Al₂O₃粒子強化6061Al基複合材料のクリープ特性

抄録

Creep tests have been carried out on the 6061Al matrix composites reinforced with 10 and 20 vol% of alumina particles to examine the effects of reinforcements on the creep properties. Furthermore, the density change was measured, and microstructures and fracture surfaces were observed after the creep deformation to get the information about the creep damages, or the formation of creep cavities.
Creep curves were generally dominated by the tertiary creep at 573 K and 673 K, although the increased extent of normal primary creep was recognized at high stresses of 573 K. Inverse transient creep followed by normal primary creep of large strain (S type curve) was observed in the low stress region of 773 K. In this case, the matrix alloy was elongated like filaments at the edge of dimples or grain boundaries in the fracture surface, which suggested that a very soft material was formed at the particle/matrix interfaces or grain boundaries and elongated during the creep deformation.
Minimum creep rate was almost same in the both composites of 10 vol% and 20 vol% alumina particles, that is, it did not depend on the volume fraction of particles. In comparison with the 6061Al alloy reinforced with the same volume fraction of short alumina fibers, the minimum creep rate of this composite was smaller than that of the particle reinforced 6061Al at 673 K and 773 K, while the minimum creep rate was almost same in both composites at 573 K.
The density of specimens decreased largely with creep time and creep strain after creep at 773 K. Particularly, an evident density decrease was recognized when the S type creep curve occured at low stress of 773 K. In this case, creep cavities extended largely due to the formation of soft material (supposed to be a semi-liquid phase or solid oxide formation) at the particle/matrix interfaces and grain boundaries.