Abstract

    The present paper provides details on the development of models for calculating the material properties of Ni-based superalloys and makes extensive comparison of calculated results against experiment. The first part of the paper concentrates on extending a previously reported capability for the calculation of mechanical properties, such that strain rate dependent flow stress curves can be calculated from room temperature to the liquid state. Subsequent application to modelling of fatigue properties is briefly discussed. The second part concentrates on extending

kinetic formalisms to calculate the volume, size and distribution of γ' in wrought and cast alloys, which are subsequently used in the prediction of mechanical properties as a function of heat treatment.

Introduction

    Work on the development of modelling tools to calculate the material properties of multi-component Ni-based superalloys has been presented at previous Superalloy meetings [1,2,3]. The use of such modelling has become quite widespread through the development of the software programme JMatPro, providing significant benefit to many users and producers of Ni-based superalloys.

    The present paper reports on recent technical work that has extended the capability of JMatPro [3] to (i) model high temperature, strain rate dependent flow stress curves, with subsequent application to the calculation of fatigue properties and (ii) the development of microstructure models for calculating the volume, size and distribution of γ' in wrought and cast alloys that can subsequently be used in the prediction of mechanical properties. In each case calculated results will be compared with experiment.

High Temperature Mechanical Properties 

    Previous work on modelling the mechanical properties of Ni-based superalloys [3,4] has concentrated on predicting proof and tensile strength as a function of temperature and strain rate, as well as creep properties [5]. Generally speaking, room temperature (RT) strength decays mono-tonically with increasing temperature until the point where it enters into a temperature regime where there is a sharp fall in strength and where flow stress then becomes much more strongly dependent on strain rate. This sharp drop in strength is due to a change from a deformation me-chanism dominated by dislocation glide (DDG) at low temperatures to one dominated by dislocation climb (DDC) at higher temperatures, where the latter is usually the controlling mechanism for creep.

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