Selective laser melting of Ti6Al4V-B4C-BN in situ reactive composites

Abstract

Desire for higher application temperatures and complex geometries for metallic materials has spurred significant development in additive manufacturing (AM) of metal-ceramic composites; however, limited process-microstructure-properties relationships exist for these materials and processing strategies. Herein we investigate the processing window and high-temperature oxidation performance of an in situ reactive, oxidation-resistant titanium metal-matrix composite reinforced with boron nitride (BN) and boron carbide (B4C) via selective laser melting (SLM) to understand the effects of processing parameters on the in situ reactive characteristics and their effects on build reliability and high-temperature oxidation performance. SLM processing required a 50% decrease in overall energy density relative to titanium's optimal parameters to avoid processing failure due to the high in situ reactivity and exothermic reaction between feedstock materials. A precise balance was necessary to combine decreasing the input energy to avoid cracking (due to in situ reactivity) while simultaneously providing enough input energy to keep the bulk density as high as possible to limit porosity that contributed to processing inconsistency at low input energy. Process optimization resulted in composites with as high as 98.3% relative density, comparable to some of the highest metal-ceramic composite densities reported in the AM literature. High-temperature oxidation testing revealed a 39% decrease in oxidation mass gain compared to AM-Ti6Al4V at 850°C, owing directly to ceramic reinforcement. Our results indicate that control of SLM processing parameters can yield advanced composites with enhanced properties and characteristics compared to the base material, revealing an array of design possibilities for researchers and engineers in many fields.