Structure and Phase State of Ti49.4Ni50.6 (at%) Hydrogenated in Normal Saline

Abstract

The paper analyzes the surface structure and phase state of Ti49.4Ni50.6 (at%) hydrogenated at 295 K in normal saline (0.9% NaCl aqueous solution with pH = 5.7) at 20 A/m2 for 0.5–6 h. The analysis shows that the average hydrogen concentration in the alloy increases with the hydrogenation time tH as follows: slowly to 50 ppm at tH = 0.5–1.5 h, steeply to 150 ppm at tH = 1.2–2 h, and linearly to 300 ppm at tH = 2–6 h. According to Bragg–Brentano X-ray diffraction data (θ–2 θ, 2 θ ≤ 50°, CoKα radiation), the alloy in its scanned surface layer of thickness ~5.6 µm reveals a TiNiHx phase with x = 0.64 and x = 0.54 after hydrogenation for 4 and 6 h, respectively. The structure of this phase is identifiable as an orthorhombic hydride similar to β1–TiFeH0.94 (space group Pmcm), rather than as a tetragonal TiNiHx hydride with x = 0.30–1.0 (space group I4/mmm). Time curves are presented to trace the lattice parameters and volume change during the formation of such an orthorhombic phase from the initial cubic B2 phase in Ti49.4Ni50.6 (at%).

Effects of gas pressure and catheter length on the breakup of discontinuous NiTi droplets in electrode induction melting gas atomization

“…Nowadays, additive manufacturing (AM) methods, including selective laser melting (SLM) [11], electron beam melting (EBM) [12], wire arc additive manufacturing (WAAM) [13], and laser-based directed energy deposition (LDED) [14] have gained significant attention in the manufacturing of NiTi parts [15][16][17][18][19][20][21][22][23]. Since the AM method can reduce the three-dimensional manufacturing process to a two-dimensional one by layer-bylayer stacking, it can be used to fabricate NiTi with complex and precise structures.…”

“…Thus, it is of vital importance to reduce the production cost by increasing the yield. Many previous studies have focused on the SLM process and the use of NiTi powder [11,[15][16][17][18][19][20][21]. Few studies have been conducted on the preparation process of the NiTi powder using EIGA, with the purpose of increasing its yield.…”

Hydrogen’s Effect on the Shape Memory Effect of TiNi Alloy Single Crystals

“…By now, hydrogen's effect on MT has been studied mainly on TiNi polycrystals [1,[3][4][5][6][7][8][22][23][24][25][26]. These studies have shown that hydrogen's effect on the mechanical and functional properties is determined by the state of hydrogen in the initial B2 phase (as metal hydrides or atoms in a solid solution), its concentration, and the type of initial phase itself (austenite or martensite) upon hydrogenation.…”

“…At low concentrations below 400 wppm (wppm represents weight part per million), hydrogen contributes to an increase in the plasticity of the martensite phase and superelasticity. When hydrogen concentrations are greater than 400 wppm, hydrogen reduces plasticity; suppresses shape memory; and in TiNi alloys with a one-stage B2-B19 MT, induces the R phase through stresses [1,[3][4][5][6][7][8][9][10][22][23][24][25][26]. Nevertheless, despite numerous experimental data, interest in studying the effect of hydrogen on the functional properties of binary TiNi alloys remains due to their wide use in the dental and medical fields [11,18,21].…”