Influence of Homogenization on the Mechanical Properties and Microstructure of the U-10Mo Alloy

Technical Report · Tue Apr 01 04:00:00 EDT 2014

DOI:https://doi.org/10.2172/1339936· OSTI ID:1339936

Nyberg, Eric A. ^[1]; Joshi, Vineet V. ^[1]; Lavender, Curt A. ^[1]; Paxton, Dean M. ^[1]; Burkes, Douglas ^[1]

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1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

In Phase 1 of this study, the mechanical properties of as-cast, depleted uranium alloyed with 10 weight percent molybdenum alloy (U-10Mo) samples were evaluated by high-temperature compression testing. Compression testing was conducted at three strain rates over a temperature range of 400 to 800°C. The results indicated that with increasing test temperature, the material flow stress decreases and the material becomes more sensitive to strain rate. In addition, above the eutectoid transformation temperature (~ 550°C), the drop in material flow stress is prominent and shows a strain-softening behavior, especially at lower strain rates. In the second part of this research, we studied the effect that homogenization heat treatment had on the high temperature mechanical properties and microstructure of the cast U-10Mo alloy. Various homogenization times and temperatures were studied ranging between 800 and 1000°C for 4 to 48 hours. Based on the microstructural response in this homogenization study, a heat treatment cycle of 800°C for 24 hours and another at 1000°C for 16 hours were selected as the times at temperature to achieve a fully homogenized sample. Samples from these conditions were then compression tested at a variety of temperatures ranging from 500 to 800°C. The microstructure of these samples were compared to the as-cast samples and to a baseline sample homogenized at 1000°C for 16 hours. The results indicate that below the eutectoid temperature (~ 550°C) all three samples showed strain hardening and followed similar trends. Above the eutectoid temperature, the yield strength of the material decreased linearly. For the as-cast sample and the sample homogenized at 800°C for 24 hours, the n-values were negative, whereas for the samples homogenized at 1000°C for 16 hours the material exhibited a perfectly plastic behavior. The as-cast sample, heat treated at 800°C for 24 hours, showed significant lamellar structure transformation that seems to have precipitated along the grain boundaries in the molybdenum-lean regions. In similar samples, homogenized at 800°C for 24 hours and tested at 650°C, the backscattered-electron scanning electron microscopy images revealed a composite structure of lamellar phase and nano-scale molybdenum-rich and -lean phases along the grain boundaries. These phases may have been responsible for the lowering of the flow stress in the material observed in the Phase 1 work. For comparison, the samples homogenized at 1000°C for 16 hours showed no such transformations.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1339936
• Report Number(s): PNNL--23348; DN3001010
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
COMPARATIVE EVALUATIONS
COMPRESSION
DEPLETED URANIUM
EUTECTOIDS
FLOW STRESS
GRAIN BOUNDARIES
HEAT TREATMENTS
LAMELLAE
MICROSTRUCTURE
MOLYBDENUM ALLOYS
PHASE STUDIES
PHASE TRANSFORMATIONS
PLASTICITY
PRECIPITATION
STRAIN HARDENING
STRAIN RATE
STRAIN SOFTENING
STRAINS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
URANIUM BASE ALLOYS
YIELD STRENGTH