Formation of pores and amorphous-nanocrystalline phases in porous TiNi alloys made by self-propagating high-temperature synthesis (SHS)

• Published in: Advanced powder technology : the international journal of the Society of Powder Technology, Japan Japan, 2019-04, Vol.30 (4), p.673-680
• Main Authors: Gunther, Victor, Yasenchuk, Yuri, Chekalkin, Timofey, Marchenko, Ekaterina, Gunther, Sergey, Baigonakova, Gulsharat, Hodorenko, Valentina, Kang, Ji-hoon, Weiss, Sabine, Obrosov, Aleksei
• Format: Article
• Language: English
• Subjects: Heat-and-mass transfer; Pore formation; Porous TiNi alloys; SHS; Surface structures
• ISSN: 0921-8831; 1568-5527
• DOI: 10.1016/j.apt.2018.12.011

[Display omitted] •Complex intermetallic oxycarbonitrides Ti4Ni2(O,N,C) constitute the surface layer.•Dual amorphous-nanocrystalline epitaxial substrate imparts an enhanced corrosion resistance.•Amorphous-nanocrystalline phases occur due to the peritectic liquid managed by reaction gases.•Porous SHS TiNi contains a lot of nonmetallics embedded into the intergranular peritectic phases. The objective of this study was to examine the mechanism how the surface of porous TiNi compounds produced by SHS method evolves. The prepared samples were investigated using light-microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS). The results indicated that the surface of all pores is represented by a granular stratum due to dendrite liquation by peritectic crystallization mechanism. The voids of 2–15 μm in size are formed owing to a capillary spreading of the liquid. Reaction gases with dissociated carbon, nitrogen, and oxygen are responsible for heat-and-mass transfer through the forming pores. High pressure-temperature effect of reaction gases on the melt causes the forming voids to coalesce, as well as transfers the peritectic liquid (PL) throughout the open pores catalyzing a distinctive spitted topography. It is through the chemisorption of gasiform nonmetallics by the pore surface melt, where these impurities are chemically bound, that it was formed a massive corrosion-resistant amorphous-nanocrystalline stratified shell deduced as an intermetallic oxycarbonitride layer.