Study of iridium and iridium--tungsten alloys for space radioisotopic heat sources. [Up to 4% W; fabrication; microstructure; tensile; oxidation; compatibility; fractures]
The physical and mechanical properties of iridium and iridium-tungsten alloys containing up to 4% tungsten were evaluated as potential cladding materials in space isotopic heat sources. The iridium--tungsten alloys are readily fabricable and are compatible with graphite, low-pressure oxygen, and simulated heat source environments up to at least 1300/sup 0/C. The solubility of oxygen and carbon in the alloys appears to be quite low, at a level of 5 ppM for oxygen and 10 ppM for carbon up to 1300/sup 0/C. The Ir--2% W has good oxidation resistance below 1000/sup 0/C. No internal oxidation or grain-boundary penetration was observed in this alloy. Also, alloying with 2% tungsten raises the recrystallization temperature of iridium by 400/sup 0/C and retards the grain growth at high temperatures. Tensile properties were determined as a function of test temperature up to 1400/sup 0/C. Alloying with tungsten increases the yield strength and slightly lowers the ductility. The ductilities of the alloys increase steadily with test temperature. In connection with this increase, the fracture mode changes from grain-boundary separation to transgranular fracture at temperatures around 800/sup 0/C and finally to ductile rupture with close to 100% reduction in area above 1000/sup 0/C. The Ir--2% alloy has the best toughness because of its high strength and good ductility at 1370/sup 0/C. The yield strength and fracture behavior of iridium and iridium--tungsten alloys were found to be very sensitive to trace impurities with concentrations in the ppM range. 21 tables, 20 figures.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 7321970
- Report Number(s):
- ORNL-5240; TRN: 77-005712
- Country of Publication:
- United States
- Language:
- English
Similar Records
Effect of thorium additions on metallurgical and mechanical properties of Ir-0. 3 pct W alloys
Metallurgical and mechanical properties of thorium-doped Ir-0. 3% W alloys
Related Subjects
07 ISOTOPES AND RADIATION SOURCES
IRIDIUM
IRIDIUM BASE ALLOYS
RADIOISOTOPE HEAT SOURCES
CLADDING
TUNGSTEN ALLOYS
COMPATIBILITY
DUCTILITY
FABRICATION
FRACTURE PROPERTIES
GRAIN GROWTH
MATERIALS
OXIDATION
RECRYSTALLIZATION
TENSILE PROPERTIES
ALLOYS
CHEMICAL REACTIONS
DEPOSITION
ELEMENTS
HEAT SOURCES
IRIDIUM ALLOYS
MECHANICAL PROPERTIES
METALS
PLATINUM METAL ALLOYS
PLATINUM METALS
REFRACTORY METALS
SURFACE COATING
TRANSITION ELEMENTS
NESDPS Office of Nuclear Energy Space and Defense Power Systems
360100* - Metals & Alloys
070300 - Isotopic Power Supplies