Microstructure and oxidation resistance of reactive plasma clad Cr_7C_3/γ-Fe ceramic composite coating

A new type oxidation resistance in situ Cr7 C3/γ-Fe ceramic composite coating was fabricated on hardened and tempered grade C steel by reactive plasma clad with Fe-Cr-C alloy powders. The oxidation resistance of the ceramic composite coating was investigated under the test condition of 900 ℃ and 50 hours. The results indicate that the coating has a rapidly solidified microstructure consisting of blocky primary Cr7 C3 and the inter-blocky Cr7 C3/γ-Fe eutectics and is metallurgically bonded to the hardened and tempered grade C steel substrate. The high temperature oxidation resistance of the coating is up to 1.9 times higher than that of grade C steel. The oxidation kinetics curve of the coating is conforming to the parabolic-rate law equation. The excellent oxidation resistance of the coating is mainly attributed to the continuous oxide films which consist of Cr203 and Fe203. The continuous oxide films can prevent the inner part of the coating from being further oxidized.

Microstructure and Corrosion Resistance of Cr_7C_3/γ-Fe Ceramal Composite Coating Fabricated by Plasma Cladding

A new type in situ Cr7C3/γ-Fe ceramal composite coating was fabricated on substrate of hardened and tempered grade C steel by plasma cladding with Fe-Cr-C alloy powders. The ceramal composite coating has a rapidly solidified microstructure consisting of primary Cr7C3/γ- and the Cr7C3/γ-Fe eutectics, and is metallurgically bonded to the degree C steel substrate. The corrosion resistances of the coating in water solutions of 0.5 mol/L H2SO4 and 3.5% NaCl were evaluated utilizing the electrochemical polarization corrosion-test method. Because of the inherent excellent corrosion-resisting properties of the constituting phase and the rapidly solidified homogeneous microstructure, the plasma clad ceramal composite coating exhibits excellent corrosion resistance in the water solutions of 0.5 mol/L H2SO4 and 3.5% NaCl.

Effect of Monolithic LaB_6 on the Ablation Resistance of ZrC/SiC Coating Prepared by Supersonic Plasma Spraying for C/C Composites

Ablation resistance of monolithic LaB-doped ZrC coating for SiC-coated carbon/carbon composites by supersonic atmospheric plasma spray was investigated under an oxyacetylene torch with a heat flux of 4.18 MW/m~2. Result shows that ZrC coating with 10 vol.% LaBhas a good ablation resistance compared with pure ZrC, ZrC with 20 vol.% LaBand SiC-doped ZrC coating. After ablation for 15 s, the weight is increased by 1.12 mg/s. The good ablation resistance is ascribed to the formation of a stabilized scale which consists of protective LaZrO-containing molten phase and ZrOparticles keeping the integrity of the coating.

Preparation of High-Entropy Alloy-Ceramic Coating Compos-ites on Steel Surfaces by Combined Process and Their Mechanical Properties

A combined process of molten salt electro-deoxidation and vacuum hot-pressing sintering was proposed to prepare AlCrFeNiTi_(x) high-entropy alloy(HEA)-TiN ceramic coating composites on low-carbon steel surfaces,where nitrides were introduced from BN isolater between graphite mold and HEA powders.The effect of Ti content on the microstructure,ultimate tensile strength,hardness,and wear resistance of the composites was investigated,and the bonding mechanism was elucidated.Results demonstrate that the composites have excellent hardness and wear resistance.The hardness of composites is significantly increased with the increase in Ti content.The extremely high wear resistance is attributed to the extremely high melting point and high thermal hardness of TiN,which can effectively prevent oxidation deformation of the worn surface.