Actually abradable coatings obtained by thermal spraying are currently used in aeronautical industry. They improve the turbines tightness increasing in that way, their yield. The most relevant property of this kind of coatings is its easy machinability. They have good friction properties due to the lubricant phases such as graphite or polyester and could be used for surface engineering. To optimizate abradable coating It is necessary to study the wear mechanics implied in tribological processes. In the Thermal Spray Center of the Universitat de Barcelona, AlSi-Polyester, AlSi-Graphite and Ni-Graphite coatings have been studied. Their tribological study includes Ball on Disk (BOD) test (according to ASTM G99-90) to determinate the coating friction coefficient. The wear mechanism is determined by the study of the wear track by means of scanning electron microscopy (SEM) and Scanning white light interferometry (SWLI). Main common wear parameters are reported and compared to the steel substrate.

Conducted are investigations of powders for plasma spray of wear resistant coatings. Studied are shape, relief and particle size of NiCr-Fe+50(80)%Cr 3 C 2 , NiCr-Fe+50(80)%SiC powders using scanning electron microscopy. Investigations is supplemented by the results of X-ray structural studies. Investigations serve to develop coatings with the improved oil trap capability, increased hardness and wear resistance, sprayed by a plasma jet. The developed coatings will be used to restore and strengthen machines components

Recent studies have demonstrated that WC-12Co and WC- 10Co-4Cr coatings were the best performing HVOF coatings against erosion. This paper looks at the influences of the HVOF process parameters for WC-12Co and WC-10Co-4Cr materials on the erosion resistance of the coatings. The effect of powder morphology, matrix chemistry and HVOF process parameters with respect to both silica slurry erosion and alumina dry erosion has been studied. All coatings were produced using the HVOF JP-5000 system with kerosene-oxygen flame. The spraying parameters were analyzed in term of sprayed particle velocity and temperature as measured with the DFV2000 optical diagnostic system. Simultaneously with in-flight particle measurements, the substrate-coating temperature was monitored by infrared pyrometry during coating deposition. The resulting coating microstructure was evaluated in terms of microhardness, porosity type and extent of wear damage after dry and slurry erosion. The material volume loss under various erosion conditions was related to the coating properties and microstructure. According to the experimental results, the following conclusions are drawn: 1) the kerosene flow rate affects the inflight particle state (velocity and temperature) and the coating porosity. 2) Cobalt-chrome matrix cermet performs better in slurry erosion while denser and harder cobalt matrix cermet performs better in dry erosion. 3) The use of kerosene-rich flame with lower oxygen stoichiometry reduces the carbide degradation and optimizes the wear performance of WC-12Co coatings in both dry and slurry erosion.

The cermet materials have been developed to protect surfaces against wear and corrosion. In cutting tools technology as well as chromium replacement, WC coatings have been used to improve life and performance at higher temperatures. This work compares the abrasion and adhesion resistance of a WC-Co mixed in a x:y relation with a NiCrBSiW alloy deposited by High Velocity Oxy-Fuel (HVOF) process using a JP-5000 gun in two conditions: as sprayed and thermally treated. Abrasion and adhesion tests were performed according to ASTM G-65 and ASTM C-633 respectively. The microstructure and composition of the coatings, failure and worn surface were evaluated using Optical (OM) and Scanning Electron Microscopy (SEM) as well as X-Ray energy Dispersive Spectroscopy (EDX) and X-Ray diffraction (XRD). Vickers microhardness under a 500g load has been averaged from 8 indentations per sample. The results showed that the coatings studied presented a similar microhardness as well as good abrasion resistance. The best behavior of the post-heated coating could be attributed to a lower porosity, better distributions and effective cohesion between hard phases. Partial recrystallization of the amorphous phase produced during the thermal spray process into sub-carbides could be related to the improvement in abrasion resistance of the post-treated coating.

In mechanical engineering there is an increasing demand for lightweight design and materials engineering from the view points of weight reduction, reduction of consumed energy and upgrading of performance. One major drawback of light metal alloys is their poor tribological properties concerning friction and wear under high surface loadings. This study focuses on the development of combined coatings on light metal substrates which show high wear resistance and low friction coefficients under dry sliding conditions. The combined coatings consist of a thermally sprayed ceramic or metallurgical primary coating to provide the wear resistance. Subsequently a coating with dry lubricating ability is deposited to achieve a low friction coefficient, either by application of a lubricant lacquer containing microscale solid lubricant particles (e.g. PTFE, MoS 2 ), by cathode sputtering of MoS 2 or by deposition of pure carbon containing coatings (a-C:H) by plasma assisted CVD.

Thermal sprayed ceramic coatings play an important role in those industrial applications where exceptional erosion and wear resistance are required. In particular, nickel-chromium based coatings containing chromium carbide particles dispersion are widely used when environment temperature rises up to 800°C. Thick Cr 3 C 2 -NiCr coatings were produced with two thermal spray processes: Air Plasma Spray (APS) and High Velocity Oxy-Fuel (HVOF). Two different powders have been selected as starting materials. Their dimensional and morphological properties were assessed to verify their sprayability, both in terms of flowability and deposition efficiency. For both APS and HVOF processes, most deposition parameters were selected, after preliminary spraying tests, on the basis of statistical analysis of results, in terms of coating density, hardness and substrate-coating interface quality. The tribological properties of the coatings were evaluated in order to investigate the influence of the deposition process on the behavior of coatings under wear conditions

Thermally sprayed coatings with Co-based alloy were evaluated for cavitation erosion resistance in order to use as erosion proof coatings. Co-based alloy coatings have been applied by Low Pressure Plasma Spray (LPS) and High Velocity Oxygen Fuel Flame Spray (HVOF) on the AISI 403 stainless steel substrates and half number of each coated specimen were post-heated at 1073K for 1 hour. The mass loss was measured for evaluation in this study. The following results have been obtained in the cavitation test; i) Both of LPS coatings (the post-heated and the as sprayed) have more excellent cavitation erosion resistance than HVOF coatings, ii) With regard to LPS coatings, the post-heated coating has the same weight loss as the as-sprayed coatings. iii)The post heat treatment to HVOF is remarkably effective to improve the cavitation erosion resistance.

