Experimental assessment of crack-tip dislocation emission models for an Al[sub 67]Cr[sub 8]Ti[sub 25] intermetallic alloy

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

OSTI ID:6590728

Meng, W G; Wert, J A ^[1]; Vaudin, M D ^[2]; Bartholomeusz, M F ^[3]

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1. Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering
2. NIST, Gaithersburg, MD (United States). Ceramics Division
3. Reynolds Metals Co., Richmond, VA (United States)

A potential explanation for the cleavage fracture of intermetallic alloys with low or moderate critical resolved shear stress (CRSS) is the existence of an energy barrier for crack-tip dislocation emission, as described by models that analyze the energetics of dislocation emission from crack tips. In the present study, an intermetallic alloy with the L1[sub 2] crystal structure, Al[sub 67]Cr[sub 8]Ti[sub 25], has been used to experimentally assess the predictions of the Rice-Thomson dislocation-emission model. The assessment is performed in two ways. First, model predictions of a fracture mode transition at elevated temperature are compared with experimental results. Bend tests performed at temperatures in the range of 293 to 1,061 K reveal that the fracture model of Al[sub 67]Cr[sub 8]Ti[sub 25] changes from predominantly cleavage fracture at room temperature to a mixed mode of cleavage and intergranular fracture at intermediate temperatures and then to predominantly intergranular fracture at high temperatures. The observed cleavage-to-intergranular fracture transition temperature is approximately 800 K, in good agreement with the model prediction. Second, model predictions of the effect of grain orientation on the fracture mode are compared with experimental results. Electron backscatter patterns and fractographic techniques were used to analyze the grain orientations and fracture modes of grains on the fracture surfaces of specimens fractured at four temperatures in the range 439 to 1,061 K. Experimental results reveal a correlation between fracture mode and slip system orientation relative to the crack, in good agreement with dislocation emission model predictions.

• OSTI ID: 6590728
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 26:2; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM BASE ALLOYS
CHROMIUM ALLOYS
DATA
EXPERIMENTAL DATA
FRACTURE MECHANICS
FRACTURE PROPERTIES
INFORMATION
INTERMETALLIC COMPOUNDS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
MECHANICS
NUMERICAL DATA
TITANIUM ALLOYS