coatings. The nitride coatings are deposited by magnetron sputtering using 02 gas, including: (i) working gas of Ar; (ii) active gas of N2. Therein, the working gas of Ar motivated the ionization of atoms or molecular and form plasma zone, active gas of N2 has effect on the formation of nitride composition, which is formed on the target if high energy ion bombarment or it is formed in moving time of atoms, even it can be formed on the substrate after depostion. As can be seen, the N2 gas flow rate affected on the formation of nitride coatings and the properties of coatings. A number of researches have been published showing the effect of N2 reactive gas content on the properties of coatings such as hardness, friction coefficient, crystal particle size, phase composition [33,77- 78, 80-81]. Thus, the role of N2 gas is very important in forming nitride coating. 7
Recognizing the importance of N2 gas, in the next section, the thesis will focus on studying the effect of N2 gas flow on the formation and properties of nitride coatings. 3.2.1. TiAlSiN coating 3.2.1.1. The effect of N2 gas flow rate of structure and chemical composition of TiAlSiN coatings The XRD patterm of TiAlSiN coatings deposited at 6 sccm N2 gas flow rate shows perfect face centered cubic (fcc) structure (acorrding to stand JCPDS No: 38-1420) with 02 peaks of TiN (111) and TiN (220). TiN (111) peak has highest intensity at 36,6o, however, when N2 gas flow rate increases up to 8 sccm, the intensity of TiN (111) peak decreases and the intensity of TiN (200) peak increases gradually. This trend occurs for the coating deposited at 10 sccm N2 gas flow rate. In addition, a TiN (311) peak is appeared at this N2 gas flow rate. Figure 3.1. The XRD patterm of TiAlSiN coatings deposited at different N2 gas flow rate. The TiAlSiN coatings with fine particle size are indicated at N2 gas flow rate of 2, 4 and 6 sccm. Moreover, the SEM image also shows these pores on the surface coatings at N2 gas flow of 2 and 4 sccm. 8
This suggests that the density of TiAlSiN coating is not high. In addition, easy to observe, the particle size of coatings increases when increasing N2 gas flow rate from 2 to 10 sccm. Figure 3.2. Surface morphology and thickness of TiAlSiN coatings at different N2 gas flow rate. The cross-section and thickness of TiAlSiN coatings on insert images, which can be seen that at the low N2 gas flow rate (2, 4, and 6 sccm), cross-section surface of the coatings are smoother and no column than that of the coatings deposited at higher N2 gas flow rate (8 and 10 sccm). This result is due to the increase in the crystal particle size of faricated coatings. Meanwhile, the thickness of the coatings was decreased form 4.32 µm to 3.58 µm when the N2 gas flow rate was increased from 2 sccm to 10 sccm. 3.2.1.2. Effect of N2 gas flow rate on the hardness of TiAlSiN coatings The results showed that the hardness of the coatings increased from 24 GPa to 33.5 GPa when N2 gas flow increased from 2 sccm to 6 sccm. The hardness of the coatings tends to decrease when the N2 gas flow continually increase from 8 to 10 sccm. Elastic modulus 9
results tend to be similar to hardness values. When N2 gas flow increases from 2 to 6 sccm, the elastic module increases from 267 to 346 GPa. The elastic modulus of the coatings continually decreases with increasing N2 gas flow rate. Figure 3.3. Effect of N2 gas flow rate on the hardness of coatings 3.2.1.3. Effect of N2 gas flow on the friction coefficient and wear of TiAlSiN coatings a) Dry condition Figure 3.4. The friction coefficient of the coatings at different N2 gas flow rate. 10
