Applied Mechanics and Materials Vols. 117-119

Abstract: Hot deformation behavior of the 30%Mo/Cu-Al₂O₃ composite was investigated by hot compression tests on Gleeble-1500D thermal simulator in the temperature ranges of 450~750°C and the strain rate ranges of 0.01~5s^-1, as the total strain is 0.7. The results show that the peak stress increases with the decreased deformation temperature or the increased strain rate. Based on the true stress-strain curves, the established constitutive equation represents the high-temperature flow behavior of the composite, and the calculated flow stresses are in good agreement with the high- temperature deformation experimental results.

Abstract: Mn18Cr2 steel is one of austenitic deformation strengthening steel. The existing form of TiN and its influence on the austenitic structure in the steel by adding small amounts of TiN nanoparticles are discussed in this study, which may provide some advices to explore new way to strengthen high manganese steel. The microstructures of Mn18Cr2 steel added small amounts of TiN nanoparticles are observed by Transmission Electron Microscopy (TEM). The results show that TiN nanoparticles exist in austenite and there have a very good match interface between the two phases, the crystal face relationship are {220}_γ//{220}_N, {422}_γ//{422}_N, (111)_γ //(200)_N , orientation relationship are <110>_γ// <110>_N, <211>_γ//<211>_N, [112]_γ // [011]_N, moreover, the relationship of (111)_γ and (200)_N is not only parallel but also coherent. Meanwhile, there are many high density dislocations, a small amount of stacking faults, twins and ε-martensite in the austenite due to the role of TiN nanoparticles.

Abstract: The aim of this work is to present experimental results of investigation on crystallization process of Co-containing Finemet-type alloys. To different Finemet alloys, there exist different changing trends of the initial crystallization temperature after Co addition. Addition of Co in Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy reduces the stability of the amorphous phase, and leads to the formation of nanocrystallites at lower temperature. While adding Co increases the stability of Fe_76.9Cu_0.6Nb_2.5Si₁₁B₉ amorphous phase, and results in higher nanocrystallites temperature. Using the method of Kissinger, possible reasons were analyzed for the variation of the apparent activation energy of crystallization determined from DSC thermograms.

Abstract: In the paper, the thermo-properties of unsaturated polyester resin (UPR)/epoxy resin(E51) composites through reactive blending method were studied by DSC. The experimental results showed that, when the amount of E51 in UPR/E51 composites reached to 2wt%, the mixture take place glass transition at 84°C which higher than that of pure UPR 15%. When the amount of E51 reached to 10wt%, the mixture take place two glass transition at 59°C、104°C respectively. The morphologies of the mixtures were investigated by SEM, and the curing process of UPR/E51 was traced and investigated by FTIR.

Abstract: The SiO₂ nanoparticles reinforced Cu-matrix composites were prepared by powder metallurgy technology．The influences of SiO₂ volume fraction on the properties of hardness、conductivitity rate and wear behavior of Cu-matrix composites were studied. The results showed that conductivity rate was decreased with the increase of the SiO₂ volume fraction；whereas the hardness was increased, then decreased and wear behavior was increased. Sintering an hour of performance was superior to the sintering half an hour.When SiO₂ nanoparticle volume fraction was achieved 2.5%, comprehensive properties of SiO₂/Cu composite were obviously increased.The microstructures revealed that the second phase particles precipitated dispersedly in copper matrix after hot extrusion. with the increase of the strengthen phase particle volume fraction, nanoparticles appeared together and gathered in grain boundary of copper matrix.

Abstract: In this paper, the Cu/MoS2/Mo composites were prepared by the powder metallurgy technology. The friction wear test was tested by the HST-100 High Speed Electric-tribometer. The microstructure and wearing surface morphology were examined by SEM and EDS. The electrical sliding wear behavior of the composites was discussed. The results indicated that the dense composites are obtained; the wear mechanisms of Cu/MoS2/Mo are mainly abrasive wear and adhesive wear with arc erosion; the effects of current intensity and sliding velocity on the wear property of the composites are complicated, and the composites show the best property when the current intensity is 60A and the sliding velocity is 40m/s.

Abstract: The oxide scale of TP304H austenitic stainless steel was analyzed with SEM, X-ray, and ESA after being oxidized at 650 °C, 750 °C and 850 °C for different time. The results show that: the initial oxide film consists of needle-like cores. With the heating proceeding, the needle-like cores grow up gathering into granular cores, and then new needle-like cores grow up on former granular cores, and gradually grow into flakes which continue to gather into more granular cores then. As the oxide film becomes thicker, this process is in continuous cycle. The subsequent needle-like or flakey cores form on the basis of previous granular cores. The content of metallic elements is analyzed to find the law of diffusion and oxidation. As the figure shows the Fe of the matrix diffuses outward and the oxidation takes place at the oxide film-gas interface, which means a series of reactions does not occur inside the matrix. Below the temperature of 650 °C, the growth of oxide film is relatively slow, while above this temperature diffusion and displacement of metallic elements and oxide film growth rate accelerates. The oxide film is easy to fall off when reaching to a certain thickness, which means that TP304H stainless steel is not suitable in high-temperature and oxidative environment for long service.

Abstract: The hot deformation behavior of the Al₂O₃/Cu-10vol%WC composite is investigated by isothermal compression test on a Gleeble 1500D thermal-mechanics simulator at the temperature ranges from 350°C to 750°C and the strain rate ranges from 0.01s^-1 to 5s^-1. The results show that high-temperature flow stress-strain curves of Al₂O₃/Cu-WC composites have typical features of the softening mechanism of dynamic recovery and dynamic recrystallization. The peak stress increases with the decreasing of deformation temperature or the increasing of strain rate. The hyperbolic-sine type equation shows good agreement with the experimental stress. Upon the basis of the above experimental results, the activation energy of the composite is calculated as 208.34kJ/mol.

Abstract: Heat treatment process of 31Mn2SiREB cast steel used in crawler plates is directly quenching at 1050°C after casting. The reasonableness of the process needs to be surveyed. In this paper, the effect of quenching temperature on mechanical properties was studied, and the micro-area composition and micro-hardness at different quenching temperature were investigated. The results show that tensile strength and impact energy increase observably with the elevating of quenching temperature. With the increase of quenching temperature, the fluctuations of micro-hardness and chemical composition at different micro-areas become obviously small. This means that the relatively homogeneous structure and composition can be acquired in higher temperature. The as-cast microstructure is extremely uneven, so pre-treatment process of normalizing or diffusion annealing ought to be carried out before quenching treatment, and quenching temperature should not be too high.

Abstract: In this paper, composite static strength test are analyzed with the Weibull and normal statistical method. Compare the Weibull analysis with the normal analysis, which shows that the A-basis value and B-basis value from the Weibull analysis respectively are less than ones from normal analysis by approximate 9.7% and 2.6% under tension loading, on the other hand they are decreased by approximate 16.1% and 5.2% under compression loading. This analysis result has the higher application worth.