Ion-assisted vapor deposition of acryl polymer thin films

Polymer thin films were prepared by an ion-assisted vapor deposition polymerization method that involves physical vapor deposition of monomer combined with low-energy ion irradiation. In a high vacuum environment, zinc diacrylate monomer was evaporated at a rate of 0.8 nm/min on gold-coated glass substrates under simultaneous irradiation by nitrogen ions of 20 nA/cm² at ion energy ranging from 500 to 2000 eV. The ion irradiation remarkably reduced the surface roughness of the deposited films. Infrared spectroscopy showed that the absorption bands of the vinyl group diminish with increasing ion energy. Formation of polymer molecules was confirmed by gel permeation chromatograph. Moreover, the film became insoluble to organic solvents when the ion energy was increased. These results indicate that polymer thin films can be prepared by vapor deposition of monomers under ion irradiation. The ion-assisted vapor deposition polymerization was also possible on insulating substrates.     

Formation and microstructural characterisation of S-phase layers in Ni-free austenitic stainless steels by low-temperature plasma surface alloying

The feasibility of generating S-phase surface layers in nickel-free austenitic stainless steels by plasma surface alloying with nitrogen (at 430 °C), carbon (at 430 °C and 500 °C) and both carbon and nitrogen (at 430 °C) has been investigated. The structure, microstructure and composition of the plasma-alloyed surfaces were characterised by X-ray Diffraction (XRD), microscopy, Glow Discharge Optical Emission Spectroscopy (GDOES) and Transmission Electron Microscopy (TEM). The experimental results have demonstrated for the first time that the S-phase can be produced in the surface of nickel-free austenitic stainless steel by low-temperature plasma surface alloying. TEM analysis has revealed that when alloyed with carbon no precipitates can be found within the carbon-rich S-phase layer; however, when alloyed with nitrogen or both carbon and nitrogen some nitride precipitates (Mn₃N₂ and Cr₂N) were found within the nitrogen-rich S-phase layer. Based on experimental results, the response of Ni-free austenitic stainless steel to plasma surface alloying has been compared to the Ni-containing counterpart, and the role of nickel in the formation of S-phase in austenitic stainless steels has been discussed.     

Selective single pulse femtosecond laser removal of alumina (Al2O3) from a bilayered Al2O3/TiAlN/steel coating

We studied surface modification of a double layer protective coating on steel induced by single fs laser pulse irradiation in ambient air. The outer alumina (Al₂O₃) layer, which protects against aggressive environments, was 1.7 μm thick and the titanium aluminum nitride (TiAlN) layer in contact with the steel surface had a thickness of 1.9 μm. The pulses (λ = 775 nm, τ = 200 fs) were generated by a Ti:sapphire laser source. The pulse energy was varied from 0.32 μJ to 50 μJ, corresponding to an incident laser fluence of 0.11 J cm^− 2 to 16.47 J cm^− 2. The surface damage threshold was found to be 0.20 J cm^− 2 and the alumina layer removal was initiated at 0.56 J cm^− 2. This selective ablation of alumina was possible in a wide range of fluences, up to the maximum applied, without ablating the TiAlN layer beneath.     

Influence of oxygen ion irradiation on the corrosion aspects of Ti-5%Ta-2%Nb alloy and oxide coated titanium

