Comparison of the structure and wear resistance of Al2O3–13 wt.%TiO2 coatings made by GSP and WSP plasma process with two different powders

International audienceThe goal of this study is to compare two Atmospheric Plasma Spraying (APS) systems for elaborating alumina/titania coatings with good wear resistance. Both torches used were a common d.c. current Gas-Stabilized Plasma gun (GSP) with argon and hydrogen as plasma forming gases, and a Water-Stabilized high-throughput Plasma gun (WSP) working with water as plasma forming substance. The feedstock were either cladded alumina/titania powder or a mixture of conventional fused and crushed Al2O3 powder with agglomerated TiO2 nanometric particles, the resulting mean size in both cases being about 50 μm. Feedstock material phases were α-alumina and anatase titanium dioxide and the composition of both powders was 13 wt.% of TiO2 in Al2O3. Coatings obtained were analyzed by scanning electron microscopy (SEM). They presented lamellar structures with titania uniformly distributed in the alumina matrix, for both spray techniques. X-ray diffraction showed that anatase phase of titania was converted into rutile phase. The wear resistance tested by slurry abrasion (SAR) has shown that the best coating was that obtained with cladded powder sprayed by GSP process. This finding matched with the highest microhardness of this coating (Vickers indentation). It is worth noting that with these two relatively dissimilar torches similar results were obtained for the wear resistance of alumina–13 wt.% titania coating

Composite coatings of alumina based ceramics and stainless steel manufactured by plasma spraying

ISSN : 1392-1350International audiencePlasma spraying was used to fabricate composite (cermet) coatings from a mixture of powders of alumina-based ceramics and stainless steel. Regarding the water-stabilized plasma spray process (WSP), the two powders were mixed in the feed container, whereas a simultaneous feeding of the powders by separate injectors (co-spraying) was carried out together with the gas-stabilized plasma spray process (GSP). Both processes belong to a family of procedures known as atmospheric plasma spraying (APS), and give rise to similar coating characteristics. The complementarity of the component mixing in the two processes was demonstrated, and the mechanical properties such as microhardness and elastic modulus of the resulting composite coatings were studied. Attention was also paid to microstructural aspects connected to wear resistance. WSP spraying of the mixed powders resulted in coatings composed of successive layers of ceramics and stainless steel, in which the relative thickness varied with the steel content. The GSP-produced cermet coating exhibited microstructures without microcracks or interconnected porosity, and such structures gave rise to good mechanical properties with respect to elastic modulus, hardness and wear resistance. Keywords: cermet, plasma spraying, microstructure, elastic modulus, wear resistance

Plasma sprayed basalt/chromium oxide coatings

International audienceVolcanic basalt and chromium oxide (Cr2O3) have been co-sprayed in air with a direct current (d.c.) plasma to obtain composite coatings. Both powders were simultaneously injected by two separated injectors. The following spray parameters: arc current, hydrogen vol % and total plasma forming gas mass flow rate were optimized as well as injector positions. Different mass ratios of both components were used to achieve coatings. An uniform distribution of basalt among the Cr2O3 lamellae has been observed with SEM for all composite coatings. XRD showed that chromia became amorphous in the composite basalt/chromia coatings

Atmospheric plasma sprayed (APS) coatings of Al2O3-TiO2 system for photocatalytic application

International audienceThe goal of this study is to examine the photocatalytic ability of coatings produced by atmospheric plasma spraying (APS). The plasma gun used is a common gas-stabilized plasma gun (GSP) working with a d.c. current and a mixture of argon and hydrogen as plasma-forming gas. The TiO2 powders are particles of about 100 nm which were agglomerated to a mean size of about 55 m, suitable for spraying. Composition of the commercial powder is 13 wt% of TiO2 in Al2O3, whereas also in-house prepared powder with the same nominal composition but with agglomerated TiO2 and conventional fused and crushed Al2O3 was sprayed. The feedstock materials used for this purpose are -alumina and anatase titanium dioxide. The coatings are analyzed by scanning electron microscopy (SEM), energy dispersion probe (EDS) and X-ray diffraction. Photocatalytic degradation of acetone is quantified for various coatings. All plasma sprayed coatings show a lamellar structure on cross section, as typical for this process. Anatase titania from feedstock powder is converted into rutile titania and -alumina partly to -alumina. Coatings are proven to catalyse the acetone decomposition when irradiated by UV rays

Structure and properties of plasma sprayed BaTiO3 coatings

International audiencePlasma spraying enables to create layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of electric and mechanical properties of BaTiO3 coatings prepared by atmospheric plasma spraying. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO3 was fed into the plasma jet as a feedstock powder prepared by a reactive sintering of micrometer-sized powders of BaCO3 and TiO2. Microstructure and phase composition are reported and discussed in connection with electric and mechanical properties. The ability of the used techniques to detect precisely the phase transformation temperatures of BaTiO3 plasma sprayed coatings is discussed as well. A depth-sensing indentation measurement was done between 290 and 520 K to provide local mechanical characterization. The elastic modulus has shown slightly higher values than that reported typically in papers focused on BaTiO3 ferroelectric thin films. The average Vickers microhardness is tested to characterize the samples in larger scale. Awear resistance in a slurry environment is reported as well. Dielectric properties are reported for the temperature window of existence of the tetragonal ferroelectric phase. Relative permittivity and loss factor are studied at frequency from 50 Hz to 1 MHz and temperature from 260 to 400 K