Accession Number:

ADA235199

Title:

Lifetimes and Failure Mechanisms of W/Re Hairpin Filaments

Descriptive Note:

Technical rept.

Corporate Author:

AEROSPACE CORP EL SEGUNDO CA LAB OPERATIONS

Personal Author(s):

Report Date:

1991-02-26

Pagination or Media Count:

30.0

Abstract:

A life test of tungsten or tungsten alloys hairpin filaments used in a high-reliability electron beam instrument has been carried out to improve knowledge of filament life and failure mechanisms as a function of temperature. These filaments are made of non-sag tungsten3 rhenium W3 Re wire. A steep reduction in filament life is observed at 2760 K which is not predicted by models which assume thermal evaporation as the principal failure mechanism. Failure analysis of the filaments shows that the sudden loss of life at 2760 K is the result of localized formation of hot spots caused by the accumulation of voids at grain boundaries. Examination of the crystal growth rates indicates that the recrystallization temperature, occurs near 2760 K for the non-sag W3 Re wire used in these filaments. This suggests that void accumulation acts as the principal life-limiting failure mechanism spontaneous recrystallization at 2760 K increases the rate of voids growth and causes a severe reduction of filament life.

Subject Categories:

  • Electrooptical and Optoelectronic Devices
  • Metallurgy and Metallography

Distribution Statement:

APPROVED FOR PUBLIC RELEASE