Liangyu Chen

Investigation of Deformation Mechanisms in β -Type Ti-35Nb-2Ta-3Zr Alloy via FSP Leading to Surface Strengthening

Friction-stir processing (FSP) is used to prepare Ti-35Nb-2Ta-3Zr alloys via different processing routes. Dislocation walls and tangles, deformation-induced α″ martensite, and deformation-induced ω phase are observed. The dominant deformation mechanisms are altered from deformation-induced α″ martensitic transformation and dislocation walls to twinning upon increasing the FSP passes. A reverse deformation-induced ω to β transformation and de-twinning process are observed together with grain refinement to the nanoscale. Meanwhile, compressive distortions along [0001]ω direction are favorable for the transformation from ω to β.

Effect of low-temperature pre-deformation on precipitation behavior and microstructure of a Zr-Sn-Nb-Fe-Cu-O alloy during fabrication

The effect of low-temperature pre-deformation on the microstructural evolution of a Zr–Sn–Nb–Fe–Cu–O alloy was investigated by optical metallography, scanning electron microscope, transmission electron microscope, and electron backscattering diffraction (EBSD). It is found that a reasonably homogeneous and fine equiaxed grain structure with uniformly distributed second-phase particles (SPPs) can be obtained in 40% pre-deformed samples (Group A) but not in directly hot-rolled ones (Group B) after hot rolling. The initial SPPs diameter in Group A is also reduced. Noticeable differences in microstructural evolutions including the distribution and size of SPPs, grain size of matrix, and texture are observed between both groups. Reasons for such discrepancies are attributed to the defects (such as dislocations and interfaces) introduced during the pre-deformation and more preferred precipitation sites formed in Group A. The aging after the pre-deformation results in new slip systems activated during hot rolling, leading to more thorough refinement of grains. In addition, the growth of SPPs is interpreted by the Lifshitz–Slyozov–Wagner model.

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen.

Microstructure and corrosion behavior of a Zr-Sn-Nb-Fe-Cu-O alloy fabricated by α+β quenching processing

In this work, the microstructure of a Zr-Sn-Nb-Fe-Cu-O alloy fabricated by α+β quenching processing (ABQ sample) was investigated by the combined utilization of scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results showed that the polygonal grains evenly distributed in ABQ sample and triangular grains distributed at triple junctions of polygonal grains with densely second phase particles (SPPs). The textures of directions tilted approximately 25° from normal direction and the rolling direction spreading along the were found in the sample, which was also detected in the regularly cold rolled and annealed sample. The occurrence of corrosion kinetics transition of ABQ sample was sight earlier than that of RAX sample. Due to a higher solid solubility of β-Zr, SPPs re-dissolved into β-Zr during α+β annealing and precipitated out afterward in those areas. Finally, discrepant corrosion rate of metal matrix and SPPs led to the formation of protrusions of matrix, which could concentrate stress and generate cracks in the oxide.