Effect of Substrate Temperature on CaHPO4 Coating on HT-C/C Composites Prepared by Ultrasonic Induction Heating Method

CaHPO4 coatings were deposited on H2O2-treated carbon/carbon composites (HT-C/C) substrates at different substrate temperatures by a ultrasonic induction heating method. The microstructures of these coatings were characterized by SEM, XRD, FTIR and EDS, and the adhesion of them to the HT-C/C substrates was evaluated by a scratch test. Meantime, the deposition kinetics of the CaHPO4 coatings was analyzed by measuring their weights using an analytical balance. The results show that the CaHPO4 coatings have a Ca/P ratio of 1.2±0.05, and some carbonate ions are found in their lattice. These coatings show no obvious changes in the morphologies, but their compactness decreases with increasing the temperature. The adhesive strength of the coatings to HT-C/C increases but their cohesive strength decreases with increasing substrate temperature. The induction heating deposition process of these CaHPO4 coatings is controlled by surface chemical reaction and the deposition activation energy is 46.7 kJ/mol.