Beta decomposition processes in Hf-rich Hf--Nb alloys
- Sandia Labs., Albuquerque, NM
The decomposition of the bcc ..beta..-phase by both athermal and isothermal processes has been investigated in Hf-rich Hf--Nb alloys. An all ..beta..-phase structure is retained in chill-cast alloys containing 30 to 50 at.% Nb (Cb), although electron diffraction streaking effects and the behavior of the temperature coefficient of electrical resistivity indicate the presence of a bcc lattice instability similar to that reported in solute lean Ti and Zr alloys. Aging a Hf/sub 0/./sub 65/Nb/sub 0/./sub 35/ alloy at 400 and 600/sup 0/C resulted in the direct precipitation of a fine dispersion of ..cap alpha..-phase needles; this morphology differs from the discs of transition ..cap alpha.. (..cap alpha../sub t/) which Carpenter et al observed in Nb-rich Nb/sub 0/./sub 68/Hf/sub 0/./sub 32/. During continued aging, the needles grow selectively to form colonies or groups of needles in which both the individual needles and the groups of needles have major axes aligned along (110)/sub ..beta../ type directions. The initial ..cap alpha..-phase particles exhibit the Burgers orientation relationship with the parent matrix; continued aging changes the electron diffraction patterns in a way that is similar to that observed in aged Ti--Mo and Ti--Mo--Al alloys where they were attributed to the ..cap alpha..-phase having a different crystallographic relationship to the ..beta..-phase (Type 2 ..cap alpha..-phase). The observed changes in the electron diffraction patterns of aged Hf/sub 0/./sub 65/Nb/sub 0/./sub 35/ cannot be described as resulting from strained Burgers ..cap alpha..-phase.
- OSTI ID:
- 6428246
- Journal Information:
- Metall. Trans., A; (United States), Journal Name: Metall. Trans., A; (United States) Vol. 9:5; ISSN MTTAB
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102* -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
360104 -- Metals & Alloys-- Physical Properties
AGING
ALLOYS
CARBON ADDITIONS
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
DIAGRAMS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
HAFNIUM ALLOYS
HARDNESS
IRON ALLOYS
LATTICE PARAMETERS
MARTENSITE
MECHANICAL PROPERTIES
MICROHARDNESS
NIOBIUM ALLOYS
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES