The effect of ductile phase (Nb) reinforcement morphology on the mechanical behavior of an intermetallic matrix (MoSi2)

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7166719

Alman, D E

This thesis was undertaken to determine the effect of a ductile reinforcement phase (Nb) morphology on the mechanical behavior of an intermetallic matrix (MoSi2). Twenty volume percent Nb was incorporated into MoSi2 in the form of particles, short fibers, aligned fibers, and with fibers of two different diameters (800 and 400 microns). Bend tests, comprehension tests and fractography were used to determine the role that Nb morphology plays on the fracture behavior of these composites. It was found that the morphology of the Nb incorporated into MoSi2 affected the fracture mechanism, hence toughness, of the composites. The addition of random short fiber or particles deflected cracks that propagated through the matrix. However, the Nb in these forms were not effective in improving the toughness via a crack deflection mechanism. The addition of continuous Nb fibers aligned perpendicular to the direction of crack propagation enhanced the toughness of MoSi2, as these fibers deformed and fractured prior to composite failure, however, there was an effect of fiber diameter. The larger diameter Nb fibers imparted the greatest toughness improvements, as these fibers deformed prior to fracture. The smaller diameter Nb did not deform prior to fracture, in fact they failed in a brittle manner. Fractography revealed that the larger diameter fibers had separated (or delaminated) from the matrix. The fiber/matrix separation relaxed the matrix constraint acting on the fiber and allowed for the fiber to undergo plastic deformation. The delamination was found to occur after the matrix had fractured and prior to deformation of the fibers. The diameter effect exhibited by the composites was attributed to the well known effect of fiber aspect ratio (l/d) on fiber pull-out. It was concluded that maximum toughness of a Nb fiber reinforced MoSi2 matrix will occur when the value of the fiber aspect ratio is within a critical range.

• Research Organization: Rensselaer Polytechnic Inst., Troy, NY (United States)
• OSTI ID: 7166719
• Resource Relation: Other Information: Ph.D. Thesis
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MATRIX MATERIALS
FRACTURE PROPERTIES
MOLYBDENUM SILICIDES
REINFORCED MATERIALS
CRACK PROPAGATION
FIBERS
INTERMETALLIC COMPOUNDS
NIOBIUM
ALLOYS
ELEMENTS
MATERIALS
MECHANICAL PROPERTIES
METALS
MOLYBDENUM COMPOUNDS
REFRACTORY METAL COMPOUNDS
SILICIDES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
360603* - Materials- Properties