Tribology and corrosion characteristics of carbon nanotube and polyetheretherketone/ carbon nanotube-coated porous titanium-tantalum shape memory alloys for biomedical applications

Abstract

An intensive development of medical technologies and surgical procedures led to placed new and more stringent requirements on the biomaterials used. Among these materials are shape-memory alloys (SMAs) like Ti-Ta. Despite the excellent biocompatibility of Ti-Ta SMAs, certain issues like corrosion behaviour and poor tribological properties limit their widespread applications as biomedical implants which need to be resolved. Thus, this research aimed to investigate microstructures, corrosion, and tribological properties effect of coating materials on porous Ti-Ta SMA through electrophoretic deposition method (EPD). Based on this fact, some multi-walled carbon nanotubes (MWCNT) and polyetheretherketone, PEEK/MWCNT-coated porous Ti-30 at.%Ta SMAs were fabricated. These SMAs were prepared using mechanical alloying followed by microwave sintering. Electrophoretic deposition (EPD) at various applied voltages were performed to coat these SMAs using CNT (at concentration of 3 mg/mL) and MWCNT/+ PEEK (at ratio of 3 mg/mL of CNT to 3, 4.5, 6, and 7.5 mg/mL of PEEK). The microstructures of both uncoated and coated SMAs were characterized using scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX), and X-ray diffractometry (XRD). The pull-off test was used to determine the adhesion of the coating, and water contact angles were measured to evaluate the surface wettability, the roughness and micro-hardness of the surfaces were also evaluated. Potentiodynamic polarization and immersion tests (in Kokubo simulated body fluid) were performed to determine the corrosion behavior of the uncoated and coated SMAs. A linear reciprocating wear test (ball on flat) was conducted to record the tribology behavior of the uncoated and coated SMAs. The EDX and XRD results showed the successful formation of MWCNT and MWCNT/PEEK coating on the surface of Ti-30 at.% Ta SMAs. The adhesion strength of the MWCNT layer (highest value of 7.27 MPa at 40 V) was weaker than that of the MWCNT/PEEK layer (maximum 31.29 MPa for 6P85V). The wettability of MWCNT coated surface was less than both MWCNT/PEEK coated and uncoated ones. The hardness of MWCNT/PEEK-coated samples was decreased with the increase of EPD voltages and PEEK contents. The best corrosion resistance for the MWCNT-coated samples was achieved at 40 V and for MWCNT/PEEK-coated specimens the best value was observed at higher voltage and PEEK concentration. The wear resistance of the coated samples was increased with the increase of EPD voltages and PEEK concentration, wherein the highest value was obtained for the specimen prepared at 85 V with 6 mg PEEK. Therefore, the present fabrication of SMAs, coating and comprehensive performance evaluation of the MWCNT/+PEEK-coated SMAs may constitute a basis for the development of potential biomaterials with enhanced biocompatibility desired for hard tissue engineering and implantations.