The effect of microstructure on the fracture resistance of Nb-Cr-Ti in situ composites

Journal Article · Tue Mar 03 04:00:00 EST 1998 · Scripta Materialia

DOI:https://doi.org/10.1016/S1359-6462(97)00562-9· OSTI ID:619468

Davidson, D L; Chan, K S ^[1]

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1. Southwest Research Inst., San Antonio, TX (United States)

Several years ago, composites formed in situ in Nb-Cr-Ti alloys were explored as high temperature materials. These composites demonstrated reasonable fracture toughness because of the ductile matrix, and because of the presence of intermetallic particles of Cr{sub 2}Nb, they were expected to show reasonably good high temperature creep resistance and strength. Although ambient temperature fracture toughness values for the composites were considerably better than those of the intermetallic, they were still below the values that should be attained in this system, given the high toughness of the matrix alloy. The values of fracture toughness expected, based on a modulus modified rule of mixtures, are in the range K{sub Q} {approx} 40 to 60 MPa{radical}m for intermetallic volume fractions of 35 to 65 percent. In trying to understand why the fracture toughness of these composites were so far below those that might be achieved, detailed studies of the interaction of the crack with the microstructure were performed. That work indicated that the intermetallic particles were fracturing in the vicinity of the crack tip, and that the dispersion of particles was not uniform. A technique was sought to reduce the size of the intermetallic particles so that particle fracture would not occur during fracture and improve their dispersion. A refinement of the microstructure was also expected to increase the fracture toughness, and perhaps improve the resistance to fatigue crack growth. To reduce the size of the intermetallic in cast materials, the solidification rate would have to be increased. Thus, rapid solidification of the alloys from the melt was pursued as a promising method to refine the microstructure and increase fracture properties of the composites. This paper compares fracture properties of the rapidly solidified material with those previously found for slowly cooled materials.

• OSTI ID: 619468
• Journal Information: Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 7 Vol. 38; ISSN 1359-6462; ISSN SCMAF7
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM ALLOYS
COMPOSITE MATERIALS
FRACTURE PROPERTIES
INTERMETALLIC COMPOUNDS
MICROSTRUCTURE
NIOBIUM ALLOYS
TITANIUM ALLOYS