Materials Science Forum Vols. 638-642

Abstract: In the thermal spraying process, spray material is heated, melted, and accelerated by a high temperature flame. Thermal spraying can produce thick materials that rapidly solidify, because the alloy droplets accumulate successively on the substrate and solidify at a cooling rate in the range of 105-108Ks-1. Depending on the cooling conditions of the substrate and on the alloy composition, deposits are produced with metastable phases or extremely fine crystalline phases. Thermal spraying is an attractive method for the production of composite deposits with fine particles formed in-situ. In particular, iron based alloy with vanadium carbide, is useful in metal molds and also in pump parts due to its high wear resistance and high corrosion resistance. In the present work, low-pressure plasma spraying of Fe-C-V/Ni-Mg and Fe-C-V-Cr-Ni/Ni-Mg blend powders were iron based composite deposits with finely dispersed vanadium carbide particles. The as-sprayed deposit produced from Fe-C-V/Ni-Mg blend powder is composed of αFe and V8C7. The as-sprayed deposit produced from Fe-C-V-Cr-Ni/Ni-Mg blend powder is made up of γFe, αFe, V8C7 and Cr7C3. The fine precipitates of approximately 0.3μm in the as-sprayed deposit are carbide. With increasing the heat-treatment temperature up to 1273K, the carbide particles coarsen. The hardness of as-sprayed deposit produced from the Fe-C-V-Cr-Ni/Ni-Mg, which has many fine carbide precipitates, is the hardest of the deposits.

Abstract: Nickel-boron coatings were synthesized on mild steel by the electroless deposition method. Some of the coatings were submitted to a hardening heat treatment at 400°C during 1 hour in an atmosphere containing 95% Ar and 5% H2. Uncoated steel, treated and untreated samples were submitted to the Taber abrasion test to assess their wear resistance. The wear track was then examined by SEM and roughness measurement. The Taber Wear Index of untreated samples was slightly better than that of steel but heat treated samples attained TWI as small as 13. The corrosion resistance of the samples was investigated by the way of polarization and electrochemical impedance spectroscopy (EIS) and the influence of the heat treatment was observed.

Abstract: From the point of view of nitriding treatment(570°C), Cu precipitation is also occurred in the steel containing 1.3mass%Cu at this temperature. In this study, the behavior of nitriding in ultra low carbon steels containing Cr and/or Al and/or V are investigated. The following results are obtained : (1)After nitriding treatment the distribution of vickers hardness(Hv) differs in added nitriding element. (2)Profile of hardness in thickness is resulted from mainly precipitation hardening of nitride. (3)The high fatigue limit of nitrided steel is occurred by residual stress in vicinity of the surface. (4) Nitride precipitation is promoted by Cu precipitation that occurs in early stage of heat treatment.

Abstract: Catalytic ability on 12 kinds of carbide powders was investigated at room temperature using NOx gas degradation. They are largely classified into two groups, depending on whether the reaction involves a nitrogen gas in air or not. The carbon dangling bonds largely contribute to the reaction, while the accompanied metal atoms play an important role for adsorbing/dissociating nitrogen gas. Mechanical milling or annealing, as long as without agglomeration, is an effective method for activating powder catalysis, producing new surfaces with plenty catalytic sites. A new concept of catalysis is presented, based on the Schottky barrier-like model, where the charge imbalance is produced at the interface between the non-uniform thin oxide and the carbide.

Abstract: Friction surfacing is a novel solid state surface coating process with several advantages over conventional fusion welding based surfacing processes. In this work, austenitic stainless steel (AISI 310) and tool steel (H13) coatings were friction deposited on mild steel substrates for corrosion and wear protection, respectively. Microstructural studies were carried out by using optical and scanning electron microscopy. Shear tests and bend tests (ASTM A264) were conducted to assess the integrity of the coatings. This study brings out the microstructural features across the coating/substrate interface and its mechanical properties, showing good metallurgical bonding between stainless steel and tool steel coating over mild steel.

