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Using Fe55 spherical fluxed alloy power as the raw material, a Fe-based alloy coating on the surface of steel was deposited by a semiconductor laser under the optimal process parameters. The microstructure and properties of the samples were analyzed by means of OM, SEM, XRD, the micro-hardness and frictional testers. The experimental results showed that a high chromium Fe-based coating with metallurgical bonded on the substrate was deposited using the optimized process parameters with the laser power of 1900W; the spot size of 6mm×4mm, the scanning speed of 5mm/s, and the overlapping ratio of 30%. The thickness of the coatings without cracks and porous was 4 mm. The microstructure of the coating was mainly cellular and dendrite crystal. The phases of the coatings are composed of α-(Fe, Ni) solid solution, Fe-Cr-Ni, Cr-Fe-B solid solution, and Cr23C6 particles. The microhardness of the coating rised to 750HV which was 4 times that of Q235 steel substrate with hardness of 175HV, the wear resistance was 27 times that of the steel substrate. Introduction As one of the main components of the key parts of high speed train, the brake disc is one of the important consumable materials. Because of the extremely serious wears by the effect of sliding friction of brake disc in the work process, it need be replaced when the brake disc was worn. The brake disc of high speed train required not only high wear resistance but also good toughness to ensure the stability of the high speed train braking processing according to the failure mechanism of the brake disc during the application. This characteristic makes people realize that new brake disc can be prepared by the method of surface strengthening. This new brake disc can be prepared by using ordinary steel with strong toughness as a substrate, and then the coating with high wear-resistant is prepared on the surface of the substrate. Laser direct deposition is one of the advanced surface preparation wear resistant coating technologies. Many important achievements have been obtained by using method of the alloy composition design, laser process parameter optimization, and carbide particle reinforced [1-8]. However, the study on in situ particles reinforced coatings with large thickness and good wear resistance by the laser direct deposition was less reported. Particularly, the coating with the thickness of 3~6mm for liner is required to meet the work conditions, and the coating prepared by traditional laser cladding method often has cracks to result in the decrease of the strength and toughness. In this paper, in order to research a new liner with high wear resistance, a Fe based coating was prepared on the surface of Q235 steel by laser using Fe55 alloy powder. The microstructure, hardness, wear resistant and the carbide particle reinforced mechanism of the samples were studied. This work would provide valuable reference for the development a new liner prepared by laser direct deposition coatings with high wear-resistant, large thickness (3-6mm) and free clacks on the surface of Q235 steel. 6th International Conference on Mechatronics, Materials, Biotechnology and Environment (ICMMBE 2016) © 2016. The authors Published by Atlantis Press 259 Experimental Materials and Methods Materials and methods of the samples preparation. The Q235 steel with the dimension of 200×100×10mm was used as the substrate. The powder was the Fe55 iron-based spherical fluxed alloy power with the particle size of 106 μm. The chemical composition of Fe55 powder were composed of 1.0wt.%C, 19wt.%Cr, 4wt.%Si, 3wt.%B, 13wt.%Ni, 60wt.%Fe. The substrate surface was ground by polishing machine and 100# abrasive paper, then it was degreased by the acetone and alcohol before laser direct deposition. a FL-Dlight02-3000W Semiconductor laser was used with the laser beam profile of rectangular. The optimized parameters were as follows with the laser power of 1900W, power feeding rate of 8.4g/min, spot size of 6mm×4mm, scanning speed of 5mm/s, and overlapping ratio of 30%.Samples were deposited on Q235 substrates with 0.2MPa Argon as the carrier gas. Experimental analysis. The coatings were cut to the sizes of 10mm×10mm by wire–cut electrical discharge machining to obtain cross-section specimens which were vertical to the laser scanning direction. Microstructures were characterized using an OLYMPUS-GX71 optical microscope (OM) and a Shimadzu-SSX-550 scanning electron microscope (SEM). Microhardness was measured using a 401MVDTM microhardness tester at a load of 100N and an indentation time of 10s.The Phase identification was performed using an X-ray diffractometer (XRD) with Cu Kα radiation (wavelength λ=1.5406A) at 40 kV and 40 mA. Friction and wear tests were conducted in an abrasive wear tester using O8×15mm samples. A 60 mesh quartz sand cloth made to simulate actual working conditions was taken as the counterface material, using a test load of 2.0 kg. The weighing method was used to obtained the wear loss amount, and the average wear loss of a single sample was the average of the values measured by 3 times. The wear resistance of test material was shown by relative wear ability e, and Q235 steel as the standard sample was compared with the coating. Results and discussion Microstructure of the Fe55 alloy coating coating. Fig. 1 showed the OM images of a single layer laser deposited coating.. The coating has a good bonding interface between the coating and the substrate which is free of cracks. It was noticed that an apparent bright band between the coating and substrate was formed as shown in Fig 1 which indicated the coating was metallurgical bonded with the substrate. Fig. 2 showed the cross-sectional OM image of the high thickness coating prepared by the laser direct deposition. It can be seen that a dividing line was obvious between each layers. The microstructure of the coatings without cracks was homogeneous and the sample was dense. The thickness of the coating was almost 4 mm. The SEM morphologies of laser deposited multilayer specimens were shown in Fig. 3. The formation of the bright band illustrated that the interface between coating and substrate was also metallurgical bonded which was flat and free of pores and cracks. The microstructure of deposited coating consists of cellular, mesh dendrite and columnar crystals (Fig. 3(b)-(d)). The microstructure gradually became coarsen from the first layer to the fourth layer, and some black precipitates were observed in the fourth layer.

The laser direct deposition iron-based alloy coating with high wear resistance