Utilization of L-PBF process for manufacturing an in-situ Fe-TiC metal matrix composite

Abstract

In-situ Fe-TiC metal matrix composite (MMC) was successfully fabricated via Laser Powder Bed Fusion (L-PBF) using an in-house gas atomized Fe-TiC composite powder. The optimization campaign of printing parameters targeted the maximum density of printed cubic samples. The highest Archimedes density of 7.615 g cm−3 was achieved by laser power of 210 W, scan speed of 763 mm s−1, and hatch spacing of 80 µm corresponding to a volume energy density (VED) of 68.78 J mm−3 given the constant layer thickness of 50 µm. The relative density of the optimized sample was also measured by Computer Tomography (CT) scanning yielding a relative density of 99.85%. According to measured chemical composition and subsequent thermodynamic calculation, the TiC phase can be up to 7.2 vol%, and X-ray diffraction analysis (XRD) confirmed the presence of TiC phase in bcc-iron. Furthermore, Scanning Electron Microscopy (SEM) of sample cross-sections revealed well-dispersed submicron and nano TiC precipitates of two morphologies and size ranges – primary cubic particles (100–400 nm in size) and secondary plate-like particles (up to 300 nm length and below 50 nm width). No micro-cracks and contaminations were detected between the matrix and reinforcement. Electron Back Scattered Diffraction (EBSD) analysis of a cross-section parallel to build direction revealed extremely fine equiaxed grains with a mean size of 1.3 µm which suggests Columnar to Equiaxed Transition (CET). CET and grain refinement were most likely induced by the presence of TiC particles and rapid solidification within L-PBF. Finally, the micro-hardness tests were conducted to evaluate the reinforcement potential of TiC particles. The mean value of 357.0 ± 9.3 HV1 was obtained for the optimized sample which is superior to pure Fe fabricated via L-PBF and a similar MMC fabricated by Electron Beam Powder Bed Fusion (EB-PBF). Furthermore, the microstructure and hardness of the optimized sample was compared to the sample from optimization campaign with the highest coincident VED and relative density. Some micro-defects were observed in the optimized build and their morphologies and origins were discussed.