Abstract: During the last years, materials science has focused more and more on the development of nanomaterials. Reasons for that are the enormous advantages these materials can offer for various applications as their special structure yields the improvement of the material properties, such as hardness, strength and ductility. However, the production of especially “massive” nanomaterials is quite complex. The present study demonstrates the possibility of producing iron- or chromium-based nanophase hardfaced coatings with a thickness of several millimetres by means of common arc welding methods (TIG, PTA). An appropriate alloy composition allows to control the structural properties of the solidifying weld metal. Specific variations of the alloying elements enable the realisation of a nanostructured solidification of the carbides and/or borides with cooling rates that are common for arc surfacing processes. In the hardfaced coatings phase dimensions of approximately 100-300 nm were achieved. Based on the results it is established that the influence of the surfacing parameters and of the coating thickness and thus the influence of the heat control on the nanostructuring process is, compared with the influence of the alloy composition, of secondary importance. Several tests showed that the generation of nanoscale structures in the hardfaced coatings allows the improvement of mechanical properties, wear resistance and corrosion resistance. Potential applications for these types of hardfaced coatings lie, in particular, in the field of cutting tools that are exposed to corrosion and wear.

Abstract: The recycling of aluminium packagings is the complex process in due to of the variety of applied varnishes. The compounds of these varnishes in the raised temperature are decomposed and the reactions products may be: gas and/or carbon and in some cases mineral compounds from pigments and the filling materials. Removing the layer organic from aluminium packagings be holds mainly on the thermal processes. In the paper are described the results of removing the varnish coats from surface of the aluminium cans for drinks. The investigations were carried out in the rotary furnace (Linn High Therm) in the temperatures 620 oC in air atmosphere. The surface of sheet after thermal process was submitted the chemical microanalysis on the scanning microscopes Inspect F. It was found that it is possible to obtain practically no oxidizing surface of aluminum sheet. On the surface were the solid residues from mineral pigments and filling materials e.g. oxides Ti, Ba and Si.

Abstract: This work presents the results of investigations of unconventionally glow-discharge nitrided 316L austenitic steel. The process of nitriding was performed using a variety of variants of sample orientation in glow-discharge chamber. The samples subject to nitriding were located directly on cathode, on the surface isolated from both cathode and anode, in so-called ‘plasma potential’, while the part of the samples with this orientation were additionally covered with screens to supported nitriding process. In order to evaluate the efficiency of various variants of nitriding, the following investigations were conducted: hardness test, element distribution profile within surface layer, metallographic tests, tribological and corrosion resistance tests.

Abstract: The transformation from metastable polymorphs to stable alpha-Al2O3 in the scale formed on a CoNiCrAlY alloy is accelerated under lower oxygen partial pressure (PO2), where both Al and Cr in the alloy are simultaneously oxidized, resulting in the formation of a dense and monolithic alpha-Al2O3 scale. Under higher PO2, where all components of the alloy are oxidized, the transformation is retarded and (Co,Ni)(Al,Cr)2O4 is also produced. The oxygen permeability in polycrystalline alpha-Al2O3 wafers exposed to steep oxygen potential gradients is evaluated at high temperatures to investigate the complicated mass-transfer phenomena through the scale formed on the alloy. The diffusion of Al and O species, which are responsible for the oxygen permeation along the grain boundaries of Al2O3, is dependent on the formation of an oxygen potential gradients. For Lu-doped Al2O3 polycrystals, it was found that Lu depressed the mobility of oxygen, but did not directly influence the migration of Al.

Abstract: Diamond/NiCrAl composite powder with a diamond content of 40vol.% is prepared by mechanical alloying process with diamond powder and NiCrAl alloy powder. Cold spraying is employed to deposit diamond/NiCrAl composite coating. To enhance the bonding between diamond particles and NiCrAl matrix, annealing treatment is applied to the as-sprayed coating. The effect of annealing treatment conditions on the microstructure and microhardness and abrasive wear performance of the coating is investigated. The results show the microstructure of the composite powder is completely retained in the coating owing to the low temperature of spray powder during cold spray process. The interface between diamond and NiCrAl matrix is enhanced by the CrxCy layers formed during annealing treatment. Moreover, the cohesion of deposited particles in the coating is improved through metal element diffusion during heat treatment. The hardness and wear performance of the coating is related to coating microstructure and the bonding at the interfaces between diamond particles and NiCrAl matrix.