P. Revel et al., MECHANICAL-PROPERTIES AND MICROSTRUCTURAL EVOLUTION OF A COBALT-BASE ALLOY COATING, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 169(1-2), 1993, pp. 85-92
Several isothermal mechanical tests have been performed on a cobalt su
peralloy to determine the parameters of a viscoplastic behavior law in
the range (20-700-degrees-C). These parameters have been identified b
y means of a systematic numerical procedure (a computer program for si
mulation and identification). The microstructural evolution during the
mechanical tests has been examined in relation to the evolution of th
e internal variables of the viscoplastic model. It was found that the
material softens at room temperature, mainly as a result of an isotrop
ic component decrease. However, at high temperatures (500-700-degrees-
C), the material hardens, mostly owing to a kinematic component increa
se. The deformation mode, i.e. the martensitic transformation, has bee
n identified for all the temperatures studied. At high temperatures ca
rbide precipitation on stacking faults and deformation bands has been
observed. Complementary tests have shown that, at high temperatures, t
he further addition of carbide precipitates dissolves by dislocation g
lide and a diffusion mechanism. At room temperature, after heat treatm
ent at 700-degrees-C, carbides precipitated on deformation bands induc
ed the formation of ''hard'' zones. These microstructural observations
have been correlated with the important part of the kinematic term in
the stress increase.