Stainless Alloys Research Articles

Can the Current Stent Manufacturing Process be Used for Making Metallic Biodegradable Stents

Stents have been routinely used for the treatment of coronary artery occlusion since the last two decades. They are made of corrosion resistant alloys such as stainless steel 316L, titanium and cobalt-chromium alloys; in addition, their manufacturing process is well developed. Currently, corrodible metals have been proposed for making stents that can degrade after serving its function (biodegradable stents). This article discusses applicability of the current laser-cutting-based stent manufacturing process for making biodegradable stents: from materials production to stent fabrication until implantation. It covers some practical and technical points extracted from literatures and authors experiences with clinicians and industrialists to be considered in developing metallic biodegradable stents.

Forming Mechanism of Cold-Press Connection Between Heterogeneous Sheets

The traditional connections between dissimilar sheets metals have some drawbacks, such as the connection difficulties, high process requirement, and high cost. As a result of these drawbacks, this article proposes a new method for the connection of dissimilar sheet metals: the cold-pressing connection method. Based on the analyses of the structure and characteristics of the connections, three schemes were designed. Experimental results indicate that the elongation of the connection increases along the length direction during the connection process. Meanwhile, the thinning degree is smallest at the middle position of the connection and increases toward the two sides. As the punch load is increased, the close degree between connected sheets increases. The connection strength test between stainless steel sheet and aluminum alloy sheet with the loading force of 290 KN shows that tensile strength of Scheme 1 is 1.4 times higher than that in Scheme 3. The tensile strength of the connection between stainless steel sheet and aluminum sheet is larger than that of the connection between stainless steel sheet and aluminum alloy sheet at the same experimental condition. This article provides the theoretical basis for the popularization of this method.

CENTRALLOY H101 MICRO

Abstract Centralloy H101 Micro is a cast austenitic stainless alloy with very good high temperature properties. The alloy has carbides in a uniform dispersion that impedes dislocation movement. This datasheet provides information on composition, physical properties, elasticity, and tensile properties. It also includes information on casting, machining, and joining. Filing Code: SS-1148. Producer or source: Schmidt & Clemens Inc..

Spectral emissivity of candidate alloys for very high temperature reactors in high temperature air environment

Emissivity measurements for candidate alloys for very high temperature reactors were carried out in a custom-built experimental facility, capable of both efficient and reliable measurements of spectral emissivities of multiple samples at high temperatures. The alloys studied include 304 and 316 austenitic stainless steels, Alloy 617, and SA508 ferritic steel. The oxidation of alloys plays an important role in dictating emissivity values. The higher chromium content of 304 and 316 austenitic stainless steels, and Alloy 617 results in an oxide layer only of sub-micron thickness even at 700°C and consequently the emissivity of these alloys remains low. In contrast, the low alloy SA508 ferritic steel which contains no chromium develops a thicker oxide layer, and consequently exhibits higher emissivity values.

원전 가압기 노즐 및 안전단 재료에 대한 기계적 물성시험 연구

최근 가압경수로형 원전의 가압기 노즐과 안전단 사이의 이종용접부에서 일차수응력부식균열에 대한 건전성 확보가 중요한 관심사항으로 대두되고 있다. 가압기 노즐은 SA508 Gr.3 저합금강이며 안전단은 F316L 스테인리스강으로, 이들 두 재료 사이에 용접재로는 Alloy 82/182가 사용되었다. 재료 결함에 대한 건전성 평가를 위해서는 재료의 기계적 물성치, 특히 인장물성과 파괴물성이 확보되어야 한다. 그러나, 일반적인 재료 규격과 시험성적서에서는 상온의 인장물성이 제공되지만 고온의 인장물성과 파괴인성이 제공되지 않는다. 따라서, 본 논문에서는 상온과 원전 운전온도에서 SA508 Gr.3과 F316L 스테인리스강에 대한 인장시험과 J-R 파괴인성시험을 수행하고 그 결과를 수록하였다. Recently the primary water stress corrosion cracking(PWSCC) has occurred in the dissimilar metal weld region between pressurizer nozzle and safe-end in nuclear power plants(NPPs). As material of the pressurizer nozzle, SA508 Gr. 3 low alloy steel was used. F316L stainless steel and Alloy 82/182 were used as safe-end and weld metal, respectively. Although mechanical properties are needed for evaluation of the structural integrity against flaw in the material, material specification and standard don't supply those properties. Therefore, the present study conducted tensile and fracture toughness tests on SA508 Gr.3 and F316L stainless steel at ambient temperature and operating temperature of NPPs and reported the tested results.

