Advanced Materials Research Vols. 712-715

Abstract: Magnesium and its alloys have been received huge attention as new kind of degradable biomaterials. However its application hindered by poor carrion resistance fluoride conversion coating was performed due to improve the corrosion resistance of Mg-Ca-Zn alloy. In the present work ccorrosion of behaviour and degradation bahaviour of fluoride treated Mg-Ca-Zn alloy were investigated. Microstructural evolutions were characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy. The corrosion resistance was examined in vitro by potentiodynamic polarization and immersion test in Kokubo solution at room temperature. The coating characterization indicated that the dense and uniform film with 6 μm thickness consists of MgO and MgF₂ formed on the alloy. Polarization tests recorded a significant reduction in the corrosion current density from 188 μAcm^-2 in bare Mg-Ca-Zn to 6.11 μAcm^-2 in fluoride treated alloy as a result of formation MgF₂ protective layer. The in vitro degradation tests showed that the average weight loss of the untreated specimens significantly higher than that of fluoride treated Mg-Ca-Zn alloy. The results revealed that the fluoride conversion coating noticeably improve the corrosion resistance of Mg-Ca-Zn alloy resistance of Mg in Kokubo solution.

Abstract: This paper presents research of influence electrolyte plasma carbonitriding on tribological properties of R6M5 high-speed steel. Shows perspectiveness of carbonitriding high-speed steels in electrolyte plasma. The results of research demonstrated increasing wear-resistance of R6M5 steel after carbonitriding in electrolyte plasma. Under the same test conditions by the method of scratch-test have been determined that the depth of the scar of a modified layer has become less in comparison with the original sample, which indicates a significant increase of wear-resistance and hardness of the surface carbonitriding layer R6М5 steel. It was set that after electrolytic-plasma carbonitriding abrasive wear-resistance of the surface layers of R6M5 steel is increased by 25%. Introduction

Abstract: The structure of low-carbon steels after saturation by nitrogen and carbon in the mode of electrolytic-plasma nitriding and carbonitriding on the surface structure of austenitic stainless steel 12Cr18Ni10Ti has been studied. Optimum modes of electrolytic-plasma nitriding and carbonitriding are determined ensuring the maximum saturation of nitrogen and carbon, the microhardness of the surface. It is established, that after electrolyte-plasma processing microstructure of steel 12Cr18Ni10Ti has martensite structure. As a result of the research it is revealed that steel 12Cr18Ni10Ti after the electrolyte-plasma processing has high hardness.

Abstract: In this study, we conducted heat treatments on W6Mo5Cr4V2Si steel using different annealing, quenching, and tempering processes. Meanwhile, the microstructure and hardness performance of this steel are analyzed. The results showed that, in the annealing temperature range of 790°C-870°C, the higher the annealing temperature was, the better the annealing effect that W6Mo5Cr4V2Si steel presented; W6Mo5Cr4V2Si steel exhibited the lowest annealing hardness of 22.6 HRC after annealing at 870°Cfor 2 h; In the condition of annealing at 830°C for 3 h, quenching at 1200 °C around, and tempering temperature range of 400 °C-700 °C, W6Mo5Cr4V2Si steel showed the highest hardness at tempering of 560 °C around, which is about 66.7 HRC. The tempering structure of this steel was mainly composed by needle or strip-typed martensite, a small amount of residual austenite, and carbide particles.

Abstract: A mathematical model for the RH refining process was developed and validated by the measured molten steel temperature in situ. It is showed that the model predicted temperature matched the measured value well and the average errors within ±5°C were 86.9%. The model results also showed that for every increase of 100°C of the initial temperature of the chamber inwall , the average molten steel temperature increased by about 8°C. For every blowing extra 50m³ oxygen, the steel temperature increased by about 7°C.

Abstract: Analyses the principal of titanium & titanium alloys oxidizing and the relation of thickness and color of the oxidizing film and the oxidizing power, The reasons are pointed out, which the low reapparition-rate and the difficult control of color of oxidizing film lie in titanium & titanium alloys anodizing with common power. The technique and equipment parameters are acquired by anodizing experiments, which ensure the identity of oxidizing film color of titanium & titanium alloys oxidizing for batch-type production, where the voltage is severed as a control object, the adjustable stable voltage and the controlling pattern of self-shutting are used, that enable the terminal voltage and the pattern of voltage inputting to be accurately controlled, and ensure the identity of oxidizing film color for batch-type production. These are utilitarian measures in the application of titanium & titanium alloys oxidizing for batch-type production.

Abstract: The mechanical properties and microstructures of zinc-based alloys with different Al-contents ranging from 30 wt% to 50 wt% were studied by means of DSC, metallography and tensile testing under different temperatures in the present work. The experimental results show that the ZA40 is of the best comprehensive properties and ZA50 better high-temperature performance among the five alloys.

Abstract: A modified model describing the austenite reaction was developed that took into account the effect of heating rate. The model considered the variation of activation energy during non-isothermal heating and one set of model parameter was adequate to predict the formation of austenite. To verify the theoretical model, the process of austenite formation during continuous heating in Cr5 roller steel with pearlite and ferrite mixed initial microstructure was analyzed by dilatation experiment. The results show that a strong logarithmic relationship between apparent activation energy and heating rate. Experimental kinetic transformations as well as critical temperatures of austenite reaction are in good agreement with the calculations. The model can be used to describe the transformation kinetics at an intermediate heating rate.

Abstract: The cyclic deformation behaviors of hotrolled AZ91 magnesium alloy are studied by asymmetrical cyclic stresscontrolled experiments at room temperature. The ratcheting behavior and fatigue failure mechanism are discussed. Results show that: (1) The ratcheting strain increases sharply with the increase of cycle number at the initial stage, and then tends to be a constant after certain cycles. (2) The fatigue crack initiation and stable propagation regions are flat with lamellar structures, while the unstable propagation and rapid fracture regions are coarse with ductile dimples and tearing edges. (3) The residual twins can be seen as potential damage to fatigue failure of the material, due to its irreversibility of cyclic plastic deformation and damage to grain boundaries.