Reduced Corrosion Resistance Research Articles

Effects of Hydrothermal Aging of Carbon Fiber Reinforced Polycarbonate Composites on Mechanical Performance and Sand Erosion Resistance.

Carbon fiber reinforced polycarbonate (CF/PC) composites have attracted attention for their excellent performances. However, their performances are greatly affected by environmental factors. In this work, the composites were exposed to hydrothermal aging to investigate the effects of a hot and humid environment. The mechanical properties of CF/PC composites with different aging times (0, 7, 14, 21, 28, 35, and 42 days) were analyzed. It was demonstrated that the storage modulus of CF/PC composites with hot water aged for seven days has the highest value in this sampling period and frequency. Through the solid particle erosion experiment, it was found that the hydrothermal aging causes the deviation of the maximum erosion angle of composites, indicating the composites underwent ductile–brittle transformation. Furthermore, the crack and cavity resulting from the absorption of water was observed via the scanning electron microscope (SEM). This suggested that the hydrothermal aging leads to the plasticization and degradation of CF/PC composites, resulting in a reduction of corrosion resistance.

Microstructure and Corrosion Resistance of Arc Additive Manufactured 316L Stainless Steel

The gas tungsten arc welding based additive manufacturing (GTAW-AM) was carried out by printing 316L austenitic stainless steel on carbon steel substrate with different arc currents (140, 160, 180 A). Microstructure and corrosion resistance of additive manufactured components were investigated. The results show that the microstructure of the GTAW-AM austenitic stainless steel is obviously changed by the arc current. With arc current increasing from 140 to 180 A, the austenite grains become coarse due to the effect of welding heat input. Meanwhile, the quantity of ferrites in the austenite matrix is decreased and the morphology transforms from lath to skeleton. Moreover, a phases are finally formed under the arc currents of 180 A owing to high welding heat input. Therefore, as the microstructure transform into coarse-grained austenites, low-quantity ferrites and new-generated a phases, the GTAW-AM austenitic stainless steel presents a significantly decrease in corrosion resistance. And the reduction of corrosion resistance is mainly due to the formation of a phase as a result from consuming the large amounts of Cr element from the matrix.

Effect of implant cleaning on titanium particle dissolution and cytocompatibility.

Peri-implantitis treatments are mainly based on protocols for teeth but have not shown favorable outcomes for implants. The potential role of titanium dissolution products in peri-implantitis necessitate the consideration of material properties in devising treatment protocols. We assessed implant cleaning interventions on (1) bacterial removal from Ti-bound biofilms, (2) Ti surface alterations and related Ti particle dissolution, and (3) cytocompatibility. Acid-etched Ti discs were inoculated with human peri-implant plaque biofilms and mechanical antimicrobial interventions were applied on the Ti-bound biofilms for 30 seconds each: (1) rotary nylon brush; (2) Ti brush; (3) water-jet on high and (4) low, and compared to sterile, untreated and Chlorhexidine-treated controls. We assessed colony forming units (CFU) counts, biofilm removal, surface changes via scanning electron microscopy (SEM) and atomic force microscopy (AFM), and Ti dissolution via light microscopy and Inductively-coupled Mass Spectrometry (ICP-MS). Biological effects of Ti particles and surfaces changes were assessed using NIH/3T3 fibroblasts and MG-63 osteoblastic cell lines, respectively. Sequencing revealed that the human biofilm model supported a diverse biofilm including known peri-implant pathogens. WJ and Nylon brush were most effective in reducing CFU counts (P<0.01versus control), whereas Chlorhexidine was least effective; biofilm imaging results were confirmatory. Ti brushes led to visible streaks on the treated surfaces, reduced corrosion resistance and increased Ti dissolution over 30 days of material aging as compared to controls, which increase was amplified in the presence of bacteria (all P-val<0.05). Ti particles exerted cytotoxic effects against fibroblasts, whereas surfaces altered by Ti brushes exhibited reduced osteoconductivity versus controls (P<0.05). Present findings support that mechanical treatment strategies selected for implant biofilm removal may lead to Ti dissolution. Ti dissolution should become an important consideration in the clinical selection of peri-implantitis treatments and a necessary criterion for the regulatory approval of instruments for implant hygiene.

