Use of small-angle neutron scattering for the characterization of anisotropic structures produced by thermal spraying

Results for the microstructural characterization of thermal spray deposits, using small-angle neutron scattering (SANS), mercury-intrusion porosimetry , and image analysis of polished cross sections,are compared. The alumina a nd yttria-stabilized zirconia deposits studied were produced by two differe nt atmospheric plasma-spraying methods - using gas-stabilized and water-sta bilized plasma systems. The void microstructure of these deposits is domina ted by two anisotropic void types - interlamellar pores and intralamellar c racks. There is also a broad distribution of spherical pores. The relative importance of these void systems is found to depend on the materials chemis try and on the spray technique. The surface area of the anisotropic voids w as determined using SANS. By varying the spray technique and material, depo sits with different dominant void systems were produced. The alumina deposi ts, manufactured by a high-power water-stabilized plasma-spray system, cons isted of a microstructure dominated by intralamellar cracks; the same mater ial deposited by a standard lower-power gas-stabilized plasma-spray system has about equal surface area in the intralamellar cracks and interlamellar voids. However, the zirconia deposit microstructure is always dominated by inerlamellar voids.