Pearlitic steel experiences excessive corrosion in a hot and humid atmosphere. The multiphase bainitic/martensitic structure was developed for a better combination of strength and ductility, especially rolling contact fatigue, but little attention to corrosion has been investigated. Corrosion behaviors of multiphase steels obtained from bainitic-austempering (BAT) and bainitic-quenching and -partitioning (BQ&P) processes were investigated via immersion and electrochemical tests in 3.5 wt.% NaCl solution. The corroded surface and rust after immersion and electrochemical tests were analyzed via electron microscopy, Fourier transform infrared spectra, and x-ray diffraction. The multiphase bainite + martensite/retained austenite island showed higher corrosion resistance than that of the pearlitic one. The acicular bainite obtained from the BQ&P process showed slightly higher corrosion resistance than the granular bainite + martensite structure obtained from the BAT process.

This work investigates the influence of carbon content on the thermal stability of SiOCN coatings derived from polysilazanes on AISI 304 stainless steel after 100 h exposure at 800 °C to Ar, Ar+H2O, and air. Different ratios of two polysilazanes, including carbon-free (perhydropolysilazane, PHPS, (P)) and carbon-rich (Durazane 1800 (D)), were used as coating materials. The carbon-free (P) coating exhibited superior oxidation resistance, forming a protective SiON layer. In contrast, the carbon-rich coating (D) resulted in duplex oxide nodules, indicating breakaway oxidation. The coatings with intermediate carbon contents showed a mixed behavior: areas with intact coatings adhered well to the substrate and provided significant protection, while localized spallation exposed the substrate to oxidation. The study highlights how PHPS and Durazane 1800 mixtures alter the precursor's behavior during pyrolysis and thermal treatment at 800 °C. These findings provide insight into the design of polymer-derived ceramic coatings for structural components in harsh environments such as power generation and aerospace.

To reduce the pollution emission from vehicles, an improvement on the combustion process is expected, leading to increased exhaust gas temperature. As a result, the development of new materials for an exhaust manifold used at higher temperatures is required. A cost-effective cast iron exhaust manifold treated by aluminising pack cementation was developed in the present work to combat the high temperature corrosion. Its kinetics under cyclic oxidation in N₂–12%O₂–10%H₂O at 850 °C was parabolic with the rate constant (k_p) of 5.66 × 10⁻¹² g² cm^–4 s^–1, about two orders of magnitude lower than that of the bare cast iron, which indicated the protectiveness of the applied coating. These results relate to the protective alumina formation for the aluminised cast iron and the formation of the less protective iron oxides for the bare cast iron after oxidation, as evidenced by the XRD and Raman spectroscopy results. The addition of 10% water vapour to N₂–12%O₂ thickened the aluminide layer from 344 μm for the sample oxidised in dry atmosphere to 409 μm for the sample oxidised humidified one. It accelerated the oxidation rate of the aluminised cast iron as the k_p value increased by 8.5 times, and also increased the hardness of the aluminised surface, as it was 364 HV for the sample exposed to dry atmosphere and 420 HV for the sample exposed to humidified one. The latter result implied the possibility of the hydrogen dissolution into the metal surface. The roles of hydroxyl ion and dissolved hydrogen on the oxidation and evolution of the aluminide layer after exposure to water vapour were proposed.

In this study, SiHfCN ceramics were synthesized from a single-source precursor obtained by reacting Durazane 1800 with tetrakis(dimethylamido)hafnium(IV) (TDMAH). In a separate preparation, Ti₃C₂ MXene was incorporated into this precursor to produce MXene-SiHfCN composite ceramics. The samples were pyrolyzed at 1000 °C and heat-treated at 1600 °C in N₂ to investigate amorphous-to-crystalline transformations. Both SiHfCN and MXene-SiHfCN formed a single-phase amorphous structure after pyrolysis at 1000 °C. At 1600 °C, SiHfCN partially crystallized into α/β-Si₃N₄ and HfC_xN_1−x phases within an amorphous/crystalline Si₃N₄ matrix. In contrast, the MXene–SiHfCN matrix remained largely amorphous, evolving into SiOCN with localized Si₂ON₂ crystallization. Additional phases, including HfC_xN_1−x, Hf oxide/oxycarbide, and a Ti carbonitride-rich phase (TiC_0.63N_1.06O_0.18Si_0.99Hf_0.11), were identified within the amorphous SiOCN. No SiC was detected in either system, indicating suppression of carbothermal reduction of Si₃N₄ up to 1600 °C in N₂. While SiHfCN exhibited pronounced macroscopic cracks, MXene-SiHfCN showed no such large cracks, though local microscopic cracking was observed. These results demonstrate that Ti₃C₂ MXene incorporation stabilizes the amorphous matrix, modifies phase evolution, and mitigates severe cracking, offering new insights into non-oxide PDC nanocomposites for ultra-high-temperature applications.