Laves Phase Formation and Segregation of Nb in Ni–Cr–Mo Superalloy over 316L by Hot Wire (HW) TIG Cladding Process

The Ni-based alloys are widely used in power plant components such as boiler and piping systems that require good creep strength and resistance to corrosion. The present study focuses on metallurgical and mechanical properties of Ni–Cr–Mo (ERNiCrMo-3) alloy cladded over 316L plate by hot wire TIG process. This alloy is prone to microfissuring and also reduced corrosion resistance due to microstructural changes caused by weld solidification. The microstructure and phasic characterization were identified using scanning electron microscopy and X-ray diffraction techniques. From the microstructural observation, it was observed that Nb present in Ni–Cr–Mo alloy tends to segregate during solidification of weld thereby promoting the Nb-rich Laves phase formation. The growth of dendrites enhanced the segregation of Nb. The coarse dendritic microstructure was due to the effect of high heat input that decreases solidification rate near the interface zone. Dimples and quasi-cleavage fracture morphology was observed on the fractured samples of the tensile test. The resistance to corrosion was evaluated using potentiodynamic polarization method using 3.5 wt% NaCl solution. The results confirmed that Ni–Cr–Mo alloy acts as an efficient clad for 316L substrate from corrosion attack.

The formation and elimination of the negative influence of porosity on the properties of the alloy castings AlSi10Mg

Aluminum alloys are often contaminated with non-metallic inclusions. A large number of these phases accelerate the tendency of porosity in castings, significantly reduce corrosion resistance and above all affect mechanical properties. Melting is one of the conventional methods for removing inclusions from melt. The efficiency of this process is influenced by several parameters such as the chemical composition of the melt, the amount of refining substances (wire, salts, tablets), the melting point and the casting method. Therefore, an experiment was performed to evaluate the effect of PROBAT FLUSS MIKRO 100 on the structural integrity in AlSi10Mg alloy. Porosity evaluation was performed by light microscopy. To confirm the results and their reflexes into the practical production of castings, a static tensile test was performed on the cast samples directly in the foundry operation.

Combination of high strength and corrosion resistance in AA5052 alloy using cryorolling and micro arc oxidation

Abstract For enhancing the strength of AA 5052 alloy, cryorolling is performed up to 50% and 75% reduction. The 75% reduction cryorolling shows excellent strength than the unrolled and 50% reduction alloy. However. Cryorolling of AA5052 alloy results in poor corrosion resistance. The reduction in corrosion resistance is due to an increase in dislocation density by cryorolling. Hence micro-arc oxidation (MAO) is adapted to coat Al2O3 on the surface to reduce the corrosion rate of cryorolled sheets. MAO is performed with three borax concentration viz. 0, 1 and 2 g in the solution. The increase in borax concentration up to 1% shows high corrosion resistance and a further increase in borax concentration has shown detrimental influence on corrosion resistance which is due to the delamination of the coating with severe cracking.

Sensitization behaviour of the nitrogen alloyed austenitic stainless steel X8CrMnMoN18-19-2

