The aim of the present study was to develop the hybrid method which allows producing highly corrosion-resistant composite titanium nitride layers on the AZ91D magnesium alloy. The hybrid method ...combines the deposition of composite titanium nitride layers using the PVD methods with the final tightening of the layers by a simple chemical-type treatment. The tightened multilayer obtained by the hybrid treatment is composed of a TiN surface layer and an aluminum sub-layer diffusively bonded with the substrate, separated by a thin transition titanium sub-layer. The effect of the composite titanium nitride layers on the corrosion resistance of the AZ91D alloy was examined by electrochemical methods. The results of the examinations show that the hybrid method yields an outstanding improvement of the corrosion resistance manifested by the corrosion potential shift by about 1300 mV. The tightening of the composite titanium nitride layers plays the crucial role in achieving this significant improvement of the corrosion resistance.
•Highly corrosion resistant composite TiN layers were produced on AZ91D Mg alloy.•The corrosion resistant TiN composite layers were produced using a hybrid method.•The hybrid treatment combines the PVD methods with a final chemical-type tightening.•The final tightening of the TiN composite layers is crucial for high corrosion resistance.•The TiN composite layers on AZ91D alloy give a corrosion potential shift of 1300 mV.
•Sealed TiN–Ti–Al layers improve AZ91D magnesium alloy corrosion and wear resistance.•Microstructure of TiN–Ti–Al layers is tight, nano-crystalline and has diffusive character.•Diffusive character ...increases layers adhesion and load bearing capacity during wear.•AZ91D alloy corrosion resistance improvement involves synergistic sealing mechanism.•The mechanism requires Al-sub-layer to enable TiN hydrothermal treatment sealing.
The microstructure and properties of the composite TiN–Ti–Al type titanium nitride surface layer with a sub-layer of titanium and aluminium produced on AZ91D magnesium alloy using a hybrid PVD method including final sealing by hydrothermal treatment were investigated. The results were analysed in terms of the microstructure–properties correlation, to approach the role of the sub-layers and the mechanisms involved in the properties improvement. The microstructure investigations indicate that the composite titanium nitride layers are tight and have nano-crystalline, diffusive character and multi zone microstructure of the type TixOy–TiN–Ti–Al–Al3Mg2–Al12Mg17. The significant corrosion resistance improvement of the AZ91D alloy obtained using the sealed composite titanium nitride layers was found to be the result of a synergistic mechanism which combined hydrothermal treatment of the layer with an action of aluminium sub-layer which is critical to make the sealing effective. The diffusive bonding via Mg–Al zone improves adhesion and the load bearing capacity of titanium nitride layers in wear conditions.
The layers based on chromium nitride were produced on the AZ91D magnesium alloy using a hybrid surface treatment. The treatment consists of nitriding of the chromium-precoated magnesium alloy. The ...proposed treatment yields diffusive, composite gradient-type chromium nitride layers which are diffusion-bonded to the substrate. The effect of these layers on the corrosion behavior of the AZ91D magnesium alloy was investigated by the potentiodynamic and impedance spectrometry methods. It was found that the formation of the diffusive, composite chromium nitride layers on the AZ91D alloy may result in a significant decrease of the corrosion activity measured by the corrosion potential. This effect is correlated with the layer thickness and becomes significant with relatively thin layers (less than 1 μm thick). Moreover, with the thin layers the impedance modulus is the highest and phase angle has a beneficial character.
► Hybrid method allows to produce diffusive chromium nitride layers on magnesium alloys. ► Chromium nitride layers on AZ91D alloy improve corrosion resistance. ► The best corrosion resistance occur when the CrN layers are sufficiently thin.
The Plasma Assisted Chemical Vapor Deposition (PACVD) treatment conducted under glow discharge conditions in an atmosphere of trimethylaluminum vapors applied to an Inconel 600 substrate yielded ...composite surface layers built of intermetallic phases of the Al–Ni system with the outer zone composed of aluminum oxides. Such layers have very advantageous performance properties, such as high hardness, good corrosion and frictional wear resistance and, good adherence to the substrate.
The present study is dedicated to microstructure characterization of the layers. The layers were examined using a variety of methods. Based on the results of these examinations, the microstructure of the composite layers was described as a multizone one with an outer Al
2O
3 zone, an intermediate AlNi
3
+
Al
2O
3 zone and a diffusion zone of type Ni(Al,Cr,Fe)
+
AlNi
3
+
Cr
7C
3. The mechanism of layer formation as well as the correlation between the microstructure and the observed improvement of the surface properties of the Inconel 600 alloy are discussed.
