•Novel Zr0.75Ce0.25O2/phosphate duplex coating was fabricated on polymer substrate.•The microhardness of the surface was improved effectively by top duplex coating.•The duplex coating exhibited good thermal shock and thermal ablation resistance.•The duplex coating protected the substrate against thermal oxidation.•Failure was attributed to the appearance of the vertical cracks and delamination.Thermal protection coating based on Zr0.75Ce0.25O2/phosphate system was fabricated on polymer–matrix composites via a combined sol–gel/sealing treatment process. Phosphates sealed the cracks and enhanced the adhesion property via chemical bonding and binding. The Zr0.75Ce0.25O2/phosphate duplex coating exhibited good thermal shock resistance and improved thermal oxidation resistance of the substrate. Due to the protection of the duplex coating, the weight loss of the specimen reduced from (4.83 ± 0.12)% to (0.98 ± 0.08)% and the mass ablation rate decreased from 0.088 ± 0.002 mg cm−2 s−1 to 0.018 ± 0.002 mg cm−2 s−1 when testing at 810 °C. Coating failure was attributed to the formation of cracks and delamination.

TiC–TiB2 particulate locally reinforced steel matrix composites were fabricated by a novel TE-casting route from an Al–Ti–B4C system with various B4C particle sizes. The formation mechanism of TiC and TiB2 in the locally reinforced regions was investigated. The results showed that TiC and TiB2 are formed and precipitated from Al–Ti–B–C melt resulting from the dissociation of B4C into Al–Ti melt when the concentrations of B and C atoms in the Al–Ti–B–C melt become saturated. However, in the case of coarse B4C powders (≥40 μm) used, the primary reaction in the Al–Ti–B–C melt is quite limited due to the poor dissociation of B4C. The poured steel melt infiltrates into the primary reaction product and thus leads to the formation of Al–Fe–Ti–B–C melt, thanks to the favorable reaction of molten Fe with remnant B4C, and then TiC and TiB2 are further formed and precipitated from the saturated Al–Fe–Ti–B–C melt. The relationship between the mechanisms of thermal explosion (TE) synthesis of TiC and TiB2 in the electric resistance furnace and during casting was proposed.Highlights► We successfully fabricated TiC–TiB2 locally reinforced steel matrix composites. ► We investigated the product microstructure and formation mechanism of TiC and TiB2. ► The formation mechanism during casting is dependent on B4C particle size. ► Fe melt promotes the full dissociation of remnant B4C particles during casting. ► The relationship between the mechanisms in the ERF and during casting was proposed.