Cheng Ai

Two-phase microstructural evolution at high temperatures for γ′-richen single crystal superalloys

Abstract The two-phase microstructural evolution and the remained fractions of γ′ were investigated by scanning electron microscope (SEM) for a series of γ′-richen single crystal superalloys from the IC alloys system. At alloys IC31 and IC32, high levels of the dissolution of γ′ cause the remarkable damages of two-phase microstructure, especially when the fraction drops to less than 45%, the γ′ phase becomes sphere significantly and the two-phase interface distorts fairly. And the relationship between different degrading stages and the remained fractions are discussed systemically. The dissolution temperatures, Tsol, of IC alloys determined by differential scanning calorimetry (DSC) are further considered. It is found that there is a good linear relationship between the Tsol and the remained fraction of the γ′ at 1200°C and the slide keeps fixed as about 0·5%/°C. Meanwhile, the remained fraction of the γ′ seems to play an important role on the mechanical properties, and a method with Tsol used to estimate the properties at 1200°C is proposed.

Effect of heat treatment and long-term age on microstructure of a Ni3Al-based single crystal superalloy

Abstract A new Re-containing Ni3Al-based single crystal superalloy was recently developed by our group. In order to obtain uniform microstructure and further improve mechanical properties of superalloy, the heat treatment regime (i.e. solution treatment and age treatment) was investigated by experimental analysis and dynamics calculation (by JMatPro), and the optimal heat treatment regime was 1335–1355°C/16 h, air cooling (AC)+1140°C/2 h, AC+870°C/32 h, AC. Meanwhile, completely heat-treated experimental alloy was long-term aged at 1150°C for 25–1000 h, which showed very good microstructural stability and the coarsening behaviour of γ′ phases agreed well with the typical Lifshitz–Slyozov–Wagner (LSW) theory.

Effect of Ta on the Solidification Behavior of Ni3Al-Base Single-Crystal Superalloys

Two kinds of Ni3Al-base SC superalloys, including IC31A (3wt.%Ta) and IC31B (6wt.%Ta) were investigated in the present study by using the differential scanning calorimetry (DSC) and isothermal quenching technology. The results showed that the larger amount of blocky γ′ phases existed in IC31B than that in IC31A. In the solidification process, the primary phase in IC31B was γ′ phases while in alloy IC31A the primary phase was γ phases. Besides, the solidification rate of IC31B in the early stage was lower than that in IC31A.

δ-Mo49Ni51 phase in a Ni3Al based single crystal superalloy during thermal exposure

Abstract In the paper, the hexagonal δ-Mo49Ni51 phase had been investigated in a Mo-rich Ni3Al based single crystal superalloy with Re additions in 3–5 wt%. The δ-Mo49Ni51 phase was identified by transmission electron microscopy (TEM), scanning electron micrograph (SEM) and electron probe micro-analysis (EPMA). Before thermal exposure, the microstructure of the alloy was the cuboidal ordered γ′ phase in coherent with the disordered γ matrix without any precipitation. During thermal exposure, the strip-like, faceted, plate-shaped δ-Mo49Ni51 phases significantly were precipitated. By the means of the composition analysis of TEM/EDS and EPMA/EDS, the elements Ni, Mo and Re were rich obviously in δ-Mo49Ni51 phase. Furthermore, the crystallography relationships between the δ-Mo49Ni51 phase and γ phase have been reported.