Applications In Corrosive Environments Research Articles

Influence of Post-Heat Treatment on Corrosion Behaviour of Additively Manufactured CuSn10 by Laser Powder Bed Fusion.

This study investigates the influence of heat treatments on the corrosion behaviour of CuSn10 tin bronze, additively manufactured using Laser Powder Bed Fusion (LPBF). LPBF enables the creation of finely structured, anisotropic microstructures, whose corrosion behaviour is not yet well understood. After production, specimens were heat-treated at 320 °C, 650 °C, and in a two-stage treatment at 800 °C and 400 °C, followed by hardness and microstructure analysis. Corrosion tests were conducted using linear polarisation, salt spray, and immersion tests. The results show that heat treatments at 320 °C and 650 °C have no significant effect on the corrosion rate, while the two-stage treatment shows a slight improvement in corrosion resistance. Differences in microstructure and hardness were observed, with higher treatment temperatures leading to grain growth and tin precipitates. The formation of a passive protective layer was detected after 30 h of OCP measurement. Results from other studies on corrosion behaviour were partially reproducible. Differences could be attributed to varying chemical compositions and manufacturing parameters. These findings contribute to the understanding of the effects of heat treatments on the corrosion resistance of additively manufactured tin bronze and provide important insights for future applications in corrosive environments.

Crystallization and additional oxide interlayers improve the tribocorrosion resistance of TiO2 nanotubular surfaces formed on Ti6Al4V

TiO2-based nanotubular surfaces have promising properties for various industrial applications, such as solar cells, fuel cells, photocatalysis, energy storage, gas sensors, and biomedical applications. However, they have very limited use in real applications, and one of the major limiting factors is the weak adhesion of nanotubular surfaces to the substrate. In this study, nanotubular surfaces are formed on Ti6Al4V alloy by anodic treatment followed by a heat treatment at 500 °C for 3 h under an open atmosphere. Microstructural investigations revealed self-organized nanotubes grown on both α and β phases. High-resolution TEM/STEM analysis showed crystallization of the nanotubular layer and formation of additional oxide interlayers resulting in a drastic improvement in tribocorrosion resistance. These findings indicated that a simple heat treatment can significantly alter the properties of nanotubular layers and can widen their usage mainly for load-bearing implant applications in corrosive environments.

Performance of Reinforced Foam and Geopolymer Concretes against Prolonged Exposures to Chloride in a Normal Environment.

The utilization of sustainable cement replacement materials in concrete can control the emission of carbon dioxide and greenhouse gases in the construction industry, thus contributing significantly to the environment, society, and the global economy. Various types of sustainable concrete including geopolymer concrete are tested for their efficacy for construction in laboratories. However, the performance and longevity of sustainable concrete for civil engineering applications in corrosive environments are still debatable. This paper aims to investigate the performance of the reinforced geopolymer (GPC) and foam concretes (FC) against corrosive chloride exposure. Two long term key parameters, i.e., corrosion rate and mechanical performance of reinforcing steel in geopolymer and foam concrete were assessed to evaluate their performance against chloride attack. For experiments, reinforced GPC and FC specimens, each admixed with 3 and 5% chlorides, were kept at varying temperatures and humidity levels in the environmental chambers. The corrosion rates of the reinforced geopolymer and foam concrete specimens were also compared with control specimens after 803 days and the tensile strength of the corroded reinforcing steel was also determined. Moreover, the long term efficacy of repaired patches (810 days), in a chloride-rich surrounding environment utilizing FC and GPC, was investigated. The results suggested greater performance of FC compared to GPC under standard environmental conditions. However, the simulated patch repair with GPC showed better resistance against chloride attack compared to FC. The research also undertook the fractographical examination of the surfaces of the reinforcement exposed to 5% admixed chloride and develops models for the corrosion rates of foam concrete as a function of the corrosion rates of geopolymer concrete and chloride content. A correlation model for the corrosion rates of FC and GPC was also developed. The findings of the current research and the model developed are novel and contribute to the knowledge of long term degradation science of geopolymers and form concrete materials. Furthermore, the findings and methodology of the current research have practical significance in the construction and repair industry for determining the remaining service life for any reinforced and steel infrastructure.

