Papers by Keyword: NiCrAlY

Abstract: The use of NiCrAlY is a great alternative as Bond Coat - BC (bonding layer) in coatings for turbine vane, and it is possible to increase its life. This work aims to study the BC layer of NiCrAlY on the substrate of 316 steel which was deposited by the High Velocity Oxygen Fuel method (HVOF) and after laser remelting irradiated_. selective laser melting which is an innovative process. The laser treatment induced changes in porosity, microhardness and wear resistance. After spraying, the samples were irradiated with a CO₂ laser beam by varying the scan speed in 50, 100 e 200 mm/s. The speed at which the metallurgical bond between the coating and the substrate occurred was of 50 mm/s. A wear test was performed to analyze the thickness of the coating, which was 60 μm, and the hardness profile and hardness profile where it presented a higher hardness in the coating after the laser treatment. The investigations range included analysis of top surface of coatings by XRD characterization oxides formed types and microscopic investigations of coatings morphology.

Abstract: In ceramics TBC ́s (thermal barrier coating) the MCrAlY layer is used like a bond coat between nickel superalloys and zirconia ceramics used in aeronautical turbine blades. However the oxidation of this layer is an important step to obtain an Al₂O₃ as TGO (thermally grown oxide), on which the zirconia ceramics is placed on to protect the turbine blades from high temperatures and oxidizers and corrosive gases generated during the burning of the fuel. To understand the oxidation process, parallel and flat surface samples are required. These surfaces will allow characterization, especially the tribologic ones. The samples were prepared through different process and sintering routes. Powders of NiCrAlY with and without binder were uniaxially pressed from 100 MPa to 250 MPa. Isostatically pressed samples at 300 MPA were also prepared. The samples were sintered in the air, at 10^-7 Torr and hot uniaxially pressed at 10 MPa. The sintering temperature started at 800 °C up to 1200 °C during one hour. The best result was from the hot pressed samples between 1000 °C and 1150 °C. Above this temperature the process became complicated and started melting at 1200 oC. Mainly due to the spherical shape of NiCrAlY particles, it was not possible to get good samples when sintering in the air.

Abstract: The high temperature environments where aeronautical turbine blades are exposed makes mandatory the use of ceramic coatings. A bond coat comprised by a MCrAlY alloy (M=Co, Ni) is necessary to match the blade metallic substrate with the ceramic, also acting as a corrosion barrier. The laser treatment of metals and alloys is based in the surface local heating, followed by high cooling rates. The laser parameters such as scanning speed and laser power, plays an important role on the morphological, mechanical and chemical characteristics of the deposited material. In the present investigation, the NiCrAlY deposition was performed in stainless steel substrates with a CO₂ laser beam. Different laser parameters of scanning speed and number of scanning cycles were implemented. The samples were characterized by optical microscopy and measurements of Vickers hardness. The results show that it is possible to achieve coatings with high hardness, free of pores or any pronounced defects, metallurgically bonded to the substrate.

Abstract: This paper presents yttria-stabilized zirconia (YSZ) coating deposition on laser surface modified H13 tool steel using atmospheric plasma spray (APS) technique. A Praxair Plasma Spray System with SG-100 gun was used to deposit coating materials on laser-modified H13 tool steel substrate surface. A bond coat layer material was NiCrAlY alloy while the top coat was yttria stabilized zirconia (YSZ) with powder size distribution range of-106 μm to +45 μm. A 2³ design of experiment (DOE) was used to deposit bond coat and top coat powders with three controlled factors of input current, powder feed rate and stand-off-distance. The design was optimised for minimum porosity and maximum hardness. The coating thickness and percentage of porosity were measured using IM7000 inverted optical microscope. Hardness properties of top coating layer were measured by using MMT-X7 Matsuzawa Hardness Tester Machine with Vickers hardness scale. The microscopy findings indicated variations of coating thickness at different parameters settings. Samples at the highest current and powder feed rate and lowest stand-off distance settings produced a lower porosity percentage and higher hardness. A higher powder feed rate with the smallest stand-off-distance allowed melted powders to travel uniformly onto the substrate surface. These findings were significant to development of thermal barrier coatings on semi-solid forming die surface.

Abstract: NiCrAlY coating system has been widely used for the advanced gas turbines to provide protection against high temperature oxidation and corrosion. Various methods have been used to develop these superalloy coatings. In present investigation, NiCrAlY superalloy coatings have been deposited on the superalloy substrate (Superni76) using commercially available NiCrAlY powder and High Velocity Oxide Fuel (HVOF) process. These coatings have been characterised in terms of their microhardness, porosity, microstructure features and surface roughness. The coatings have been oxidized cyclically (1hour heating and 20minutes cooling) in air at 900οC. The weight change curves have been plotted and the parabolic rate constant has been evaluated. The oxides formed after oxidation has been studied by using various techniques like optical microscopy, FESEM/EDAX and XRD. It has been observed Al¬2O3, NiCr2O4 and Cr2O3 formed upon oxidation of the coatings provide protection to the substrate alloy.