# Laser-Based Additive Manufacturing of Zirconium
## 3 Results
### Microstructure and Phase Analysis  
Figure 1a shows the low magnification image of LENS(tm)-deposited Zr in Ti6 Al4V alloy with no laser pass on the surface. As visible from the SEM image, there was a clear interface between Ti6 Al4V and the deposited Zr. However, there was no cracking or no visible delamination. Some porosity is present in the LENS(tm)-processed layers with pore size of 34.1 \(\pm\) 8.1 \(\upmu\)m. The total LENS(tm)-deposited Zr layer was found to be 1.76 \(\pm\) 0.12 mm. Observation of the SEM acquired microstructure in Figure 1 revealed the presence of two distinct zones in the deposited Zr region. The uppermost zone or Zone 1 was 1430.55 \(\pm\) 89.53 \(\upmu\)m in thickness. Zone 2, above the interface with Ti6 Al4V substrate, was 297.88 \(\pm\) 52.59 \(\upmu\)m in thickness. The equiaxed grains in Zone 1 had an average grain size of  
0.69 \(\pm\) 0.07 \(\upmu\)m. This secondary phase along with the equiaxed grain can be observed in Figure 1b. In addition to this equiaxed structure, a secondary phase was observed. In the Zone 2, some patchy phases were also observed. SEM image in Figure 1c shows the transition from the equiaxed grained structure of Zone 1 to an elongated and marginally dendritic structure in Zone 2. Figure 2a shows the structure of LENSTM-deposited Zr with a single laser pass on the surface after deposition. In this sample, there were three distinct zones visible above the interface with Ti6 Al4V alloy unlike two zones observed in the samples without any laser pass on the surface. Overall, the thickness of the LENSTM-deposited zone in this sample was 1330.39 \(\pm\) 14.39 \(\upmu\)m. Porosity was also less, with an average pore size of 45.6 \(\pm\) 6.51 \(\upmu\)m. The different zonea, as well as their thicknesses, are shown in Figure 2a. The patchy phase that was observed in the sample with no laser pass was also seen in these samples after a laser pass. It was found to be more prominent and larger in size. Higher magnification imaging of Zone 1 in the Zr region with one laser pass showed the spherical to equiaxed grained microstructure of Zr after LENSTM processing, as seen in Figure 2b. In the sample with one laser pass, the grain size remained unchanged and was 0.66 \(\pm\) 0.07 \(\upmu\)m. On top of these grains, some secondary phases were also seen. The lowermost zone immediately above the Ti6 Al4V interface was also similar for both the sample. Hence, the laser scan on the surface after LENSTM deposition effectively created the extra zone. It created the Zone 1 (in Figure 2b) and the depth of this zone could be indicative of the effective depth of the laser remelting process. Figure 2c,d show the embedded phase that was found to be more prominent in the samples after laser pass. These particles shows a high contrast, irregular structure (Figure 2c), but had a smooth transition with the equiaxed phase around them (Figure 2d). Compared to the LENSTM-processed samples without any laser pass, the  
Figure 1: LENSTM-deposited Zr on Ti6 Al4V (Ti64) alloy: (**a**) The coating; (**b**) uppermost zone or Zone 1; (**c**) transition to Zone 2 of the coating. secondary phase appeared to be less distributed and more agglomerated; the phase was larger in size and not as widely spread for laser pass samples. These differences can be seen in Figure 3a,b. Figure 4a shows the phase analysis from the XRD data of the feedstock Zr powder. The feedstock powder prior to processing was found to contain only a single phase of Zr; only \(\alpha\) phase was detected. Figure 4b,c show the results of the same for LENS\({}^{\text{TM}}\)-processed Zr on Ti6 Al4V without and with a single laser pass, respectively. In both the cases, retention of \(\alpha\) phase, hcp structure, of zirconium was prominent. Along with the \(\alpha\) phase, the \(\beta\) phase with bcc structure was also noticed.