Journal of Inorganic Materials ›› 2017, Vol. 32 ›› Issue (8): 806-812.doi: 10.15541/jim20160648

• Orginal Article • Previous Articles     Next Articles

Corrosion Resistance of HVOF-sprayed Nano- and Micon-structured WC-η Coatings against Molten Zinc

Tao YANG(), Hai-Bin WANG, Xiao-Yan SONG(), Xue-Mei LIU, Chao HOU, Xue-Zheng WANG   

  1. College of Materials Science and Engineering, Key Laboratory of Advanced Functional Materials, Education Ministry of China, Beijing University of Technology, Beijing 100124, China
  • Received:2016-11-25 Revised:2016-12-26 Online:2017-08-10 Published:2017-07-19
  • About author:YANG Tao. E-mail: yt2014@emails.bjut.edu.cn
  • Supported by:
    National Natural Science Foundation of China (51601004);Beijing Natural Science Foundation (2131001, 2154045)

Abstract:

WC-η (i.e. Co6W6C, Co3W3C, etc) composite powder was synthesized by in situ reduction and carbonization reactions using tungsten oxide, cobalt oxide and carbon black as raw materials. Mean particle size of the as-synthesized composite powder is about 155 nm. Thermal spraying powder with a high density and an excellent flowability was prepared using WC-η composite powder by agglomeration and heat-treatment. Cemented carbide coatings were then fabricated by high velocity oxy-fuel (HVOF) spraying technique using nanostructured and commercially available low-carbon WC-12Co thermal spraying powders as feedstock. The results show that equiaxed W2C particles form at certain amount in the nanostructured coating while cracks propagate mainly along grain boundaries and phase interfaces. However, the micron-structured coating still contains W besides W2C, which mainly distribute in outer surface of WC grains. The micron-structured coating has stronger tendency to get transgranular fracture. As a result, the cracks go forward along a relatively straight path. Due to higher density, finer grain size and much larger interface area, the nanostructured coating has simultaneously higher hardness and fracture toughness as compared to the micron-structured coating. After immersion into molten zinc for 200 h, the micron-structured coating suffers from more serious cracking along the directions perpendicular and parallel to the interface between coating and substrate, which causes the large-scale exfoliation of coating material and the corrosion of substrate. In contrast, zinc diffusion is not observed in the nanostructured coating and only a few cracks perpendicular to the coating/substrate interface are locally produced. Moreover, the inner surfaces of the crack are covered with tungsten and cobalt oxides, which inhibit corrosion of the nanostructured coating in molten zinc. Therefore, the nanostructured coating has a promising corrosion resistance against molten zinc.

Key words: WC-η composite powder, nanostructured coating, toughness, crack propagation path, corrosion resistance to molten zinc

CLC Number: 

  • TG174