Hard and wear and corrosion resistant Al–Ni type intermetallic layers, with an external Al
2O
3 zone, were successfully produced on Inconel 600 using a duplex method. The duplex method combines glow ...discharge assisted oxidizing with pre-coating the Inconel substrate with aluminum by magnetron sputtering. The oxidizing process carried out at 560
°C for 4
h leads to a diffusion-induced transformation of the aluminum coating and adjacent Inconel into a 15
μm thick composite layer of Al
2O
3+AlNi+AlCr
2+AlNi
3+Cr(Fe,Ni)+Ni(Cr,Fe,Al). The structure of the layer was examined in cross-section by transmission electron microscopy (TEM). The surface zone of the layer is constituted by nanocrystalline Al
2O
3 covering the main zone of the AlNi layer. In this zone, near its border with the oxide zone, are small agglomerates of nanocrystalline Al
2O
3. The upper and thicker part of the AlNi zone also contains precipitates of the AlCr
2 phase. The AlNi zone is separated from Inconel by a diffusion zone of Ni(Cr,Fe,Al). In this region grains of AlNi
3 are found with groups of Cr(Fe,Ni) phase grains. As a consequence, the region is locally strongly enriched with chromium. This suggests that the formation of AlNi induces an uphill diffusion of chromium into the Inconel substrate.
The paper describes the microstructure of the composite layers produced on chromium pre-coated AISI 1045 steel by oxynitriding under glow discharge conditions (duplex method). The layers were ...examined by the cross-section method using transmission electron microscopy. Their microstructure was composed of the 4 zones: a near-surface CrN–Cr2O3 mixture zone about 1 μm thick, a Cr2N zone about 4 μm thick, a chromium zone–the thickest–about 50 μm, and the thinnest (Cr,Fe)7C3 zone about 0.5 μm thick. Cr2O3 also occurred in the form of nano-crystalline aggregates, about 1 μm in size, situated in the upper part of the Cr2N zone. All the zones had a fine-grained structure, except the finest nano-crystalline zone situated at the surface. It was found that, during oxynitriding, the cracks present in the chromium coating are filled up by chromium nitrides and oxides. This may explain the observed improvement of the corrosion resistance.
Unlike aluminium oxide surface layers, magnesium oxide layers obtained by anodising processes exhibit some drawbacks, especially chemical instability in the presence of humidity, resulting in ...susceptibility to cracking and spalling. This work was dedicated to the development of a new hybrid method allowing us to produce composite aluminium oxide surface layers on magnesium alloys to ensure better performance properties than those achieved by magnesium oxide layers produced by commercial anodising. Composite aluminium oxide layers were produced on magnesium AZ91D alloy using a three stage hybrid method: magnetron sputtering deposition of an aluminium coating, followed by anodising in classical or plasma electrolytic oxidation (PEO) variant, combined with final tightening of the layer by hydrothermal treatment. The structure and the properties of the composite oxide layers were characterised. The investigations proved that the hybrid method using classical anodising is a promising method to improve the corrosion resistance of the AZ91D alloy much more efficiently than commercial anodising, but at the cost of decreased wear resistance. Based on preliminary investigation, a modified variant of the hybrid method using PEO treatment was found to result in both high wear and corrosion resistant composite aluminium oxide layers on AZ91D alloy, making it a prospective solution.
•Corrosion resistant composite Al oxide layers were produced on AZ91D Mg alloy.•a hybrid treatment was developed to produce composite Al oxide layers.•The hybrid treatment combines PVD, anodising or PEO with final sealing.•Only the composite Al oxide layers produced using PEO exhibit high wear resistance.•The composite layers obtained by PEO are an alternative for AZ91D alloy anodising.
The grain boundary misorientations and CSL frequencies of a population of about 250 boundaries in ultra high purity α-iron doped with small quantities of carbon and sulphur have been determined by a ...SEM microdiffraction BKD (Backscattered Kikuchi Diffraction) technique. The aim is to examine the effect of these elements on the character of the grain boundary population (CGBP). Samples containing about 75 wt. ppm of sulphur and/or 150 (200) wt. ppm carbon were recrystallized at 725 °C after cold hydrostatic extrusion to ϵ = 1.1 It was found that the addition of sulphur and carbon modifies the CGBP of α-iron. Sulphur clearly increases the density of low angle grain boundaries (LANGB), but only in the pure FeS binary alloy. The fractions of the LANGB and coincidence site lattice grain boundaries (CSLGB) in the FeCS alloy are rather similar to those of FeC and thus the CGBP could be controlled by carbon. As a consequence, the lowest fraction of high energy random grain boundaries (RANGB) appears in the FeS alloy at about two-thirds of the total population. The effect of carbon and sulphur on the CGBP is interpreted in terms of grain boundary selection as a consequence of an impurity-specific dragging effect or a precipitation pinning effect on the migration of boundaries during recrystallization and subsequent grain growth.
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