Effect of the metallic matrix on the sliding wear of plasma assisted debinded and sintered MIM self-lubricating steel

Abstract

A new processing route to obtain a homogeneous dispersion of discrete particles of solid lubricant in the volume of sintered steels produced by metal injection moulding (MIM) was recently presented. In this technique, both thermal debinding and sintering are carried out in a single thermal cycle using a Plasma Assisted Debinding and Sintering (PADS) process. The homogeneous dispersion of discrete particles of solid lubricant was achieved by in situ formation of graphite nodules due to the dissociation of a precursor (SiC particles) mixed with the metallic matrix powders during the feedstock preparation. Nodules of graphite (size≤20μm) presenting a nanostructured stacking of graphite foils with thickness of a few nanometres were obtained. In this work, the effect of the metallic matrix composition on the sliding wear behaviour (dry reciprocating sliding tests; normal load 7N; frequency 2Hz; stroke 10mm; 5mm diameter 52100 steel ball) of 3% SiC plasma assisted debinded and sintered (T=1150°C, 1h) self-lubricating steel is presented and discussed. Three different matrix compositions (Fe+0.6% C; Fe+0.6% C+4.0% Ni; Fe+0.6% C+4.0% Ni+1.0% Mo) were analysed. The mechanical properties were greatly increased by the addition of Nickel and further improved (2x) by the presence of Molybdenum. Increasing the hardness of the composites induced a strong decrease of the average friction coefficient, which reached values as low as 0.04. The counter body wear rate was greatly affected by the matrix composition (4x). Similar behaviour was observed for the wear rate of the specimen. The results were discussed in terms of wear mechanisms, which were characterised using SEM and micro Raman spectroscopy.