The corrosion resistance of Ti-5%Ta-2%Nb alloy and DOCTOR (double oxide coating on titanium for reconditioning) coated titanium by O⁵⁺ ion irradiation were compared and investigated for their corrosion behaviour. O⁵⁺ ion irradiations were carried out at a dose rate of 1 × 10¹⁷, 1 × 10¹⁸ and 1 × 10¹⁹ ions/m² at 116 MeV. The surface properties and corrosion resistance were evaluated by using scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX), glancing-angle X-ray diffraction (GXRD) and electrochemical testing methods. The results of electrochemical investigations in 11.5 N HNO₃ indicated that the open circuit potential (OCP) of DOCTOR coated titanium is nobler than Ti-5%Ta-2%Nb alloy. The potentiodynamic polarization study of Ti-5%Ta-2%Nb alloy and DOCTOR coated specimen indicated decrease in passive current density with increase in ion doses (1 × 10¹⁷ to 1 × 10¹⁹ ions/m²) indicating decrease in anodic dissolution. Nyquist arc behaviour in the electrochemical impedance study substantiated the enhancement in oxide layer stability by O⁵⁺ ion irradiation. AFM results revealed that the DOCTOR coated Ti surface was dense without gross voids, and the surface roughness decreased by O⁵⁺ ion irradiation, but increased after corrosion test. EDX and GXRD patterns of DOCTOR coated Ti sample indicated that the coating was mainly composed of rutile TiO₂. Based on the above results, the O⁵⁺ ion irradiation effect on corrosion behavior of Ti-5%Ta-2%Nb alloy and DOCTOR coated titanium are discussed in this paper.     

Corrosion properties of plasma nitrided AISI 410 martensitic stainless steel in 3.5% NaCl and 1% HCl aqueous solutions

Samples of an AISI 410 martensitic stainless steel were plasma nitrided at a temperature of 420 °C, 460 °C or 500 °C for 20 h. The composition, microstructure and hardness of the nitrided samples were characterised using a variety of analytical techniques. In particular, the corrosion properties of the untreated and plasma nitrided samples were evaluated using anodic polarisation tests in 3.5% NaCl solution and immersion tests in 1% HCl acidic water solution. The results showed that plasma nitriding produced a relatively thick nitrided case consisting of a compound layer and a nitrogen diffusion layer on the 410 stainless steel surface. Plasma nitriding not only increased the surface hardness but also improved the corrosion resistance of the martensitic stainless steel. In the immersion test, nitrided samples showed lower weight loss and lower corrosion rate than untreated one. In the electrochemical corrosion tests, the nitrided samples showed higher corrosion potentials, higher pitting potentials and greatly reduced current densities. The improved corrosion resistance was believed to be related to the iron nitride compound layer formed on the martensitic stainless steel surface during plasma nitriding, which protected the underlying metal from corrosive attack under the testing conditions.     

On the first breakdown in AA7075-T6

The first breakdown in AA7075-T6 was studied by an in situ observation system in which a combination of a magnified image of the surface and the instantaneous polarization curve allowed determination of the corrosion process as a function of potential. As-polished (to 1 μm) AA7075-T6 clearly exhibited dissolution of a thin surface layer corresponding to a sharp increase of current just above the first breakdown potential. No surface layer dissolution was observed for samples that were either ion milled or chemically etched to remove the effects of polishing. This susceptible surface layer was apparently the result of the mechanical polishing process. The surface microstructure of an as-polished sample was analyzed by TEM and several distinct features were found: (1) a unique thin layer with thickness of 100 nm on average; (2) many fewer fine hardening particles in the thin surface layer than in the bulk matrix, which suggests that the fine particles were destroyed and eliminated by polishing; (3) high aspect ratio nano-grains elongated along the final polishing direction; (4) a high concentration of Zn and Mg at the nano-grain boundaries. The attack of the surface layer might initiate at the active nano-grain boundary followed by nano-grain dissolution.     

Repair of EDM induced surface cracks by pulsed electron beam irradiation

This study investigates the use of the large-area electron beam irradiation technique to improve the properties of the EDM’d surface of AISI 310 stainless steel so that a tolerable, or even desirable recast layer may be produced. The short cycle-time of the irradiation process combined with the large incident area of 60 mm diameter makes it an attractive surface modification technique for metal moulds and engineering components. This study showed that by varying acceleration voltages and the number of irradiation cycles (shots), that as well as an improvement of surface finish, repair of cracks induced by the EDM process is possible. The mechanism of this repair is also investigated. XRD analysis also shows that crystalline texture can be introduced by the irradiation process with the (1 1 1) planes of the austenite phase orienting parallel to the surface. This has potential advantages for introducing anisotropic layers for enhanced corrosion resistance.     

