Variation of plasma spray deposits microstructure and properties formed byparticles passing through different areas of plasma jet

Different trajectories of powder particles in the plasma jet during sprayin g result in different states of the particles/molten droplets on impact, re sulting in the variation of microstructure and homogeneity of the deposits. The distribution of trajectories in the jet is related to the overall spra y setup, i.e. to the spray parameters such as number and geometry of power injectors, flow rate and type of the powder feeding gas, powder size distri bution and its chemical and mechanical properties, etc. This paper studies the deposits microstructure and properties (density, porosity, phase compos ition, etc.) and relates the to the distribution of particles in the plasma jet during spraying. Free-standing tubes are selected then as an example o f the industrially important application and their microstructure is compar ed with microstructures of flat samples documenting microstructure variatio n related to different particle trajectories in the jet. The two materials studied are Alumina (Al2O3 + 3 wt.% TiO2) and natural ZrSiO4. Significant m icrostructure variation related to particle trajectories were found for alu mina deposits; for example, the alpha phase content varied between about 5 and 50%, the porosity volume varied between about 3.8 and 8% (about 2x), an d the pore surface area varied between about 1.5 x 10(4) to about 6.5 x 10( 4) cm(2) cm(-3) (about 4x). Also the microstructure anisotropy documented b y small-angle neutron scattering varied significantly. Variation in the mic rostructure of the ZrSiO4 seemed to be less significant.