Abstract
The material behavior of three Ni-base superalloys (Inconel® 718, Allvac® 718PlusTM and Haynes® 282® ) during in-phase cyclic mechanical and thermal loading was investigated. Stress controlled thermo-mechanical tests were carried out at temperatures above 700 ∘ C and different levels of maximum compressive stress using a Gleeble® 3800 testing system. Microstructure investigations via light optical microscopy (LOM) and field emission gun scanning electron microscopy (FEG-SEM) as well as numerical precipitation kinetics simulations were performed to interpret the obtained results. For all alloys, the predominant deformation mechanism during deformation up to low plastic strains was identified as dislocation creep. The main softening mechanism causing progressive increase of plastic strain after preceding linear behavior is suggested to be recrystallization facilitated by coarsening of grain boundary precipitates. Furthermore, coarsening and partial transformation of strengthening phases was observed. At all stress levels, Haynes® 282® showed best performance which is attributable to its stable microstructure containing a high phase fraction of small, intermetallic precipitates inside grains and different carbides evenly distributed along grain boundaries.
Highlights
A strong demand for higher efficiency, reduced fuel consumption, CO2 and NOx emissions as well as weight reduction in aircraft engines lead to a substitution of presently used materials by novel light-weight, high temperature materials like γ -TiAl alloys
Main performance criterion for die material was defined as service time until a maximum plastic strain of 0.1 was reached
To better interpret results from physical simulations, deformed microstructures were investigated by use of light optical microscopy and field emission gun scanning electron microscopy
Summary
A strong demand for higher efficiency, reduced fuel consumption, CO2 and NOx emissions as well as weight reduction in aircraft engines lead to a substitution of presently used materials by novel light-weight, high temperature materials like γ -TiAl alloys. Isothermal forging, as state of the art process, uses Mo-based die material to withstand high processing temperatures. Bohler Schmiedetechnik GmbH & Co KG has developed a hot-die forging process with die temperatures above 700 ◦C. These temperatures necessitate the use of high temperature resistance materials as die material [1]. Aim of the present work was to compare the applicability of the three Ni-base superalloys as promising die material for TiAl turbine blade hot-die forging
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