High temperature extrusion of a multicrystalline Co-Ni-Ga High-Temperature Shape Memory Alloy and its influence on the microstructure and functional propertiesTuesday (15.05.2018) 15:50 - 16:15 Part of:
Co-Ni-Ga alloys were guided by research on the Ni-Al binary system, which has been intensively studied over the last years. One commercial advantage of Co-Ni-Ga alloys lays also in the content of reasonably priced constituents. From a technical point of view, these alloys show good workability due to the presence of a ductile second phase and represent a wide range of transformation temperatures, which makes them to promising HTSMAs candidates. Furthermore, the fully pseudoelastic response of Co-Ni-Ga at temperatures up to 400 °C makes this alloy attractive for elevated temperature damping applications.
Previous studies demonstrated an excellent pseudoelastic response and cyclic stability at room temperature in single-crystalline Co-Ni-Ga alloys along the <001> orientation under compression [1-3]. Additionally, maximum theoretical transformation strain of 4.8% in compression and 8.6% in tension were predicted for <001> orientations based on energy minimization theory . As Co-Ni-Ga alloys feature strong orientation dependence for transformation strains , polycrystals suffer from deformation constrains, which can be kept at minimum when processing achieves an appropriately textured material.
Extrusion moulding is one possibility to get an appropriate textured material. However, polycrystalline Co-Ni-Ga suffers from brittleness and early fracture mainly due to intergranular contraints and can be extruded by temperatures about 900 °C. The current study presents the results from high temperature extrusion proceeding of Co-Ni-Ga with a view on the microstructural evolution and functional properties of extruded material.