Materials Science Forum Vols. 561-565

Abstract: Severe strain has been introduced to commercially purity (CP) titanium samples by means of friction roll processing (FRP), which represents an alternative severe plastic deformation technique by inducing shear strain. FRP has an excellent possibility of controlling surface microstructure combining with subsequent annealing. The resultant microstructure refinement and texture evolution has been investigated. Hardness of sample was measured to compare mechanical properties of samples before and after FRPed. Parameters including the different indentations given to the sample and sample feeding speed were experimentally conducted to find the optimum condition for investigating effect on microstructure evolution. After subsequent annealing, the evolutions of microstructure and texture were observed by field emission scanning electron microscopy (FESEM) and analyzed by scanning electron microscopy/ electron back scatter diffraction pattern (SEM/EBSP) technique. Transverse texture was found to be the preferred orientation existing in the thin top layer of the sample after FRP and annealed at 823K for 1h.

Abstract: A growing interest in nanostructured materials brought about development of their fabrication methods. A great interest has been paid in this context to the methods of grain refinement which can be induced by plastic deformation. Hydrostatic extrusion was recently proposed as an alternative method of grain size reduction down to nanometer scale in metallic materials. The aim of the present contribution is to describe, in a systematic way, advantages of this processing method, such as the possibility of processing hard-to-deform materials and obtaining large dimesions products. Special attention was given to the role of hydrostatic pressure and the effectiveness of the process in terms of grain refinement and high angle grain boundaries formation. Limitations of hydrostatic extrusion, such as restriction on strain in one pass and morphological texture are also discussed together with possibilities of their overcoming.

Abstract: The purpose of this study is to reveal the cause of hardening of magnesium base alloys by the high pressure torsion processing (HPT) using X-ray diffraction. HPT was applied to Mg base alloys of the Mg-Sm system (2.8-5.5 mass %Sm). HPT was performed under pressure 4GPa at 20 oC and 200 oC. HPT results in significant strengthening of the Mg-Sm alloys due to the formation of sub microcrystalline structure. The dynamic recrystallization was realized through the pole figure measurement and the photograph of X-ray back scattering. The Mg supersaturated solid solution decomposition during HPT was observed by the X-ray profile analysis and the calculation of lattice constants of the Mg phase.

Abstract: Warm flow compaction is a new, simple and economy process that can produce complex powder metallurgy parts. A special apparatus for measuring the lateral flow capability of the powder was designed and manufactured. It can be used to analyze the feasibility of forming complex cross-shaped parts. The preparation of the powder blend and effects of pressing speed, temperature and axial pressure on the lateral flow capability of a tungsten-base powder mix were investigated. Results showed that the lateral-pressure increased with increased pressing speed and increased applied axial-pressure. The lateral-pressure decreased as lateral-distance increased. Biggest lateral-pressure was obtained when the powder blend was pressed at around 96 °C, at which the binder start to melt. In this study cross-shaped powder metallurgy parts were successfully prepared by warm flow compaction.

Abstract: Feasibility of semisolid forging of cast iron using rapid resistance heating was experimentally investigated. Gray pig iron FC250 and spheroidal graphite cast iron FCD600, whose carbon equivalents are both 4.3% in mass, were used for the experiments. Since these cast irons have a narrow semisolid temperature range, an AC power supply with an input electric energy control function was used. In this study, the resistance heating characteristics of the cast irons were firstly examined, and then their semisolid forging experiments were conducted. In the forging experiments, the conditions of the forgings such as microstructures and hardness properties were examined, and the feasibility of the semisolid forging of cast iron using resistance heating was discussed. As a result, it was found that the method presented here is highly feasible.

Abstract: Equal channel angular extrusion (ECAE) is an effective means of producing ultrafine-grained materials with extraordinary mechanical properties. Texture evolution and microstructure in pure copper single crystals processed by ECAE for up to five passes via route C are investigated to understand mechanisms of plastic deformation and grain refinement during ECAE. The experimental textures after the third pass ECAE process recovers that after one pass ECAE process. The main textures approaches a stable one after four passes of ECAE process via Route C while the intensity of main texture components decreases gradually. Local TEM-OIM measurements shows that grain subdivision in ECAE-processed samples occurs with the formation of many low angle grain boundaries.

Abstract: Experiments on surface features were carried out in honing zirconia engineering ceramics using fine grains. In ultrasonic honing, the surface fracture ratio increased quickly when the depth of cut is more than 3 μm, while in common honing it performed an ascending trend from depth of cut 1.5 μm. The value of surface roughness in ultrasonic honing increased along with the depth of cut; while it descends contrast to the depth of cut when the honing velocity is less than 0.58 m/s in traditional honing. As for honing velocity over 0.74 m/s, it deceased firstly to the minimal value for depth of cut 1μm, then began to ascend along with depth of cut. The value of surface roughness descended to minimum value for the range of honing velocity 0.41-0.58 m/s in traditional honing, while the optimized honing velocity ranged 0.58-0.75 m/s in ultrasonic machining. The surface roughness in ultrasonic honing was superior to that in traditional honing.

Abstract: It has been reported that accumulative-roll-bonded (ARB) aluminum having ultrafine grains shows an intriguing mechanical character that it is hardened by annealing and contrarily softened by deformation. In order to understand the mechanism of such a peculiar phenomenon, we have investigated the dislocation damping with ultrasonic spectroscopy and total amount of dislocations with the X-ray diffraction measurement. From the present measurements, we have found that the dislocations introduced by the ARB process are tangled but can be released with a large stress. Such dislocations accumulated in ultrafine grains play a significant role in the plastic deformation.

Abstract: In this study, cylindrical billets of Mg-3Al-1Zn (AZ31) alloy have been synthesized by spray forming technique. The alloy billets were hot-extruded into rods with proper processing parameters. The microstructures and mechanical properties of alloys were investigated. The results indicated that spray formed AZ31 alloys have a homogeneous and equiaxial grains with average grain size of 20μm. The further grain refinement with an average grain size of 5μm was attributed to the continuous dynamic recrystallization during the extrusion processing. The room temperature mechanical properties of the extruded rods are remarkably higher than those of as-cast AZ31 alloy. The average tensile ultimate and yield strength of the alloy are 321MPa and 237MPa, respectively, with an elongation of 15.2%.

Abstract: The microstructural structures of SiCp/AZ61magnesium matrix composite were studied in three different casting processes, and their hardness was measured. The results indicated that SiCp/AZ61 composites fabricated in stirring melt casting process, compared to those in fully liquid stirring casting process and in semi-solid stirring casting process, possessed fairly uniform distribution of SiC particulates and few porosity rate. It was an ideal metal matrix composites fabricated process. The Vickers hardness of non-reinforcement AZ61 magnesium alloy is higher than that of semi-solid billet, and the Vickers hardness of SiCp/AZ61 composite is obviously higher than that of the matrix. In the meantime, the Vickers hardness of SiCp/AZ61 composite can be continuously enhanced with an increasing of volume fraction of SiC particles.