Advanced Materials Research Vols. 83-86

Abstract: A new method for laser milling of Al2O3 ceramic based on deteriorative layer controlled is presented in which no assistant gas was used during the laser milling. The new milling technology is developed by means of laser scanning of ceramic surface and forming a deteriorative layer directly. Laser milling parameters are determined through crystal phase’s analysis of the deteriorative layer. The laser milling depth, surface quality, and milling mechanism with different milling parameters were studied systematically on an Nd: YAG CNC laser and multi-layer laser milling experiments were also conducted with optimized processes on the surface of Al2O3 ceramic workpiece. Therefore, the practical experimental results are that each depth of layer milling is between 0.35-0.5 mm and the surface roughness of laser milling reaches to Ra 2-3.2μm. The experimental study has thus provided deeper understanding on laser milling technology for Al2O3 ceramic both in theory and application.

Abstract: Plastic deformation process resulting in ultra fine grained materials which are rapidly grasping applications due to their superior mechanical properties remain an area of continued research interest. Generally, the influence of die land length and web to flange ratio in grain refinement subsequent to plastic deformation process have not being adequately exploited especially in complex die opening geometries. In the present study, the effect of these parameters on extrusion pressure and morphological change in I-shaped die opening geometry is investigated and reported. A forward extrusion rig is designed and manufactured for the purpose of experimental investigation. The upper bound analysis shows that increasing die land length leads to increasing relative extrusion pressure. Optimum web to flange ratio of 0.45 is numerically simulated and recommended to extrude I-shaped lead alloy with minimum load requirement. The experimental results reveal that increasing area ratio leads to quasi-sinusoidal pattern in surface hardness of I-shaped section irrespective of strain rate value. Increasing web to flange ratio, therefore, leads to increasing anisotropy of the I-shaped lead alloy. The extruded sections were examined with optical metallurgical microscope, and it is observed that increasing strain rate results in profound refinement of grain and inclusions in lead alloy even at room temperature.

Abstract: Fe-Ni-Mn martensitic steels show excellent age hardenability but suffer from embrittlement after aging. Discontinuous coarsening of grain boundary precipitates was found as the main source of embrittlement. Effect of cold rolling and equal channel angular pressing on the mechanical properties of an Fe-10Ni-7Mn steel was investigated. Cold rolling for 20%, 40%, 60%, 80% and 90% and equal channel angular pressing for four passes through the Bc route were carried out on a solution annealed material with subsequent aging at 753 K. Hardness measurement, tensile test and scanning electron microscopy were used to study mechanical properties and microstructural features of the as-deformed and aged alloys. Improvement in tensile properties of the as-deformed and aged alloys was found. A tensile strength of about 1840 MPa along with 3% elongation were determined for cold rolled by 90% thickness reduction and aged alloy, while conventional steel shows a premature fracture stress of 820 MPa with zero ductility. It was also indicated that after heavy cold rolling ductility increases in comparison to the equal channel angular pressed and aged alloy.

Abstract: A new starch-based binder as a natural polymer has been developed for metal injection molding (MIM). In this study tapioca starch which is cheap and readily available in Malaysia has been used as a binder which composed of starch, glycerol, linear low density polyethylene (LLDPE), citric acid and stearic acid. This developed binder system was mixed with 316 L stainless steel powder to prepare the feedstock at three different of powder loadings of 56, 57 and 58% vol. The rheological behavior of the binder and feedstock were evaluated at different temperatures using a capillary rheometer. The rheological behavior of binder shows less than 10 Pa s and the flow behavior index of the feedstocks were determined to less than 1, which indicates the flow characteristic is pseudo-plastic which is suitable for MIM process. Finally, among these three feedstocks, the feedstock of 57% vol. powder loading was selected and its viscosity values within expected shear rate range are less than 1000 Pa s.

Abstract: Automation of industrial activities is one of the most essential needs in recent years since the operator has smaller role in the process. Creation of the various robotic systems in the different industries causes relaxing the operators from working in hard positions, increases the accuracy, efficiency and velocity in the process and decreases the wastage and price of product. In this paper, the study on melting station and continuous casting line in Mobarakeh Steel Complex is provided. The needs for elimination of difficulties and increasing the automation level of steel slabs casting line with checking the all stations from robotic and automation point of view for stations with the capability of automation system necessitates a suitable robotic system. In this case, selected robot should be able to support the velocity, accuracy, load capacity and other characteristics. Considering the sensitive conditions around the electric arc furnace (E.A.F), a suitable sampling robot with 3-degree freedom in which all three joints moves in revolute form (RRR) has been designed.

Abstract: Mechanochemical process was applied for brass alloy production using chemical grade oxide powders. Alpha brass was produced when CuO, ZnO and PbO were milled under argon atmosphere in the presence of graphite (as reducing agent). Concurrent reduction of zinc, copper and lead oxides took place in the argon atmosphere, whereas the reactions of the reduction did not proceed well in the closed chamber that filled with air. These reactions were promoted by milling time up to 100 hours. The amount of reduction tends to decrease for longer times.

Abstract: In this study, AISI H13 steel was plasma nitrided in two different atmospheres, containing 25%N2-75%H2 and 4%N2-96%H2 at a constant temperature of 530oC and 6h-holding time. Dry wear behavior of nitrided samples was determined with pin-on-disc method at 25oC and 500oC, under 10N and 30N loads. The results indicated that the nitrided steels, which had a thin multiple phases white layer (produced at 4%N2-96%H2 atmosphere), didn’t have any wear resistance in ambient and elevated temperatures. However, the nitrided steels, having thick single phase white layer (produced at 25%N2-75%H2 atmosphere), showed better wear resistance in ambient temperature than in elevated temperature.

Abstract: This work presents the main results of several tests carried out to define the best milling tools for routing carbon fiber reinforcement plastics, mainly in use for airframes. The new milling tools are shaped by multiple left-hand and right-hand helical edges, which form small pyramidal edges along the cutting length. Several carbide substrates and coatings were tested. After the analysis of tests and modifications on the tool prototypes, the final results allow the definition of routing endmills optimized for carbon fiber composites.