Properties Of Al₂O₃ Dispersion Strengthened NiCr Matrix Composites Coatings

In this study, Al2O3–dispersion– strengthened NiCr alloy powder were produced by the planetary ball milling,centrifugal spray drier and high temperature heat treatment. The effect of different milling times,Al2O3 to NiCr volume ratio and grain size of raw powder on the performance of spray powders were researched. The effects of different heat treatment temperature on the performance of powders were investigated. The liquidity,loose density and tap density of powders were tested. In order to meeting the thermal spraying powders requirements, the optimally heat treatment temperature were seek. The powders including of matrix precursor NiCr were sprayed using a plasma spraying (Atmospheric plasma spray (APS); Microplasma spray (MPS)) process. Coating microstructures were analyzed by X-ray diffraction (XRD), Scanning electron microscope (SEM), and Energy dispersive spectrometry (EDS). Characteristics and mechanism of high temperature oxidation was investigated. And the erosive wear behaviors at the 650℃and mechanism were researched. The main results are summarized as follows:1. Micro-nanometer composite powder were produced by the planetary ball milling, After spray drying the coacervate powder particle size between 45-75μm, The majority of powder are the spheres. After heat treatment at 1050℃, the powder still maintained the micro-nanometer microstructure, the liquidity,loose density and tap density of powders fit for the plasma spray.2. NiCr and composite coatings prepared by plasma spray, the typical lamellar structure in the NiCr coating, the complex phase structure in the composite coatings. The coatings performance relies on the ball milling powder performance, the dispersion-strengthened powder's structure is more homogeneous, the coating's microhardness is more higher.3. The results of high temperature oxydation showed that: the oxidation film on the composite was tearing and unsound because the Al2O3 particles dispersion distribute in the composite coatings, so the inoxidizability of the NiCr coating is better than composite coatings.4. The results of high temperature erosion at 650℃showed that: it is the plastic eroding mechanism for the NiCr coating and plastic accompany with brittle mechanism for the composite coatings, the composite coatings have a good high temperature erosion resistance.