Self-propagating High-temperature Synthesis of Al2O3-TiB2 Coatings by Aluminothermic Reactions

The Al2O3-TiB2 coatings were fabricated on Q235 steel by self-propagating high-temperature synthesis (SHS) process using aluminothermic reactions with aluminum, titania, boron oxide and ferric oxide powders. The effect of the content of excessive aluminum in the reactants on Al2O3-TiB2 coatings was studied when only Al-TiO2-B2O3 system was used for preparation of the coatings. The results indicate that the combustion reaction cannot occur when excessive aluminum is over 40wt% and the coating has good quality when excessive aluminum is 20wt%. In order to improve the bonding of the coating and substrate and optimize the ratio of Al2O3/TiB2, composite reaction systems Al-TiO2-B2O3 and Al-Fe2O3 were used for the preparation of Al2O3-TiB2 coatings. The XRD result shows that the coatings contain FeAl intermetallic compound which can improve efficiently the interface bonding of the coating and substrate. The percentage of Al-Fe2O3 system in reactants has only a small effect on the hardness of Al2O3-TiB2 coating, which is about 22000 MPa (Hv), but has an obvious effect on the morphology and interface bonding of the coatings.