The crystal chemistry of martensite in NiTiHf shape memory alloys

Zarinejad, Mehrdad; Liu, Yong; White, Timothy John

doi:10.1016/j.intermet.2008.04.004

Cited by 55 publications

(34 citation statements)

References 32 publications

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“…Accommodation of Cu in the monoclinic martensitic TiNi takes place by substitution of the Ni atom, and it is assumed that replacements are controlled primarily by the size mismatch of Cu [36]. The atomic radii of Ti, Ni and Cu are 1.45 Å, 1.29 Å and 1.28 Å, respectively.…”

Section: Resultsmentioning

confidence: 99%

Effect of Cu Content on Atomic Positions of Ti50Ni50−xCux Shape Memory Alloys Based on Density Functional Theory Calculations

Gou

Liu

2015

Metals

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Abstract:The study of crystal structures in shape memory alloys is of fundamental importance for understanding the shape memory effect. In order to investigate the mechanism of how Cu content affects martensite crystal structures of TiNiCu alloys, the present research examines the atomic displacement of Ti50Ni50−xCux (x = 0, 5, 12.5, 15, 18.75, 20, 25) shape memory alloys using density functional theory (DFT). By the introduction of Cu atoms into TiNi martensite crystal to replace Ni, the displacements of Ti and Ni/Cu atoms along the x-axis are obvious, but they are minimal along the y-and z-axes. It is found that along the x-axis, the two Ti atoms in the unit cell move in opposite directions, and the same occurred with the two Ni/Cu atoms. With increasing Cu content, the distance between the two Ni/Cu atoms increases while the Ti atoms draw closer along the x-axis, leading to a rotation of the (100) plane, which is responsible for the decrease in the monoclinic angle. It is also found that the displacements of both Ti atoms and Ni/Cu atoms along the x-axis are progressive, which results in a gradual change of monoclinic angle and a transition to B19 martensite crystal structure.

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Section: Resultsmentioning

confidence: 99%

Effect of Cu Content on Atomic Positions of Ti50Ni50−xCux Shape Memory Alloys Based on Density Functional Theory Calculations

Gou

Liu

2015

Metals

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“…The weight percentage of the Ni 4 (Ti,Hf) 3 precipitate in the aged alloys were determined by quantitative X-ray diffraction using the fundamental parameter Rietveld refinement procedure, as detailed in Ref. [33], by considering the crystal structure models of the martensite and precipitate. A TA 2920 differential scanning calorimeter was used to determine the M s temperature of these alloys at a 10 C/min cooling rate.…”

Section: Experimental Methodsmentioning

confidence: 99%

Transformation temperature changes due to second phase precipitation in NiTi-based shape memory alloys

2009

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“…Among these tertiary elements that favor high temperature applications of SMA, Hf is a chemical element economically accessible. There are three kinds of Ni-Ti-Hf SMA: interstitial (Ni 50-X Ti 50 Hf X .at%: rich in titanium), equiatomic (Ni 100-X/2 Ti 100-X/2 Hf X .at% (5 ≤ X ≤ 20)) and substitutional (Ni 50 Ti 50-X Hf X .at%: rich in nickel) (Zarinejad et al, 2008). The present paper studied the latter due to the fact that it has been broadly discussed in literature (Sanjabi et al, 2005), when compared to the former two kinds.…”

Section: Introductionmentioning

confidence: 99%

Effects of composition on transformation temperatures and microstructure of Ni-Ti-Hf shape memory alloys

Soares

Castro

2019

REM, Int. Eng. J.

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High transformation temperature shape-memory alloys (HTSMA) usually present a martensitic transformation temperature (Ms) starting at 100 ºC. That is the case of high nickel Ni-Ti-Hf alloys. This article presents experimental results obtained from arc melting of Ni 50 Ti 50-X Hf X .at% (X = 8, 11, 14, 17 and 20 .at%) alloys. This process homogenized every composition with similar relative crystallinity. Results confirm that transformation temperatures (TT) increase with increasing the amount of Hf. A martensitic matrix is formed by two metastable phases: R and B19'. From all the alloys studied, the B19' phase presented the highest percent fraction. Gradually adding Hf 3 .at% promoted a slow increase of crystalline fraction of R phase and a slow reduction of phase (Ti, Hf) 2 Ni, located at grain boundaries. Coherent/semi-coherent interface between (Ti, Hf) 2 Ni phase and the matrix may intensify the driving force for the formation of R phase, present on X-ray diffractograms.

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The crystal chemistry of martensite in NiTiHf shape memory alloys

Cited by 55 publications

References 32 publications

Effect of Cu Content on Atomic Positions of Ti50Ni50−xCux Shape Memory Alloys Based on Density Functional Theory Calculations

Effect of Cu Content on Atomic Positions of Ti50Ni50−xCux Shape Memory Alloys Based on Density Functional Theory Calculations

Transformation temperature changes due to second phase precipitation in NiTi-based shape memory alloys

Effects of composition on transformation temperatures and microstructure of Ni-Ti-Hf shape memory alloys

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