Y.X. Tong

Properties of Porous TiNbZr Shape Memory Alloy Fabricated by Mechanical Alloying and Hot Isostatic Pressing

In the past decades, systematic researches have been focused on studying Ti-Nb-based SMAs by adding ternary elements, such as Mo, Sn, Zr, etc. However, only arc melting or induction melting methods, with subsequent hot or cold rolling, were used to fabricate these Ni-free SMAs. There is no work related to powder metallurgy and porous structures. This study focuses on the fabrication and characterization of porous Ti-22Nb-6Zr (at.%) shape memory alloys produced using elemental powders by means of mechanical alloying and hot isostatic pressing. It is found that the porous Ti-22Nb-6Zr alloys prepared by the HIP process exhibit a homogenous pore distribution with spherical pores, while the pores have irregular shape in the specimen prepared by conventional sintering. X-ray diffraction analysis showed that the solid solution-treated Ti-22Nb-6Zr alloy consists of both β phase and α″ martensite phase. Morphologies of martensite were observed. Finally, the porous Ti-22Nb-6Zr SMAs produced by both MA and HIP exhibit good mechanical properties, such as superior superelasticity, with maximum recoverable strain of ~3% and high compressive strength.

Preparation and shape memory properties of TiO2/PLCL biodegradable polymer nanocomposites

Abstract The preparation of TiO2/poly(L-lactide-co-ɛ-caprolactone) (PLCL) nanocomposites and their properties were reported. TiO2 nanoparticles were surface modified by ring-opening polymerization of ɛ-caprolactone (ɛ-CL). The resulting poly(ɛ-caprolactone)-grafted TiO2 (g-TiO2) was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The g-TiO2 can be uniformly dispersed in chloroform and the g-TiO2/PLCL nanocomposites were successfully fabricated through solvent-casting method. The effects of the content of g-TiO2 nanoparticles on tensile properties and shape memory properties were investigated. A significant improvement in the tensile properties of the 5% g-TiO2/PLCL mass fraction nanocomposite is obtained: an increase of 113% in the tensile strength and an increase of 11% in the elongation at break over pure PLCL polymer. The g-TiO2/PLCL nanocomposites with a certain amount of g-TiO2 content have better shape memory properties than pure PLCL polymer. The g-TiO2 nanoparticles play an additional physical crosslinks which are contributed to improvement of the shape memory properties.

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.

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.

New Formulas of Shear Strain during Equal-channel Angular Pressing Process with Consideration of Influences of Velocity and Motion Trajectory

The influences of die parameters on shear strain were investigated by using two-dimensional finite element simulation. New formulas of shear strain were proposed. According to the results of formulas, the shear strain showed a linear dependence on the difference between internal and external fillet radius and the slope was determined by the intersection angle. The simulation results indicated that the velocities of the points from different zones were different in the specimen and the motion trajectories of different points did not follow geometrical laws. The influences of the average velocity and the motion trajectory on shear strain were incorporated in the formula to calculate the shear strain produced during equalchannel angular pressing process. The reliability of simulation results has been partially validated by experiments.