Study of harmonic microstructure development during Spark Plasma Sintering (SPS) of β-CEZ titanium alloy

¹ Universite de Lorraine, Institut Jean Lamour (IJL), UMR 7198 - CNRS, Nancy, France
² Université Paris 13, Laboratoire des Sciences des Procédés et des Matériaux (LSPM), Villetaneuse, France
³ Department of Mechanical Engineering, College of Science and Engineering, Ritsumeikan University, Noji-Higashi, Kusatsu-City, Shiga, Japan
⁴ Universite de Lorraine, Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (LEM3), UMR 7239, Metz, France

Abstract

The present study focuses on the formation of harmonic microstructures in a metastable β titanium alloy, the β-Cez alloy (T_β =890°C). Previous studies showed that harmonic structures obtained by a powder metallurgy route led to an increase in mechanical properties. In this study, the harmonic structure was obtained after a Mechanical Milling of the Initial Powder followed by Spark Plasma Sintering.

The phase transformations occurring in the Initial Powder and Mechanical Milled powders during a heat treatment similar to the SPS one were studied. Electrical resistivity, high energy XRD and SEM-EBSD were used to characterize the evolution of phases and microstructures and highlight the effect of the thermal treatment and the milling. It was shown that after thermal treatment of Mechanical Milled powders, a harmonic α + β microstructure is obtained consisting of nodular α grains in the powder shell and α lamellae in the powder core. The stress/strain induced martensite formed during the milling associated with the heavier deformation at the powder surface areas contributes highly to the formation of network arrangement of nodular α grains by a recovery/recrystallization phenomenon of β and α phases during the heating.