Refinement Mechanism Of Hypereutectic Fe-Cr-C-Ti-Nb-N-CeO₂ Hardfacing Alloy

Hypereutectic Fe-Cr-C alloys are widely used in surfacing additive manufacturing field due to their excellent wear resistance.The primary M7C3 carbide in the hypereutectic Fe-Cr-C alloy is its main strengthening phase,which determines the wear resistance of the alloy.However,when the size of the primary M7C3 carbide was large,it was easy to crack and peel off from the matrix,thereby reducing the service life of the alloy.By adding alloying elements Ti,Nb,and N to refine the M7C3 carbides,it can improve its anti-cracking and spalling performance,while there is a phenomenon of uneven size of M7C3 carbides.Therefore,it is significant to further refine the primary M7C3 carbides and to improve their size uniformity so as to enlarge the application of hypereutectic Fe-Cr-C hardfacing alloys.In this paper,the rare earth oxide CeO2 was added to the hypereutectic Fe-Cr-C-Ti-Nb-N hardfacing alloy.The first principles method was used to calculate bonding work,interface energy,electronic structure and bonding properties between the primary M7C3carbides and CeO2,（Ti,Nb）（C,N）carbonitrides and CeO2.The phonon spectrum and binding energy of（Ti,Nb）（C,N）carbonitride were calculated.The effectiveness of CeO2as a heterogeneous core of primary M7C3 carbide and（Ti,Nb）（C,N）carbonitride in hypereutectic Fe-Cr-C-Ti-Nb-N-CeO2 hardfacing alloy was analyzed.The microstructure of hypereutectic Fe-Cr-C-Ti-Nb-N-CeO2 hardfacing alloy was analyzed and observed by metallography,XRD,SEM,etc.CSM was used to determine the wear resistance of the alloy.Due to the complex crystal structure of M7C3,in order to reduce the mismatch between CeO2 and M7C3,CeO2（111）plane and M7C3（0001）plane were used to build the interface.Three interface models have been established between the CeO2（100）surface and the M7C3（0001）surface.Among them,the interface bonding work of the O1-M7C3 interface is the largest,which is 16.29J/m²,and the interface energy is the smallest,which is-9.49J/m².From a thermodynamic point of view,this interface is stable.The bonds of the O1-M7C3interface are mainly ionic ones.Therefore,CeO2 has the conditions as a heterogeneous core of M7C3 and tends to form an O-terminated heterogeneous nucleation interface.By calculating the phonon spectrum and binding energy,the most stable structure of（Ti,Nb）（C,N）carbonitride is Ti3Nb CN3.The two-dimensional lattice mismatch between Ti3Nb CN3（111）plane and CeO2（100）plane is 6.47%,which meets the medium effective heterogeneous nucleation condition.Four interface structures（O-Ti Nb,O-CN,Ce-Ti Nb and Ce-CN）are established between Ti3Nb CN3（111）surface and CeO2（100）surface.Among them,the interface bonding work of O-Ti Nb interface is the largest,which is 7.66J/m²,and the interface energy is the smallest,which is-0.82J/m².The bonds of the O-Ti Nb interface are mainly covalent ones.Therefore,CeO2 has the conditions as a Ti3Nb CN3 heterogeneous core and tends to form an O-terminated heterogeneous nucleation interface.It is found that the primary M7C3 carbides in the hypereutectic Fe-Cr-C-Ti-Nb-N hardfacing alloy with CeO2 are smaller and evenly distributed.Rockwell hardness is increased from HRC60 to HRC62.The wear rate is reduced from 4.65×10-6 mm³/N·m^-1 to2.89×10-6 mm³/N·m^-1.The carbide cracking and spalling are reduced,and wear resistance is increased.