Effect of Hydrogen Redistribution during Aging on the Martensitic Transformation and Superelasticity of Nanocrystalline TiNi Alloy

Батурин, А. А.; Лотков, А. И.; Гришков, В. Н.; Rodionov, Ivan; Zhapova, Dorzhima

doi:10.4028/www.scientific.net/jmnm.31.30

Cited by 1 publication

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“…At the same time, such alloys after their long contact with a hydrogen-containing environment, e.g., biological, are prone to embrittlement [5][6][7][8]. At near-room temperatures (290-310 K), the rate of diffusion process in TiNi is low such that a large amount of hydrogen first goes into its surface layers and then diffuses deep into the material [9,10]. As has been shown [10][11][12], the saturation of TiNi alloys with hydrogen decreases the temperatures of thermoelastic martensite transformations from a cubic B2 phase to a rhombohedral R and a monoclinic B19 phase, and this impairs their superelasticity and shape memory effect [8,10,13,14] and causes their cracking and fracture [15,16].…”

Section: Introductionmentioning

confidence: 99%

“…At near-room temperatures (290-310 K), the rate of diffusion process in TiNi is low such that a large amount of hydrogen first goes into its surface layers and then diffuses deep into the material [9,10]. As has been shown [10][11][12], the saturation of TiNi alloys with hydrogen decreases the temperatures of thermoelastic martensite transformations from a cubic B2 phase to a rhombohedral R and a monoclinic B19 phase, and this impairs their superelasticity and shape memory effect [8,10,13,14] and causes their cracking and fracture [15,16]. One of the contributory factors for such functional and mechanical degradation is the formation of hydrides [16], and structural studies are needed to clarify their effect on the properties of TiNi alloys.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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%).

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