Accession Number : ADA295660

Title :   Effect of Impurities on the Electronic Structure of Grain Boundaries and Intergranular Cohesion in Tungsten.

Descriptive Note : Progress rept. FY93-FY94,

Corporate Author : ARMY RESEARCH LAB WATERTOWN MA MATERIALS DIRECTORATE

Personal Author(s) : Krasko, Genrich L.

PDF Url : ADA295660

Report Date : FEB 1995

Pagination or Media Count : 16

Abstract : The cohesion of a grain boundary (GB) is believed to be the controlling factor limiting the ductility of high-strength metallic alloys. and particularly those containing W. Intergranular embrittlement is usually associated with segregation of impurities at the GBs. Impurities present in ppm concentrations can result in a dramatic decrease in plasticity. This paper reviews recent results on both semi-empirical and first-principles modelling of the energetics and the electronic structures of impurities on a sigma3 (111) GB in W. Our calculations have shown that impurities, such as N, 0. R S, and Si, weaken the intergranular cohesion resulting in loosening of the GB. The presence of B and C on the contrary, enhances the interatomic interaction across the GB. The so-called site-competition effect should play an important role affecting impurity distribution in W GBs. Among the impurities analyzed, B in the GB has the lowest energy and thus would tend to displace other impurity atoms from the GB. Microalloying with 10-50 ppm B may be an effective way of improving tungsten's ductility. These results are important for understanding the fundamental physics of intergranular embrittlement. (MM)

Descriptors :   *HIGH STRENGTH ALLOYS, *ATOMS, *DUCTILITY, *TUNGSTEN, *GRAIN BOUNDARIES, *COHESION, STRUCTURAL PROPERTIES, ELECTRON DENSITY, EMBRITTLEMENT, IMPURITIES, SEGREGATION(METALLURGY), PLASTIC PROPERTIES, ENERGETIC PROPERTIES.

Subject Categories : Properties of Metals and Alloys
      Fabrication Metallurgy

Distribution Statement : APPROVED FOR PUBLIC RELEASE