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PVD and CVD gradient coatings on sintered carbides and sialon tool ceramics

Dobrzański L. A., Staszuk M.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 2

552--576

EN

Purpose: The main objective of the work is to investigate the structure and properties of multilayer gradient coatings produced in PVD and CVD processes on sintered carbides and on sialon ceramics, and to define the influence of the properties of the coatings such as microhardness, adhesion, thickness and size of grains on the applicable properties of cutting edges covered by such coatings. Design/methodology/approach: The investigation studies pertaining to the following have been carried out: the structures of the substrates and coatings with the application of transmission electron microscopy; the structure and topography of coating surfaces with the use of electron scanning microscopy; chemical composition of the coatings using the GDOES and EDS methods; phase composition of the coatings using X-ray diffraction and grazing incident X-ray diffraction technique (GIXRD); grain size of the investigated coatings using Scherrer’s method; properties of the coatings including thickness, microhardness, adhesion and roughness; properties of the operating coatings in cutting trials. The models of artificial neural networks have been worked out which involve the dependencies between the durability of the cutting edge and properties of the coatings. Findings: Good adhesion of the coatings to the substrate from sintered carbides is connected with the diffusive mixing of the components of the coating and substrate. In the case of PVD coatings obtained on sialon ceramics, the highest adhesion to the substrate (Lc=53-112 N) has been demonstrated by the coatings containing the AlN phase of the hexagonal lattice having the same type of atomic (covalence) bond in the coating as in the ceramic substrate. The damage mechanism of the investigated coatings depends to a high degree on their adhesion to the substrate. The durability of cutting edges covered by the investigated coatings depends principally on the adhesion of the coatings to the substrate, and to a lesser degree on the other properties. Practical implications: While selecting a proper coating material on ceramic cutting edges, it is advisable to remember that the coatings having the same type of atomic bond as the ceramic substrate have higher adhesion to the substrate. Another relevant aspect of the research presented in the paper is the fact that the adhesion of the coatings contributes significantly to the durability of the cutting edge, whereas the microhardness of the coatings, their thickness and grain size have a slightly lower influence on the durability of the tool being coated. Originality/value: The paper presents the research involving the PVD and CVD coatings obtained on an unconventional substrate such as sialon ceramics. Furthermore, to define the influence of coating properties on the durability of cutting edges, artificial neural networks have been applied.

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Effect of high temperature deformation on the structure of Ni based superalloy

Nowotnik A.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 27, nr 2

115-122

EN

Purpose: A study on the hot deformation behaviour and dynamic structural processes (dynamic precipitation operating during deformation at elevated temperatures) of nickel based superalloy was presented. Design/methodology/approach: Compression tests were carried out on precipitations hardenable nickel based superalloy of Inconel 718 at constant true strain rates of 10-4, 4x10-4s-1 within a temperature range of 720-1150° C. True stress-true strain curves and microstructure analysis of hot deformed alloy were described. Microstructure examination has been carried out on the compressed samples of Inconel 718 alloy using an optical microscope - Nikon 300 and in the scanning electron microscope HITACHI S-3400 (SEM) in a conventional back-scattered electron mode on polished sections etched with Marble's solution. Findings: Structural observations of deformed at high temperatures, previously solution treated Inconel alloy revealed non uniform deformation effects. Distribution of molybdenum-rich carbides was found to be affected by localized flow within the investigated strain range at relatively low deformation temperatures 720 - 850° C. Microstructural examination of the alloy also shown that shear banding, cavities growth and intergranular cracks penetrating through the whole grains were responsible for decrease in the flow stress at temperature of 720, 800 and 850° C and a specimen fracture at larger strains. On the basis of received flow stress values activation energy of a high-temperature deformation process was estimated. Mathematical dependences (σ pl -T and σ pl - ) and compression data were used to determine material's constants. These constants allowed to derive a formula that describes the relationship between strain rate (ε), deformation temperature (T) and flow stress σ pl. Research limitations/implications: Even though, the light optical microstructure observation of deformed samples revealed some effects of heterogeneous distribution of the phase components, in order to complete and confirm obtained results it is recommended to perform further analysis of the alloy by using transmission electron microscopy technique (TEM). Practical implications: Interaction of precipitation process developed during deformation below solvus temperature and heterogenuos deformation (flow localization) can become a significant aspect of high temperature performance of precipitation hardenable alloys and may perhaps also allow produce specific microstructures of such deformed materials. Originality/value: It is a scarcity of data which are to describe specific features of phase transformation processes in precipitation hardenable alloys. In addition, existing data do not allow to simplify structural features of dynamic precipitation and simplifying structural description of the process. The compression tests on age hardenable alloys and the analysis of dynamic precipitation process have got a practical meaning.

