## 1 Introduction  
Shape memory alloys (SMAs) are the main classification of smart alloys owing to their unique properties. Smart materials are metallic alloys that respond to mechanical stresses and temperature, creating internal deformation of about 2-10%. Smart alloys are considered thermo-mechanical materials used in many mechanical applications due to their ability to return (remember) to their shape after the removal of external loads [1]. The shape memory effect is created when the SMAs undergo applied stresses at a constant temperature, while super elasticity is created at a temperature higher than the austenite finish temperature (Af) and constant stress; hence, the SMAs return to their original shape after removing the load. Ni-Ti alloys (Nitinol) are important shape memory alloys that consist of two main phases; the first phase is austenite (B2) and the second phase is martensite (B19). The austenite phase is created at a high temperature and transforms into the martensite phase at a low temperature. Phase transformation from the austenite phase to the martensite phase is affected by many factors such as the heating-cooling cycle, Ni concentration, and the processing conditions when using the casting route [2]. Shape memory alloys are commonly used in mechanical and biological applications that require smart alloys due to their unique properties, such as recovery to their original shape, with a large amount of deformations. Each one of these properties consists of two-phase transformations: the first is the martensite phase, which occurs at high pressure and low temperature (Mf), and the second is the austenite phase, which occurs at low pressure and high temperature (Af). For a specific temperature that is lower than the transformation temperature, the martensite phase was created (twin) as a soft phase and was deformed by (de-twinning). Many metal alloys tend to draw back to their original shape when heated above the transformation temperature; however, increasing the applied stress can create plastic deformation. Many metallic alloys have a recovery of about 0.1%, while the SMAs have a recovery of about 7-8% [1; 3].  
Generally, there are two techniques used to fabricate SMAs: powder metallurgy or the casting method, which are classified as vacuum induction melting (VIM), electron beam melting (EBM) and vacuum arc re-melting (VAR). The preferred technique is vacuum arc re-melting (VAR) as it offers a high purity shape memory alloy, especially Ni-Ti-Ag. On the other hand, Ni-Ti based SMAs are not suitable for many purposes; therefore, to improve the properties of Ni-Ti SMAs, various elements have been added such as Fe, Co and V, which are used to decrease the transformation temperature. Au, Zr, Pt and Hf are used to raise the transformation temperature, and Cu is used to decrease the hysteresis loop, especially when adding Fe and Nb [2]. Ag is an important element due to its superior and anti-bacterial material and its stability. Hence, Ag is considered the best element incorporated into Ni-Ti-based alloys to produce Ni-Ti-Ag composite material with higher strength compared with Ni-Ti-based alloys and higher anti-bacterial activity [4; 5; 6; 7; 8; 9; 10; 11]. The main manufacturing processes used to produce SMAs are the casting method and powder metallurgy method, followed by heat treatment to minimize the internal stresses and improve the properties of the manufactured SMAs [12]. The aim of this work is to synthesize Ni-Ti-Ag SMAs by the casting method using a VAR furnace and to study the effect of the addition of Ag on the microstructure and mechanical properties of SMAs.