The kinetics of coarsening or γ' precipitates under applied compressive stress were investigated in monocrystalline Ni-Al alloys (nominal composition 13.36 at. Al) aged at 640 ℃. The specimens tested were doubly tapered cylinders or right circular cylinders. The maximum stress used was ～150 MPA; plastic deformation was less than 4 at the longest aging time (1021 h). The scatter in the data was large and is attributed to experimental factors discussed in the text. We find that compressive stress retards the kinetics of coarsening by 20-25 at 105 MPa. The particle size distributions become broader as the stress increases. We attribute the slower kinetics under compressive stress to its effect on the coefficient of diffusion of Al. A semiquantitative model in support of this idea is the subject of a companion paper.
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