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):

Report Date:

1995-02-01

Pagination or Media Count:

16.0

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 tungstens ductility. These results are important for understanding the fundamental physics of intergranular embrittlement. MM

Subject Categories:

  • Properties of Metals and Alloys
  • Fabrication Metallurgy

Distribution Statement:

APPROVED FOR PUBLIC RELEASE