The silicide coatings (Mo,W)Si2+(Mo,W)5Si3 on graphite, interaction with carbon

Powders of (Mo,W)Si2+(Mo,W)5Si3(Mo,W)Si2+(Mo,W)5Si3 eutectics were prepared and melted on the surfaces of graphite samples. Ratio rMo of atomic concentrations in silicides for Mo (CMo) and W (CW), rMo=CMo/(CMo+CW)rMo=CMo/(CMo+CW), was changed from rMo = 0 to rMo = 1 with the 0.1 step. The two grades of graphite materials were investigated: dense structural graphite “MPG6” and more porous graphite “GMZ”. The influence of rMo on the phase composition of obtained coatings was investigated as well as interaction of the silicide melts with graphite. For rMo ⩽ 0.3 there were found laminas (0.5–2.5 μm)∗(2–25 μm) of SiC particles of the first type only inside (Mo,W)5Si3 and/or (Mo,W)5Si3C phases without contact with disilicides (Mo,W)Si2. The SiС particles of the second type were found in a contact with disilicides (Mo,W)Si2 as well as with (Mo,W)5Si3 and/or (Mo,W)5Si3C phases, these SiC particles are more coarse than SiC particles of the first type. It was established that Nowotny phase (Mo,W)5Si3C and hexagonal disilicides (Mo,W)Si2 are present in the silicides coatings not for all values of rMo. Due to the melts infiltration in graphite silicides react there with the carbon and forms particles of the (Mo,W)C (for rMo ⩽ 0.4) and the (Mo,W)2C (for rMo ⩾ 0.3) or both types (for 0.4 ⩾ rMo ⩾ 0.3) of refractory metals carbides inside graphite.

► We present study of interaction of Mo, W silicide eutectics melts with graphite.
► Concentration intervals for MeC and Me2C formation inside graphite were determined.
► Reactions of carbon soot with Mo,W disilicides were investigated experimentally.
► Formation of SiC particles inside silicide layer of coating was observed.