Car manufacturers are constantly working to improve their engines. As a result, the demands on the materials used are also growing. With exhaust gas temperatures in new engine generations rising in part to over 1,000 degrees Celsius, increasing use is being made of parts manufactured from nickel alloys from ThyssenKrupp VDM. “Turbochargers in particular are a promising growth market for us,” says Holger Lüking, head of the company’s Automotive Sales department. ThyssenKrupp VDM already supplies several high-temperature materials for this area which are finding increasing use in so-called downsized (small-displacement, high-output) engines. The Werdohl/Germany-based company has now developed a high-tech solution for turbocharger gaskets. The enhanced high-temperature properties of Nicrofer 5120 CoTi, in particular its creep resistance, increase the durability and reliability of these highly stressed engine parts.
Turbochargers are used in cars to reconcile the objectives of performance and eco-friendliness, as they boost engine output without increasing fuel consumption. Downsizing, i.e. reducing engine displacement while maintaining performance, causes exhaust gas temperatures to rise to over 1,000 degrees Celsius. “Standard high-temperature stainless steels can no longer meet these requirements. High-alloy austenitic steels and nickel alloys from ThyssenKrupp VDM can be used at temperatures from 550 to around 1,200 degrees Celsius,” explains Lüking. Superalloys from ThyssenKrupp VDM are used in up to seven different parts of the complex turbocharger system. The key is to find the material that exactly meets all the specific requirements and optimizes the cost-performance ratio.
There’s no such thing as a standard turbocharger. Every car model requires an individual solution. “That’s why we always approach our customers directly and jointly develop a tailor-made solution,” explains Frank Scheide, Account Manager Automotive at ThyssenKrupp VDM. The company’s product range includes 15 different high-temperature materials in coil and wire form. For the new turbochargers, the greatest demand is currently for the age-hardening material Nicrofer 5120 CoTi, Alloy C263, as well as the solid-solution and carbide-hardening material Nicrofer 6025 HT, Alloy 602CA. Nicrofer 6025 HT is used, for example, in the Porsche VTG where it demonstrates its outstanding properties at very high temperatures in gasoline engines.
“The hotter gasoline engines in particular still have potential that can be tapped using ThyssenKrupp VDM’s high-performance materials,” says Lüking. High gasoline prices and stricter exhaust regulations are increasingly forcing car manufacturers to produce smaller engines, which are made more powerful by turbochargers, for example. In this way, small four-cylinder engines can deliver the output and torque of large six-cylinder models. The future will be more efficient, but also hotter.
ThyssenKrupp VDM’s own research and development department ensures customers always have access to the very latest materials findings. Its work involves developing new alloys as well as developing new applications for established materials. Within the ThyssenKrupp Group, ThyssenKrupp VDM can also call on the materials experts in the titanium and stainless steel units. The individual components of an engine have to be fine tuned to the effects of the extremely high temperatures.
One currently successful result of R&D work at ThyssenKrupp VDM is a tailored high-tech solution for the manufacture of turbocharger gaskets. The material Nicrofer 5120 CoTi has been adapted to automotive applications and will shortly also be available in coil form. The special feature of Nicrofer 5120 CoTi is its strong yet flexible molecular structure. To achieve this, the material is hardened in a furnace over a period of 16 hours at different pre-defined temperatures. “In the process, so-called intermetallic phases are integrated into the matrix and prevent sliding of the planes, giving the alloy greater strength and at the same time elasticity,” says Scheide
Gasket systems for turbochargers are increasingly being manufactured from age-hardenable materials. The established Nicrofer 5219 Nb (Alloy 718) is already the standard gasket material for highly stressed applications. But as exhaust gas temperatures rise, even this material is reaching its limits. ThyssenKrupp VDM offers Nicrofer 5120 CoTi as an additional option. It guarantees improved durability and reliability under the critical conditions of a direct turbocharger connection. Its qualities are further enhanced by a special gasket shape. “For example, our customers are processing Nicrofer 5120 CoTi into so-called C-gaskets. These are static sealing elements for machines and equipment with high requirements which demonstrate significantly greater elasticity at high temperatures than other metallic gaskets,” says Frank Scheide. “The gasket production process has become more complex. We have a suitable solution for these more demanding requirements, as proven by initial tests with established engine manufacturers.”