选区激光熔化IN718合金固溶过程成分均匀化规律的研究

Study on Composition Homogenization of IN718 Alloy Fabricated by Selective Laser Melting During Solid Solution Treatment

选区激光熔化技术具有成形自由度高、成形精度高、成形效率高的优势,在高温合金的曲面结构的制造中具有巨大的应用潜力。本工作采用选区激光熔化技术制备IN718合金,并对合金进行不同条件下的固溶热处理,利用SEM、TEM以及XRD等多种手段研究了沉积态合金中的成分偏析、析出相的分布、固溶过程中成分均匀化的规律、最短固溶时间和固溶温度之间的函数关系,以及固溶冷却过程中析出相的形成过程。结果表明:合金制备过程中较快的凝固速率使得合金在晶界处及亚结构的边界处产生了Nb、Ti元素的成分偏析带,偏析带的厚度约为50 nm,并且在成分偏析带形成了Laves相和MX相。在高于980℃的条件下对沉积态合金进行固溶处理,成分偏析带回溶,最短固溶时间与最低固溶温度的关系为:t=1/3167·exp (21597/T)。固溶后较低的冷却速率会使合金中产生γ″相,增加合金的硬度。

Selective laser melting technology has the advantages of high forming freedom,high forming precision and high forming efficiency.It has great application potential in manufacturing curved surface structure of superalloy.In this work,IN718 alloy was prepared by selective laser melting technology,and the alloy was subjected to solution heat treatment under different conditions.The composition segregation,the distribution of precipitates,the law of composition homogenization in the process of solution,the functional relationship between the shortest solution time and solution temperature,and the formation process of precipitates in the process of solution cooling were studied by means of SEM,TEM and XRD.The results show that the faster solidification rate during the preparation of the alloy makes the composition segregation band of Nb and Ti elements appear at the grain boundary and the boundary of substructure.The thickness of the segregation band is about 50 nm,and Laves phase and MX phase are formed in the composition segregation band.When the temperature is higher than 980℃,the component segregation will solute to the matrix.The relationship between the shortest solution time and the lowest solution temperature is:t=1/3167·exp 21597/T.The lower cooling rate will cause the formation ofγ″phase during solution cooling process,which will increase the hardness of the alloy.