Basic Research On Preparation Technology Of Nicrcoaly Protective Cladding Coating Reinforced By Nanometer La₂O₃

This paper presented a scientific basic research on preparation technology of NiCoCrAlYprotective cladding coating reinforced by nanometer La2O3. Nanometer particles dispersion, powdercompaction mould designing and cladding sample preparation have successfully solved. Meanwhile,single cold compaction process of cladding powder was simulated by MSC.MARC and laser claddingprocess was simulated by ANSYS.The major work done and the results obtained are as follows:1. By investigating various dispersion behaviors of nanometer La2O3particles in pure water,1:1water-ethanol mixture and pure ethanol, it was decided that the most suitable dispersion solvent forpreparing nanometer La2O3suspension is pure ethanol. Four dispersion methods on the dispersioncapability of nanometer La2O3suspensions were studied, and they were ball milling, ultrasonic,ultrasonic followed by ball milling and ball milling followed by ultrasonic. For the purposes ofcomparing their dispersion capability, sedimentation test, Zeta-potential measurement test, particlessize measurement test and TEM test are carried out. Suspension ability coefficient was also definedwith expectation to estimate the stability of nanometer La2O3suspension through granularity size, andtheir relationship curve was worked out. The results showed that ultrasonic followed by ball millingenjoy an excellent capability of dispersion for nanometer La2O3suspension. Its mechanism wasdiscussed, and breakage models of nanometer La2O3particles were developed.2. Numerical simulation on the single cold compaction process of NiCoCrAlY cladding powderwas shown by the aid of the FEM software MSC.MARC. Firstly, a reasonable2-D finite elementmodel of the powder compaction process was built, making sure the materials model of NiCoCrAlYcladding powder, initial condition and boundary condition for single cold compaction process, andacquiring the regular of the displacement along the height direction and the diameter direction.Secondly, take the maximum relative density as the theoretical relative density in order to list therelationship of the porosity, densification, relative density and the height with the pressure. Finally,obtaining the height of the sample and the relative density of the sample’s top surface and bottomsurface based on matlab image recognition, which verifies the validity and reliability of the model.3. According to the characteristic of laser cladding，a reasonable3-D thermo finite element（FE）model was built with APDL parametric design language in consideration of those including the heatsource model，latent heat，changes of material attribute，dynamic boundary conditions and dynamicthermal resistance. Experiments of laser cladding were carried out to prepare NiCoCrAY coatings on Ni based high temperature alloy. Comparison of the calculation results and experimental results showsthat the numerical results agree well with the experimental ones，which verifies its reliability andvalidity of the model.4. To get an optimal cladding process parameters, different laser scanning speed of TC4titaniumalloy for cladding layer quality was investigated. Three kinds of adding amount of nanometer La2O3,those were1%wt,2%wt and3%wt, were studied on their influence on cladding layer dilution rate,microstructure and hardness by the optimal cladding process parameters. Finally, thermal shockproperty in high temperature of the cladding layer without adding nanometer La2O3particles or notwere investigated.