High temperature sliding wear behavior and mechanisms of cold-sprayed Ti and Ti-TiC composite coatings

Ti and Ti-based alloys are used in many aerospace and automotive components due to their high strength-toweight ratio and corrosion resistance. However, room and elevated temperature wear resistance remain an issue, thus requiring some form of secondary hard phase, e.g., refractory carbides, as well as solid lubrication to mitigate wear. In this study, cold spray Ti-xTiC (x = 14, 24 and 35 vol%) composite coatings were deposited on mild steel substrates with comparisons made to a baseline cold-sprayed Ti coating. The dry sliding friction and wear behavior were studied from 25 degrees C to 575 degrees C and during thermal cycling in this temperature range. While the room temperature friction coefficient of all the coatings remained relatively constant at -0.5, the wear rate continually decreased from -1 x 10-3 to -2 x 10-5 mm3/N center dot m with increasing TiC loading. Raman spectroscopy measurements determined that the same TiO2 tribochemical phases (rutile and anatase) were present on the room temperature sliding wear surfaces, thus responsible for similar friction coefficients. With increasing sliding temperatures to 575 degrees C, the Ti-35%TiC composite coating exhibited the best overall tribological behavior, i.e., the friction coefficient decreased to -0.3 along with a negative wear rate of -6.6 x 10-5 mm3/N center dot m (material gain on the wear track was recorded due to oxidation and transfer from the counterface). These friction and wear reductions were determined to be due to the formation of stable, low interfacial shear strength oxide glaze layers on the wear surfaces, composed of TiO2, WO3, and CoWO4 (transfer from WC-Co counterface). In addition, selfadaptive friction behavior was observed during thermal cycling as a result of the microstructural and tribochemical differences in the tribolayers.

Automated summary

Ti and Ti-based alloys are commonly used in aerospace and automotive components, but face challenges in wear resistance at elevated temperatures. The study found that Ti-xTiC composite coatings exhibit improved friction and wear performance compared to baseline Ti coatings, with Ti-35%TiC showing the best overall performance at 575 degrees C. The tribological behavior was attributed to the formation of stable oxide layers on the wear surfaces containing TiO2, WO3, and CoWO4.