Thermal monitoring of microstructure and carbide morphology in direct metal deposition of Fe-Ti-C metal matrix composites

In this paper, real-time cooling rate of Fe-Ti-C Metal Matrix Composites (MMCs) made by Direct Metal Deposition (DMD) are measured to monitor microstructure and carbide morphology. This research proves that carbide morphology developed by DMD of Fe-TiC composite coating on AISI 1020 carbon steel is highly affected by cooling rate and pre-heat. For this purpose, the DMD process is monitored by a thermal camera to obtain real-time values of the cooling rate resulted from a range of selected scan speeds. Two approaches are studied for the single-track depositions: (a) single speed and (b) dual speeds in which the scan speed changes during the deposition. The dual speed generates different preheat values during deposition and thus deviates the cooling rate. Consequently, the effect of cooling rate and preheat temperature are studied on carbide morphologies. Results show that scan speed plays the main role in the formation and distribution of TiC particles in the deposited layer by affecting the cooling rate and dilution (melt pool composition). Based on this research, it is possible to control the cooling rate in order to achieve specific carbide morphologies in the deposited layer. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) are used to characterize the deposited layers' microstructure.