Austenitic stainless steels have been used in many different industrial branches. Nitrogen alloyed austenite´s with up to 20 wt. % manganese and 0.8 wt. % nitrogen have been available on the market as nickel-free grade for some years. In these steels, the austenitic matrix is stabilized without the addition of nickel, while the corrosive resistance and mechanical properties are significantly improved by addition of Mn and N. As with all stainless steels, the chemical composition and heat treatment have a decisive influence on structure, mechanical properties and corrosion resistance. Solution annealing, quenching and work hardening are applied to combine excellent mechanical properties (Rm from 900 MPa to 2,000 MPa, A5 > 50 %, Av > 350 J) with high corrosion resistance. Solution annealing is applied to eliminate undesired precipitation phases (Cr2N, M23C6 and sigma phase), distribute the alloy elements homogeneously in the austenite and assure the high corrosion resistance. If the distribution of the alloy elements (Cr, Mo and N) is impaired by suboptimal heat treatment, processing or high temperature conditions, the corrosion resistance can be reduced. Precise knowledge of the sensitization behaviour of these high nitrogen alloyed steels is necessary. Therefore, the sensitization behaviour of the nitrogen alloyed austenitic steel X8CrMnMoN18-19-2 (1.4456) was investigated by thermal ageing in the temperature rage of 500 °C to 900 °C for up to 100 h. Thermodynamic calculations were used to predict the formation of different phases. The microstructure of the various sensitization states was evaluated by scanning electron microscopy (SEM) and compared with the corrosion resistance characterized by the electrochemical potentiodynamic reactivation (EPR) test and the KorroPad method. The reduction of corrosion resistance is correlated with the occurrence of M2N nitrides in the microstructure and two sensitization diagrams were created based on the experimental results.

Influence of surface pre-treatment with mechanical polishing, chemical, electrochemical and ion sputter etching on the surface properties, corrosion resistance and MG-63 cell colonization of commercially pure titanium.

The impact of four pre-treatment techniques on the surface morphology and chemistry, residual stress, mechanical properties, corrosion resistance in a physiological saline solution and cell colonization of commercially pure titanium is examined in detail. Mechanical polishing, electrochemical etching, chemical etching in Kroll's reagent, and ion sputter etching with argon ions were applied. Surface morphologies reflect the nature of surface layer removal. Significant roughening of the surface and a characteristic microtopology become apparent as a result of the sensitivity of chemical and ion sputter etching to the grain orientation. The hardness in the near surface region was controlled by the amount of residual stress. Etching of the stressed surface layer led to a reduction in residual stress and surface hardness. A compact passivation layer composed of TiO, TiO2 and Ti2O3 native oxides imparted high corrosion resistance to the surface after mechanical polishing, chemical and electrochemical etching. The ion sputter etched surface showed substantially reduced corrosion resistance, where the corrosion process was controlled by electron transfer. The specific topology affected the adhesion of the cell to the surface rather than the cell area coverage. The cell area coverage increased with the corrosion stability of the surface.

Effect of laser treatment on morphology and corrosion behaviour of the plasma electrolytic oxidation coatings developed on aluminized steel

The present study focusses on laser surface modification of the plasma electrolytic oxidation (PEO) coatings developed on aluminized steel. The effect of varying laser fluency on the surface morphology and the corrosion behaviour of the PEO coatings was studied. Three different laser fluencies of 38.16, 53.42 and 68.69 J/cm2, corresponding to the 25%, 35% and 45% of the maximum power (60 W) were employed for the surface alteration. Laser treatment of the PEO coatings at lower and intermediate fluencies resulted in the development of a hydrophobic surface, thereby improving the corrosion resistance, whereas the laser treatment at higher fluency has resulted in the hydrophilic surface, with reduced corrosion resistance. The PEO sample laser-treated with intermediate fluency has produced a superhydrophobic surface with a contact angle of 153.2°. Potentiodynamic polarization (PDP) studies revealed that the PEO coated aluminized steel sample, laser-treated with intermediate fluency, exhibited superior corrosion resistance with a corrosion current density (icorr) of 1.21E−6 mA/cm2, which is 104 times lower than the aluminized steel.

Effects of Y2O3 nanoparticles on the high-temperature oxidation behavior of IN738LC manufactured by laser powder bed fusion

Oxidation tests at 1095 °C were performed on cubes of IN738LC doped with Y2O3 nanoparticles processed by laser powder bed fusion (LPBF). Adding Y2O3 nanoparticles led to grain coarsening and the formation of Y4Al2O9, both of which were expected to lead to reduced corrosion resistance in this alloy through a change from an Al-type oxide scale to Cr-type. However, 0.05 wt% Y2O3 addition was found to nonetheless be beneficial for corrosion resistance. Results and mechanisms for this were discussed and further work was recommended, in particular for the grain coarsening.

