Inhibition of stress corrosion cracking in 304 stainless steel through titanium ion implantation

The effects of titanium ion implantation on the stress corrosion cracking (SCC) behaviour of 304 austenitic stainless steel were studied. Slow strain rate tests (SSRTs) were conducted on 304 steel in air and in 5?wt-% NaCl solution. The microscopic effects of ion implantation were evaluated by Stopping and Range of Ions in Matter Procedures (SRIM). Fracture morphologies and microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The fracture surfaces illustrate that ion implantation significantly inhibits the corrosion pits that initiate SCC. A dense passive film, which inhibits SCC, was formed during the ion implantation process. SCC initiation was restrained due to the dense dislocation nets that were generated by titanium ion implantation.

Highlights

• Ion implantation inhibits SCC susceptibility.

• The lack of Cr at the grain boundary leads to the expansion of SCC along the grain boundary.

• Implantation-induced damage leads to high-density dislocations.

• The surface was amorphised due to high-density dislocations.

     

X-ray photoelectron spectroscopy studies of the degradation of PVF2 coatings

X-ray photoelectron spectroscopy studies of PVF₂ coatings on coil-coated sheet metal are presented. Test specimens, artificially aged and exposed to six different exposure sites in the Nordic countries, were analysed by photoelectron spectroscopy. The analysis gives detailed information on the chemical composition of the coating, reveals the main deterioration processes taking place and enables an evaluation of the exposure modes used.

---

Résumé On présente des études par spectroscopique X photoélectronique de revêtements PVF₂ sur enroulements de feuilles de métal. Les éprouvettes d'essai, vieillies artificiellement et exposées à des emplacements différents dans les pays nordiques, ont été analysées par la spectroscopie X photoélectronique. L'analyse donne une information détaillée sur la composition chimique du revêtement, elle révèle les principaux processus de détérioration et permet une évaluation des modes d'exposition utilisés.

     

Transformation of stress-induced martensite in 304 stainless steel by ion implantation

Type 304 stainless steel made largely martensitic by rolling was implanted with nitrogen, nickel, and neon. Transformation of the martensite to austenite was found by transmission election microscopy for the nitrogen and nickel implantations, but not for the neon. The transformation was found to be confined to the implanted layer. Lattice expansion was measured for nitrogen implantation, and an unusual electron-diffraction effect apparently due to surface strain was observed for the highest nitrogen concentration.     

Corrosion properties of titanium based hard coatings on steel

Titanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA-CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA-CVD process parameters. The incorporation of chlorine in the coating can be varied by the process parameters with TiCl₄ or completely avoided using metallo-organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel. A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN-coated substrates of complex geometry. The PA-CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low-alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.     

X-ray photoelectron spectroscopy studies of polymer surfaces

X-ray photoelectron spectroscopy showed that a normal flame treatment caused a high level of oxidation in low-density polyethylene. 0.02% of the antioxidant 2,6-ditertbuty-p-cresol did not reduce the degree of oxidation or the level of adhesion in contrast to the extrusion of low-density polyethylene. It is estimated that the depth of oxidation is between 40 and 90 Å which is much less than for a moderate chromic acid treatment or with extrusion. There were no significant changes in the XP-spectra or adhesion levels of flame treated samples after 12 months.     

X-ray photoelectron spectroscopy studies on ethylene oxychlorination catalysts

Copper chloride on alumina catalyst used for oxychlorination of ethylene represents a typical system where copper is in a dynamic equilibrium between Cu⁺ and Cu⁺⁺ oxidation states. Surface studies on redox, structural and compositional properties have been undertaken to monitor the changes that occur on the catalyst during use and pinpoint causes for its deactivation. For this, a fresh and a spent catalyst were been chosen for characterization. A core consisting of copper in Cu⁺ state and present as CuAlO₂ is formed at the centre of the catalyst sphere. Formation of such a nonreversible phase under reaction conditions upsets the redox equilibrium. XPS also shows the absence of potassium in the core and its precipitation as a new phase on use, probably KCl, formed by the decomposition of active component KCuCl₃. These factors facilitate deactivation. IPCL Communication No. 96     

X-ray photoelectron spectroscopy studies of polymer surfaces

X-ray photoelectron spectroscopy (XPS) has been used to study the chromic acid etching of polyethylene (low density) and polypropylene film surfaces. Both core and valence levels have been used to monitor changes in surface composition and these results correlated with contact angle measurements. Besides the expected observation of oxygenated species, the technique detects a sulphur containing species, identified as -SO₃H. Information about the depth of polymer attack has been obtained from two types of data (comparative core level intensities and angular variation of relative peak intensities) which provide depth resolution. Differences in behaviour of the two polyolefins are discussed in connection with previous non-surface specific data.     

