Study of the Dynamics of High Temperature Brittle Intergranular Fracture by Acoustic Emission

摘要

A study of high temperature brittle intergranular fracture (HTBIGF) in which acoustic emission (AE) data and fractography were used together to make deductions about the dynamics of fracture is discussed. The AE event rate was proportional to the rate of overall crack growth, and the average crack increment per AE event correlated well with spacing of striations observed on the fracture surface. The AE from HTBIGF was also compared with ambient temperature intergranular fracture and high temperature ductile fracture. HTBIGF generated about 50 percent of the emission of fully brittle fracture, and at least an order of magnitude more than that from ductile fracture. The observation of discrete bursts of AE of this magnitude, coupled with the striation on the fracture surface, indicates that HTBIGF takes place in discrete brittle steps. This is consistent with the segregation of sulfur as an embrittling species to the region of the crack tip, promoting stepwise decohesion, rather than a continuous crack growth process.