Flow characteristics and intrinsic workability of IN718 superalloy

Fei Chen,Juan Liu,Hengan Ou,Bin Lu,Zhenshan Cui,Hui Long

doi:10.1016/j.msea.2015.06.093

Abstract

This study focuses on deformation characteristics of superalloy IN718 by formulation of a new flow stress model and detailed evaluation of intrinsic workability through the generation of three-dimensional (3D) processing maps with the support of optical microstructural observations. Based on thermomechanical simulation tests using a Gleeble-1500 machine, the flow stress model for superalloy IN718 was built and the flow stress throughout the entire deformation process was described by a peak stress only depending on Zener–Hollomon parameter and strain. The developed model exhibited the strain softening due to dynamic recrystallisation (DRX). The intrinsic workability was further investigated by constructing 3D processing maps. The 3D processing maps described the variations of the efficiency of power dissipation and flow instability domains as a function of strain rate, temperature and strain, from which the favourite deformation conditions for thermomechanical processing of IN718 can be established.

Highlights

In addition to achieving the alteration of their shapes, thermomechanical processing including hot forging is commonly used to tailor the service properties of metals and alloys through microstructural evolution in industrial production [1]
For metals with dynamic recovery (DRV), the flow stress at a constant strain rate initially increases with the increase of the strain because work hardening is a dominant mechanism in microstructural evolution, and this follows by a steady trend because of the balance between work hardening and DRV
The critical review paper by Lin et al [5] provided a summary of the constitutive models that may be divided into three categories: (1) phenomenological constitutive model [6,7], (2) physical-based constitutive model [8,9] and (3) artificial neural network (ANN) flow stress model [10,11]

Summary

Introduction

In addition to achieving the alteration of their shapes, thermomechanical processing including hot forging is commonly used to tailor the service properties of metals and alloys through microstructural evolution in industrial production [1]. In order to accurately simulate hot forging process by means of numerical techniques such as finite element method, it is important to precisely understand the constitutive equations which describe the dependence of the flow stress on the strain, strain rate and temperature. Zhou and Baker [33] studied the microstructural evolution behaviour during dynamic and metadynamic recrystallisation processes by using hot compression tests They found that the recrystallised grain size is sensitive to the deformation temperature and strain rate. In order to predict the grain size of IN718 superalloy during holding period after hot forging, Zhang et al [35] investigated the effects of the hot deformation parameters (temperature, strain rate and strain) and holding time on the grain growth by using a mathematical equation. The workability for IN718 superalloy was further evaluated with the support of optical microstructural observations in deformed IN718

Material and experiments

Modelling of flow stress and determination of parameters

Intrinsic workability analysis

Conclusions