TY - JOUR

T1 - On the Formation Mechanism of Banded Microstructures in Electron Beam Melted Ti–48Al–2Cr–2Nb and the Design of Heat Treatments as Remedial Action

AU - Wartbichler, Reinhold

AU - Clemens, Helmut

AU - Mayer, Svea

AU - Ghibaudo, Christian

AU - Rizza, Giovanni

AU - Galati, Manuela

AU - Iuliano, Luca

AU - Biamino, Sara

AU - Ugues, Daniele

N1 - Publisher Copyright: © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH

PY - 2021/12

Y1 - 2021/12

N2 - The formation mechanism of banded microstructures of an electron beam melted engineering intermetallic Ti–48Al–2Cr–2Nb alloy, the solidification behavior, and the heat treatment response are investigated via a process parameter study. Scanning electron microscopy, hardness testing, X-ray diffraction, electron probe microanalysis, thermomechanical analysis, electron backscatter diffraction, heat treatments, as well as thermodynamic equilibrium calculation, and numerical simulation were performed. All specimens show near-γ microstructures with low amounts of α 2 and traces of β o. Fabrication with an increased energy input leads to an increased Al loss due to evaporation, a lower α-transus temperature, and to a higher hardness. Banded microstructures form due to abnormal grain growth toward the bottom of original melt pools, whereas α 2 in Al-depleted zones enables a Zener pinning of the γ-grain boundaries, leading to fine-grained areas. Via numerical simulation, it is shown that increasing the energy input leads to larger maximum temperatures and melt pool sizes, longer times in the liquid state, and more remelting events. Solidification happens via the α-phase and increasing the energy input leads to an alignment of (111) γ in building direction. Furthermore, banded microstructures respond heterogeneously to heat treatments. Heat treatment is introduced based on homogenization via phase transformation to obtain isotropic microstructures.

AB - The formation mechanism of banded microstructures of an electron beam melted engineering intermetallic Ti–48Al–2Cr–2Nb alloy, the solidification behavior, and the heat treatment response are investigated via a process parameter study. Scanning electron microscopy, hardness testing, X-ray diffraction, electron probe microanalysis, thermomechanical analysis, electron backscatter diffraction, heat treatments, as well as thermodynamic equilibrium calculation, and numerical simulation were performed. All specimens show near-γ microstructures with low amounts of α 2 and traces of β o. Fabrication with an increased energy input leads to an increased Al loss due to evaporation, a lower α-transus temperature, and to a higher hardness. Banded microstructures form due to abnormal grain growth toward the bottom of original melt pools, whereas α 2 in Al-depleted zones enables a Zener pinning of the γ-grain boundaries, leading to fine-grained areas. Via numerical simulation, it is shown that increasing the energy input leads to larger maximum temperatures and melt pool sizes, longer times in the liquid state, and more remelting events. Solidification happens via the α-phase and increasing the energy input leads to an alignment of (111) γ in building direction. Furthermore, banded microstructures respond heterogeneously to heat treatments. Heat treatment is introduced based on homogenization via phase transformation to obtain isotropic microstructures.

UR - http://www.scopus.com/inward/record.url?scp=85118845429&partnerID=8YFLogxK

U2 - 10.1002/adem.202101199

DO - 10.1002/adem.202101199

M3 - Article

VL - 23.2021

JO - Advanced engineering materials

JF - Advanced engineering materials

SN - 1438-1656

IS - 12

M1 - 2101199

ER -