Modeling of phase transformations of Ti6Al4V during laser metal deposition

[EN] The low density, excellent high temperature mechanical properties and good corrosion resistance of titanium and its alloys have led to a diversified range of successful applications. As a consequence, there is a demand of increasing the capabilities of processing such alloys. The laser cladding technique allows direct metal deposition with an excellent metallurgical bond and a pore free fine grained microstructure. A nonlinear transient thermo-metallurgical model was developed to study the technique with titanium alloys to get a better understanding of the thermal and metallurgical underlying aspects. The calculated temperatures and phase transformations are compared with experimental tests. © 2011 Published by Elsevier Ltd.This work is has been done under the research project MAT2008-06882-C04 funded by the Spanish government (MICIIN).Suárez, A.; Tobar, MJ.; Yañez, A.; Pérez, I.; Sampedro, J.; Amigó Borrás, V.; Candel Bou, JJ. (2011). Modeling of phase transformations of Ti6Al4V during laser metal deposition. Physics Procedia. 12(Part A):666-673. https://doi.org/10.1016/j.phpro.2011.03.083S66667312Part

Processing Parameter Effects on Residual Stress and Mechanical Properties of Selective Laser Melted Ti6Al4V

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. Post-process heat treatments can be applied to SLM components to remove in-built residual stress and improve ductility. Residual stress buildup and the mechanical properties of SLM parts can be controlled by varying the SLM process parameters. This investigation studies the effect of layer thickness on residual stress and mechanical properties of SLM Ti6Al4V parts. This is the first-of-its kind study on the effect of varying power and exposure in conjunction with keeping the energy density constant on residual stress and mechanical properties of SLM Ti6Al4V components. It was found that decreasing power and increasing exposure for the same energy density lowered the residual stress and improved the % elongation of SLM Ti6Al4V parts. Increasing layer thickness resulted in lowering the residual stress at the detriment of mechanical properties. The study is based on detailed experimental analysis along with finite element simulation of the process using ABAQUS to understand the underlying physics of the process

An analytical model of energy distribution in laser direct metal deposition

The direct metal. deposition (DMD) process is suitable for functional rapid prototyping, rapid tooling and part refurbishment, and can be operated with CO2, Nd:YAG (neodymium-doped yttrium aluminium, garnet) or high-power diode lasers. In this work, a quasi-stationary coaxial DMD system is modelled-in terms of power balances. Novel modelling methods and matching to experimental results are used to derive a series of equations, from which the power distribution, melt pool length and mean melt pool temperature can be derived for different initial laser powers, system parameters and build material properties. The model is applied to a real system and predicts results in agreement with established values. The model highlights laser radiation reflection from the melt pool and conduction to the substrate as the major power distribution routes and reveals the importance of evaporation losses from the melt pool at higher laser powers. Application of the model is able to explain some of the differences in the process found when using alternative types of lasers as the power source