High temperature sliding of TiC based hardmetal coatings against TWIP steel

Steel manufacturing often requires high temperatures (HT) posing a serious challenge to forming tools. Thermal spray coatings provide a cost-effective option for protecting such surfaces against HT, corrosive environments, and severe wear. Novel thermal sprayed coatings based on cubic hard materials such as TiC and TiCN provide an alternative to widely used Cr₃C₂-NiCr. While Cr₃C₂-NiCr coatings possess superb oxidation resistance and excellent wear resistance at HT, they are prone to degradation in the presence of Mn, commonly alloyed in many modern steels. A paradigmatic example is twining-induced plasticity steel (TWIP), a novel steel grade with outstanding properties combining high strength with ductility.

We manufactured two types of (Ti,Mo)(C,N)-29% Ni hardmetal powders by agglomeration and sintering using TiCN with varying C/N-ratio (0.7/0.3; 0.3/0.7), deposited by HVAF and compared them to Cr₃C₂-NiCr. Detailed analyses of the powders and coatings showed their chemical composition and microstructure. To investigate their HT sliding behaviour against TWIP steel, HT pin-on-disc tribotests were performed isothermally at 800 °C. TiC-based coatings showed clear benefits, with almost no wear, while the Cr₃C₂-coating showed significant wear loss. Both compositions of TiC-based powders and coatings are potential coatings for prospective forming applications of modern high Mn steels, such as TWIP.