Ta2AlC and Cr2AlCAg-based composites -: New solid lubricant materials for use over a wide temperature range against Ni-based superalloys and alumina

The tribological performances of the two new composite materials, consisting of the layered ternary carbides (MAX phases), Ta2AlC or Cr2AlC, and 20 vol.% Ag, were investigated in the temperature range from ambient to 550 degrees C against a Ni-based superalloy, SA (Inconel 718) and alumina counterparts. Over the entire temperature range, the wear rates, WRs, during dry sliding against the SA counterparts for the Ta2AlC-Ag and Cr2AlC-Ag composites were <5 x 10-5 and <10(-4) mm(3)/Nm, respectively. The friction coefficients, mu, were <0.5. The WRs of the SA counterparts were also relatively low (<10(-4) mm(3)/Nm). Under thermocycling conditions, the tribological performance of the MAX/Ag composites-Inc7l8 tribocouples act better with sliding distance. When the composites were tested against Al2O3, their WRs at moderate temperatures were also approximate to 10(-5) mm(3)/Nlm, butat550 degrees C the WRs increased by about an order or magnitude. Both composites had tensile strengths, sigma(t), >150MPa, compressive strengths, sigma(c), >1.5 GPa at ambient temperature and sigma, > 100 MPa at 550 degrees C. Their good tribological performance together with decent mechanical properties and excellent machinability render them promising materials for various high temperature tribological applications. (C) 2007 Elsevier B.V. All rights reserved.