Model of intense pulsed ion beam and simulation study of energy deposited on target

Gaussian type models have been established according to the real detected voltage of magnetically insulated ion diode and intense pulsed ion beam density near the focus of the diode. The energy deposition of Al target irradiated by intense pulsed ion beam has been simulated by Monte Carlo method based on these models. The results of energy depositions of the irradiation of single energy ions and the Gaussian distribution IPIB have been obtained. Especially cases of ion beam irradiating Al target at different angles on one dimension and two dimensions are discussed. The evolution processes of the energy deposition of ions in target have been simulated during a pulse. In addition, incident angles of H⁺ ions and C⁺ ions ranging from 20 to 40° have been researched. We obtained the conclusions that C⁺ ions of the beam affect the physical properties of near surface region, but H⁺ ions affect the deeper layer. The energy of intense pulsed ion beam mainly deposits on target surface, so melting and evaporation begin both from target surface.     

Effect of ultrasonic surface treatment of steel 40Kh13 on the microstructure of nitrided layer formed by high-intensity low-energy implantation with nitrogen ions

X-ray diffraction and transmission electron microscopy were used to study the microstructure and phase composition of surface layers of steel 40Kh13 subjected to irradiation with high-intensity low-energy ion beams, ultrasonic surface modification, and combined treatment including ultrasonic surface modification and ion implantation. It was found that the ultrasonic modification of steel surface leads to changes in the structure of tempered martensite and the formation of grain structure with a grain size of 0.3 μm and nanosized special carbides Cr₂₃C₆ in the martensite lamellae. The ion implantation into this steel results in the formation of a nitrided layer consisting of a nitride region, which represents a mixture of several phases (α-, γ′-, ?, and ultrafine chromium nitrides), and a zone of internal nitriding (α″ and nitrogen-containing martensite α_N). The preliminary ultrasonic modification causes an increase in the nanohardness and in the thickness of the nitrided layer, which is due to the more intense penetration of nitrogen atoms into the surface layer and an increase in the volume fraction of iron nitrides and density of ultrafine chromium nitrides in this layer.     

Study of corrosion resistance and microstructure of the 0.45 wt% C steel modified by pulsed high energy density plasma

A 0.45 wt% C steel was modified by pulsed high energy density plasma (PHEDP), which was composed of particles of aluminum and nitrogen. A layer of thin film was formed on it. The modified steels were studied by an electrochemical corrosion test and transmission electron microscope (TEM) observations. Results showed that the corrosion resistance ability of 0.45 wt% C steel improved after modification, and the film was composed of nanocrystal-aluminum-nitride-phase (AIN), with crystal size of less than 20 nm. The nanocrystal-structured film contributes to the improvement of the corrosion resistance. The improvement is not only related to the microstructure of the film but also to its surface morphology, and both are controlled by the parameters of the PHEDP.     

The initial stage of pitting corrosion on coated steels investigated by photon rupture in chloride containing solutions

A photon rupture method, film removal by a focused pulse of pulsed Nd-YAG laser beam irradiation, has been developed to enable oxide film stripping at extremely high rates without contamination from the film removal tools. In the present study, Zn-55mass%Al alloy and Al-9mass%Si alloy-coated steel specimens covered with protective nitrocellulose film were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in 0.5 kmol m⁻³ H₃BO₃-0.05 kmol m⁻³ Na₂B₄O₇ (pH = 7.4) with 0.01 kmol m⁻³ of chloride ions to investigate the initial stage of localized corrosion. At low potentials, oxide films on both coated alloys were reformed after the nitrocellulose films were removed by this method. The oxide film formation kinetics follows an inverse logarithmic law, in agreement with Cabrera-Mott theory. However, at high potentials, localized corrosion producing corrosion products occurs at the area where nitrocellulose film was removed. Nevertheless, when the applied potential is less noble, the dissolution current of the Zn-55mass%Al-coated steel samples is higher than that of Al-9mass%Si-coated samples.     

Wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam

The wear resistance and wear mechanism of AZ31 magnesium alloy irradiated by high-intensity pulsed ion beam (HIPIB) at an ion current density of 100 A/cm² with shot number from one to ten are investigated by dry sliding wear tests. The cross-sectional microstructure and surface microhardness of the irradiated AZ31 magnesium alloys are examined by optical microscopy (OM) and Vickers tester, respectively. It is found that surface hardness increased with increasing shot number, from an original value of 570 MPa to a maximal value of 820 MPa with ten shots, and the wear rate of the samples irradiated with five and ten shots was about one order of magnitude less than that of the original sample. The transition from severe metallic wear to mild oxidative wear induced by HIPIB irradiation was identified through a combined analysis in surface morphology and chemical composition of wear tracks, mechanically mixed materials, wear debris and wear scars of counterface steel ball by using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), which is mainly attributed to the significant increase in microhardness resulting from grain refinement on the irradiated surface.     

Anti-corrosion characteristics of nitride-coated AISI 316L stainless steel coronary stents

The corrosion resistance of TiN and TaN coatings deposited on AISI 316L stainless steel thread-coiled coronary stents by pulsed bias arc ion plating is evaluated by electrochemical methods in deaerated Tyrode's simulated body fluids (37 ± 1 °C). The free corrosion potential of the TaN-coated stents is found to be nobler than that of the TiN-coated and uncoated stents throughout most of the immersion time. The potentiodynamic polarization test results indicate that the TaN coatings offer better passivation stability and anti-breakdown performance. The longer-term 6-month immersion tests disclose slight localized corrosion on the surface of both coatings, but no film delamination or large area pitting can be observed indicating reasonably good corrosion resistance after the long period.     

Effect of nitrogen ion irradiation on the nano-tribological and surface mechanical properties of ultra-high molecular weight polyethylene

Generation of wear debris is the principal obstacle limiting the durability of ultra-high molecular weight polyethylene (UHMWPE) in biomedical applications. Aiming to enhance UHMWPE wear resistance, surface modification with swift heavy ion irradiation (SHI) appears as a potential and attractive methodology. Contrary to ion implantation techniques, the swift heavy ions range can reach tens to hundreds microns and its extremely high linear energy is able to induce effective chemical modifications using low fluence values. Nano-wear performance and surface mechanical properties of samples of pristine and SHI irradiated (using N₂⁺ ions at 33 MeV and a fluence of 1 × 10¹² ions/cm²) were characterized by depth sensing indentation (DSI) and scanning probe microscopy (SPM). It turned out that modifications induced by irradiation at the surface layers were successful to reduce nano-wear volume and creep deformation. These improvements were related to beneficial changes in hardness, elastic modulus, hardness to elastic modulus ratio and friction coefficient.     

Detailed of X-ray diffraction and photoluminescence studies of Ce doped ZnO nanocrystals

Pristine and Ce doped ZnO nanopowders were synthesized by simple refluxing technique. A detailed X-ray diffraction analysis was carried out to evaluate the contribution of dopant ion concentration on strain and lattice parameters. A particle size of 20 nm was obtained via TEM studies. Spherical morphology was obtained for Ce doped ZnO nanocrystals. Multiple emission bands were observed for pristine and doped ZnO samples where, 401 nm emission band corresponds to a contribution due to free excitons recombination through an exciton-exciton collisions. With the Ce addition, the surface defects increases and the emission intensity decreases.     

Pulse-periodic source of high-energy plasma flows at air for thermal technology applications

Principles of generation of high-energy pulse plasma flows and design of a hybrid electromagnetic plasmadynamic system-pulsed-periodic plasmatron are described. This electromagnetic plasmadynamic system operates at standard atmospheric pressure with high frequency. The plasma flow velocity reaches 3-5 ? 10³ m/s with a temperature up to 15 ? 10³ K. The results of investigations of pulsed-periodic plasmatron operations and carbon steel (0, 45% C) surface layer modification are presented.     

