Nanocrystalline TiC reinforced Ti matrix bulk-form nanocomposites by Selective Laser Melting (SLM): Densification, growth mechanism and wear behavior

Selective Laser Melting (SLM) Additive Manufacturing (AM) process was used to produce nanocrystalline TiC reinforced Ti matrix bulk-form nanocomposites. The influence of "volumetric energy density" (epsilon) on densification activity, microstructural feature, nanohardness, and wear behavior of SLM-processed parts was studied. The densification levels of TiC/Ti parts remained above 97% as epsilon >= 120 J/mm(3). A further decrease in epsilon lowered the densification rate, due to the occurrence of balling effect. The TiC reinforcement experienced an interesting morphological change from the coarsened dendritic TiC (360 J/mm(3)) to the accumulated whisker-structured TiC (180 J/mm(3)) and to the uniformly dispersed nanoscale lamellar TiC (<= 120 J/mm(3)). As epsilon of 120 J/mm(3) was properly settled, the dynamic nanohardness (90.9 GPa) and elastic modulus (256 GPa) of SLM-processed TiC/Ti nanocomposites showed respectively similar to 22.7-fold and similar to 2.4-fold increase upon that of the unreinforced Ti. A uniform distribution of friction coefficient with a low average value <0.2 was obtained, leading to a considerably reduced wear rate of 1.8 x 10(-7) mm(3)/(Nm). A disappearance of nanostructured TiC reinforcement at an elevated epsilon of 360 J/mm(3) lowered the mechanical properties of TiC/Ti part consisting of the coarsened dendritic TiC. (C) 2011 Elsevier Ltd. All rights reserved.