HIGH SPEED HIGH PRESSURE TORSION EFFECTS ON A DIFFICULT DEFORMABLE SHAPE MEMORY ALLOY

High pressure torsion (HPT) is a severe plastic deformation process, able to reduce grain size, down to nanostructure or amorphous level, in bulk materials. In the experiments a modified high speed HPT (HS-HPT) technique was used. It was ideally suited for products about 50 mm in diameter, contributing to a meaningful increase of mechanical properties. This type of severe plastic deformation generates large plastic deformation in entire volume of sample under the effect of high pressure cumulated with high rotation. On the strength of friction and pressure the sample was heated, took place grain fragmentation up to (ultra) fine grains, nanocrystalline or amorphous areas, without recrystallization. The effect of severe plastic deformation via High Pressure Torsion (HPT) on microstructure of the Cu-Al-Ni shape memory alloys was investigated by optical (OM). The reversible martensitic transformation temperatures were investigated using differential scanning calorimetry (DSC) as effect of microstructure refinement appropriate to different deformation degrees. The hardness tests demonstrate that creating ultrafine grain with high strength can produce reliable lightweight metallic parts. The presence of monoclinic and orthorhombic martensite, together with nanocrystalline areas were confirmed by X-ray diffraction (XRD).