| Titanium and its alloys are important materials for industrial fields such as spaceflight, aviation, rocket, missile, naval ships, energy sources and chemical engineering in virtue of their low density, high melting temperature, high strength and high corrosion resistance. One of key problems is, however, a poor wear resistance of titanium materials, to which the users desiderate a solution. Based on Xu-Tec a new method, named triple-cathode plasma surface alloying technology has been developed in the present studies, which can be used to improve the wear resistance of the damp surface of convex of titanium turbine blade in aeroengine. A surface alloying layer with metallic carbides that have a high hardness and a sound bonding was successfully formed on a substrates of titanium materials.The basic principle of this new technology is that another orificialized cavity cathode is installed between the two cathodes of Xu-Tec, which makes up of a new system of triple-cathode plasma surface alloying processing. Plasma from orifice of cavity cathode runs, directly, to the surface to be treated and then forms an alloying layer on the substrate. The carbon composition in the plasma is hydrogen-free resulted from the cavity target cathode which is made of a solid state graphite. Other target cathode can be used to bring the elements of metals. Thus the plasma contains simultaneously the demand's elements for metallic carbides and can be used to form metallic carbides on the surface of titanium materials with hydrogen-free in one operation.Besides having a feature of point plasma source, the plasma from the orifice of cavity cathode presents the characteristics of the "Hope (abbreviation for the first letters of hollow, orifice, plume and ejecting) effect", the "burning hole effect" and the " flat step effect" of voltage and electric current of the cavity cathode. It was those features that make this technology being a advanced one and forming an intellective property right of ours own.By the triple-cathode plasma surface alloying technology hydrogen-free plasma carburizings have successfully been carried out on the substrates of titanium TA2 ortitanium alloy TC4 (Ti6A14V), which presents a new and practical method of plasma carburizing with hydrogen-free on the surface of titanium materials. The minimum carburizing temperature has been found to be 930℃ for titanium TA2, and 950℃ for titanium alloy TC4. Carburizing layer appears a structure of two layer, and one is outer layer of TiC with 10μ m and other is border upon one of diffusion layer. The layer has the highest hardness 1700HV and a good toughness and bonding.By the new technology Mo-C,W-C and W-Mo-C multi-element plasma surface alloying with hydrogen-free have successfully been carried out on the substrates of titanium TA2 or titanium alloy TC4 (Ti6A14V), which has carried out an alloying layer with the metallic carbides which are of a high wear resistance.The experimental results of Mo-C two-element surface alloying with hydrogen-free indicate that the types of metallic carbides are Mo2C, MoC and TiC in the metallic carbide one of alloying layer. The minimum temperature of two-element surface alloying is 830 ℃. The alloying layer has the highest hardness 2400HV for titanium TA2 or titanium alloy TC4. The bonding of the layer is sound and the brittleness increases with increasing of the hardness.The study results of W-C two-element surface alloying with hydrogen-free show that the types of metallic carbides are WC , W2, W6C2.54, WC1-x and TiC in the compound carbide one of alloying layer. For titanium TA2, the minimum two-element surface alloying temperature is 870℃. With alloying temperature increase the thickness of the alloying layer becomes thicker, but the hardness appears a fluctuant. The highest hardness is 2400HV. For titanium alloy TC4, the minimum alloying temperature is 830℃. With alloying temperature and time increase the thickness and hardness of the alloying layer increase. The highest hardness is also 2400HV. The bonding and toughness... |
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