In-situ carboboride-reinforced metal matrix composites via spark plasma sinterning-laser surface melting hybrid processing: Microstructure and wear behavior

This study compares the microstructure, hardness, and dry-sliding wear behavior of a new multicomponent Fe-C-B-W-Mo-V-Cr-Ti carboboride/metal (martensite) matrix composite fabricated via spark plasma sintering (SPS) and laser surface melting (LSM), against its sand-cast reference – multicomponent cast iron (MCCI). The SPS/LSM specimens exhibited a 1 mm thick, porosity-free surface layer with a hierarchical composite microstructure. This layer consists of hard eutectic colonies (“Chinese script” (CS) and ledeburite) and equiaxed (Ti,W)-rich multiphase carboboride/C-O-N inclusions within a martensitic matrix. Internally, the CS colonies consist of interconnected (W,Mo,Cr,V) 2 (B,C) 5 eutectic plates branching within the local martensitic matrix, whereas the ledeburite colonies consist of a matrix of (Fe,Cr,W,Mo,V) 3 (C,B) plates penetrated by fine martensitic rods. Although similar to MCCI in morphology and phase composition, the SPS/LSM structure was notably refined. Heat treatment (HT) of the SPS/LSM specimens (annealing at 1150 o C for 2h followed by oil quenching) increased matrix carbon, retained austenite volume fraction and dislocation density, and induced alloying element redistribution between microconstituents. The SPS/LSM composite outperformed MCCI in dry-sliding wear resistance (1.7 times as-fabricated, 1.5 times post-heat treated). Laser melting and post-heat treatment increased the wear resistance of the SPS alloy by a factor of 3.2. The SPS/LSM and SPS/LSM/HT composites wore through low-cycle fatigue, with limited microcracking and delamination, abrasion and surface oxidation. In contrast, MCCI exhibited severe surface deterioration characterized by extensive plastic flow and lateral build-up formation, which preceded material removal.