The present investigation compares blast erosion characteristics of coatings that are prepared with abrasion resistant surface treatment materials and various consolidation processes. Furthermore, it elucidates operating mechanisms in blast erosion of various sprayed coatings. The investigation presents the blast erosion test conditions and assessment of test results and discusses the effects of coating materials on abrasion loss and impingement angle on abrasion loss. It includes illustrations on SEM observation and cross-sectional observation of damaged areas. In addition, information on blast erosion resistant characteristics of materials tested and wear mechanism in blast erosion is also provided.

A method for creation of a process window for on-line monitoring and controlling of the particle velocity and temperature during plasma spraying in order to enable desired coating microstructure is presented. The desired coating is specified by determination of the ranges within which the different microstructure features and the powder deposition efficiency are allowed to vary. Multiple linear regression models, relating the particle velocity and particle temperature to the coating criterions is utilized to successively delimit the particle velocity and temperature ranges. This results in a process window, giving the limits within which the particle velocity and temperature are allowed to vary in order for the desired coating to be produced.

Titanium alloys exhibit high specific strength characteristics. They are for this reason widely used by aeronautical engineers mostly to design airframes and gas turbine components. Very often, surface treatments are applied to locally increase the surface properties, especially to obtain a better resistance against wear. Thermal spraying is largely used to manufacture these coatings. This technology requires a specific surface preparation prior to the spraying stage. This surface preparation conventionally consists in surface degreasing and grit-blasting which has some drawbacks, among them a significant decrease of the components fatigue resistance due to the notch-sensitive behavior of these alloys. The PROTAL process consists in combining surface cleaning based on laser ablation to the deposition stage thus avoiding grit-blasting. This paper aims to present an overview of the possibilities offered by this process for the coating of titanium alloys; the criticality of the different processing parameters is studied and discussed.

Different weld overlays were welded by using different weld processes. Both Ni based alloys and Co based alloys were welded on either a c-steel (Weldox 700) or a stainless steel similar to superduplex (UNS 32760). The weld overlays were investigated and compared with respect to effect of the number of layers, chemical compositions of the surface, critical crevice corrosion temperature, microstructure, hardness, friction coefficient, adhesive and abrasive wear resistance. Wear testing was performed on the Co based alloys only. Some electrolytically deposited Ni-coatings were also investigated with respect to crevice corrosion. Both an austenitic and a superduplex stainless steel were tested as reference materials.

Microcracks in thermal barrier coatings are inherent from the plasma spraying process. Such cracks might constitute a threat to the coating. The influence of pre-existing cracks in the global direction of the interface between the bond coat and the top coat on the risk of delamination is addressed through finite element simulations. Stress concentrations at the interface due to the roughness of the plasma sprayed bond coat are accounted for by a sinusoidal interface. The effect of oxidation of the bond coat is modelled by including a thin oxide layer between the ceramic coat and the bond coat. It was found that the crack tip position of pre-existing cracks, as well as the presence of an oxide layer, significantly influences the risk of delamination. As the oxide thickness increases, the risk of crack propagation increases. It is also found that not all pre-existing cracks can propagate. For some crack tip locations, the crack remains closed during the entire loading sequence.

The current study was undertaken as part of an ongoing effort at CTSR towards development of 'Process Maps' for thermal spray coatings of molybdenum. Extensive study of the spray stream of molybdenum powders in a plasma jet was carried out. The study was undertaken for three distinct nozzle (anode) geometries and different spray conditions for each nozzle. The results demonstrate that the particle velocities and temperatures vary in an interdependent manner over a narrow range for any single nozzle. When nozzles with different geometeries are used the velocity and temperature range can be extended considerably. By estimating the residence time of particles in the plasma jet and defining a 'melting index' for the particles, a cross comparison of nozzles provides insight into the particle state achieved in each case.