Papers by Author: Minoru Furukawa

Abstract: High purity aluminum (Al) and copper (Cu) single crystals of different crystallographic orientations were processed for one pass by equal-channel angular pressing (ECAP). The deformed structures were examined using orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). This paper examines the experimental results in terms of the values of the shear factors based on simple shear theory.

Abstract: This paper describes experiments in which high purity aluminum (Al) and copper (Cu) single crystals of different crystallographic orientations were processed for one pass by equal-channel angular pressing (ECAP). The deformed structures were examined using optical microscopy (OM), orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The results for Al single crystals are compared with those for Cu single crystals.

Abstract: Experiments were conducted to evaluate the mechanical properties of a spray-cast Al- 7034 alloy processed by severe plastic deformation. The alloy was received with an average grain size of ~2.1 μm and processed by equal-channel angular pressing (ECAP) at a temperature of 473 K to give a grain size of ~0.3 μm after 6 or 8 passes. Following ECAP, the mechanical properties were evaluated at room temperature (298 K) and at an elevated temperature of 673 K. In tensile testing at ambient temperature, the stress-strain curves show very short regions of strain hardening after ECAP and low values for the ultimate tensile strength by comparison with the unpressed alloy. This lack of strength is due to the high pressures imposed by ECAP and the consequent fragmentation and dissolution of the rod-like MgZn2 precipitates. It is shown that the strength may be restored by performing an appropriate ageing treatment after ECAP. Superplastic ductilities were recorded at a temperature of 673 K with tensile elongations exceeding 1000%. Careful inspection of the polished surfaces of samples pulled to fracture in the superplastic condition revealed the occurrence of extensive internal cavitation. Quantitative measurements showed the development of these internal cavities is consistent with conventional superplastic alloys.

Abstract: The precipitation and evolution of microstructure in a spray-cast Al-7034 alloy and a commercial wrought Al-2024 alloy were studied after equal-channel angular pressing (ECAP) using transmission electron microscopy and differential scanning calorimetry (DSC). Microstructural examination showed the grain sizes of both alloys were reduced to the range of ~0.3–0.5 μm through ECAP. The DSC analysis identified the occurrence of thermal effects involving the formation, coarsening, dissolution and melting of the precipitate phases and concurrent recrystallization. The heating and ageing response of the alloys processed by ECAP was identified by micro-hardness testing of the samples after interrupted heating and ageing treatments.

Abstract: This paper describes experiments in which high purity copper single crystals of two different orientations were processed for one pass by equal-channel angular pressing (ECAP) and the deformed structures were examined using optical microscopy (OM), orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The first single crystal (0° specimen) was oriented within the entrance channel of the die so that the {111} slip plane and the <110> slip direction were parallel to the theoretical shear plane and shear direction, respectively. The second crystal (20° specimen) was oriented with the {111} slip plane and the <110> slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and shear direction, respectively. For the 0° specimen, after passing through the shear plane there were two crystallographic orientations representing the initial orientation and an orientation rotated by 60° in a counter-clockwise sense from the initial orientation. For the 20° specimen, there was an orientation rotated by 20° in a counter-clockwise sense from the initial orientation after passing through the shear plane.

Abstract: It is now recognized that processing by equal-channel angular pressing (ECAP) leads to very significant grain refinement in polycrystalline materials with the as-pressed grains typically having sizes within the submicrometer range. Furthermore, the materials produced by ECAP exhibit many useful properties including a high strength at ambient temperatures and, if these ultrafine grains are retained to elevated temperatures, a potential for superplastic forming. This paper examines the fundamental characteristics of grain refinement by making use of two sets of experimental observations: experimental data obtained from the pressing of aluminum single crystals through one pass of ECAP and hardness measurements taken on polycrystalline aluminum for samples subjected to ECAP for up to a total of eight passes. These experimental results are used to develop a microstructural model that provides a satisfactory explanation for the grain refinement occurring in ECAP.

Abstract: The conventional materials used in superplastic forming operations generally have grain sizes of ~2 µm or larger and they exhibit superplasticity at relatively low strain rates. Processing by equal-channel angular pressing (ECAP) produces materials having ultrafine-grain sizes, usually in the submicrometer range. If these ultrafine grains show reasonable stability at elevated temperatures, the alloys may exhibit a capability for achieving superplastic elongations at high strain rates. This paper examines the development of ultrafine-grained structures and superplastic ductilities in a spray-cast aluminum 7034 alloys through ECAP. The results show that ECAP is a very effective procedure for achieving grain refinement and superplasticity at rapid strain rates.