Fretting of Aluminum Oxide, Hydroxyapatite and Carbon Nanotubes Reinforced Ultra High Molecular Weight Polyethylene (Pages 22-34)

Chinmayee Nayak, S. Ariharan, Priya Kushram and Kantesh Balani

Department of Materials Science and Engineering, Indian Institute of Technology-Kanpur, Kanpur-208016, India

Abstract: Wear of Ultra High Molecular Weight Polyethylene (UHMWPE) is the foremost ground of revision Total Hip Joint Replacement (THR) surgery. In the present work, the combination of Alumina (Al2O3), Hydroxyapatite (HAp), and Carbon nanotube (CNT) is reinforced in compression molded UHMWPE (U) to assess the mechanical and the tribological properties. The average hardness of all the composites is observed to be up to 80% higher than the UHMWPE (88.4 MPa), and UHMWPE-20 wt.% Al2O3 (UA) is found to be the hardest with hardness of ~162.4 MPa because of the relatively good bonding between Al2O3 and UHMWPE. The uniqueness of this work resides in, investigating the fretting wear behavior of Al2O3, HAp, and CNT reinforced nanocomposites and understanding the effect of various quantities of reinforcements in UHMWPE matrix in terms of reinforcement factor (Rf) and debonding factor (Df). The coefficient of friction (CoF) and frictional force during fretting wear test were noted as ~0.23 and ~1.9 N, respectively for UHMWPE. UA showed lowest CoF (~0.17) and frictional force (~1.5 N) among all the samples. The abrasive wear, cyclic fretting, crack, and delamination mechanisms are evident in electron micrographs of the fretting wear scars of as-processed nanocomposites, which can be attributed to wear volume loss. The wear rate of the nanocomposites is 0.4×10-5 mm3/Nm, which is 20% lower than the raw UHMWPE (0.5×10-5 mm3/Nm). Hertzian contact pressure values of all the nanocomposites are higher (up to 26%) than UHMWPE (80.1 MPa) and in spite of having highest Hertzian contact pressure (101.3 MPa), UA showed 20% lesser wear rate than U, suggesting the relatively strong interfacial characteristics of Al2O3 in UHMWPE. The lower reinforcement factor values rendered higher debonding factor, and the samples UA showed lowest debonding factor. The results indicate that the bonding between reinforcements and matrix can strengthen the UHMWPE and the combined properties such as hardness, and lubricity of Al2O3, HAp, and CNT in UHMWPE matrix can substantially improve its mechanical and tribological properties.

Keywords: Ultra high molecular weight polyethylene, Al2O3, Hydroxyapatite (HAp), Carbon nanotube (CNT), fretting, Hertzian contact.