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.