Tribological Behavior of NiMoAl-Based Self-Lubricating Composites

Abstract

The present study focused on the development of NiMoAl-based self-lubricating composites using solid lubricants as the second phase by powder metallurgy. For this, Cr₂AlC MAX phase, Cr₂AlC-Ag, and MoS₂ powders were mixed with the NiMoAl-based matrix and subsequently hot pressed to produce bulk composite samples. The average hardness and wear resistance of the matrix were found to be increased with the addition of MoS₂, Cr₂AlC MAX phase, and Cr₂AlC-Ag powder to the NiMoAl matrix. The addition of Cr₂AlC to NiMoAl was more effective in improving the wear resistance than MoS₂. The addition of Cr₂AlC and Cr₂AlC-Ag has increased the hardness by about 75% than that with the addition of NiMoAl alloy. A scanning Kelvin probe system was used to study the surface properties of the tribofilm in detail through work function mapping from the edge area to the wear area (groove). Among all the samples, the one with the addition of Cr₂AlC-Ag powder to the NiMoAl matrix possesses the best tribo-mechanical properties. Cr₂AlC-Ag composite addition to NiMoAl was found to decrease the wear rate by one-third and to reduce the coefficient of friction by one-fourth, compared to the base NiMoAl alloy. This was attributed to the high-sintered density and formation of strong tribofilms consisting of mixed oxides such as Ag₂MoO₄ and Al₂O₃, as confirmed by micro Raman spectra.