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research-article

Predicting microstructure evolution during directed energy deposition additive manufacturing of Ti-6Al-4V

[+] Author and Article Information
Cengiz Baykasoglu

Department of Mechanical Engineering, Hitit University Corum, 19030 Turkey
cengizbaykasoglu@hitit.edu.tr

Oncu Akyildiz

Department of Metallurgical and Materials Engineering Corum, 19030 Turkey
oncuakyildiz@hitit.edu.tr

Duygu Candemir

Hitit University Department of Metallurgical and Materials Engineering Corum, 19030 Turkey
duygukorsacilar@hitit.edu.tr

Qingcheng Yang

University of Pittsburgh Department of Mechanical Engineering and Material Science Pittsburgh, PA 15261
qzy25@psu.edu

Albert C. To

508 Benedum Hall 3700 O'Hara Street Pittsburgh, PA 15261
albertto@pitt.edu

1Corresponding author.

ASME doi:10.1115/1.4038894 History: Received September 25, 2017; Revised December 20, 2017

Abstract

Laser engineering net shaping (LENS) is one of the representative processes of directed energy deposition (DED) in which a moving heat source having high-intensity melts and fuses metal powders together to print parts. The complex and non-uniform thermal gradients during the laser heating and cooling cycles in the LENS process directly affects the microstructural characteristics, and thereby the ultimate mechanical properties of fabricated parts. Therefore, prediction of microstructure evolution during the LENS process is of paramount importance. The objective of this study is to present a thermo-microstructural model for predicting microstructure evolution during the LENS process of Ti-6Al-4V. Firstly, a detailed transient thermal finite element model is developed and validated for a sample LENS process. Then, a density type microstructural model, which enables calculation of the a-phase fractions, (i.e. Widmanstätten colony and basketweave a-phase fractions), ß-phase fraction and alpha lath widths during LENS process is developed and coupled to the thermal model. The microstructural algorithm is first verified by comparing the phase fraction results with the results presented in the literature for a given thermal history data. Secondly, the average lath width values calculated using the model are compared with the experimentally measured counterparts, where a reasonable agreement is achieved in both cases.

Copyright (c) 2017 by ASME
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