Electropolishing effects on corrosion behavior of 304 stainless steel in high temperature, hydrogenated water

The corrosion rate of electropolished 304 stainless steel surfaces (UNS S30400) is found to be lower by more than a factor of three relative to that determined previously for machined surfaces in mildly alkaline, hydrogenated water at 260 °C. This favorable result is attributed to significant changes in nanocrystallinity of the corrosion oxide layer caused by the removal of surface microstrain, which had been imparted during the machining process. In the absence of microstrain, a low-porosity, protective, corrosion layer forms that is composed of extremely small and uniformly-sized spinel oxide crystals. Application of scanning electron microscopy (FEG-SEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS) in conjunction with ion milling and target factor analyses, found the corrosion layer to consist of micrometer-size crystals of a ferrite-based spinel oxide (non-protective) over-laying nanometer-size crystals of a chromite-based spinel oxide (protective). Composition of both phases is unchanged from that previously observed on corroded, machined surfaces and is representative of solvus phases in the immiscible Fe(Fe_1−nCr_n)₂O₄ spinel binary. The smaller size (10 vs. 26 nm) and greater surface density (∼10,000 vs. 835 μm⁻²) of the chromite-based crystals relative to those formed on machined (i.e., cold-worked) surfaces, however, is consistent with the absence of preferred high energy nucleation sites on strain-free surfaces. Therefore, electropolishing, which removes surface microstrain induced by cold-working, represents a preferred reference surface condition.     

Improvement of high temperature oxidation resistance of AISI 316L stainless steel by incorporation of Ce-La elements using intense pulsed plasma beams

It is well documented that adding some active elements (such as Y, Ce, La, Er, others) to austenitic stainless steels helps to improve their high temperature oxidation resistance. In the present work we report preliminary results of incorporation of Ce and La into austenitic stainless steel AISI 316L using a new approach based on high intensity pulsed plasma beams. The characteristic feature of this approach relies upon the fact that incorporation of Ce-La occurs in the transiently melted near-surface layer of the substrate. Improving the near surface layer properties was connected with two facts: (i) material melting and cooling with very high rate and (ii) incorporation Ce-La to the molten phase. Modified samples were oxidized at 1000 °C for 80 h in air at atmospheric pressure. The obtained effects were similar to those observed in chromia-forming alloys doped by other conventional surface treatment techniques: oxide scales formed on the treated samples were more fine-grained, compact and adhered better than those formed on the un-treated samples, whereas the protective layer was produced closer to the surface.     

Iron oxidation kinetics study by using infrared spectral emissivity measurements below 570 °C

The oxidation kinetics of iron below 570 °C is investigated through the dependence of the spectral emissivity on the surface oxidation state. Using the theory of radiative effects of thin films, the oxide scale thickness is obtained as a function of time. A parabolic growth has been observed in all the cases, and applying Wagner’s theory, the oxidation parabolic rate constants have been calculated at four temperatures. The temperature dependence of these results has additionally been used to obtain the activation energy of the oxidation process in iron. The parabolic rate constants and activation energy values are in good agreement with the theoretical predictions, and this suggests that the lattice diffusion mechanisms for the high temperature magnetite growth also occur until 400 °C. The experimental results are also useful to test the applicability of emissivity measurements for in situ oxidation kinetics studies in the spectral range where the scales are optically thin.     

Increasing surface hardness of austenitic stainless steels by pack nitriding process

This paper investigated the possibility of increasing the surface hardness of austenitic stainless steels under very low nitrogen dissociation pressures of metal nitride powders using pack nitriding process. Thin sheet of 304 type of stainless steel of approximately 1 mm in thickness was used as a substrate for the study. Based on the results of thermochemical calculations, Cr₂N powder was selected as a nitrogen source from a series of metal nitride powders considered for the pack nitriding process, which included Si₃N₄, Mn₄N, BN, AlN and TiN. The pack nitriding was carried out in a sealed alumina retort at temperatures of 860 °C and 910 °C for up to 48 h. The surface was then characterised using techniques of SEM, XRD and microhardness testing. It was observed that the process used increased the surface hardness of the steel, but it also induced precipitation of chromium nitrides in the matrix even under the nitrogen dissociation pressures below 50 Pa. It was also observed that, in the nitrided layer, the γ phase of the steel was partially transformed to the α phase under the pack nitriding process conditions studied.