Fatigue Crack Propagation in a (Co,Cr)-(Cr,Co)7C3 Composite.
Abstract
Fatigue crack propagation in the Co,Cr-(Cr,Co)7C3 in-situ composite has been characterized at room temperature in the as-grown condition and following post-solidification isothermal exposure or thermal cycling. The dependence of da/dN on delta K follows the Paris-Erdogan relation over the range delta K approx 10 MN/m(superscript 3/2) to 50 MN/m (superscript 3/2). Fracture toughness is low in the as-grown condition and is attributed to restricted matrix slip and a low stacking fault energy in the cobalt-rich matrix coupled with the absence of delamination. The heat treatments enhance fracture toughness and this is shown to be the result of precipitation of (Co,Cr)23C6 in the matrix and/or fiber coarsening with an attendant increase in the interfiber spacing. At the lower end of the delta K range fatigue cracking is primarily crystallographic (stage I) in nature. Stage II cracking, with the fracture surface normal to the stress axis, is operative at the upper end of the delta K range.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1978
- Accession Number
- ADA064851
Entities
People
- Alan Lawłey
- M. H. Abdel Latif
Organizations
- Drexel University