Researchers have unintentionally created an alloy that’s four times harder than pure titanium. It could be an unexpected solution to knee and hip implants wearing out.

The alloy is beta-Ti3Au, a combination of titanium and gold. A team lead by Professor Emilia Morosan of the Rice University in Houston originally created it as an experiment in new forms of magnet.

On the face of it, adding the relatively soft metal gold to titanium doesn’t sound like a recipe for a harder material, but the researchers discovered that was the case in an unexpected way. The BBC reports that they were trying to turn the alloy into a powder to check its purity, only to find the mortar and pestle covered in diamond that they used was not up to the task. The ‘secret’ to the toughness is the way the atoms arrange themselves when the alloy is created at high temperatures.

According to the researchers, the most likely use of the new alloy would be in medical implants. Titanium is already a commonly used material because bone can grow around it, and implants from the new alloy could last considerably longer as well as being lighter and cheaper to produce. As many implants have to be replaced after around 10 years, switching to the new alloy could make it much more likely implants will last the rest of the person’s life.