Pt-modified Ni aluminides, MCrAlY-base multilayer coatings and TBC systems fabricated by Spark Plasma Sintering for the protection of Ni-base superalloys

Pt-modified Ni aluminides and MCrAlY coatings (where M=Ni and/or Co) are widely used on turbine blades and vanes for protection against oxidation and corrosion and as bond coatings in thermal barrier coating (TBC) systems. The present work shows the ability of a new fabrication technique, the Spark Plasma Sintering, to develop rapidly new coating compositions and microstructures. This technique allows combining powders and metallic foils on a superalloy substrate in order to obtain multilayered coatings in a single short experiment. Fabrication of MCrAlY overlays with local Pt and/or Al enrichment is shown, as well as fabrication of coatings made of ζ-PtAl2, ε-PtAl, α-AlNiPt2, martensitic β- (Ni,Pt)Al or Pt-rich γ/γ′ phases. The realization of a complete TBC system with a porous and adherent Yttria Stabilized Zirconia (YSZ) layer on a γ/γ′ low mass bond coating is also demonstrated. Difficulties of fabrication are reviewed and discussed, such as Y segregation, risks of carburization, local overheating, or difficulty to coat complex shape parts. Finally, some first results of cyclic oxidation are given

Effects of carburization process on the mechanical properties of carburized mild steel

Due to the complexity of parameters in carburizing, there has been relatively little work on process variables during the surface hardening process. This work focuses on the effects of carburization process on the mechanical properties of carburized mild steel, at constant temperature, 850°C with different time, 2 hours, 4 hours and 6 hours and quenched in oil. The objectives of this project are to study the influence of carburization process for mild steel and to study the material performance after carburization process. After carburization process, the test samples were subjected to standard test and form the data obtained, ultimate tensile strength and Young’s modulus were calculated. The case hardness of the carburized samples were measure. It was observed that the mechanical properties of mild steels were found to be strongly influenced by the process of carburization. It was conclude that the sample carburized at 850°C soaked for four hours followed by oil quenching were better because they showed the higher ultimate tensile strength at 541.41096 MPa

Insights on finite size effects in Ab-initio study of CO adsorption and dissociation on Fe 110 surface

Adsorption and dissociation of hydrocarbons on metallic surfaces represent crucial steps to carburization of metal. Here, we use density functional theory total energy calculations with the climbing-image nudged elastic band method to estimate the adsorption energies and dissociation barriers for different CO coverages with surface supercells of different sizes. For the absorption of CO, the contribution from van der Waals interaction in the computation of adsorption parameters is found important in small systems with high CO-coverages. The dissociation process involves carbon insertion into the Fe surface causing a lattice deformation that requires a larger surface system for unrestricted relaxation. We show that, in larger surface systems associated with dilute CO-coverages, the dissociation barrier is significantly decreased. The elastic deformation of the surface is generic and can potentially applicable for all similar metal-hydrocarbon reactions and therefore a dilute coverage is necessary for the simulation of these reactions as isolated processes.Comment: 12 pages, 6 figures. Submitted to Journal of Applied Physic

Comparisons of modified Vasco X-2 and AISI 9310 gear steels

Endurance tests were conducted with four groups of spur gears manufactured from three heats of consumable electrode vacuum melted (CVM) modified Vasco X-2. Endurance tests were also conducted with gears manufactured from CVM AISI 9310. Bench type rolling element fatigue tests were conducted with both materials. Hardness measurements were made to 811 K. There was no statistically significant life difference between the two materials. Life differences between the different heats of modified Vasco X-2 can be attributed to heat treat variation and resultant hardness. Carburization of gear flanks only can eliminate tooth fracture as a primary failure mode for modified Vasco X-2. However, a tooth surface fatigue spall can act as a nucleus of a tooth fracture failure for the modified Vasco X-2

Carbon nanotubes as a 1D template for the synthesis of air sensitive materials: about the confinement effect

