Study On The Interfacial Stability Mechanism Of Laser Cladding YSZ@Ni Coating Based On DFT And MD Method

Nano-YSZ@Ni thermal barrier coating prepared by laser cladding technology has a broad application prospects in the field of aerospace.Therein the interface stability is the main factor affecting the performance of nano-thermal barrier coating.Based on the current experimental methods,are difficult to observe the real-time evolution process of the interface between the coating and substrate during laser cladding,the density functional theory?DFT?and molecular dynamics?MD?method were used to study the interfacial conjunction strength of YSZ@Ni/Fe-based or Ni-based alloy systematically in this paper.The stability mechanism of interface is analyzed from atomic scale and the ductile-brittle transition process of the interface is explored.Then,the energy states and electronic structure between interface are also researched.Furthermore,the interfacial atomic diffusion and its effects on interfacial stability are investigated,the results show that:Firstly,the interfacial conjunction strength is systematically investigated between YSZ@Ni coatig and Fe matrix.The evolution mechanism of energy states and electronic structure between ZrO₂/Ni,Ni/FeCr and ZrO₂/FeCr interfaces are calculated by first principles.It is found that ZrO₂?100?/Ni?100??O|Ni?interface is morst stable among the ZrO₂/Ni interface models.The work of separation?W?of Ni/Fe?100?,?110?and?111?interface models are calculated respectively.It is found that the largest W value is for Ni?100?/Fe?100?interface model.After Cr doped,the formation enthalpy??H?and cohesive energy??E?decreases obviously and the W increases for Ni?100?/Fe Cr?100?interface model compared with its original model,which is indicated that the stability of Ni/Fe interface is strengthened by dopant with chromium.The Mulliken population results show that the trend of Mulliken bonding strength for ZrO₂/Ni?O|Ni?,ZrO₂/FeCr?O|Fe?and ZrO₂/FeCr?O|Cr?interface models is as QO-Ni>QO-Cr>QO-Fe.Comparing the local population strength ratio?RLBOP?between intra-layers and inter-layers,the largest RLBOP is for Ni?111?/Fe?111?interface and the lowest is for Ni?100?/Fe?100?interface.After Cr doping,the RLBOP of Ni?100?/FeCr?100?interface model is became more smaller,indicating that the interface toughness can be improved by Cr doping.The electronic density difference shows that the brittle tendencies of Ni?110?/Fe?110?and Ni?111?/Fe?111?interface models are derived from their butterfly-like covalent bond properties,and the toughness of the Ni?100?/Fe?100?and Ni?100?/FeCr?100?interface models are derived from its uniform distribution of metal bond properties.Secondly,the interfacial atomic diffusion is explored between YSZ@Ni coatig and Fe matrix.The minimum energy path?MEP?method was used to calculate the diffusion process of interface atoms in the ground state in this paper.It is found that the atomic diffusion in Zr?Ni and Fe?Ni are an endothermic reaction,but the Cr?Ni diffusion process depends on the position of Cr atoms at the interface.When the Cr atoms are at the nearest neighbor,the diffusion between Ni?Cr is also an endothermic reaction.When the Cr atoms are at the next-nearest neighbor or the concentration of Cr atoms is increased,the diffusion between Ni?Cr is an exothermic reaction.Furtherly,the diffusion ability of Fe,Cr and Ni atoms at different temperatures was investigated by molecular dynamics?MD?.It is found that the trend of diffusion coefficient for Fe,Cr and Ni is DFe>DCr>DNi in the melting and solidification process.However,the diffusion coefficient of three atoms decreased sharply,and the trend of that turned over to be DNi>DFe?DCr when the system begin to nucleation on the micro changing range of tempareture.Lastly,the interfacial stability is systematically investigated between YSZ@Ni coatig and Ni matrix.It is found that the ?H of Al₂O₃ in bonding layer is smaller than that of TiO2 by first principles calculation,indicating that the former is easier to form than the latter.The Mulliken population analysis shows that the population strength of ZrO₂/Al?O|Al?interface is only 0.133 and it is the most unstable structure.Followed by ZrO₂/Al₂O₃?Zr|O?interface model,the maximum population strength is obtained for ZrO₂/Ni?O|Ni?interface model.Furtherly,the diffusion ability of Ni,Fe,Al and Ni atoms at different temperatures was investigated by molecular dynamics?MD?.It is found that the trend of diffusion coefficients for the three atoms in the Ni/NiFeAl interface model is DNi>DFe>DAl,and that for the three atoms in the Ni/NiAlTi interface model is DNi>DTi>DAl during the whole heating and cooling process.After normalization,the trend of diffusion coefficients for NiFeAl Ti quaternary system turned to be DNi >DFe>DTi>DAl.