# SHS Produced TiB\({}_{2}\)-Si Powders for Selective Laser Melting of Ceramic-Based Composite
## 3 Results and Discussion
### Combustion Dynthesis in the Ti-B-Si System
In the system under consideration, the formation of only trace amounts of TiSi was observed in the non-stoichiometric mixtures. At a high temperature, the amount of silicon is deficient for TiSi\({}_{2}\) formation, while at a low temperature, the TiSi\({}_{2}\) formation is unlikely. At a temperature below the Si melting point (1414 \({}^{\circ}\)C), the eutectic reaction (L = Ti + TiSi\({}_{3}\)) is not detected. The combustion front progresses from top to bottom of the specimen with an undulating movement in the presence of silicon. This combustion mode differs from the smooth planar wave observed in an undiluted Ti-B. As the combustion temperature is decreased by the silicon diluent, the wave propagation is recorded to be unstable. The undulating movement produces a layered structure in the product as shown in Figure S1. This type of wave propagation is influenced by a liquid phase in the front; thus, the Arrhenius plot of the activation energy for the slow step in the combustion reaction may be determined. The effective activation energy was estimated as 184 kJ assuming no change in the phase composition, Figure S1. In [25], the effective activation energy of 539 kJ and 318 kJ has been reported for the reaction to form TiB\({}_{2}\) and 410 kJ for the combustion of Ti + 1.5B with the formation of the TiB\({}_{2}\) + TiB mixture. Inferior values of the activation energy suggest a liquid state mechanism rather than the participation of a solid phase in the combustion reaction in the Ti-B-Si system. During the combustion of the Ti + 2B + 2 Si mixture, a wave is propagated with a velocity of 0.24 cm\(\cdot\)s\({}^{-1}\) reaching the maximum combustion temperature of 1530 \({}^{\circ}\)C, as in Figure 1b. Figure 2 represents the product after the SHS process demonstrating a highly porous bulk, which easily can be powdered by milling. Figure 2b demonstrates the SEM image of the product of Ti + 2B + _n_Si (n = 1.5-2 moles) mixture after milling, which represents a collection of particles (<50 \(\mu\)m) and their agglomerates (-0.1 mm). The diameters of the chosen particulates, labelled as _Da1_, _Da2_, _Da3_ in Figure 2c, were estimated to be 436 nm, 349 nm, and 267 nm, respectively, asserting particulates sizes in the 200-450 nm range. Figure 2: Scanning electron microscope (SEM) images of porous bulk TiB\({}_{2}\)-Si product produced by SHS (**a**), the TiB\({}_{2}\)-Si powder after milling (**b**,**c**), and the X-ray diffraction (XRD) pattern of the combustion product (**d**). Morphology of the starting powders defines the degree of particles packing throughout the deposited layer. It is well-documented that spherical particles improve the flowability of powders and, therefore, highly affect the quality of the printed product. The SHS method utilized for the preparation of the TiB\({}_{2}\)-Si feedstock allows for the production of irregular-shaped particles with the required size. The \"pomegranate-like\" particle represents the collection of nano- and ultra-fine TiB\({}_{2}\) particulates \"gluing\" together by silicon, as in Figure 2c. This kind of structure may positively contribute to the process of melting/solidification. During laser heating, the ceramic phase TiB\({}_{2}\), which is tightly embedded in Si without formation of the chemical bonds, attains affinity to viscous silicon, thus promoting the sintering and compaction process. Figure 2d displays the XRD pattern of the powder revealing the presence of hexagonal titanium diboride (PDF#65-1073) and no spurious phase formation. The as-synthesized products of Ti+2B+2 Si, corresponding to a composition of 56 wt.%TiB\({}_{2}\)-44 wt.%Si, were grinded and sieved to the powder fractions of 90 \(\upmu\)m, 45 \(\upmu\)m, and 20 \(\upmu\)m particle size. Particle size distribution (PSD) and shape factor influence flowability; moreover, the quality of the final product is affected by the thickness and uniformity of each powder layer in the build box [26].