Strain states and unique properties in cold-rolled TiNi shape memory alloys
Explore the source record for details and available documents.
Liang, Qianglong↗
Engineering topics
Zheng, Yufeng
Publications and source records attributed to Zheng, Yufeng.
Nucleation and growth of α phase in a metastable β-Titanium Ti-5Al-5Mo-5V-3Cr alloy: Influence from the nano-scale, ordered-orthorhombic O" phase and α compositional evolution
We investigated the nucleation and growth of α precipitates in the presence of nano-scale, titanium-rich, ordered-orthorhombic O" precipitates formed during heating at 5 °C/min to 400 °C in a metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr. The O" precipitates are found to assist α nucleation by serving as preferential nucleation sites. In the very initial stages of its precipitation, the α phase is found to have formed via a coupled diffusional-displacive mode as titanium-rich plates. At this stage, aluminum partitions equally between the β matrix and the growing α precipitates, but slowly diffuses up-hill into the α phase during isothermal aging at 400 °C for 15 h. The interplay between such pre-formed metastable phases and α can be exploited to tailor the microstructure, by refining the α distribution, and consequently improve the mechanical properties of β-Ti alloys. Finally, our work paves the way for exploiting this cascade of metastable phases for further microstructural engineering of β-Ti alloys.
36 MATERIALS SCIENCE↗
Phase Inversion in a Two-phase, BCC+B2, Refractory High Entropy Alloy
A phenomenon of "phase inversion", presumably the first ever experimental evidence in metallic alloys, is shown in a refractory high entropy alloy (RHEA), Al0.5NbTa0.8Ti1.5V0.2Zr. Phase inversion in crystalline solid systems is driven by the differences in elastic modulus of the two phases. Quenching from a high-temperature single phase field, the RHEA exhibits a co-continuous mixture of a disordered BCC and an ordered B2 phase, that upon isothermal annealing at 600°C develops via spinodal decomposition into a continuous B2 matrix with discrete cuboidal BCC precipitates aligned along the <001> directions. Longer term annealing at 600°C results in the development of necking constrictions along the B2 channels, eventually pinching-off these channels and making the BCC phase continuous with discrete B2 precipitates. This inversion the process can be related to the simultaneous operation of two processes:(i) spheroidization of the initially discrete cuboidal BCC precipitates driven by a reduction in the total interface energy and (ii) an increase in the stiffness of the B2 phase, relative to the BCC phase, due to chemical composition changes during annealing, forcing the B2 regions to become discrete driven by the reduction in the total elastic strain energy.
Soni, Vishal↗