Phase formation and structure in rapidly quenched Ni50Al50 alloy

Abstract

A novel synthesis process combining arc melting and rapid quenched system has been developed to manufacture Ni50Al50 alloy which is not easy to form using conventional fabrication approaches. In this work, Nickel-Aluminum alloys with nominal composition Ni50at%Al50at% were prepared by melting pure nickel pieces (99.97%) and pure Al pieces (99.999%) under the protection of argon atmosphere using induction furnace followed by experiments performed by a new in-situ solidification method with arc melting. Alloy so produced is characterized by a compact structure with a minimum porosity. X-ray phase analysis revealed the existence of a one-phase structure of the rapidly quenched Ni50Al50 alloy. In this study, rapid quenching in liquid nitrogen from a high-temperature (1638 °C) state resulted in a non-uniform grain size distribution for Ni50Al50 alloy. Some grains were as small as 20 nm, while larger grains reached about 100 nm, with an average diameter of 74.8 nm. In contrast, cast ingots made with an induction furnace had larger average grain sizes (160-600 nm). These findings demonstrate the potential to create nanocrystalline structures in the Ni50Al50 alloy through rapid solidification in liquid nitrogen, offering the possibility of milling the synthesized alloy into nano-powders for composite matrix use during sintering. The nano-structuration behaviors and microstructures for Ni50Al50 alloy synthesis and powders nanoparticles obtained by milling have been investigated with the aids of Optical Microscopy (OM), X- Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).The results show that the samples rapidly quenched in liquid nitrogen from high temperature as solidus state with temperature slightly lower than 1638°C, restrain the precipitation of NiAl phase as clusters, consequently, the NiAl specimens above solidus follow by rapidly quenched in liquid nitrogen among NiAl nanoparticles make the phase distributes homogeneously.