Dr Steven Matthews is a senior lecturer in the School of Engineering and Advanced Technology at Massey University in Auckland. In this video, he first explains some of the history of thermal plasma spraying and then describes numerous applications of this coating process. For example, in the aero industry, a large number of jet engine components are plasma sprayed with a ceramic material to serve as a thermal barrier coating.
The plasma spray technique in terms of its use for thermal spraying and coatings was really developed in the mid 1960s, and it underwent huge expansion and development in the 1970s and 80s, mainly to meet the demand of the aero industry. There’s a huge number of components in jet aircraft engines and gas turbine engines that needed very specific coatings to be able to operate under the harsh conditions that they’re exposed to. Aero engines and aerospace applications is still one of the greatest applications of plasma spray technology.
And one of the key areas in there is the application of what are called thermal barrier coatings, and a thermal barrier coating is actually a coating system. It consists of two layers – the top layer is a ceramic coating and that provides insulation, and the layer below that is a bonding layer.
Now by using these thermal barrier-coating systems in addition to internal cooling of the substrates as well, they’re able to reduce the temperature that the metal substrate sees by several hundred degrees Celsius, and this is hugely advantageous for aero engines, because to increase their thermal efficiency, they need to operate at as higher temperatures as they possibly can.
Other applications of thermal spray, they are used – or plasma sprays specifically – they’re used in the medical industry to apply both titanium and hydroxyapatite coatings.
They’re used in two main areas – one is for things like teeth implants or jaw repairs and also for typical hip replacement, knee replacements, things like this.
In terms of future power technologies, plasma spraying is being used to produce what are called the solid oxide fuel cells. So fuel cells are one of the key areas of power generation in the future, and they need very specific materials and very specific microstructures.
It’s also being used in instances where people are developing new engines for cars, and they’re looking at changing from cast-iron cylinder blocks to aluminium-alloy cylinder blocks because they’re a lot lower in weight, so you get a lot better fuel efficiency. But the problem is that the aluminium material is not very wear resistant, and so what they are doing is they’ve developed a plasma gun that can actually rotate.
So they make the engine block and they have this rotating plasma gun that they put down inside the cylinder and it sprays a coating on the inside of the cylinder. So that means they can make the engine block out of an aluminium alloy, spray the inside of it with a very wear-resistant material and then finish that, and you’ve got all the benefits from the lightweight aluminium but they’ve got this very hard and wear-resistant coating on the inside of the engine.
Dr Steven Matthews, School of Engineering and Advanced Technology, Massey University, Auckland
Holster Engineering Ltd, Tokoroa
Aircraft engine animation courtesy of Moulay Youssef Bouhouch
Mitchell Dorfman, Sulzer Metco (USA) Ltd
Still of titanium dental rod, courtesy DRosenbach, Creative Commons Licence 3.0
Still of titanium hip implant, Douglas Fraser, courtesy of Thayer School of Engineering at
Hip implant X-ray, courtesy of National Institutes of Health, part of the United States Department of Health and Human Services
Car with bonnet up, courtesy of Aiden O’Sullivan Creative Commons Licence 2.0
Still of aluminium cylinder block with magnesium, courtesy 160SX Creative Commons Licence 3.0
Still of BMW 6-cylinder block, courtesy Beemwei Creative Commons Licence 3.0