Effect of zirconium content on the microstructure and corrosion behavior of as-cast Ti-Al-Nb-Zr-Mo alloy

Investigation about how to enhance the corrosion properties of Ti alloys is essential to their actual applications in corrosive environments. Herein, the specific influences of Zr content on the corrosion behavior of Ti-6Al-3Nb-xZr-1Mo alloys (x = 2, 6, 10, 20 and 40 wt%) are systematically investigated using microstructure characterization, electrochemical and weight loss measurements. The results signify that all investigated alloys are composed of α and β phases; however, the increase of Zr content endows alloys with the refined thickness of lamellar α phase and enhanced volume fraction of intergranular retained β phase. Meanwhile, the corrosion resistance monotonously improves along with increasing the Zr content, directly characterized by the decreased corrosion current density, improved polarization resistance as well as reduced corrosion rate. The improvement in corrosion performance is a result of the alleviated micro-galvanic corrosion formed between α and β phases, increased volume fraction of corrosion-resistant β phase and modified composition of oxide film. One should note that the corrosion mode changes from the uniform corrosion to the mixed pitting and uniform corrosion with the Zr addition up to 40 wt%. Besides, surface analysis of samples after immersion tests reveals that the lamellar α phase is more susceptible to corrosion compared to the adjacent intergranular β phase, attributed to its higher concentration of Ti and Al elements. The current findings provide data that can be referenced for designing high-corrosion resistance materials for marine, biomedical applications and hydrochloric acid industries through composition optimization.

Corrosion Protection of Injection Molded Porous 440C Stainless Steel by Electroplated Zinc Coating

Zinc electroplating was used to enhance corrosion resistance of porous metal injection molded 440C stainless steel. Controlled porosity was achieved by the powder space holder technique and by using sodium chloride as a space holder material. The internal pore structure of porous 440C was deposited by zinc using electroplating with three different electrolytes of zinc acetate, zinc sulfate, and zinc chloride. Our results show that all zinc depositions on porous 440C samples significantly improved corrosion resistance. The lowest corrosion was observed with zinc acetate at 30 wt.% porosity. The developed zinc coated porous 440C samples have potential in applications in corrosive environments.

Preparation and characterization of pure SiC filters with an asymmetric structure

In this work, SiC filters with an asymmetric structure were successfully constructed, consisting of solid-state-sintered SiC (S–SiC) supports and in-situ synthesized SiC membranes. The S–SiC supports were prepared by a pressureless sintering technique. Following the preparation of the supports, SiC membranes ~30 μm in thickness were formed in-situ on their surfaces through a dip-coating process combined with carbothermal reduction. Using X-ray diffraction, only the peaks of the SiC phase were detected for both the S–SiC supports and the SiC membranes, indicating the high purity of the asymmetric SiC filters. The distribution of the pore throat size in the SiC membranes was narrow with an average value of ~130 nm, suggesting a high filtration precision. The flexural strengths of the S–SiC supports at room temperature and 1000 °C were 123.6 ± 18.1 MPa and 114.0 ± 4.5 MPa, respectively, enabling the asymmetric SiC filters to withstand high temperatures and high pressures during service. Moreover, asymmetric SiC filters presented excellent acid and alkali corrosion resistance, indicating their great potential for applications in corrosive environments.

Investigation of the mechanical properties of corroded sintered silver layers by using Nanoindentation

The aim of this study is to gain a better understanding of the behaviour of sintered silver layers for e.g. power electronic applications in corrosive environments. It explicitly deals with the influence of corrosion products on the mechanical properties using Nanoindentation measurements. In addition to these measurements, analytical investigations and porosity analyses are performed. Existing studies mainly deal with the investigation of unaged sintered silver layers or the influence of thermomechanical ageing on the mechanical properties. In contrast, this study focuses on the investigation of the influence of corrosion on the mechanical properties of sintered silver layers. The results show that an increased Young's modulus can be detected by Nanoindentation measurements on corrosion-stressed highly porous sintered silver. In addition, increased indentation hardness is also determined. Besides the already known influences on the Young's modulus, a significant influence on the corrosion pattern of the sintered silver layers can be shown. The results are discussed with regard to a filled pore system of the samples.

