Abstract
Creep cavities associated with sigma phase particles appeared at grain boundaries in 316 stainless steel specimens crept under the stress condition of 37MPa and 53MPa at 750°C. In order to sinter the cavities formed, the specimens were annealed, hot-isostatically pressured and compressively crept at 750°C. Precise density measurements and SEM observations on these specimens were made to study the rate of sintering.
The results obtained were as follows;
(1) Small cavities (<2μm) disappeared by annealing, whereas large crack-like cavities (>2μm) still remained after annealing. The sintering rate calculated by the grain boundary diffusion model was very much higher than the experimental one. This showed that sintering of cavities was not controlled by grain boundary diffusion.
(2) The rate of sintering was considerably accelerated under the hot-isostatic pressure condition of 37MPa.
(3) The effect of compressive creep (20 to 53MPa) on sintering was most marked. Very large crack-like cavities (≥10μm) disappeared quickly by compressive creep. The rate of sintering in compressive creep was more than double as quick as that in hot-isostatic pressure. It was considered that the compressive strain removed the constraint to sintering of cavities and activated the atomic diffusion from grain boundaries to cavity surface.