At N2 gas flow of 2 sccm, the stability can be seen during the sliding process with an average friction coefficient value of ~ 0.74. The average friction coefficient increased from 0.78 to 0.795 at the N2 gas flow of 4 and 6 sccm, respectively. The friction coefficient of the coatings continually increased with increasing the N2 gas flow. Moreover, the unstableness in during the sliding is also increased. This is indicated in the unstable increase and decrease for deposit at N2 gas fow of 8 and 10 sccm. b) Oil condition The average friction coefficient of the coatings at low N2 gas flows at 2, 4, 6 sccm ranges from 0.08 - 0.1 and increases to above 0.1 at N2 gas flow of 8 sccm and 10 sccm. Specifically, the lowest friction coefficient is obtained at the N2 gas flow of 2 sccm and the highest is obtained at the N2 gas flow of 10 sccm 3.2.1.4. Effect of N2 gas flow rate on the adhesion strength of TiAlSiN coatings In this stuty, adhesion strength is determined by Scratch test method with a diamond tip attached to the stylus. The load value of the diamond tip is increased gradually from 0 N to 30 N or 50 N and when load value is reached, the coatings starts to appear peeling off the surface substrate, which is called the critical load. The critical load value increases from 18.3 N to 23.9 N when increase in the N2 gas flow rate from 2 to 6 sccm. If the N2 gas flow rate continues to increase up to 8 sccm, the critical load would be decreased. The other hand, adhesion strength between the coating and the substrate will be decreased. The adhesion strength between the coating and the substrate is shown in detail on the Table 3.2 11
Table 3.2. Adhesion strength at diffirent N2 gas flow and using bufferlayer. 2ccm 4sccm 6 sccm 8 sccm 10sccm Cr bufferlayer Critical 18.3 20.7 23.9 19.9 17.6 36.5 load(N) 3.2.2. TiAlBN coatings 3.2.2.1. The effect of N2 gas flow rate of structure and chemical composition of TiAlBN coatings The coated sample at 4 sccm N2 gas flow rate, there are three peaks of TiN which is observed at the posistion of 36.6o, 61.8o and 77.9o, corresponding to the crystal orientation (111), (220) and (222), respectively in the pattern. According to JCPDS standard No: 38- 1420, TiN with face-centered cubic structure (FCC). Moreover, XRD diffraction patterns also indicated the intensity and the position of peaks varying with N2 gas flow rate. The intensity of TiN (111) is highest at N2 gas flow of 4 sccm. If N2 gas flow rate continues to increase above 4 sccm, the intensity of TiN (111) peak will be decreased and the lowest intensity at 10 N2 gas flow rate. 3.2.2.2. Effect of N2 gas flow rate on the hardness of TiAlBN coatings As can be seen that the smallest hardness is obtained at N2 gas flow rate of 2 sccm. When the increasing N2 gas flow rate, the hardness of the TiAlBN coatings increase and reaches the maximum value (~ 41 GPa) at N2 gas flow of 4 sccm. If N2 gas flow rate continues to increase upto 6 and 10 sccm, the hardness of the coatings tends to decrease gradually. Results of elastic modulus tend to be similar to the hardness values. The elastic modulus increases from 207 GPa to 396 GPa 12
when N2 gas flow rate increases from 2 to 4 sccm. If the N2 gas flow rate increases continually, elastic modulus of the TiAlBN coating will be reduced. 3.2.2.3. Effect of N2 gas flow on the friction coefficient and wear of TiAlBN coatings a) Dry condition Friction coefficient results of the TiAlBN coating indicated that the friction coefficient of the coating increases when the incresing N2 gas flow rate. At low N2 gas flow rate (2 - 6 sccm), the friction coefficient of the coating is stable in during sliding distance. However, when the increasing N2 gas flow rate, the friction coefficient of the coatings shows the oscillation in during sliding distance. On the insert figure, the results indicated that friction coefficient of the coatings increase 0.46 to 0.69 when the increasing N2 gas flow rate from 2 to 10 scc. b) Oil condition The results indicated that the friction coefficient of the coatings increases from 0.053 to 0.054 when the increasing N2 gas flow rate from 2 to 4 sccm. The N2 gas flow rate continues to increase from 6 to 10 sccm, the friction coefficinent of the coating would be increased from 0.98 to 0.135. 3.2.2.4. Effect of N2 gas flow rate on the adhesion strength of TiAlBN coatings The results indicated that the highest adhesion strength of the caoting is obtained in the range of 4 to 6 sccm, corespoding to critical load from 19.1 N to 20.3 N. If N2 gas flow rate continues to increase above 6 sccm, the critical load tends to decrease. Moreover, 13
