| Mo2FeB2 ternary boride cermet has excellent wear resistance and corrosion resistance,and has widely applications in mold manufacturing and equipment manufacturing.At present,it is mainly prepared by vacuum sintering process.The in-situ synthesis of Mo2FeB2 through welding metallurgical reaction can not only overcome the disadvantages of high vacuum sintering process cost,long manufacturing cycle,limited size and shape,etc.,but also can be flexibly used to modify the surface heat and wear resistance of the part.Therefore,the development of Mo2FeB2 ternary boride material is of great significance for applications.The Mo2FeB2 cermet synthesized by welding metallurgical reaction has coarse hard phases,which is difficult to withstand impact loads and poor wear resistance.This article systematically studies the effects TiC and rare earth(RE)content on the morphology(size and shape)of Mo2FeB2 hard phases to deal with these problems and optimizes the content of TiC and rare earth.In this paper,two series of Mo2FeB2 alloy powders with different TiC and RE(rare earth)contents are designed and prepared,and the deposited metal is prepared by carbon arc deposition technology.Employing Scanning electron microscopy(SEM),X-ray diffraction,and electron probe(EPMA),Microhardness test and wear test,etc.to study the effects of TiC and RE(rare earth)content on the morphology,microstructure and wear resistance of Mo2FeB2 hard phases,and theoretically analyze the welding metallurgy process,the formation of phases and the phase transition of deposited metal.Through the statistical analysis of the correlation between the amount of RE content and the size of hard phases,the mechanism of refinement of the hard phase of Mo2FeB2 by the rare earth was explored.The TiC-Mo2FeB2 cladding is mainly composed of Mo2FeB2,M3B2(M:Mo,Fe,Cr),Fe-Cr,CrB,MoB,Fe2B and TiC.TiC and(Mo0.72Ti0.28)C appear in the deposited metal.It is found that TiC can refine and change the morphology of Mo2FeB2 hard phases during the metallurgical process.With the increase of content of TiC,the number of Mo2FeB2 hard phases increased and the shape changed significantly,gradually transitioning from a butterfly-like shape to a large block-like shape.Thermodynamic calculations show that TiC,Fe2B,and MoB are first formed in the liquid metal above 2400?.The temperature decreases from 2400? to 1800?,and MoB and Fe2B continue to form and increase.In liquid metal above 1800?,The MoB and Fe2B produced by the high-temperature reaction generate Mo2FeB2 by in-situ reaction.When TiC is content is 0%,5%,10%and 15%,the average microhardness of cladding is 992 HV,1035 HV,1018 HV and 689 HV,respectly.The average microhardness of cladding is about 3.8 to 5.8 times of the Q235 base metal.The wear weight loss of cladding is 5.2 mg,2.3 mg,2.8 mg,and 8.6 mg when TiC content is 0%,5%,10%,and 15%,respectively.The wear performance of cladding is better than that of Q235 base metal,the wear resistance of the deposited metal with TiC content of 5%is 14.6 times that of the base material of Q235,and the wear resistance is the best.Rare earth as surface active elements can reduce surface tension and reduce the critical nucleation work radius.At the same time,rare earth are adsorbed at the interface front of grain growth,change the surface energy of grains and tend to segregate at grain boundaries and phase boundaries,hindering the growth of the phase plays a role in refining the grains.In the Mo2FeB2 claddings with rare earth,the number of Mo2FeB2 hard phases increased significantly.Compared with the microstructure without rare earth,the large,butterfly-like white hard phases disappeared,and the strip-shaped Mo2FeB2 was replaced instead.When the amount of rare earth added is 2%,the hard phase distribution of Mo2FeB2 in cladding is relatively uniform and the size is small.Its average size is 4.78 ?m,which is 1/3.44 without added rare earth.The addition of rare earth increased the amount of hard phase Mo2FeB2 formed,so that the area fraction of the hard phase was as high as 66%.When the amount of rare earth added is 2%,the hard phase is refined,and its area fraction reaches 72.32%,which is an increase of 14.2%over that without the addition of rare earth.When the rare earth content is 0%,2%,4%and 8%,the wear weight loss of the cladding is 5.2 mg,2.4 mg,2.7 mg and 3.6 mg,respectively.Among them,the wear resistance of the cladding is 14 times that of the Q235 base metal when the amount of rare earth is 2%,and the wear resistance is the best.Adding an appropriate amount of rare earth Y to the deposited metal can refine the structure,which can improve the toughness.The wear morphology of the cladding with rare earth is mainly adhesive wear. |
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