Advanced Materials Research Vols. 652-654

Abstract: The microstructure and mechanical properties of the as-cast Zn-25Al-5Mg-2.5Si-xGd alloys at room and elevated temperature have been investigated in this work. The results show that the addition of element Gd leads to the grain refining and the formation of Al3Gd phase and GdZn12 phase in the microstructure, and the mechanical properties of the alloys rise at first and then drop with the Gd content increasing. When Gd content is 0.8wt.%, the optimization of microstructure and mechanical properties is obtained. The alloy can be increased by 13.9%, 37.7% and 45.6% in tensile strength and be increased by 13.4%, 76.9% and 78.2% in hardness at room temperature, 100°C and 180°C, respectively.

Abstract: A cast TiAl alloy with directional γ-TiAl/α2-Ti3Al lamellar microstructure showed excellent strength retention at high temperatures and distinguished ambient ductility level as well. But both the ductility and strength at room temperature exhibited somewhat undulation. According to the microstructure and fracture surface observations, the negative diversification of the test results is attributed to the presence of mis-oriented lamellar colonies. The tilted lamellar colonies larger than a critical value can trigger the tensile fractures and therefore diminish the tensile strength and ductility significantly.

Abstract: The Finnis-Sinclair many-body potential was fitted for binary FeAl alloy with B2 structure. As the examination to the acquired potential function, some properties were calculated, and the results agree with the experiments well. Further, properties of point defects, such as divacancies were studied as an application.

Abstract: The grain refining effects of Al-Ti, Al-TiC and Al-Ti-C master alloys on commercially pure aluminum were compared, and the grain refinement mechanism of TiAl₃ and TiC among master alloys was discussed. The results show that: the grain refinement of the master alloys Al-TiC and Al-Ti toward pure aluminum mainly stems from the heterogeneous nucleation role of TiC and TiAl₃ particles, but with the extension of heat preservation time of fused mass, its role of heterogeneous nucleation will decline due to dissolution of TiAl₃ and aggregation and precipitation of TiC. The preferable grain refinement effects of Al-Ti-C master alloys toward pure aluminum are mainly due to the fact that when TiAl₃ and TiC particles are acted commonly as heterogeneous nucleation particles, the heterogeneous nucleation effect of TiC particles will be enhanced because of the presence of TiAl₃.

Abstract: The relationship of microstructure and properties of Ti-6.5Al-1.5Mo-2.5V-2Zr titanium alloy heat-treated in the α+β phase field was studied. It was found that globular or bimodal microstructures were obtained for alloy annealed at 400-950°C. Ductility decreased with increasing annealing temperature, while the strength showed a minimum at 800°C. The properties at the center of billet are lower than that at the edge due to the low cooling rate after forging. With the increase of test temperature, the strength decreased and ductility increased.

Abstract: The deformation behavior of DC cast Al-2Si and Al-15Si alloys have been studied by means of compression test at temperature range of 300-500°C and strain rate range of 0.01-5 s-1. The results show that the flow stress of the Al-Si alloys increases with decreasing compression temperature and increasing strain rate. The flow curves determined from the compression tests exhibit that the deformation of the materials is controlled by two competing mechanisms: strain hardening and flow softening. Higher silicon content in the alloys also leads to higher flow stress during deformation and tend to show more significant flow softening. Particle damage during the deformation may have an influence on the flow curves of the alloys.

Abstract: The microstructure and mechanical property of directionally solidified NiAl-Cr(Mo)-Hf/Ho alloy were studied. The results indicate that the alloy is composed of NiAl matrix and Cr(Mo) phase, the dispersion of Hf is identical with the NiAl matrix, and at the cell boundary, the dispersion of Ho is disperse. As the pull speed increase from 8mm/min to 15mm/min, the size of eutectic cell decreases, the lamellar size descends, too. After the homogenization heat treatment at 1473K for 20h, the size of eutectic cell increases, and the second phase precipitates, the hardness of the alloy decreases.

Abstract: By analyzing the climatic factors and aluminum alloys corrosion data in 10 atmospheric corrosion sites, the aluminum alloy atmospheric corrosion prediction model was built. The reasonableness of the corrosion model was verified by using the BP artificial neural network to learn, train, simulate, and compare with the corrosion test results of aluminum alloy samples in 10 typical atmospheric corrosion test stations. The results show that a stable forecasting model can be built based on the BP artificial neural network, which well predicted the corrosion rates of aluminum alloys in 10 typical atmospheric corrosion test stations.

Abstract: The precipitation behavior of γ' phase after continuous solution cooling tests was examined in superalloy FGH96. The results indicate that, with the increase of cooling rate, the mean diameter of secondary γ' precipitates decreases as well as the shape changes from cuboid to spherical. Either under water cooling or cooling at 10 °C/min and 25 °C/min, the highest strength can not be obtained.

Abstract: The stress-induced martensitic transformation in Ni₄₇Ti₄₄Nb₉ was examined using X-ray diffraction (XRD) during in situ uniaxial loading and unloading. A new martensitic (020) peak in XRD patterns is observed under strain from 10% to 12%. It indicates that the martensitic texture has reached the optimum orientation. After unloading, approximately 8% irreversible strain still remains. It is associated with the reorientation of martensites and the plastic deformation of the B2-phase. In addition, the deformed β-Nb particles would also reduce the driving force for the reverse transformation. The details of lattice-strain and shared applied stress (SAS) in the B2-phase and β-Nb phase are also discussed in this work.