Effect of vapour phase hydrogen peroxide,as a decontaminant for civil aviation applications,on microstructure,tensile properties and corrosion resistance of 2024 and 7075 age hardenable aluminium alloys and 304 austenitic stainless steel

Abstract

A response to the chemical or biological contamination of aircraft requires the use of a suitable decontaminant. Among possible chemical decontaminants, vapour phase hydrogen peroxide appears to be a likely candidate in terms of a combination of efficacy, low environmental impact and potential for materials compatibility. The present paper examines the effect of hydrogen peroxide, both in the vapour phase and as a liquid concentrate on two common structural materials used in aviation, namely 2024 and 7075 age hardenable aluminium alloys and on 304 austenitic stainless steel, the latter as employed in galley and lavatory surfaces. The present paper characterises both the effects of hydrogen peroxide on the microstructure of the materials and the impact that decontamination has on the tensile properties and corrosion resistance of these materials. Microstructural effects are both relatively small in magnitude and confined to a region immediately beside the exposed surface. No systematic effect is found on either the tensile properties or the post-exposure corrosion resistance of the three alloys examined. These observations are encouraging in terms of the use of vapour phase hydrogen peroxide for decontamination applications.     

Effect of hydrogen on mechanical properties of β -titanium alloys

Conflicting opinions exist in the literature on the manner in which hydrogen influences the mechanical properties ofβ-titanium alloys. This can be attributed to theβ-stabilizing effect of hydrogen in these materials leading to major changes in the microstructure as a result of hydrogen charging. The resulting (extrinsic) effect of hydrogen on the mechanical properties can possibly cover up the direct (intrinsic) influences. On the basis of experimentally determined thermodynamic and kinetic data regarding the interaction of hydrogen withβ-titanium alloys, hydrogen concentrations of up to 8 at.% were established in three commercial alloys by means of hydrogen charging from the gas phase. In order to separate intrinsic and extrinsic effects the charging was carried out during one step of the two-step heat treatment typical of metastableβ-titanium alloys, while the other step was performed in vacuum. The results on the single-phaseβ condition represent the intrinsic hydrogen effect. Monotonic and cyclic strength increase at the expense of ductility with increasing hydrogen concentration. The brittle to ductile transition temperature shifts to higher values and the fatigue crack propagation threshold value decreases. The microstructure of the metastable, usually two-phaseβ-titanium alloys is strongly affected by hydrogen, although the extent of this effect depends not only on the hydrogen concentration but also on the temperature of charging. This microstructural influence (extrinsic effect) changes the mechanical properties in the opposite direction as compared to the intrinsic hydrogen effect.     

Effect of hydrogen on structure and slow strain rate embrittlement of mill annealed Ti6AI4V

Abstract

The slow tensile straining of smooth specimens of mill annealed Ti6Al4V with different hydrogen contents revealed hydrogen induced slow strain rate embrittlement when the hydrogen content exceeded about 2000 ppm. The effect of hydrogen on the mechanical behaviour of the Ti6Al4V at lower hydrogen levels was not so pronounced and may be interpreted in terms of the partitioning of hydrogen between the α and β phases and the effect of hydrogen in solution on the lattice parameters of these phases. Hydrogen levels in excess of about 1200 ppm promote an increase in the amount of β phase at the charging temperature employed and the effect of this on mechanical properties is discussed. The effect of hydrogen solubility and hydride precipitation at the α/β interface on hydrogen induced slow strain rate embrittlement is also considered.

MST/3431     

Modelling of materials properties in duplex stainless steels

Abstract

Work is being undertaken to develop a new multiplatform software programme for predicting a wide range of materials properties for various alloy types. These properties include thermophysical and physical properties, mechanical properties, time–temperature transformation (TTT)/continuous cooling transformation diagrams etc. and the calculations are being applied to a variety of multicomponent alloy types, such as Ni based superalloys, steels, Ti alloys, Al alloys. The current paper concentrates on duplex stainless steels and describes the scientific background used for the calculation of TTT diagrams and mechanical properties for these materials. It is shown that there is very good agreement between the calculated TTT diagrams and the observed results from the literature for the formation of the σ, χ, and the chromium rich α' phase, while the calculated proof stress, tensile stress and hardness are in good agreement with the available experimental data. The effects of solution treatment temperature and the volume fraction of σ phase on mechanical properties are also discussed.     

