Ball indentation studies on the effect of aging on mechanical behavior of alloy 625

The effect of aging on mechanical behavior of Alloy 625 was investigated us ing the non-destructive Stress-Strain Microprobe (SSM) system. SSM is based on an automated ball indentation (ABI) technique, and involves multiple in dentations by a small spherical indenter at a single penetration location u nder strain-controlled conditions. The technique permits evaluation of mech anical properties such as yield strength, ultimate tensile strength, streng th coefficient and strain hardening exponent. Alloy 625 was aged at six dif ferent temperatures in the range of 873-1173 K for 500 h each. ABI tests we re carried out at room temperature and at 473 K. The variation of yield and ultimate tensile strengths with aging temperature exhibited a peak in stre ngth following aging at 973 K. The peak stress was 1.5 times the strength o f the unaged material, and the strength after aging at 1173 K was nearly eq ual to that of the unaged material. The peak in strength is attributed to t he precipitation of the gamma " phase. The fall in strength due to aging ab ove 973 K is attributed to the precipitation, growth and dissolution of del ta-phase precipitates. These studies demonstrate that ABI can be used as a non-destructive technique to determine changes in mechanical properties of nickel base alloy components due to aging. (C) 1999 Elsevier Science S.A. A ll rights reserved.