Study On Microstructure Evolution And Property Modulation Of Fe-based Amorphous Composite Coating Synthesized By Laser Cladding

In modern industrial production,many mechanical parts need to work continuously under a certain chemical medium,heavy load,high speed,and varying loads.Fatigue,wear and corrosion are the main failure forms,which raises higher requirements on the surface quality of materials.In this paper,the composition of the amorphous alloy was innovatively designed and the laser cladding process parameter settings were optimized.The all-metal component amorphous alloy was used as the precursor,and the laser cladding technology was used to prepare amorphous composite coatings with excellent comprehensive properties on the surface of 45 steel.It had certain academic research and industrial application prospects.In this paper,two groups of all-metal component alloy systems of Fe Nb Ti?Ta?and Fe Cr Mo?Y?were designed based on the innovative composition design concept of"near formation enthalpy+effective atomic size difference".Amorphous alloy powders were prepared by high-energy ball milling mechanical alloying.The phase of milled powders were analyzed by XRD.The thermal stability and crystallization kinetics of the amorphous alloys were analyzed by DSC.Finally,the orthogonal cladding experiment was carried out on the surface of 45 steel.The self-developed magnetic powder dispenser was used to arrange the powder during the cladding.The microstructure,hardness,wear resistance and corrosion resistance of the cladding layer were tested and analyzed.The correlation between composition-process-structure-property was explored to achieve optimal control of coating structure and performance.The research results showed that the Fe Nb Ti?Ta?alloy system could be successfully prepared into completely amorphous alloy powder through mechanical alloying,and the alloy system's glass forming ability increased as the content of Ta element increased.But the Fe Cr Mo?Y?alloy system couldn't be prepared into completely amorphous alloy powder through mechanical alloying,which might be caused by the two alloy systems having different mixing enthalpies and atomic size differences,the large negative mixing enthalpy and the atomic size difference were favorable for the formation of the amorphous phase.It showed that the composition design concept of"near formation enthalpy+effective atomic size difference"was not universal,and it was necessary to define the mixing enthalpy and atomic size difference of the alloy system when designing the composition.The Fe Nb Ti?Ta?alloy system ball milling amorphization process was:the alloy element powder first formed a supersaturated solid solution by diffusion,and then the solid solution was destabilized to form an amorphous phase.Fe₆₀Nb₁₅Ti₁₅Ta₁₀ amorphous powder had a wide supercooled liquid region?up to 67 K?and a large crystallization activation energy?186 KJ/mol?.The fitted"S"type crystallization volume fraction with temperature could clearly show the crystallization degree of the amorphous alloy powder in each temperature range,and calculated the Avrami index n=2.33 and the nucleus growth dimension d=2,the crystal growth mechanism parameter m=3,which indicated that the crystallization mode of the amorphous alloy powder was a two-dimensional plane growth in which the nucleation rate decreased and the crystal nucleus was controlled by volume diffusion.The self-developed magnetic powder dispenser had uniform powder distribution and stable operation.The results of laser cladding experiment showed that the laser power and scanning speed had a significant effect on the quality of the cladding layer and showed a certain regularity,but the effect of defocus was not significant.The optimized process parameters:laser power was 1200 W,scanning speed was 5 mm/s,and defocus was 10 mm.The cladding layer had no obvious defects and had good bonding with the substrate and obvious delamination.Different laser cladding process parameters would significantly affect the microstructure of the cladding layer,and it was difficult to prepare a completely amorphous cladding layer.Most of the cladding structure was mainly composed of amorphous phase,part of plum-like cell crystals,and small equiaxed crystals.The hardness,wear resistance and corrosion resistance of all cladding layers had been greatly improved compared to the substrate.Among them,the average hardness of the best sample cladding layer was 742.48 HV?substrate was 227.14 HV?,and the average friction coefficient was 0.0599?substrate was 0.3089?,self-corrosion current was 0.0097 A?substrate was 0.0611 A?,self-corrosion potential was-1.03 V?substrate was-1.08 V?.