Effects of Mn, Zn Additions and Cooling Rate on Mechanical and Corrosion Properties of Al-4.6Mg Casting Alloys.

The mechanical properties of the Al-Mg alloy can be enhanced by adding metallic elements, but a continuous distribution of precipitates at grain boundaries leads to intergranular corrosion during sensitization treatment. In the present work, Mn, Zn additions, water cooling and furnace cooling were executed to investigate their effects on the mechanical and corrosion properties of the Al-4.6Mg alloy. Our results show that adding Mn to Al-4.6Mg alloys may produce grain refinement and dispersion strengthening, increasing tensile strength and hardness. The presence of Mn did not affect the corrosion resistance of Al-Mg alloys. Adding Zn to the Al-4.6Mg alloy increased tensile strength and hardness, but decreased corrosion resistance. Combined, the addition of Mn and Zn to the Al-4.6Mg alloy exhibited the highest tensile strength and hardness, but seriously reduced corrosion resistance. Furnace cooling substituted for water quenching could avoid intergranular corrosion, but slightly decreased the tensile strength and hardness by 7.0% and 6.8%, respectively.

Analysis of morphological, microstructural, electrochemical and nano mechanical characteristics of TiCN coatings prepared under N2 gas flow rate by chemical vapour deposition (CVD) process at higher temperature

In the present study, Titanium carbon nitride (TiCN) thin films have been synthesized over Si (100) substrate using chemical vapour deposition (CVD) process under N2 gas flow rate to study the suitability of CVD for the growth of TiCN coating over machine tools. The morphological, structural, corrosion behavior and mechanical properties of the coatings have been characterized using a scanning electron microscope (SEM), atomic force microscopy (AFM), x-ray diffraction (XRD), corrosion test and Nano-indentation. SEM images revealed a smoother morphology of the TiCN coating surface without any pores. The AFM results revealed an increase in surface roughness from 40.88 nm to 48.25 nm. The particle size of TiCN thin film also found to be increasing with a higher N2 flow rate. The XRD peaks of TiCN were observed in the range of 37°-38°. 44°-44.5° and 61°- 62° attributed to (111), (200) and (220) crystal plane. The XRD results also confirmed the presence of stress in the coatings. The polarization test indicates a reduction of corrosion resistance with a higher N2 gas flow rate. The mechanical properties investigated by the nano-indentation method indicated an increase in Hardness (H) and Young's modulus (E) of the coating with a higher N2 flow rate. The maximum H and E of the coatings were observed as 27.85 GPa and 486.22 GPa respectively.

Role of porosity on electrochemical corrosion behavior of porous Ti-20Nb-5Ag alloy in simulated body fluid

Porous titanium alloys are presently well-considered materials for orthopedic applications owing to their superior mechanical properties, excellent biocompatibility and high resistance to corrosion. Also, porous alloys are potentially minimizing the risk of stress-shielding effect as compared to bulk implant materials. In this present work focused to examine electrochemical corrosion behavior of porous Ti-20Nb-5Ag alloy (wt%) with different porosity levels. This designed alloy composition of elemental powders was mixed through mechanically alloying. The mechanically alloyed powder blended with four different amounts of NH4HCO3 (wt%), use to prepare the porous Ti-20Nb-5Ag alloy with porosity ranging from 22% to 68%. After the successful development of porous samples, we investigated the effect of porosity levels on electrochemical corrosion behavior of porous Ti-20Nb-5Ag alloys by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF) at 37 °C. The results show that an increasing the trend of porosity level causes a reduction of corrosion resistance. With increasing porosity, the corrosion current density increased and decreases the electrochemical polarization resistance in the SBF solution.

