Effect of Withdrawal Rate and Heat Treatment on Ni-Based Superalloy Microstructure

摘要

The most promising method for casting gas turbine engine blades is the direct crystallization method during which a complex multilevel structure is formed in Ni-based superalloy. The main hardening is achieved by precipitation of the γ'-phase particles consisting of Ni_3Al intermetallic compound. In addition, carbide hardening is realized in the ZhS30 super alloy. The microconstituents size and the dispersion degree of the dendritic structure have a direct influence on the heat resistance and the mechanical characteristics of the blade. The effect of withdrawal rate and heat treatment on ZhS30 super alloy microstructure was investigated in this work. It was found that the maximum density of dendrites and increased proportion of globular carbides compared with carbides such as "Chinese Hieroglyph" correspond to a withdrawal rate of 3 mm/min. In addition, when we cast at this rate it is possible to obtain single-crystal blades. Energy-dispersive microanalysis has shown that heat treatment leads to chemical composition equalization of the dendrites axes and inter-axis regions, and also provides partial dissolution of the non-equilibrium eutectic with the formation of micropores and partial dissolution of carbides. Also the result of heat treatment is the formation of a uniformly ordered γ'-phase, which is homogeneous in size 0.35-0.45 μm and has regular cubic morphology.