Title:	Grain-Boundary and Free-Surface Segregation in Titanium Alloys (Continuation)
DNr:	SNIC 2015/1-403
Project Type:	SNIC Medium Compute
Principal Investigator:	Annika Borgenstam <annbor@kth.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2015-11-01 – 2016-07-01
Classification:	20506
Homepage:	http://www.hero-m.mse.kth.se/
Keywords:

Abstract

Segregation of solute elements to grain boundaries (GBs) is very common in polycrystalline metallic materials and is technically important for its effects on the microstructures and mechanical properties of materials. GB-segregation has been studied experimentally and computationally in steels and some other alloys, yet work on titanium alloys is largely absent. There is evidence that segregation of oxygen to bcc β-Ti GBs promotes the formation of a continuous layer of hcp α-Ti at GBs, which reduces the tensile ductility and fracture toughness. In order to suppress the formation of GB-α-Ti, a possible strategy is to find another GB segregant with an opposite effect on phase stabilities. The aim of the proposed calculations is to find the segregation energies of alloying elements. Due to the large number of possible alloying elements in titanium, experimental evaluation of segregation will be costly and time-consuming. Using high-throughput first-principles calculations, it is possible to narrow down the scope of candidates for experimental validation. The GB structure under consideration is ∑3(111)[1-10] boundary of bcc structure for its relatively small supercell size. The base atom will be a mixture of Ti and V/Mo in order to obtain a stable bcc structure at 0K. The mixture is realized by virtual crystal approximation (VCA). Clean and segregant-decorated GBs are to be calculated, as well as decorated bulk and free surface (FS).