Materials Science Forum Vols. 561-565

Abstract: In the present investigation, several novel techniques including sequential motion compaction, ceramic rolling and frame-confined rolling have been developed to improve the formability of spray deposited porous aluminum alloy preforms. The experimental results show that these techniques can greatly improve the workability of the spray deposited performs. Especially, sequential motion compaction can be used to densify the preforms of large dimensions which are difficult to further processing by the traditional techniques to fully dense.

Abstract: A blade with a damper platform, with excellent anti-vibration characteristic and high efficiency, has become one of the most important types of blades being developed in the aeronautical engines. During the precision forging process of this blade, the friction between dies and workpiece has important effects on metal flow, deformation defects, load and energy etc. So researching the effects of friction conditions on the forging process of blade with a damper platform has been a crucial problem urgent to be resolved. In this paper, the precision forging process of titanium alloy blade with a damper platform under different friction conditions has been simulated and analyzed based on the DEFORM-3D software platform. The obtained results reveal the influence laws of friction on temperature field and load-stroke curves, and provide a significant basis for determining technological parameters of the blade forging process.

Abstract: The texture of Ti and Zr rods, subjected to equal-channel angular pressing (ECAP) by routes C and BC, is considered as a source of information about the actual loading scheme, operating mechanisms of plastic deformation, the structure condition of material. Processes of grain reorientation under rolling and ECAP are compared and distinguishing features of the latter are revealed. Effects of grain fragmentation and dynamic recrystallization on the texture are discussed.

Abstract: By taking into account an interconnection between substructure non-uniformity and substructure anisotropy, a new approach to study the substructure non-uniformity is developed as applied to metal rods, subjected to Equal-Channel Angular Pressing (ECAP). The X-ray method of Generalized Pole Figures (GPF) was used for construction of distributions of substructure parameters. Some experimental data are presented, illustrating possibilities and efficiency of the used approach.

Abstract: The butt joining of dissimilar sheets using a shot peening process was investigated. Shot peening is a surface treatment and improves the performance of engineering components. In shot peening, the substrate undergoes a large plastic deformation near its surface due to a hit with many shots. Thus, plastic flow characterized by a shear droop occurs at the edge of the substrate due to shot peening. When the dissimilar sheets with the edge of the notch geometry are connected without level difference and shot-peened the connection, the sheets can be joined due to the plastic flow generated by the large plastic deformation during shot peening. In the experiment, a compressed-air-type shot peening machine was employed. The influences of processing conditions on the joining of the dissimilar sheets were examined. The joint strength increased with the kinetic energy of shots. It was found that the present method using shot peening process was effective in joining dissimilar sheets.

Abstract: SUS 304 austenitic stainless steel was processed by HPT at room temperature with different rotation speed. It was found that the microstructure evolution and composed phases along the progress of HPT were sensitive to the strain rate (rotation speed). During deforming with the low strain rate, the deformation-induced dynamic phase transformation (DPT) from austenite (γ) to martensite (α’) occurred and the microstructure is characterized by elongated submicron α’ grains after 10 revolutions. While the euqiaxed nanocrystalline α’ grains were produced after HPT at the continuously alternative low and high strain rate. XRD analyses showed that multiple DPT of γ→α’→γ→α’ took place during HPT at the continuously alternative low and high rotation speed. Based on the experimental results, it was proposed that the euqiaxed ultrafine grained structure were produced by multiple DPT under the high strain and strain gradient.

Abstract: A lining process for carbon steel using shot peening was investigated. In the shot peening experiment, the dissimilar foil set on the carbon steel substrate is pelted with many shots at a high velocity. The foil is bonded to the surface of the substrate due to plastic deformation induced by the collision of the shots. In the experiment, an air-type shot peening machine with an electrical heater was employed. The substrates are commercially carbon steel S45C, and the foils are commercially pure aluminum, pure copper, and pure nickel. The effects of shot conditions and the heating temperature on the joinability were examined. To improve surface characteristics such as wear resistance and corrosion resistance, the surface alloying of the lined workpiece was also attempted. The metal foils were successfully joined to the surface of the substrate. It was found that surface properties of carbon steel could be improved by the shot lining process.

Abstract: Iron aluminides exhibit good resistance to high-temperature oxidizing and sulphidizing environments and have potential for structural applications at high temperatures under corrosive environments. In this study, an Fe-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Fe and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Fe/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Fe/Al sheet. Accumulated foils were rolled and bonded at room temperature or 573 K. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). Vickers microhardness testing was used for hardness determination. A homogeneous intermetallic compound of Fe3Al or FeAl could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 3.6 ks at 1173 K.

Abstract: Superfine and nano-sized Fe powders were prepared by a spark plasma discharge process in deionized water. The powders were characterized by Field Emission Scanning Electron Microscope (FESEM) with Oxford Inca EDX, and X-ray diffraction (XRD). The experimental results indicate that the powders prepared by the process have a bimodal size distribution, high purity, single phase, good spherical shape and high yield.

Abstract: By using self-made vibrating wavelike sloping plate setup, semisolid billets with fine spherical or rosette grains have be prepared by semi-continuous casting, and the solidified shell on the sloping plate surface can be effectively avoided. Burst nucleation in the whole melt and dendrite fracture causes the formation of fine spherical microstructures. Under the current experimental conditions, proper casting temperature ranges of 660°C~680°C and the amplitude value of under 2mm proper are suggested. When the reheating temperature is 575°C and the holding time is 60min for AZ91D alloy, 597°C and 90min for Al-6Si-2Mg (wt-%) alloy, semisolid forging process can be successfully implemented. Thixo-forming products of two alloys are fine with smooth appearance, good microstructures and properties.