Effect of yttria-stabilized zirconia content on morphology, mechanical properties and in-vitro bioactivity behaviour of powder metallurgy stainless steel 316L

Abstract

Among the metallic materials, stainless steel 316L (SS316L) is widely used in hip and knee replacement surgery due to its cost-effectiveness, good mechanical properties, and biocompatibility. However, the stress shielding phenomenon provokes bone resorption and consequent adverse effects on prosthesis fixation because of its high Young's modulus. Furthermore, the weak mechanical bond with the bone tissue due to its biological inertness delays the healing process. By incorporating various yttria-stabilized zirconia (YSZ) contents (i.e. 2, 3, and 4 wt.%), SS316L/YSZ composite was fabricated using the powder metallurgy method. Powder blends consisting of SS316L and YSZ were milled at a speed of 200 rpm for 2 h using 10 mm in diameter hardened steel balls with a ball-to-powder ratio (BPR) of 10:1. All composites were compacted at 200 MPa and sintered at 800 °C for 2 h. Morphological observations, mechanical characterizations and bioactivity tests were performed to evaluate the feasibility of the SS316L/YSZ composite as an implanted biomaterial. Results indicated that all YSZ contents presented Young's modulus of the composite ranging between 33.91 and 21.71 GPa, overcoming the problem of stress shielding. The compressive strength of SS316L/YSZ composite decreased remarkably from 208.92 to 5.43 MPa with increasing YSZ content. In-vitro biological evaluation tests confirmed that with increasing YSZ content, the rate of apatite deposition on the SS316L/YSZ composite's surface had an increasing trend after four days of immersion in Hank's Balanced Salt Solution (HBSS). Based on the results, the powder metallurgy-fabricated SS316L/2YSZ composites have the desired mechanical properties and good osteointegration, making them feasible materials for orthopedic implant applications.