Three-Dimensional Printing of Ceramics through "Carving" a Gel and "Filling in" the Precursor Polymer.

Achieving a viable process for three-dimensional (3D) printing of ceramics is a sought-after goal in a wide range of fields including electronics and sensors for harsh environments, microelectromechanical devices, energy storage materials, and structural materials, among others. Low laser absorption of ceramic powders renders available additive manufacturing (AM) technologies for metals not suitable for ceramics. Polymer solutions that can be converted to ceramics (preceramic polymers) offer a unique opportunity to 3D-print ceramics; however, due to the low viscosity of these polymers, so far, their 3D printing has only been possible by combining them with specialized light-sensitive agents and subsequently cross-linking them layer by layer by rastering an optical beam. The slow rate, lack of scalability to large specimens, and specialized chemistry requirements of this optical process are fundamental limitations. Here, we demonstrate 3D printing of ceramics enabled by dispensing the preceramic polymer at the tip of a moving nozzle into a gel that can reversibly switch between fluid and solid states, and subsequently thermally cross-linking the entire printed part "at-once" while still inside the same gel. The solid gel, which is composed of mineral oil and silica nanoparticles, converts to fluid at the tip of the moving nozzle, allows the polymer solution to be dispensed, and quickly returns to a solid state to maintain the geometry of the printed polymer both during printing and the subsequent high-temperature (160 °C) cross-linking. We retrieve the cross-linked part from the gel and convert it to ceramic by high-temperature pyrolysis. This scalable process opens up new opportunities for low-cost and high-speed production of complex three-dimensional ceramic parts and will be widely used for high temperature and corrosive environment applications, including electronics and sensors, microelectromechanical systems, energy and structural applications.

Electrochemical Performance of Fe40Al-X (X = Cr, Ti, Co, Ni) Alloys Exposed to Artificial Saliva.

Fe–Al intermetallic compounds have been considered excellent candidates as alternative alloys for various applications in corrosive environments compared to other Fe-based alloys. Their excellent corrosion resistance is due to the development of an Al-based passive layer. The performance of the passive layer can be improved by adding a third alloy element. Therefore, in this study the electrochemical performance of the Fe40Al intermetallic alloy modified by the addition of a third alloy element (Cr, Ti, Co, Ni) is evaluated. The corrosion resistance of intermetallic alloys has been evaluated by electrochemical tests (potentiodynamic polarization curves, and measurements of open circuit potential, linear polarization and electrochemical impedance) in artificial saliva. The performance of intermetallic alloys was compared with that of Ti. The results obtained showed that the addition of Ni and Ti substantially improves the corrosion resistance of the base intermetallic. The corrosion resistance shown is comparable or greater than that shown by Ti. However, the addition of Co reduces the corrosion resistance of the base intermetallic.

Galvanostatic Electrodeposition of Thin-Film Ir–Ni Electrocatalyst on Copper Foam for HER Performance in Alkaline Electrolyte

Iridium–nickel (Ir–Ni) film is of great interest for catalytic and corrosive environment applications. Ir–Ni thin films as an electrocatalyst for hydrogen evolution reaction (HER) were galvanostatically electrodeposited on copper (Cu) foam from an electrolyte containing 13.5 mM sodium hexabromoiridate(III) and 40.5 mM Ni sulphate hexahydrate, simultaneously compared with electrodeposited Ir and Ni thin films. The top surface morphology of the film was characterized by scanning electron microscopy. The chemical composition of the film was determined by energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. The electrocatalytic performance was performed by linear sweep voltammogram and cyclic voltammetry. The results showed that Ir–Ni thin film adhered to Cu foam and the surface appeared much rougher than the surface of Ni film. The chemical composition of Ir in the deposit was 80 ± 1.2 at.%. The film was composed of nanograins. The top surface of as-deposited film was mainly composed of metallic state. However, the top surface of the film consisted of oxides states, such as Ni oxides or Ni(OH)2, and Ir oxides after electrochemical measurements. As-deposited Ir–Ni thin film with large real active area exhibited high efficient electrocatalytic activity for HER, and achieved a current density of 10 mA cm2 at an overpotential of 60 mV and a Tafel slope of 40 mV dec−1, which is superior to pure Ir and Ni thin films. The remarkable increase in electrocatalytic activity for Ir–Ni film was ascribed to both increased surface area of active centers due to relatively rough and electrocatalytic synergism of Ir and Ni for the HER. Ir–Ni thin film electrodeposited on a foam copper electrode was used as an electrocatalyst for HER. The surface of as-deposited film was composed of metallic state. As-deposited Ir–Ni thin film with large real active area exhibited high efficient electrocatalytic activity for HER, and achieved a current density of 10 mA cm2 at an overpotential of 60 mV and a Tafel slope of 40 mV dec−1, which is superior to pure iridium and Ni thin films. As-deposited film possessed a good stability by accelerated degradation studies.

