Search

Heat treatment is important for optimizing the strength performance and improving the toughness of titanium alloys. In this study, we investigated the impact of three heat treatment methods (β-annealing, double annealing, and solid-solution and aging treatment) on the mechanical properties and fracture morphology of Ti555211 titanium alloy. The results show that after β-annealing treatment, the alloy retains a high strength, while showing almost no ductility, and no yield strength. The alloy after double annealing has a high elongation rate (~54%) and lower strength. After solid-solution and aging heat treatment, the alloy was able to retain both high strength and a certain degree of ductility. The optimal heat-treatment process is solid-solution treatment at 820 °C/2 h and aging at 560 °C/12 h, which results in a maximum tensile strength of 1404 MPa and an elongation rate of 11%.

Unveiling the microstructural and electronic properties of β-Ga 2 O 3 on different substrates is vital to realize the high quality and performance of β-Ga 2 O 3 . Here, the microstructure disorder, defect characters and orbital structures of β-Ga 2 O 3 on the Al 2 O 3 , MgO, and SiC substrates with different terminations are studied. Although several growth mechanisms for β-Ga 2 O 3 are observed on the same substrate, β-Ga 2 O 3 prefers to deposit the octahedral Ga atom firstly on the Al 2 O 3 and MgO substrates, and the latter can restrain the oxygen-vacancy formation and migration. The structural disorder, band offsets and gap states can be improved upon depositing β-Ga 2 O 3 on a substrate with metal terminations under the oxygen-poor conditions. Compared to the Al 2 O 3 substrate, β-Ga 2 O 3 on the SiC substrate shows a smaller structure disorder and a higher defect formation energy, in particular under the oxygen-rich conditions, since β-Ga 2 O 3 prefers to deposit the tetrahedral Ga atom firstly on the SiC substrate to form a SiC-Ga 2 O 3 interface with less dangling bonds. The type-II band alignment of the SiC-Ga 2 O 3 interface can be changed into the type-I character with larger band offsets when β-Ga 2 O 3 is deposited under the oxygen-rich conditions, irrespective of the termination of the SiC substrate. These results provide a useful understanding of the effect of substrates on the quality and performance of β-Ga 2 O 3 and a scientific basis for the application of substrate-Ga 2 O 3 interfaces.

In this study, the welded joints of dissimilar titanium alloys Ti600/Ti-22Al-25Nb were strengthened by isothermal forging. Different deformation parameters, including temperature, deformation speed, and reduction, were chosen. By isothermal forging, the original coarse dendritic grains of the welded joints were broken up effectively to form a large number of equiaxed grains. Meanwhile, many second phases were precipitated in the grain. Additionally, the dynamic globularization kinetics of second phases within the welded joints were quantitatively characterized and investigated. The results showed that the dynamic globularization kinetics and globularization rate were sensitive to the deformation conditions, and were promoted by a reduced strain rate and an elevated deformation temperature.

Lamellar pores have superior biocompatibility due to their similarity to the lamellar structure of natural bones. In the present work, porous Ti6Al4V alloys with lamellar pores were successfully fabricated by directionally freeze casting. The lamellar structure/processing relationships were systematically studied through analyzing the interaction between ice front and alloy powders. The structural feature of translamella bridges is observed in the lamellar structure. The volume shrinkage of porous Ti6Al4V alloys is in the range of 44-60%. This is much higher compared with that of the porous ceramics. The solid content in the slurry exerts a strong influence on the porosity, while the freezing ice front velocity affects the structural wavelength and pore width. With the increase in ice front velocity, the structural wavelength decreases by an exponential function. The lamella formation mechanism and porosity gradient along the freezing direction were discussed. Young's modulus and yield stress of porous Ti6Al4V alloys fall in the range of 2-12 GPa and 40-300 MPa, respectively. The dominant compressive deformation mode is lamella buckling and splitting. The fabricated porous Ti6Al4V alloys possess higher relative yield stress., (Copyright © 2019 Elsevier Ltd. All rights reserved.)