Tribological behavior of select MAX phases against Al 2O 3 at elevated temperatures

Abstract

The layered M n+1 AC n ternary carbides – MAX phases – Ta 2AlC, Ti 2AlC, Cr 2AlC and Ti 3SiC 2 were tested under dry sliding conditions against alumina at 550 °C and 3 N load (for a stress of ≈0.08 MPa) using a pin-on-disk tribometer. Ta 2AlC and Ti 2AlC exhibited low specific wear rates, SWRs, (≤1 × 10 −6 mm 3/N m), while the coefficients of friction, μ, were ∼0.9 and ∼0.6, respectively. At 0.4, μ of Ti 3SiC 2 was the lowest measured, but the SWR, at ≈2 × 10 −4 mm 3/N m, was high. With a μ of 0.44 and a SWR of 6 × 10 −5 mm 3/N m the Cr 2AlC sample was in between. No visible wear of Al 2O 3 counterparts was observed in all the tribocouples. Tribofilms, which were mainly comprised of X-ray amorphous oxides of the M and A elements and, in some cases, unoxidized grains of the corresponding MAX phases, were formed on the contact surfaces. The correlations between observed tribological properties and tribofilm characteristics are discussed.