The effect of two-step heat treatment on hardness, fracture toughness, and wear of different biased diamond-like carbon coatings

A conventional furnace heat treatment critically reduces hardness and fracture toughness after a certain temperature. This study reports the effects of two-step heat treatment on hardness, fracture toughness, and wear of bias varied diamond-like carbon (DLC) coatings deposited without buffer layer on silicon substrates using unbalanced magnetron sputtering system. Pristine specimens were directly heated (1-step) at 300 °C in a tube furnace for 30 min and took out after 20 h furnace cooling. For 2-step 300 °C, pristine specimens were heated at 150 °C for 30 min and furnace cooled for 20 h and then re-heated at 300 °C followed by the same procedure. The residual stresses in pristine DLC specimens were calculated with Stoney equation. Raman spectroscopy was performed to understand atomic disorder and clustering under bias and heat treatment effects. The reciprocating wear test was performed to understand the effect of bias voltage and heat treatment on wear volume of DLC coatings. Indentation studies were performed to analyze hardness, cracking behavior, and fracture toughness of bias varied pristine to re-heated specimens. 1-step 300 °C heat treatment decreases hardness and fracture toughness up to 20% in general, whereas, the 2-step 300 °C heat treatment process generally retained pristine values along with the prominent increase of 43% hardness and 9% fracture toughness for specimens which are deposited at a bias of − 60 V and − 140 V respectively.