Vincent Ji

Dependence of stresses on grain orientations in thin polycrystalline films on substrates : an explanation of the relationship between preferred orientations and stresses

Several experimental results have showed that the degree of (200) preferred orientation increased with increasing compressive stress, on contrary, the degree of (111) preferred orientation increased with increasing tensile stress in plane of the film. To explain this relationship between preferred orientations and stresses, we have made calculations of the stresses in plane of the film for the various (h k l)-oriented grains in a polycrystalline film composed of the fcc metal Cu, Al, Ag, Au, Ni, Pb and Th, respectively. The results of the calculations showed that, the stresses in plane of the film depended not only on the grain orientations (h k l), but also on the direction in the plane of the film excepting in (100)- and (111)-oriented grains. They were similar for all fcc metals studied with (100)-oriented grains having the lowest average stress in the plane of the film and the (111)-oriented grains the highest.

The influence of Nb ion implantation upon oxidation behavior and hardness of a Ti-48 at.% Al alloy

Abstract The influence of Nb ion implantation with different doses upon microhardness and high-temperature oxidation resistance of a Ti-48 at.% Al alloy was investigated. The results showed that the surface microhardness of the alloy was significantly increased by Nb implantation with doses from 3 × 10 15 ions cm −2 to 3 × 10 16 ions cm −2 , and reached a constant level at a dose of 3 × 10 17 ions cm −2 . The isothermal oxidation resistance of the alloy at 900 °C and 950 °C in an atmospheric environment could be remarkably improved by Nb ion implantation with a dose of 3 × 10 17 ions cm −2 , which was attributed to the effect of the implanted Nb atoms on the nucleation and formation of the oxides and the oxidation scale microstructure. The influence of both the primary and secondary effects of Nb ion implantation upon the microhardness and oxidation behavior of Ti-48 at.% Al alloy is discussed.

Effect of internal stresses on the fracture toughness of a TiAl-based alloy with duplex microstructures

Abstract A series of fine duplex microstructures with different volume ratios of equiaxed γ and lath colonies (α2+γ) were achieved from an isothermally forged Ti–46.5Al–2Cr–2Nb alloy. The internal stress determination using X-ray diffraction techniques and plane-strain fracture toughness tests were carried out at room temperature, and the effects of the internal stresses on the fracture toughness were investigated. It was found that the internal stresses play an important role in determining the fracture toughness of the TiAl-based alloy. The compressive internal stresses in γ phase and the tensile internal stresses in α2 phase may be responsible for the delamination along the γ/α2 boundaries. For the microstructures with different volume fraction of lamellar grains, the fracture toughness increases with the internal stresses, which facilitate the formation of shear ligaments; and the effects of the α2 phase and equiaxed gamma grains on the internal stresses and the fracture toughness were discussed.

A study of mechanical properties and microscopic stress of a two-phase TiAl-based intermetallic alloy

In order to study the effects of the microstructures on the mechanical properties and internal stresses of a TiAl-based alloy, a series of fine duplex microstructures with different volume ratios of equaxied grains and +2 lath colonies of a TiAl-based alloy were produced by isothermal forging and heat treatment. Tensile tests were carried out at room temperature, and X-ray elastic constants were determined experimentally. The mechanical state of a given phase in the alloy, induced by uniaxial tensile loading, was characterized by X-ray diffraction. It was found that the macroscopic mechanical properties and microscopic stresses strongly depend on the microstructures, and there is a difference between the macroscopic properties and the microscopic properties, and the reasons are discussed.

X-ray elastic constant determination and microstresses of α2 phase of a two-phase TiAl-based intermetallic alloy

Abstract The elastic constants of α 2 phase of a two-phase TiAl-based intermetallic alloy were determined experimentally by X-ray diffraction method. From these results, the residual stresses and the mechanical state of α 2 phase in the alloy, induced by a uniaxial tensile loading, were characterized by X-ray diffraction. It was found that the X-ray elastic constants of α 2 phase differ from those of γ phase and the macroscopic ones, the mechanical state of α 2 phase shows a great difference compared with that of γ phase, and the reasons were discussed.

The non-destructive estimation of the superficial mechanical properties of components in the INCONEL 600 alloy by X-ray diffraction peak width

INCONEL 600 alloy is largely used as nuclear power center components. The non-destructive determination of the superficial mechanical proprieties is indispensable for the qualification of the fabrication process and for the service duration estimation in aggressive environment. X-ray diffraction (XRD) technique is non-destructive and can be used to determine microscopic internal stresses from the broadening of the XRD peaks. The average magnitude of XRD peak broadening is related directly to the hardness, the elastic limit or degree of cold work of the material which can be used as a means of quantifying the surface mechanical properties. With an empirical relationship between the {311} XRD peak width and the conventional mechanical proprieties (hardness, elastic limit, hard work degree) for INCONEL 600 alloy, the superficial mechanical characteristics can be estimated from diffraction peak width for just finished parts or for maintenance pieces. Several TEM observations are also realized for microstructure study.

The cryogenic properties of Al-Li single crystals

Abstracts are not published in this journal