Atom migration mechanisms influence a wide range of phenomena: solidification kinetics, phase equilibria, oxidation kinetics, precipitation of phases, and high-temperature deformation. In particular, solute diffusion mechanisms in α-Ti alloys can help explain their excellent high-temperature behaviour. The purpose of this work is to study self- and solute diffusion in hexagonal close-packed (hcp)-Ti, and its anisotropy, from first-principles using the 8-frequency model. The calculated diffusion coefficients show that diffusion energy barriers depend more on bonding characteristics of the solute rather than the size misfit with the host, while the extreme diffusion anisotropy of some solute elements in hcp-Ti is a result of the bond angle distortion.
The high affinity of O, N, and C with α-Ti has a serious detrimental influence on the high-temperature properties of these alloys, promoting the formation of α-case. These elements dissolve in interstitial sites and diffuse very fast in α-Ti (10 3 -10 8 times higher than the self-diffusivity of Ti) at high temperature accelerating the growth of α phase surface layer. Understanding the diffusion mechanisms of these elements is crucial to the design of high-temperature Ti alloys. This work aims to determine the stable interstitial sites and migration paths of O, N, and C in α-Ti. Diffusion coefficients were evaluated applying an analytical model, the multi-state diffusion method, and kinetic Monte Carlo simulations informed by first-principles calculations. The results show the reliability of these two methods with respect to the experimental data. In addition to octahedral sites, less traditional interstitial sites are shown to be stable configurations for these elements instead of tetrahedral sites. This requires to update the transition pathway networks through which these elements have been thought to migrate in α-Ti. C 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License. [http://dx
The fluid dynamics of multi-component alloy systems subjected to high energy density sources of heat largely determines the local composition, microstructure, and material properties. In this work a multi-component thermal fluid dynamics framework is presented for the prediction of alloy system development due to melting, vaporisation, condensation and solidification phenomena. A volume dilation term is introduced into the continuity equation to account for the density jump between liquid and vapour species, conserving mass through vaporisation and condensation state changes. Mass diffusion, surface tension, the temperature dependence of surface tension, buoyancy terms and latent heat effects are incorporated. The framework is applied to describe binary vapour collapse into a heterogeneous binary liquid, and a high energy density power beam joining application; where a rigorous mathematical description of preferential element evaporation is presented.
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The rapid development of new infrastructure programmes requires an accelerated deployment of new materials in new environments. Materials 4.0 is crucial to achieve these goals. The application of digital to the field of materials has been at the forefront of research for many years, but there does not exist a unified means to describe a framework for this area creating pockets of development. This is confounded by the broader expectations of a digital twin (DT) as the possible answer to all these problems. The issue being that there is no accepted definition of a component DT, and what information it should contain and how it can be implemented across the product lifecycle exist. Within this position paper, a clear distinction is made between the “manufacturing DT” and the “component DT”; the former being the starting boundary conditions of the latter. In order to achieve this, we also discuss the introduction of a digital thread as a key concept in passing data through manufacturing and into service. The stages of how to define a framework around the development of DTs from a materials perspective is given, which acknowledges the difference between creating new understanding within academia and the application of this knowledge on a per-component basis in industry. A number of challenges are identified to the broad application of a component DT; all lead to uncertainty in properties and locations, resolving these requires judgments to be made in the provision of safety-dependent materials property data.
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