A many-body interatomic potential was used for Nickel (Ni) crystal with facecentered cubic (FCC) lattice and Titanium (Ti) with hexagonal close-packed (HCP) lattice and Nitinol alloys within the second-moment approximation. The tight-binding model (the Cleri and Rosato potentials) was employed to carry out three dimensional molecular dynamics simulations upon application of uniaxial tension at nanoscale of studied materials, which contained various vacancy rates. We performed molecular dynamics (MD) simulations to study the yield mechanisms in Ni and Ti nanowires and Nitinol alloys. The coupled effects of various shapes, sizes, and locations of vacancy defects on the mechanical strength and structural deformation of nanowires are presented. The formation energies of vacancy defects are also evaluated. It was found that as the number of vacancies increases, the yield stress decreases. The results showed that breaking time changes with the increase in number of vacancy. To understand the effects of the vacancies on the mechanical properties of Ni and Ti nanowires and Nitinol alloys, tensile and fatigue tests are simulated.