By James Walsh, MMTA
The search for new hard materials is often challenging, but the vast application potential is a strong incentive to continue this pursuit. One recent success lies with scientists in a lab at Rice University in the US where a super-hard metal has been made, by melting together titanium and gold. The alloy, beta-Ti3Au, is the hardest known metallic substance compatible with living tissues and has potential for making longer-lasting medical implants, a trait it claims from the spontaneous build-up of an inert and stable oxide layer.
Current knee and hip implants have to be replaced after about 10 years due to wear and tear. Evidence from wear experiments reveal that this enhanced hardness is associated with a low coefficient of friction (COF). The other beneficial economic factor comes with the ability of this compound to adhere to ceramic parts which can reduce the weight and cost of medical components.
Preparation of the compound is an important aspect of the superior properties, and temperature can make a big difference. Making the beta-Ti3Au alloy, which is three parts titanium and one part gold, at high temperatures produces an almost pure crystalline form of the alloy, and it is this crystal structure that is four times harder than titanium. At lower temperatures, the atoms arrange in another cubic structure, called the alpha structure, which is about as hard as regular titanium.
Titanium is known to be the most bio-compatible metal due to its resistance to corrosion from bodily tissues and fluids, its bio-inertness, high fatigue limit and capacity for osseointegration, which refers to the direct structural and functional connection between living bone and the implant.
This new alloy may also have applications in the drilling and the sporting goods industries, among many other potential fields. The challenge now, is to bring this material to market and identify how viable it will be for new manufacturing techniques such as 3D printing.
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