热处理对激光增材制造IN718合金组织及析出相演变的影响

Effect of heat treatment on microstructure and precipitate evolution of IN718 alloy prepared by laser additive manufacturing

研究了经过固溶+双时效(SA)、均匀化+双时效(HA)、均匀化+固溶+双时效(HSA)3种热处理后IN718合金的微观组织、析出相的演变。结果表明,沉积态试样中的显微组织为柱状晶结构,并贯穿多个沉积层;经过SA热处理后开始发生再结晶;经HA和HSA热处理后再结晶程度显著提高。热处理能够促进沉积态中的柱状晶逐渐向等轴晶转变。沉积态试样中存在γ基体、Laves相和一些碳化物;经过SA热处理后溶解了大部分的Laves偏析相,并在晶界、晶内、枝晶间析出大量的针状δ相,还有部分碳化物残留;经过HA热处理后,Laves偏析相、δ相全部溶解,只有少量的碳化物残留;经过HSA热处理后Laves偏析相全部溶解,在晶界处析出部分δ相,还有少量的碳化物残留。沉积态试样中没有γ′、γ″相析出,3种热处理状态均有大量的γ′、γ″相析出。

Evolution of microstructure and precipitates of the IN718 alloy after heat treatments was investigated by using solid solution+double aging(SA), homogenization+double aging(HA), homogenization+solid solution+double aging(HAS), respectively. The results show that the microstructure in the as-deposited specimen is a columnar crystal microstructure and runs through multiple sedimentary layers. Recrystallization occurs after SA heat treatment. Recrystallization is significantly improved after heat treatment of HA and HSA. Heat treatment can promote the progressive transformation of columnar crystals into equiaxed crystals. There are γ matrix, Laves segregation phase and some carbides in the as-deposited specimen. After SA heat treatment, most of the Laves segregation phase is dissolved, and a large number of acicular δ phases precipitate between the grain boundaries, the crystals, and the dendrites, and some carbides remain. After HSA heat treatment, the Laves segregation phase is completely dissolved, and some δ phase precipitate at the grain boundary, and a small amount of carbides retain. There is no γ′ and γ″ phase precipitated in the as-deposited specimen, and a large number of γ′ and γ″ phases precipitate in the three heat treatment states.