Title: Microstructure evolution in thin sheet laser welding of titanium alloy

Authors: Bikash Kumar; Daniel Kebede; Swarup Bag

Addresses: Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India ' Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India ' Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India

Abstract: The effect of cooling rate on microstructural morphology and mechanical properties of laser welded thin sheet Ti6Al4V alloy is studied. The numerical investigation has been performed to predict the weld pool geometry at different heat input by pulse Nd:YAG laser. The cooling rate is estimated from simulated time-temperature history. The solidified structure is complex and may acquire various microstructural transformations with different morphology of mainly α and β phases depending upon the particular cooling rate followed. Diffusional, α′-martensitic and mixed structures are found in the welded joint. Massive diffusion-controlled α lamellae has found in the range of 52-325 K/s. Volume fraction of α′-martensitic phase in the fusion zone increases with cooling rate. It shows that the dimensional variation of α lamellae plays an important role on mechanical properties. Substantial improvement of the mechanical properties with increase in cooling rate is characterized by the volume fraction of primary α-phase and the α + β lamellae spacing.

Keywords: Ti-6Al-4V alloy; α and β phases; laser welding; Nd:YAG; thin plate; thermal analysis; cooling rate; microstructure; mechanical properties; grain size.

DOI: 10.1504/IJMMS.2018.092875

International Journal of Mechatronics and Manufacturing Systems, 2018 Vol.11 No.2/3, pp.203 - 229

Received: 04 Sep 2017
Accepted: 30 Jan 2018

Published online: 19 Jun 2018 *

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