Advanced Materials Research Vols. 194-196

Abstract: The massive transformation, austenite (γ) → ferrite (α), in Fe-4Cr alloy subjected to cooling from the high-temperature austenite down to room temperature at cooling rates of 75, 150, 330 K min^-1 were experimentally investigated by means of high-resolution differential dilatometry. It is found that the onset transformation temperature and the overall transformation time decrease with increasing the cooling rate applied. Furthermore, by fitting the calculated transformed fraction according to developed phase-transformation model to the experimental data obtained by differential dilatometry, the kinetic parameters are obtained which show the activation energy for growth and the activation energy for nucleation are considerably different, this may be due to considerably different interfacial structure with the matrix for minute embryos and for the much larger growing particles.

Abstract: In this paper, the problem of plastic strain energy density as a evaluation of low-cycle fatigue (LCF) properties for A356 alloys with various Ti content and Ti-addition methods is considered. The experimental results reveal that it is not the Ti-addition methods but the Ti content that has played an important role in influencing on the plastic strain energy density, thus on the LCF life. Whether for the electrolytic A356 alloys or for the melted A356 alloys, the alloys with 0.1% Ti content can consume higher cyclic plastic strain energy during the cyclic deformation compared with the alloys with 0.14% Ti content due to the better plasticity, giving rise to a better fatigue resistance and a longer LCF life. Because of the different macro or micro deformation mechanism, the fracture surface of electrolytic A356 alloy exhibits the diverse microstructural morphologies under the various strain amplitude.

Abstract: The aim of this paper is to study the microstructures and hardness of silver alloys after internal oxidation process. The Ag-5Sn and Ag-5Cu alloys were prepared by melting and cast into ingots and then they were internal oxidized at the temperature range from 550 to 750°C, for 24 hours under oxidizing atmosphere by feeding oxygen gas with the pressure of 1 kg/cm², gas flow rate 5 l/min and cooled in the furnace. The microstructures, Vickers microhardness and phase compositions were investigated. The results showed that the microstructures of the based metal revealed dendritic structure and they were transformed to equiaxed grains after internal oxidation. The internally oxidized layer of Ag-5Sn alloy is SnO₂ with the hardness about 106-133 HV. The internally oxidized layer of Ag-5Cu alloy is CuO with the hardness about 65-73 HV.

Abstract: The microstructures and corrosion resistance of AZ91 and AZ91+0.5 wt.% erbium (Er) magnesium alloys were studied, respectively. The results show that the Er addition in scrap AZ91 magnesium alloy can improve the corrosion resistance, markedly. The discontinuous precipitation phase (DPP) for Mg₁₇Al₁₂ was retarded and the amount of DPP was decreased by 41% due to the formation of Al₈ErMn₄ phase during solidification. The amount of continuous precipitation phase (CPP) in grains was decreased by 8% because of the formation of Al₇ErMn₅ phase during solidification.

Abstract: The effect of solution treatment from 1050°C to 1200°C, soaking time 15min on microstructure, mechanical properties and precipitation behavior of Cr20Ni32AlTi alloy was investigated. The results are as follows: with the increasing of the solution treatment temperature from 1050°C to 1200°C, the average grain size increases remarkably from 17μm to 110μm, the strength of alloy decreases while the elongation increases. The amount of carbide precipitation in the alloy decreases with the increasing of solid solution temperature. The optimum solution treatment temperature for the investigated Cr20Ni32AlTi alloy is 1150°C~1200°C.

Abstract: The interaction among Cerium, Arsenic and Iron at high temperature were studied by means of electron probe microanalysis, optical microscopy and X-ray diffraction. The result shows that the binary compound CeAs is the main interaction product when the atomic ratio of Ce to As is 1:2. The eutectic compound Fe₂As can be precipitated from ferrite with the temperature decreasing, and the gray phase in bright field might be a ternary compound Ce₁₂Fe_57.5As₄₁.

Abstract: The hot deformation behavior of Fe-25Mn-3Si-3Al TWIP steel were investigated by isothermal single-pass compression on Gleeble-3500 thermal simulator at the temperature range of 900°C to 1100°C and the strain rate range of 0.01s^-1 to 1s^-1. The results showed that the true stress-strain curves of Fe-25Mn-3Si-3Al steel had a typical feature which often appears during the hot deformation process of metals and alloys with high stacking fault energies. In true stress-strain curves, No obvious flow stress peak was observed. With the increase of strain, flow stress reaches the saturation value, indicating that the hot deformations of these conditions are dynamic recovery. The hot compression deformation of Fe-25Mn-3Si-3Al steel can be represented by Arrhenius model. The constitutive equation of Fe-25Mn-3Si-3Al steel under hot compression deformation is calculated by a linear regression analysis. The activation energy for hot deformation of the experimental steel is 422.51kJ/mol.

Abstract: The dynamic viscosities of molten Zr₅₅Ni₅Al₁₀Cu₃₀ and Zr₅₀Cu₅₀ alloys were measured by using rotating cylinder method under non-vacuum condition. According to the lnη~1/T curves, discontinuous changes were found and the activation energy was calculated. The activation energy of molten Zr₅₅Ni₅Al₁₀Cu₃₀ alloy is obviously larger than that of molten Zr₅₀Cu₅₀ alloy. Amorphous sample of Zr₅₅Ni₅Al₁₀Cu₃₀ with 3mm diameter was prepared successfully under non-vacuum condition, but there are crystallization phases in Zr₅₀Cu₅₀ amorphous sample with 2mm diameter. The relationship between viscosities of molten Zr-Cu based alloys and their glass forming ability (GFA) was discussed, and viscosities of molten Zr-Cu based alloys play an important role on their GFA.

Abstract: Transformation point of titanium alloy is an important material parameter in hot forming and heat treatment for titanium alloy. Used the transformation points of TC6 titanium alloy determined by metallographic method as desired outputs, a model for forecasting the transformation point of TC6 titanium alloy was established using MATLAB neural network toolbox under the guidance of back propagation neural network. Used the established model to forecast the transformation point of TC6 titanium alloy and analyze the effects of the contents of nine elements on the transformation point of TC6 titanium alloy, and the results show that the transformation point of TC6 titanium alloy increases with enhancement of N, O, C and Al contents, while decreases with the enhancement of Cr, Si, Mo, Fe and H contents.

Abstract: The corrosion behavior of CuCr, CuZr and CuCrZr alloys in NaCl solution is reported in this paper. The corrosion performance has been evaluated in NaCl solution atmosphere. The results show the corrosion resistance of pure copper decrease with the addition of the alloying elements initially. However, in the later exposure stages, the corrosion resistance of CuZr and CuCrZr alloy deteriorates significantly while the corrosion resistance of CuCr alloy is slightly better than that of pure copper. In addition, the results of the electrochemical experiments indicate that the different behavior for the element Cr and Zr in the base material and corrosion scales lead to the change of the corrosion resistance.