Microstructure and mechanical properties of ZrC coating on zirconium fabricated by interstitial carburization

Herein, ZrC coating was fabricated on the surface of zirconium via interstitial carburization. High-carbon steel was selected as the carbon source to supply the interstitial carbon atoms and was hot-pressed with zirconium substrate at 1150 °C and uniaxial pressure of 2 MPa. The interstitial carbon atoms diffused into the surface of Zr forming a ZrC coating. The microstructure of the coating was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron backscattered diffraction (EBSD). The obtained coating was completely dense and pure ceramic, consisting of a single ZrC phase with a volume fraction of 100%. The diameter of ZrC grains exhibited a gradient distribution with a range of 180 nm to 5.9 μm. The thickness of the coating was proportional to the square root of the carburizing time, following the classical parabolic law, reaching a coating thickness of 7.2 μm after carburizing for 10 h. The microhardness tested on the coating surface reached 1500 HV and nanohardness measured on the cross-section of the ZrC coating reached 27 GPa, displaying a remarkable improvement compared to the zirconium substrate (192 HV and 3.6 GPa). The average fracture toughness of ZrC coating measured via Vickers indentation was 1.9 MPa·m1⁄2. In response to a scratch where the scratch load increased linearly from 0 to 100 N, the coating demonstrated excellent adhesion with the substrate. As per the obtained results, we expect that the interstitial carburization method can also be applied to various Zr-based alloys. •ZrC coating on Zr substrate is fabricated by interstitial carburization.•The coatings are completely dense and pure ceramic.•The ZrC grain sizes increase intensely with depth, showing a gradient microstructure.•The coating exhibits excellent hardness, fracture toughness and scratch resistance.