Investigation of severe plastic deformation method procedure parameters for manufacturing biomedical materials with improved mechanical properties

In this thesis alpha phase pure titanium and near beta Ti13Nb13Zr was processed with Equal Angular Channel Extrusion (ECAE) and Ti13Nb13Zr was processed with Hydrostatic (HE) extrusion in order to obtain ultrafine grained biomaterials. With these two techniques efficiency were compared for Ti13Nb13Zr with its mechanical and microstructural properties. With ECAE procedure different procedure parameters such as; process velocity, temperature were used in order to understand its effect on microstructure and mechanical properties. From this point of view optimal process parameters were observed for bot pure titanium and Ti13Nb13Zr. A novel ECAE route was used that combine low and warm temperature in subsequent extrusions. After application of this combined route its effect on mechanical properties and microstructure were observed. Initial Ti13Nb13Zr were observed and beta lath were determined with 260 nm width. Initial pure titanium grain sizes were observed as 58 µm. With severe plastic deformation methods these size decreased. For pure titanium after 8 pass with ECAE the final grain size was determined as 550 nm. For Ti13Nb13Zr after HE procedure beta lath width was observed as 80 nm. After ECAE of Ti13Nb13Zr the final grained were observed to be more granular that HE processed Ti13Nb13Zr due to the rotations in the subsequent passes. The final grain size was measured as 410 nm from EBSD results. Electron back scattering diffraction (EBSD) and Transmission Electron Microscope were used for nano-scale investigation. EBSD measurements were applied in a larger area of specimen which results higher accurate measurement. Thus, grain size measurements applied with EBSD as far as possible. Moreover form XRD results grain size of ultrafine grained specimens that manufactured with ECAE procedure, obtained with Williamson-Hall Approach. With this method ultrafine grained final grain size concluded as 420 nm. Severe plastic deformation methods applied in order to improve mechanical strength and for pure titanium mechanical strength were ̴1.5 times higher than initial state. For ECAE- Ti13Nb13Zr the maximum tensile strength increased only 60 MPA which equals 1.1 times of initial state. HE- Ti13Nb13Zr ultrafine grained materials maximum mechanical strength was ̴1.41 times higher than initial state. HE- Ti13Nb13Zr ultrafine grained materials ductility value decreased to 9.032 mm from 19.56 mm. ECAE- Ti13Nb13Zr ductility decreased to 6.91mm.After ECAE of pure titanium ductility decreased as in Ti13Nb13Zr. Titanium elongation was decreased to 8.34 mm from 13.90 mm. Despite of increase in the mechanical properties wear resistant were not increased significantly. With experimental design of ECAE procedure, optimal process parameters were obtained as; 0.1 mm/sn extrusion velocity, 300 ˚C process temperature and route Bc. For this experimental design quality characteristic was selected as homogeneity of micro structure that obtained from Vickers hardness test. In order to obtain novel combined temperature routes efficient mechanical tests and microstructural observations were applied and the tensile strength were determined for 2 times pressed at 450 ˚C and 1 Pass 100 ˚C +1 Pass 450 ˚C specimens respectively 758.40 MPa and 792.34 MPa. According to the EBSD investigation the grain size of these two specimen groups measured and for 2 times pressed at 450 ˚C 1.7 µm and for 1 Pass 100 ˚C +1 Pass 450 ˚C 1.9 µm were found. The angle between grains were measured as %36 for 2 times pressed at 450 ˚C and %41 for 1 Pass 100 ˚C +1 Pass 450 ˚C. Young modulus of specimens determined as 143.19 GPa for 1 Pass 100 ˚C +1 Pass 450 ˚C and 152.57 for 2 times pressed at 450 ˚C. After analyzing all of these results it can be concluded that combine temperature route improved process efficient. In order to understand these ultra-fine grained materials behavior as biomaterials cell cultures were applied. More over surface modifications were also applied to these materials in order to understand its effect on ultrafine grained materials. After 96 hours of cell culture the cell quantity were determined as 53x102 for sand blasted ultrafine grained pure titanium and this value was 40x102 for initial state. Cell culture tests also applied to ECAE processed ultrafine grained Ti13Nb13Zr and obtained as 116x103 which was 98x103 for initial state. Surface wettability was determined as 14.02˚ for sand blasted pure titanium which shows it is a hydrophilic surface. This value was 82.56 ˚ for initial state. Ultrafine grained abutments and abutments screws were manufactured and fatigue test were applied according to ISO14801 and the micro gap between implant and abutment decreased 5.74 µm. Mechanical and surface properties for biomedical compability improved with ECAP procedure for TNZ and pure Ti G4. The novel combined temperature ECAP process route found to be more productive for pure Ti grade 4. Severe plastic deformation of TNZ compared for HE ve ECAP processes and HE process found to be more productive for TNZ as a SPD procedure. The optimal process parmeter for Pure Ti Grade 4 found to be 300 °C, 0.1 mm/s ram speed, and route Bc. In these optimisation study the quality characteristic was selected as homogenous hardness of microstructure.