Strain aging in tungsten heavy alloys

Journal Article · Tue Jan 01 00:00:00 EST 1991 · Scripta Metallurgica; (United States)

DOI:https://doi.org/10.1016/0956-716X(91)90365-8· OSTI ID:5126396

Dowding, R J; Tauer, K J ^[1]

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1. Army Materials Research Agency, Watertown, MA (United States). Materials Technology Lab.

This paper reports on tungsten heavy alloys which are two-phase mixtures of body center cubic (BCC) tungsten surrounded by a face center cubic (FCC) matrix. The matrix is most often composed of nickel and iron in a ratio of 70:30 but, occasionally, the matrix may also contain cobalt or copper. Nickel, however, is always the primary matrix component. The tungsten heavy alloy is fabricated through powder metallurgy techniques. Elemental powders are blended, pressed to shape, and sintered. Depending upon the tungsten content, the sintering temperatures are usually in the range of 1450{degrees}C to 1525{degrees}C. These temperatures are high enough that, as a result, the matrix is at the liquid phase and the process is known as liquid phase sintering. At the liquid phase temperature, the matrix becomes saturated with tungsten, but this does not change the FCC character of the matrix. The sintering is usually done in a hydrogen atmosphere furnace in order to reduce the oxides on the tungsten powder surfaces and create clean, active surfaces which will enhance the adherence between the tungsten and the matrix. The hydrogen atmosphere also creates the presence of excess dissolved hydrogen in the alloy. It has been shown that the hydrogen degrades the toughness and ductility of the heavy alloy. A post-sintering vacuum heat treatment is generally required to insure that there is no residual hydrogen present. The as-sintered tensile strength of a 90% tungsten, 7% nickel, 3% iron alloy (90W) is in the range of 800 to 940 MPa and can be increased significantly by cold working, usually rolling or swaging. Swaging to reductions in area of 20% can result in tensile strengths of 1250 MPa or more. As the strength increases, the elongation, which may have been 30% or more, decreases to less than 5%.

• OSTI ID: 5126396
• Journal Information: Scripta Metallurgica; (United States), Vol. 25:1; ISSN 0036-9748
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MATRIX MATERIALS
BONDING
TUNGSTEN
TUNGSTEN ALLOYS
TENSILE PROPERTIES
BCC LATTICES
COBALT
COPPER
DUCTILITY
FCC LATTICES
HEAT TREATMENTS
HYDROGEN EMBRITTLEMENT
IRON
LIQUID PHASE EPITAXY
NICKEL
POWDER METALLURGY
RESIDUAL STRESSES
ALLOYS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CUBIC LATTICES
ELEMENTS
EMBRITTLEMENT
EPITAXY
FABRICATION
JOINING
MATERIALS
MECHANICAL PROPERTIES
METALLURGY
METALS
STRESSES
TRANSITION ELEMENTS
360103* - Metals & Alloys- Mechanical Properties
360101 - Metals & Alloys- Preparation & Fabrication