Jun Wei Liu

Effects of Annealing on Microstructure and Phase Transformation Temperature of NiTiNb Shape Memory Alloy after Equal Channel Angular Pressing

The effect of annealing temperature（300-600°C）on the microstructure and transformation temperature of NiTiNb shape memory alloy rods deformed with equal channel angular pressing（ECAP） method was analyzed. The results show that the hard brittle phase （Ti,Nb）2Ni was decreased after ECAP. With the rising of annealing temperature, the number of β-Nb phase increase while eutectic declines. The DSC analysis shows that the martensite and reverse transformation temperature increase with annealing temperature. After annealing with 500°C, the martensite/austenite transformation starting temperatures rise to -64.6°C and -30.1°C, respectively.

The Effect of Titanium Addition on Microstructure and Properties of Laves Phase Cr2Nb Alloy Synthesized by Hot Pressing

The composite materials with a nominal composition of Cr2Nb-24wt.%Ti were fabricated by mechanical alloying followed by hot pressing. The microstructures and properties were investigated on the composites contained with Laves phase prepared through 20 hours mechanical alloying of chromium, niobium and titanium elemental powders and hot pressing at 1250°C for half an hour. The results indicate that the near full-dense Laves phase Cr2(Nb,Ti) based alloy with homogeneous composition and microstructure is obtained by mechanical alloying and hot pressing techniques. The dispersed soft second phase Nb solid solutions with the fine grain size less than 1μm are distributed uniformly on the matrix. The sample has a relative density of 99%, fracture toughness of 5.32MPa•m1/2 and compress strength of 2080MPa. Due to the effect of fine-grain and alloying addition, the toughening of the Cr2(Nb,Ti) based alloy has been fully realized.

Effect of Extrusion Pass on Microstructure and Transformation Temperature of NiTiNb Alloy

In this research, the Effect of extrusion pass on microstructure and transformation temperature of NiTiNb alloy was researched. The results shows that ECAP can efficiently break the hard and brittle (Ti, Nb)2Ni phase. At the same time, β-Nb phase particles were precipitated and grow up after ECAP process.Due to enhancement of interfacial energy, train energy and non-chemical free energy, transformation temperatures including: As, Af, Ms and Mf increases with extrusion pass.

Research Basis of NiTi-Based Shape Memory Alloy Pipe Coupling

In this paper, characteristics of SMA were analyzed and the research basis was researched. The connecting mechanism and mechanism of pipe coupling was introduced. Otherwise, in our research, after connecting by pipe coupling, the pipe can endure high pressure and occur blasting when the pressure reaches to 84MPa.

Influence of Predeformation Temperature on Recovery Performance of Ni47Ti44Nb9 Alloy Φ16mm Pipe Joint

Using the method of expanding diameter in low temperature and water bath heating, this paper studied the effect of pre-deformation temperature on shape memory recovery characteristics of Ni47Ti44Nb9 alloy Φ16 mm pipe joint. The results showed that the transformation hysteresis and the radial recoverable strain were relative stable along with the addition of pre-deformation temperature, which were 122°C±4°C and 7.1%±0.3% respectively. Moreover the radial recovery rate of inner diameter declined smoothly with the addition of pre-deformation temperature. Systems considering the three parameters of transformation hysteresis, recoverable strain and strain recovery rate, it seemed the excellent predeformed temperature for Ni47Ti44Nb9 alloy Φ16 mm pipe joint was in-65~-70°C.

The Microstructure Evolution and Twinning Characterization of AZ31 Mg Alloy Sheet in Low-Temperature Bending Process

The relationship among stress, cavities and twinning in the room-temperature bending process of hot-rolled AZ31 Mg alloy sheet was researched. It can be seen that the mount of twins which was tightly affected by stress value increases with the distance to press point. Otherwise, the cavities and twinning which seem totally independent, in fact affect with each other. Some cavities were hindered by twins and can not further grow up. Then, the relationship between slip and twinning was also roughly discussed. The dislocation lines in twins can be thought to release the stress focus and were beneficial for deformation.

Research on Structural Inheritance Characteristic and the Related Normalizing Elimination Process for 300M Steel

The characteristic of structural inheritance for 300M steel was explored and the eliminating effect of normalization was investigated. Then, both the first and secondary normalization process was optimized by comparing eliminate effect. It is known that obvious characteristic of structural inheritance can be shown with the condition of 810°C-840°C×30min/OC after over-heated treatment. The first normalization process whose condition is 950°C~1100°C×2.5h/air cooling has the good effect on eliminating structural inheritance. While, the secondary normalization process whose condition is 960°C~1060°C×2h/air cooling+925°C×2.5h/air cooling owns the better effect on eliminating structural inheritance.

The Research on Hot Compression Mechanism of Light Alloy

In this research, in order to explore the main mechanism of direct and two-stage compression in as-cast light alloy, the mechanical property, microstructure evolution and the flowing of second phase particles were studied, before and after deformation. Then, the influence of the strain volume in first stage on flowing stress of the second stage deformation also was researched.

Effects of Homogenization on Microstructures and Mechanical Properties of as Cast AZ91 Mg Alloy

The microstructural evolution and mechanical properties of as cast AZ91 Mg alloy enduring different homogenization conditions were researched. The results show that the peak stress and plasticity obtain improvement with the increase of heat treated time and temperature until 693K. When the temperature is higher than 743K, the sample will occur the over-burned and directly lead to the decrease of mechanical properties. Otherwise, with the increase of heat treated time and temperatures, the second phase gradually precipitate from the solution, while the grain evolution is not obvious. In the compression process for the samples after heat treatment, some twins could be found in the grains.

A Calculation Study on the Synthesis Routes of Oh-Al13 Cluster

Based on the method of LST/QST improved in the molecular orbital DMol3 program, with the aid of the minimum energy path (MEP) in the climbing image nudged elastic band (CI-NEB) method, the Oh-Al13 cluster is investigated under different synthesis process, i.e. Al6+Al7→Al13. The results show that: there are two stages in the synthesis reaction: the distortion stage and the configuration revolution stage. In the first stage, the metastable structures are forced to change into stable structures. In the configuration evolution stage, two different cases exist. For the synthesis of crystal clusters it is an automatic exothermic reaction if all reactants being of typical crystal symmetrical elements, i.e., Al6+Al7M®Oh-Al13. While an energy barrier must be overcome if one of reactants having fivefold or tenfold symmetrical axes, i.e.,Al6+Al7、Al6M+Al7 and Al6M+Al7M. So the five-symmetry structures are only appearing in rapidly solidified processes except crystallization processes.