VARIATION OF PLASMA SPRAY DEPOSITS MICROSTRUCTURE AND PROPERTIES FORMED BY PARTICLES PASSING THROUGH DIFFERENT AREAS OF PLASMA JET
KAREL NEUFUSS, JAN ILAVSKY, BLAHOSLAV KOLMAN, JI DUBSKY, PAVEL ROHAN, PAVEL CHR SKA
Ceramics - Silikaty
abstract
Different trajectories of powder particles in the plasma jet during spraying result in different states of the particles/molten droplets on impact, resulting in the variation of microstructure and homogeneity of the deposits. The distribution of trajectories in the jet is related to the overall spray setup, i.e. to the spray parameters such as number and geometry of powder injectors, flow rate and type of the powder feeding gas, powder size distribution and its chemical and mechanical properties, etc. This paper studies the deposits microstructure and properties (density, porosity, phase composition, etc.) and relates them to the distribution of particles in the plasma jet during spraying. Free-standing tubes are selected then as an example of the industrially important application and their microstructure is compared with microstructures of flat samples documenting microstructure variation related to different particle trajectories in the jet.The two materials studied are Alumina (Al2O3 + 3wt.% TiO2) and natural ZrSiO4. Significant microstructure variation related to particle trajectories were found for alumina 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), and the pore surface area varied between about 1.5 x 104 to about 6.5 x 104 cm2 cm-3 (about 4x). Also the microstructure anisotropy documented by small-angle neutron scattering varied significantly. Variation in the microstructure of the ZrSiO4 seemed to be less significant.
keywords:setup; MD USA; trajectories; phase composition; feeding; alpha phase; DIFFERENT AREAS; VARIATION OF PLASMA
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