钛合金离子渗氮表面完整性研究

Surface integrity of ion nitrided titanium alloy

对Ti-6Al-4V钛合金真空离子渗氮层的表面完整性进行测试。分析了渗氮温度、时间等工艺参数对渗层表面粗糙度、残余应力等的影响规律和机制。研究表明,在650~900℃范围内,随着渗氮温度的升高和渗氮时间的增加,表面粗糙度总体呈现增加的趋势。其中,渗氮温度从700℃增加到750℃,渗氮层表面粗糙度大幅增加,残余应力转变为残余压应力,且应力绝对值显著增加。证明钛合金反应扩散渗氮机制启动温度在700~750℃范围内,从而,钛合金离子渗氮适合的温度应大于750℃。同时表明,钛合金渗氮层表面完整性与反应扩散渗氮行为密切相关。在渗氮温度不高于850℃,渗氮时间不超过16 h的条件下,因渗氮引起的表面粗糙度增加不超过0.3μm,渗层表面残余压应力可达-500 MPa。

Surface integrity of the ion nitrided layer on Ti-6Al-4V alloy was tested. The influence of nitriding temperature and time on surface roughness and residual stress was discussed. The results indicated that the surface roughness increases as the nitriding temperature increased.The surface roughness shows a increase,while the residual stress transform to a compressive residual stress,with a high absolute value,as the nitriding temperature increased from 700 ℃ to 750 ℃. Therefore,the reaction-diffusion mechanism in titanium nitriding process should start-up between the temperature range 700-750 ℃,which suggests that the nitriding process should be conducted above 750 ℃. It also means that the surface integrity is also closely correlated to the reaction-diffusion mechanism during the nitriding process. Moreover,the increase of surface roughness is less than 0. 3μm and the compressive residual stress can reach to-500 MPa,as the nitriding temperature is below 850 ℃ and the nitriding time is less than 16 h.