Characterisation of mechanically alloyed feedstock for laser-powder bed fusion: titanium silicon carbide metal matrix composite

Abstract

The research presented investigates the characterisation of new materials for the additive manufacturing (AM) industry. Herein, a metal matrix composite (MMC) with a titanium (Ti6Al4V) matrix reinforced with silicon carbide (SiC) is characterised. The research investigated an innovative and novel feedstock production process involving elements of mechanical alloying, tailored to the requirements of the layer based additive manufacturing (ALM) process. Systematic evaluation and subsequent characterisation of process parameters including laser power, scan speed and hatch spacing are presented. A new and novel experimental route is discussed. Detailed findings are presented with a robust methodology for producing elemental feedstock in small batch sizes, and process parameter characterisation for in-situ alloying for laser bed fusion. Evidence showed that acceptable parameters could be found for mechanical alloying with a rotational speed of 500 rev/min and an alloying time of twenty-four minutes that showed minimal and acceptable changes in size and morphology, therefore enabling the feedstock to be used within the Laser-Powder Bed Fusion (L-PBF) process also referred to as Powder Bed Fusion (PBF). New knowledge is presented in the form of experimental methodologies, namely single bead evaluation in relation to energy density, the evaluation and comparison of single beads, the use of mini-chambers to experiment with reduced levels of feedstock, the two-rail system to accurately deliver powder for single layer experimentation and equations developed to calculate energy density for single beads and the maximum volume of reinforcement material achievable from particle size data. MMC material was successfully synthesised due to the use of the methodologies described, with silicon carbide (SiC), silicon oxide (SiO2) and titanium silicide (Ti5Si4) detected as chemical compositions within the sample.