Effects of repeated cycling cryogenic treatment on the microstructure and mechanical properties of hydrogenated diamond-like coatings

摘要

Hydrogenated diamond-like coatings with an sp3C fraction of 63% were deposited onto E35 high-speed tool steel substrates and subjected to a repeated deep cryogenic treatment (DCT) for six hours at different temperatures. The morphologies and microstructures of the specimens were characterized using scanning electron microscopy and transmission electron microscopy. The hybridization of carbon atoms was analyzed via X-ray photoelectron spectroscopy and micro-Raman spectroscopy. The mechanical characteristics of the coatings, including the adhesion critical load between the coatings and substrates, residual stress in the coatings, hardness, and friction, were characterized. Variations were observed in the height of the cauliflower-like aggregates formed in the coatings subjected to different treatments. The sp3C fraction and hardness of the coatings increased after DCT at -140 degrees C, and the enhancement efficiency decreased with increasing number of DCT cycles. The friction co-efficients of the coatings cryogenically treated at -140 degrees C decreased, whereas those of the coatings cryogenically treated at -190 degrees C increased. The wear volumes of the DCT coatings, except the coating that was treated continuously at -190 degrees C for 6 h, upon dry-sliding against alumina were larger than that of the as-deposited coating.