Hot working characteristic of as-cast and homogenized Ni-Cr-W superalloy

The hot working behavior of as-cast Ni-Cr-W superalloy has been studied using, constant strain rate isothermal compression tests in the temperature range 1000-1200 degrees C and strain rate range 0.001-10 s(-1). At lower strain rates (<= 0.1 s(-1)), the flow curves exhibited a peak stress characteristic followed by a steady-state flow stress at large strains while continuous flow softening occurred at higher strain rates. The stress exponent value of 5.56 and apparent activation energy of 456 kJ/mol was calculated by a standard kinetic equation over the entire range of temperatures and strain rates. The power dissipation map exhibited a single domain in the temperature range 1050-1200 degrees C and strain rate range 0.01-0.001 s(-1) with a peak efficiency of about 44% occurring at 1200 degrees C and 0.001 s(-1). Microstructural observations revealed that this domain represented dynamic recrystallization (DRX) and must be the optimum conditions for hot working the material. As predicted by continuum criterion, flow instabilities occurred in the form of adiabatic shear bands when deformed at strain rates above 0.1 s(-1) and at temperatures below 1000 degrees C, and intercrystalline cracking occurred when deformed at 1200 degrees C and 10 s(-1). Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.