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Abstract The effects of solution temperature and cooling rate on microstructure and micro-hardness of a hot compressed Ti-6Al-4V alloy are investigated. The microstructure observations reveal the occurrence of static recrystallization during solution treatment. The lamellar α phases firstly decompose into the short-rod phases, and then gradually spheroidize. The increased solution temperature can accelerate the transformation of α grain boundary from the low-angle grain boundaries (LAGB) to the high-angle grain boundaries (HAGB). So, the growth and spheroidization of α grains become more and more obvious. Meanwhile, the precipitation of secondary α phases is promoted. The micro-hardness is significantly improved after the solution treatment, i.e., the micro-hardness undergoes the rapid decrease and slow increase with raising the solution temperature. In addition, the cooling rate has great impact on the microstructures and micro-hardness. With reducing the cooling rate, the mean size of equiaxed α grains and the thickness of lamellar α phases obviously increase. Highlights • Effects of post-deformation heat treatment on microstructures and micro-hardness of Ti-6Al-4V alloy are studied. • Lamellar α phases firstly decompose into the short-rod phases, and then gradually spheroidize. • The increased solution temperature accelerates the transformation of α grain boundary from LAGB to HAGB. • Micro-hardness undergoes the rapid decreases and slow increase with the increase of solution temperature. • The mean size of equiaxed α grains and the thickness of lamellar α phases increase with reducing cooling rate. [ABSTRACT FROM AUTHOR]

In this study, CrN and CrAlN coatings were deposited on the surface of aerospace titanium alloys using the arc ion plating technology to investigate the effect of the microstructure of the coatings on the mechanical and erosion resistance properties. The cross-sections of the coatings were observed by Scanning Electron Microscope(SEM), the microstructures were characterized by Transmission Electron Microscope(TEM), and the crystalline structures were tested by X-ray diffraction (XRD); furthermore, the hardness of the coatings was determined by a micro-Vickers hardness tester, the film-base bond strength was measured by a scratch tester, the change in curvature was measured by laser scanning and the residual stress was calculated. The fracture mechanism of the coating was elucidated by simulating the fracture pattern of the cross-section of the erosion crater. The results indicated that the thicknesses of the CrN and CrAlN coatings were almost the same, but the number of large particles on the surface of the CrAlN coating was higher. Both sets of coatings exhibited a nanocrystalline structure with a grain size of around 10 nm. Due to the doping of the Al element, the CrAlN coatings exhibited a hardness of 2846 HV and a higher residual stress of −1.831 GPa. Both the CrN and CrAlN coatings showed lower erosion rates than the titanium substrate at 30° and 90° angles of attack. The results of finite element simulations indicated that the more ductile CrN coating exhibited a better stress absorption capacity, and a typical brittle fracture failure mechanism was observed for both sets of coatings. • CrN and CrAlN coatings with good erosion resistance were obtained. Compared with the titanium alloy substrate, the erosion rate of the coated sample is only 1/8 of the titanium alloy substrate at 30°, and only 1/3 of the titanium alloy at 90°. • The erosion fracture process of the hard coating was explored, in which the cracks were mainly in the direction perpendicular to the film-base interface, and were easily deflected by stress concentration at the microparticles and the interface. • Both CrN and CrAlN coatings are typical brittle fracture failure mechanisms, but the tougher CrN coating has better stress absorption capacity. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and microstructural evolution of a Ti-55511 alloy in α+β region are investigated by uniaxial compressive tests at elevated temperatures. Transmission Electron Microscope (TEM) and Electron Backscattered Diffraction (EBSD) are employed to observe the microstructures. The spheroidization of lamellate α phases and the dynamic recrystallization (DRX) of β grains are analyzed. It is observed that the flow characteristics are prominently affected by deformation parameters, i.e., the flow stress, peak stress and flow softening stress decrease with the reduced strain rate or the increased deformation temperature. When the deformation temperature is slightly raised or the strain rate is properly reduced, the fraction of spheroidized α phase greatly increases. The substructures are formed in the lamellate α phase, and the β phase wedges into the lamellate α phase. Then, the lamellate α phase is fragmentized and spheroidized. The DRX of β grains is promoted with the raised strain rate or the reduced deformation temperature. Additionally, the higher dislocation density and obvious dislocation pile-ups can be noticed at the α/β interface, which induces the DRX nucleation of β grains at the α/β interface. • Hot deformation behavior and microstructure evolution of a Ti-55511 alloy in α+β region are investigated. • The fraction of spheroidized α phase increases with increasing deformation temperature or reducing strain rate. • The substructures are easily formed in the lamellate α phase, and the β phase wedges into the lamellate α phase. • The DRX of β grains is promoted with the raised strain rate or the reduced deformation temperature. • The obvious DRX of β grains easily nucleate at the α/β interface. [ABSTRACT FROM AUTHOR]