Research On Ti-Co-Cu-Fe-Ni-Cr High-entropy Alloy Coatings Prepared By High-energy Micro-arc Spark-Computer Numerical Control Deposition

High-energy micro-arc spark deposition?HEMASD?has gained special status in re-manufacturing field due to its exceptional characteristics such as low heat input,rapid cooling rate,metallurgical bonding between coating and substrate,and easy selection for electrodes.However,the traditional HEMASD process is carried out by hand,which results in the uncontrollability of the microstructure,composition,performance and apparent characteristics of coatings owing to the intervention of human factors.Moreover,the traditional HEMASD process can't accomplish the precise preparation of complex curve/surface coatings.How to realize the automation and digitization of the traditional HEMASD process becomes an urgent problem to be solved in order to meet industry requirements for the preparation of complex curve/surface uniform coatings.Aiming to solve the problem,a HEM AS-computer integrated deposition system?HEMAS-CIDS?is created based on a 3-axis CNC milling machine through designing a special deposit holder.The HEMAS-CIDS realizes the seamless integration of the CIMS technology and the traditional HEMASD welder.A new HEMASD process,HEMAS-computer numerical control deposition?HEMAS-CNCD?process,is developed based on the HEMAS-CIDS.HEMAS-CNCD achieves the automation and digitization of the traditional HEMASD process.Oriented to the conundrum of the preparation for complex curve/surface coatings via HEAMS-CNCD,complex curve/surface coatings are designed and constructed based on NURBS theory,a spot-welding deposition strategy is developed,and equi-chord/equi-arc length deposition interpolation methods are presented for NURBS curve/surface coatings.The successful preparation of NURBS curve/surface coatings using equi-chord/equi-arc length deposition approaches proves that it's feasible and effective to produce complex curve/surface coatings via the HEMAS-CNCD process.In order to realize the accurate control of depositing process for complex surface coatings,the method of NURBS mapping projection curve?NURBS-MPC?depositing trajectory planning and control is proposed in this work.Any predefined planar curve can be mapped on a predefined NURBS surface using the method.Thus,the preparation of arbitrary complex curve coatings on the predefined NURBS surface can be obtained using HEMAS-CNCD.This work proves that it is feasible and effective to control the depositing trajectories of complex surface coatings via NURBS-MPCs,which provide the theory basis for the planning and control of depositing trajectories for surface coatings.An offline software based on Matlab and an online software based on the parametric programming function of FANUC CNC systems are developed for the HEMAS-CNCD process.Both of them can accomplish the design,verification and program generation of complex curve/surface coatings.Furthermore,arbitrary complex curve/surface coatings can be deposited using the online software via assigning parameters.Since the concept of multi-component high-entropy alloy?MC-HEA?is proposed,it has become a research frontier in global materials field.The composition design of MC-HEAs has been a research hot and conundrum in the academic community.Oriented to the composition design of MC-HEA electrodes for HEMAS-CNCD,the mixing enthalpy matrix?MEM?is presented in this work,and the traditional thermodynamics of MC-HEAs is rewritten into matrix pattern,then rewritten into functional pattern for MC-HEA systems?MC-HEASs?.A MC-HEA electrode-computer aided design software?MC-HEAE-CADS?is developed based on Matlab software.Oriented to E¹ …Eⁱ …E^n-1E_xⁿ pattern MC-HEASs,a composition design approach of MC-HEAS electrodes is presented based on the characteristic points?CPs?of the MC-HEAS thermodynamic parameter curves?MC-HEAS-TDPCs?.This design approach makes researchers to grasp and predict thermodynamic characteristics of a MC-HEAS as a whole,and master the microstructure of MC-HEASs corresponding to CPs?namely maximum/minimum points?after proportioning,melting,characterization and analysis.The variation law of the microstructure of MC-HEASs with composition variables can be easily grasped through comprehensively analyzing the whole?the TDPCs of a MC-HEAS?and the individuals?the microstructure of MC-HEAs corresponding to CPs?.Aiming to the preparation of flame-retardant coatings of aircraft engines,the composition design approach for a MC-HEAS based on the CPs of TDPCs is proved to be feasible and effective through composition designing and characterization analyzing the CoCuFeNiCr_x?x ?[0 4]?MC-HEAS containing the elements with a certain degree of flame-retardant properties.The Ti-Co-Cu-Fe-Ni-Cr multi-component alloy coatings with various entropy value status?VEVS?are produced on TC11 titanium alloy substrate via HEMAS-CNCD using the MC-HEAs corresponding to the CPs of the CoCuFeNiCr_x?x ?[0 4]?MC-HEAS as electrodes.The characteristics and law of mass transfer in HEMAS-CNCD is analyzed.The formation and mechanism of positive and negative heat sources is expounded.The mass transfer law,heat source mechanism,and thermodynamic mechanism is clarified for the solid solution formation of VEVS Ti-Co-Cu-Fe-Ni-Cr coatings.This work shows that the nonlinear growth characteristics of TC11-substrate mass transfer can effectively increase the content of electrode elements in coatings.It makes the mixing entropy of the MC-HEA coatings to transform from low entropy status to medium entropy status even to high entropy status.The microstructure of VEVS Ti-Co-Cu-Fe-Ni-Cr coatings is composed of BCC or BCC+FCC solid solution.The extremely high cooling rate of HEMAS-CNCD makes the VEVS Ti-Co-Cu-Fe-Ni-Cr coatings,which don't meet the thermodynamic conditions of forming solid solution?s?,to form solid solution microstructure.Because the microstructure of coatings is strongly dependent on the electrode composition,two type coatings of multi-scale micro/nano crystalline coating and amorphous coating are prepared on TC11 titanium alloy substrate using CuNiSiTiZr and CuNiTiZr as electrodes respectively.The laser ablation tests show that the Ti-Co-Cu-Fe-Ni-Cr multi-component alloy coatings,Cu-Ni-Si-Ti-Zr micro/nano crystalline coatings and Cu-Ni-Ti-Zr amorphous coatings can enhance the ablation resistance properties effectively.The successful preparation of various coatings above-mentioned shows that HEMAS-CNCD has great potential in preparing coatings with special microstructure.The CNC process of HEMAS-CNCD makes it easy to popularize in the industries and has broad application prospect.