Microstructural characterisation of four compositions of Ni3Al-based alloys (industrially designated as 463, 465, 790 and 794) prepared by a vacuum gas atomization technique was performed for 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 was 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, root mean square strains, dislocation density, degree of long range order, antiphase boundary probability, antiphase boundary domain size etc. The results revealed considerably higher values of a on hot-pressing with anisotropic values of domain sizes and root mean square strains. The domain sizes decreased and root mean square strains increased upon hot-pressing. A dislocation density as high as 1011/cm2 was observed in hot-pressed samples. With increasing alloying additions and on hot-pressing the degree of long-range order decreased. A broadening study of superlattice reflections revealed an increase in antiphase boundary probability and a decrease in antiphase boundary domain sizes in the hot pressed states of the materials. Grain sizes were reduced on hot pressing with most complex alloy 790 having smallest grain sizes. The values of hardness and work hardening coefficients were high on Cr containing alloy (465, 790) compared to Fe containing (794) and unalloyed (463) alloys.

Effect of Alloying, on the Microstructure and Mechanical Properties of Ni3Al. Shee, S.K., Pradhan, S.K., De, M.: Journal of Alloys and Compounds, 1998, 265[1-2], 249-56