when Cr metal is used as bufferlayer, the adhesion strength of the coatings is increased for two times, compared to no-bufferlayer. Table 3.5. Adhesion strength at diffirent N2 gas flow and using bufferlayer. 2ccm 4sccm 6 sccm 8 sccm 10sccm Cr bufferlayer Critical 17.8 19.1 20.3 15.6 16 42.4 load(N) 3.2.3. TiAlVN coatings 3.2.3.1. The effect of N2 gas flow rate of structure and chemical composition of TiAlVN coatings Only one TiN (220) with fcc (face centered cubic) or TiAlVN at 4 sccm N2 gas flow rate. When the increasing N2 gas flow rate of 6 sccm, three TiN peaks with fcc structure, including TiN (111), (200) and (220). If N2 gas flow rate continues to increase upto 8 and 10 sccm, the obtained coatings have dual phase which consist of hcp phase – AlN and fcc phase – TiN. The other hand, the obtained coatings have single phase at low N2 gas flow rate (4-6 sccm) and dual phase (fcc + hcp) at higher N2 gas flow rate (8-10 sccm). 3.2.3.2. Effect of N2 gas flow rate on the hardness of TiAlVN coatings The hardness of the coatings increases from 30.6 GPa to 36.5 GPa when N2 gas flow rate increased from 4 to 6 sccm. If N2 gas flow rate continues to increase up to 8 and 10 sccm, the hardness of the coating tends to decrease. 3.2.3.3. Effect of N2 gas flow on the friction coefficient and wear of TiAlVN coatings a) Dry condition 14
The friction coefficient of the coatings exhibited the same tendency in the initial stage. After that, the friction coefficient tends to decrease gradually for all the coatings, except for the coating deposited at 10 sccm N2 flow rate. The lowest friction coefficient was observed in the coating deposited at the N2 flow rate of 4 sccm (~ 0.52). When the N2 gas flow rate increases from 6 to 8 sccm, average friction coefficient of the coatings also increased from 0.58 to 0.73 and reaching the highest friction coefficient for the coating deposited at the N2 flow rate of 10 sccm. b) Oil condition The results indicated that friction coefficient of the coatings increased from 0.094 to 0.143 in oil condition when the N2 gas flow rate increases from 4 to 10 sccm. Compared to dry condition, the friction coefficient of the coatings in oil condition has reduced from 5 to 6 times. c) Effect of heating temperature on the friction coefficient of the coatings The friction coefficient of the coating increases when the coatings are heated at 500 oC. The result was attributed to the formation of Al2O3 on the surface coating or the increase in the grain size of the coatings while the Magnéli phases have not formed yet at this temperature. When the temperature increases up to 600oC and 700oC, the friction coefficient of the coating would be decreased to be 0.45 and 0.38, respectively. 3.2.3.4. Effect of N2 gas flow rate on the adhesion strength of TiAlVN coatings The results indicated that the highest adhesion strength of the coating (24.4 N) is obtained at the N2 gas flow rate of 6 sccm. The 15
lowest adhesion strength of the coating (18.3 N) is observed at the N2 gas flow rate of 10 sccm. When Cr or Ti metal are used as bufferlayer, the adhesion strength of the coatings is increased from 1.5 to 2 times, compared to no-bufferlayer. Table 3.8. Adhesion strength at diffirent N2 gas flow and using Cr or Ti as bufferlayer. 4sccm 6 sccm 8 sccm 10sccm Cr buffer Ti buffer Critical load 22.1 24.4 19.9 18.3 41 47.2 (N) 3.2.4. The comparision of mechanical properties of the coatings: TiAlSiN, TiAlBN and TiAlVN Table 3.9. Results of mechanical properties of TiAlSiN, TiAlBN & TiAlVN Adhesion Friction coefficient strength Elastic Hardness modulus No- (GPa) Dry Oil Buffer (GPa) buffe condition condition layer layer 36.5 TiAlSiN 33.5 346 0.795 0.105 23.4 (Cr) 42.4 TiAlBN 41 396 0.52 0.075 19.1 (Cr) 0.58; 41 0.45 at (Ti); TiAlVN 36.5 372 600oC) 0.112 24.4 47.2 and 0.38 (Cr) at 700oC 16
