The brittle-ductile transition in gamma-TiAl single crystals

Journal article

Fracture tests in the temperature range 20-800°C were performed on single crystal γ-TiAl (Ti-54.7% Al) specimens. All tests were by four-point bending; the specimens were precracked by spark discharge so that Klc could be determined. Two orientations of specimens were used, chosen so that the influence on the fracture behaviour of the 'ordinary' dislocations (b = a/2 < 110]) and 'superdislocations' (b = a < 101]) could be distinguished. Klc rises steadily from ∼ 1.5 MPa m1/2 at 20°C to ∼ 3.5 MPa m1/2 at ∼ 600°C for both specimen types. The brittle-ductile transition (BDT) temperature, above which specimens yielded rather than fracturing, is in the range 600-700°C, and varies with strain rate. The strain rate variation allows activation energies for the BDT process to be determined: 1.4 eV for the 'ordinary' dislocation specimens and 5.9 eV for the 'superdislocation' specimens. Below ∼ 300°C, fracture is by cleavage from the precrack; above ∼ 300°C, stable crack growth occurs before final fast cleavage fracture.

Authors: Booth, A; Roberts, S

• Publication status: Published
• Journal: ACTA MATERIALIA
• Volume: 45
• Issue: 3
• Pages: 1045-1053
• Publication date: 1997-03-01
• DOI: 10.1016/S1359-6454(96)00230-3
• ISSN: 1359-6454