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Effect of Cooling Rate on Fracture Behavior of Mill-Annealed Ti-6Al-4V

R. E. Lewis,J. G. Bjeletich,T. M. Morton,F.S. Crossley-1976-01-01
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TL;DRAbstract

Different cooling rates during duplex-annealing of mill-annealed Ti-6Al-4V 1-in. plate produce essentially indistinguishable microstructures and similar tensile properties, but significantly varying fracture properties. Duplex-annealing was performed by an initial heating at 1775°F (968.3°C) for 1/2 h and air-cooled; then reheated at 1450°F (787.4°C) for 1 h and cooled (1) by water quench, (2) in the air, or (3) in the furnace. Yield strength values, relatively unaffected by the annealing and cooling rate treatments, were grouped at 140±2 ksi (965 ± 14 MPa). Fracture toughness, however, varied from a low of 38 ksi √in. (42 MPa · √m) in the material with the fastest cooling rate (1) to nearly similar values of 50 and 51 ksi √in. (55 and 56 MPa · √m) for cooling rates (2) and (3), respectively. The stress-corrosion crack-growth, threshold stress intensities for the three cooling rates were (1) 34 ksi √in. (37.5 MPa · √m), (2) 30 ksi √in. (33 MPa · √m), and (3) 22 ksi √in (24.2 MPa · √m).

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Different cooling rates during duplex-annealing of mill-annealed Ti-6Al-4V 1-in. plate produce essentially indistinguishable microstructures and similar tensile properties, but significantly varying fracture properties. Duplex-annealing was performed by an initial heating at 1775°F (968.3°C) for 1/2 h and air-cooled; then reheated at 1450°F (787.4°C) for 1 h and cooled (1) by water quench, (2) in the air, or (3) in the furnace. Yield strength values, relatively unaffected by the annealing and cooling rate treatments, were grouped at 140±2 ksi (965 ± 14 MPa). Fracture toughness, however, varied from a low of 38 ksi √in. (42 MPa · √m) in the material with the fastest cooling rate (1) to nearly similar values of 50 and 51 ksi √in. (55 and 56 MPa · √m) for cooling rates (2) and (3), respectively. The stress-corrosion crack-growth, threshold stress intensities for the three cooling rates were (1) 34 ksi √in. (37.5 MPa · √m), (2) 30 ksi √in. (33 MPa · √m), and (3) 22 ksi √in (24.2 MPa · √m).

Keywords

Materials scienceAnnealing (glass)Fracture toughnessAir coolingComposite materialUltimate tensile strengthScanning electron microscopeMicrostructure

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