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MATERIALS TECHNOLOGY


Materials innovation cuts cobalt dependency


Wear resistant sintered material reduces the need for cobalt in vehicle powertrain applications Tenneco’s research started from two existing


availability and price volatility of cobalt. High- temperature, wear resistant applications that presently rely on cobalt – such as heavy-duty turbocharger wastegate bushings, EGR valves and high-performance engine valve seats – will benefit from the new material. Trials using an alternative sintered steel formulation have shown that the cobalt content of Tenneco’s sintered materials can be significantly reduced without compromising wear resistance. “Potential material shortages and controversy


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around cobalt mining, coupled with extreme price volatility, mean we must reduce our dependence on cobalt,” says Gian Maria Olivetti, vice-president global engineering at Tenneco Powertrain. “While it remains the most effective material to combat wear in dry running valve seat applications and other components subjected to big temperature ranges, we have used our experience in powder metallurgy to develop a low-cobalt sintered formulation alternative that delivers similar wear properties to the best current materials.” It is the huge variations in temperatures from


below 0°C up to 1,000°C which bushings in EGR valves, turbocharger wastegate systems or exhaust- gas valves must cope with that makes the tribology challenging, as Jens Wellmann, Tenneco Powertrain product manager for turbocharger components, explains. “Especially in the lower temperature range up to about 400°C, high-cobalt materials can outperform the typical non-cobalt materials. The first question we had to answer was: ‘What is the explanation for high-cobalt material’s low wear rates?’. And the second question was: ‘How much cobalt is effectively needed to produce that effect?’.”


20 /// Testing & Test Houses /// April 2020


❱❱ Turbocharger wastegate shaft bushings and EGR valves will benefit from new materials with reduced content of cobalt, top; micro structure (x500) of Tenneco’s newly developed sintered steel material FM-t88A with 17 per cent cobalt content


n innovative material from Tenneco’s Powertrain division is achieving wear- resistant performance with greatly reduced cobalt content, helping engine manufacturers mitigate the limited


sintered products: FM-8100, an iron-based cobalt- free sintered material, and FM-T95A, a cobalt-based (54 per cent Co by weight) sintered material comparable to the cast materials used for tribological applications. Between these two extremes, five materials with varied cobalt content were evaluated for wear performance across a range of temperatures. Investigation of the worn specimen showed that


the cobalt-containing Tenneco sintered materials formed a wear-reducing tribolayer at lower temperatures than the cobalt-free one, which answered the first question. Comparing the samples, the same effect was


examined on 17-35 per cent Co materials, which answered question two. From these results, a new material was developed – FM-T88A – a sintered steel with 17 per cent Co. This met production and quality requirements, including manufacturability and mixing of the metal powder, the sintering process, machinability and quality assurance. With the help of a vehicle manufacturer, the wear


resistance of FM-T88A was tested against series production materials in a simulated installation and loading test of a turbocharger wastegate bushing running at temperatures up to 800°C. “The results showed that at 200°C, FM-T88A


displays a significantly reduced depth of wear compared to a cobalt-free material and is at a comparable level of wear resistance to the high- cobalt material,” says Wellmann. At all other temperatures the new material’s performance closely mirrored the high-cobalt materials. According to Olivetti, 50 per cent of the cobalt


mined globally is used in batteries for EVs, and demand is growing year-on-year. By minimising the amount of cobalt used in wear-resistant, high- temperature sintered materials, Tenneco believes it can help its customers mitigate the limited availability and price volatility of cobalt. T&TH


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