U弯变形及退火处理对690合金晶界网络分布的影响

Effects of U-bending and annealing on grain boundary network in Alloy 690

采用取向成像显微技术对镍基690合金U弯样品及经退火处理后样品进行分析,研究对U弯样品进行表面晶界工程处理(GBE)的方法。结果表明:U弯样品沿厚度方向上存在形变量梯度,致使退火后样品的晶界网络在厚度方向上产生规律变化,局部区域(约10%拉伸变形层区域)形成高比例低∑重合位置点阵(CSL,∑≤29)晶界(约80%)。弯曲形变量对再结晶形核密度及孪晶形成几率的影响决定GBE处理效果,GBE处理的合适变形量稍大于再结晶的临界变形量:形变量过小时,不利于提高孪晶形成几率,甚至不发生再结晶;形变量过大时,不利于形成大尺寸的晶粒团簇,都不利于形成高比例低∑CSL晶界。

The grain boundary networks of U-bended and annealed specimens were characterized using orientation image microscopy(OIM)in Ni-based alloy 690,the surface grain boundary engineering(GBE)was investigated.The results show that the deformation amount vary in thickness direction of the bended specimen,resulting in changes of the grain boundary network characteristics in the thickness direction.A region including high proportion of low-Σcoincidence site lattice(CSL,Σ≤29)boundaries(about 80%)is formed,which is the layer with about 10%tension of U-bending.Additionally,the deformation amount has a significant effect on the nucleus density and twinning frequency during recrystallization,furthermore influencing the grain boundary network after GBE.A deformation is slightly larger than the critical deformation condition of recrystallization,which can optimize the grain boundary network during GBE.Lower deformation will decrease the frequency of twinning,even avoiding recrystallization.Higher deformation will increase the recrystallization nucleus density,which results in smaller grain-cluster and higher random boundary density.Both the two conditions are disadvantageous factors for forming high proportion of low-ΣCSL grain boundaries.