Effects of the Si contents of an infiltrating aluminium alloy on the microstructure and strength of SiC matrix composites

Abstract

Abstract The Si content of an Al alloy infiltrated into SiC matrix composites affected the microstructure and strength of SiC matrix composites. As the Si content increased from 0 to 10 wt%, the relative volume fraction of Ti 3 Si(Al)C 2 increased, and the Al 4 C 3 decreased gradually and eventually disappeared. However, as the Si content continued to increase from 10 to 20 wt%, the relative volume fraction of Ti 3 Si(Al)C 2 decreased. The phase compositions and microstructure affected the bending strength. The three-point bending strength of the infiltrated SiC ceramics was almost twice that of the original SiC. Meanwhile, the maximum three-point bending strength of SiC ceramics infiltrated with the 5 wt% Si alloy was 430 MPa due to the formation of Al 4 C 3 , while with 10 wt% Si alloy, that of the infiltrated ceramic was 433 MPa due to the formation of Ti 3 Si(Al)C 2 . However, the three-point bending strength of the samples infiltrated with 5 wt% Si alloy decreased from 430 MPa to 243 MPa after the samples were exposed to air for 30 days due to the reaction of Al 4 C 3 with H 2 O and O 2 . In contrast, the Ti 3 Si(Al)C 2 phase was stable, and the strength of the samples infiltrated with 10 wt% Si alloy almost did not change after 30 days of air exposure.