Study Of The Liquid Structure In Ti-Ni-Cu Alloy System

Ti-based bulk metallic glasses have all the advantages of bulk metallic glasses, and they have high tensile strength, compressive strength, lower density, excellent biocompatibility and high reduced glass transition temperature as well. Thus, Ti-based amorphous alloys are of scientific and commercial interest in many fields. They can be used as precision instruments parts, biological materials, and high temperature and corrosion resistance structural materials. The investigation of the liquid structure of Ti-based alloys is very important for the fabrication, development and application of Ti-based bulk metallic glasses.The liquid structures of Ti-Ni, Ti-Cu, Ni-Cu binary alloy systems and Ti-Ni-Cu ternary alloy system are investigated by ab initio molecular dynamics simulation in this paper.Ni and Cu atoms have similar atomic sizes and chemical properties, thus, the liquid structures of Ti-Ni and Ti-Cu alloy systems are very much alike. In the liquid structures of Ti-Ni binary system, the chemical short-range order of unlike-atoms Ti and Ni atoms are dominant. The most Voronoi polyhedron around Ti atoms is, followed by deformed-bcc and perfect icosahedral clusters. According to the fraction of the polyhedra, Ni atoms can be considered as central atoms in the liquid of Ti-Ni system. In addition, the most Voronoi polyhedron around Ni atoms is also icosahedral-like clusters. The fractions of the top five kinds of Voronoi polyhedra around Ni atoms nearly remain unchanged as the Ni content changes. The diffusion coefficients of Ti and Ni atoms have similar trend as the Ni content changes, and the coefficients of Ni atoms are a little higher than that of Ti atoms. In the compositions of Ti75Ni25, Ti67Ni33 and Ti40Ni60, the diffusion coefficients of Ti and Ni atoms are close and relatively low. It suggests that the Ti and Ni atoms are prone to cooperative diffusition.In the liquid of Ti-Cu binary alloy system, it is found that the bonding of Ti-Cu atoms is dominant (CSRO). When the Cu content is low, Ti-Ti and Ti-Cu chemical short-range orders coexist. As the Cu content increases, Ti-Cu CSRO gradually becomes dominant CSRO in the liquid structure. The bonding of Cu-Cu atoms is affected slightly by the composition changing. The circumstance of Voronoi polyhedra aound Cu atoms in Ti-Cu system is very similar to that around Ni atoms in Ti-Ni system. Cu atoms can be considered as central atoms. Around Cu atoms, icosahedral-like clusters are dominant clusters. The fraction of icosahedral-like clusters expressed as (0 2 8 1) obviously increase as Cu content increases. And the fraction of perfect icosahedral clusters expressed as (0 0 12 0) decrease on the whole as Cu content increases, however, the fraction is the least in compositions of Ti75Cu25 and Ti40Cu60. The situation of the atoms diffusion in Ti-Cu system is very much alike with Ti-Ni system. In Cu-rich compositions, the coefficients of Ti and Cu atoms are quite close. Ti and Cu atoms are prone to cooperative diffusion. In the composition of Ti43Cu57, the coefficients of Ti and Cu atoms are the lowest.In Ni-Cu alloy system, Ni-Cu alloys are completely miscible solid solution, Ni and Cu atoms in liquid are likely to be random distribution. The icosahedral-like clusters are dominant Voronoi polyhedra around Ni and Cu atoms. The diffusion coefficients of Ni and Cu atoms are close, and have similar variation trend.The effects of similar elements on structures of the liquid Ti5oNi(5o-X)Cux (x=0,10, 20,25,30,40, and 50) alloys are investigated by ab initio as well. In the liquid alloys, Ti atoms tend to concentrate around Ni and Cu atoms. Furthermore, Ni atoms are more attractive to Ti atoms than Cu atoms. However, in the Cu-rich compositions, the probability of forming Ti-Ni bonding and that of forming Ti-Cu bonding are nearly equal, which may favor the amorphous formation. The icosahedral-like clusters are dominant short-range order. In addition, the dynamical parameters are also discussed. The self-diffusion coefficients of Ti and Ni atoms are close and relatively low.