Superhard nanocrystalline silicon carbide films

Abstract

Nanocrystalline silicon carbide films were deposited by thermal plasma chemical vapor deposition, with film growth rates on the order of 10 m / min. Films were deposited on molybdenum substrates, with substrate temperature ranging from 750-1250°C. The films are composed primarily of ␤-SiC nanocrystallites. Film mechanical properties were investigated by nanoindentation. As substrate temperature increased the average grain size, the crystalline fraction in the film, and the hardness all increased. For substrate temperatures above 1200°C the average grain size equaled 10-20 nm, the crystalline fraction equaled 80-85 %, and the film hardness equaled approximately 50 GPa.

Novel Processing of Unique Ceramic-Based Nuclear Materials and Fuels

“…Such nano-crystalline ceramics are the focus of intense research as they have the potential for unique properties such as "super hardness" and significantly high toughness [118][119][120][121].…”

“…Tymiak et al [124] have reported hardness value of about 37 GPa with grain sizes around 20 nm, for SiC films deposited by hypersonic plasma particle deposition. Recently, Liao et al [121] have reported hardness as high as 50 GPa for nanocrystalline SiC films with grain sizes of 10-20 nm, deposited by thermal plasma CVD.…”

“…The superior properties of nanocrystalline ceramics are governed primarily by the crystal structure [119,121,125]. There have been attempts to simulate the atomic structure and understand the materials properties of PDCs at fundamental level by modeling and computational studies [126][127][128][129], but these studies have not addressed the unique properties that are sometimes observed in these materials.…”

“…They ascribe the extremely high values of fracture toughness observed to a low concentration of flaws. Liao et al [121] experimentally investigated hardness, crystal size, and crystallinity as a function of the substrate temperature for nanocrystalline β-SiC films deposited by thermal plasma chemical vapor decomposition, and observed increase in all three, with increase in the substrate temperature. Recently, Szlufarska et al [118] studied atomistic processes occurring during nanoindentation of amorphous silicon carbide (a-SiC) by molecular dynamic simulations and found onset of plasticity at different indentation depths.…”

“…In this context, nanoindentation, which is widely used to characterize the mechanical properties at the nanoscale [141], is particularly helpful in determining the true or mesoscale properties of ceramics that have inherent micro-pores. In a recent study, Liao et al [121] successfully used nanoindentation to determine hardness of super-hard SiC films deposited by thermal plasma chemical vapor deposition. They found higher hydrogen flow rate during the deposition process resulted in greater crystallinity, bigger crystals sizes (27 nm) and lower hardness (30 GPa).…”