Corrosion Behavior of 316L Stainless Steel and Alloy 625 in Supercritical Water Oxidation for Coking Wastewater Treatment

The corrosion behavior of 316L stainless steel and alloy 625 were deteced in superciritical water oxidation (SCWO) process for coking wastewater treatment. The operation conditions were 500 °C, 25 MPa, oxygen ratio of 3.5 and the reaction time of 150 h. Surface morphologies of metal samples, oxide structure and compositions across the oxide thickness of the metal samples after SCWO were analyzed using SEM and ESD, and the corrosion rates for both samples were obtained. Pitting corrosion was found on the surface of 316L stainless steel with a corrosion rate of 0.334 mm/a. While no remarkable corrosion was found on the surface of alloy 625, and the corrosion rate is 0.052 mm/a.

PP024. Effects of intravenous magnesium sulfate on the characteristics of eclamptic seizures induced by electrical stimuli in a rat preeclampsia/eclampsia model

Eclampsia is a serious complication of pregnancy and remains a leading cause of maternal mortality worldwide. Magnesium sulfate is commonly used in the prophylaxis and treatment of eclampsia. However, uncertainty remain regarding its anticonvulsant mechanism(s) of action. This study examined the effects of intravenous magnesium sulfate on the characteristics of eclamptic seizures in a rat preeclampsia/eclampsia model. All rats were implanted with stainless nickel-cadmium alloy bipolar electrodes one week before fertilization. Next, an experimental rat preeclampsia (PE) model was induced on gestational day 14 by anaesthetising rats and infusing over 1 hour into their tail veins lipopolysaccharide (LPS) (1.0μg/kg body weight) (with control rats receiving normal saline). The rats were then divided into three groups: a normal pregnancy (NP) group (n=6) which received a continuous infusion of saline; a control PE model group (n=7) (which had previously received the LPS treatment) which also received a continuous infusion of saline; and a treated PE model group (n=8) (which had previously received the LPS treatment) which received a continuous infusion of magnesium sulfate (60mg/kg/day). The continuous infusions in all three groups were delivered by implanted osmotic minipumps . Measurements were made of blood pressure, albuminuria, serum ALT, AST, and creatinine, BUN and serum magnesium concentrations. On gestational day 18, all experimental rats received a standardized electrical stimulus. Seizure activity was assessed using electroencephalogram (EEG) recordings. Terminations of pregnancy were performed on gestational day 21. Resorptions and pup birth weights were recorded. The pregnant LPS treated rats developed many features of human PE (e.g. hypertension, proteinuria, liver and kidney dysfunctions). The mean concentration of Mg(2+) in the magnesium sulfate therapy group (0.86±0.24mmol/L) was significantly higher (p<0.05) than in both the control PE model group (0.61±0.12mmol/L) and the NP group (0.62±0.09mmol/L). The magnesium sulfate therapy group had a significantly (p<0.05) increased latency period (21.7±8.9min) to evoke a full motor seizure compared to both the NP group (4.8±2.2min)and the control PE model group (3.3±1.4min), there being no significant difference (p>0.05) between the latency periods of the NP group and the control PE model group. Overall, the magnesium sulfate therapy regimen completely prevented seizure activity in 3/8 (37.5%) of the treated PE model rats compared to 6/6 (100%) of the NP rats and 7/7 (100%) of the control PE rats. The treated PE model group also had significantly (p<0.05) reduced seizure duration (26±4s) compared to both the NP (40±7s) and the control PE model (45±9s) groups. As well, there was a significantly (p<0.05) shorter EEG seizure amplitude change in the treated PE model group (58±6μv). In this rat preeclamsia/eclampsia model, the anticonvulsant characteristics of magnesium sulfate have been shown to include significantly increasing seizure latency period, reducing seizure duration and decreasing seizure EEG amplitude.

High Power Diode Laser-Treated HP-HVOF and Twin Wire Arc-Sprayed Coatings for Fossil Fuel Power Plants

