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<p>The present study explores fine-scale microstructure, chemistry, and dislocation substructure formation, and their effect on phase decomposition and transformation during and after additive manufacturing (DED-LENS<sup>TM</sup>) of Ti-6Al-4V alloy. Optimized processing parameters were used to produce bulk alloy specimen. Electron microscopy was carried out to obtain details about microstructure and dislocation sub-structure formation as well as to analyze elemental distribution within the microstructural features. High temperature x-ray diffraction (XRD) and differential scanning calorimetry characterizations were conducted to study the phase transformation in as-deposited specimen. The prior β grain boundary regions either remain free from grain boundary (GB) α phase or contains smaller GB α variants. Lamellar α phase appears beside prior β grain boundaries while basket-weave structure with acicular α lamellae is present inside prior β grains. Larger primary and secondary acicular α lamellae evolve as part of basket-weave structure during deposition of a new layer, whereas refined tertiary and quaternary <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\alpha \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>α</mi> </math></EquationSource> </InlineEquation> lamellae form on reheating of previously deposited layers. Reheating also results in rearrangement of dislocations and α/α interface formation that assists β penetration and promotes spheroidization of α lamellae. β nucleation from retained dislocations inside <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\alpha^{\prime }\)</EquationSource> <EquationSource Format="MATHML"><math> <msup> <mi>α</mi> <mo>′</mo> </msup> </math></EquationSource> </InlineEquation> martensites further accelerates spheroidization. Morphology of different α/α′ phase along with substructure and nonequilibrium elemental distribution effects α → β phase transformation temperature post-deposition. The retained compressive residual stress also decreases with increase in temperature heat treatment and cause peak shifting and peak broadening in XRD pattern.</p>

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Fine-Scale Microstructure, Elemental Distribution, and Dislocation Substructure Formation and Their Influence on Post-deposition Phase Transformation in Additive Manufacturing of Ti-6Al-4V Alloy

  • 期刊论文

  • 发表日期：

    2025年10月16日

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  • Souvik Sahoo,
  • Anuja P. Joshi,
  • K. U. Yazar,
  • Shibayan Roy

摘要

The present study explores fine-scale microstructure, chemistry, and dislocation substructure formation, and their effect on phase decomposition and transformation during and after additive manufacturing (DED-LENSTM) of Ti-6Al-4V alloy. Optimized processing parameters were used to produce bulk alloy specimen. Electron microscopy was carried out to obtain details about microstructure and dislocation sub-structure formation as well as to analyze elemental distribution within the microstructural features. High temperature x-ray diffraction (XRD) and differential scanning calorimetry characterizations were conducted to study the phase transformation in as-deposited specimen. The prior β grain boundary regions either remain free from grain boundary (GB) α phase or contains smaller GB α variants. Lamellar α phase appears beside prior β grain boundaries while basket-weave structure with acicular α lamellae is present inside prior β grains. Larger primary and secondary acicular α lamellae evolve as part of basket-weave structure during deposition of a new layer, whereas refined tertiary and quaternary \(\alpha \) α lamellae form on reheating of previously deposited layers. Reheating also results in rearrangement of dislocations and α/α interface formation that assists β penetration and promotes spheroidization of α lamellae. β nucleation from retained dislocations inside \(\alpha^{\prime }\) α ′ martensites further accelerates spheroidization. Morphology of different α/α′ phase along with substructure and nonequilibrium elemental distribution effects α → β phase transformation temperature post-deposition. The retained compressive residual stress also decreases with increase in temperature heat treatment and cause peak shifting and peak broadening in XRD pattern.