Elevated temperature tribological behavior of Ni based composites containing nano-silver and hBN

In order to explore the possible synergetic action of a combination of low and high-temperature solid lubricant, nickel-base composites containing nano-powders of silver and hBN were prepared by powder metallurgy (P/M) method. The silver content was varied from 8 to 20 wt.% while keeping the hBN content at a fixed level of 8 wt.%. The friction and wear properties of composites were investigated in the range from room temperature to 600 °C by carrying out dry sliding wear tests against a ring made of AISI52100 steel using a flat-on-flat configuration under a constant load of 20 N and fixed sliding speed of 1 m/s. The hardness of the composites was found to decrease with addition of solid lubricants and it has been attributed to the poor sintering characteristics of hBN. The friction coefficients were observed to decrease with increasing temperature. However, friction coefficients of silver and hBN containing composites were observed to be lower than the base alloy having no lubricant at all the temperatures which has been attributed to the presence of solid lubricants and their synergy. The presence of Ag and BN at the worn surface was confirmed by XRD analysis.