This article deals with high power diode laser (HPDL) surface modification of twin wire arc-sprayed (TWAS) and high pressure high velocity oxy-fuel (HP-HVOF) coatings to combat solid particle erosion occurring in fossil fuel power plants. To overcome solid particle impact wear above 673 K, Cr3C2-NiCr-, Cr3C2-CoNiCrAlY-, and WC-CrC-Ni-based HVOF coatings are used. WC-CoCr-based HVOF coatings are generally used below 673 K. Twin wire arc (TWA) spraying of Tafa 140 MXC and SHS 7170 cored wires is used for a wide range of applications for a temperature up to 1073 K. Laser surface modification of high chromium stainless steels for steam valve components and LPST blades is carried out regularly. TWA spraying using SHS 7170 cored wire, HP-HVOF coating using WC-CoCr powder, Ti6Al4V alloy, and high chromium stainless steels (X20Cr13, AISI 410, X10CrNiMoV1222, 13Cr4Ni, 17Cr4Ni) were selected in the present study. Using robotically controlled parameters, HPDL surface treatments of TWAS-coated high strength X10CrNiMoV1222 stainless steel and HP-HVOF-coated AISI 410 stainless steel samples were carried out and these were compared with HPDL-treated high chromium stainless steels and titanium alloy for high energy particle impact wear (HEPIW) resistance. The HPDL surface treatment of the coatings has improved the HEPIW resistance manifold. The improvement in HPDL-treated stainless steels and titanium alloys is marginal and it is not comparable with that of HPDL-treated coatings. These coatings were also compared with “as-sprayed” coatings for fracture toughness, microhardness, microstructure, and phase analyses. The HEPIW resistance has a strong relationship with the product of fracture toughness and microhardness of the HPDL-treated HP-HVOF and TWAS SHS 7170 coatings. This development opens up a possibility of using HPDL surface treatments in specialized areas where the problem of HEPIW is very severe. The HEPIW resistance of HPDL-treated high chromium stainless steels and titanium alloys, HPDL-treated TWAS SHS 7170 and HP-HVOF coatings, and their micrographs and X-ray diffraction analysis is reported in this article.

Oxide Film Growth Kinetics on Metals and Alloys: II. Numerical Simulation of Transient Behavior

A number of passive film growth models have been advanced in the past, each founded on different assumptions and providing different rate laws. A new, generalized growth model has been developed and the numerical simulation of the transient behavior of oxide film growth on metals and alloys is reported here. This model is based on the transport of anions and cations (in a Cr2O3 film for stainless alloy). In contrast to most models up to date, it describes the time-variant behavior of film and film/solution potential differences. Because these potential differences are expressed as exponential functions of film thickness, asymptotic behaviors can be studied and it is shown that a square root law results for very thin and very thick films. Growth rate for intermediate films and during transient periods, on the other hand, is determined by numerical integration. Parameters which were introduced by the model and whose values are unknown are conveniently regrouped into only four lumped parameters, which are easily estimated by numerical optimisation. It is shown that experimental oxide film thickness measurements on stainless alloys in high-temperature aqueous environments can be reproduced. It is further shown that the diffusional rate expressions of all the species contributing to growth are analogous, explaining why it is possible to fit growth kinetics with a single type of point defect.

An Outlook on Magnesium-Based Biodegradable Implants

[Extract] In this ageing population, the use of implants for repair of bone fractures is increasing rapidly. Mini-implants such as plates and screws are often used for bone fracture healing. Currently non-degradable implants made of metallic materials such as stainless steel, titanium alloys or chromium-cobalt alloys are commonly used. However, the long-term exposure of these non-degradable implants greatly increases the risk of complications such as foreign body reactions and inflammation due to the release of metal ions or particles as a result of corrosion/wear. This necessitates a secondary surgical process to remove the implant after healing of the tissues. In fact, repeat surgery is a risk and also increases the costs to both the patient and the health care system.

Atom-probe tomography of surface oxides and oxidized grain boundaries in alloys from nuclear reactors

ABSTRACTThe preparation of site-specific atom-probe tomography (APT) samples containing localized features has become possible with the use of focused ion beams (FIBs). This technique was used to achieve the analysis of surface oxides and oxidized grain boundaries in this paper. Transmission electron microscopy (TEM), providing microstructural and chemical characterization of the same features, has also been used, revealing crucial additional information.The study of grain boundary oxidation in stainless steels and nickel-based alloys is required in order to understand the mechanisms controlling stress corrosion cracking in nuclear reactors. Samples oxidized under simulated pressurized water reactor primary water conditions were used, and FIB lift-out TEM and APT specimens containing the same oxidized grain boundary were prepared and fully characterized. The results from both techniques were found fully consistent and complementary.Chromium-rich spinel oxides grew at the surface and into the bulk material, along grain boundaries. Nickel was rejected from the oxides and accumulated ahead of the oxidation front. Lithium, which was present in small quantities in the aqueous environment during oxidation, was incorporated in the oxide. All phases were accurately quantified and the effect of different experimental parameters were analysed.