Mechanical and corrosion behaviour of aluminum alloy 5083 and its weldment for marine applications

Abstract 5xxx series aluminum alloys find increasing applications in the marine fabrication industries due to its unique mechanical and corrosion properties. The present attempt focuses the effect of metallurgical changes in mechanical behavior and corrosion resistance of Aluminium alloy 5083-H111 and its weldment. Gas tungsten arc welding (GTAW) process was used to fabricate the weld coupons using the filler metal ER 5183. Microstructure analysis was carried out in the fusion zone and compared to the heat affected zone and parent metal region. The mechanical behavior of the weld was compared with its parent metal by performing microhardness, impact toughness, tensile behavior and formability test. Electrochemical corrosion test revealed better corrosion resistance for parent metal sample than the weldment. The existence of Mg3Al2 precipitates in the weldment led to the reduction in corrosion resistance

Effects of crystallization on mechanical behavior and corrosion performance of a ductile Zr68Al8Ni8Cu16 bulk metallic glass

The effects of heat treatment on the microstructures, crystallization kinetics, mechanical performance, and anti-corrosion behavior of a hypoeutectic Zr68Al8Ni8Cu16 bulk metallic glass (BMG) were studied. Through annealing, the precipitated phases were crystalline Zr2Cu and Zr2Ni. The total crystallinity was determined to be 10% and 77% for the samples annealed at 673 K and 713 K, respectively. The partial crystallization of the alloy leads to a dramatic deterioration in the ductility as compared to the as-cast BMG. Furthermore, the decrease in the ductility was accompanied by an increase in the crystallinity. The as-cast Zr-based BMG exhibited a greater corrosion resistance in the HCl solution than that of the annealed alloy. The depletion in the Zr and Al cation fractions of the surface oxidation film, which resulted from the precipitation of reactive nanocrystalline phases from the glassy matrix, is responsible for the reduced corrosion resistance.

Studies on electro-chemical corrosion of carbon fiber reinforced aluminium alloy AA7075

Carbon fiber reinforced AA7075 is known for good thermal properties and thus used as heat dissipating material. However, few such applications involve corrosive environments too, and hence there is a need to study the behavior of these composite materials under corrosive environment. In the present work, milled carbon fiber reinforced AA7075 composites were produced by vacuum hot pressing with varying amounts of milled carbon fibers. The relative densities of the composites were measured. SEM-EDS, TEM and XRD techniques were also employed for characterization. The composites were then characterized for electro-chemical behavior in 3.5 wt.% aqueous NaCl solution by electrochemical polarization technique. Results showed that the corrosion potentials Ecorr have shifted to more negative direction and thus showed increase in corrosion current density, leading to increase in corrosion rate with increasing vol.% of carbon fibers. These results were complemented by SEM micrographs of the composites after corrosion test, which revealed that corrosion occurred at the interface of carbon fiber and matrix due to formation of galvanic coupling between carbon fiber and matrix. Thus, reduced corrosion resistance in composites as amount of fibers increases, is attributed to increase in number of galvanic cells that form at the interface.

Local intragranular misorientation accelerates corrosion in biodegradable Mg

Mg-based implants are used in biomedical applications predominantly because of their degradable property. In this paper, the effect of local misorientations (intragranular misorientation) on the corrosion behavior of high-purity Mg (HPM) was systematically investigated according to microstructure characterization and corrosion measurements. The results showed that local misorientation introduced into grains by deformation could result in corrosion around the grain boundary (GB), which ultimately reduces the corrosion resistance of HPM. After removing the local misorientation by annealing, the corrosion around GB could be eliminated. This work is expected to inspire better control over the degradation behaviors of biomedical Mg through microstructure design to be used for various biomedical applications. Statement of significance1. Fine grains, fine grains with large local misorientation, and coarse grains could be obtained, respectively, in high-purity Mg by sequential hot rolling, compression deformation, and annealing treatments.2. Large local misorientation introduced into grains could lead to corrosion around the grain boundary and ultimately reduce corrosion resistance.3. In the absence of local misorientation, refining grain size could improve the corrosion resistance of Mg.

