The purpose of this study was to determine the creep/sintering characteristics of thermally sprayed zirconia coatings and attempt to understand the influence of microstructure on the creep resistance of deposits. The major modification, compared with more typical practice, was employment of powder feedstock with agglomerated sub-micron size particles (Nanox), which is compared to one of the best commercially available powders (HOSP). Thick plasma sprayed coatings were prepared and their physical and mechanical properties were characterized. Creep/sintering experiments were then conducted to investigate the response of the materials when exposed to high temperatures under load. The results showed that it could be possible to correlate the splat thickness to the creep behaviour of the coatings.

Retaining non-melted nano-particles of zirconia in nanostructured coatings has been a challenge in the past. Recently an air plasma spray process was developed to produce coatings which retain up to 30-35% by volume non-melted particles, resulting in a unique structure. The creep/sintering behavior of such thermal barrier coatings deposited from nanostructured feedstock has been measured and compared with deposits produced from hollow sphere powder (HOSPTM). Both feedstocks contain 6-8wt% Y 2 O 3 as stabilizer. Flexure and compression creep testing were conducted under several different loads and temperatures to obtain creep exponents and parameters.

Thermally sprayed ceramic coatings deposited from nanostructured feedstock powder have often shown improved mechanical properties comparing to coatings produced from convention feedstock. Bimodal structured ceramic deposits have been reported to demonstrate better properties such as wear resistance, adhesion strength and toughness. For thermal barrier coatings, high temperature performance is a key point especially creep/sintering. In this study creep/sintering rate of plasma sprayed, bimodal structured, yttria stabilized zirconia coatings were investigated. The creep behaviour was investigated using free standing thick (3 mm) coating layers loaded in the four point bending setup at two temperatures : 800 and 1000 ºC in air. Under the same test conditions the creep results for nanostructured coatings and conventional plasma spray coatings have been compared together and the former one in both temperatures showed a lower creep rate.

During the past few years thermally sprayed ceramic coatings deposited from nanostructured feedstock powder have often demonstrated improved properties relative to coatings produced from convention powder. Nanostructured or bimodal structured ceramic coatings have been reported to exhibit better wear resistance and adhesion strength. For thermal barrier coatings, key properties include thermal conductivity and thermal stability. In this study thermomechanical properties of plasma sprayed, bimodal structured, yttria stabilized zirconia coatings were investigated. The thermal stability was examined by measuring the hardness and elastic modulus of free standing coating layers before and after heat treatments in air at 600-800 °C. The creep behaviour was investigated using free standing coating layers loaded in the four point bending configuration at temperatures of 1000 °C in air. The results for bimodal structured coatings have been compared with the behaviour of conventional plasma spray coatings under the same test conditions.

For more than two decades researchers have been working on thermal barrier coatings to improve the performance of diesel engines. However, these coatings have still not achieved widespread application in conventional diesel engines. The original motivation for this work was the improvement of fuel economy, since even a few percent improvement would result in huge savings in the transportation industries, but the coatings also effect exhaust emissions, component wear, and the sensitivity of engines to fuel quality. Wear at high temperatures, where conventional lubricants are not effective, is a serious problem in low heat rejection engines. Ceramic materials such as thermal barrier coatings in cylinder liners must have an acceptable wear rate and coefficient of friction. In this work we compare the wear behaviour of nanostructured thermal spray zirconia coatings with conventional zirconia coatings. First, process parameters that allowed the nanoparticles present in the feedstock powder to be retained in the coating were found. Then pin on disc wear tests of the two types of coatings were carried out at room temperature. The coating containing retained nanoparticles exhibited a lower coefficient of friction and less wear loss under discontinuous testing than the conventional coating.