Characterization of Nanostructured WC-Co Deposited by Cold Spraying
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hang-Jiu Li, Guan-Jun Yang, Pei-Hu Gao, Jian Ma, Yu-Yue Wang, and Cheng-Xin Li (Submitted March 12, 2007; in revised form June 6, 2007) Nanostructured WC-Co coating was deposited by cold spraying using a nanostructured WC-12Co powder. The critical velocity for the particle to deposit was measured. The coating microstructure was characterized by X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The coating hardness was tested using a Vickers hardness tester. The deposition behavior of single WC-Co particle was examined. WC particle size was measured for comparison of deposit properties to that of sintered bulk. The result shows that the nanostructured WC-Co coating can be successfully deposited by cold spraying using nanostructured powders. The coating exhibited a dense microstructure with full retention of the original nanostructure in the powder to the coating. The test of microhardness of the coating yielded a value of over 1820 Hv0.3, which is comparable to that of sintered nanostructured WC-Co. The deposition behavior of WC-Co powders as superhard cermet materials in cold spraying and powder structure effects is discussed.
Keywords
WC-Co, nanocrystalline material, cold spray, annealing, critical velocity, microhardness
1. Introduction WC-Co cermets are most important wear-resistant coating materials employed for thermal spraying. It is essential to reserve the designed phases of powders to the deposit to optimize wear resistance of deposit based on the theory of hardmetals. However, the requirement of heating of powder to certain degree during thermal spraying results in dissolution of carbide by the melted binder phase and thermal dissociation of WC, and also burning of carbon by oxidation (Ref 1, 2). These thermal effects lead to decarburization, which not only reduces wear-resistant hard phase, but also leads to the formation of brittle binder phase (Ref 3). Therefore, preventing carbide from decarburization is the essential concerns, during deposition of WC-based coatings. Numerous investigations were dedicated to study the phenomena associated with the decar-
This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 1416, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007. Chang-Jiu Li, Guan-Jun Yang, Pei-Hu Gao, Jian Ma, Yu-Yue Wang, and Cheng-Xin Li, State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, XiÕan Jiaotong University, XiÕan, Shaanxi 710049, P.R. China. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
burization of carbide during plasma spraying (Ref 4-8) and high velocity oxy-fuel spraying (Ref 1, 9-13) in last sev
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