Flow characteristics and intrinsic workability of IN718 superalloy

This study focuses on deformation characteristics of superalloy IN718 by formulation of a new flowstress 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 recrystallization (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

Processing Maps: A Status Report

In the last two decades, processing maps have been developed on a wide variety of materials including metals and alloys, metal matrix composites, and aluminides, and applied to optimizing hot workability of materials and for process design in bulk metal working. Processing maps consist of a superimposition of efficiency of power dissipation and the instability maps, the former revealing the "safe" domain for processing and the latter setting the limits for avoiding undesirable microstructures. The dynamic materials model, which forms the basis for processing maps, is discussed in relation to other materials models. The application of dynamical systems principles to understanding of deterministic chaos in the system will help in achieving a greater degree of microstructural control during processing. The patterns in the hot working behavior as revealed by the processing maps of several classes of alloys relevant to technology are reviewed briefly. Processing maps have also been applied to analyze several industrial problems including process optimization, product property control, and defect avoidance, and a few examples are listed. With the processing maps reaching a matured stage as an effective tool for optimizing materials workability, expert systems and artificial neural network models are being developed to aid and prompt novice engineers to design and optimize metal processing without the immediate availability of a domain expert, and the directions of research in this area are outlined

Texture-dependent mechanical properties of metals and alloys

The influence of texture on elastic anisotropy, plastic anisotropy, formability, yield strength, ductility, fatigue, fracture toughness, and environmentally-aided fracture is reviewed with 86 references. Texture effects are significant, especially in hcp metals. Texture hardening adds to grain-boundary strengthening, but at the expense of ductility. The mechanism of texture development and its control in deformation processing are discussed

Dynamic recrystallization during hot deformation of aluminum: A study using processing maps

The hot deformation behavior of aluminum of different purities has been studied in the temperature range of 250 °C to 600 °C and strain-rate range of 10 3 to 102 s’1. On the basis of the flow stress data, the strain-rate sensitivity (m) of the material is evaluated and used for establishing power dissipation maps following the Dynamic Materials Model. These maps depict the variation of the efficiency of power dissipation [η = 2m/(m +1)] with temperature and strain rate. A domain of dynamic recrystallization (DRX) could be identified in these maps. While the strain rate at which the efficiency peak occurred in this domain is $10_{-3}$ $s^{−1}$ the DRX temperature is purity dependent and is 375 °C for 99.999 pct Al, 450 °C for 99.995 pct Al, 550 °C for 99.94 pct Al, and 600 °C for 99.5 pct Al. The maximum efficiency of power dissipation for DRX in aluminum is about 55 pct. The sigmoidal increase of grain size with temperature in the DRX domain and the decrease in the DRX temperature with increase in the purity of aluminum are very similar to that observed in static recrystallization, although DRX occurred at much higher temperatures

Influence of oxygen on dynamic recrystallization during hot working of polycrystalline copper

The characteristics of dynamic recrystallization (DRX) during hot working of copper containing various amounts of oxygen are studied in the temperature range 650–950 °C and strain-rate range $0.001–100 s^{-1}$. Using the dynamic materials model, the efficiency of power dissipation given by [2m(m + 1)], where m is the strain-rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. One of the domains in the processing map has been correlated with DRX, and in the DRX domain the temperature and strain rate for the efficiency peak dependend on the oxygen content. Up to about 150 ppm of oxygen, the DRX strain rate and temperature decrease; at higher oxygen contents, a steep decrease in DRX strain rate and an increase in DRX temperature have been recorded. The results are qualitatively explained on the basis of a simple DRX model where the rate of nucleation of a recrystallized grain boundary and the rate of its migration are considered. Oxygen present both as interstitial atoms and as oxide particles increases the rate of dislocation generation and hence the rate of nucleation of DRX. This results in lowering of the DRX strain rate. The large back stress caused by the presence of the oxide particles is responsible for the increase in DRX temperature

Effect of zinc content on the processing map for hot working of α brass

The hot deformation behavior of α brass with varying zinc contents in the range 3%–30% was characterized using hot compression testing in the temperature range 600–900 °C and strain rate range 0.001–100 s−1. On the basis of the flow stress data, processing maps showing the variation of the efficiency of power dissipation (given by Image where m is the strain rate sensitivity) with temperature and strain rate were obtained. α brass exhibits a domain of dynamic recrystallization (DRX) at temperatures greater than 0.85Tm and at strain rates lower than 1 s−1. The maximum efficiency of power dissipation increases with increasing zinc content and is in the range 33%–53%. The DRX domain shifts to lower strain rates for higher zinc contents and the strain rate for peak efficiency is in the range 0.0001–0.05 s−1. The results indicate that the DRX in α brass is controlled by the rate of interface formation (nucleation) which depends on the diffusion-controlled process of thermal recovery by climb