EFFECT OF LOW HYDROSTATIC PRESSURES, ON THE DIFFUSIONAL PHASE-TRANSFORMATION IN DISPERSED MULTILAYERED SYSTEMS

The effect of low hydrostatic pressures on the growth kinetics of phas es in two-layer and multilayer Ni-Al diffusion specimen was studied by x-ray diffractometric, microprobe, optical and electron microscopic m ethods at temperatures T = 0.4-0.6 T-m (T-m = melting temperature of t he principal Ni2Al3 phase). Two types of specimens were investigated: massive two-layer, consisting of similar to 3.10(-3) m thick sheets of nickel and aluminum presintered together, and finely dispersed multil ayered, consisting of alternating layers of 10(-7)-5.10(-7) m thick ni ckel and aluminum sheets. It was found that the application of pressur e accelerated the formation of the Ni2Al3 and NiAl phases in both type s of diffusion specimens. This effect is attributed to the action of p ressure in preventing the formation of diffusional porosity at phase i nterfaces, and improving diffusional contact between adjoining layers.