The Effect of Hafnium Content on the Transformation Temperatures of Ni49Ti51-xHfx. Shape Memory Alloys

Angst, David R.; Thoma, Paul E.; Kao, Ming-Yuan

doi:10.1051/jp4/199558747

Cited by 65 publications

(63 citation statements)

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“…Fig. 77 summarize the effect of third element on transformation temperature reported in the literature [310][311][312][313][314]. It is found that most alloying elements lower transformation temperature; but there are only a few, notably Pd, Pt, Au, Zr and Hf, which increase transformation temperature.…”

Section: Effect Of Alloying Element On Transformation Temperaturementioning

confidence: 94%

Physical metallurgy of Ti–Ni-based shape memory alloys

Otsuka

Ren

2005

Progress in Materials Science

3,928

2,030

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Section: Effect Of Alloying Element On Transformation Temperaturementioning

confidence: 94%

Physical metallurgy of Ti–Ni-based shape memory alloys

Otsuka

Ren

2005

Progress in Materials Science

3,928

2,030

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“…Those elements have shown an effective increasing of the transformation temperatures over 575 K for amounts higher than 20 at. pct, [7,8] but they have also shown a poor stability upon thermal treatments even at temperatures slightly higher than A f or in martensite. [9,10] Another way to enlarge the range of applications of SMAs, apart from the addition of extra elements to the Ni-Ti system, is the use of nonconventional production techniques for casting, such as rapid solidification by melt spinning.…”

Section: Introductionmentioning

confidence: 99%

Shape memory properties of Ni-Ti based melt-spun ribbons

Santamarta¹,

Cesari²,

Pons³

et al. 2004

Metall Mater Trans A

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Shape-memory properties of equiatomic NiTi, Ni 45 Ti 50 Cu 5 , and Ni 25 Ti 50 Cu 25 ribbons made by melt spinning have been studied by temperature inducing the martensitic transformation under constant tensile loads. Recoverable strains above 4 pct can be obtained under ϳ100 MPa loads for the NiTi and Ni 45 Ti 50 Cu 5 ribbons, transforming to B19Ј martensite. The B19 martensite is formed in the Ni 25 Ti 50 Cu 25 ribbon after crystallization, and according to the lowering in transformation strain as Cu content increases, the recoverable strain is close to 2.5 pct for ϳ150 MPa load. The transformation temperatures exhibit a linear dependence on the applied stress, which can be quantitatively described by means of a Clausius-Clapeyron type equation. The NiTi and Ni 45 Ti 50 Cu 5 ribbons exhibited some degree of two-way shape-memory effect (TWSME) after thermomechanical cycling. Texture analyses performed on the different ribbons allow us to better understand the transformation strains obtained in each ribbon. The amounts of shapememory effect (SME) and nonrecoverable strain shown by the studied ribbons are of the same order as those already observed in bulk materials, which makes melt spinning an ideal substitute to complicated manufacturing processes if really thin samples are needed. However, applicable stresses in melt-spun ribbons are limited by a relatively "premature" brittle fracture caused by irregularities in ribbon thickness.

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“…Amorphous Ni-Ti-Hf alloys can also be obtained by melt-spinning and first results after crystallization have been reported on an alloy from this family by Dalle et al 15) Conventionally cast Ni-Ti-Hf alloys are well known for their high martensitic transformation temperatures when Hf exceeds 10 at%. 16,17) Despite the reduction of the transformation temperatures with respect to the bulk alloy, melt spun Ni-Ti-Hf ribbons still may show high transformation temperatures. 18,19) In Santamarta et al 18) and Cesari et al, 19) a completely crystalline as cast Ni 50 Ti 32 Hf 18 ribbon and its evolution under thermal treatments in martensite and in austenite, respectively, has been already characterized.…”

Section: Introductionmentioning

confidence: 99%

Crystallization in Partially Amorphous Ni50Ti32Hf18 Melt Spun Ribbon

et al. 2004

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A partially amorphous Ni 50 Ti 32 Hf 18 melt spun ribbon has been characterized by means of calorimetry, X-ray diffraction and transmission electron microscopy, showing that the amorphous regions are mostly concentrated in the wheel side as a consequence of a higher cooling rate during the fast solidification (i.e. higher solidification rate). Special emphasis has been given to the crystallization process of the amorphous regions, studying the evolution of the microstructure and the martensitic transformation. Although several crystallization procedures have been carried out by thermal treatments, either slightly under or over the crystallization temperature measured by DSC, T C , the final microstructure and calorimetric behavior of the fully crystalline samples does not depend on the applied temperature. The fully crystalline samples contain regions with small crystallites produced during the thermal treatment (showing that the crystal nucleation energy is rather low for this alloy) together with the large crystals originated during the melt-spinning. At room temperature (RT), both types of crystals are in martensitic state. The new crystallized regions with small grain size show notably lower transformation temperatures and higher hysteresis in comparison to the big crystals already existing before the crystallization treatments. However, an additional mechanism, apart from the crystal size, affects the transformation temperatures, likely related to the presence of more defects (mainly grain boundaries) in the crystallites created by thermal treatments. These defects could act as nucleation sites for the martensite and increase the transformation temperatures with respect to the as cast spherical crystallites of similar sizes.

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The Effect of Hafnium Content on the Transformation Temperatures of Ni₄₉Ti_51-xHf_x. Shape Memory Alloys

Cited by 65 publications

References 0 publications

Physical metallurgy of Ti–Ni-based shape memory alloys

Physical metallurgy of Ti–Ni-based shape memory alloys

Shape memory properties of Ni-Ti based melt-spun ribbons

Crystallization in Partially Amorphous Ni<SUB>50</SUB>Ti<SUB>32</SUB>Hf<SUB>18</SUB> Melt Spun Ribbon

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