Abstract
The dispersion of nanometer-sized silicon carbide particles into alumina or silicon nitride matrix results in significant improvements both in the fracture strength and the creep resistance. In this study the strengthening mechanisms of these two properties are analyzed and discussed. For the fracture strength, crack-tip bridging by nano-particles is considered to be one of the primary mechanisms. Small brittle particulate inclusions have been shown to cause crack-tip bridging at short distances behind the crack tip. This mechanism leads to modest toughness but very steep R-curve. For the creep resistance, much attention is paid to the interfaces between the intergranular nanoparticles and the matrix, and its role in creep inhibition. The intergranular nanoparticles are rigidly bonded to the matrix, which causes the inhibition of grain boundary sliding, leading the remarkably improved creep resistance. It is also demonstrated that the creep rates are remarkably decayed below specific stresses, suggesting the presences of the threshold stresses of creep. These stresses agree with those predicted from the Ashby's model, where motion of grain boundary dislocations responsible for vacancy nucleation and annihilation is considered to be pinned by hard particles.
