Abstract
While repair is mainly used to restore the original part geometry and properties, hybrid manufacturing aims to exploit the benefits of each respective manufacturing process regarding either processing itself or resulting part characteristics. Especially with the current implementation of additive manufacturing in the production of TiAl, turbine blades for both hybrid manufacturing and repair new opportunities are enabled. One main issue is the compatibility of the two or more material types involved, which either differ regarding composition or microstructure or both. In this study, a TNMTM-alloy (Ti-Nb-Mo) was manufactured by different processes (casting, forging, laser additive manufacturing) and identically heat-treated at 1290 °C. Chemical compositions, especially aluminum and oxygen contents, were measured, and the resulting microstructures were analyzed with Scanning Electron Microscopy (SEM) and High-energy X-ray diffraction (HEXRD). The properties were determined by hardness measurements and high-temperature compression tests. The comparison led to an overall assessment of the theoretical compatibility. Experiments to combine several processes were performed to evaluate the practical feasibility. Despite obvious differences in the final phase distribution caused by deviations in the chemical composition, the measured properties of the samples did not differ significantly. The feasibility of combining direct energy deposition (DED) with either casting or laser powder bed fusion (LPBF) was demonstrated by the successful build of the dense, crack-free hybrid material.
Highlights
Due to suitable high-temperature properties, such as high specific high-temperature strength (100–150 MPa cm3 /g), high specific rigidity (35–42 GPa cm3 /g), high oxidation, and creep resistance, intermetallic γ titanium aluminide alloys with a density of ρ = 3.9–4.1 g/cm3 are considered to be substitutes for nickel-based superalloys with approximately twice the density (ρ = 7.9–8.5 g/cm3 ) [1,2].The limited ductility and fracture toughness of the material [3,4], as well as the high reactivity of titanium, especially with oxygen, water, and nitrogen, are challenging both for the use and the production of titanium aluminide components
Cast and forged samples were intentionally selected to have a higher oxygen content than technically possible so that the oxygen contents were high for all samples, and the influence of the manufacturing route on the phase formation after heat treatment could be investigated
The investigated direct energy deposition (DED) samples differ uniformly from material samples produced by other methods in that their aluminum content is at least 0.4% higher, which can be balanced when considered in the powder production process
Summary
The limited ductility and fracture toughness of the material [3,4], as well as the high reactivity of titanium, especially with oxygen, water, and nitrogen, are challenging both for the use and the production of titanium aluminide components. One of the main applications is the use of low-pressure. Materials 2020, 13, 4392 turbine blades at an operating temperature of approx. TNMTM is a group of forging alloys fully solidified through the β phase and protected by MTU Aero Engines AG. Leistritz Turbinentechnik GmbH uses it to manufacture low-pressure turbine (LPT) blades [5], which are installed in the geared turbofan PW1110G. The target element distribution of the main alloy elements is adjusted according to the desired distribution of the three phases—α2, γ, and β/β0(B2) [1]—and is in the range Ti(42-44)Al-(3-5)Nb-(0.1-2)Mo-(0.1-0.2)B (in at.%)
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