Gradation Extrusion - Integration of Severe Plastic Deformation into Impact Extrusion Process

Conventional Severe Plastic Deformation (SPD) processes, such as equal channel angular pressing (ECAP) and high pressure torsion (HPT), have been used for mechanical improvement of commercially pure titanium. These techniques usually impose a relatively homogeneous deformation to the whole material volume. In this way, the mechanical properties generated due to the grain refinement from the process are uniformly distributed throughout the workpiece. A new technique, known as Gradation Extrusion, has been developed with the objective to produce a deformation gradient in the workpiece through a process that combines SPD forming and impact extrusion. This method allows to create a fine-grained structure near the surface and an increasing grain size in radial direction of the extruded bar. This microstructure distribution influences the material properties, providing to the material a high mechanical strength near the surface and a relatively good ductility due to the less refined core. These properties are interesting for several applications, such as dental implant or bolt manufacturing. A high level of mechanical strength is obtained, while a sufficient level of ductility is maintained which is needed to form the inner shape of the product. This work aims to evaluate the main advantages of the proposed method to possible industrial applications. Numerical simulations, experimental tests, microstructure analysis and microhardness tests were developed to assist the investigation.