Journal
SURFACE & COATINGS TECHNOLOGY
Volume 389, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.surfcoat.2020.125579
Keywords
Ceramic coating; Refractory metal; Hot pressing; Diffusion barrier; Semipermeable film; Growth rate
Funding
- National Natural Science Foundation of China [51602255]
- Programs of Key Research and Development Plan of Shaanxi Province [2018ZDXM-GY-145]
- Innovation Capability Support Program of Shaanxi [2018GHJD-17]
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A tungsten carbide coating on tungsten was fabricated by hot-pressing tungsten with high-carbon steel. The interstitial carbon atoms in the high-carbon steel diffused into the tungsten, forming a WC coating. The coating is completely nonporous, and the volume fraction of the carbide phases is close to 100%. By comparing the microstructures of the coatings fabricated by one-step hot-pressing at 1100 degrees C and 1150 degrees C, we found that increasing the temperature by 50 degrees C can markedly increase the growth rate of the coating as desired, but this increase of temperature generates undesired. carbide (Fe6W6C) at the coating/substrate interface. Based on the inference that Fe atoms are diffusible in tungsten but indiffusible in WC at 1150 degrees C, we proposed a two-step hot-pressing method to fabricate coatings at 1150 degrees C without introducing. carbide. The sample was first hot-pressed at 1100 degrees C for 4 h to prepare a pure WC layer and then hot-pressed at 1150 degrees C for further carburization. The WC layer prepared at 1100 degrees C was utilized as a semipermeable film to filter out Fe atoms and allow the diffusion of carbon atoms at 1150 degrees C. The two-step hot-pressing method worked as desired, and the obtained coating exhibits a distinct gradient microstructure with columnar WC grains. Compared to that of the one-step hot-pressing method at 1100 degrees C, the total carburization time for obtaining a coating with a saturated hardness of 2400 HV is shortened from 8 h to 6 h. Therefore, the two-step interstitial carburization can be used to efficiently fabricate high-quality and high-performance tungsten carbide coatings.
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