Optimization of the electrical properties of Ti–Nb stabilized ferritic stainless steel SOFC interconnect alloy upon high-temperature oxidation: The role of excess Nb on the interfacial oxidation at the oxide–metal interface

Interfacial oxidation of Nb and Si at 650 °C on Laves phase forming Ti–Nb stabilized ferritic stainless steel (Fe–19Cr–0.9Si–0.2Nb–0.1Ti (at.%), grade EN 1.4509) was studied by electrochemical impedance spectroscopy and photoelectron spectroscopy. It was found that excess Nb efficiently hinders the formation of electrically resistive SiO2 layer at the oxide–metal interface. The beneficial role of Nb was attributed to its high segregation rate and the formation of conductive oxides at the interface. However, the oxidation was strongly influenced by age-precipitation of the Laves (FeNbSi)-type intermetallic phase, which removed free Nb from the alloy solution and thus allowed SiO2 layer to form more easily. These results can be applied to optimize the oxide scale composition by Nb alloying of the ferritic stainless steel to maintain high performance under various operation conditions, particularly in solid oxide fuel cell applications.

Stress corrosion cracking in dissimilar metal welds with 304L stainless steel and Alloy 82 in high temperature water

For a better understanding toward stress corrosion cracking (SCC) in dissimilar metal welds with 304L stainless steel and Alloy 82, the SCC growth behavior in the transition regions of weld joints was investigated via slow strain rate tensile (SSRT) tests in 280 °C pure water with a dissolve oxygen level of 300 ppb. Prior to the SSRT tests, samples with dissimilar metal welds were prepared and underwent various pretreatments, including post-weld heat treatment (PWHT), shot peening, solution annealing, and mechanical grinding. In addition to the SSRT tests, measurements of degree of sensitization and micro-hardness on the transition regions of the metal welds were also conducted. According to the test results, the samples having undergone PWHTs exhibited relatively high degrees of sensitization. Distinct decreases in hardness were observed in the heat-affected zones of the base metals in all samples. Furthermore, the fracture planes of all samples after the SSRT tests were located at the stainless steel sides and were in parallel with the fusion lines. Among the treating conditions investigated in this study, a PWHT would pose a detrimental effect on the samples in the aspects of mechanical property and degree of SCC. Solution annealing would lead to the greatest improvement in ductility and SCC retardation, and shot peening would provide the treated samples with a positive improvement in ductility and corrosion retardation, but not to a great extent.

Influence of surface treatment of iron, magnesium, and aluminum alloys on the character of wetting by aqueous solutions

We study the limiting angles of wetting of surfaces of low-carbon and stainless steels, copper, brass, aluminum alloys, and magnesium alloys by water, aliphatic alcohols, monocarboxylic acids, and some inhibitors. It is shown that the surfaces of metals with passive film are more hydrophobic than the surfaces of low-carbon steel, medium-carbon steel, and magnesium. The plasma electrolytic oxidation of aluminum and magnesium alloys enhances the hydrophilicity of their surfaces. The introduction of chromium to an oxide ceramic coating facilitates the hydrophobization of the surface. The mechanical pulse hardening of steel leads to the formation of a nanostructure of the surface, hydrophobizes it, and increases the adsorption of surface-active substances. Preliminary 2.5–15% plastic deformation increases the wettability of the surface by water, increasing the adsorption of organic inhibitors and somewhat decreasing the adsorption of inorganic inhibitors. The in-service degradation of pipe steel (30 years) decreases the wetting angles, the values of which are comparable with those for plastically deformed steel at 2.5% strain.

Oxidation behavior of an austenitic stainless FeMnSiCrNi shape memory alloy

The oxidation behavior at 800°C in air of an austenitic stainless Fe14.29Mn5.57Si8.23Cr4.96Ni (wt.%) shape memory alloy was investigated by thermogravimetry, OM, SEM (EDS), XRD, GAXRD, TEM, and DSC. The results showed that its oxidation process obeys a parabolic law. After 100h exposure, the oxide scales are composed of outer Mn2O3, middle Mn3O4, and inner MnCr2O4. A ferrite layer exists between the oxidation layer and matrix. The ferrite results from the transformation of oxidation-induced Mn-depleted layer, and its thickness increases with increasing oxidation time. Profuse chi phase precipitates inside matrix and at the interface between matrix and ferrite layer.

