Akademik Veri Yönetim Sistemi
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, cilt.257, ss.288-301, 2018 (SCI-Expanded)
Bulk-form nanocomposites of TiC-reinforced 316L stainless steel matrix were fabricated by selective laser melting (SLM), an emerging powder-bed additive manufacturing technique which allows the direct fabrication of usable end-products, using various volumetric laser energy densities (a). The microstructural features of the distribution and sizes of TiC nanoparticles, as well as the grain sizes and tribological performances of the SLMprocessed nanocomposite parts, were sensitive to the applied eta. Increasing eta enhanced the dispersion state of nanoscale TiC owing to intensified Marangoni flow and the corresponding capillary force, which prevented TiC aggregation and promoted a uniform dispersion of reinforcements in the solidified matrix. However, with increasing eta, the TiC particle size also increased, and some nanoparticles lost their initial nanostructure because of significant thermal accumulation within the molten pool. Increasing eta also caused increases in the grain sizes of the fabricated nanocomposite because of the decreasing cooling rate. A simulation model was developed to enhance understanding of the manufacturability of these new materials, as well as to predict the temperature evolution and thermal behaviors of the molten pool under various eta. The simulation modeled the effects of various eta values on the temperature distribution evolutions and the corresponding effects of Marangoni convection during the SLM process. The temperature distribution was significantly influenced by the applied a; the maximum temperature gradient within the molten pool was increased significantly with increased a. The simulation results validated the experimental results and the underlying physical mechanism of the molten pool. The microhardness of the SLM nanocomposite decreased sharply with increased grain size due to the lower cooling rate, but increased with further increases in eta because of the enhanced densification degree. Nanocomposites processed under the optimum condition of eta = 200 J/mm(3) showed the lowest wear rates accompanied by the formation of adherent and strain-hardened tribolayers on the worn surfaces of the nano composites, suggesting improved tribological performance.