Abstract: Pure Fe3Al and Fe3Al+4%Cr alloys were corroded at 1000 °C for up to 200 h in N2-0.1%H2S-mixed gas in order to study their corrosion behavior in H2S-containing atmosphere. The formed scales consisted primarily of α-Al2O3, FeAl2O4, and Fe2O3. In these oxide scales, hydrogen and sulfur dissolved according to the reaction; H2S→2H+S. Corrosion products of Cr were not identified in the scales from the XRD analysis, indicating that Cr dissolved in the oxide scales. Fe3Al+4%Cr alloy displayed poorer corrosion resistance than Fe3Al alloy, indicating that chromium accelerated the corrosion rates of Fe3Al alloys.
Abstract: Hot deformability and fracture of as-cast Fe-Cr-Mn-Ni stainless steel ingots with high nitrogen and high carbon contents were studied. Effective stress-strain curve indicates a decrease of the UTS from 510MPa to 90MPa with increase of temperatures from 600°C to 1200°C. Effective stress-strain curves exhibited typical work hardening until the final stage of fracture from 600°C up to 900°C. The fracture elongation decreased from 600°C with the increase of temperature up 850°C, but started to increase appreciably as the work softening becomes dominant in the stress-strain curves above 950°C, suggesting the increase of ductility above 950°C is associated with dynamic recrystallization. The high temperature deformability was enhanced above 1000°C by homogenization of the as-cast alloy due to the dissolution and redistribution of segregated particles, providing the homogeneous distribution of the nucleation site of dynamic recrystallization. . The presence of fatal crack at 1,250°C and the loss of hot ductility can be attributed to the partial melting in austenite grain boundaries at high temperatures.
Abstract: Due to their resistance to wear and corrosion, the use of Zinc-Aluminum (Zn-Al) alloys in general and Zinc-Aluminum 5 (ZA5) alloys, in particular, have spread in the last two decades in industrial applications. These alloys normally solidify in a coarse dendritic structure which affects their surface quality and mechanical behavior. Therefore, their structure is normally refined by rare earth materials, such as Titanium (Ti), Titanium-Boron (Ti-B) or zirconium (Zr). In this research, the effect of adding Tantalum (Ta) to ZA5, at the following percentages: 0.02%, 0.04%, 0.06%, 0.08%, and 0.10%, on its microstructure and fatigue life is investigated. The results of this work revealed, within the experimental range, that the addition of Ta as a grain refiner at all rates could change the coarse dendritic structure of ZA5 into a fine nodular one. It was also found that adding Ta at 0.04% to ZA5 increased its fatigue life at a stress level of 160 MPa. However, adding Ta at a rate percentage higher than 0.04% and at stress level exceeding 160 MPa resulted in deterioration of its fatigue life.
Abstract: Metal coating nowadays is very essential in heavy industry and many other applications, however, a coating system is designed and built to obtain pyrolytic Chrome-Oxide Cr2O3, so oxygen is distributed through the coating in order to enhance its properties depending on metal-organic compounds (MOC). A very large number of experiments have been performed to study the effect of oxidant comparing with inert atmosphere. A chemical vapor deposition method for preparing chromium oxide Cr2O3 coatings from bis-arene chromium compounds has been performed, followed by studying the effect of oxidant substances concentration on the kinetics of growth of coatings. The main finding is that coatings exhibit excellent adhesion, high microhardness, and wear resistance. The coating process is characterized by high adaptability and relatively low cost.
Abstract: In this study, the authors evaluated pressure distribution on a backing plate in friction-stir processing (FSP) utilizing an embedded pressure pin connected to a load sensor. They conducted FSP on aluminum alloy plates repeatedly offsetting the path-lines from the center of the pin and recorded change of forming pressure with tool position, which was compiled from the bearing load of the pin. The authors mapped the results to visualize the two-dimensional contact pressure distribution on a backing plate during FSP. They then compared the height distribution of the wall fabricated by friction-stir forming (FSF) utilizing a die having a groove with the observed distribution of pressure. Consequently, maximum pressure was observed beneath the rim of the tool probe at the retreating side (RS), and the highest points of the wall were observed at the RS.
Abstract: Laser welding with hot wire addition is a new type of welding method. In order to search for appropriate laser welding technological parameters, main technological parameters have ran orthogonal optimization tests, root face layers have ran orthogonal experiments, impacts on root face forming qualities of technological parameters have been analyzed. Experimental results show that, the most influential technological parameter of weld width is welding speed, by lowering welding speed heat heat input in per unit of time will be increased, weld width decreases with the increase of defocusing amount and decrease of density of power.
Abstract: In order to study the effect of laser spot superposition on aluminum alloy sheet forming by laser peening, the finite element analysis method was introduced to simulating the forming of 7075 aluminum alloy with different spot superposition case. The results showed that the forming effect and stress distribution of the metal sheet was effected by the laser spot superposition modes. The forming effect of transverse spot superposition mode was better than the other three spot superposition modes.
Abstract: A numerical simulation study of collision effect on damage evolution in electromagnetic forming (EMF) was presented. EMF technology can greatly improve the forming limit of metal sheet duo to the high rate. However, collision behavior is also an important factor for the formability of sheet. Free form model and conical die model were carried out to study the effect of collision behavior on mechanical properties of Al alloy sheet. The EMF process of 1050 Al alloy sheet was analyzed and discussed by numerical analysis software LS-DYNA. The combined strategy of boundary element method and finite element method was adopted to realize the coupling calculation of electromagnetic field and structural field. Based on the GTN material model, the evolution of void volume fraction of 1050 Al sheet were calculated and analyzed. Comparing the free form model results and the die form model results, showed that the collision behavior could reduce the void volume fraction of sheet, but excessively high collision speed lead to the sheet rebound, which aggravated the damage of material and reduce the accuracy of the product. Therefore, the appropriate discharge voltage in this work was found to improve mechanical property of sheet on the premise of forming precision.
Abstract: Sandbalsting is a method used for surface treatment and at the same time this process also improves the mechanical properties of the material. ASTM A516 Grade 70 is widely used in industrial sector as it provides very good mechanical properties in tough conditions. The main usage of this material is in moderate and low operating services. This paper focus on the effect of sandblasting process on ASTM A516 Grade 70 on improving the mechanical properties and fatigue life of this material. Samples have been blasted with sand grade SAE G-80. The focus of this paper is the result of the microhardness, tensile and fatigue test before and after the sandblasting process to study the improvement in mechanical properties as well as the fatigue life. The research was extent to the microstructure analysis using SEM to study the change in microstructure after sandblasting process and fatigue test. Result shows that the hardness increases with respect to blasting time. Result also shows 2.3% increment in tensile strength after sandblasting and there is significant increment in fatigue life. Result also shows that the sandblasting process decreases the grain size of the material. It was proven that the sandblasting process will increase the hardness and decrease the grain size of the material with respect to sandblasting time. At the same time, there is a significant improvement in mechanical properties and fatigue life by applying sandblasting process on the tested material.
Abstract: Machined surface carries the inherent features of machining process. Investigation of surface topography generated by machining process is helpful to extract the features of surface development process. In the present study, roughness profiles measured on machined surface generated by EDM are considered as time series and used for extraction of inherent features of surface topography through phase space reconstruction. Presence of self-similarity in surface topography is assessed by estimating a second order fractal dimension, called as correlation dimension. Saturation of correlation exponents with the increase of embedding dimension indicates the presence of chaos in surface topography.