Effect of Heat Treatment Temperature on Martensitic Transformation and Superelasticity of the Ti49Ni51 Shape Memory Alloy

Abstract

The martensitic transformation and superelasticity of Ti49Ni51 shape memory alloy heat-treatment at different temperatures were investigated. The experimental results show that the microstructures of as-cast and heat-treated (723 K) Ni-rich Ti49Ni51 samples prepared by rapidly-solidified technology are composed of B2 TiNi phase, and Ti3Ni4 and Ti2Ni phases; the microstructures of heat-treated Ti49Ni51 samples at 773 and 823 K are composed of B2 TiNi phase, and of B2 TiNi and Ti2Ni phases, respectively. The martensitic transformation of as-cast Ti49Ni51 alloy is three-stage, A→R→M1 and R→M2 transformation during cooling, and two-stage, M→R→A transformation during heating. The transformations of the heat-treated Ti49Ni51 samples at 723 and 823 K are the A↔R↔M/A↔M transformation during cooling/heating, respectively. For the heat-treated alloy at 773 K, the transformations are the A→R/M→R→A during cooling/heating, respectively. For the heat-treated alloy at 773 K, only a small thermal hysteresis is suitable for sensor devices. The stable σmax values of 723 and 773 K heat-treated samples with a large Wd value exhibit high safety in application. The 773 and 823 K heat-treated samples have large stable strain–energy densities, and are a good superelastic alloy. The experimental data obtained provide a valuable reference for the industrial application of rapidly-solidified casting and heat-treated Ti49Ni51 alloy.

Effect of Fe Addition on Microstructure and Mechanical Properties of As-cast Ti49Ni51 Alloy

“…Since each alloy is tested three times, each alloy has three stress–strain curves; in Figure 5, the experimental data on the selected stress–strain curves are close to the average of the three measurements. For the as-cast Ti 49 Ni 51 alloy, with the increase of stress, B2 austenite phase can be transformed into martensite phase, showing a martensite transformation plateau in the stress–strain curves [30]. No martensite transformation plateau is found on the nominal stress–strain curve in Figure 5, because the matrix phases of the four alloys are not the B2 TiNi phase with the large grain sizes, but the TiNi phase with body-centered cubic structure.…”

“…The Ti 49 Ni 51 alloy is a shape memory alloy with excellent properties because of its excellent superelasticity under medium temperature aging [30]. Therefore, in this paper, the Ni-rich Ti 49 Ni 51 alloy is used as the base alloy.…”

Toz metalurjisi ile Üretilen NiTi Alaşımına Al'un Etkisi

“…Toz metalürjisi ile üretilen NiTi numunelerinin mikroyapılarında austenit NiTi, martensit NiTi ve NiTi2 fazlarının oluştuğu birçok araştırmacı tarafından belirtilmektedir [31,[38][39][40]. SHS yönteminde üretilen NiTi malzemede NiTi2 fazın varlığı kaçınılmaz olmasının temel sebebi bu fazın tercihen oluşmasıyla ilgilidir [41].…”

Damage Adaptive Titanium Alloy by In-Situ Elastic Gradual Mechanism

“…Ti-10V-2Fe-3Al-0.11O is a near-β-type alloy tending to phase transformations at high stress levels from the β phase to the reversible α" martensite and the ω phase [25,26]. Since it has long been recognized that phase transformations at the crack tip lead to a retardation in crack growth, the contribution from the reversible MT was studied using the Ti-10V-2Fe-3Al-0.82O alloy, which has a slightly higher critical stress to the MT than the hot-forged alloy due to the depression effect of grain refinement.…”