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Synthesis, consolidation and properties of niobium(5) silicon(3) and laminated niobium(5) silicon(3)/niobium composites

Kajuch, Jan
http://rave.ohiolink.edu/etdc/view?acc_num=case1060712767

Abstract Details

1993, Doctor of Philosophy, Case Western Reserve University, Materials Science and Engineering.
Formation of Nb5Si3 from elemental Nb and Si powders was studied using a mechanical alloying (MA) process. It is shown that compound formation proceeds by a self-propagating exothermic reaction in both interrupted and continuous milling processes, but in the interrupted process reaction is completed in a much shorter time. The kinetics of compound formation in both processes were investigated. On the basis of experimental results, a kinetic model was proposed for the formation of Nb5Si3 via the interrupted and continuous milling process. It is suggested that precipitation of Nb5Si3 particles during cooling in the interrupted process was responsible for the exothermic reaction when milling resumed, while self-propagating high temperature synthesis (SHS) is the driving force for the compound formation in the continuous milling process. In addition to the MA process, the Reactive Sintering (RS) technique was employed for the production of the monolithic Nb5Si3 and composite Nb5Si3/Nb compacts from elemental Nb and Si powder mixtures. The homogeneity of the Nb-Si powder blend, particle size and the heating rates significantly affected microstructures produced after hot-press consolidation. Model laminates of mechanically alloyed Nb5Si3 and nominally pure niobium were prepared via vacuum hot pressing and structural adhesive bonding. Significant (5 fold) toughness increases were obtained in the laminates produced by both the diffusion and structural adhesive bonding method. The mechanical behavior of the Nb reinforcement in Nb5Si3/Nb laminates was also investigated under a variety of stress states and test temperatures. Tests were conducted at room temperature (298 K) and liquid nitrogen (77 K) on as-received Nb foils, on Nb5Si3/Nb laminates, Nb foils extracted from the hot-pressed laminates, and those simply exposed to vacuum at high temperature (1473 K/5 h). It is shown that Nb grain size, solid solution of Si in Nb, degree of constraint, and test temperature significantly affect the mechanical behavior of Nb. Unconstrained Nb foils failed in a ductile manner at room temperature, while a mixture of cleavage and ductile fracture was exhibited by the constrained Nb present in the diffusion bonded laminates. A similar ductile-to-brittle transition in fracture appearance was observed in tests conducted at 77 K, however the toughness of the laminates was relatively unaffected by this change in fracture mode. (Abstract shortened by UMI.)
John Lewandowski (Advisor)
202 p.
Engineering, Materials Science
Niobium, silicon composites; Synthesis and consolidation

Recommended Citations

Citations

  • Kajuch, J. (1993). Synthesis, consolidation and properties of niobium(5) silicon(3) and laminated niobium(5) silicon(3)/niobium composites [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1060712767

    APA Style (7th edition)

  • Kajuch, Jan. Synthesis, consolidation and properties of niobium(5) silicon(3) and laminated niobium(5) silicon(3)/niobium composites. 1993. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1060712767.

    MLA Style (8th edition)

  • Kajuch, Jan. "Synthesis, consolidation and properties of niobium(5) silicon(3) and laminated niobium(5) silicon(3)/niobium composites." Doctoral dissertation, Case Western Reserve University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060712767

    Chicago Manual of Style (17th edition)

case1060712767
566
© 1993, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.