Molecular Orbitals and the Atomistics of Fracture.
Abstract
If a metal contains very few inpurities and is mechanically tested in an inert environment, its fracture mode will be either transgranular cleavage or transgranular ductile microvoid coalescence. If, however, the metal is of commercial purity, the brittle fracture mode can switch from ceavage to intergranular separation. This transition is undesirable because intergranular fracture is generally a very low energy process. The occurence of intergranular fracture in a specific situation will depend on a number of metallurgical variables: grain size, yield strength, test temperature, and notch radius. However, in all reported cases, one observation is common. Impurities which have a very low solubility in the bulk have segregated to the grain boundaries and weakened them. The bulk concentration of these impurities need only be several hundred ppm for grain boundary concentrations of 5-10 atomic percent to be observed. Examples of this impurity induced weakening of grain boundaries include sulfur in iron and nickel, phosphorus, tin, and antimony in steel, bismuth in copper, and oxygen in refractory metals. If the environment is not inert, intergranular separation may occur even though the fracture mode in an inert environment would be transgranular. One much studied example of this is hydrogen embrittlement.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 10, 1982
- Accession Number
- ADA111398
Entities
People
- C. L. Briant
- K. H. Johnson
- M. E. Eberhardt
- R. P. Messmer
Organizations
- University of Pennsylvania