Materials Science Forum Vols. 575-578

Abstract: To replace the heavily contaminative and long price CuCo2Be alloy, the titanium bronze of no more than 3.5wt% alloying agents was introduced in this article, and its best techniques of heat treatment and cold deformation were confirmed. The metallurgical structures and fracture patterns were observed and analyzed respectively, and the microstructure was also surveyed by TEM. Results showed that titanium bronze belonged to deposition strengthening, and the main precipitated phase Ni3Ti distributed dispersedly in the group, whose size was about 20nm. Compared to the CuCo2Be alloy, the grain size of titanium bronze is more sensitive to temperature. So the titanium bronze can not be applied under overaging situation.

Abstract: In this paper, hot compression tests were carried out using a Gleeble-3500 simulator to establish the law of hot deformation and recrystallization behavior, and to generate the corresponding processing maps. The influence of Mo was also investigated by comparing the results of hot deformation in such steel. The addition of molybdenum to stainless steel slightly increases the hot deformation stress and recrystallization temperature, while reduces the efficiency of power dissipation η.

Abstract: This work aims to investigate the influence of hot deformation on dynamic recrystallization(DRX) behavior of 7050 aluminum alloy by means of physical simulation method. The hot compression tests were carried out on Gleeble 1500 machine in temperature range of 250-450°C and strain rate range of 0.01–10 s-1. Transmission electronic microscopy (TEM) was employed to observe and analyze the microstructure and DRX behavior in different deformation conditions. The results show that the effects of deformation temperature and strain rate on microstructural evolution of the alloy are remarkable. When temperature is lower than 350°C, only the dynamical recovery( DRV) occurs and typical sub-grains appear. In the range of 350-400°C, the incomplete DRX occurs and the recrystallized grain size increases with increasing temperature. The complete DRX occurs at 450°C and the fine equiaxied grains with high-angle boundaries develop resultantly. The DRX grain size increases as strain rate decreases. The desirable microstructure and properties can be obtained by optimizing the forging process parameters.

Abstract: The combustion process of Mg-TiO2 system was preliminarily investigated from three aspects of thermodynamics, reaction kinetics and the technological parameters. The result indicates that the adiabatic temperature of Mg-TiO2 system is between 2060K and 2140K because the major existent modalities of TiO2 is the rutile and anatase, this meets the empirical criterion that the SHS reaction will be self-sustaining; The solid-solid reaction occurs at about 767K; Ti powders can be produced only when the ratio between Mg and TiO2 arrives at 2.9:1; The higher the vacuum, the more complete the reaction; The combustion temperature arrives at its peak when the pressure of green compact arrives at 250MPa; the velocity of the combustion wave increases with the augmentation of the pressure of green compact. So the proper control of the technological parameters can change the reaction temperature, reaction rate and the components of reaction products.

Abstract: In this paper, Al-5.6Zn-2.8Mg-1.6Cu-0.24Cr-1.1Li, Al-8.0Zn-2.4Mg-2.4Cu-1.1Li-0.18Zr and Al-11.8Zn-2.9Mg-2.8Cu-1.1Li-0.24Zr (in wt%) alloys were artificially aged at 80,100,120,140 and 160°C for different time, respectively. The ageing process, microstructure and hardness of different alloys are investigated by Vickers hardness and transmission electron microscopy (TEM). With the increment of zinc content, addition of Li to Al-Zn-Mg-Cu alloy containing high alloying elements has little effect on the nucleation of precipitates, but the growth of precipitates has been inhibited. Very fine precipitates with high density are formed during ageing due to the existence of high alloying elements, which result in highly strengthening alloy. As the alloying content is too high to exceed the solution saturation of matrix, coarse second phases are formed in grain boundary.

Abstract: By low temperature gas multi-component thermochemical treatment, C, N, and O three elements are simultaneously infiltrated into the surface of steel 20, forming a dense, homogeneous, 50μm penetrating layer and about 150μm transition layer. X ray diffractometer and sweep electron microscope are used to measure the phase components and surface morphology. The results show that the penetrating layer is mainly composed of oxides and nitrides. After gas multi-component thermochemical treatment, the hardness on the surface penetrating layer of steel 20 may reach up to over 800HV, 3 times more than that of the original material; the hardness of transition layer is about 300HV, also higher than that of the original material. Within the temperature range of the test, the surface hardness increases with the rise of heating temperature, and the thickness of penetrating layer also increases with the rise of temperature. The tribological experiment shows that after multi-component thermochemical treatment, the lowest friction factor of steel 20 is 0.25, while the friction factor of the original material is 0.5; the wear resistance was improved.

Abstract: Using Gleeble-3500 thermal simulation testing machine, the high-temperature mechanical properties of GCr15 Bearing steel was tested. The zero plastic temperature (ZPT) and zero strength temperature (ZST) were measured, so the optimum plastic temperature range and brittle temperature range were fond. The appearances of fracture at different temperature were analyzed by using scanning electronic microscope, and the fracture mechanism at different temperature area of the steel was discussed. which was thought as the theoretical basis for establishing the secondary cooling zone system of continuous casting.

Abstract: The modulus of elasticity of wood, fiberboard and wood-fiberboard composite was measured by nondestructive test (longitudinal transmission vibration method). The predicting model of the modulus of elasticity of wood-fiberboard composite was discussed. This study has shown that the wood ratio has substantial effect on the modulus of elasticity of wood-fiberboard composite. The modulus of elasticity of wood-fiberboard composite can be predicted from volume fraction of wood by simulation formula. The model Eq.(3) can be used to predict the modulus of elasticity of the wood-fiberboard composite from the modulus of elasticity and volume fraction of wood and fiberboard when M=0.92~0.97. The model Eq.(4) can be used to predict the modulus of elasticity of the wood-fiberboard composite from the modulus of elasticity and volume fraction of wood and fiberboard when M=0.97~0.99.

Abstract: The article gives an overview of suitability of three kinds of phosphorus-containing glass systems: phosphate, alumosilicate phosphate and fluorophosphate for production of thick-films. Amorphous compositions based on metaphosphate glasses characterize high electric resistivity, thermal expansion coefficients matching with substrate, appropriate viscosity-temperature relationship, and suitable chemical reactivity, that they can be applied in thick-film technology for screen printed resistors on alumina substrate as an alternative of lead borosilicate glasses. Alumosilicate phosphate glasses are the base for the wide range of glass-crystalline high temperature materials (operating up to 10000C) for sealing of the silicon chip in microelectronics. Perfect adhesion of glass ceramics with substrate (the transition zone 5-7.5 μm) is provided by the formation of chemical bond with the oxidized surface of silicon and by the occurrence of analogous structural elements on the silicon surface and in the glass-ceramics. Due to the unique optical properties, low melting temperature of fluorine containing borophosphate glasses (FBP) can be used as brazing material (optical glue) for SiO2 glass optical fiber construction knots.

Abstract: In steel wire processing it is difficult to reach a homogenous structure throughout the cross-section of the wire particularly in greater diameters. One alternative for producing a homogenous structure is to find a cooling path with a wide transformation temperature range. Fully austenite steel wire rolled at high temperatures can be decomposed into ferritic-martensitic dual phase structure using relatively slow cooling rates. Test materials were low alloyed low carbon steels with variations in alloying elements. Gleeble-1500 thermomechanical simulator was utilised to study the effect of cooling rate on decomposition of austenite after deformation. The microstructures were studied with an optical microscope. In certain low alloyed steels slow cooling rates eliminate the bainite transformation and instead martensite is formed. The final microstructure depends mainly on the carbon content but also on the amount of other alloying elements and their effects on the austenite phase.