Research On Process And Structure Of Sub-micron/Nano Solid Self-lubricant Laser Cladding Coating

In order to obtain the submicron/nano self-lubricating coating that is lubricant in a work condition of wide temperature range. A convenient and available pulse YAG laser cladding technique was employed to prepare the solid self-lubricating coating on the surface of 1045 steel, for the purpose of making foundation for the continuing technique of using HVOF to spray self-lubricating coating.In order to adapt to the change of environment of manufacturing, two composite systems with self-lubricating property in wide temperature range were designed, which are submicro WS2 series and nano-hBN series. A gas shielding and water-cooler device for the protection of the laser-molten pool was developed. The techniques of mixing micron and sub-micron(or nanometer) powder particles and the the method of laser cladding were studied.Solid lubrication phases can't melt into melting pool, because of being decomposed of WS2, and rising onto coating surface of hBN in laser cladding. Experimental Results show that the continuous, smooth and metallurgically-bonded coatings have been produced by using encapsulated WS2 and hBN with nano-nickel powder through high-energy milling.The microstructure of cladding layer and behavior of melting pool in the process of laser cladding were examined and studied with SEM(+EDX) and XRD. Results shows that: 1) In unencapsulated WS2 coating,,some WS2 particles are decomposed into W and SO2, and many white blocks which are tungsten atoms deposited at the bottom of the melting pool because of its'high density, and the number of white blocks was increasing with the content of WS2 in composite powder. The microstructure of the cladding layer were mainly composed ofγ-Ni and solid self-lubricating phase(including CaF2, WS2 and CrS ). In unencapsulated BN coating, the content of BN in which was little, but the figuration of 10%BN was the best in all laser cladding. 2) Compared with unencapsulated WS2 coating, the decomposition of encapsulated WS2 particles highly decreased, the microstructure was more uniform, and the pores in coating were small. In encapsulated hBN coating, some harden phase CrxBy was found in the high density coating.Hardness of the cladding layer testing shows that distribution of hardness fall by step from surface to interface. That's because the cladding layer was diluted by Fe from base metal. The average hardness is about 500HV for Ni45 series and 900HV for Ni60 series. Comparing with WS2, BN is good contributing factor to hardness of coating. From the testing of triboloy, we can find the phase of self-lubricant make high influence for the decline of coefficient of coating. The best results concentrate between 0.3 and 0.4.To sum up, solid self-lubricating composite coating was successfully prepared by YAG laser cladding technique. Further study is moving on step by step now.