Advanced Materials Research Vols. 652-654

Abstract: Porous NiAl intermetallics with different porosities were successfully prepared by self-propagating high-temperature synthesis (SHS). Examination of the reaction process between Ni and Al as well as the oxidation properties of the resultant materials was carried out. The melting of Al is the precondition for the reaction between Ni and Al, the reaction process can be explained by dissolution-precipitation mechanism. Only minor weight gain (0.06%~0.24%) and stable pore structures of porous materials after 200 hours oxidation at 650°C indicate that porous NiAl intermetallics have excellent oxidation resistance.

Abstract: This research investigates the microstructure and growth behavior of the intermetallic compound(IMC) of Sn-1.0Ag-0.5Cu,Sn-1.0Ag-0.5Cu-0.05Ni and Sn-1.0Ag-0.5Cu-0.05N-0.02B/Cu solder joint interface. The interfacial reactions between Cu and the solders at 250±1°C were examined. Experimental results indicated that the IMCs of the above alloy systems on the soldering interface were Cu₆Sn₅ and (Cu_x, Ni_1-x)₆Sn₅, respectively. The grain size of primary Sn decreased observably with the micro addition of B and a large number of fine reinforcement particles were found in the solder. With the aging time increasing, the (Cu_x, Ni_1-x)₆Sn₅ micrograph of the Sn-1.0Ag-0.5Cu-0.05N-0.02B solder joint interface was changed from sawtooth-like to shape-layer, but the thickness of IMCs increased unobservably.

Abstract: Solid-state phase transformation has an important influence on mechanical property of Zn alloy with high Al content. The dynamic microstructure evolution of eutectoid transformation for the Zn alloy with high Al content was observed by high temperature metallography microscope. The phase of the Zn alloy with high aluminum at 300°C was analyzed by the high temperature X-ray diffractograms. The results show that eutectoid transformation originates in the grain boundary and develops rapidly as the heating temperature rises.The variation of eutectoid transformation completion with the time increasing in the dynamics process can be expressed by M=100(1-e^{-0.0023t1.3137})

Abstract: The oxidation behaviour of AlCuTiFeNiCr high-entropy alloy with was studied at 850 oC in atmosphere. The oxide layer of long-term oxidation behavior were examined using optical, X-ray powder diffraction (XRD) with the aid of scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis (EDX). The oxidation kinetics follows a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds.

Abstract: The regular pattern of evolution of TiC and TiAl₃ during the remelting process of Al-Ti-C alloy wires was analyzed and the impact mechanism was discussed. The results show that: when the temperature of the remelting mass is at 730°C, with the increase of the heat preservation time of remelting, the degree of agglomeration of the original dispersed TiC will increase, and they are pushed toward crystal boundaries by α-Al during the solidification process, while TiAl₃ will dissolve, aggregate, and grow. When the remelting temperature is at 1000°C, as the heat preservation time increases, not only the agglomeration degree of TiC increases significantly compared to that at 730 °C and the sizes and shapes of TiAl₃ change significantly as well. The morphology of TiAl₃ will change from being lump-and-short-rod-like to needle-and-flake-like. Before and after remelting, the Al-Ti-C alloys are both composed of TiAl₃ and TiC, with no other phases formed.

Abstract: The effect of aging on the corrosion property of Al-7Si-0.3Mg Alloy immersed in 3.5% NaCl solution was studied by Tafel polarization curves and corrosion weight loss measurement in this paper. The Vickers hardness of the alloy during aging was measured on Zwick hardness testing machine. The electrochemical behavior of the Al-7Si-0.3Mg alloys after the under aged, peak aged and over aged were analyzed, respectively. The results show that the hardness of the alloy increases at first with the increasing of aging time and gets to the maximum at 4 hour, and descends gradually with the aging time (over aged). Icorr under peak aged status get to the highest value and to the lowest one during under aged status. Correspondingly, corrosion properties under peak aged status are the worst case and the best with under aged status.

Abstract: The precipitation kinetic and behavior of δ phase in Inconel 718 alloy at 900, 930 and 960°C have been studied using the quantitative X-ray diffraction (XRD) method. The results indicated that the nucleation site and way of δ phase depended on temperature by the observation of microstructures. During the aging process, the δ phase nucleated on the grain boundaries and twin boundaries preferentially, while the δ phase precipitated directly from the interior of grain when the temperature was above 900°C. At a certain aging temperature, the relationship between the δ phase content and the aging time fitted an Avrami-type equation.

Abstract: Research on multipass plastic deformation of 7A04 ultra-high strength aluminium alloy by isothermal compression experiments on the 6300KN extrusion press. Experiment results show that elongation reaches its maximal value 9.25% after the first deformation. It is obvious that fibrous tissues appeared along the metal flow direction in the deformed 7A04 ultra-high aluminium alloy, with heterogeneous distribution of precipitated η (MgZn2) phase in the matrix, which results in lower strength (Rm=335MPa, Re=212.5MPa). As the times of deformation increases, precipitated phases grow gradually and the plasticity of alloys decreases dramatically, which reaches its minimal value 5.17% after the fourth deformation. With η(MgZn2) phase disperses gradually, the strength of the alloy increases gradually, and reaches its maximal value 386.7MPa after the fourth deformations. It is proved that 7A04 high-strength aluminium alloy has better synthetic mechanical properties after four times deformation.

Abstract: The kinetics of phase transformation in Cu-15Ni-8Sn-XSi alloys alloy was studied through the measurement of the relationship between electric conductivity and volume friction of the new phase. The phase transformation kinetics equation was deduced from the Avrami empirical formula based on the linear relationship between the electrical conductivity and the volume fraction of the phase transformation. The electrical conductivity calculated by the physical model was also obtained. As comparisons, a new model based on least square support vector machines (LSSVM) and capable of forecasting electrical property of Cu-15Ni-8Sn-XSi alloys has been proposed and tested on the same data. The present calculated results of both the physical and artificial intelligence models are in very good agreement with the experimental values. Two models are feasible and efficient to forecast the electrical conductivity of Cu-15Ni-8Sn-XSi alloys.

Abstract: The Cu-based bulk glassy alloys in Cu-Zr-Ti-Ni systems were prepared by means of copper mold casting. The structure and corrosion resistance of Cu-based bulk glassy alloys were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), electrochemistry method, lost weight method. The result indicates the supercooled liquid temperature interval (ΔT_x) is up to 70.98 K for Cu₅₀Zr₂₅Ti₁₅Ni₁₀ bulk glassy alloy. The maximum diameter was up to 5.0 mm for the Cu₅₅Zr₂₅Ti₁₅Ni₅ bulk glassy alloy. For electrochemistry corrosion in 3.5% NaCl solution, self-corrosion electric current density of the Cu₅₀Zr₂₅Ti₁₅Ni₁₀ bulk glassy alloys is obviously lower than that of stainless steel and brass, so corrosion resistance of Cu-based bulk glassy alloys is better than stainless steel and brass at the same corrosion condition. The lost weight method showed that the corrosion rate of brass, stainless steel and glassy alloy is respectively 10.08 g/(m²•h), 6.08 g/(m²•h) and 2.19 g/(m²•h) in the 3% NaCl solution, which also indicates that the corrosion resistance of Cu-based bulk glassy alloys is better than stainless steel and brass. The Cu-based bulk glassy alloys can be used in the special field demanding to have the super high strength, hardness and corrosion resistance.