Nano-indentation has been performed to elucidate the relationship of β grain orientation on the stress-induced martensitic (SIM) deformation in metastable β Ti-10 V-2Fe-3Al (Ti-1023) alloy. Electron backscatter diffraction (EBSD) identified specific crystallographic orientations such as near <001> , <101> and <111> of austenite β grains have been chosen for this study. Berkovich and cono-spherical diamond indenters have been utilized to measure orientation-dependent SIM deformation and small-scale mechanical properties. Hardness increased (~ 4.1 to ~ 4.3 GPa) and reduced modulus decreased (~ 104 to ~ 97 GPa) as the grain orientation varied from <111> , through <101> to <001> . A detailed microstructural analysis of indented surface topographies via scanning electron microscope (SEM) and atomic force microscopy (AFM) reveals the formation of symmetric surface deformation features and stair step morphologies for near <101> and <001> grain orientations, which are attributed to the activation of multiple secondary {112} <111> slip systems as confirmed through slip trace analysis. Further, the presence of stress-induced orthorhombic-<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\alpha^{\prime\prime}}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>α</mi> <mo>″</mo> </msup> </math></EquationSource> </InlineEquation> martensites for near <111> and <101> grain orientations have also been noticed. However, cross sectional characterization via focused ion beam (FIB) milling followed by transmission electron microscope (TEM) provides evidence of strain-induced HCP-<InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\alpha^{\prime}$</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>α</mi> <mo>′</mo> </msup> </math></EquationSource> </InlineEquation> martensites beneath the indent tip in all the <001> , <101> and <111> β grain orientations. It can be inferred that variable threshold stress, owing to the stress gradient from the sample surface to the indent tip, exists to activate SIM transformation in each orientation. The observations suggest that, for enhanced SIM, <111> is the most favored grain orientation, followed by <101> , while the <001> orientation is the least favored. Graphical Abstract

Orientation dependence of stress-induced martensite formation during nano-indentation in metastable β Ti-10 V-2Fe-3Al alloy

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发表日期：

2026年6月29日

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Abhishek Rastogi,
Suresh Neelakantan

摘要

Nano-indentation has been performed to elucidate the relationship of β grain orientation on the stress-induced martensitic (SIM) deformation in metastable β Ti-10 V-2Fe-3Al (Ti-1023) alloy. Electron backscatter diffraction (EBSD) identified specific crystallographic orientations such as near <001> , <101> and <111> of austenite β grains have been chosen for this study. Berkovich and cono-spherical diamond indenters have been utilized to measure orientation-dependent SIM deformation and small-scale mechanical properties. Hardness increased (~ 4.1 to ~ 4.3 GPa) and reduced modulus decreased (~ 104 to ~ 97 GPa) as the grain orientation varied from <111> , through <101> to <001> . A detailed microstructural analysis of indented surface topographies via scanning electron microscope (SEM) and atomic force microscopy (AFM) reveals the formation of symmetric surface deformation features and stair step morphologies for near <101> and <001> grain orientations, which are attributed to the activation of multiple secondary {112} <111> slip systems as confirmed through slip trace analysis. Further, the presence of stress-induced orthorhombic- ${\alpha^{\prime\prime}}$ $α^{″}$ martensites for near <111> and <101> grain orientations have also been noticed. However, cross sectional characterization via focused ion beam (FIB) milling followed by transmission electron microscope (TEM) provides evidence of strain-induced HCP- $\alpha^{\prime}$ $α^{'}$ martensites beneath the indent tip in all the <001> , <101> and <111> β grain orientations. It can be inferred that variable threshold stress, owing to the stress gradient from the sample surface to the indent tip, exists to activate SIM transformation in each orientation. The observations suggest that, for enhanced SIM, <111> is the most favored grain orientation, followed by <101> , while the <001> orientation is the least favored.

Graphical Abstract