This paper gives an account of pin-on-disc low stress abrasive wear and erosion wear tests on the specimens made by oxy-acetylene flame spray-fusing technology to explores the effect of WC content on the wear resistance of oxy-acetylene flame spray-fusing overlays. In the test, Ni60, NiWC25 and NiWC35 three kinds of various WC content Ni-base self-fluxing alloys were used as the typical wear resistance materials compared with 16Mn material and high Cr cast iron arc surfacing overlay. In pin-on-disc wear tests, SiC, Al 2 O 3 and SiO 2 different abrasive were used, and in erosion wear tests 30° and 90° erosion wear tests were performed. This paper also analyzed the wear mechanisms of spray-fusing overlays that possess different WC content by means of hardness tests and overlay's structure analysis. The results show that WC content influences the wear resistance of spray-fusing overlays greatly, but in various wear type and conditions, its effect's degree and tendency are quite different.

To improve wear resistance of the atmospheric thermal plasma sprayed molybdenum coating, diamond deposition on the molybdenum plate and the atmospheric plasma sprayed molybdenum coating by the combustion flame chemical vapor deposition (CVD) was carried out. Diamond has excellent properties such as low surface energy, hardness, chemical corrosion resistance ability and so on. Besides, since the combustion flame CVD is the process carried out in the air, diamond/ molybdenum complex coating can be deposited without any vacuum facilities by using this technique if molybdenum coating is deposited by atmospheric thermal spray. In this study, acetylene welding torch was used as diamond synthesis apparatus and mass flow ratio C 2 H 2 /O 2 was varied from 0.9 to 1.3. Consequently, many diamond particles which were 10 micrometer in diameter respectively were deposited on the molybdenum plate by only 20 minutes combustion flame irradiation in the case of 1.2 in mass flow ratio of C 2 H 2 /O 2 . Especially, the molybdenum coating was covered with diamond films consists of 10 micrometer diameter particles in the case of over 1373K in deposition temperature. Besides, according to the results of wear testing, wear mass loss of diamond deposited coatings were much lower than that of original thermal sprayed molybdenum coatings. From these results, this process was found to have a high potential in order to improve wear resistance of thermal sprayed coating.

Microstructure of electroless plated Ni-Co coating on plasma-sprayed Cr 3 C 2 -NiCr coating which was previously applied onto lCrl8Ni9Ti stainless steel was characterized, and its tribological properties during sliding against different materials were evaluated. It was found that the electroless plated Ni-Co coating on the Cr 3 C 2 -NiCr coating had lower cobalt content and a finer structure than that deposited directly on lCrl8Ni9Ti stainless steel. All the self-mated as-sprayed Cr 3 C 2 -NiCr coating, the self-mated electroless plated Ni-Co coating on the Cr 3 C 2 -NiCr coating, the self-mated electroless plated Ni-Co coating on lCrl8Ni9Ti stainless steel and the frictional pair of the electroless plated Ni-Co coating on lCrl8Ni9Ti stainless steel against the Cr 3 C 2 -NiCr coating exhibited higher friction and wear coefficients during sliding. The frictional pair of the electroless plated Ni-Co coating on the Cr 3 C 2 -NiCr coating against the Cr 3 C 2 -NiCr coating displayed excellent tribological properties with a friction coefficient of 0.10 and a wear coefficient less than 10 -6 mm 3 Nm -1 during dry sliding in air. The electroless plated Ni-Co coating on the Cr 3 C 2 -NiCr coating somewhat reduced friction and wear coefficients during sliding against plasma sprayed TiO 2 coating. The above results could be attributed to that the electroless plated Ni-Co coating on the Cr 3 C 2 -NiCr coating could weaken the adhesive intensity between the suitable counterpart materials during sliding.

This work examines nanocrystalline thermal spray coatings prepared under several power and stand off distances. The coating material was nanocrystalline alumina + titania and zirconia (ATZ) powder mixture deposited using an air plasma spray process. The experimental design employs a full factorial method totaling four samples. The mechanical properties of four coatings were compared via scratch and hardness testing. The scratching process was monitored for transverse loads during the test and the variation in load monitored. The profiles of scratches were analyzed using white light interference profilometry and studied further via SEM. The results indicate that the microstructure reflected features observed in the scratch test. It was also shown that the scratch process and morphology depend on the normal load and spray process.

By use of homemade arc spraying system patented, which could make melted metal droplets atomized fully and make its flying velocity achieve ultrasonic velocity, TiAl alloy coatings were manufactured on the aluminum alloy (LY12) substrate surface. The slide wear resistance of TiAl alloy coatings was investigated. The effect of spraying parameters, coatings' chemical composition and microstructure on the slide-wear resistance of coatings was examined. Then the slide-wear mechanism of the coatings was discussed. The results showed that the slide wear resistance of TiAl alloy coatings by ultrasonic arc sprayed is 17 times higher than it of the aluminum alloy (LY12) substrate under the condition of dry slide-wear.