In the present study, a novel and practical method, white light interference, was proposed to characterize the lamellar pores covered by thermally sprayed YSZ and LZ splats. In this method, only an ordinary optical microscopy (OM) was employed. Colorful Newton rings and parabolic shapes of the lamellar pores were widely observed by OM. The crack spacing and the shapes of the lamellar pores captured by OM were well consistent with those by scanning electron microscopy (SEM) and focus ion beam (FIB). Besides, mechanical analyses were carried out and the results were well consistent with those by OM. Most importantly, the essential fact that the lamellar pores resulted from transverse cracking/delamination in thermal sprayings was highly elaborated.

Thermally-sprayed LZ/YSZ double-layer coatings are promising candidate for the next generation thermal barrier coatings (TBCs) due to exceedingly low thermal conductivity and superior high-temperature phase stability. However, a delamination failure at LZ and YSZ interface were widely observed during TBCs service. Till today, the interfacial microstructure between LZ and YSZ remains unclear. In the present study, LZ splats were deposited on YSZ substrate to serve as a LZ/YSZ interface. The interfacial microstructure was explored by focused ion beam (FIB) and high-resolution transmission electron microscope (HR-TEM). The interfacial defects at splat interface were clearly observed and thoroughly discussed. These results would shed light on deeply understanding the interfacial failure of double-layer LZ/YSZ coatings.

This work evaluates the high-temperature oxidation behavior of thermal barrier coatings by means of impedance spectroscopy. TBCs consisting of YSZ topcoats and NiCoCrAlYTa bond coats were deposited on Ni-based superalloy substrates by atmospheric plasma spraying. Test specimens were heated in air at 1000 °C for different periods of time from 5 h to 250 h. SEM-EDS analysis of the thermally grown oxide (TGO) shows that it mainly contains alumina and grew at a parabolic rate with increasing oxidation time. The resistance of the TGO, as determined by impedance spectroscopy, was found to increase at similar rate. Impedance spectroscopy also revealed an increase in YSZ grain boundary resistance corresponding to grain boundary cracking that occurred in the first 50 h of heating. The YSZ grain boundary resistance remained relatively constant over the interval of 50 to 150 h, but showed a slight decrease beyond 150 h mainly due to sintering effects.

The aim of this study is to better understand the formation of nonbonded splat-to-splat interfaces in thermally sprayed ceramic coatings. To that end, the surfaces between splats in plasma-sprayed La 0.5 Sr 0.5 CoO 3 (LSCO) coatings were examined and compared to free splat surfaces. The results show that free splat surfaces are relatively smooth, while adjacent surfaces at intersplat interfaces are quite rough. The observation implies that nonbonded splat-to-splat interfaces were never bonded, having fractured due to interface shear stress generated during splat cooling.

ZrOCl 2 •8H 2 O and NH 4 OH were regarded as original materials to prepare zirconia sol by co-precipitation, and nano-zirconia coatings were prepared by sol plasma spraying. The structure of the coatings was analyzed by SEM, XRD, and influence of power and stabilizer, concentration and dispersed phase on the coatings was investigated primarily. The result showed that the sol was non-crystal structure after spontaneously dried, the coatings were mixed of nanostructure of monoclinic and cubic phase after plasma jet heated. Increasing power decreased the content of non-crystal phase, adulterating yttria had good crystal phase stabilization, and the content of monoclinic phase decreased greatly. Coatings were denser when higher concentration and ethanol qua dispersed phase were used. Porosity of coatings decreased prior and increased later along with concentration increasing.

The use of gas mixtures containing hydrocarbons for plasma generation results in higher plasma enthalpy because, molecular gases must dissociate before ionization which requires larger energy input. The torch developed at CACT which operates with CO 2 +CH 4 gas mixtures was used for coating deposition with input power in a range of 30 to 45 kW. This study was focused on the effect of CO 2 +CH 4 mixtures on the particle parameters during spraying of Ni alloy powder. Results of gas composition analysis at various distances from the nozzle exit are presented. The particle in-flight conditions, coating microstructure, and deposition efficiency also were analyzed.

In this work, plasma flow inside a cascaded DC torch, effect of a plasma gas composition (Ar or CO 2 +CH 4 ), and torch performance were studied. Both laminar model and k-ε turbulence model were employed and compared in the simulations. The results revealed that carbon contained gases can significantly increase the arc voltage and torch power. This gas mixture increases the arc voltage by up to 200% in comparison with argon. Voltage-current characteristics were also simulated for the current range of 200-400A. Differences in the torch performance can be attributed to the gases specific properties. For instance, at the same temperature the considered plasma gases have similar electric conductivities but the enthalpy of molecular CO 2 +CH 4 is much higher. Experimental validation indicates that k-ε turbulence model provides better agreement.

Thermal spray torches commonly use argon for plasma generation. Low thermal properties of argon, however, limit the thermal efficiency of the torches. Use of molecular gases, which must dissociate before ionization, requires larger energy input resulting in enthalpy increase of the plasma. In this paper, the effect of various gas compositions (Ar, Ar+H 2 , and CO 2 +CH 4 ) on the torch voltage-current characteristics, power and thermal efficiency were studied. At the same time, in-flight YSZ particle conditions were compared. The higher thermal conductivity and efficiency of CH 4 +CO 2 gas mixture produce more favorable sprayed particle conditions, in particular temperature. At a 50mm spray distance, YSZ particle temperatures were 2470°C and 2896°C for Ar+H 2 and CH 4 +CO 2 , respectively. Typical arc voltage for the torch operating in CO 2 +CH 4 was 130-180V compared to 45-60 V for Ar+H 2 . Thermal efficiency was also 20-40% higher.

Materials are developed and improved by adjusting both the alloy chemistry and the processing conditions to achieve desired microstructures and properties. Traditionally, these improvements have been made by a slow and labor-intensive series of experiments. But it is now possible to replace this expensive trial and error process by carrying out only a few ‘key’ experiments in conjunction with thermodynamic calculations. These calculations are powerful tools for alloy design, enabling improvement in the selection of alloy chemistry and the parameters used for fabrication steps such as heat treatments. In order to have the utmost confidence in the results obtained from the calculations, it is essential to have high quality thermodynamic databases. Such databases can be used not only in phase equilibrium calculations but also as the critical input for further kinetic simulations. In the present paper, we present our work on the development of reliable thermodynamic databases for nickel-based superalloys and iron alloys. We first briefly describe the methodology of developing these databases and then discuss some specific examples using the databases. With the aid of these examples, the usefulness of thermodynamic databases in aiding the development of advanced materials is discussed.