Modeling of Microstructure Evolution of Ti6Al4V for Additive Manufacturing

AM processes are characterized by complex thermal cycles that have a deep influence on the microstructural transformations of the deposited alloy. In this work, a general model for the prediction of microstructure evolution during solid state transformations of Ti6Al4V is presented. Several formulations have been developed and employed for modeling phase transformations in other manufacturing processes and, particularly, in casting. The proposed model is mainly based on the combination and modification of some of these existing formulations, leading to a new overall model specifically dedicated to AM. The accuracy and suitability of the integrated model is enhanced, introducing new dedicated features. In fact the model is designed to deal with fast cooling and re-heating cycles typical of AM processes because: (a) it is able to consider incomplete transformations and varying initial content of phases and (b) it can take into account simultaneous transformations.The model is implemented in COMET, an in-house Finite Element (FE)-based framework for the solution of thermo-mechanical engineering problems. The validation of the microstructural model is performed by comparing the simulation results with the data available in the literature. The sensitivity of the model to the variation of material parameters is also discussed.

[1]  Miguel Cervera,et al.  Finite element modeling of multi-pass welding and shaped metal deposition processes , 2010 .

[2]  A. Wilson,et al.  Differential scanning calorimetry study and computer modeling of β ⇒ α phase transformation in a Ti-6Al-4V alloy , 2001 .

[3]  Miguel Cervera,et al.  Numerical modelling and experimental validation in Selective Laser Melting , 2017 .

[4]  R. Pederson,et al.  A model for Ti–6Al–4V microstructure evolution for arbitrary temperature changes , 2012 .

[5]  Alberto Cardona,et al.  Evolution of Microstructure During Shaped Metal Deposition , 2010 .

[6]  L. Costa,et al.  Laser powder deposition , 2009 .

[7]  Z. Guo,et al.  Resistivity study and computer modelling of the isothermal transformation kinetics of Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo–0.08Si alloys , 2001 .

[8]  J. Planell,et al.  Formation of α-Widmanstätten structure: effects of grain size and cooling rate on the Widmanstätten morphologies and on the mechanical properties in Ti6Al4V alloy , 2001 .

[9]  John W. Cahn,et al.  Transformation kinetics during continuous cooling , 1956 .

[10]  Ma Qian,et al.  Additive manufacturing of strong and ductile Ti–6Al–4V by selective laser melting via in situ martensite decomposition , 2015 .

[11]  W. A. Johnson.  Reaction Kinetics in Processes of Nucleation and Growth , 1939 .

[12]  H. J. Rack,et al.  Phase transformations during cooling in α+β titanium alloys , 1998 .

[13]  Miguel Cervera Ruiz,et al.  Shaped Metal Deposition Processes , 2013 .

[14]  M. Avrami.  Granulation, Phase Change, and Microstructure Kinetics of Phase Change. III , 1941 .

[15]  Jaimie Tiley,et al.  Modeling the tensile properties in β-processed α/β Ti alloys , 2006 .

[16]  J. Planell,et al.  Influence of tempering temperature and time on the α′-Ti-6Al-4V martensite , 1996 .

[17]  D. P. Koistinen,et al.  A general equation prescribing the extent of the austenite-martensite transformation in pure iron-carbon alloys and plain carbon steels , 1959 .

[18]  T. DebRoy,et al.  In-Situ Observations of Phase Transformations in the Fusion Zone of Ti-6Al-4V Alloy Transient Welds Using Synchrotron Radiation , 2003 .

[19]  C. Selcuk.  Laser metal deposition for powder metallurgy parts , 2011 .

[20]  S. Biamino,et al.  An Overview of Additive Manufacturing of Titanium Components by Directed Energy Deposition: Microstructure and Mechanical Properties , 2017 .

[21]  J. Sieniawski,et al.  Microstructure and Mechanical Properties of High Strength Two-Phase Titanium Alloys , 2013 .