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

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 pm corresponding to a volume energy density (VED) of 68.78 J mm(-3) given the constant layer thickness of 50 pm. 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 sub-sequent 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 pm 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. (C) 2022 Published by Elsevier B.V.

Automated summary

In this study, in-situ Fe-TiC metal matrix composite (MMC) was successfully fabricated using Laser Powder Bed Fusion (L-PBF) technique, and the printing parameters were optimized to achieve the maximum density of printed samples. The optimized sample showed high relative density, fine grain structure, and excellent hardness. The presence of TiC particles in the sample contributed to grain refinement and enhanced hardness.