硼掺杂梯度对硬质合金金刚石涂层的影响

Effect of boron doping gradient on cemented carbide diamond coatings

为提高硬质合金刀具上金刚石涂层的结合性能,采用热丝化学气相沉积法在YG 8硬质合金基体上沉积高、低梯度硼掺杂微米金刚石(high gradient boron-doped micron crystal diamond,HGBMCD;low gradient boron-doped micron crystal diamond,LGBMCD)涂层和无硼掺杂的微米金刚石(micrometer crystal diamond,MCD)涂层,探究沉积过程中硼掺杂浓度的梯度大小对金刚石涂层的形核和生长性能的影响。结果表明:随着硼的掺入,金刚石的形核密度增大,生长6 h后的金刚石晶粒更均匀细小,其中LGBMCD的晶粒尺寸大部分在2~3μm;而石墨相在梯度硼掺杂金刚石涂层中的生长会被抑制,HGBMCD中IDia/IG高达14.65,残余应力仅为–0.255 GPa,且Co2B、CoB等硼钴化合物含量随硼掺杂梯度的减小而增大;金刚石涂层的残余应力因硼的掺入逐渐从压应力转变成拉应力,残余应力大小先减小后增大;洛氏压痕显示,随着硼的掺入,金刚石涂层的结合性能提高,LGBMCD的结合性能最好,在1470 N下可达到HF2级。因此,适当的硼掺杂梯度有利于提高金刚石涂层的质量和结合性能。

To improve the binding properties of diamond coating on carbide tools, three micrometer crystal diamond coatings were successfully deposited on YG8 carbide substrate via hot-filament chemical vapor deposition, whose boron gradient ranged from high(HGBMCD) to low(LGBMCD) and zero(MCD). The effect of the gradient size of the decreasing concentration of boron doping method on the nucleation and growth properties of diamond coatings during deposition was investigated. The results showed that the nucleation density of diamond increased with the doping of boron and that the diamond grains became smaller and more uniform after six-hour growth. Among them, the grain size of LGBMCD was mostly in the range of 2 to 3 μm. In addition, the graphite phase in the gradient boron-doped diamond coating was inhibited throughout the growth process, and IDia/IGwas up to 14.65 in HGBMCD. The concentrations of the boron and cobalt compounds(i.e., Co2B and CoB) increased as the boron doping gradient decreased. Meanwhile, the residual stress in the diamond coatings gradually changed from compressive stress to tensile stress due to the doping of gradient boron, and the calculated residual stress decreased first and then increased, with the minimum residual stress of–0.255 GPa. Rockwell indentation showed that the gradient doping of boron improved the binding properties of diamond coatings, and that the optimal binding properties were observed at the LGBMCD, which was up to HF2 level at1 470 N. Therefore, a proper boron doping gradient was demonstrated to improve the quality and binding performance of diamond coatings.