The effect of niobium morphology on the fracture behavior of MoSi[sub 2]/Nb composites

Journal Article · Tue Jan 31 23:00:00 EST 1995 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

OSTI ID:6607445

Alman, D E ^[1]; Stoloff, ^[2]

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1. Bureau of Mines, Albany, OR (United States). Albany Research Center
2. Rensselaer Polytechnic Inst., Troy, NY (United States). Materials Engineering Dept.

The morphology of the niobium reinforcement added to MoSi[sub 2] affected the fracture behavior (and hence toughness) of MoSi[sub 2]/20 vol pct Nb composites. The addition of discontinuous random niobium in the form of particles or short fibers deflected cracks that propagated through the MoSi[sub 2] matrix. However, this did not result in any improvements in toughness, as matrix cracks preferentially propagated through the Nb/MoSi[sub 2] interphase region. The addition of aligned niobium fibers, oriented perpendicular to the direction of matrix crack propagation, directly participated in the fracture of the composite. Depending on the diameter of Nb embedded in the MoSi[sub 2] matrix, these fibers either fractured in a brittle manner or ruptured in a ductile manner. Small (400-[mu]m) diameter continuously aligned Nb fibers fractured by brittle cleavage during testing. Therefore, the addition of these fibers was not as effective in improving the toughness of MoSi[sub 2] as the addition of larger (800-[mu]m) diameter continuously aligned Nb fibers, which ruptured in a ductile manner. It was observed that the larger diameter fibers had separated from the matrix through the propagation of cracks in the reaction zone adjacent to the fibers and that these cracks formed prior to yielding of these fibers. In contrast, the smaller diameter fibers remained well bonded to the matrix and, thus, were constrained by the MoSi[sub 2] matrix from yielding. This resulted in brittle fracture behavior of the Nb fiber. There appeared to be an effect of aspect ratio on the fracture of the ductile embedded fibers.

• OSTI ID: 6607445
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 26:2; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
COMPOSITE MATERIALS
CRACK PROPAGATION
ELEMENTS
FRACTURE PROPERTIES
MATERIALS
MECHANICAL PROPERTIES
METALS
MOLYBDENUM COMPOUNDS
MOLYBDENUM SILICIDES
MORPHOLOGY
NIOBIUM
ORIENTATION
REFRACTORY METAL COMPOUNDS
SILICIDES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS