Phase equilibria effects on the enhanced liquid phase sintering of tungsten-copper

Journal Article · Mon Nov 01 04:00:00 EST 1993 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02646516· OSTI ID:5730503

Johnson, J L; German, R M ^[1]

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1. Pennsylvania State Univ., Univ. Park, PA (United States)

The sintering behavior and mechanical properties of W-Cu are improved by the addition of elements that have solubility for W, e.g., Co, Ni, Fe, and Pd. The degree of enhancement with small concentrations of additive is dependent on specific phase diagram features, and the ranking of effectiveness does not follow the trend observed for the activated solid-state sintering of W. These observations are explained through a combination of liquid phase sintering and activated sintering theories that considers the combined W, Cu, and activator phase equilibria effects. In small concentrations, Ni and Pd have little effect on densification because they go into solution with Cu, resulting in only a slight increase in the solubility of W in the liquid phase. In this case, the sintered density, strength, hardness increase with increasing additive concentration due to enhanced densification through solution-reprecipitation. Cobalt and Fe are the most effective activators due to their limited solubility in Cu and the formation of a stable intermetallic phase with W at the sintering temperature. This promotes the formation of a high-diffusivity interboundary layer which enhances solid-state sintering of the tungsten grains at temperatures at which a liquid phase is present. With Co and Fe additions, the sintered density, strength, and hardness peak with activator concentrations of 0.35 to 0.5 wt pct. An evaluation of models for activated solid-state sintering and liquid phase sintering indicates a substantial solid-state contribution to densification when a high-diffusivity interboundary layer is present and the solubility of W in the liquid phase is small.

• OSTI ID: 5730503
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 24:11; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360101* -- Metals & Alloys-- Preparation & Fabrication
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
COBALT
COPPER ALLOYS
DENSITY
DIAGRAMS
ELEMENTS
FABRICATION
HARDNESS
INTERMETALLIC COMPOUNDS
IRON
MECHANICAL PROPERTIES
METALLURGICAL EFFECTS
METALS
NICKEL
PALLADIUM
PHASE DIAGRAMS
PHASE STUDIES
PHYSICAL PROPERTIES
PLATINUM METALS
SINTERING
SOLUBILITY
TRANSITION ELEMENTS
TUNGSTEN ALLOYS