Genesis of Microstructures in Friction Stir Welding of Ti-6Al-4V |
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Authors: | Gnofam Jacques Tchein Dimitri Jacquin Dominique Coupard Eric Lacoste Franck Girot Mata |
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Affiliation: | 1.Univ. Bordeaux, I2M, CNRS,Talence,France;2.Department of Mechanical Engineering, Faculty of Engineering,University of the Basque Country, UPV/EHU,Bilbao,Spain;3.University of Bordeaux, I2M CNRS,Gradignan Cedex,France;4.Arts et Métiers ParisTech, I2M, CNRS,Talence,France;5.IKERBASQUE, Basque Foundation for Science,Bilbao,Spain |
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Abstract: | This paper is focused on the genesis of microstructures in friction stir welding (FSW) of the Ti-6Al-4V alloy. Several titanium joints, initially prepared with four different preheat treatments, were processed by FSW. Detailed microstructural analyses were performed in order to investigate change in the microstructure during the process. In this work, the FSW processing allows a controlled and stable microstructure to be produced in the stirring zone, regardless of the initial heat treatment or the welding conditions. The welded material undergoes a severe thermomechanical treatment which can be divided into two steps. First, the friction in the shoulder and the plastic strain give rise to the necessary conditions to allow a continuous dynamic recrystallization of the β phase. This operation produces a fine and equiaxed β grain structure. Second, once the pin has moved away, the temperature decreases, and the material undergoes a heat treatment equivalent to air quenching. The material thus exhibits a β → β + α transformation with germination of a fine intergranular Widmanstätten phase within the ex-fully-recrystallized-β grains. |
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