Mechanical and tribological properties of nanostructured TiN/TiBN multilayer films

Nanostructured multilayer films of TiN/TiBN with different bilayer thicknesses (Λ) were deposited onto Si(1 0 0) wafers (for mechanical analyses) and AISI M42 tool steels (for tribological measurements) at room temperature by reactive unbalanced magnetron sputtering in an Ar–N₂ gas mixture. The effects of different Λ values on mechanical and tribological properties were studied by atomic force microscope (AFM), scanning electron microscope (SEM), microindentation measurements, Rockwell-C tester, nano- and micro-scratch tester, impact tester, pin-on-disc tribometer, and Fourier-transform infrared spectroscopy (FTIR). It was found that the mechanical and tribological properties of multilayer films (typically 1.4 ± 0.1 μm in thickness) were closely related to Λ (varied from 1.4 to 9.7 nm). For the best multilayer film with Λ = 1.8 nm, a maximum hardness of 29.5 GPa was achieved and the best cohesive and adhesive strength was evidenced in terms of critical load values of L_C1 (37 N), L_C2 (>80 N) and the highest adhesion strength (HF1). Moreover, by the dynamic impact testing this multilayer film could endure impact cycles up to 4 × 10⁵ without adhesive failure. It was also found that the nano-scratch test under single-pass and constant-load conditions showed that the frictional coefficients decreased with Λ and increased with normal load due to the ploughing effect. The enhanced hardness in the multilayer films with small Λ values improved the wear resistance and lowered the frictional coefficients. The frictional coefficients obtained at 5 N were kept at 0.5 and increased from 0.52 to 0.65 when Λ increased from 1.8 to 9.7 nm at 2 N. By FTIR analyses, the multilayer films with Λ = 1.8 and 2.2 nm showed the presence of h-BN which provided a lubricating function resulted in lower frictional coefficients and wear rates. The tribological properties of the TiN/TiBN multilayer films with different Λ values are also explained in terms of mechanical properties and wear mechanisms.     

Cu/TiBN电接触材料的导电性及抗电弧侵蚀机理

采用渗硼烧结法合成了一种新型TiBN粉体材料,它兼有陶瓷性和金属性,电阻率为2.6×10-3Ω·cm。以TiBN和TiN为增强相,采用粉末冶金法制备了Cu/TiBN和Cu/TiN电接触材料,系统的研究了不同含量TiBN和TiN的电接触材料的微观结构和物理性能。结果表明,与TiN相比,TiBN增强相能明显改善Cu基电接触材料的导电性能、抗氧化性能、硬度和抗电弧侵蚀性能。当含量为5wt.%时,Cu/TiBN电接触材料的抗电弧侵蚀能力最好,重量损失仅为1.5mg。电弧侵蚀时,在Cu/TiBN表面生成TixOy、B2O3和N2等产物,这些产物能明显改善Cu/TiBN电接触材料的抗电弧侵蚀能力。新开发的Cu/TiBN电接触材料具有优异的物理性能和抗电弧侵蚀性能,在电接触行业中拥有广阔的应用前景。     

Thermal stability of superhard Ti-B-N coatings

Ternary transition-metal boron nitride Ti-B-N offers outstanding hardness and thermal stability, which are increasingly required for wear resistant applications, as the protective coatings are subjected to high temperature, causing thermal fatigue. Ti-B-N coatings with chemical compositions close to the quasibinary TiN-TiB₂ tie line and boron contents below ∼ 18 at.% contain a crystalline supersaturated NaCl structure phase, where B substitutes for N. Annealing above the deposition temperature causes precipitation of TiB₂, which influence dislocation mobility and hence the hardness of TiB_0.40N_0.83 remains at a very high level of ∼ 43 GPa with annealing temperature T_a up to 900 °C. Growth of Ti-B-N coatings with B contents above ∼ 18 at.% results in the formation of nm sized TiN and TiB₂ crystallites embedded in a high volume fraction of disordered boundary layer. The compaction of this disordered phase during annealing results in a hardness increase of TiB_0.80N_0.83 coatings from the as-deposited value of ∼ 37 GPa to ∼ 42 GPa at T_a = 800 °C. Excess B during growth of TiB_2.4 coatings causes the formation of bundles of ∼ 5 nm wide TiB₂ subcolumns encapsulated in a B-rich tissue phase. This nanocolumnar structure is thermally stable up to temperatures of ∼ 900 °C, and consequently the hardness remains at the very high level of ~ 48 GPa, as nucleation and growth of dislocations is inhibited by the nm sized columns. Furthermore, the high cohesive strength of the B-rich tissue phase prevents grain boundary sliding.     

The effect of nitrogen flow rate on TiBN coatings deposited on cold work tool steel

TiBN coatings have high hardness and high adhesion. Due to these excellent properties there has been increasing interest in TiBN coatings. In this study, TiBN coatings were deposited on AISI D2 cold work tool steel and silicon wafers by closed field unbalanced magnetron sputtering (CFUBMS). The structural, mechanical and adhesion properties of these coatings were analysed by X-ray diffraction, scanning electron microscopy, microhardness test, indentation test and scratch tests. TiBN coatings produced by magnetron sputtering exhibited a dense and columnar structure. These results indicate that TiB₂, TiN and h-BN exist in crystalline forms at all coatings. The highest hardness was obtained at the lowest nitrogen flow rate. Very few cracks were observed at the edge of the indentation marks at the highest nitrogen flow rate. The highest critical load obtained with scratch test was identified as 102?N.     

