Effect of alloying on the microstructure and mechanical properties of Ni3Al

Abstract

Microstructural characterisation of four compositions of Ni3Al based alloys (industrially designated as 463, 465, 790 and 794) prepared by a vacuum gas atomization technique has been done in the powder and hot pressed forms of the materials by adopting the most recent version of X-ray line profile studies (assuming pV functions) along with high resolution optical and scanning electron microscopy. Mechanical properties of the hot pressed samples has been measured by microhardness studies. X-ray line profile study reveals the defect related features of the microstructures in terms of the parameters such as change in the lattice parameters, stacking and multilayer fault densities (α and β), particle (domain) sizes, r.m.s strains, dislocation density, degree of long range order, antiphase boundary (APB) probability, APB domain size etc. The results revealed considerably higher values of α on hot-pressing with anisotropic values of domain sizes and r.m.s strains. The domain sizes decrease and r.m.s strains increase on hot-pressing. A dislocation density as high as 1011 cm cm−3 has been observed in hot-pressed samples. With increasing alloying additions and on hot-pressing the degree of long-range order decreases. A broadening study of superlattice reflections reveals an increase in APB probability and a decrease in APB domain sizes in the hot pressed states of the materials. Grain sizes are reduced on hot pressing with most complex alloy 790 having smallest grain sizes. The values of hardness and work hardening coefficients are high on Cr containing alloy (465, 790) compared to Fe containing (794) and unalloyed (463) alloys.