Structural and Morphological Features of TiNi-Based Powder Manufactured by the Method of Hybrid-Calcium Reduction

Abstract

An investigation of the structural features and surface morphology of a PV-N55T45 TiNi-based powder manufactured by the method of hybrid-calcium reduction is performed. The TiNi intermetallic compound is found in a two-phase state – B2 and В19′, and the following secondary phases are revealed: Ti₂Ni, Ti₄Ni₂(О, N, С), TiNi₃, and Ti₃Ni₄. It is observed that TiNi-based powder has dual – compact and spongy – morphology. The compact powder particles consist of oval coarse grains of TiNi separated by a massive Ti₂Ni interlayer. In the spongy particles, in contrast to the compact ones, the TiNi-phase prevails in the form of a single conglomerate of fine grains measuring 10–20 μm. In the Ni-enriched regions of the TiNi matrix the B19′-martensite is observed in multiple structural-morphological variants. In the compact particles the martensite structure represents orthogonal twin plates having different orientations within one grain. In the spongy particles, there is a different type of the martensite structure with multiple crystals of the B19′-martensite with the pyramidal lath morphology. On the surface of certain particles there is terraced relief formed due to bulk diffusion of atoms, surface diffusion of adatoms, and their interaction with the substrate defects.