Effect of bias on structure and mechanical properties of Ni - doped TiB2 - based coatings prepared by magnetron sputtering
A series of Ni - doped TiB2 - based coatings were prepared by double - target non - reactive magnetron sputtering.The composition was determined by X-ray energy spectrometer, the structure of the coating was analyzed by X-ray diffraction and scanning electron microscopy, and the hardness, modulus, fracture toughness, film-based adhesion and tribological properties of the coating were characterized by nano indentation, vickers indentation, scratch and friction and wear. The results show that: the tib2-ni coating prepared by this process has a hexagonal TiB2 structure, and the growth structure is very dense, with no obvious columnar growth structure and low surface roughness. Hardness is greater than 40GPa; The coating has good fracture toughness. The fracture toughness and cohesive force increase with the increase of bias. At the same time, the friction coefficients of the prepared coatings are all in the range of 0.5 ~ 0.6, and the wear rate is in the same order of magnitude.
The TiB2 based coating prepared by magnetron sputtering has high hardness and high chemical stability, so it has been widely used in many aspects, and can be used to protect the surface of cutting tools, molds and aerospace parts. Although tib2-based coating has high hardness, materials with high hardness are usually brittle and easily lead to failure when they undergo deformation. Low toughness limits the application of tib2-based coating in engineering, and improving its toughness has become a very important research direction. In general, the increase of toughness will easily lead to the decrease of hardness, and it is difficult to achieve both.
Metal and ceramic materials are widely used in many aspects. The main characteristic of metal is that it has high toughness. Ceramic has high hardness but low toughness. In recent years, ceramic/metal nanocomposite coatings prepared by incorporation of ductile materials into ceramic based coatings have been extensively studied. Some studies have doped Ni or Ti into many carbides and nitride coatings, such as Ni doped TiC, TiN and CrN, Ti doped SiN, etc. The metal doping will lead to changes in hardness and toughness. Akbari et al. found ti-ni-n coating with hardness greater than 25GPa and good toughness.
Based on the above research, this paper studies the different metal doped for TiB2 crack resistance, the influence of found Ni doping on the anti-cracking performance is z * obvious, but in the previous studies, found that although there are improved, but there are obvious columnar growth, shows that the performance of the coating has much room for improvement, based on this, this article adopts the double targets of intermediate frequency and rf power magnetron sputtering equipment by changing the substrate bias TiB2 - Ni coating was prepared by different bias. The structure and properties of the prepared coating were studied, and the effects of bias pressure on its growth structure, hardness, fracture toughness, film adhesion and tribology were discussed.
1.1 raw materials and preparation
The coating was prepared with MS450 high-vacuum double-target magnetron sputtering equipment. By changing the substrate bias, tib2-ni coating with different bias was deposited on the conning Eagle glass, single crystal Si(100) and M2 high-speed steel substrate. The TiB2 target (100mm in diameter, 4mm in thickness, 99.9 in purity)
1.2 coating characterization
Using Bruker D8 type X ray diffraction (XRD) was carried out on the coating phase analysis, CuK alpha, theta/theta mode, set the step length as 0.01 °, scanning range 20 ° ~ 70 °. The growth structure of the coating was observed using Hitachi S4800 high resolution field emission scanning electron microscope (SEM). The acceleration voltage was 4kV. The hardness measurement of the coating was carried out on the MTS NANO G200 nanometer indentation instrument, and the diamond Berkovich head was used. In order to reduce the influence of the substrate, the z* large injection depth was set at 150nm(about 1/10 of the film thickness).Each sample was measured at 8 points and averaged, and the plasticity index was calculated from the loading and unloading curves. The Revetest Revetest instrument of CSM was used to analyze the binding force between the coating and the substrate, and the pressure head was a diamond Rockwell pressure head with a radius of 200 m. The loading force was 0 ~ 100N, and the loading length was 3mm. Vickers indentation test using hv-1000 microhardness tester. FEI QuantaTM 250FEG SEM was used to characterize the scratch morphology and vickers indentation morphology with a voltage of 5kV.The tribological properties of the coating were characterized by CETR umt-3 friction testing machine, and the ball and disk reciprocating mode was used.The experiment was carried out at room temperature and humidity of 62 5%.The dual ball is Al2O3 ball with a diameter of 6mm, which is loaded as 2N.The reciprocating velocity and frequency of the dual sphere are 5cm/s and 5 Hz.The depth distribution of wear marks was obtained by using the kla-tencor alpha-step IQ surface profiler.
2, the conclusion
(1) magnetron sputtering equipment was used to prepare Ni doped TiB2 base coating at different bias pressures.
(2) in terms of structure, all prepared tib2-ni coatings only have a hexagonal TiB2 structure. The low-bias coating tends to be amorphous, and the high-bias coating has good crystallinity. All the coatings have dense growth structure, no obvious columnar structure and low roughness (less than 1nm).
(3) in terms of performance, the hardness is higher than TiB2 and greater than 40GPa; It is found that the ductility is good through the ductility index and indentation test. Through the scratch test, the coating adhesion increases with the increase of the transformer pressure, high bias tib2-ni coating has a good adhesion; In terms of tribological properties, the friction coefficients of the prepared coatings are all between 0.5 and 0.6, and the wear rate is within the range of 1.2 10-15 to 3.2 10-15 m3/N m, maintaining the same order of magnitude.
(4) through the study of structure and properties, tib2-ni coating prepared by high substrate bias (about -110v) shows better performance.
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