氮化气氛对高温合金内生氮化处理的影响

Effect of nitriding atmosphere on internal nitridation of superalloy

在1 150℃/20h氮化条件下对ВЖ155合金进行了不同气氛的内生氮化处理,研究了氮化气氛对氮化过程和氮化表面的影响。通过在氮气中混入H2和Ar来调整氮化气氛组成,并采用金相、XRD和扫描电镜等手段对氮化后表面产物和氮化层深度进行了表征。结果表明：高纯N2中微量残余氧将导致氮化后合金表面存在富Cr和Ti的氧化膜,但混入5%H2（体积分数）后可消除表面氧化物;当混合气体中N2含量较高时,合金表面存在富Cr和Ti的氮化物,随着气体中N2含量减少表面氮化物随之减少,当N2的体积分数低于40%时,表面氮化物基本消失,同时氮化层深度随N2含量增加而增加,表明氮化气氛对氮化速率具有重要影响。因此,采用40%N2＋5%H2＋55%Ar（体积分数）的氮化气氛组成可以实现抑制氮化表面氮化物和提高氮化速率2方面综合效果。

Under the nitriding condition of 1 150℃/20 h,theВЖ155 alloy was subjected to different internal nitriding treatments.The effect of nitriding atmosphere on the nitriding process and nitriding surface was studied.The composition of the nitriding atmosphere was adjusted by mixing H2 and Ar in nitrogen,and the surface product and nitrided layer depth after nitriding were characterized by means of metallography,XRD and scanning electron microscopy.The results show that the residual oxygen in the high-purity N2 will lead to the existence of Cr and Ti-rich oxide films on the surface of the alloy after nitriding,but the oxide films can be eliminated by being mixed with 5 vol% H2;when N2 content in the mixed gas is high,Cr and Ti-rich nitrides exist on the surface of the alloy.As the N2 content in the gas decreases,the surface nitride decreases.When the volume fraction of N2 is lower than 40%,the surface nitrides disappear,meanwhile the depth of the nitriding layer increases with the increase of N2 content.It can be seen that the nitriding atmosphere has an important influence on the nitriding rate.Therefore,a combination of 40 vol%N2＋5 vol%H2＋55 vol% Ar nitriding atmosphere can achieve a combined effect of suppressing nitriding nitrides and increasing the nitridation rate.