The interaction between deformation, fracture initiation and fracture propagation in two phase Co-CoAl alloys

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Fracture initiation and propagation in two phase alloys containing fairly large volume fractions of nonplastically deforming inclusions have been analyzed. The Argon, Im and Safoglu treatment of fracture initiation of elastic inclusions as a result of back stresses resulting from strain accommodation of the phases has been extended to relatively large volume fractions of second phase. This allows calculation of the distribution of fractured particles as a function of alloy strain provided the fracture stress of the elastically deforming phase is known. The analysis has been applied to the Co-CoAl two phase alloy for volume fractions of CoAl ranging from about two to twenty-five pct. Quantitative metallographic analysis of fractured specimens indicates very good agreement between the measured fraction of fractured particles and those predicted from the theory without recourse to any adjustable parameters. Critical crack propagation in alloys of this type can also be analyzed on the basis of a fracture mechanics approach of Rice which was modified to consider that the crack spacing decreases with increasing strain due to cumulative hard phase cracking. The tensile strengths of the alloys can then be predicted with recourse to one adjustable parameter which varies with hard phase volume fraction. The deduced variation of this parameter with hard phase volume fraction, however, is as expected. © 1980 American Society for Metals and the Metallurgical Society of AIME.

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Metallurgical Transactions A