Luận văn Fabrication and characterization of nitride coatings on WC-Co hard alloy by magnetron sputtering

Nội dung tài liệu: Luận văn Fabrication and characterization of nitride coatings on WC-Co hard alloy by magnetron sputtering

1. 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
2. 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
3. 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
4. - 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
5. 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
6. 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
7. 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 o Temperature of the substrate: Roon temperature (25 C) 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
8. 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
9. 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
10. 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