Cobalt ferrite and cobalt iron nanowires with an average diameter of 50 nm and lengths up to several micrometers were synthesized inside multi-walled carbon nanotubes (MWNTs) under mild reaction conditions, i.e. 100 °C and atmospheric pressure, using an aqueous nitrate precursor salt filling the tubes. The concept of a confinement effect inside carbon nanotubes has been advanced to explain the formation of CoFe2O4 under such mild reaction conditions. The formation of caps near the tube tips at the beginning of the nitrate decomposition meant that each nanotube was considered as a closed nanoreactor, in which the reaction conditions could be very different to the macroscopic conditions outside the tube. The subsequent reduction of the CoFe2O4 allowed to obtain CoFe nanowires cast in the carbon nanotubes. These nanowires exhibit a high resistance towards oxidation, whereas bulk CoFe is known to undergo oxidation at room temperature and atmospheric pressure. This phenomenon was attributed to oxygen diffusion problems due to the confinement effect of the carbon nanotubes

Computational Thermodynamics and Kinetics in Materials Modelling and Simulations

Over the past two decades, Computational Thermodynamics and Kinetics have been tremendously contributed to materials modeling and simulations and the demands on quantitative conceptual design and processing of various advanced materials arisen from various industries and academic institutions involved in materials manufacturing, engineering and applications are still rapidly increasing

Computer Generation of Metal Components by Simultaneous Deposition of Mould, Cores and Part

A new solid freeforming method based on co-delivery of mould powder materials and part powder materials using vibration-controlled, dry powder valves is presented in this paper. Thin layers of stainless steel powder are delivered to the forming area according to the cross-section of the CAD file to produce the component. Mould powder which has low sinterability is delivered to the non-forming areas of the same layer. All powders are delivered by computer-controlled, acoustic powder valves. The flow rate and switching of the valves provides the composition and shape control during fabrication. The stacked layers of loose powder are then sintered in a conventional furnace. The mould materials are removed after sintering. This method avoids the high thermal stress problem in selective laser sintering, avoids high capitalisation, makes use of conventional furnaces and allows for the incorporation of three dimensional function gradients. Test pieces including step wedge and Spierpinski’s cube were fabricated. Advantages, limitations and problems are discussed.Mechanical Engineerin

Mechanical and Wear Properties of Carburized Mild Steel Samples

The heat treatment and carburization has been acknowledged by some means of improving the various properties of metals and alloys. In the present investigation the mechanical and wear behaviours of mild steels carburized at different temperature range of 850, 900 and 9500C have been studied and it is found that the simple heat treatment greatly improves the hardness, tensile strength and wear resistance of the mild steels. The aim has been to examine the effects of these different carburization temperatures and conditions on the mechanical and wear properties of the carburized mild steels. For above purpose firstly the mild steels are carburized under the different temperature range as stated above and then it is tempered at 2000 C for half an hour after this the carburized and tempered mild steels are subjected for different kind of test such as abrasive wear test, hardness test, tensile test and the toughness test. The results of these experiment shows that the process of carburization greatly improves the mechanical and wear properties like hardness, tensile strength and wear resistance and these properties increases with increase in the carburization temperature but apart from this the toughness property decreases and it is further decreases with increase in carburization temperature. The experimental results also shows that the mild steels carburized under different temperature range as stated above, with in which the mild steels carburized at the temperature of 9500C gives the best results for the different kinds of mechanical and wear properties because at this temperature it gives highest tensile strength, hardness and wear resistance, so it must be preferred for the required applications

An investigation of carburization resistance performance of ethylene furnace tube alloys

Carburization tests and analysis were performed on some samples of radiant tube alloys of ethylene furnaces at three petrochemical plants. These tubes had undergone carburization in service with some losing their structural integrity. This study evaluates and compares the carburization resistance performances of some of these tubes in service and identifies the cause of their degradation. The polished surfaces of the test samples were visually observed. The depth of carburization zones for each test sample was measured. Scanning electron microscopy and energy dispersive x-ray spectroscopy were used to examine the carburization zones and the rest part of the specimens and to characterize the microstructure and elemental composition of the tubes’ material. Optical microscope (Image analyzer) was used to examine the etched surface of each of the test samples. Microhardness testing was performed to determine their mechanical strength. Visual inspection revealed the sagging in some of the tubes. Metallurgical assessment indicated that the selected furnace tubes showed relative greater depths of carburized zones when compared with other tube materials tested. Microstructure of the tubes showed coarse Cr-carbide precipitation and continuous carbide networks at austenite grain boundarie