Ultrathin Graphene-Like Carbon-Coated Iron Oxide Nanocrystals for Applications in Corrosive Environments

Here we report a solution-phase strategy for depositing ultrathin graphene-like carbon onto iron oxide nanocrystals (NCs) for corrosion resistance in magnetic and electrocatalytic applications. The...

Deposition and characterization of electroless Ni on fluoride free pretreated AZ91 magnesium alloy

Poor corrosion resistance of magnesium alloys restricts their widespread applications in corrosive environments. The electroless nickel deposition is well established approach to combat the corrosion in various environments but limited due to the usage of various hazardous chemical species such as HF, fluorides and hexavalent chromium. The electroless nickel deposition on magnesium alloys is difficult due to the formation of poor oxide/hydroxide layer which may overcome by facilitating by the suitable surface pretreatment. An environment friendly pretreatment and a novel duplex-electroless nickel (ENi) plating methods on AZ91 magnesium alloy is developed and reported in the present paper. Two types of environment friendly baths, alkaline and acidic were formulated to pretreat the AZ91 magnesium alloy prior to electroless nickel plating. The duplex electroless Ni-P layer was successfully obtained to increase the corrosion resistance of AZ91 alloy; the first layer in alkaline pH (10.5) followed by another Ni-P layer either in alkaline (pH∼10.5) or acidic pH (5.0) bath. Morphology of the coating was characterized by scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDS). Corrosion resistance was characterized by using potentiodynamic and electrochemical impedance spectroscopy (EIS) in 0.5% NaCl solution. Results showed coating with the submicron size nodules produced at alkaline pH while amorphous at an acidic (pH∼5.0). A large increase in the corrosion resistance of AZ91 alloy was obtained with the duplex ENi layer using prior treatment in the phosphoric acid containing solution.

Effects of PVD DLC Coating on 7075-T6 Alloy Fatigue Strength

7075-T6 aluminium alloy is under investigation in the last decades because of its sensitivity to corrosion and its poor surface behaviour. The alloy is widely used in many mechanical, aeronautical and structural engineering appliances because of its high strength-to-weight-ratio. Notwithstanding its strength and light weight advantages, its applications in corrosive environments, with fatigue applied loads, is still under research. The mechanical and chemical driving forces have still to be accurately evaluated and the role of each one identified. Results of tests on rotating bending fatigue (R = -1) 7075-T6 uncoated and PVD DLC coated specimens are reported in this paper under various stress levels and number of cycles to failure. Fracture surfaces were observed via SEM characterization in order to assess the role of the chemical aggressive environment, the residual stress field and the applied load.

Effect of Electroplating Variables on Electrodeposition of Ni Rich Ni-Ir Alloys from Citrate Aqueous Solutions

Nickel–iridium (Ni–Ir) alloy system is of great interest for catalytic and corrosive environment applications. In this study, Ni-Ir alloys were galvanostatically electrodeposited on copper substrates from citrate aqueous solutions in a three-electrode cell system. The effects of deposition variables, including pH, temperature and current density, on the faradaic efficiency (FE), chemical composition, surface morphology and crystallographic structure of the films were studied. The electrochemical behaviors of Ir, Ni and co-deposited alloys were investigated using cyclic voltammetric, chronopotentiometric and chronoamperometric techniques. The results show that Ni–Ir alloys as thick as 25.7 μm with Ir–content as high as 15 at% and the FE as high as 36% were obtained. By adjusting these deposition parameters, the optimum pH, temperature and current density for deposition of Ni-Ir alloys were 5.0, 70°C and 60 mA·cm−2, respectively. As the deposition variables were varied, the abundant of Ni-content in the deposit was obtained. The alloy was composed of nanocrystalline phase. The deposition of Ni ions was favored, and the co-deposition of Ni-Ir alloy was a normal deposition. The chronoamperometric transient nucleation at the potentials of −0.25 and −3.0 V were consistent with the model of diffusion-controlled 3D nucleation.

