16-02-2011, 12:09 PM
presented by:
C.VIGNESH
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INFLUENCE OF WHISKER REINFORCEMENT ON THE ABRASIVE WEAR BEHAVIOR OF
SILICON NITRIDE- AND ALUMINA-BASED COMPOSITES
Abstract
The abrasive wear of brittle materials is generally modeled as an inverse function of both the bulk hardness and fracture toughness.
According to these models,an increase in the hardness or fracture toughness of a material will enhance its wear resistance.
However,less is known about how whisker-reinforcement influences the properties that are dependent upon the short-crack toughness, such as abrasive wear.
Alumina-based ceramics improve the wear.
the addition of SiC reinforcement to silicon nitride ceramics does not result in improved wear resistance.
Introduction
Because of the complexity of wear processes, a detailed understanding of how ceramic materials react in tribological environments continues to elude both materials and design engineers.
However, in almost every case, large-scale toughening requires that these mechanisms be activated over some distance behind the tip of a propagating crack.
Thus, while the long-crack toughness of the bulk material may be enhanced by the presence of the whisker reinforcement, he short-crack toughness of the bulk material may remain unchanged, or even be degraded,by the presence of these whiskers.
Microstructural characteristics of the ceramics and ceramic composites
Abrasive wear behavior
Conclusion
A detailed study of the influence of randomly oriented Sic whisker reinforcement on the abrasive wear behavior of silicon nitride- and alumina-based ceramics suggests that it is the residual stress state of the whisker-matrix interface that determines the wear resistance of the composite material.
The addition of SiC whiskers to a Si3N4 matrix sets up tensile stresses at the whisker-matrix interfaces, enhancing the bulk toughness of the composite.
The addition of Sic whiskers to an alumina matrix, on the other hand, results in the creation of compressive stresses at the whisker-matrix interface, producing a relatively stronger bond that can better withstand the rigors of an abrasive wear environment.
This result, the Al203 + SiCw composite is consistently a more wear resistant material than are the Si3N4+ SiCw composites