The Stress Distribution and Thermal Behavior of TiBN and TiBN／TiN Coatings in Milling AISI H13 Work Tool Steel

The FEM model of TiBN ant TiBNI TiN coated cutting tool in milling of H13 steel was developed. Process variables such as temprature and stress in the coating layer as well as in the substrate were analyzed. The efficacy of the present FEM analysis was verified by conducting controlled milling experiments on AISI H13 to collect the relevant tool life and force data. The results show that the stress in a coated tool can significantly be reduced compared to an uncoated cutting tool, possibly due to surface coatings improving the tribolagical properties of cutting tools. Coatings with good thermal properties also help to improve the thermal behavior of cutting tool.     

Effect of prior plasma nitriding applied to a hot-work tool steel on the scratch-resistant properties of PACVD TiBN and TiCN coatings

Ternary TiBN and TiCN coatings on a hot-work tool steel substrate with and without plasma nitriding (PN) prior to plasma-assisted chemical vapour deposition (PACVD) were investigated. Compositional analysis with a radio frequency glow discharge optical emission spectroscope (rf-GDOES) showed mixtures of TiBN + TiN and TiCN + TiN in the PACVD TiBN and TiCN coatings, respectively. Each coating layer had a compositional gradient across the coating depth and slightly into the substrate. The microhardness profiles (HV_0.1) of the substrate with and without PN from the interface with the coating to the substrate core were determined. The depth of the effective nitrided diffusion layer was confirmed from the examination of its optical microstructure. The adhesion of these two coatings to the substrate was evaluated through scratch tests in the progressive mode. It was found that with increasing load, both of the coatings on the substrate with and without prior nitriding deteriorated in the same failure modes. Critical loads corresponding to the first microcracking related to cohesive failure, spallation related to adhesive failure, breakthrough and worn out were determined and used to quantify the scratch resistance of these coatings. With PN prior to PACVD, both the cohesion and adhesion properties of the TiBN and TiCN coatings were remarkably improved. This improvement was attributed to a functionally gradient hardness configuration from the coating through the nitrided diffusion layer to the substrate.     

多弧离子镀制备TiN/TiBN纳米复合涂层的结构和性能

为了满足复合材料高速切削加工的需要,用金属Ti靶和纯TiB2靶作为靶材料,在N2气氛下用多弧离子镀方法制备了TiN/TiBN纳米复合涂层。利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)和原子力显微镜(AFM)分析涂层的组织结构、成分和表面形貌;利用显微硬度计、划痕仪和球盘摩擦仪分析调制周期对涂层力学性能的影响。结果表明:TiN/TiBN纳米复合涂层的调制周期范围为5.5~21nm,主要成分为晶相TiN、非晶BN和TiB2;调制周期对涂层的力学性能有较大的影响,随着调制周期的减小,硬度增加,调制周期最小时最大硬度达到29GPa;最大膜基结合力为88N,且所有样品均表现出较高的膜基结合力。随着转速的增大,摩擦因数与表面粗糙度两者表现出相同的变化趋势,摩擦因数最大值为0.31,其低摩擦因数与自润滑的BN相的存在有关。调制周期减少,界面积增加,TiN/TiBN纳米复合涂层的力学性能增强。     

电弧离子镀制备TiBN纳米复合涂层

目的在纯N_2气氛环境下,低温制备TiBN纳米复合涂层,为TiBN涂层工业化生产积累科学数据。方法采用离子源增强阴极电弧离子镀系统,在硬质合金衬底上制备TiBN纳米复合涂层,系统研究了N_2气压对TiBN涂层晶体结构、表面形貌、硬度和耐磨性能的影响。结果 N_2气压对TiBN纳米复合涂层的晶体结构、表面形貌、硬度及摩擦系数的影响明显。随着N_2气压的升高,TiBN涂层中的TiN晶相逐渐增多,TiB_2晶相逐渐减少,为TiN晶粒和TiB_2晶粒镶嵌于非晶BN基体的复合结构。在0.5 Pa气压下,涂层硬度达3150HV。对于对磨材料硬质合金而言,TiBN涂层的摩擦系数为0.4左右。结论离子源增强电弧离子镀技术可以用于TiBN涂层的制备,制备出的TiBN涂层为纳米晶镶嵌于非晶的纳米复合涂层,涂层的显微硬度较高。在TiBN纳米复合涂层的工业化生产中,沉积N_2气压不宜偏高。     

TiBN粉体的合成、微观结构及其导电性能研究

采用渗硼烧结法合成了一种新型TiBN粉体材料,它是B在TiN中形成的固溶体。TiBN粉体颗粒具有特殊的微纳米复合结构,由尺寸可达到纳米级的TiBN晶体和非晶所组成,非晶多分布在颗粒边界,最小厚度为2nm左右。TiBN粉体兼有陶瓷性和金属性,电阻率为2.655×10^-5Ω·m,优于TiN、TiB₂、TiCN等陶瓷材料。该新方法可以在580℃/1 h条件下合成出单相TiN粉体材料,合成温度比现有TiN合成温度降低500℃以上。TiBN粉体材料可用于制备电接触材料、结构陶瓷材料,同时在作为锂电池、超级电容器、燃料电池和光伏电池的电极、集电体方面有诱人的研究价值和广阔的应用前景。     

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Wear-resistant Ti–B–N coatings have been synthesized by reactive arc evaporation of Ti–TiB₂ compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiB_x phase mixture is observed at low N₂ partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from −20 to −140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.