X-ray photoelectron spectroscopy studies of polymer surfaces

The effect of melting polyethylene on aluminium has been re-examined using X-ray photoelectron spectroscopy. Even at 150° C, low and high density polyethylenes show degrees of oxidation similar to that observed with conventional pretreatments; large increases in adhesion are also observed. The results are discussed in relation to transcrystalline regions and weak boundary layers.     

Surface oxide dissolution in titanium subhydrides studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy

The surface sensitive spectroscopic techniques of Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) have been applied to the study of oxide dissolution of titanium subhydrides. In an earlier study using AES, it was shown that the rate of oxygen dissolution into titanium increased sharply at ~350° C. These data correlated well with physical property measurements that indicated an exothermic reaction was occurring at these temperatures which corresponded to the reaction of free titanium with atmospheric oxygen. In the present study the work has been expanded to include studies of TiH _x (x=1.15, 1.62). It has been found that dissolution of the native oxide on titanium subhydrides occurs at a temperature substantially higher (~ 500° C) than that required for titanium. It appears that the outward diffusion of hydrogen is inhibiting the inward diffusion of oxygen on the subhydride samples at temperatures below 500° C.Mound Facility is operated by Monsanto Research Corporation for the United States Department of Energy under Contract Number DE-AC04-76-DP00053.     

Characterization of transition joints of commercially pure titanium to 304 stainless steel

Solid-state direct bonding between commercially pure titanium and type 304 austenitic stainless steel has been carried out in the temperature range of 850–950 °C, under a uniaxial pressure of 3 MPa for 1 h. The diffusion bonds have been evaluated using light microscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD) technique and tensile testing. Light microscopy shows that different intermediate layers are formed in the reaction zone, and the width of these layers increases with an increase in bonding temperature. EPMA revealed that, at any particular bonding temperature, Ti traverses a minimum distance in the 304 stainless steel side, whereas Fe, Cr and Ni travel comparatively larger distances in the Ti side. This microanalysis also indicated different step formations in the concentration profile of Ti, Fe and Cr over different composition ranges in the diffusion zone indicating formation of intermetallic phases that were detected by XRD. Brittle intermetallic phases lower the strength and ductility of the diffusion bonded couples significantly. Best room temperature tensile strength, 217 MPa, has been obtained at 850 °C processing temperature due to minimal deleterious effects.     

Influence of ion implantation and overlay coatings on various physico-mechanical and wear properties of stainless steel,titanium and aluminium

This work represents the data on the wear behaviour of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, namely ion implantation of boron and nitrogen and overlay coatings of titanium carbide and nitride.The surface treatments were characterized by phase identification, hardness, bend strength, as well as adhesion of overlay coatings. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear.The experimental results showed that surface treatments produced measurable changes in hardness and strength. The results of adhesive wear tests indicated that the wear resistance of all the substrate materials can be considerably improved by overlay coating with superhard materials in dry as well as lubricated test conditions. Ion implantation resulted in improvement of wear properties for only a limited regime of adhesive wear under lubricated conditions and for the abrasive mode of wear. Overlay coatings produced a marked improvement in abrasive wear tests under lubricated conditions on all substrate materials.     

Evaluation of hard coatings on steel by particle erosion

There is a great need for better methods to characterize the mechanical properties of coated materials, especially for thin hard well-adhering films on, for example, steel. In this paper particle erosion is proposed as a potential test for the performance of coated materials.High speed steel was coated with a 1 μm TiN layer and exposed to particle erosion using various erosion parameters. The removal of the coating was monitored by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The change in intensity of the Fe Kα peak versus the particle dose was used to obtain a measure of the proportion of the substrate area revealed.A theoretical model was developed to describe the erosion process in terms of the particle dose and two characteristic film parameters. These are the mean area affected by a single impact and the mean number of consecutive impacts in one site necessary to make the coating spall.These quantities are closely related to practical adhesion, and controlled particle erosion is therefore proposed as a technique to evaluate adhesion.     

Oxide films formed on aluminium-enriched surfaces of 304 stainless steel in high-temperature water containing Co ions

Aluminium-enriched surfaces of 18Cr-8Ni stainless steel were subjected to oxidation in 285° C water containing 1 p.p.b. dissolved cobalt for 336 H. Microanalytical studies (scanning electron microscope, X-ray dispersive energy analysis, ion mass spectroanalysis, and ion microprobe mass analysis) were employed to examine the behaviour of cobalt in the oxides formed. It is concluded that (1) the main oxide formed on aluminium-enriched surface is a diaspore, (2) diffusion heat treatment improves the oxidation rate, and (3) the cobalt level decreases constantly from the surface to the interface of the oxide formed on aluminium-enriched samples.     

