Plasma-sprayed Samples Research Articles

Environmental Response of Plasma Sprayed Nanostructured Coatings

Erosion corrosion and environmental chamber corrosion studies conducted on plasma sprayed samples from three different spray dried and densified nanopowders showed good resistance to corrosion. A dense, uniform and even distribution of splats and small number of microvoids and pores offered a high resistance to erosion-corrosion in sodium chloride polystyrene slurry. The coatings offer a high resistance in salt spray chamber environment.

Performance of plasma sprayed and detonation gun sprayed Cu–Ni–In coatings on Ti–6Al–4V under plain fatigue and fretting fatigue loading

Cu–Ni–In powder was coated on Ti–6Al–4V fatigue test samples using plasma spray and detonation gun (D-gun) spray processes. Coatings were characterized in terms of microstructure, porosity, microhardness, residual stresses and surface roughness. Uniaxial plain fatigue and fretting tests were carried out at room temperature on uncoated and coated specimens. D-gun sprayed coating was dense with lower porosity compared with the plasma sprayed coating. D-gun sprayed coating was harder than the plasma sprayed coating and substrate because of its higher density and cohesive strength. Surfaces were very rough in both the coatings. While D-gun sprayed coating surface had higher compressive residual stresses, plasma sprayed coating surface exhibited lower values of compressive residual stresses and even tensile residual stresses. The ill effect of surface roughness was overcome by the beneficial influence of higher compressive residual stresses on the surface and higher surface hardness and so the D-gun sprayed samples exhibited superior plain fatigue lives compared with uncoated specimens. Though the plasma sprayed samples had relatively lower hardness, higher surface roughness and almost similar values of residual stresses on the surface compared with the uncoated specimens, they exhibited longer plain fatigue lives. This may be attributed to the layered structure of the coating. Though D-gun sprayed samples experienced higher friction forces, they exhibited superior fretting fatigue lives due to the presence of higher compressive residual stresses, higher surface hardness and higher surface roughness compared with uncoated specimens. The very rough surface of plasma sprayed samples enhanced their fretting fatigue lives compared with the uncoated samples. Higher surface hardness and higher compressive residual stress of the D-gun sprayed specimens were responsible for their superior fretting fatigue lives compared with the plasma sprayed specimens.

Bioceramic hydroxyapatite at high pressures

A bioceramic hydroxyapatite, Ca10(PO4)6(OH)2 polycrystalline sample was studied under high pressures in a diamond anvil cell to investigate its structural, electrical, and mechanical properties under compression. Anisotropic compression effects were observed in x-ray diffraction studies below 8 GPa. Nanoindentation hardness measurements on pressure-treated hydroxyapatite samples show hardness value of 4.0±0.5 GPa which is comparable to the plasma-sprayed samples. Electrical studies show that the bioceramic sample retained its insulating properties to 65 GPa. The present studies demonstrate that a fully dense and translucent hydroxyapatite sample is attained above 10 GPa at 300 K.

Outgassing from and deuterium retention in beryllium and Be/C mixed-material plasma-facing components

Thermal desorption spectrometry (TDS) is used to examine the outgassing characteristics of as-received beryllium samples and the deuterium retention and desorption behavior of beryllium following plasma exposure. The samples consist of a hot-pressed powder metallurgy product and a plasma-sprayed product. The number of molecules outgassed from a plasma-sprayed sample is ten times that outgassed from a press-sintered sample and a higher desorption temperature is necessary to outgas a plasma-sprayed sample. The majority of the molecules outgassed from each sample type are in the form of hydrogen molecules and water vapor. In addition, the post-plasma-exposure desorption of deuterium from both products are compared. Following identical plasma exposures at close to room temperature, a factor of ten less deuterium is retained in plasma-sprayed samples, presumably due to the columnar structure of the resultant sprayed material that would have enhanced pathways to the sample surface. After higher surface temperature exposure (≈500°C), the retention in the plasma-sprayed material is a factor of three less than the retention in the pressed-powder material. Finally, the impact on deuterium retention of carbon-containing surface layers formed during the plasma exposure is evaluated.

