TY - THES

T1 - A tailored TiAl alloy for the powder bed based laser additive manufacturing

AU - Schimbäck, David

N1 - embargoed until 02-04-2020

PY - 2019

Y1 - 2019

N2 - Modern combustion-based propulsion systems for automotive use and aerospace jet engines rely on innovative high-temperature lightweight materials and advanced manufacturing processes. Due to their high melting point and low density, alloys based on intermetallic titanium aluminides have a particularly high potential, which is already being used industrially. Through the development of powder-based additive manufacturing processes, conditions have been created in recent years representing a paradigm shift for the future production of components as well as their properties and design. For this purpose, samples of an intermetallic γ-titanium aluminide alloy, the so-called TNM alloy, were produced via a powder-bed-based selective laser melting (SLM) and subjected to extensive metallurgical characterization by means of light and scanning electron microscopy, electron probe microanalysis, differential scanning calorimetry and X-ray diffraction. In order to avoid a micro notch effect due to increased porosity, which has a negative effect on fatigue and (fracture) toughness properties in the case of high-strength materials, a hot-isostatic pressing was carried out as the first heat treatment step. Subsequently, a heat treatment was performed to adjust a microstructure with balanced properties for the use at high temperatures to ensure a sufficient elongation at break and fracture toughness at room temperature. The aim of the microstructural investigations was to characterize the initial state of the powder, to record occurring porosity, to investigate chemical anisotropies and to adapt the microstructure for high-temperature applications. By means of the results of the applied methods, the density of the as-SLM material could be increased to 99.9% and a suitable heat treatment for the present alloy was developed which includes a homogeneous nearly lamellar microstructure with globular γ-phase (NLγ) as well as a fully lamellar microstructure (FL). Furthermore, the mechanical properties of the material were investigated by creep tests and three-point bending tests.

AB - Modern combustion-based propulsion systems for automotive use and aerospace jet engines rely on innovative high-temperature lightweight materials and advanced manufacturing processes. Due to their high melting point and low density, alloys based on intermetallic titanium aluminides have a particularly high potential, which is already being used industrially. Through the development of powder-based additive manufacturing processes, conditions have been created in recent years representing a paradigm shift for the future production of components as well as their properties and design. For this purpose, samples of an intermetallic γ-titanium aluminide alloy, the so-called TNM alloy, were produced via a powder-bed-based selective laser melting (SLM) and subjected to extensive metallurgical characterization by means of light and scanning electron microscopy, electron probe microanalysis, differential scanning calorimetry and X-ray diffraction. In order to avoid a micro notch effect due to increased porosity, which has a negative effect on fatigue and (fracture) toughness properties in the case of high-strength materials, a hot-isostatic pressing was carried out as the first heat treatment step. Subsequently, a heat treatment was performed to adjust a microstructure with balanced properties for the use at high temperatures to ensure a sufficient elongation at break and fracture toughness at room temperature. The aim of the microstructural investigations was to characterize the initial state of the powder, to record occurring porosity, to investigate chemical anisotropies and to adapt the microstructure for high-temperature applications. By means of the results of the applied methods, the density of the as-SLM material could be increased to 99.9% and a suitable heat treatment for the present alloy was developed which includes a homogeneous nearly lamellar microstructure with globular γ-phase (NLγ) as well as a fully lamellar microstructure (FL). Furthermore, the mechanical properties of the material were investigated by creep tests and three-point bending tests.

KW - Additive Fertigung

KW - Selektives Laserschmelzen

KW - Titanaluminide

KW - Mikrostruktur

KW - Kriechversuche

KW - selective laser melting

KW - additive manufacturing

KW - titanium aluminides

KW - microstructure

KW - creep testing

M3 - Master's Thesis

ER -