Materials Science Forum Vols. 561-565

Abstract: Hydrostatic extrusion (HE) as a method of metals forming is known for about 100 years. Recently, it has been utilized as an efficient way of grain size refinement down to nanometer scale. In the case of engineering metals, HE processing alters not only grain size but also second phase particles such as intermetallic inclusions and precipitates. During HE processing, these particles significantly change their size, shape and spatial distribution. These changes are accompanied by improvement in properties of processed metals such as fatigue and fracture toughness. In the present work, changes of second phase particles induced by HE are described in a quantitative way for aluminium alloys. Their impact on mechanical properties is also discussed.

Abstract: In order to prepare new functional macromolecule material, the coupling reaction of acenaphthene catalyzed by [Bmim]Cl/FeCl3 ionic liquid was investigated under mild reaction conditions and without any additional organic solvent. Pure 3,3’-biacenaphthene, which is used as intermediate of function aromatic polymer material, was obtained by recrystalling and column chromatography from the reaction mixture and was determined by GC/MS, 1HNMR and FTIR analysis. The influence of various reaction conditions on the coupling reaction of acenaphthene were studied by GC analysis and the optimum synthesis conditions of the reaction were obtain. Under optimun conditions, the yield of 3,3’-biacenaphthene will be 63.5 % and selectivity of that will be 85.6 %. Further more, [Bmim]Cl/FeCl3 is environmentally benign catalyst and solvent and can be reused.

Abstract: Submicron-grained Ti-50.9at%Ni alloy was prepared by Equal Channel Angular Extrusion (ECAE) at medium temperature(500°C). Microstructure evolution and phase transformations of Ti-50.9at%Ni alloy after ECAE processes at medium temperature have been investigated by optical microscope, TEM and DSC tests. It is found that the initial coarse grains of Ti-50.9at%Ni alloy were refined into submicron grains, smaller than 0.5 um in size, after eight passes ECAE at 500°C. Martensitic transformation temperatures decreased remarkably after one pass ECAE and more gently with increasing the pass number of ECAE. R phase transformation was stimulated after ECAE processes and underwent within a larger temperature range with an ambiguous thermal peak. The reverse R phase and reverse martensitic transformations, during heating, were separated eventually after eight passes ECAE.

Abstract: Electron backscattered diffraction analysis has been used to investigate the effect of shear deformation on microstructural evolution of a Ni-30Fe alloy during hot deformation. The alloy was compressed by 50% or 75% in thickness at a strain rate of 1/s in a single pass at 1023K using a hot compression simulator. Three-dimensional finite element analysis was carried out to evaluate inhomogeneous strain distribution introduced in the specimens by the simulator. As the equivalent strain increased, the fraction of high angle grain boundaries (HAGBs) with misorientaions between 15o and 30o increased almost in the similar way regardless of the presence of shear strain. The fraction of HAGBs having misorientations in excess of 30o increased mainly at the expense of low angle grain boundaries with misorientations smaller than 15o. Such the expense occurred at much higher rate with shear strain than without shear strain. The shear component is effective to develop HAGBs in austenite grain interiors.

Abstract: The advent of high-strength and high-precision thin-walled parts with inner ribs adapts to the increasing demand of aerospace industry, astronautics industry, military industry, and so on. For a new metal forming technology, how to determine the reasonable blank is a key problem required solved firstly in the research of power spinning process of parts with transverse inner rib. In this paper, based on the platform ABAQUS/Explicit, a reasonable 3D FE model for power spinning of parts with transverse inner rib has been established, the power spinning process of parts with transverse inner rib has been simulated under conditions of four typical blanks and the reasonable blanks for different forming processes have been obtained. The results show the following:(1) Blank with equal half-cone angle is the best selection to deform workpiece with proper height rib; (2) while for the workpiece with excessive height rib which exceed the forming limit, blank with rib is the exclusive selection, although it is difficult to be prepared comparing with non-rib blank.

Abstract: The microstructure characters of pure Iron during cold rolling were studied by HEXD (high-energy x-ray diffraction). The experimental result shows that the Debby ring of HEXD before cold rolling is discrete and very strong, the discrete diffraction points become continue and smooth with the increase of cold rolling reduction. The {001}<110> textures transform to the {001} texture after cold rolling, in this process the grains divisional are analyzed by the HEXD result.

Abstract: The sheet metal parts play important role in aero structures. Due to the requirement of strength and constraint of weight in aircraft, the aluminum alloy is widely used in sheet metal forming parts. Most of sheet metal parts form the contour in O-condition, and then solution treat to improve the strength and mechanical property. The deformation of sheet metal parts usually takes place after the heating cycle and quenching into the water or solution. The straightening operation will apply to corrective the contour of parts. Thus, the non-value added operation would increase the production cost. By using statistical methodology to analysis deformation data of sheet metal parts, this study use Cause-Effect Analysis to find the relation between deformation and relative factors, such as material, thickness and contour. The results of this analysis can provide an efficient and economical approach for the designer, process planner, and technician in manufacturing the sheet metal parts.

Abstract: Shot peening is a surface treatment and improves the performance of engineering components. More recently, a new type of microshot has been developed to enhance peening effect. In the present study, the influence of microshot peening on the surface layer characteristics of cold tool steel was investigated. In the experiment, the microshot peening apparatus with a heating furnace was produced experimentally. The projective method of the microshot was a compressed air type. The peening microshots of 0.1mm diameter were cemented carbide and the workpiece was commercially cold tool steel SKD11. Surface roughness, compressive residual stress, and hardness in the peened workpiece were measured. The effect of microshot peening on the fatigue strength of cold tool steel was also examined. The use of hard microshot such as cemented carbide was found to cause a significantly enhanced peening effect for cold tool steel.

Abstract: The objective of this work is to obtain the mapping of the granular flow during the irreversible deformation processes in spatially extended polycrystalline systems (SEPCS) in order to describe and analyse the phenomenology and mechanics of the granular flow. In general, it was established for commercial alloys that, the granular flow is linked with the hyperbolic motion due to dislocation dynamics and self accommodation of grains. Also, the recession velocity of grains in the stain field on the surface of SEPCS increased with the distance along the tension axis from the origin of the coordinate system of reference. This behaviour is very similar to the Hubble flow associated with the expansion process of the universe, where the recession velocity of the galaxies increased in a linear relationship with their distance. In this physical framework the main results are analysed in the context of the unified interpretation of the Hubble flow, plastic flow and super plastic flow [1-6].

Abstract: Microstructures developed by warm extrusion for Mg97Zn1Y2 alloy including long-period stacking order (LPSO) phase have been investigated using SEM and TEM. The extruded magnesium alloy with LPSO phase exhibits high strength and sufficient ductility. Such superior mechanical properties appear by warm extrusion around the temperature of 623K. The microstructure of the extruded alloy consists of matrix of fine-grained hcp phase and elongated grains with fine-lamellae including LPSO phase. The grain size of hcp matrix was about 1μm, indicating that remarkable grain refinement was occurred by extrusion since the grain size of as-cast alloy was about 500μm. Special attention has been paid on the enrichment of solutes at stacking faults and grain boundaries in the fine-grained matrix, which would contribute not only to the strengthening but also to the stability of fine-grained structure because of its role of an inhibiter against grain coarsening.