Optimization Studies on the Secondary Treatments and Mechanical Behavior of Ti48Al2Cr2Nb Alloy Produced By Electron Beam Melting (EBM) Method

Date

2024-6-27

Author

Bilgin, Güney Mert

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Reducing structural weight is crucial in aviation engine development for lower emissions, enhanced performance, and cost efficiency. Titanium aluminides (TiAl) are potential substitutes for nickel-based superalloys due to their high-temperature strength and low density. However, their low ductility and fracture toughness present challenges for conventional processing methods. In this study, Ti48Al2C2Nb alloys were produced using electron beam melting (EBM) additive manufacturing. The as-built samples exhibited extreme brittleness due to coarse γ-bands, aluminum content inconsistencies, and high dislocation density, rendering them impractical for aviation applications. To address these issues three secondary thermal treatments were applied: hot isostatic pressing (HIP) at 1200 °C under 100 MPa, annealing at 1200 °C (HT1), and annealing at 1400 °C (HT2). HIP induced a slight increase in α2 phase fraction and grain size, while HT1 accentuated the banded structure without significantly increasing α2 content. HIP and HT1 reduced dislocation density and inherent strain. HT2 transformed the duplex microstructure into a fully lamellar morphology with the highest texture. Room and high temperature tensile tests demonstrated that HIP, HT1, and HT2 treatments effectively mitigated brittleness. HIP reduced anisotropy at room temperature, with a 9.53 MPa difference in yield strength between specimens tested perpendicular and parallel to the building direction, compared to a 65.15 MPa variation in HT1 samples. At 800 °C, samples treated with HIP and HT1 exhibited a ductile transition, while HT2 processed samples retained brittleness. Consequently, this study reveals the potential of secondary heat treatments and novel scanning strategies in improving the mechanical characteristics of additively manufactured Ti48Al2C2Nb alloy for high-temperature applications.

Subject Keywords

Additive Manufacturing (AM), Electron Beam Melting (EBM), Ti48Al2Cr2Nb Alloy, Annealing, Isostatic Pressing (HIP)

URI

https://hdl.handle.net/11511/110163

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Graduate School of Natural and Applied Sciences, Thesis