A B S T R A C TApplication of severe plastic deformation (SPD) technology to process effective biomedical titanium alloys has shown promising results at laboratory scale. However, more research is still required before adopting this technology from laboratory scale to industrial scale production. This review presents performance and prospects of SPD for effective ultra-fine/nanograin structure-biomedical titanium alloys. Effective biomedical titanium alloys should have desired properties for the medical application. The properties include; high static and fatigue strengths, surface hardness for wear resistance, good ductility, corrosion resistance and biocompatibility. Based on current works reported in the literature, the review focused on; high-pressure torsion (HPT), equal channel angular pressing (ECAP), asymmetric rolling (AR), accumulative roll bonding (ARB) and repetitive corrugation and straightening (RCS). Overview of biomedical application of titanium alloys and desired material properties is presented. A detail discussion on the working principle, performance (e.g. induced strength, hardness, grain size and texture etc.) and material deformation homogeneity of each SPD method are presented. Also, prospects and challenges of each SPD method to be implemented at industrial scale for continuous and mass production are highlighted. The review concludes with the effectiveness of SPD processes, characteristics of processed samples and suggestion of future work for SPD to process effective biomedical titanium alloys at industrial scale.
This paper presents a numerical investigation on strain properties of Ti6Al4V alloy processed by constrained bending and straightening (CBS) severe plastic deformation (SPD) technique. CBS is a new SPD method that has been proposed to enhance continuous processing of metal sheets and improve magnitude and homogeneity of induced properties such as strain. The model considers a rectangular sheet of Ti6Al4V alloy processed with CBS at 2, 4 passes denoted as N2, N4 each combined with 10, 5, 3 mm feed length denoted as F10, F5, F3 respectively. ABAQUS Standard FEA Software was used to simulate and investigate the magnitude and homogeneity of equivalent plastic (EP) strain induced in material. Results show that for all feeds, magnitude values of EP strain at N4 passes were higher than those at N2 passes. The magnitude of EP strain increased with the number of passes. Values of both magnitude and homogeneity of EP strain were highest at F3 feed followed by those at F5 and F10 feeds respectively. The study has promised that CBS is the potential process for continuous production of metal sheets with improved EP strain magnitude and homogeneity.
Hybrid Polymeric Composites (HPC) structural materials pose a challenge of developing microcracks and delaminations under impact and dynamic loads. This paper presents the development and testing of an Intelligent Hybrid Polymeric Composite (IHPC) beam embedded with Ni-Ti Shape Memory Alloy (SMA) with crack growth retarding ability. Upon heating to austenite finish temperature (A f), Ni-Ti SMA wire contracts as a result of detwinned martensite-austenite phase transformation. The contraction of the SMA was utilized to stiffen and retard crack growth in the IHPC beam, hence resulting to an increase of mode I fracture stress intensity factor (K IC). The SMA wire specimens were aged at 250°C, then prestrained at 3% in order to stabilize austenite start (A s) and austenite finish (A f) transformation temperatures. The values of A s and A f for Ni-Ti SMA were determined. The IHPC and Polymeric Virgin (PV) notched beams were fabricated from epoxy resin. A four point bending test was performed on the beams to determine the effect of actuated Ni-Ti SMA on mode I fracture stress intensity factor K IC. The test was done at two temperatures, at T1 (below A s) and at T2 (A f). Results showed that actuation of the Ni-Ti SMA increased the value of K IC for IHPC beams at T2 by 189% over the value of K IC for PV beams at T1. Actuation of the Ni-Ti SMA increased the value of K IC for IHPC beams at T2 by 41% over the value of K IC for IHPC beams at T1. Results showed that at T1 the loaded PV and IHPC beams fractured with unsteady crack propagation, while at T2 the loaded IHPC beams fractured with steady crack propagation. An increased value of K IC and steady crack propagation at T2 indicated that the SMA improved the crack retarding ability of the HPC beam.
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