Substrate temperature and water vapour effects on structural and mechanical properties of TiO x N y coatings

Dc reactive sputtering was successfully implemented to deposit titanium oxynitride thin films using a titanium metallic target, argon, nitrogen and water vapour as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas that of the water vapour was systematically changed from 0 to 0.1 Pa. The study aims at comparing the structural and mechanical properties of the coatings deposited at room temperature (293 K) and at 673 K. Surface morphology of the film was examined by atomic force microscopy and showed different aspects according to the growth temperature. Topography mainly depends on the amount of water vapour introduced during the deposition process. Some significant changes of the crystallographic structure, due to the high substrate temperature were correlated with the evolution of the surface aspect and roughness parameters. Determination of the phase occurrence by X-ray diffraction was also carried out and appeared to be a significant parameter in understanding the evolution of mechanical properties like nanohardness (H _n) and Young’s modulus (E). H _n and E values obtained by nanoindentation ranged from 16.5 to 7 GPa and from 240 to 100 GPa, respectively. For both temperatures, mechanical properties of titanium oxynitride thin films were notably reduced as a function of the water vapour supply, especially for partial pressures higher than 4 × 10⁻² Pa. These mechanical behaviours were correlated and discussed with the phase occurrence and the amorphous structure of titanium oxynitride thin films.     

A rapid method for investigating the absorption of formaldehyde from air by wool

Formaldehyde emitted from household products, such as furniture produced with medium density fibreboards, has been reported as causing health concerns in both domestic and business environments, these concerns being generally known as ‘sick building syndrome’. A number of differing approaches to removing formaldehyde from the atmosphere have been investigated. It is known that formaldehyde binds to wool fibres when the formaldehyde is in the liquid phase. However, few investigations into the sorption potential of wool for vapour phase formaldehyde have been made. This article details a rapid, novel method to directly measure the uptake of formaldehyde by wool and by inference, other materials. The data detailed in this article also demonstrates the significant ability of wool to sorb formaldehyde in the vapour state.     

The oxidation behaviour of metals and alloys at high temperatures in atmospheres containing water vapour: A review

The kinetics of oxide formation in the presence of water vapour are discussed and compared with oxidation in dry atmospheres. The main protective oxide systems are considered, i.e. alumina, chromia, silica, titania and iron and nickel oxides, and with the possible exceptions of alumina and nickel oxide, oxidation rates are increased by the presence of water vapour. Scale morphology is also influenced by water vapour, and an important observation is that whisker formation is encouraged; this is believed to be due to the more rapid dissociation of water vapour compared to oxygen. In general, water vapour promotes the formation of a more porous scale. This is related to an increase in cation diffusion and consequent vacancy condensation, thereby developing a porous structure. The thermochemistry of oxide formation is discussed, and here oxide stability and hydroxide formation are considered. A significant observation is that where hydroxides or oxyhydroxides form, they generally have higher volatility than the corresponding oxide, and this leads to loss of protection.The effect of water vapour on oxide growth processes is considered. It is demonstrated that all aspects of oxide growth including adsorption, dissociation and diffusion of reactants are altered in the presence of water vapour compared with similar processes in dry conditions. The important first stages of the reaction involving adsorption and dissociation are controlled by the catalytic activity and acid base nature of oxides. For oxides formed at high temperatures very limited information is available, but, in general, data obtained at room temperature is confirmed and strongly suggests that dissociation of any gas molecule is favoured by defects in the surface. Dissociation of water seems to be more rapid at lower temperatures than, for example, oxygen, but this difference may be less pronounced at higher temperatures. Fast diffusion of water in oxides is possible due to “proton hopping”, in which protons localised at oxide ions move by transfer from one oxygen to another. Since the OH⁻ ion concentration is increased there is a resultant increase in cation vacancies, and this, in part, is responsible for the observed increase in oxidation rates. A further factor to consider is the possibility of molecular diffusion, and it has been demonstrated that where pores or voids are present in the scale, and the void contains both hydrogen and water vapour, oxidation of the surface nearest the metal will occur by reaction with water to form new oxide and the reaction product hydrogen, while a reduction reaction occurs at the surface of the void nearest the gas phase to produce water vapour. Thus it can be seen that this process provides for rapid inward diffusion of oxygen while the void gradually moves outwards from the metal/oxide interface to the oxide/gas interface.Finally, the review considers the effect of water vapour on the mechanical properties of the scale. Scale adhesion can be improved (iron oxides) or made worse (alumina and chromia) by the presence of water vapour. It is shown that while there is experimental evidence for altered mechanical behaviour, there is very little data on relevant mechanical properties. It is possible, therefore, that water vapour either alters mechanical properties of some oxides, or, as has been demonstrated, the oxide growth process has been changed. Alternatively, at least for the cases where increased oxidation rates were caused by the presence of water vapour, the observed differences between wet and dry behaviour may simply be a function of the greater scale thickness. A significant effort has been made to develop models that can be used to predict the onset scale spallation observed in industrial boilers using process steam. The further development of these models is strongly dependent upon obtaining relevant input data, and this is considered a major challenge for materials scientists.Some areas for future research are proposed.     

