Xu Jun Mi

Development of Low Cost and Low Elastic Modulus of Ti-Al-Mo-Fe Alloys for Automotive Applications

Ti-Al-Mo-Fe alloys were developed as low cost beta Ti alloys for automotive springs, and designed based on Molybdenum equivalency and Bo-Md molecular orbital method. Low priced Mo-Fe master alloys were introduced as alloying elements for the cost and elastic modulus reduction. Eight Ti-Al-Mo-Fe alloy candidates were pre-designed according to the Bo-Md method. Primary laboratory scale ingots were thus melted by ISM (Induction Skull Melting). After primary property evaluation, the Ti-2Al-9.2Mo-2Fe alloy was optimized finally and large scale ingot was made by VAR for further property evaluation. Resultantly, it shows that the alloy has lower elastic modulus (60-70 GPa) and good tensile properties in the solution condition, and compares well with the other developed commercial beta alloys.

Mechanical Characterization of Ti-Mo-Fe Titanium Alloy

Microstructure characterization and hardening behavior of a new designed Ti-12.1Mo-1Fe alloy during solution and aging treatment was investigated in the present study by OM, Vickers hardness. The results showed that the beta transus temperature of new Ti-12.1Mo-1Fe alloy was about 780°C. Further observation of ω phase should be performed by TEM later. It is also found that ω phase played a more important role than α phase in hardening. The hardening due to ω phase can lead to a high hardness about 470 Hv but the coarse α phases result in a hardness below 300 Hv.

Aging Behaviors of Ti-Al-Mo-Fe Titanium Alloy

Ageing behaviors and microstructural characterization by aging condition of Ti-Al-Mo-Fe alloy was investigated. Due to the formation of ω phase, it occurs a drastic change in mechanical properties of β alloys. There is large increasing in hardness and yield strength, accompanied with serious ductility reduction. However, it has been proved that proper control of ω phase volume fraction can bring to improve strength with a reasonable ductility. In this work new beta titanium alloy was designed and developed in Ti-Al-Mo-Fe alloy to investigate the hardening behavior of ω and α precipitation during aging. The results showed that a small amount of athermal ω was observed in the β matrix during water quenching from above the β transus temperature. Isothermal ω formation was also found during aged at temperatures ranging from 573 K to 773 K although it has a limited time of stability at 773 K. The hardening due to isothermal ω precipitation exhibits no over-aging effect as long as ω phase exists inside the matrix. The hardness of this alloy is very sensitive to size and volume fraction of ω phase and its existence, which depends on aging temperature, time and alloy compositions.

Study on High Temperature Properties of CuCrAg Alloy

In this paper, nominal composition of Cu-0.3Cr-0.07Ag (at%) was designed. The high temperature properties and microstructure were investigated by Transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show that the tensile strength of CuCrAg decreases as temperature rises, which was associated with the coarsen precipitates according to TEM observation. Furthermore, observations of fracture morphology reveal that the mechanism transforms into brittle fracture from ductile fracture at elevated temperature. Creep curves were found to vary as a function of applied stress and temperature, the stress exponent values are 8.7, 4.6, 4.3 at 673K, 773K, 873K respectively. The mechanism is dislocation climbing at 773K and 873K while creep behavior at 673K could be explained by the invariant substructure model.

Modeling the Hot Deformation Behavior of Ti-50.8%Ni Shape Memory Alloy

The characteristics of isothermal deformation behavior of Ti-50.8%Ni shape memory alloys were investigated by thermal simulation tests, which were performed on Gleeble-3500 thermal simulation machine. The range of deformation temperatures was 800°C to 1050°C and that of strain rates was 0.01s-1 to 10s-1. The stress-true strain curves were corrected by considering deformation-heating and friction. The results show that the flow stress increases with the decrease of deformation temperatures or the increase of strain rates. The constitutive relationship of hot deformation was established on the basis of the Arrhenius equation and the average activation energy of 182 KJ/mol was obtained.