Guided Wave Propagation and Damage Detection in Composite Pipes Using Piezoelectric Sensors

Composite materials have many attractive properties, e.g. light-weight combined with high mechanical strength, and are recognized as an enabling technology for deep-water high pressure high temperature (HPHT) and corrosive environment applications. However, composite still has a barrier to entry in relation to steel due to limited field experience and lack of systematic failure prediction and assurance of in-service performance. Advances in such areas would enable the use of composites in a wider range of applications. Evaluation of in-service prototypes offers a partial solution but is costly. Thus a method that allows constant health monitoring of the composite in real-time and in-situ would be extremely useful. Ultrasonic guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. To investigate the feasibility of guided wave-based SHM for composite pipes, propagation characteristics of guided waves in an epoxy hybrid carbon/glass fibres pipe are systematically studied using finite element (FE) simulation and experiments. Both axisymmetric modes of propagation, the longitudinal L(0,n) and torsional T(0,n) modes are considered in the simulation process, however only the longitudinal modes can be captured by the piezoelectric sensors. Additionally, the tuning curves experimentally plotted are used to obtain the frequency with the maximum amplitude of each guided mode. Finally, guided waves in the composite pipe are tested with artificial defects (gel coupled coins) to understand the behaviour of guided waves after interaction with the defects. The different condition of artificial defects, e.g., the defect size and defect location are studied to find out the proper condition and limitation of using guided waves to monitor and inspect composite pipes.

Thickness-dependent phase evolution and bonding strength of SiC ceramics joints with active Ti interlayer

A robust solid state diffusion joining technique for SiC ceramics was designed with a thickness-controlled Ti interlayer formed by physical vapor deposition and joined by electric field-assisted sintering technology. The interface reaction and phase revolution process were investigated in terms of the equilibrium phase diagram and the concentration-dependent potential diagram of the Ti-Si-C ternary system. Interestingly, under the same joining conditions (fixed temperature and annealing duration), the thickness of the Ti interlayer determined the concentration and distribution of the Si and C reactants in the resulting joint layer, and the respective diffusion distance of Si and C into the Ti interlayer differentiated dramatically during the short joining process (only 5min). In the case of a 100nm Ti coating as an interlayer, the C concentration in the joint layer was saturated quickly, which benefited the formation of a TiC phase and subsequent Ti3SiC2 phase. The SiC ceramics were successfully joined at a low temperature of 1000°C with a flexural strength of 168.2MPa, which satisfies applications in corrosive environments. When the Ti thickness was increased to 1μm, Si atoms diffused easily through the diluted Ti-C alloy (a dense TiC phase was not formed), and the Ti5Si3 brittle phase formed preferentially. These findings highlight the importance of the diffusion kinetics of the reactants on the final composition in the solid state reaction, particularly in the joining technique for covalent SiC ceramics.

Concrete Infill Monitoring in Concrete-Filled FRP Tubes Using a PZT-Based Ultrasonic Time-of-Flight Method.

Concrete-filled fiber-reinforced polymer tubes (CFFTs) have attracted interest for their structural applications in corrosive environments. However, a weak interfacial strength between the fiber-reinforced polymer (FRP) tube and the concrete infill may develop due to concrete shrinkage and inadequate concrete compaction during concrete casting, which will destroy the confinement effect and thereby reduce the load bearing capacity of a CFFT. In this paper, the lead zirconate titanate (PZT)-based ultrasonic time-of-flight (TOF) method was adopted to assess the concrete infill condition of CFFTs. The basic idea of this method is that the velocity of the ultrasonic wave propagation in the FRP material is about half of that in concrete material. Any voids or debonding created along the interface between the FRP tube and the concrete will delay the arrival time between the pairs of PZT transducers. A comparison of the arrival times of the PZT pairs between the intact and the defected CFFT was made to assess the severity of the voids or the debonding. The feasibility of the methodology was analyzed using a finite-difference time-domain-based numerical simulation. Experiments were setup to validate the numerical results, which showed good agreement with the numerical findings. The results showed that the ultrasonic time-of-flight method is able to detect the concrete infill condition of CFFTs.