A study of wear resistance of plasma-sprayed and laser-remelted coatings on aluminium alloy

Two kinds of alloys Ni–Cr–B–Si and Ni–Cr–B–Si+WC were plasma sprayed onto aluminium alloy. The coatings were remelted successively with a CO 2 laser. A comparison of the wear resistance properties of both laser-treated and plasma-sprayed samples with those of aluminium alloy was conducted. A scanning electron microscope (SEM) was used to analyse wear phenomena of samples. Experimental results showed that the laser-treated and plasma-sprayed samples demonstrated, in general, good wear resistance. The laser remelted Ni–Cr–B–Si sample exhibited the highest wear resistance, and the laser remelted samples were much better than the as-sprayed samples. The plasma-sprayed Ni–Cr–B–Si+WC sample had better wear resistance than the sample without WC. However, the laser-treated Ni–Cr–B–Si+WC sample did not enhance its wear resistance compared with laser-treated Ni–Cr–B–Si sample. The worn surface analysis showed that the alloyed layer of the laser-treated samples was very compact, the worn surface was smooth and granular peeling was hardly observed. The worn surface of the plasma-sprayed sample was rather loose and there was granular peeling on the worn surface.

Wear resistance of laser-clad Ni–Cr–B–Si alloy on aluminium alloy

Using a 5 kW CO 2 laser, two kinds of plasma-sprayed coatings, Ni–Cr–B–Si and Ni–Cr–B–Si+WC alloys, were remelted on aluminium alloy. The wear resistance of both laser-treated samples and plasma-sprayed samples were investigated using a pin-on-disc sliding friction wear tester. A scanning electron microscope (SEM) was used to analyse the abrasion phenomena of the samples and a transmission electron microscope (TEM) was used to study the microstructure of the laser-clad zone. Experimental results showed that the laser-clad samples had double the wear resistance of the plasma-sprayed samples, and that the laser-clad Ni–Cr–B–Si sample exhibited the highest wear resistance. The results of wear surface analysis showed that the microstructure of the alloyed layer of the laser-clad samples was quite compact and the surfaces were also very smooth, and there was less peeling phenomenon of the granules. The microstrucutre of the plasma-sprayed sample was rather loose and there were a lot of granular peelings left on the worn surface. A study of the microstructure showed extensive amorphous and ultra-crystalline structures in the laser-clad zone, to which the increase in hardness and wear resistance may be attributed.

Mercury intrusion porosimetry of plasma-sprayed ceramic

Limitations and corrections for the application of mercury intrusion porosimetry (MIP) in measuring plasma-sprayed ceramic (alumina-titania) deposits are studied. The data reduction procedures of the MIP technique are discussed; the importance of which changes between different machines and samples. Thus, it is proposed that each published result should be accompanied by the specific data reduction procedures and assumptions used so that data may be compared. Preparation of plasma-sprayed ceramic samples has a significant influence on the MIP result. Sample fragmentation into irregular pieces (below about 1.2 mm effective diameter) prior to the MIP measurement resulted in an increase of surface effects such that the surface roughness dominated the MIP data and the measured porosity volume increased. Variation in sample thickness between 0.8 and 4.7 mm did not change the measured porosity. Orientation (parallel or perpendicular to the substrate) of the flat surface did not have a measurable effect on the MIP results.

Conductivity measurements of various yttria-stabilized zirconia samples

Samples of yttria-stabilized zirconia manufactured by the following fabrication procedures, were obtained from commercial sources: (i) hot isostatic pressing; (ii) tape casting; (iii) vacuum plasma spraying, and (iv) calendering. The ionic conductivities of these samples were measured by (a) impedance spectroscopy; (b) the four-point probe method; (c) the current-interruption technique, and (d) the van der Pauw technique. The tape-cast and hot pressed samples showed good and very reproducible conductivity values. The vacuum plasma sprayed samples showed an anisotropy in their conductivity, with the cross-plane value being several times lower than the in-plane value. A simple model based on the porous microstructure of these samples can explain this observation. Sintering of the plasma sprayed samples minimized the anisotropy and significantly improved their conductivity values. The calendered samples also showed a similar anisotropy in their conductivity data when they were inadequately sintered.