Design and Preparation of Smart Adaptive Structure Made with SMA-SMP Composite

Shape memory composites (SMCs) combined with shape memory polymer (SMP) and shape memory alloy (SMA) having excellent mechanical properties and shape memory properties are considered to be ideal materials used in smart adaptive structure. In order to broaden the application of SMCs, a temperature controlled telescopic boom was designed and prepared. The design criteria indicated that temperature sequence was as follow: T room temperature< Tg < As, and the deformation temperature was better around Tg+30°C. And the TiNi wires should be displayed in the longitudinal axe and outer race of the boom, and the minimum curved diameter of innermost layer could be calculated by. The recover behavior of the sample corresponded to the design, and the recover process could be repeated more than 10 times.

Effect of C12-14 Alcohols on the Thermomechanical Properties of Epoxy Shape-Memory Polymer

A critical parameter for a shape memory polymer (SMP) lies in its shape memory transition temperature. For an amorphous SMP polymer, it is highly desirable to develop methods to tailor its Tg, which corresponds to its shape memory transition temperature. Starting with an amine cured aromatic epoxy system, epoxy polymers were synthesized by introducing flexible aliphatic alcohol. The thermal and thermomechanical properties of these epoxy polymers were characterized by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). All the crosslinked epoxy polymers with Tg’s above room temperature were found to possess shape memory properties.

Hot Deformation Behavior of TiNiFe Shape Memory Alloy: A Study with Processing Map

Isothermal compression of the TiNiFe shape memory alloy has been carried out on a Gleeble-3500 thermal simulation machine at the deformation temperature ranging from 1023K to 1323K, the strain rate ranging from 0.01s-1 to 10s-1 with total strain of 0.8. On the basis of dynamic material model, the processing map is established with two instability regions and a desirable domain which demonstrate optimum hot working conditions within the experimental parameters. By means of Electron Back Scattering Diffraction, we come to the conclusion that both dynamic recovery and dynamic recrystallization exist in the desirable domain with deformation temperature ranging 1123 K and strain rate 0.1s-1. The uneven deformation exits in the low deformation temperature with high strain rate area, such as 1023 K and10 s-1. And with 1323K and 0.01s-1 strain rate, the recrystallized grains are abnormal grow up.

The Microstructure and Properties of Ti50Ni47Fe3 and Ti50Ni46.75Fe3Cr0.25 Shape Memory Alloy

Comparing with Ti50Ni47Fe3 alloys, the influences of Cr on the mechanical and shape memory properties of Ti50Ni47Fe3 alloys are investigated by study on phase transformation and microstructure analysis. The results show that Ti50Ni47Fe3 and Ti50Ni46.75Fe3Cr0.25 shape memory alloys exhibit two-stage martensitic transformation. The transformation temperatures decrease with the addition of Cr. The microstructure of the Ti50Ni47Fe3 and Ti50Ni46.75Fe3Cr0.25 alloys consists of TiNi matrix, Ti2Ni phase. Fe element prefers to substitute for Ni in the matrix than black particles. Cr all substitute for Ni in the matrix and not be analyzed in the Ti2Ni phase. The mechanical property of Ti50Ni46.75Fe3Cr0.25 alloy is better than Ti50Ni47Fe3 alloy.

Effect of Annealing Temperature on the Transformation Temperature and Texture of Ni47Ti44Nb9 Cold-Rolled Plate

Transformation behaviors and texture of Ni47Ti44Nb9 cold-rolled plates were studied by differential scanning calorimetry and X-ray diffraction test. R phase transformation does not occur in Ni47Ti44Nb9 cold-rolled plate annealed at 350°C-750°C followed by quenching into the water. Martensite transformation temperature first increases and then decreases with increment of annealing temperature, and the maximum achieves at 700°C. The heat of reverse martensite transformation increases, while hardness decreases as annealing temperature increases. The major texture of cold-rolled plate is {332} and spread from {332} to {110}. When the annealing temperature is above 600°C, the major textures are {332} and {111} recrystallization texture in secondary cold-rolled plate.