Influence of precipitation on initial high-temperature oxidation of Ti–Nb stabilized ferritic stainless steel SOFC interconnect alloy

Oxidation phenomena on Laves phase forming Ti–Nb stabilized ferritic stainless steel (EN 1.4509) were studied at 650 °C by electron microscopic and electron spectroscopic methods. These investigations reveal a strong competition between Nb and Si for interfacial oxidation at the oxide–metal interface that is affected by different segregation rates of Nb and Si at elevated temperatures. In particular, formation of Si containing Laves (FeNbSi)-type intermetallic compounds in the bulk results in non-uniform distribution of Si oxide at the interface. This has direct implications to the electrical properties of this alloy in solid oxide fuel cell (SOFC) applications. Furthermore, these results provide better understanding to the controversial role of second phases (e.g. Laves, chi) on high-temperature oxidation (as recently discussed by Dae Won Yon, Hyung Suk Seo, Jae Ho Jun, Jae Myung Lee, Do Hyuong Kim, Kyoo Young Kim in Int J Hydrogen Energy 2011;36:5595–5603).

Directionally Solidified Laser Cladding

To repair a directionally solidified aero blade, laser cladding on GH710 substrate using stainless steel powder and Ni-based alloy powder by Nd:YAG laser was carried out. The condition of achieving directional solidification in the open and normal temperature environment was researched. The effect of technical parameter and powder composition on the microstructure of the cladding layer was analysed. The microstructure of the cladding layer was investigated. The results show that the directionally solidified cladding layer was acquired by the appropriate technical parameter. It was difficult for the Ni-based powder cladding layer to get directionally solidified cladding layer in comparison with the stainless steel powder.

Surface charging patterns of stainless alloys – Effect of ageing in conditions of primary cooling circuit of pressurized water reactors

The predominance of electrostatic interactions in the mechanism of particle deposition onto solid surfaces is well documented. Therefore, an electrostatic approach has been used to predict the behavior of activated corrosion products in the primary cooling circuit of a pressurized water reactor (PWR). Only few results have been published on the potential at the interface of metallic alloys and aqueous solutions, even at room temperature. In this study, we present results about the characterization of representative materials such as Inconel 690, stainless steel 304 and Zircaloy 4 at room temperature, for pristine polished samples as well as after an 80-day ageing step in physico-chemical conditions similar to those of a primary circuit (360°C, boron 1gL−1 (as H3BO3), lithium 2mgL−1 (as LiOH), hydrogen 30cm3kg−1). The surface potentials of these alloys have been determined using a streaming current method for pH from 3 to 7. Isoelectric points between 4.1 and 4.6 have been found for all samples and there is no effect of the ageing step. These values have been confirmed by adhesion studies of grafted latex particles either positively charged (amidine surface groups) or negatively charged (carboxylate groups) at pH 3.3 and pH 5.5. The results show that particles deposition is favored only when they carry a charge opposite to the substrate surfaces.

Development of Composite Abrasives for Various Materials

The development of composite abrasives considering the cleanability of the polished work piece was previously reported. In glass polishing, composite abrasives exhibit improved polishing characteristics and result in superior cleanability in comparison with conventional polishing compounds. In this study, the application of these composite abrasives to the polishing of stainless alloy, cast iron and sapphire are investigated. New manufacturing methods and polymer particles are proposed for the various material applications. The experimental results show that composite abrasives improve the polishing removal rate for metal and sapphire substrates.

High Temperature Phase Stability and Microstructural Characterization of D9 Stainless Steel-Zirconium Metal Waste Form Alloys

Zirconium present in stainless steel-zirconium metal waste form (MWF) alloys form Ni–Zr and Fe–Zr intermetallic phases which act as a sink for radionuclide and improve resistance to localized corrosion as well as selective radionuclide leaching. The present study looks into the behavior of Zr intermetallics in MWF alloys with the variation of Zr content after heat treatments. Two MWF alloys of D9 SS (Ti modified 15Cr–15Ni–2.5Mo stainless steel) with 8.5 and 17 wt% Zr were heat treated at 1,323 K for 2 and 5 h and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The stability of the Zr intermetallic compounds was examined by high temperature XRD. The results from XRD study showed the presence of NiZr, Ni5Zr, Ni7Zr2, FeZr2, and Fe3Zr peaks along with fcc Fe based solid solution. The MWF alloy with 17 wt% Zr exhibited α-ferrite peak in as-cast condition which was not observed after heat treatment. From the SEM micrograph the agglomeration of intermetallic phases was observed after heat treatment and the grain size of the intermetallic phases increased with duration of heat treatment. The high temperature XRD study revealed that all the intermetallic phases were stable up to 1,173 K and above this temperature Ni–Zr intermetallics started disappearing. However Fe–Zr intermetallics were stable till 1,373 K. The paper presents the high temperature phase stability of D9 SS-Zr MWF alloys.