The process of high-pressure sliding (HPS) is a method of severe plastic deformation developed recently for grain refinement of metallic materials under high pressure. The sample for HPS is used with a form of sheet or rod. In this study, an HPS facility with capacities of 500 tonnes for vertical pressing and of 500 and 300 tonnes for horizontal forward and backward pressings, respectively, was newly built and applied for grain refinement of a Mg alloy as AZ61, Al alloys such as Al-Mg-Sc, A2024 and A7075 alloys, a Ti alloy as ASTM-F1295, and a Ni-based superalloy as Inconel 718. Sheet samples with dimensions of 10 to 30 mm width, 100 mm length, and 1 mm thickness were processed at room temperature and ultrafine grains with sizes of~200 to 300 nm were successfully produced in the alloys. Tensile testing at elevated temperatures confirmed the advent of superplasticity with total elongations of more than 400 pct in all the alloys. It is demonstrated that the HPS can make all the alloys superplastic through processing at room temperature with a form of rectangular sheets.

High-pressure sliding (HPS) is a process of severe plastic deformation (SPD) for significant grain refinement and it is similar to high-pressure torsion (HPT) as both processes are operated under high pressure. Whereas the HPT process uses disk or ring samples, the HPS process is applicable to rectangular sheet samples. In this study, it is demonstrated that the HPS process is also applicable to rod samples. To achieve a homogeneous microstructure throughout the cross section of the rod, the sample is rotated along the longitudinal axis after each processing. The HPS process is carried out on pure Al, Al alloys (Al-3%Mg-0.2%Sc, A2024 and A7075) and a Mg alloy (AZ61) under a pressure in the range of 1-2 GPa. It is shown that a homogeneous microstructure is developed in all samples through rotation along the longitudinal axis by 60 degrees after each processing. The Al alloys and the Mg alloy exhibit grain sizes well less than 500 nm and superplastic elongation well more than 400% for the A2024 and A7075 alloys and well more than 1000% for the Al-3%Mg-0.2%Sc alloy and the AZ61 alloy. It is thus antgicipated that the HPS process provides good potential for scaling-up the sample size through not only sheets but also rods.

In this study, the method of high-pressure sliding (HPS) was applied for grain refinement of an A2024 alloy. Samples in a rod shape were used in this HPS process. To achieve homogeneous grain refinement throughout the cross section of the rods, the samples were rotated around the longitudinal axis of the rod every after HPS processing. Microstructural observations revealed that the grain size was refined to 140 nm. Tensile tests showed that the samples exhibited superplasticity with a maximum elongation of 480% at 623 K and 1.0 10 3 s 1 and with a strain rate sensitivity of 0.36.

Fig. 1 Schematic illustration of High Pressure Sliding (HPS). (a) Cross sectional view and (b) 3 dimensional views.