Thermal spray wear resistant coatings include a variety of ceramic. Great material choices in a number of applications. No doubt. Just not under these circumstances, and here’s why.
Ceramic is brittle by nature. Depending on wear mechanism, it (they) can chip, crack, even form fine powders, at or below the surface. Unlike metals or plastics under high contact stress, ceramics cannot undergo plastic deformation. Not in any measurable sense. As a result, ceramic coatings fracture under stress.
Unfortunately, even under extreme temperatures, ductility remains insignificant. The brittle condition remains largely unchanged. Not only are ceramic coatings vulnerable to higher stress, but in circumstances where there is a tensile component, too. This makes them poor candidates for abrasive wear. Being without a low elastic modulus, you see.
But mechanical wear is just one issue for ceramic coatings. Whether thermal spraying, plasma spray, hvof, many are susceptible to thermal shock fracture. This is because their heat transfer is so poor.
Imagine large heat gradients forming local “hot spots.” There, large tensile stresses or cracking can develop. This, alone, can lead to fracture. And frictional heat relating to sliding motion is no exception.
Erosive wear can also become an issue. Based on ceramics sensitivity to strain, their wear rate to erosion or material removal can be most vulnerable when impingement angles near ninety degrees. As compared with metals, which fair equally poor, when impingement angles are much lower.
To maximize wear performance from your ceramic coating, be sure the eroding medium is softer. If the eroding medium is harder, the erosion rate can be minimized. Just create as much fracture toughness as possible. And be sure to request reduced porosity, smaller grain size, too. Under those circumstances, ceramic based thermal spray wear resistant coatings are best.