基体预渗碳对Ti-6Al-4V合金表面TiN(Ti)硬质膜层性能的影响

Effect of substrate carburizing on properties of TiN (Ti) hard coatings deposited on Ti-6Al-4V alloy

摘要:

硬质膜层在服役过程中,往往由于膜基界面强度的不足导致膜层过早的发生界面的剥落失效,这种剥落失效主要是由界面残余热应力诱导的显微裂纹的失稳扩展引发的。残余热应力主要来源于基体与膜层材料在热膨胀系数、弹性模量等物理性能的不匹配。为了降低这种不匹配性,在制备TiN硬质膜层之前,本文通过辉光离子扩渗技术在TC4基体表面形成具有一定深度、梯度结构的渗碳硬化层,然后利用等离子增强离子镀技术制备了单层及多层复合Ti/TiN膜层,研究基体预渗碳层对其表面不同结构TiN(Ti)硬质膜层性能的影响。结果表明,基体经过预渗碳强化处理后,相比于单一TiN或多层复合Ti/TiN硬质膜层,复合渗镀层的表面硬度能提高近2倍,膜基结合强度最高可达80N以上。同时,经过硬化后的基体显著抑制了其表面复合硬质膜层的界面脆性断裂倾向,复合膜层在外加载荷作用下的与基体的协同变形能力得到加强,强韧性显著提高。

Abstract:

Interface fracture often occurs in systems of soft substrate and hard coatings during the service process. That fracture is related to the weak interface strength and also the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was formed on TC4 substrate before the deposition of TiN(TiN) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings are synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings is studied. The results showed that the composite coatings’ hardness could be increased nearly 2 times and the bonding strength was enhanced to over 80N, comparing with mono- and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency was restrained obviously by the harden substrate, and the coordinative deformation ability of coating at extra load was optimized. The composite coating composed of pre-carburized layer and TiN hard coating showed a higher strength and toughness.