MULTI-PHASE Cr-BASED ALLOYS FOR AGGRESSIVE HIGH TEMPERATURE ENVIRONMENTS

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Attractive high-temperature mechanical properties and oxidation/hot corrosion resistance have been achieved in a new family of Cr{sub 2}Ta-reinforced Cr alloys. However, inadequate room-temperature toughness remains a key challenge, with the best Cr-Cr{sub 2}Ta alloys exhibiting only modest toughness in the range of 12-14 MPa m{sup 1/2}. The addition of MgO has been shown to significantly improve the room-temperature mechanical properties of unalloyed Cr and was investigated as a means for improving the room-temperature mechanical properties of the Cr-Cr{sub 2}Ta alloys. Microstructural analysis of a series of Cr and Cr-6MgO base alloys was used to investigate the proposed ductilization mechanism of ... continued below

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Brady, MP August 24, 2001.

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Attractive high-temperature mechanical properties and oxidation/hot corrosion resistance have been achieved in a new family of Cr{sub 2}Ta-reinforced Cr alloys. However, inadequate room-temperature toughness remains a key challenge, with the best Cr-Cr{sub 2}Ta alloys exhibiting only modest toughness in the range of 12-14 MPa m{sup 1/2}. The addition of MgO has been shown to significantly improve the room-temperature mechanical properties of unalloyed Cr and was investigated as a means for improving the room-temperature mechanical properties of the Cr-Cr{sub 2}Ta alloys. Microstructural analysis of a series of Cr and Cr-6MgO base alloys was used to investigate the proposed ductilization mechanism of nitrogen gettering by a MgCr{sub 2}O{sub 4} spinel phase, which forms during consolidation of Cr and MgO powders. Nitride and related impurity precipitates have been linked to reduced ductility in Cr at room-temperature. Surprisingly, nitride (and carbide) impurity precipitates were found i n hot-pressed Cr-6 MgO base alloys despite room-temperature tensile ductility of 5%. These precipitates were found adjacent to MgO/MgCr{sub 2}O{sub 4} particles and were somewhat more blunt than those observed in unalloyed Cr. The addition of TiO{sub 2} to unalloyed Cr resulted in similar morphological changes to the nitride and carbide impurity precipitates; however, the TiO{sub 2} dispersed alloy was brittle at room-temperature. Why MgO dispersions are effective in ductilizing Cr, but others such as TiO{sub 2} are not, is not clear and is the subject of ongoing study. Efforts to introduce the effect in Cr-Cr{sub 2}Ta-MgO alloys were not successful, and it was concluded that significant modification of the Cr matrix phase in the Cr-Cr{sub 2}Ta alloys by macroalloying is necessary to improve room-temperature mechanical properties. Preliminary attempts at macroalloying with Fe were quite successful and resulted in an increase in room-temperature toughness to 18-20 MPa m{sup 1/2} in Cr-C r{sub 2}Ta + Fe alloys.

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  • Fossil Energy Advanced Research Materials 2001 Review, Knoxville, TN (US), 04/30/2001--05/02/2001

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  • Report No.: P01-111636
  • Grant Number: AC05-00OR22725
  • Office of Scientific & Technical Information Report Number: 788536
  • Archival Resource Key: ark:/67531/metadc723654

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  • August 24, 2001

Added to The UNT Digital Library

  • Sept. 29, 2015, 5:31 a.m.

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  • March 30, 2016, 5:38 p.m.

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Brady, MP. MULTI-PHASE Cr-BASED ALLOYS FOR AGGRESSIVE HIGH TEMPERATURE ENVIRONMENTS, article, August 24, 2001; Tennessee. (digital.library.unt.edu/ark:/67531/metadc723654/: accessed December 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.