Characterisation of Feed and Produced Material in Screw Extrusion of Titanium
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A novel method of extrusion of materials with high viscosity is being developed at NTNU, the method is based on screw extrusion, which is more known in the plastic industry. The process, at the end of the development cycle will hopefully reduce cost in production of titanium and its titanium alloys, as well as open doors for new titanium alloys. The work will be based on characterisation of titanium sponge and corresponding screw extruded material. With the use of metallurgical methods such as elemental analysis, hardness testing, heat treatments, light microscopy and tensile testing the titanium sponge and screw extruded material will be evaluated and modified for optimisation of the process and a better quality product. Heat treatments of titanium sponge showed a decrease in hardness and the presence of recrystallization. The effect of lowered strength in titanium sponge was tested in compression shear deformation experiments. The tests showed a correlation between lowered hardness of titanium sponge and an increased consolidation. However, the testing method needs further work and optimisation. The screw extruded profiles show a relative large increase in chemical contamination and varying deformation over the cross section of the material. The material also showed inhomogeneity along the cross section parallel to the extruding direction. A protective atmosphere during screw extrusion is needed. Further processing of profiles should probably include compression of profiles at high temperatures to ensure enhanced diffusion bonding, removal of cracks and stress relief.