This study assesses the abrasive wear resistance of Cr 3 C 2 -NiCr coatings produced by HVOF spraying. Abrasion tests were conducted in a three-body solid-particle rubber-wheel test rig using silica and alumina grits under different loads. The results indicate that abrasion performance is controlled by cohesion between splats, which can be further improved. The removal of carbide particles was the main wear mechanism and is controlled by the content and size of the Cr 3 C 2 particles. It is shown that the abrasive wear resistance of carbide-based cermet coatings is significantly higher than that of mild steel.

Plasma sprayed yttria stabilized zirconia (YSZ) coatings are being increasingly used as thermal barrier coatings(TBCs) for gas turbine parts. However oxidation problems are critical for durability of TBC. Al 2 O 3 addition to YSZ is considered as an oxygen barrier microstructure at elevated temperature. Therefore it helps to the growth rate of the thermally grown oxide layer between top coat and bond coat. Spray properties and rapid solidification determine the final characteristics of the coating. Plasma current, plasma gas flow rate and spray distance factors have main effect on occurrence of microstructure. Therefore plasma spray parameter optimisation is required for TBC manufacturing. Statistical designs of experiments have been shown to provide efficient approaches to systematically investigate the process parameters of plasma spray process. In this study Al 2 O 3 -YSZ particle composite TBC deposited with different plasma spray process parameters by using Taguchi method for optimisation.

With the modification of plasma spray parameters, porosity ratio of top coat can control along the cross-section. This improves the thermal cycle resistance and decrease the thermal conductivity. Plasma sprayed ZrO 2 /8 wt.–% Y 2 O 3 –NiCrAlY TBC systems which have different porosity (%8-12) and range of 250-350µm thicknesses of top coats, during thermal cycling tests with different hold times at 1350 °C have been performed. The main failure modes: delamination cracking, TGO growth rate and phase transformation are strongly dependent on the hold temperature and time. The correlation between TBC thermal cycle lifetimes and duration of high temperature hold time per cycle is shown and discussed with depending on thickness and porosity ratio.

Biocompatibility of hydroxyapatite (HAp) coatings have led to its use in a wide range of applications in both dentistry and orthopaedics. The plasma spraying method is the most commonly used method for the production of Hap (Ca 5 (PO 4 ) 3 OH) coatings on Ti alloys. When HAp is injected into the plasma jet, several phases can coexist under the effect of a temperature gradient occurring in the bulk of the particle. The amounts of residual compounds, amorphous and recrystallized phases are related to the conditions of spraying such as gas flow rates, feed rate, spray distance, plasma current and cooling effect. Plasma-sprayed HAp coatings were analyzed by X-ray diffraction and electron microscopy.

WC-CoCr coatings are deposited by HVOF process for improving surface resistance of low alloyed steels. In this study we examined the wear characteristics of WC-CoCr coatings on low alloyed steel substrate under different test conditions, using a sliding wear test unit with abrasive ball. In experimental studies discussed the effects of test load, temperature, work medium and sliding distance on the wear characteristics of coatings. Weight loss, wear track depth and width were observed . It was found that the weight loss of coatings increased in dry medium conditions. Wear weight loss was significantly reduced in lubricated condition due to decreasing friction. The wear track surface profile changed with lubrication and increasing temperature in test conditions. Under the base oil lubricated conditions the WC-CoCr coating performed well.

Plasma-sprayed thermal barrier coating (TBC) systems are widely used in gas turbines blades in order to increase turbine entry temperature (TET) with better efficiency. Yttria stabilized zirconia (YSZ) has been usually chosen as the top thermal barrier coating material because of its low thermal conductivity, high thermal expansion coefficient and good corrosion resistance. However as a new candidate commercial TBC material, ceria stabilized zirconia (CSZ) currently looks to be promising. Ceria and ceria based ceramics show an outstanding potential for use at temperatures exceeding 1200 °C. CSZ coatings do not only have high temperature stability, good corrosion resistance and high fracture toughness but also lower thermal conductivity and higher thermal expansion coefficient than YSZ coatings. The sintering and phase transformation characteristics of both ceramic thermal barrier coatings under high temperature conditions are complex phenomena. In this paper, microstructural differences, sintering behaviours (1200 oC, 10h, 25h and 50h) and phase transformations of the plasma sprayed ceria stabilized zirconia (CSZ: ZrO 2 –2.5 wt.%Y 2 O 3 – 25 wt.%CeO 2 ) and conventional yttria stabilized zirconia (YSZ; ZrO 2 –8 wt.%Y 2 O 3 ) coatings and their powder materials have been investigated and compared using thermal analysis techniques, XRD and scanning electron microscope.