EFFECT OF LOW HYDROSTATIC PRESSURES ON PHASE FORMATION IN THE DISPERSED MULTILAYER SYSTEM NI-AL

The methods of X-ray phase and X-ray microprobe analysis, optical, and electron microscopy are used for an investigation of the phase growth kinetics in the system Ni Al at temperatures T almost-equal-to (0.4 to 0.6) T(m) (T(m) melting temperature of the basic phase Ni2Al3) in dependence on the hydrostatic pressure of Ar P = 1 x 10(5) and 5 x 10(7) Pa. Two types of samples are used: 1. a massive double layer obtained by sintering of Ni and Al plates with thickness almost-equal-to 3 x 10(-3) m and 2. dispersed multilayer samples in which thin layers of Ni and Al (almost-equal-to 1 x 10(-7) M to 5 x 10(-7) M) were alternating. In both types of samples the small pressures speed up the growth of the intermetallide Ni2Al3, transforming with time to NiAl. This effect is connected with the perfection of interface boundaries as a result of elimination of cavities under pressure. In double layer samples Ni-Al this leads to an increase of the diffusion front across the interface boundary Ni2Al3(NiAl)-Al, in multilayer samples, where separate phase inclusions are formed, to a more active nucleation on more perfect interphase boundaries.