Effects of high-temperature heat treatment on the mechanical properties of unidirectional carbon fiber reinforced geopolymer composites

Unidirectional carbon fiber reinforced geopolymer composite (C-uf/geopolymer) is prepared by a simple ultrasonic-assisted slurry infiltration method, and then heat treated at elevated temperatures. Effects of high-temperature heat treatment on the microstructure and mechanical properties of the composites are studied. Mechanical properties and fracture behavior are correlated with their microstructure evolution including fiber/matrix interface change. When the composites are heat treated in a temperature range from 1100 to 1300 degrees C, it is found that mechanical properties can be greatly improved. For the composite heat treated at 1100 degrees C, flexural strength, work of fracture and Young's modulus reach their highest values increasing by 76%, 15% and 75%, respectively, relative to their original state before heat treatment. The property improvement can be attributed to the densified and crystallized matrix, and the enhanced fiber/matrix interface bonding based on the fine-integrity of carbon fibers. In contrast, for composite heat treated at 1400 degrees C, the mechanical properties lower substantially and it tends to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve. (C) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.