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Theory of liquid-phase sintering: model experiments on W-Ni-Fe heavy alloy system

Technical Report ·
OSTI ID:5002852
; ;
Current liquid-phase sintering theories predict negligible densification prior to the formation of a liquid phase. While these theories are fully applicable to a few model systems, their validity is questionable under more general circumstances. Experiments on a 93% W-Ni-Fe heavy alloy show that nearly 94% of the total shrinkage occurs prior to liquid formation. In this study, densification behavior has been studied by means of constant heating rate dilatometry. The microstructural evolution during sintering was monitored by quantitative microscopic examination of samples quenched from various temperatures during heating. The actual amount of densification that occurs prior to liquid formation is observed to be a function of both material process parameters. It was found that the contribution of solid-state-enhanced sintering to densification increases with slower heating rates. Thus, the role of rearrangement in densification during liquid-phase sintering is of less importance in common commercial systems (like W-Ni-Fe), where the additive phase exhibits solubility for the major phase. Rearrangement becomes important only at faster heating rates, especially in low solubility systems. This paper demonstrates that the mechanisms proposed by current theories are inadequate to explain densification behavior during liquid-phase sintering. Finally, an alternative approach to understanding liquid-phase sintering is suggested; and the new theory is outlined.
Research Organization:
Rensselaer Polytechnic Inst., Troy, NY (USA). Dept. of Materials Engineering
OSTI ID:
5002852
Report Number(s):
AD-A-190537/1/XAB
Country of Publication:
United States
Language:
English

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Related Subjects

36 MATERIALS SCIENCE
360101* -- Metals & Alloys-- Preparation & Fabrication
ALLOYS
COPPER
CRYSTAL STRUCTURE
DENSITY
ELEMENTS
FABRICATION
FLUIDS
GRAIN GROWTH
IRON ALLOYS
LIQUIDS
METALS
MICROSTRUCTURE
NICKEL ALLOYS
PHYSICAL PROPERTIES
SINTERING
SOLUBILITY
TRANSITION ELEMENTS
TUNGSTEN ALLOYS
TUNGSTEN BASE ALLOYS