分步退火及初始晶粒对Hastelloy C-276合金晶界特征分布影响

Effects of Two-Step Annealing and Initial Grain Size on the Grain Boundary Character Distributions of Hastelloy C-276

不同初始晶粒尺寸的Hastelloy C-276合金经冷轧变形后,分别采用一次退火和二次退火方法进行热处理,其晶界特征分布采用电子背散射衍射技术进行表征.结果表明,初始较大晶粒组织有利于晶界特征分布的优化,特殊晶界比例比小尺寸晶粒组织提高了近10%,达到了78.8%,同时形成了平均尺寸为200μm晶粒团簇组织.在相同晶粒尺寸条件下,采用二次退火工艺可以明显改善合金的晶界特征分布,∑3n晶界比例得到较大幅度的提高,并形成了良好的团簇组织.这是由于较多的非共格∑3晶界,容易产生∑9和∑27晶界,从而形成更多的三叉晶界,阻断了大角度晶界的连通性.

Hastelloy C-276 samples with different initial grain sizes were subjected to one-step and two-step annealing heat treatments after cold-rolling process and their grain boundary character distributions（ GBCDs） were characterized by electron backscatter diffraction（ EBSD） techniques. The results showthat the large-sized initial grains tend to optimize the GBCD. Compared with that in the small-sized grain ones,the fraction of coincident site lattice（ CSL） boundary in Hastelloy C-276 samples with large-sized initial grains increases nearly 10%,which is up to 78. 8%. Meanwhile,the clusters with average size of 200 μm are formed. For the samples with same-sized grains,the GBCD can be well improved by the two-step annealing treatment,where the fraction of ∑3 nboundaries can be increased significantly and the better clusters can be formed. The more incoherent ∑3 boundaries,the more ∑9 and ∑27 boundaries can be generated,leading to the more triple junctions. Therefore,the connectivity of the high-angle grain boundary network is disrupted effectively.