Microstructure prediction of Ti6Al4V processed by Laser Cladding

Abstract

Abstract Titanium is the fourth most abundant structural metal in the world. It is known to have a high strength, light weight, good formability and high corrosion resistance. Due to these properties, Titanium and its alloys are used in many industries, such as aerospace and automobile. Note that due to its high price, one can find Ti6Al4V in demanding applications. This master thesis defines quantitatively predicting of the microstructure of a titanium alloy, Ti6Al4V, worked with laser cladding process. The main goal is to define the proper phase transformation conditions that lead to reliable phase predictions. Outcomes are checked from the results obtained by two experimental observations in laser cladding process for the Ti6Al4V. Both studies obtained qualitative results according to the phases that formed the microstructure of the alloy and the hardness value of three different points located in the deposits. As a first reference, H.S. Tran used Constant Track Length building strategy. The second study has been made by MMS team at University of Liège, but it has not been published yet. They used a Decrease Track Length building strategy. The initial experimental work was done by H.Paydas . This master thesis is based on the implementation of a Fortran code that defines the phase transformations of Ti6Al4V. Inside the code, the thermal conditions and the equations with their parameters are defined. The project was based on Crespo’s model that calculates the phase transformation kinetics of this titanium alloy. After applying the same model, some differences have been made in order to achieve the desired results according to the improvement works done by H.S Tran and MMS team. This document presents a flow work starting with the basic theoretical background about Additive Manufacturing, Titanium and its alloys. After, Ti6Al4V is presented: its chemical composition, the different phases that can describe its microstructure and the equations that define the transformations from one phase to the other. The parameters and conditions defining those equations are determined and compared with previous literature, concretely with Crespo. Finally the results and conclusions are presented. Keywords: Laser Cladding (LC), Ti6Al4V, microstructure, thermal history, Fortran.