JOURNAL OF NEW MATERIALS
Year:2011 | Volume:2 | Issue:1|Papers Count:8

Aluminum foam sheets produced by accumulative roll-bonding process via decomposition of a blowing agent, have a great capability for fabricating sandwich structures including aluminum foam cores. A comprehensive design of these structures demands the optimization of foaming parameters, particularly foaming heat treatment. Using preheated furnaces as alternative to infrared image furnaces, which are commonly used for foaming heat treatment, could lead to easier and less expensive foam production. Optimizing the parameters for such heat treatment is the main subject of this study. In order to achieve a preform for foaming heat treatment tests, TiH2 powders were distributed in the aluminum matrix by 7 passes of repeated roll-bonding and cutting. The fabricated preforms were heat treated to convert to the foams in a preheated resistance furnace. Optimized heat treatment parameters for achieving the best combination of porosity and cell morphology were obtained. The best result was aluminum foam with 37.2 % porosity.

Metallic multilayers have drawn worldwide attentions in recent years since they exhibit many attractive characteristics in mechanical, electrical and magnetic properties. In this research Cu-Ag multilayer composites were produced by accumulative roll bonding (ARB) method. The variation of layer structure during ARB cycles and codeformation of Cu and Ag layer were studied by scaning electron microscopy (SEM). The results showed that the continuity of the constituent layer remained intact until the end of the ninth cycles. During codeformation of layers the copper hard phase necked and the silver soft phase undulated. finally, factors affecting layer continuity and codeformation were investigated.

The importance of surface integrity of electric discharge machined components has been recognized by the industry and it is still continues to be the major concern among the researchers. This paper presents a study of the relationship between EDM input parameters (duty cycle, pulse-on time and tool polarity) and surface integrity. This study shows that, in both cases of tool polarity (positive and negative), with increasing pulse on-time and duty cycle, the rate of hardness decline in the layers near the machined surfaces is augmented and the depth of the heat effected zone is increased, Also In the negative polarity the amount of hardness decline and depth of the heat effected zone is low. According to the results of the EDX analysis, in the positive polarity, the rate of penetration and carbon diffusion is higher than the negative polarity.

Welding of power plant shafts have many problems like, martensite formation, remained Austenite, sensitivity to cold crack and residual stress. Accurate selection of welding process and variable, determination of suitable filler metals and appropriate post weld heat treatment will decrease this kind of problems. Because of existence of carbon and alloying elements in steel shaft 26 NiCrMoV 11-5, low hydrogen Cr-Mo fillers for overlaying welding on steel shaft surface was selected. Normalizing and Annealing heat treatments were selected and compared with as-welded specimen. The purpose of this work was specifying desirable post weld heat treatment and evolution of microstructure in weld and HAZ zones with micro hardness, LOM, SEM and XRD. According to metallographic and XRD results it was concluded that in welded specimen with Cr-Mo filler rod and normalized heat treatment, the amount of carbide phases were decreased, and hardness variation in weld zone and base metal was low when compare with other process. As a result, welded specimen with Cr-Mo filler rod and normalized heat treatment had appropriate microstructure and uniform hardness distribution.

TWinning Induced Plasticity (TWIP) steels, with high manganese percent (17-35%), are used in automotive bodies. Their microstructure at room temperature is austenitic and due to low stacking fault energy, major deformation mechanism in them is twinning inside austenite grains which, on the other hand, leads to enhance mechanical strength in steel. In order to improve the mechanical properties, by adding carbide forming elements to steel, their strength has been increased. To this end, the castings of steel, microstructure analysis by optical and scanning electron microscopy (SEM) were studied. The results showed that the cold-rolling this steel, will increase the strength and ductility to great exgant.

In the present work, Bismuth- Sodium-Barium Titanate (BNBT) electroceramics were prepared by mechanical alloying (MA) and their structure, microstructure, chemical composition and thermal behavior were investigated by XRD, SEM, EDX, DTA/TG, respectively. The XRD results indicated that the peaks related to the primary materials are disappeared at initial milling times and after sufficient milling time (150 h) the BNBT perovskite phase is appeared. By continuation of milling to 300 h the perovskite phase almost totally developed. In addition, due to the peak broadening at 2q higher than 35 (particularly at 150 h of milling), the presence of a considerable amount of amorphous phase is obvious in the structure. The microstructural analysis revealed that, by progression of milling, the powder particle size is reduced continuously and the equiaxed morphology is developed. Furthermore, chemical composition assessment demonstrated that the desirable distribution of elements has been accomplished by development of MA. Moreover, the presence of the amorphous and perovskite BNBT phases was confirmed by thermal analysis.

The element-free Galerkin method (EFG) and the natural element method (NEM) are two well know methods in the computational mechanics and meshless methods. In this paper, a computational technique is presented based on coupling of EFG and NEM for large plastic deformation simulation in the tensile test and forward extrusion process. The coupling between EFG and NE is achieved by using the natural element shape functions as the weight functions for the element free Galerkin method. In this method, contrary to EFG method, the imposition of the essential boundary conditions is straight forward and shape functions fulfill the Kronecker delta property. The inspection cases are tensile test simulation in axi-symmetry state and forward extrusion simulation for circular shape components from round billets. In this method, the punch stroke value is divided to sub-steps whereas a new set of nodes become active at the end of each sub-step of deformation. Hollman-Ludwik law is selected to explain the material behavior after the yielding point. The validity of the proposed method is verified by comparing the results from EFG-NE simulation results with those obtained from finite element simulation (ANSYS result). It is concluded that the results obtained by EFG-NE method is in good agreement with those from FEM and therefore, the coupled EFG-NE method is capable to handle large plastic deformation simulation.

In this work the effects of welding parameters such as: Linear velocity (V), Rotational speed (W), and water temperature on microstructure and mechanical properties of (UFSW) 4343- Al alloy was investigated and it was compared with air (FSW) the tests out on both air and under water FSW with different welding pitch (V/W) and 4343 Al alloy butt joint. Visual inspection results show that surface quality of the welded samples in air and under water are similar, in addition optical microscope (OM) and scaning electron microscope (SEM) examination results show that by increasing of environment cooling intensity in constant V/W, the grain size, Si2Fe precipitated phase and b phases of weld nugget were decreased, the maximum decrease in grain size, Si2Fe and b phase was gained in V/W=0.1 mm/r. The Hardness and tensile tests of welded nuggets show, that by increasing of environment cooling intensity in a constant V/W, hardness, tensile strength and yield strength of weld nugget was increased and percentage of elongation was decreased, Moreover maximum hardness, tensile strength and yield strength of weld nugget was gained in V/W=0.1 mm/r that welded in under water at 2oC water.