The Analyses of Glass-Reinforced Plastic Pipeline Failures and Possible Solutions

Glass-reinforced Plastics (GRP) has been considered as an alternative material to carbon steel for applications in corrosive environments. The main objective of utilizing GRE pipes is to prevent corrosion and leaks in the pipelines. This increases the reliability of the system by preventing leaks, and thereby also reducing life cycle costs. However, some premature failures had been found after the application of GRP pipes in oil fields. Such failures as fractures around the joint, wrinkles of the inner layer, and circumferential cracks on the body part of the pipeline are the top three major failures which usually appear in practice. This paper analyzes the main causes of these three major failures and attempts to offer several possible solutions to them.

Improving corrosion resistance of Al‐11mass%Si alloy through a large number of ECAP passes

AbstractUltrafine‐grained (UFG) Al‐11mass%Si alloy, processed by multi‐pass equal‐channel angular pressing (ECAP) at 573 K, was investigated on corrosion behavior in 0.6 M NaCl solution. Potentiodynamic polarization tests and scanning electron microscopy observation showed that a large number of ECAP passes resulted in lower corrosion current density, more positive corrosion potential, and rather smooth corroded surface with shallow corrosion pits. The uniform distribution of fine secondary‐phase particles on UFG Al matrix weakened the susceptibility to pitting corrosion while inhibited general microgalvanic reactions. The present results indicate that grain refinement of aluminum matrix to the UFG state and uniform redistribution of broken particles (including eutectic silicon and secondary phases), via severe plastic deformation at elevated temperature undergoing dynamic recrystallization, can significantly improve the corrosion resistance of Al alloys, besides the known exceptional mechanical advantages. The simple and effective ECAP procedure makes UFG Al alloys more attractive for high strength structural application in corrosive environment.

Influência da energia de soldagem em uniões de lâminas finas através de laser pulsado de Nd:YAG

A soldagem laser vem sendo utilizada como um importante processo de manufatura. Ela pode ser utilizada tanto no modo contínuo quanto no modo pulsado. No processo onde se utiliza laser pulsado é possível realizar soldas de costura em lâminas finas, através da sobreposição dos pulsos. Nesse caso a velocidade de soldagem é definida pela taxa de sobreposição, taxa de repetição e diâmetro do pulso. A soldagem de sobreposição de lâminas finas apresenta problemas típicos como distorção excessiva da junta soldada, falta de contato entre as lâminas a serem soldadas (presença de um gap de ar), perfuração da junta e presença de altos níveis de tensões residuais. O processo de laser pulsado é preferido em relação ao processo por laser contínuo, pois ele possibilita um melhor controle da energia de soldagem. O presente trabalho estudou a influência da energia do pulso, no caso processo de soldagem laser Nd:YAG, na soldagem de lâminas finas ( 100µm ) de aço inoxidável austenítico AISI 316L, utilizado no revestimento de sensores (que trabalham em ambiente corrosivo) da indústria sucroalcooleira. Utilizou-se energia de pulso de 1,0 a 2,25 Joules, com incremento de 0,25 Joules e largura temporal de 4 ms. As soldas foram realizadas com proteção gasosa de argônio. Foram realizadas análises macrográficas das juntas soldadas, através de secções transversais das mesmas e, ensaios de microdureza Vickers e ensaios de tração. Os resultados obtidos mostraram que o controle da energia do pulso, em processo de soldagem por laser de lâminas finas é de fundamental importância para a geração de juntas soldadas com boas propriedades mecânicas e livres de descontinuidades. O limite de resistência da junta soldada aumentou no início e depois sofreu um pequeno decréscimo em função do aumento da energia do pulso. O processo mostrou-se muito sensível à presença de gap entre as lâminas.