# SHS Produced TiB\({}_{2}\)-Si Powders for Selective Laser Melting of Ceramic-Based Composite
## 1 Introduction
Fine particles may undergo a significant aggregation, while large particles reduce the maximum layer packing density. Optimization and precise control of combustion synthesis (e.g., combustion temperature, velocity, cooling rate, etc.) ensure production of the feedstock exhibiting the pre-requisite characteristics. An increasing demand for properly designed engineering ceramics needed for armor, hypersonic aerospace vehicles, and electronically conductive ceramics has resumed an interest in titanium diboride-based materials due to their high melting point and high temperature stability, remarkable hardness and stiffness combined with a good fracture toughness, and their electrical- and thermal-conductivity [13]. The main limiting factor for wide application of these materials is their poor sinterability related to the exaggerated grain growth and spontaneous mechanical degradation by an internal stress-induced cracking during cooling from a high sintering temperature [13,14]. Another disadvantage is reasoned by the economic factors, particularly the high cost of the consolidation ongoing at temperatures in the range of 1800-2300 \({}^{\circ}\)C. One of the approaches to fabricate the materials of high density is a liquid phase sintering with metallic additives, which promotes a fast particle re-arrangement and further densification [15]. The liquid phase sintering, however, also fosters rapid mass transport through the melt and considerably accelerates grain growth. Therefore, to prevent the grain growth, the use of a minimum volume of liquid phase or the implementation of grain growth retarding additives is needed. The drawbacks in producing and shaping products are the main concerns, which can be solved by a powder-based AM technique such as SLM enabling layer-by-layer fabrication of complex 3D structures. In [16], the fabrication of TiB\({}_{2}\) reinforced Al-matrix composites by the combustion synthesis was reported; however, the printed parts of uncontrolled porosity were obtained. TiB\({}_{2}\) decorated AlSi10 Mg composite (NTD-Al) powder was prepared in [17] using a gas-atomization procedure. Ti-TiB (monoboride) cermets were in situ produced from Ti-(5-15 wt%TiB\({}_{2}\)) mixtures using SLM, and they demonstrated promising results for future developments [18, 19, 20]; however, titanium diboride based ceramics have not yet been produced with the help of AM. The present work reports a strategy for the preparation of TiB\({}_{2}\)-Si powders for AM by the self-propagating high temperature synthesis (SHS). TiB\({}_{2}\)-Si bulks were fabricated out of the combustion synthesized \"pomegranate-like\" TiB\({}_{2}\)-Si precursor powders, which, to the best of our knowledge, are unique and have not been yet documented elsewhere. Laser melting of a single-component powder (either Si or TiB\({}_{2}\)) is a rather complicated process due to a very narrow processing window, especially for ceramics of a high melting point. A tendency of melt surface to shrink and minimize the surface energy results in the formation of re-solidified droplets. Therefore, the high-melting point powders (such as TiB\({}_{2}\)) are usually mixed with the relatively low-melting point binding powders (here Si). The addition of silicon to TiB\({}_{2}\) yields to increase fluidity, which reduces cracking during solidification and minimizes shrinkage porosity. The presence of silicon significantly decreases the surface tension and viscosity of the pool. The optical properties of silicon, studied in a broad range of laser wavelength (500-1500 nm) under the atmospheric pressure, demonstrated that an average absorption of a silicon slab (20-260 \(\upmu\)m) makes 61%, 41%, and 0.5% at 500 nm, 1000 nm, and 1500 nm of laser wavelength, respectively [21]. Generally, powdered materials exhibit a significantly higher absorptance than their dense form; thus, silicon absorption at 1.07 \(\upmu\)m wavelength of Yb-fiber laser is >41%. On the other hand, borides have been shown to be good absorbers in the range of 500-900 nm with the reflectance of about 50%.