6 - Metal-reinforced alumina

Abstract

Alumina (Al2O3) ceramics have today become a multibillion dollar global industry which has changed the world in the last few decades. Alumina uniquely combines low cost with extreme hardness, extreme electrical resistivity, extreme corrosion resistance, and high refractoriness, and it is the most biocompatible material in current clinical use. Of the 1.3 million hip replacements implanted annually in the global $7 Billion hip replacement industry, 55% now use alumina or zirconia-toughened alumina (ZTA) bearings. A decade ago, alumina or ZTA bearings were rare and still considered experimental. This meteoric rise has led to strong interest in ceramic hip resurfacing and a ceramic knee, a field currently solely serviced by metal bearings. This is not possible with alumina, and is right at the limit of what is possible with ZTA. A quantum leap in toughness could bring alumina ceramic hip resurfacing and an alumina ceramic knee to the mass market. As discussed in Chapter 2, metal microfiber reinforcement can provide this quantum leap in toughness as it can produce up a 600-fold toughness enhancement, and commonly 100-fold or more (two orders of magnitude) increase in work of fracture over the parent ceramic. Zirconia toughening of alumina can only give a threefold work of fracture enhancement of alumina. Alumina is the number one wear-resistant ceramic used in wear-resistant linings in the global $500 Billion mining industry. For high impact applications, such as jaw crushers and heavy-duty ore-chute liners, the tough cermet tungsten carbide (Chapter 8) is the material of choice, but it is more than four times more expensive than alumina. Metal microfiber-reinforced alumina could potentially compete with tungsten carbide in this role. However metal fiber-reinforced SiC composite technology developed by author Ruys, and discussed in Chapter 4, is a much lower cost high-impact wear-resistant ceramic technology, much better suited to competing with tungsten carbide. This chapter outlines the background to alumina bearings in orthopedics and alumina in the mining industry. This is followed by a comprehensive literature review of alumina ceramic matrix composites. The chapter then concludes with an overview of research done by the authors on metal microfiber-reinforced alumina as a biomaterial, and a synopsis of the proposed manufacturing process for such a material.