# Novel Composite Powders with Uniform TiB\({}_{2}\) Nano-Particle Distribution for 3D Printing
## 3 Results and Discussion
The powders with typical particle sizes of 50 and 10 \(\upmu\)m, respectively, were analyzed by EBSD, applying a fine scan with a 0.1 \(\upmu\)m step size. Figure 4a shows an example of an EBSD IPF map of the 50 \(\upmu\)m composite powder with TiB\({}_{2}\) phase particles in black contrast. It shows that the micrometer-sized equiaxed grains exhibited random orientations. Figure 4b shows EDS mapping of the elemental distribution of titanium of the same powder, which evidences the homogeneous particle dispersion. In conventional solidification microstructures obtained by casting [6; 21], the majority of TiB\({}_{2}\) particles are clustered at the grain boundaries among the equiaxed \(\alpha\)-Al grains. In the case of the gas-atomized powders, however, SEM observation shows that TiB\({}_{2}\) particles (indicated by arrows) were distributed both within the grain and along the grain boundaries (as shown in Figures 2(c1-f1) and 4). According to [9; 22], the particles are engulfed when the moving front is above the critical velocity. The improved distribution of TiB\({}_{2}\) particles is obtained thanks to the high cooling rate, which promotes the velocity of the advancing solidification front. Furthermore, the transition between particle pushing and engulfment is mainly determined by the interfacial energies between the phases in the system. It has been proven that the TiB\({}_{2}\) particles and the \(\alpha\)-Al grains tend to form a high-coherency orientation relationship between the two atomic structures to reduce the solid-particle interfacial energy [6], which assists the engulfment to ensure the uniform distribution of the TiB\({}_{2}\) particles. Figure 4: (**a**) EBSD IPF map of a 50 \(\upmu\)m composite powder; (**b**) EBSD EDS map of a 50 \(\upmu\)m composite powder. Orientation relationships of TiB\({}_{2}\) particles within a grain: (**c**) small particles; (**d**) large particles. (**e1,e2**): The [0001] and <11-20> pole figures of certain engulfed TiB\({}_{2}\) particles; (**f1,f2**): The [111] and <\(-110>\) pole figures of the surrounding aluminum; (**g1,g2**): The [0001] and <2-1-10> pole figures of other engulfed TiB\({}_{2}\) particles; (**h1,h2**): The [001] and <110> pole figures of the surrounding aluminum. There are two commonly reported orientation relationships of the nucleation of \(\alpha\)-Al on TiB\({}_{2}\) during solidification, noted as OR1 and OR2. OR1 is more commonly encountered according to previous studies [6; 23]. Figure 4c,d give an example of small and large particles, respectively, in one grain. It was observed that most TiB\({}_{2}\) particles within one grain have two Euler angles which means that they have two orientation relationships with the surrounding aluminum. OR 1 and OR2 co-exist within one grain, as shown in Figure 4c; Figure 4d shows an example of the big particle with OR1. Figure 4(e1,e2,f1,f2) present the {0001}\(<\)11-20\(>\) pole figures of certain engulfed TiB\({}_{2}\) particles and the {111}\(<\)\(-\)110\(>\) pole figures of the surrounding aluminum. The paralleled crystallographic planes and orientations are marked by red and green circles, respectively. The orientation relationship is consistent with OR1:  
(0001)TIB2 \(\mid\) {111}\(\mid\)Al  
[11-20]TIB2 \(\mid\) {1-110}\(\mid\)Al  
Figure 4(g1,g2,h1,h2) present the {0001} \(<\)2-1-10\(>\) pole figures of other engulfed TiB\({}_{2}\) particles and the {001}\(<\)110\(>\) pole figures of the surrounding aluminum. The orientation relationship matches with OR2:  
(0001)TIB2 \(\mid\) {001}\(\mid\) {2-1-10}\(\mid\) {TIB2 \(\mid\) {110}\(\mid\) {Al}  
The statistical analyses of the orientation relationship of recorded TiB\({}_{2}\) particles inside grains and along grain boundaries are summarized in Tables 1 and 2, respectively. Overall, the majority of particles inside the grains (Table 1) form an OR1 relationship with Al as the {0001}TIB2 direction is closest to the {111}\(\mid\)Al direction [23]. Especially for large-sized TiB\({}_{2}\) particles, OR1 appears more frequently.