Effects of Microstructure on the High Temperature Constitutive Behavior of IN100

Abstract

An experimental program was conducted in order to determine the effects of microstructure on the high temperature constitutive behavior or powder-processed IN100. The relevant application is the high pressure turbine disk in a gas turbine engine. Eight different microstructures were prepared, with 260 o C yield strengths ranging from 945 to 1165 MPa.For each microstructure, tensile tests and cyclic constitutive tests were conducted at 260 o C and 650 o C. This paper reports on the tensile test results. The tensile curves were fit to a modified Ramberg-Osgood constitutive model, which contains four material constants. It was found that two of the constants were sensitive to microstructure, while two others were not. The constant K 1 , which is analogous to the strength coefficient in the traditional power-law hardening expression, varied in exactly the same way as the yield strength. The variations in yield strength and K 1 were consistent with the Huther-Reppich strength model, with the secondary γ' size being the dominant microstructural term. There was also a smaller effect of tertiary γ' and grain size. The hardening exponent n, which is basically the inverse of the hardening exponent in the traditional power-law hardening expression, was sensitive to secondary γ' size and also to the presence of primary γ', but not to grain size.

The Effects of Heat Treatment and Microstructure Variations on Disk Superalloy Properties at High Temperature

“…7) is consistent with the predominance of precipitate shearing by strongly coupled dislocation pairs for all samples given aging heat treatments. The associated models [7,14] would imply strength is proportional to (f/d) 0.5 here. However, shearing of relatively small γ T ′ would not require coupled dislocations to travel through the precipitate.…”

“…The changes in various mechanical properties due to heat treatment in similar disk superalloys have been recently related to effects on microstructural features including morphology of the γ ′ precipitates [7], grain boundary serrations [8], and grain boundary carbides [9]. Processing-microstructure models are in active development [10,11] that could potentially model how processing paths can tailor such microstructural features.…”

Microstructure-sensitive modeling of polycrystalline IN 100

“…Uniaxial isothermal fatigue tests were conducted at 650°C (Milligan et al, 2004) for each material with microstructure attributes listed in Table 1. Two characteristic types of strain-controlled histories are used for our purposes in fitting the models, one type with variable strain amplitude and strain rate cycling with strain hold periods at maximum (or minimum) strain peaks, and the other type with variable amplitude cycling but no strain hold periods.…”

Grain Boundary Curvature in a Model Ni-Based Superalloy

“…This alloy was produced as part of a program to develop analytical models for the mechanical behavior and microstructural development in alloys such as IN100 [10] and was chosen for the investigation described here because it contains low levels of impurities, has a highly homogenous microstructure, and has a fine initial grain size.…”