CHAPTER 4. FABRICATION OF TiAl-X(Si, B)N/CrN MULTILAYER HARD COATINGS TiAl-X (Si, B) N / CrN multilayer hard coating are deposited by dc magnetron sputtering on Si substrate and WC-Co alloy substrate, using two targets of Ti50Al40X10 (X: Si,B) and Cr. The basic parameters of sputtering include: Power (300W), pressure (5 mtor), distance between target and substrate (50 mm), Ar gas flow of 36 sccm. Meanwhile, N2 gas flow of 6 sccm for TiAlSiN/CrN multilayer coating and 4 sccm for TiAlBN/CrN coatings. Deposition time was changed to investigate the thickness of single coatings as follows: TiAlSiN, TiAlBN: 10-15 minutes and CrN: 1-3 minutes. 4.1. TiAlSiN/CrN multilayer coatings 4.1.1. Structure of TiAlSiN/CrN coatings 4.1.1.1. Phase structure Figure 4.1. XRD patterns of TiAlSiN/CrN multilayer coating (a); CrN single-layer coating (b); TiAlSiN single-layer coating (c). The XRD patterns results of the multi-layer TiAlSiN/CrN coating (Figure 4.1c) show that the peaks of the multi-layer coating are combinated with TiAlSiN and CrN single-layer coating. However, 17
the position of the peaks is shifted, compared to the peaks of TiN and CrN. It can be contributed the replacement of Cr atoms to the position of Ti atoms with different atomic radii causes the dislocation of lattice parameters. 4.1.1.2. Morphological structure Figure 4.2. Surface morphology and cross-section of TiAlSiN/CrN multi-layer coating :(a,d)- 2 layers; (b-e)- 4 layers; (c-f): 12 layers. When the bilayer period thickness of TiAlSiN-CrN coatings decreases, the particle size increases. The other hand, bilayer period of TiAlSiN-CrN coatings increases when the particle size would be decreased. 4.1.2. Hardness and elastic modulus of TiAlSiN/CrN multilayer coatings 4.1.2.1. Effect of bilayer period on the hardness of the coatings The hardness results is a range from 21 to 31.2 GPa. Maximum hardness values were determined at 245 nm bilayer period thickness (TiAlSi-127 nm & CrN-118 nm). When the bilayer period 18
thickness of the coatings increases, the hardness of the film tends to decrease. 4.1.2.2. Effect of layers on the hardness of the coatings When increasing the number of layers from 2 to 12 layers, the hardness of the coating increases rapidly from 18.3 to 31.4 GPa. If the number of layers continues to increase, the hardness value of the TiAlSiN/CrN multi-layer coatings does not change significantly. 4.1.3. Friction coefficient of TiAlSiN/CrN multilayer coatings The average friction coefficient of WC-Co alloy substrate is 0.74, while the average friction coefficient of TiAlSiN and CrN monolayer coatings is 0.81 and 0.66, respectively and TiAlSiN/CrN multilayer coatings is 0.71. 4.1.4. Adhesion strength of TiAlSiN/CrN multilayer coatings The adhesion strength between the coatings and substrate is significantly improved by using buffer layer. When Cr as buffer layer is not used, the critical load is obderved at 26.3N, while the Cr metal as buffer layer is used for the deposition of TiAlSiN/CrN multilayer coatings, the critical load value is indicated above 30N. 4.2. TiAlBN/CrN multilayer coatings 4.2.1. Structure of TiAlBN/CrN multilayer coatings 4.2.1.1 Phase struture The results showed that the peaks of the multi-layer coating (Figure 4.9c) is combinated with the peaks of monolayer coatings. 4.2.1.2. Morphological structure When the bilayer period thickness decreases from (815 + 663 nm) to (79 + 86 nm), the particle size of the coatings also decreases (Figure 4.10 a-c). It can be attributed on the TiAlBN coatings which have fine particle size, compared to CrN coating, when the bilayer 19