Yttrium implantation effect on 304L stainless steel high temperature oxidation at 1000°C

Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDXS) and in situ X-ray diffraction techniques were carried out to observe the oxide scale evolutions of yttrium implanted and unimplanted commercial 304L stainless steels during and after their high temperature oxidation at 1000°C for 100 h. Our results clearly demonstrate that yttrium implantation promotes a faster oxide scale growth and the formation of a more uniform chromia layer due to a higher chromium selective oxidation compared to unimplanted 304L stainless steel. Moreover, the presence of yttrium also leads to the formation of an enriched silicon layer at the metal-oxide interface limiting the growth of iron-based oxides which were not detected (even during cooling) in the case of yttrium implanted samples. These results allow to understand the low weight gain of yttrium implanted 304L stainless steel observed by thermogravimetry and underline the beneficial effect of yttrium implantation on the 304L oxidation resistance at high temperature.     

Surface composition and near-surface hardness studies on high dose boron-implanted 304 stainless steel

The modification of boron-implanted near surface of 304 stainless steel having strained and strain-free surfaces was studied. The energy of the boron ion was 130 keV at a dose of 2·5×10¹⁷ ions cm⁻². Ion-implantation is known to modify the tribological properties of metals, however, it is not well-understood as to how such a shallow implanted layer can affect the microhardening. A full understanding of the process involved is yet to emerge. In the present work the ion implanted layer was characterized for boron depth profiles using AES and XPS. The implanted layer is observed to contain B₂O₃, Fe₂B, FeB and CrB₂ compounds with small fractions of chromium and iron oxides. The strain-free surface of 304 SS shows an increase in microhardness by ∼ 80% after boron ion implantation at 2 gf and the strained surface by ∼ 30% at the same load. The annealing effects on microhardness for mechanically polished and implanted samples were also investigated in the temperature range 100 to 400°C. The possible correlation of near-surface microhardness increase with boride formation is discussed.     

304不锈钢激光熔覆Co-Ti3SiC2自润滑复合涂层微观组织与摩擦学性能

采用激光熔覆同步送粉法在304不锈钢上制备出自润滑耐磨涂层,熔覆粉末配比为纯Co,Co-2％Ti3 SiC2(质量分数,下同)和Co-8％Ti3 SiC2.借助扫描电子显微镜(SEM),能谱分析仪(EDS)和X射线衍射仪(XRD)对熔覆涂层进行表征,系统地研究304不锈钢与涂层在室温和600℃下的摩擦学性能与磨损机理.结果表明:激光熔覆Co-Ti3 SiC2涂层的平均显微硬度高于基体(240.3HV0.5),N1,N2和N3涂层的硬度分别为285.7HV0.5,356.3HV0.5和463.8HV0.5,涂层主要由连续基体γ-Co固溶体,硬质相Fe2 C,Cr7 C3和TiC,润滑相Ti3 SiC2组成.在室温下,基体和N1,N2,N3涂层的摩擦因数分别为0.56,0.62,0.68和0.42,N1,N2,N3三种涂层的磨损率分别为9.15×10-5,7.81×10-5,4.66×10-5 mm3/(N·m),均明显低于基体(66.42×10-5 mm3/(N·m));在高温下,基体和N1,N2,N3涂层的摩擦因数为0.66,0.54,0.52和0.46,N1,N2,N3三种涂层磨损率分别为37.79×10-5,35.6×10-5,18.83×10-5 mm3/(N·m),均低于基体(41.3×10-5 mm3/(N·m)).在室温和600℃下,涂层具有高于304不锈钢基体的显微硬度,且Co-8％Ti3 SiC2涂层呈现出最好的自润滑耐磨性能.     

Large-railgun residue material analyzed by X-ray photoelectron spectroscopy

Samples of a black powdery residue material which appeared on the rails of a large-scale railgun system were analyzed using X-ray photoelectron spectroscopy. No copper content could be detected in the residue materials associated with nominally sliding contact or arc-driven test shots.     

Bias effects on the tribological behavior of cathodic arc evaporated CrTiAlN coatings on AISI 304 stainless steel

In this study, CrTiAlN coatings were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The coating morphology and properties including surface roughness, adhesion, hardness/elastic modulus (H/E) ratio, and friction behavior were analyzed to evaluate the impact of the substrate bias voltage on the coating microstructure and properties. The results suggest that for an optimized value of the substrate bias voltage, i.e. − 150 V, the CrTiAlN coatings showed increased Cr content and improved properties, such as higher adhesion strength, hardness, and elastic modulus in comparison to the coatings deposited by other substrate bias voltage. Moreover, the optimum coatings achieved a remarkable reduction in the steel friction coefficient from 0.65 to 0.45.