Tungsten/tungsten nitride performance at elevated temperature

Abstract

Multilayer physical vapour deposition (PVD) coating of W/W₂N (tungsten/tungsten nitride) on Orvar Supreme steel was tested under the different conditions to investigate their friction and wear behaviour with their mechanical properties. Coatings were sputtered by reactive magnetron sputtering in a N₂/Ar atmosphere. Pin on disc test was performed on Orvar Supreme steel at room temperature to elevated temperature (800°C). Steel ball (100Cr6) and alumina ball are used to evaluate the frictional and wear properties. Scanning electron microscopy (SEM) and energy dispersive X-ray analyses were performed to obtain the microstructure and chemical composition of the material. Mechanical properties of coating were evaluated using nanoindentation and scratch test.     

Generation of internal stress and its effects

Abstract

Internal stresses may be generated continually in many polycrystalline materials. Their existence is manifested by changes in crystal defect concentration and arrangement, by surface observations, by macroscopic shape changes and particularly by alteration of mechanical properties when external stresses are simultaneously imposed.     

Effect of argon and substrate bias on diamond thin film surface morphology

Nanocrystalline materials are of high interest, because mechanical and physical properties of such materials are different from those or coarse-grained type. Continuous and smooth nanocrystalline diamond (NCD) thin films were successfully grown on mirror polished silicon substrates, using double bias plasma-enhanced hot filament chemical vapour deposition technique. A gas mixture of Ar:CH₄:H₂ and CH₄:H₂ was used as the precursor gas. The effect of the gas composition, flow rate and substrate bias during deposition on diamond crystallite size was investigated. Changing the growth parameters facilitates control of grain size of polycrystalline diamond thin films from microcrystalline to nanocrystalline. The structure of fine-grained NCD films has been studied with scanning electron microscopy and Raman spectroscopy.     

Studies on hydrogen embrittlement of nitrogen containing austenitic alloys

Abstract

The influence of hydrogen on the mechanical properties of four austenitic CrNiMo and CrMn alloys with nitrogen contents up to 0.57 wt-% were investigated concerning their resistance against hydrogen embrittlement in correlation to nitrogen content, chemical composition, and hydrogen diffusivity and solubility. Tensile tests were carried out at room temperature and at strain rates between 10^-4 and 10^-6 s^-1 with simultaneous hydrogen charging and after precharging to different hydrogen contents. The mechanical properties have been found to be dependent on both strain rate and hydrogen content in the material. Simultaneous hydrogen charging and mechanical testing have accelerated the failure process owing to a faster hydrogen uptake especially at low strain rates. Hydrogen has shown a softening effect in the elastic range of the stress strain curve, which becomes more pronounced with decreasing strain rate. The favoured mechanism of hydrogen damage of alloys with high nitrogen contents seems to be the hydrogen enhanced localised plasticity mechanism. A correlation between hydrogen embrittlement and stress corrosion cracking has been discussed. It has been established that both the damaging processes in nitrogen containing steels are influenced by the same mechanism.     

Structural and spectroscopic ellipsometry characterization for electrodeposited ZnO growth at different hydrogen peroxide concentration

This work deals with textural and optical characterization of zinc oxide (ZnO) layers obtained by potentiostatic electroplating at various hydrogen peroxide concentrations (from 0 up to 5 mM). The electrodeposition process was studied by cyclic voltametry and chronoamperometry. The [002] preferred growth orientation of hexagonal phase is obtained for the lowest hydrogen peroxide concentration (1 mM), while additionally X-ray diffraction peaks are observed for hydrogen peroxide concentration ranging from 3 to 5 mM. The optical constants and the thickness of films were determined by spectroscopic ellipsometry measurements. The refractive index of all thin films shows normal dispersion behavior. It was also found that refractive index values decrease with increasing hydrogen peroxide concentration. Further, it was revealed that the changes in the optical properties are correlated to the changes in the surface structure.     

Impact behaviour of 90Cu–10Ni using subsized specimens – role of temperature and hydrogen

Abstract

The effects of temperature and hydrogen charging on the impact loading behaviour of 90Cu–l0Ni (alloy CA 706, hot rolled and annealed) were investigated. Results showed that lower temperatures and hydrogen charging increased the amount of energy absorbed by the test specimens. Lowering the test temperature also increased the peak load sustained by the specimens. These observations are related to temperature and hydrogen effects on the physical properties of the two types of second phase particle which are present in this alloy.

MST/686     

Growth and characterization of Hg1-xCdxTe epitaxial films by isothermal vapour phase epitaxy (ISOVPE)

Growth of Hg_1-xCd_xTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized by using the Hall effect and capacitance-voltage (C-V) measurements.     

