Teilchenkontrolliertes Kornwachstum in γ-TiAl Hochtemperaturlegierungen für die Additive Fertigung

Translated title of the contribution: Particle controlled grain growth in γ-TiAl high temperature alloys for additive manufacturing

Gloria Graf

Research output: ThesisMaster's Thesis


In γ-TiAl alloys the fully lamellar microstructure shows improved creep properties in comparison to other microstructural variants. For the adjustment of a fully lamellar microstructure a heat treatment in the α-single phase region is necessary. At such high temperatures grain growth can occur, which leads to a coarse grain size and therefore a reduced ductility. However, precipitates can hamper grain growth during the heat treatment, hence, leading to a finer grain size and an improved ductility. Therefore, this study covers the influence of precipitates on the grain growth of the additive manufactured Ti-Al-Nb-W-Si-C-Zr-B alloy. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) investigations were conducted on the powder of the mentioned alloy and the powder of two other alloys, with a slightly modified chemical composition. These investigations revealed that ζ-Ti5Si3 silicides are already present in the powder. Furthermore, specimens were produced with the additive manufacturing method of electron beam melting (EBM) and afterwards annealed between 1320 °C and 1400 °C, applying various annealing times. As a result of the EBM process a bimodal grain size distribution develops at the beginning of the heat treatment. Consequently, normal and abnormal grain growth occur as competing processes at short annealing times until the grain size distribution becomes unimodal. Both processes are highly influenced by the precipitates present in the microstructure. At longer annealing times the grain size distribution becomes unimodal, resulting in normal grain growth. Carbides are fully dissolved at longer annealing times and only the remaining silicides and borides are suppressing grain growth. These silicides were proven to be (Ti,Nb,Zr)5(Si,Al)3 silicides by means of atom probe tomography (APT) and also show a higher solubility for Nb, Zr, C and B. APT investigations on fully lamellar specimens further revealed that the alloying elements W, Si and C partition to the α2-phase, whereas Zr partitions to the γ-phase. Si, Zr and C show a strong preference for the phase to which they partition, which causes hampered transformation kinetics and further leads to a finer lamellar spacing and a stabilization of the α2/γ-lamellae against coarsening. This has a positive impact on the creep properties. Given that the elements cause solid solution hardening in the phases the creep properties are enhanced additionally.
Translated title of the contributionParticle controlled grain growth in γ-TiAl high temperature alloys for additive manufacturing
Original languageGerman
Awarding Institution
  • Montanuniversität
  • Clemens, Helmut, Co-Supervisor (internal)
  • Mayer, Svea, Supervisor (internal)
Award date25 Oct 2019
Publication statusPublished - 2019

Bibliographical note

embargoed until 28-05-2024


  • Additive Manufacturing
  • Electron Beam Melting (EBM)
  • powder
  • titanium aluminide
  • TiAl
  • grain growth
  • abnormal grain growth
  • normal grain growth
  • silicides
  • carbides
  • precipitations
  • atom probe tomography (APT)
  • Zr
  • Si
  • C

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