In my thesis, the title is selected as: "Study on fabrication and properties of nitride coatings on WC-Co hard alloys by magnetron sputtering".. Scope of thesis - Fabrication and charac
Trang 1GRADUEATE UNIVERSITY SCIENCE AND TECHNOLOGY
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LUONG VAN DUONG
FABRICATION AND CHARACTERIZATION OF NITRIDE COATINGS ON WC-Co HARD ALLOY BY MAGNETRON
Trang 2PREFACE
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
Trang 3Science, 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
Trang 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
Trang 5TiAlBN/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
Trang 6The 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
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
Trang 7deposited 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 layer coatings, the multi-layer coatings are depostited at the condition as follows:
single 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)
Trang 8CHAPTER 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
Trang 9Recognizing 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 N 2 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
Trang 10This 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 N 2 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 N 2 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
Trang 11results 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 N 2 gas flow rate on the hardness of coatings 3.2.1.3 Effect of N 2 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 N 2 gas
flow rate
Trang 12At 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 N 2 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