Pumpkin seed oil cake/polyethylene film as new food packaging material,with perspective for packing under modified atmosphere

Biopolymer packaging materials show increasing perspective in food packaging. Main limitation remains their high water sensitivity and poor water vapour barrier properties, compared to non polar materials of synthetic origin like polyethylene. In this paper, biopolymer layer obtained from by‐product of oil industry (pumpkin seed oil cake) was laminated on polyethylene in order to obtain new packaging material that would preferably combine water barrier properties of polyethylene and oxygen barrier properties of biopolymer composite material and perform satisfactory mechanical properties. Obtained two‐layer material showed good barrier properties for water vapour (7–8 g/m² 24h), as well as oxygen (12–45 cm³/m² 24h) and light. In addition, mechanical and water sensitivity tests were performed and results showed that new material inherited biopolymer film water sensitivity and mechanical properties with slight improvement. Measured tensile strength and elongation at break was 2–4 MPa and 150–250% in transversal direction and 6–8 MPa and 100–150% in longitudinal direction. Packing in modified atmosphere assay showed that new material can be used for this purpose with good control of oxygen concentration, while packing under increased concentration of CO₂ could be performed for shorter storage period. New two layer material shows promising properties for sensitive food packing under modified atmosphere conditions with reduced use of synthetic, oil‐based materials.     

Study of the influence of the structural grain size on the mechanical properties of technical materials

The mechanical properties of technical materials depend on their structure. They are influenced not only by their chemical composition, but particularly by the structural grain size. Significant changes in the mechanical behaviour of materials are related both to surface and volume properties, and not only in the field of mechanical parameters. A wide range of physical and chemical parameters changes as well. Nano‐materials are the materials, the structural grain size of which is in the dimensional area from 10^?9 to 10^?7 m. Nano‐particles and nanostructures are thus so small that their behaviour is affected by atomic forces, properties of chemical bonding, and quantum phenomena. The wave nature of the very small particles begins to manifest itself. The aim of the authors is to contribute by their paper to the solution of the problems in the field of material engineering. This means to investigate the specifics in the behaviour of technical materials depending on the change in the structural grain size towards the nano‐areas, as well as the design and use of new techniques of mathematical and physical modelling including the operative measurement method.     

DSC and DMA studies of participate reinforced metal matrix composites

Thermal studies have been carried out on a series of particulate (SiC and Al₂O₃) reinforced 6061 Al metal matrix composites. Differential scanning calorimetry and dynamic mechanical analysis have provided information on the formation/dissolution of precipitate phase(s) and the effect of temperature on the short-term storage modulus of the materials, respectively. These studies were also used to identify the phase changes responsible for the maximum damping properties of the materials.     

Mechanical properties of TiO2-filled CNT/PMMA composites

ABSTRACT

The present study investigated the effect of TiO₂ fillers on the mechanical properties of CNT/PMMA composites. TiO₂/PMMA/CNT composites were prepared by using twin screw extruder and test samples by injection moulding. Results indicated that incorporation of CNT in PMMA causes decreases in tensile stress, elongation at break, and on impact properties. It is observed that addition of CNT and TiO₂ seems to be beneficial in increasing mechanical strength via increasing the interface dispersed phase.     

Influence of neodymium on microstructure and mechanical properties of AZ31B wrought magnesium alloy

Abstract

The influences of rare earth neodymium on microstructure and mechanical properties of as cast and hot rolled AZ31B wrought magnesium alloy were investigated. The results show that the mechanical properties of both as cast and hot rolled AZ31B alloys decrease due to Nd addition. Nd reacts with Al to form Al₂Nd phase when Nd is added. Bulky and brittle Al₂Nd intermetallic degrades the mechanical properties. Moreover, the addition of Nd weakens the grain refining effect of Al on as cast AZ31B alloy, resulting in grain coarsening. Coarse grains also cause the decline of the mechanical properties of as cast AZ31B–Nd alloy. The negative influence of the bulky and brittle intermetallics on mechanical properties of AZ31B alloy can be relieved by large deformation because the intermetallics can be sufficiently broken up during the deformation process.     

Quantifying the metallurgical response of a nuclear steel to welding thermal cycles

Solid-state phase transformations can drastically influence the evolution of stress in welds due to the strains associated with the transformations and related changes in mechanical properties. As such, finite-element predictions of welding residual stresses need reliable materials data including, where applicable, information on phase transformation kinetics and phase- and temperature-dependent material properties. Owing to a scarcity of such data, many authors have used uncalibrated empirical modelling approaches for the prediction of welding residual stresses. This paper addresses this critical shortage for an important nuclear pressure vessel (SA508) steel. Austenite formation, grain growth and decomposition data are presented and subsequently used to calibrate transformation models. These models are shown to accurately predict microstructure and residual stresses for experimental test cases.

This paper is part of a Themed Issue on Measurement, modelling and mitigation of residual stress.