# Shape Memory Alloy Reinforced Self-Healing Metal Matrix Composites
## 3 Synthesis of Shape Memory Alloy Reinforced Self-Healing Metal Matrix Composites
However, the presence of a stable titanium oxide layer on the surface of the NiTi strip reduced its wettability, leading to lower interface strength. To overcome this, the SMA strips were treated by immersing them in an aquatic acid solution of 4.8%HF-10.5%HNO\({}_{3}\) for 5 min to remove the oxide layer. [PERSON] et al. [71] fabricated NiTi-reinforced Zinc Alloy ZA-8 (Zn-0.8 Al-0.015 Cu) composite by Casting technique. Two types of samples, namely the \"loop\" and \"rod\" types, were fabricated to investigate the relative effectiveness of two methods for load transfer from the reinforcement to the matrix material. The first method involved transferring the load directly by establishing interfacial bonding between the matrix and reinforcement, while the second method relied on the indirect transfer through a mechanical connection to a bolt integrated within the matrix. For fabricating the \"loop\" sample, the NiTi wires were treated by fluxing in an aqueous solution of 4.8%HF-10.5%HNO\({}_{3}\) for 5 minutes, followed by washing in distilled water, drying, and coating with Indalloy Flux #2 for 3 min to enhance the bonding between the reinforcement and matrix. The NiTi wires were then trained by heating them in a preform-frame made of steel bars (100 mm \(\times\) 20 mm \(\times\) 2 mm) and threaded steel rods (5 mm diameter) to 500 \({}^{\circ}\)C for 1 h, followed by quenching in room temperature water for 5 times, in order to create a permanent looping structure that could act as structural support for load transfer. Before casting, the inner bolts were removed, and the frame was positioned in a permanent steel mold, both of which had been preheated to a temperature of 150 \({}^{\circ}\)C. Preheating helps to minimize thermal shocks, improve mold filling, enhance the flowability of the molten alloy, and promote proper solidification of the material during casting. Additionally, preheating can also aid in reducing any potential defects or inconsistencies in the final casted product. The ZA-8 alloy was melted at 600 \({}^{\circ}\)C for 1 hour in a BN-coated graphite crucible before being poured into the preheated mold with the preform. The crucible was coated with BN to prevent carbide formation and enhance castability. The resulting synthesized looped sample had reported dimensions of 12.7 mm in thickness and 38.1 mm in width. For the \"rod\" type sample, threaded steel rods and steel bars of the same dimensions as those used for the looped sample were employed as a frame to fabricate the wound SMA preform. The as-received NiTi wires were used without any surface treatment for fabricating this type of sample. The rod samples were fabricated using identical melting and casting techniques as the looped samples. The dimensions of the synthesized rod sample were reported as 12.1 mm in thickness (or 12.7 mm for the second sample) and 34.9 mm in width. [PERSON] et al. [68] fabricated NiTi-reinforced SHMMC by casting (Al-3 at.%Si matrix reinforced with two vol\(\%\) NiTi SMA wires). The fabrication process involved several steps. Initially, a master alloy was prepared by melting high-purity aluminum (99.99% purity, Alfa Aesar, Haverhill, MA, USA) and silicon (99.9999% purity, Alfa Aesar) at 850 \({}^{\circ}\)C until a homogenous liquid solution was formed. This master alloy was then cast into a graphite mold. Subsequently, the appropriate proportions of the master alloy and aluminum were melted at 750 \({}^{\circ}\)C to form a liquid solution, obtaining an Al-3 at.%Si alloy matrix. To fabricate the SHMMCs, the molten matrix material was poured into a specially designed graphite mold that was coated with BN and equipped with a wire holder containing pre-aligned NiTi wires (Ni-49.3 at.%Ti, \(\mathcal{O}\) = 0.87 mm, Memry Corporation, Bethel, CT, USA). Prior to casting, the mold was heated to 350 \({}^{\circ}\)C to ensure proper temperature conditions.