Effects of temperature and pH on the electrochemical behaviour of alloy 600 in simulated pressurized water reactor primary water

The effects of temperature and pH on the electrochemical properties of Alloy 600 were studied in oxygenated borate buffer solutions by the measurements of open circuit potential (OCP), anodic potentiostatic polarization, Mott-Schottky analysis (MSA), and electrochemical impedance spectroscopy (EIS). At each temperature and pH, the stabilized anodic passive current density was independent of the formation potential, and the slope of the M − S plot for the passive film formed at +0.3 VOCP (OCP + 0.3 V) is positive, indicating that the passive films formed on Alloy 600 have n-type semiconductor character. With increasing temperature (in each solution), the OCP and the impedance modulus decreased, while the passive current density and the defect density calculated from MSA increased, indicating a significant reduction in corrosion resistance. With the increase in pH value, the passive current density decreased, the absolute value of impedance increased slightly, revealing a slight increase in corrosion resistance. According to the optimization of Mixed Potential Model (MPM) on the experimentally measured EIS data for Alloy 600 at OCP and +0.3 VOCP, a series of fundamental parameters related to the micro-characteristic of passive film were extracted. In the barrier layer of the passive film, the concentration of cation interstitials is much higher than that of anion vacancies, indicating that the former was a dominant defect. With increasing temperature, the linear increase in the defect density and film thickness resulted in a linear increase of the anodic current density. However, with increasing pH, the decrease of defect density and the slight increase of film thickness caused a linear reduction in anodic current density. Elevated temperature has a more significant deterioration effect on the corrosion resistance of Alloy 600 than the increased pH value. Additionally, all the kinetics parameters describing the generation of cation interstitials and oxygen vacancies at the substrate/film were obtained.

Investigation on microstructure and properties of AlxCoCrFeMnNi high entropy alloys by ultrasonic impact treatment

In the present study, ultrasonic impact treatment was applied to promote the as-cast AlxCoCrFeMnNi (x = 0, 0.5, 1.0 and 1.5) high entropy alloys, and the microstructures, phase composition and surface properties were investigated. The increase in Al mole fraction from 0 to 0.5, 1.0 and 1.5 led to the different phase compositions from single FCC, duplex FCC + BCC to single BCC phase as well as the increased microhardness and reduced corrosion resistance. Ultrasonic impact treatment did not change the phase compositions of AlxCoCrFeMnNi alloys, while the successive network structures were broken and the short rod-like structures formed rather than long strip-like structures in the impacted hardening layer. The microhardness of AlxCoCrFeMnNi alloys (x = 0, 0.5 and 1.0) were improved by 92% (approximately 308.5 HV, 312.5 HV and 450.8 HV, respectively) after ultrasonic impact treatment due to the refine microstructures and precipitation strengthening mechanisms. Owing to the application of ultrasonic impact treatment the surface roughness of AlxCoCrFeMnNi alloys (Ra = 0.54–0.57 μm) decreased. Additionally, the impacted hardening AlxCoCrFeMnNi alloys exhibited higher corrosion resistance than the as-cast alloys resulted from the lower surface roughness.

Influence of carbon diffusion on microstructure and wear behaviour of duplex stainless steel surface layers on lamellar grey cast iron

AbstractSurface welding with duplex stainless steel was performed to enhance the wear and corrosion properties of grey cast iron, which is used as material for applications as pump components in maritime and chemical environments. The method used for surface welding and the corresponding process parameters determine the chemical composition and microstructure, which both determine the corrosion and wear properties of the surface layer. High heat input leads to high chemical dilution and thus, reduced corrosion resistance. Slow cooling rates, which are recommended for welding of grey cast iron components, facilitate the formation of carbides in the fusion zone of the chromium‐rich duplex stainless steel surface layer. On the one hand, carbides lead to increased hardness and thus, improved wear resistance of the surface layers. On the other hand, carbides and high chemical dilution rates reduce the corrosion resistance and therefore should be avoided. Under high cooling rates, the risk of cracking in the heat affected zone of the grey cast iron increases due to martensitic phase transformations. The paper describes the correlation of process parameters, microstructure and chemical composition with a focus on carbon diffusion and carbide formation, ever considering the effect on the wear behaviour in an oscillation tribometer and under erosion‐corrosion conditions.