The in-situ TEM observation of microcrack nucleation in titanium aluminide

Journal Article · Mon Aug 01 00:00:00 EDT 1994 · Scripta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-716X(94)90283-6· OSTI ID:7086773

Zhang, Y; Wang, Y B; Chu, W Y; Hsiao, C M ^[1]

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1. Univ. of Science and Technology, Beijing (China). Dept. of Materials Physics

Rice and Thomson assumed that the emissions of dislocation from a crack tip would lead to plastic blunting of the crack tip, and the materials were categorized as intrinsically cleavage if a condition for decohesion of the crystal plane ahead of the crack was reached before those for dislocation emission from the crack. For the ductile material, the TEM in-situ observation showed that a main crack tip might still be sharp after the dislocations had been emitted from the crack tip and the dislocation free zone (DFZ) had been formed; thus, the local stress near the crack tip in the DFZ was high enough to equal the cohesive strength, and then a microcrack with size of nanometers nucleated in the DFZ. The microcracks initiated in the DFZ would blunt into voids through the movement of the existing dislocation and/or those emanated from the crack tip and the nearby dislocation source. The discontinuous void resulting from the blunting of the microcracks in the DFZ would link with each other and with the main crack, resulting in ductile fracture. For brittle materials, the authors wonder whether the DFZ also exist and whether a microcrack with the size of nanometers nucleated preferably in the DFZ. If such occurred, the microcrack initiated in the DFZ should propagate into a cleavage crack rather than blunt into void. The goal of the present work was to check the possibility of dislocation emissions, DFZ formation, and initiation and propagation of a microcrack in the DFZ for the brittle material. For the titanium aluminides, e.g., Ti-24Al-11Nb or TiAl, a brittle fracture occurred by slow stable crack growth characterized by a well-defined resistance curve, i.e., the resistance of the cleavage crack propagation increased with crack growth.

• OSTI ID: 7086773
• Journal Information: Scripta Metallurgica et Materialia; (United States), Vol. 31:3; ISSN 0956-716X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
CRACK PROPAGATION
NIOBIUM ALLOYS
TITANIUM BASE ALLOYS
DISLOCATIONS
EXPERIMENTAL DATA
MECHANICAL TESTS
TRANSMISSION ELECTRON MICROSCOPY
ALLOYS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DATA
ELECTRON MICROSCOPY
INFORMATION
LINE DEFECTS
MATERIALS TESTING
MICROSCOPY
NUMERICAL DATA
TESTING
TITANIUM ALLOYS
360103* - Metals & Alloys- Mechanical Properties