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

• Published in: Thin solid films 2023-06, Vol.775, p.139865, Article 139865
• Main Authors: Peng, Jihua, Qiu, Xianting, Li, Xiaoling, Zhang, Guoge
• Format: Article
• Language: English
• Subjects: Cryogenic treatments; Diamond-like coatings; Hybridization; Mechanical performance; Microstructure
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2023.139865

•Strengthening diamond-like carbon coating (DLC) by deep cryogenic treatment (DCT).•Tuning DLC surface morphology by DCT.•Inducing sp2→sp3 in DLC by DCT. 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 °C, and the enhancement efficiency decreased with increasing number of DCT cycles. The friction coefficients of the coatings cryogenically treated at –140 °C decreased, whereas those of the coatings cryogenically treated at –190 °C increased. The wear volumes of the DCT coatings, except the coating that was treated continuously at –190 °C for 6 h, upon dry-sliding against alumina were larger than that of the as-deposited coating.