# Novel Composite Powders with Uniform TiB\({}_{2}\) Nano-Particle Distribution for 3D Printing
## 2 Experimental Procedures  
In a previous study, the nanometer sized TiB\({}_{2}\) reinforced Al composites were synthesized via an in-situ reaction process. The size of the in-situ synthesized particles ranged from 20 to 500 nm, but with a predominant number of nanometer sized particles (less than 100 nm) [15]. In the present study, Pure Al was melted at 900 \({}^{\circ}\)C with electrical resistance furnace under the protection of an argon atmosphere. The mixed salts of K\({}_{2}\)TiF\({}_{6}\) and KBF\({}_{4}\) according to an atomic ratio of Ti/2B were preheated at 250 \({}^{\circ}\)C for 2 h and were introduced into the molten aluminum in 15 min. Mechanical stirring of 600 rpm was carried out and heating was maintained at 900 \({}^{\circ}\)C for 30 min to allow the in situ TiB\({}_{2}\) particulates to form in the matrix. The reaction slag was skimmed from the surface of the melt. Mg and Al-10 Cu master alloys were subsequently added into the melt and homogenized for 10 min. Afterwards, the composite powders were produced by conventional gas atomization. Atomization of the Al-Cu-Mg composite melt was carried out in a confined nozzle atomizer. A schematic diagram of a gas atomization unit and the facility used in the work are shown in Figure 1a,b, respectively. The capacity of the facility used in this experiment is 25 kg melt for a single charging. Prior to melting and atomization, both the melting and the cooling chambers were evacuated to 10\({}^{-2}\) Pa several times, each time being back filled with nitrogen. During heating of the alloy, its temperature is acquired by means of a thermocouple in the melt. The atomization temperature is 800 \({}^{\circ}\)C with a gas pressure of 2.8 MPa. The atomized powder was allowed to cool down to room temperature in the nitrogen gas atmosphere of the atomizer. Afterward, the powders were collected in air. The chemical composition of the composite powders was 3.8 wt. % Cu, 1.3 wt. % Mg and 7.6 wt. % TiB\({}_{2}\) particles with Al balance (a prototype of a 2024 Al alloy with TiB\({}_{2}\) addition), measured by inductively coupled plasma atomic emission spectroscopy analysis (ICP-AES). The powder size distribution was measured by Mastersizer 2000 analyzer. In order to study its microstructure, the as-synthesized powder was sieved into four different size ranges: 63-75 \(\upmu\)m (group A); 45-53 \(\upmu\)m (group B); 10-26 \(\upmu\)m (group C); \(\leq\)10 \(\upmu\)m (group D). The microstructure of the different gas atomized TiB\({}_{2}\)/Al composite powder fractions as well as the distribution of TiB\({}_{2}\) particles was investigated by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and electron backscattered scattering detection (EBSD). EBSD samples were prepared by Focused Ion beam (FIB) in order to detect both the TiB\({}_{2}\) and Al phase. The crystal structure was characterized by synchrotron radiation X-ray diffraction at the beamline BL14 Bl of the Shanghai Synchrotron Radiation Facility (SSRF) using a diffractometer of negligible instrumental broadening (less than 0.001\({}^{\circ}\)), equipped with a double crystal monochromator and a position sensitive point detector. The wavelength of the X-ray used was 0.124 nm.  
Diffuse reflectance spectroscopy (DRS) was measured from 200-2500 nm using an UV-Visible-NIR Lambda 950 Perkin Elmer spectrometer equipped with a 150 mm diameter integrating sphere coated with Spectralon with 1 nm spectral resolution. A Spectralon reference was used to measure the 100% reflectance and internal attenuators were used to determine 0% reflectance in order to remove background and noise. The samples were placed in a quartz cuvette, sealed, and mounted on a Teflon sample holder for the DRS measurement. The reflectance spectra were subsequently converted to Kubelka-Munk (K-M) to calculate the absorption spectra of the powder. This conversion is performed by the device software, using the K-M equation: \(f(R)=\ \frac{(1-R)^{2}}{2R}\), where \(R\) is reflectivity.