Frontiers in Materials (Jul 2020)
The Influence of Twinning on the Strain–Hardenability in TRIP/TWIP Titanium Alloys: Role of Solute–Solution Strengthening
Abstract
Transformation Induced Plasticity and Twinning Induced Plasticity (TWIP) titanium alloys are well-known to display a good combination of strain–hardenability and ductility. However, a large range of strain–hardening rates, which cannot be predicted by the actual design method based on electronic parameters, is obtained. In order to explain this wide range of properties, two different alloys displaying a large difference of strain–hardening rates, but similar chemical stability, have been studied and compared: Ti–12Mo and Ti–8.5Cr–1.5Sn (in wt%). Evolution of both twin size and density during in situ tensile tests has been followed by SEM/electron backscatter diffraction mapping, and two distinct behaviors can be highlighted: the growth of existing twins (Ti–12Mo) and the nucleation of new twins (Ti–8.5Cr–1.5Sn) upon loading. The last one may lead to an improvement of the dynamic Hall–Petch effect by multiplication of twin/matrix interfaces, with subsequent improvement of the macroscopic strain–hardening. It is thought that this competition may be related to the crystal lattice distortion induced by the alloying elements and the subsequent reduction of the migration velocity of the twin/matrix interfaces.Impact StatementThis work reports on distinct behaviors of mechanical twins in TRIP/TWIP titanium alloys, highlighting for the first time a competition between growth of existing twins and nucleation of additional twins upon loading. This effect is assumed to be due to the solute-strengthening effect in the studied alloys and modify, as a consequence, the strain–hardenability of the TRIP/TWIP alloys.
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