B. Tian

Effect of annealing temperature on martensitic transformation of Ti49.2Ni50.8 alloy processed by equal channel angular pressing

Abstract The effect of annealing temperature on the martensitic transformation of a Ti 49.2 Ni 50.8 alloy processed by equal channel angular pressing (ECAP) was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The as-ECAP processed and subsequently annealed Ti 49.2 Ni 50.8 alloys consist of B2 parent phase, Ti 4 Ni 2 O phase and B19′ martensite at room temperature. Upon cooling, all samples show B2→R→B19′ two-stage transformation. Upon heating, when the annealing temperature is less than 400 °C, the samples show B19′→R→B2 two-stage transformation; when the annealing temperature is higher than 500 °C, the samples show B19′→B2 single-stage transformation. The B2–R transformation is characterized by wide interval due to the dislocations introduced during ECAP.

TRANSFORMATION BEHAVIOR AND SHAPE MEMORY EFFECT OF A CoAl ALLOY

This paper investigates the microstructure, martensitic transformation and shape memory effect of Co-16Al alloy. The optical micrographs of Co-16at.%Al alloy quenched from 1200°C show that the e martensite occurs at room temperature, while some remaining γ phase can also be observed. This microstructure analysis can be supported by XRD pattern. It is shown that the alloy undergoes a martensitic reverse transformation at about 220°C during heating. However, no transformation from the fcc phase to hcp phase is detected by DSC measurement upon cooling. It is thought that the precipitation of β phase by aging at high temperature may suppress the martensitic transformation. The tension strain is 12% and the fracture strength is above 800MPa. No obvious yield deformation is observed from the stress-strain curve. SEM images exhibits many dimples on the fracture surface, which means the fracture mechanism is ductile rupture. Bending test show that only 25% deformation can be recovered due to shape memory effect w...

Phase transformation and microstructure of Ni–Mn–Ga ferromagnetic shape memory alloy particles

In the present paper, ball milling is used to produce Ni 49.8Mn28.5Ga21.7 particles of micrometer size. Although the characteristics of transformation are not observed in the as-milled particles from 150 to 523 K from differential scanning calorimetry (DSC) study, the particles exhibit the same transformation behaviour as the bulk sample after annealing at 1073 K for 2 h. The as-annealed particles show good thermal cycling stability even after five thermal cycles. Temperature memory effect during the reverse martensitic transformation is found in the as-annealed particles. The particles exhibit regular shape, with 10M martensite structure at room temperature.

Effect of aging on martensitic transformation and superelasticity of TiNiCr shape memory alloy

The effect of aging on microstructure, martensitic transformation and superelasticity of a Ti48.4Ni51.1Cr0.5 alloy was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) analysis and tensile tests. When the alloy was aged at 400 °C for 30 min, Ti3Ni4 precipitate appears. When aged at a temperature between 400 °C and 500 °C, the samples show a two-stage martensitic transformation. The aged Ti48.4Ni51.1Cr0.5 alloy exhibits a well-defined superelasticity at room temperature. The recovery ratio increases with increasing aging temperature from 300 to 450 °C. Further increase of aging temperature leads to the decrease of recovery ratio. The stress hysteresis shows the opposite dependence on aging temperature. The relationship between aging treatment and martensitic transformation and superelasticity can be rationalized by the evolution of Ti3Ni4 precipitate.

Martensitic Transformation and Shape Memory Effect of NiCoMnSn High Temperature Shape Memory Alloy

This article studies the dependence of martensitic transformation on Mn:Sn ratio in Ni43Co7Mn50−xSnx alloy and the shape memory behavior of Ni43Co7Mn43Sn7 in detail. The results show that all the transformation temperatures show a linear decrease with the decrease of Mn:Sn ratio. The similar tendency is also found in the change of Tc. Ni43Co7Mn43Sn7 alloy exhibits a moderate shape memory effect and the maximum shape recovery strain is 2.96%. Temperature memory effect is also observed in Ni43Co7Mn43Sn7 alloy.

Microstructure and Damping Property of Polyurethane Composites Hybridized with Ultraviolet Absorbents

This article investigated the microstructure and damping property of TPU composites with different contents of ultraviolet absorbents. It can be found that the ultraviolet absorbents formed fiber-shaped precipitations in the TPU matrix. The UV-328 was randomly distributed in the matrix and exhibited a weak interfacial bonding with the matrix. In comparison, the UV-329 was well embedded in the matrix and formed a relatively better interfacial bonding and compatibility with the TPU matrix. The damping factor tanδ of both 328-composites and 329-composites had been reduced gradually with increasing content of ultraviolet absorbents at the glass transition temperature range due to the fact that the ultraviolet absorbents were in the crystalline state which decreased the volume content of the viscoelastic TPU matrix. But the tanδ increased at the temperature range of higher than the glass transition temperature, which should be related to the dominance of interfacial frictions between the ultraviolet absorbents and the matrix on the energy absorption.

The Preparation and Characterization of NiTi/CNT/Polyurethane Composite

The polyurethane matrix composites consisting of CNT and NiTi springs are prepared and the microstructure, mechanical property and damping property of the composites are investigated. It was found that the CNT and NiTi spring exhibit a good interfactial bonding with the matrix. The elastic modulus and tensile strength have been enhanced by the addition of CNT and NiTi spring. The NiTi spring is helpful to increase the recovery strain and enhance the energy absorption of the composites by the pseudoelastic deformation under the large deformation. The NiTi spring can not increase the damping property under low vibration amplitude because the pseudoelastity of the spring is not actuated when the deformation is small.