热处理态激光立体成形Inconel 718高温合金的组织及力学性能

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HEAT TREATMENT LASER SOLID FORMING SUPERALLOY INCONEL 718

研究了经过高温均匀化固溶处理+中间δ时效处理+双级时效处理的激光立体成形Inconel 718合金的组织及力学性能,并考察了热处理后合金的位错组态.结果表明,由于热处理过程中的再结晶行为,合金组织由沉积态的初始柱状晶转化为等轴晶.Laves相完全固溶,针状δ相以及γ″强化相分别在晶界处以及γ基体上大量弥散析出.激光立体成形Inconel 718合金热处理态的抗拉强度、屈服强度、延伸率以及断面收缩率均达到锻件标准.位错与γ″相的相互作用为位错切割γ″相以及位错绕过γ″相,在位错绕过γ″相的区域,位错密度比位错切割γ″相区域高.由于热处理态δ相尺寸大于锻件,位错会在δ相中发生塞积.碳化物和位错之间也存在强烈的相互作用,通过钉扎和拖曳作用来阻碍位错运动.

With the development of additive manufacturing technology of metal, laser solid forming （LSF） has become an important fabricating method for high performance and complex Inconel 718 alloy components. However, there still exist a certain microsegregation and a large uneven distribution of residual stress in as-deposited Inconel 718 alloy due to rapid heating and cooling in LSF. Heat treatment is a necessary method for further improv- ing the microstructure and mechanical properties. In this work, the microstructure and mechanical properties of LS- Fed Inconel 718 alloy heat treated with high temperature solution, 8 phase aging and double aging treatment was in- vestigated, the dislocation configuration of heat treated LSFed Inconel 718 alloy was characterized. It is found that the recrystallization occurs after the heat treatment, which leads to the transition from the columnar grain in the asdeposited to the equiaxed grain. Laves phase is dissolved completely after the heat treatment, and the needle phase and the γ″ phase precipitate along the grain boundary and in the γ phase matrix, respectively. The strength, elongation and reduction of area of the heat treated Inconel 718 alloy satisfy the wrought standards. There are two kinds of interactions between the dislocation and the γ″ phase, the shearing mechanism and the Orowan bypass mechanism, which play the dominant role corresponding to the lower and the higher distribution density of γ″ phase, respectively. Additionally, the dislocations pile up at the δ phase owing to the larger size of the δ phase in the heat treated Inconel 718 alloy compared with that in the wrought. The dislocation glide can be also hindered by carbide due to the pinning and drag effect.