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Finite element modelling of the fracture behaviour of surface treated Ti-6Al-4V alloy

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Author(s): W. Ziaja

Journal: Archives of Computational Materials Science and Surface Engineering
ISSN 1689-9210

Volume: 1;
Issue: 1;
Start page: 53;
Date: 2009;
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Keywords: Titanium alloys | Surface layer | Analysis and modelling | Computational material science

ABSTRACT
Purpose: Surface treatments of the titanium alloys are frequently applied in order to modify the surface layer microstructure and to improve tribological properties or resistance to high temperature oxidation of the alloy. Various surface engineering techniques can be used to increase the surface hardness, e.g. deposition of the coatings composed of metallic carbides, nitrides or more recently DLC. The stiffness and strength properties of the coating and substrate materials differ significantly. Cracking of the usually brittle coating leads to stress concentration and localized plastic deformation of the substrate which can facilitate propagation of microcracks into the substrate. This can result in premature failure of the hard coated component. In the paper the crack penetrating hard coating was analysed and the influence of coating and substrate properties on crack driving force was numerically investigated.Design/methodology/approach: Two dimensional finite element analysis of the four point bending test of surface modified titanium alloy with the crack penetrating hardened layer was carried out.Findings: The effect of the coating thickness and stiffness, residual stresses in the coating, yield strength of substrate material and yield properties of diffusion hardened layer on crack driving force was determined.Research limitations/implications: Some extension of the numerical model should be introduced in order to take into account the interactions of the crack with microstructure of the material.Practical implications: The results could be used for selection of parameters of surface layer with complex structure in the process of the design of load bearing components against fracture.Originality/value: The fracture behaviour of hard coated materials was most frequently studied for indentation and friction conditions and considerably less concern was devoted to coated systems under tension or compression.
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