Polymorphic nature of {332}<113> twinning in BCC alloys

P. Kwasniak¹ , F. Sun² , S. Mantri³ , R. Banerjee³, F. Prima²

(1). Center of Digital Science and Technology, Cardinal Stefan Wyszynski University in Warsaw, Woycickiego 1/3, 01-938 Warsaw, Poland
(2). PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris, 75005, Paris, France
(3). Department of Materials Science and Engineering, University of North Texas, Denton, TX, 76207, USA

Twining and transformation induced plasticity (TWIP/TRIP) plays a crucial role in modern, lightweight Ti alloys with stellar mechanical properties. Both mechanisms utilise the low thermodynamic stability of the beta phase to provoke strain induced atomic rearrangement acting as efficient deformation mode [1-2].  Although the atomic scale basis of TRIP process are relatively well known [3], similar knowledge about TWIP phenomenon is more controversial. Present reports describe martensite-mediated formation of {332}<113> twins [4] as well as direct twining mechanism depending on the chemical composition of the investigated system [5,6]. Such discrepancy leads to fundamental issues in terms of understanding and controlling the TWIP process, impeding its further extension. In this study, we present the crystallographic analysis supported by first principles calculations of the shear-shuffle mechanism of {332}<113> twining providing a universal clarification of the experimentally observed deformation pathways. We show that twin operation is close in nature to known martensitic transformation with equivalent lattice strain values that are supplemented by additional shear component. Depending on the alloy stoichiometry, the transition structure can thus relax to both beta or distorted martensite configuration. The postulated concept of TWIP process perfectly reproduce the atomic structure of {332}<113> twin boundary and elucidates available contradictory twining mechanisms.

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