Morphological changes of. gamma. -prime precipitates in nickel-base superalloy single crystals

Thesis/Dissertation · Sat Dec 31 23:00:00 EST 1983

OSTI ID:5952222

MacKay, R A

Changes in the morphology of the ..gamma..' precipitate were examined during tensile creep at temperatures between 927 and 1038/sup 0/C in (001)-oriented single crystals of a Ni-Al-Mo-Ta superalloy. In this alloy, which has a large negative misfit of -0.80 pct., the ..gamma..' particles link together during creep to form platelets, or rafts, which are aligned with their broad faces perpendicular to the applied tensile axis. The dimensions of the ..gamma.. and ..gamma..' phases were measured as directional coarsening developed and were related to creep time and creep strain in an attempt to trace the changing morphology under various stress levels. In addition, the effects of initial microstructure, as well as slight compositional variations, were related to raft development and creep properties. The results showed that directional coarsening of ..gamma..' began during primary creep, and under certain conditions, continued to develop after the onset of steady-state creep. The length of the rafts increased linearly with time up to a plateau region. The thickness of the rafts, however, remained constant up through the onset of tertiary creep; this is a clear indication of the stability of the finely-spaced ..gamma..-..gamma..' lamellar structure.

• Research Organization: Case Western Reserve Univ., Cleveland, OH (USA)
• OSTI ID: 5952222
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOYS
ALUMINIUM ALLOYS
CRYSTAL STRUCTURE
HEAT RESISTANT MATERIALS
HEAT RESISTING ALLOYS
MATERIALS
MOLYBDENUM ALLOYS
MORPHOLOGY
NICKEL ALLOYS
NICKEL BASE ALLOYS
PRECIPITATION
SEPARATION PROCESSES
TANTALUM ALLOYS
VERY HIGH TEMPERATURE