**3. Results and Discussion**

### *3.1. Base Metal Microstructures*

The optical microstructures of the Ti-6Al-4V and Nitinol alloys are shown in Figure 2a,b respectively. Both microstructures showed equiaxed grains, and the average grain sizes of the Ti-6Al-4V and the Nitinol were 7 ± 1 μm and 50 ± 8 μm, respectively. The optical microstructure of the Ti-6Al-4V revealed alpha grains (brighter phase) in a transformed beta matrix (darker phase). Predominantly, a single-phase equiaxed microstructure was seen, with distinct twin lines in the Nitinol. Nitinol transforms to an austenitic phase when heated to a point above its austinite start (As) temperatures, but reverts back to its stable state of a martensitic phase when cooled [5]. Depending on the Ni content, the start and finish temperatures of the phase transformation varies. However, it is safe to assume that the present alloy remained predominantly austenitic at room temperature, with possible tiny volumes of a martensitic phase.

**Figure 2.** Optical microstructures of the base metals (**a**) Ti-6Al-4V and (**b**) Nitinol.
