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Title: Characterization of Cast U-6Nb Sprue

Abstract

Shape casting of uranium-6 wt. pct. niobium (U-6Nb) can produce near net shape components, providing a higher efficiency alternative to wrought processing. A substantial amount of materials characterization in support of direct casting process development has been performed and documented. This supplemental work describes the mechanical behavior of the hot top region of shape cast U-6Nb in order to determine and quantify the effect of casting defects, such as gas porosity and inclusions, on U-6Nb performance. The annular hot top region of a hollow cylindrical casting was sectioned and metallographic, bend, and tensile specimen blanks were machined from various locations around the part. Porosity ranging from 5-13% was observed, depending on the region sampled (i.e. top, bottom or outer portion of casting). Optical and scanning electron microscopy showed prior gamma grain size ranging from <10 up to 300 μm. There are uranium oxide and carbide inclusions present at the 50-150 μm size range; these were identified based on their morphology and color. Martensitic herringbone twinning and a lamellar structure was observed as well as what may be platelets of retained $γ$° in a matrix of $α$". The tensile test specimens were lathe machined and subjected to a low temperature artificialmore » aging heat treatment consisting of a hold at 200°C for 2 hours, followed by furnace cooling in a helium atmosphere. Quasi-static mechanical tests showed a ductile void coalescence fracture mode with failure strains from 2-16% and a linear increase in stress up to approximately 400 MPa. Prior studies on low porosity regions sampled from a similar casting reported a failure strain of 15-21% in the artificially aged condition. The significant loss in ductility in the hot top region is attributed to increased porosity.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [2];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. LLawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1544947
Report Number(s):
LLNL-TR-771462
962703
DOE Contract Number:  
AC52-07NA27344
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Torres, S. G., Wu, A. S., Urabe, D. S., Freeman, D. C., Lotscher, J. P., Ancheta, D. S., Otting, D. M., Beith, K. S., and Campbell, G. H. Characterization of Cast U-6Nb Sprue. United States: N. p., 2019. Web. doi:10.2172/1544947.
Torres, S. G., Wu, A. S., Urabe, D. S., Freeman, D. C., Lotscher, J. P., Ancheta, D. S., Otting, D. M., Beith, K. S., & Campbell, G. H. Characterization of Cast U-6Nb Sprue. United States. doi:10.2172/1544947.
Torres, S. G., Wu, A. S., Urabe, D. S., Freeman, D. C., Lotscher, J. P., Ancheta, D. S., Otting, D. M., Beith, K. S., and Campbell, G. H. Mon . "Characterization of Cast U-6Nb Sprue". United States. doi:10.2172/1544947. https://www.osti.gov/servlets/purl/1544947.
@article{osti_1544947,
title = {Characterization of Cast U-6Nb Sprue},
author = {Torres, S. G. and Wu, A. S. and Urabe, D. S. and Freeman, D. C. and Lotscher, J. P. and Ancheta, D. S. and Otting, D. M. and Beith, K. S. and Campbell, G. H.},
abstractNote = {Shape casting of uranium-6 wt. pct. niobium (U-6Nb) can produce near net shape components, providing a higher efficiency alternative to wrought processing. A substantial amount of materials characterization in support of direct casting process development has been performed and documented. This supplemental work describes the mechanical behavior of the hot top region of shape cast U-6Nb in order to determine and quantify the effect of casting defects, such as gas porosity and inclusions, on U-6Nb performance. The annular hot top region of a hollow cylindrical casting was sectioned and metallographic, bend, and tensile specimen blanks were machined from various locations around the part. Porosity ranging from 5-13% was observed, depending on the region sampled (i.e. top, bottom or outer portion of casting). Optical and scanning electron microscopy showed prior gamma grain size ranging from <10 up to 300 μm. There are uranium oxide and carbide inclusions present at the 50-150 μm size range; these were identified based on their morphology and color. Martensitic herringbone twinning and a lamellar structure was observed as well as what may be platelets of retained $γ$° in a matrix of $α$". The tensile test specimens were lathe machined and subjected to a low temperature artificial aging heat treatment consisting of a hold at 200°C for 2 hours, followed by furnace cooling in a helium atmosphere. Quasi-static mechanical tests showed a ductile void coalescence fracture mode with failure strains from 2-16% and a linear increase in stress up to approximately 400 MPa. Prior studies on low porosity regions sampled from a similar casting reported a failure strain of 15-21% in the artificially aged condition. The significant loss in ductility in the hot top region is attributed to increased porosity.},
doi = {10.2172/1544947},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {4}
}