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Corrosion behaviour of metallic biomaterials used as orthodontic wires

Ziębowicz A., Walke W., Barucha-Kępka A., Kiel M.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 27, nr 2

151-154

EN

Purpose: The aim of the work was evaluation of the corrosion resistance of the commercial metallic orthodontic wires from different manufacturers in simulated intra-oral environment. Design/methodology/approach: Corrosion resistance tests were carried out in artificial saliva at the temperature 37 ± 1° C with the use of the VoltaLab ® PGP 201 system for electrochemical tests. The saturated calomel electrode (SCE) was applied as the reference electrode and the auxiliary electrode was a platinum foil. The evaluation of pitting corrosion was realized by recording of anodic polarization curves with the use of the potentiodynamic method. In order to evaluate crevice corrosion resistance the samples were polarized in the potential equal to 0.8 V by 900 seconds. Findings: Results of corrosion resistance tests of the CrNi, NiTi and CuNiTi wires showed comparable data of parameters obtained in the artificial saliva. Research limitations/implications: The obtained results show the influence of artificial saliva on the electrochemical corrosion of orthodontic wires. In order to demonstrate the higher risk of corrosion, which can have two consequences: a loss of the physical properties and the release of Ni ions (which have been shown to be toxic and the cause of allergic reactions) - additional research on fatigue corrosion should be carried out. Originality/value: The analysis of the obtained results show that that commonly used materials for making orthodontic wires (because of their interesting properties - elasticity and shape memory) can be used in different orthodontic treatment stages to correct numerous clinical conditions. The most favorable characteristics were observed for the new NiTi samples (American Orthodontics).

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Corrosion behaviour of Co-Cr-W-Ni alloy in diverse body fluids

Walke W., Paszenda Z., Ziębowicz A.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 5

293-296

EN

Purpose: The aim of the work was evaluation of corrosion resistance of implantable Co-Cr-W-Ni alloy in simulated body fluids: human blood (artificial plasma), urine (artificial urine) and bone tissue (Tyrode solution). Design/methodology/approach: Corrosion resistance tests were carried out in the selected physiological body fluids at the temperature 37 ± 1°C with the use of the VoltaLab PGP 201 system for electrochemical tests. The saturated calomel electrode (SCE) was applied as the reference electrode and the auxiliary electrode was a platinum foil. The evaluation of pitting corrosion was realized by recording of anodic polarization curves with the use of the potentiodynamic method. In order to evaluate crevice corrosion resistance the samples were polarized in the potential equal to 0,8 V by 900 seconds. Roughness of all the samples was evaluated with the use of the SURTRONIC 3+(Taylor/Hobson) surface analyzer. Findings: Results of corrosion resistance tests of the Co-Cr-W-Ni alloy showed the diverse values of parameters obtained in the individual solutions. The suggested surface treatments ensure good crevice corrosion resistance of the Co-Cr-W-Ni alloy in all the tested physiological fluids. Research limitations/implications: The obtained results show the necessity of selection of the appropriate physiological solution, reflecting the specificity of body environment. In order to fully characterize the material in the human body environment, additional research on stress and fatigue corrosion should be carried out. Originality/value: The analysis of the obtained results show favorable influence of the suggested surface treatment of the Co-Cr-W-Ni alloy. Regardless of the selected physiological solution, the most favorable characteristics was observed for the electropolished and passivated samples.