Evolution of hard carbon layers on Ti-45Al-2Nb-2Mn-1B by plasma enhanced chemical vapor deposition of hydrocarbons and hydrogen

Abstract

Extension of pulsed DC plasma enhanced CVD (PECVD) of carbon from hydrocarbons resulted in thick hard carbon layers on Ti-45Al-2Nb-2Mn-1B. PECVD for less than 2 h led to the formation of surface interlayers of TiC and Ti2AlC compounds under the hard carbon layer. After 5 h until 20 h, the formation of carbons layers surpassed the growth of TiC and Ti2AlC layers and resulted in a thicker hard carbon layer. This can be explained with the deceleration of carbon diffusion into the base alloy that resulted in the accumulation of a hard structure of carbon on the outer surface. The thickness of the hard carbon layers reached up to ∼40 μm, which were revealed using SEM microcopy. The hardness on the outer surface of hard carbon layer was around 600–1500 HV0.5 (5.88–14.71 GPa). EDX analysis across the surface layers showed ∼50–100 at. % carbon on the outermost layers. Raman spectroscopy of carbon layers showed sp3 (D) and sp2 (G) peaks of carbon at ∼1330 and ∼1560 cm−1 and peaks of TiC at ∼200 cm−1 peaks.