Advanced Materials Research Vols. 915-916

Abstract: The specimens of single crystal superalloy DD6 with 0.10% Hf and 0.47% Hf were prepared in the directionally solidified furnace. The effect of Hf content on the isothermal oxidation resistance of the second generation single crystal superalloy DD6 was studied at 1000°Cin ambient atmosphere. Morphology of oxides was examined by SEM, and their composition was analyzed by XRD and EDS. The experimental results show that the oxidation resistance of DD6 alloy with 0.47% Hf is better than that of the alloy with 0.10% Hf. The alloy with different Hf content all obeys parabolic rate law during oxidation for 100h at 1000°C. The increase of Hf content can promote the Al₂O₃ formation and decreases the proportion of NiO. The oxide grain size and the thickness of the oxide layer all reduce with increasing of Hf content. The oxide scale of the alloy with different Hf content is made up of an outer NiO layer with a small amount of Co₃O₄, inner Al₂O₃ and Cr₂O₃ layer with a small amount of TaO₂.

Abstract: As a model material, commercial pure titanium was rolled to plates with different dislocation boundaries. The dynamic mechanical response of Ti specimen was analyzed during impacted with Split Hopkinson Pressure Bar (SHPB) at different strain rates, and microstructure evolution was investigated using optical microscopy and transmission electron microscopy. It was found that adiabatic shear sensitivity was decreased with increasing strain rates for all as-annealed, 25% and 50% cold rolled states. To the contrary, for 70% cold rolled state the adiabatic shear sensitivity was increased with increasing strain rates. The microstructure of adiabatic shear bands (ASBs) were developed from elongation morphology to fine equiaxed grains in the specimens of 25% cold rolled state, and ASBs became broader with increasing strain rate.

Abstract: Thermal fatigue property of a directionally solidified nickel-base superalloy with different notch radius was studied. The results show that cycle numbers of crack initiation increase and resistance of thermal fatigue decreases with the rise of notch radius at the upper temperature of 1050°C. Thermal fatigue crack initiates at carbide or oxidized cavity. The join of oxidized cavity makes crack propagate. The propagation rate lowers with the increasing notch radius. Crack propagation direction is along <110> direction in {111} plane. The stress concentration drops and thermal fatigue property improves with the increase of notched radius.

Abstract: The effect of forging and solution temperature on the microstructure and mechanical properties of 316LN stainless steel has been investigated by optical microscope, tensile testing machine and scanning electron microscope (SEM). The results show that the average grain size of the steel was refined from 150μm to 70μm after forging and solution treatment. With increasing solution temperature, the tensile strength and yield strength decreased. On the contrary, the elongation of the steel increased with increasing solution temperature except at 1200°C. The tensile strength of the samples forged at 1100°C is better than those of the samples forged at 1000 and 1200°Cafter solution treatment. Tensile fracture morphologies observation showed that all the specimens have ductile fracture morphologies. With increasing solution temperature, the toughness of the steel becomes better and better except at 1200°C. Both the microstructure and mechanical properties of the 316LN stainless steel have been improved after forging at 1100°C and following by solution treatment at 1150°C.

Abstract: Casting temperature has important influence on microstructure and tensile properties of casting products. Effects of different casting temperatures (670°C, 700°C, 730°C and 760°C) on as cast microstructure and tensile properties both at ambient temperature and elevated temperature of AS31-0.1%Sr (mass fraction) alloy were studied.The experimental results show that there exist polyhedral shape, fine fibers shape and a few Chinese script Mg2Si particles in AS31-0.1%Sr alloys. The grains at the casting temperature of 700°C are finest. The ultimate strength,yield strength and elongation at both ambient temperature and 150°C first increase when the casting temperature increases from 670°C to 700°C and then decrease with the casting temperature continuously increasing to 760°C.

Abstract: Compression tests of Mg-4Al-3Ca-1.5Zn-1Nd-0.2Mn Magnesium alloy as-extruded had been performed in the compression temperature range from 200°C to 350°C and the strain rate range from 0.001 s¹ to 1 s¹ and the flow stress data obtained from the tests were used to develop the power dissipation map, instability map and processing map. The optimum parameters for hot working of the alloy had been determined. According to the processing maps, the most optimal temperature range is 280°C to 350°C and most optimal strain rate range is 0.001 S^-1 to 1 S^-1.

Abstract: CuInSe₂ (CIS) is a promising material for thin film solar cell applications. In this work, CIS powders have been synthesized by solvothermal route at different reaction time. X-ray diffraction patterns and Raman spectra of the products reveal that the optimal reaction time is 36 h at 200 °C in order to obtain pure CIS phase. SEM images show an irregular morphology of synthesized CIS material. The formation pathway of CIS has also been studied. Cu-Se compounds are formed at the beginning of the reaction, which act as an important intermediate for the formation of CIS products. This result is not consistent with the reported mechanism.

Abstract: The impact performance of ZnAl27Cu2.5MgMn alloy from room Temperature to 2500 °C has been investigated by pendulum impact testing. The surface morphology of impact fracture is observed by scan electron microscope (SEM). The results indicate that impact energy of the alloy decreases as the temperature increases when the temperatures are lower than 100°C. Between 100°C and 200°C, impact energy increases as the temperature increases. And when the temperature exceeds 250°C, impact energy decreases dramatically. Impact energy gets to the maximum at room temperature. Impact behavior of the alloy can be evaluated by the width of impact spectrum curve. The wider the peak of impact spectrum curve, the higher the impact toughness. Whereas impact toughness is worse if peak is narrow.

Abstract: The cooling slope technique has been developed in recent years, which controls the nucleation and growth of the primary grains during solidification to achieve fine and non-dendritic microstructures. In this study, A356 Al alloys were processed through a modified cooling slope technique to obtain fine, non-dendritic microstructures, in which the cooling rate of the cast crucible was controlled. Three process parameters, namely pouring temperature, inclined slope angle, and the cooling rate of the cast crucible, were varied during the processing. The cooling slope was water-cooled with a constant water flow rate. The solid fraction and the size distributions of the primary grains along the vertical and horizontal positions of the cast ingots were measured individually. The macro-segregation was examined in terms of the distribution of the solid fraction. The yields of the ingots were calculated for studying the efficiency of the cooling slope technique. The effects of the three process parameters on the microstructures, macro-segregation, and yields were studied by the Taguchi method.

Abstract: Steel sheet has one major drawback, it is attacked by moisture at low temperatures and oxygen at high temperatures. Fortunately, coatings can provide protection to steel sheet from corrosion. Aluminum and aluminum zinc coatings can be applied by different methods. These are chemical vapor deposition coating (CVD), slurry coating, vacuum coating, spray coating, cladding, electroplating, electrophoresis, diffusion coatings, cementation, calorizing and hot dipping. This paper aims at providing a survey of these processes.