TY - JOUR

T1 - Influence of focus offset on the microstructure of an intermetallic γ-TiAl based alloy produced by electron beam powder bed fusion

AU - Ghibaudo, Christian

AU - Wartbichler, Reinhold

AU - Marchese, G.

AU - Clemens, Helmut

AU - Ugues, Daniele

AU - Biamino, Sara

N1 - Publisher Copyright: © 2023

PY - 2023/3/3

Y1 - 2023/3/3

N2 - It is well established in literature that, when processing intermetallic γ-TiAl components by electron beam powder bed fusion, a banded microstructure is frequently formed because of an inhomogeneous Al distribution since more pronounced evaporation of Al occurs at the top of the melt pool. This feature is particularly promoted when highly energetic process parameters (high beam currents, slow beam speeds, narrow line offsets) are used. Therefore, an approach already suggested in the literature to reduce the Al loss is to minimize the energy level of the process parameter during production. However, there is a limit to such kind of approach: minimizing the beam current or increasing the beam speed, or increasing the line offset will, at a certain point, results in not being able to achieve a completely dense material and thus some process-induced porosity, the so-called lack-of-fusion defects, starts to occur in the produced parts. In this study, the effect of an additional parameter of the electron beam powder bed fusion process is taken under consideration: the focus offset (FO), i.e. the distance between the focusing plane of the electron beam with respect to the powder bed. The effect of the FO on the residual porosity, microstructure, phase composition, hardness as well as chemical composition is investigated, thus having the possibility to demonstrate that also the FO can affect the Al loss and play a fundamental role in the generation of a homogenous microstructure, contributing to mitigate the appearance of a banded microstructure.

AB - It is well established in literature that, when processing intermetallic γ-TiAl components by electron beam powder bed fusion, a banded microstructure is frequently formed because of an inhomogeneous Al distribution since more pronounced evaporation of Al occurs at the top of the melt pool. This feature is particularly promoted when highly energetic process parameters (high beam currents, slow beam speeds, narrow line offsets) are used. Therefore, an approach already suggested in the literature to reduce the Al loss is to minimize the energy level of the process parameter during production. However, there is a limit to such kind of approach: minimizing the beam current or increasing the beam speed, or increasing the line offset will, at a certain point, results in not being able to achieve a completely dense material and thus some process-induced porosity, the so-called lack-of-fusion defects, starts to occur in the produced parts. In this study, the effect of an additional parameter of the electron beam powder bed fusion process is taken under consideration: the focus offset (FO), i.e. the distance between the focusing plane of the electron beam with respect to the powder bed. The effect of the FO on the residual porosity, microstructure, phase composition, hardness as well as chemical composition is investigated, thus having the possibility to demonstrate that also the FO can affect the Al loss and play a fundamental role in the generation of a homogenous microstructure, contributing to mitigate the appearance of a banded microstructure.

UR - http://www.scopus.com/inward/record.url?scp=85147798259&partnerID=8YFLogxK

U2 - 10.1016/j.jmapro.2023.01.061

DO - 10.1016/j.jmapro.2023.01.061

M3 - Article

VL - 89.2023

SP - 132

EP - 141

JO - Journal of manufacturing processes

JF - Journal of manufacturing processes

SN - 0278-6125

IS - 3 March

ER -