In order to utilize the blasting process for preparing surfaces of precision products, the factors affecting the work piece distortion and the degree of the distortion were investigated. The long and flat shaped specimens of the different materials and the thickness were blasted, and the phenomena induced by the blasting were investigated. In the result, almost the linear relationship between the surface roughness and the maximum deflection existed. In addition, the equivalent load was applied to the simple model of the distortion, and the correlative expression among the maximum deflection, the specimen's size, and the equivalent load was deduced. The results made it possible to select and design beforehand the products, and to optimize the blasting condition.

To avoid constraints due to the conventional surface preparation before thermal spraying (degreasing and sandblasting), the PROTAL process was developed implementing a Q-switched Nd-YAG laser to prepare the surface simultaneously to the coating build-up. The original system was designed with a single laser head and could meet with some limitations versus the thermal spray plume size, for example in the case of HVOF or twin wire arc spraying. In this work, a device with two laser heads was implemented thus increasing the size of the surface area which is prepared to receive the impinging material droplets. Then, after a presentation of the integration of such laser system in the thermal spray environment, some results will be presented. No significant surface topography modification can be noticed after the laser beam impact, this paper aims at clarifying the bonding mechanisms of thermal spray coatings manufactured implementing the PROTAL process. The case of a metallic coating deposited on a metallic substrate is especially discussed.

The effect of pack boronizing on microstructure and hardness of WC-12wt%Co coating sprayed on a low carbon steel (SS400) was studied using two kinds of HVOF-sprayed WC-Co coatings consisting of a single phase of WC and several phases of WC, W 2 C and Co 3 W 3 C, respectively. Pack boronizing was applied at 1273K for 3.6ks under an argon flow atmosphere, using 5%B4C, 5%KBF4 and 90%SiC powders. Microstructures obtained were characterized by X-ray diffraction, SEM and EDX analyzer. After boronizing, WC and CoW 2 B 2 phases were detected in the both sprayed WC-Co coatings. This suggests that not only WC but also W 2 C and Co 3 W 3 C of WC-Co coatings decomposed by boronizing, resulting in the development of CoW 2 B 2 . However, many porosities with a size of more than 10µm were formed on the coating consisting of WC, resulting in a low hardness of HV600. On the contrary, the coating with W 2 C and Co 3 W 3 C has little porosity and a high hardness of HV2600.

The Protal process combines surface preparation using a laser and thermal spraying in one production step. The laser preparation is based on a photomechanical reaction induced by the interaction between a laser of high instantaneous power and a polluted surface. The mechanism of bonding and the coating-substrate interface are then changed in comparison with grit blasting resulting in a significantly reduced substrate roughness. This study is aimed at finding the optimal Protal process parameters for the coating adhesion of a Ni5%Al sprayed on Ti6Al4V and IN718 alloys. The parameters investigated are laser beam intensity, the time delay between the laser impact and the spray impact, powder feed rate, substrate roughness and temperature. A test plan including these parameters is analysed by means of a fractional factorial design of experiment method. The adhesions of the coatings are measured using the ASTM C633 standard test. Data are analysed by a multiple linear regression model using a least squares fit. In addition, the coating/substrate interface is examined by optical and electron scanning microscopy (SEM) techniques as well as by Auger electron spectroscopy. Substrate roughness, substrate temperature and laser intensity are all shown to have a negative correlation with adhesion strength within the investigated range. Areas of diffusion are noticed at the coating/substrate interface.

Die-casting moulds are subjected to severe conditions of cyclical thermal and mechanical loads, as well as chemical and mechanical wear. Dies mostly fail due to a combination of wear mechanisms. Heat checking, erosion, melt corrosion and soldering often lead to complete die failure. Ceramic plasma-sprayed coatings have a great potential for die protection, since they are chemically inert, and show high form stability at elevated temperatures. Furthermore, they show good resistance against thermal shock due to the porous state of the coated layer and low Young’s modulus. In the present study, the influence of hot isostatic pressing on thermal fatigue resistance of plasma spraying coatings is investigated. Thermal and thermomechanical tests were applied to characterise their ability to protect dies. The coatings were evaluated by residual stress measurements, metallography, hardness test and X-ray diffraction.

The effects of resin sealing on WC-NiCr HVOF sprayed coatings were studied using the anodic polarization measurements and the potentiostatic polarization measurements in sulfuric acid aqueous solution. Three types of coatings, without sealing, with sealing applied once and twice were prepared. Regarding the anodic polarization measurements the current densities of the coatings with sealing were less than that of the coating without sealing in the potential range of 0.1 V to 1 V (vs. Ag/AgCl, sat. KCl). According to the potentiostatic polarization measurements the current densities of the coatings with sealing were also less than that of the coating without sealing. Fe was detected in the electrolyte which the coating without sealing was immersed in on the potentiostatic polarization measurements. This meant that the substrate dissolved into the electrolyte because the coatings contain Fe less than 0.13 wt%. In addition, the coating sealed once were compared with that sealed twice. And it became clear that sealing effectively prevents substrates from dissolving and improves corrosion resistance of coating in sulfuric acid aqueous solution, which agreed with the result of salt spraying test.

Whilst innovative advancements in thermal spray technology, especially in terms of characterization of starting powders, coating processes and optimisation of coating process parameters have resulted in coatings of improved quality, there is an ever increasing demand to push the frontiers of coating applications. Post-treatment of thermal spray coatings either by HIPing (Hot Isostatic Pressing) or vacuum heating can thus offer one such opportunity by presenting a combination of coating and substrate properties not achievable by individual processes. Hence the aim of this study was to investigate the potential of two integrated process technologies of thermal spraying and HIPing. Tribo-mechanical properties of WC-Co coatings deposited by the HVOF process in the as-sprayed and post-treated conditions were thus investigated in this study. Results are discussed in terms of coating microstructure, sliding wear resistance, elastic modulus, hardness, residual strain and rolling contact fatigue resistance. These results indicate that significant improvements in coating performance can be achieved by appropriate design of post-treated components.

The high temperature oxidation resistance behavior of atmospheric plasma sprayed CoNiCrAlY coating with a thin layer of Cr 2 O 3 employing chromate treatment was investigated. The high-temperature oxidation test was performed at 1423K for 7.2, 14.4 and 32.4ks, respectively. The formation of the oxide layer on the CoNiCrAlY coatings with Cr 2 O 3 thin layer by chromate treatment was compared with that of the non-Cr 2 O 3 thin layer. The oxide layer formed on the both types of MCrAlY coatings grows with increasing the elevated temperature and the holding time. Also, the thickness of the oxide layers was proportional to the square root of time. The thickness of the oxide layer on CoNiCrAlY coatings with the thin layer of Cr 2 O 3 was only 60% as compared with that of the non-Cr 2 O 3 thin layer in high temperature oxidation tests at 1423K.