Refinement And Doping Effects Of Yttrium On Carbides In Hypereutectic Fe-Cr-C-TMe(Ti,Nb) Hardfacing Alloys

Hypereutectic Fe-Cr-C hardfacing alloys have been widely applied in the additive manufacturing and remanufacturing industrial fields,whose excellent wear resistance mainly depends on M₇C₃ carbide.During the process of abrasive wear,the coarse M₇C₃carbides are prone to cracking and spalling.M₇C₃ carbides can be refined by Ti and Nb additives to improve the cracking and spalling resistance,while their sizes are non uniform.Therefore,it is significant to improve wear resistance of hypereutectic Fe-Cr-C hardfacing alloy and expand its wide application by the further refinement and uniformity improvement of M₇C₃ carbides.In this paper,Y₂O₃ was added in hypereutectic Fe-Cr-C-TMe(TMe=Ti,Nb)hardfacing alloys.The work of adhesion,interfacial energy,electronic structure and bond characteristics of Y₂O₃(YAl O₃)and TMeC(TiC,Nb C)were calculated by first principles method,and the effectiveness of heterogeneous nucleation agents was analyzed.The microstructures of the hypereutectic Fe-Cr-C-TMe hardfacing alloys with Y₂O₃ were observed by means of metallography,SEM and TEM.The doping of TMe and Y atoms in M₇C₃ carbide was studied,and the effects of TMe and Y atoms on its stability,mechanical property and anisotropy were calculated.The lattice mismatch between Y₂O₃(111)and TiC(110)crystal faces is 8.6%and that of YAl O₃(001)and TiC(100)crystal faces is 2.5%.The interfacial work of adhesion(W_ad)of O-terminated Y₂O₃(111)//TiC(110)interface is 6.07 J/m² and its interfacial energy(?)is-1.22 J/m².The W_ad of O-terminated YAl O₃(001)//TiC(100)interface is 5.73 J/m² and its?is 2.16 J/m².It indicates that Y₂O₃ and YAl O₃ meet the conditions to act as heterogeneous nucleation substrates of TiC and O-termination heterogeneous nucleation interfaces are preferable formed.The microstructure observation results show that M₇C₃ carbide is further refined.Y₂O₃(YAl O₃)is combined with TiC tightly,which indicates that Y₂O₃ and YAl O₃ can act as heterogeneous nucleation substrates of TiC and refine it.Thus,the heterogeneous nucleation substrates number of M₇C₃ carbide is increased.The lattice mismatch between Y₂O₃(111)and Nb C(110)crystal faces is 6.8%and that of YAl O₃(001)and Nb C(100)crystal faces is 5.4%.The W_ad of O-terminated Y₂O₃(111)//Nb C(110)interface is 9.75 J/m² and its?is-0.87 J/m².The W_ad of O-terminated YAl O₃(001)//Nb C(100)interface is 6.56 J/m².It indicates that Y₂O₃ and YAl O₃ meet the conditions to act as heterogeneous nucleation substrates of Nb C and O-termination heterogeneous nucleation interfaces are preferable formed.The microstructure observation results show that M₇C₃ carbide is further refined.Y₂O₃(YAl O₃)is combined with Nb C tightly,which indicates that Y₂O₃ and YAl O₃ can act as heterogeneous nucleation substrates of Nb C and refine it.Thus,the heterogeneous nucleation substrates number of M₇C₃ carbide is increased.By comparing the heterogeneous nucleation interface properties of Y₂O₃(YAl O₃)//TMeC models,it can be known that the strengths of Y₂O₃(YAl O₃)//Nb C interfaces are larger than that of Y₂O₃(YAl O₃)//TiC interfaces.In addition,the hardness of hypereutectic Fe-Cr-C-TMe hardfacing alloys can be improved by adding Y₂O₃,and to reduce the cracking and spalling of M₇C₃ carbides,so as to improve the wear resistance of hardfacing alloys.The wear rate of hypereutectic Fe-Cr-C-Nb hardfacing alloy is 3.39×10^-6mm³/N?m^-1,which is smaller than the 3.64×10^-6 mm³/N?m^-1of hypereutectic Fe-Cr-C-Ti hardfacing alloy.Similarly,the wear rate of hypereutectic Fe-Cr-C-Nb-Y₂O₃ hardfacing alloy is1.54×10^-6 mm³/N?m^-1,which is smaller than the 1.79×10^-6 mm³/N?m^-1of hypereutectic Fe-Cr-C-Ti-Y₂O₃ hardfacing alloy.Therefore,the wear resistance of hypereutectic Fe-Cr-C hardfacing alloys with Nb(Nb+Y₂O₃)additives is better than those with Ti(Ti+Y₂O₃)additives.No imaginary frequency appears in phonon spectrum of TMe and Y atoms doped M₇C₃ carbides,which indicates that they are stable.Elastic modulus,intrinsic hardness and their anisotropies of TMe and Y atoms doped Fe₃Cr₄C₃ carbides are decreased.TMe atoms introduce metal bonds and ionic bonds with stronger polarity,which increases the brittleness of crystal structure and leads to the ideal strength decrease.The deformability of Fe₃Cr₄C₃ carbides was improved by doping Y atoms to form Y-C covalent bonds and reduce the polarity of Fe-C and Cr-C bonds.The fracture elongations of(2110)and(1120)crystal faces in Fe₃Cr₃YC₃ carbide are increased to 14%and 13%respectively,and its anisotropy is obviously decreased.It shows that the cracking resistance of different crystal faces in Fe₃Cr₄C₃ carbide can be improved by Y atom doping.The prediction of deformation capacity relationship between Ti,Nb and Y atoms doped Fe₃Cr₄C₃ carbides is:Fe₃Cr₃YC₃>Fe₃Cr₃Nb_0.5Y_0.5C₃>Fe₃Cr₃Ti_0.5Y_0.5C₃>Fe₃Cr₃Nb C₃>Fe₃Cr₃TiC₃>Fe₃Cr₄C₃.