Intercrystalline Corrosion Research Articles

Fabrication of Y2O3-doped MgO refractory raw materials based on magnesium hydroxide from salt-lake brine

High-purity magnesia refractories were fabricated by brine magnesium hydroxide from the salt-lake brine (Qinghai Salt Lake) and Y2O3 as an additive at 1780 °C. It avoided the substantial CO2 emissions and ultra high temperature sintering process (＞1900 °C) when compared with the conventional magnesite-calcination technical approach. The results confirmed that Y2O3 was dispersed on the MgO grains boundaries in the fabricated MgO aggregates, resulting in a decrease in apparent porosity and enhancing the grains' boundaries. With 3 wt% addition of Y2O3, the apparent porosity and bulk density of the sample reached to 15.9 % and 3.10 g/cm3 from 37.9 % to 2.30 g/cm3 of blank control group, respectively. Compared to the blank control without Y2O3-adding, the sample with 5 wt% Y2O3 exhibited a 54.17 % increase in the resistance to molten slag. SEM results indicated that the incorporation of Y2O3 in samples increased the porosity of small pores and enhanced grains boundaries, thereby suppressing slag's penetration. Furthermore, the Y2O3-adding was employed to disperse the MgO grains boundaries and existed as separate phases for grains boundaries enhancement. The slag attack of the fabricated MgO–Y2O3 refractory raw materials were controlled by an inter-crystalline corrosion process.

The influence of structure, sensitization and corrosion on the fatigue properties of austenitic steel

The article will be focused on examining and comparing the influence of structure, sensitization and corrosion on the fatigue properties of austenitic stainless steel. The methodology of the experiment includes fatigue tests of samples attacked by intercrystalline corrosion. Therefore, the test samples were subjected to heat treatment for sensitization. Then these samples were subjected to long-term exposure in an aggressive corrosion solution. Experiments deal with microstructural material analysis, fractographic analysis, mechanical and fatigue tests.

Improvement in Fatigue Strength of Chromium–Nickel Austenitic Stainless Steels via Diamond Burnishing and Subsequent Low-Temperature Gas Nitriding

Chromium–nickel austenitic stainless steels are widely used due to their high corrosion resistance, good weldability and deformability. To some extent, their application is limited by their mechanical characteristics. As a result of their austenitic structure, increasing the static and dynamic strength of the components can be achieved by surface cold work. Due to the tendency of these steels to undergo intercrystalline corrosion, another approach to improving their mechanical characteristics is the use of low-temperature thermo-chemical diffusion processes. This article proposes a new combined process based on sequentially applied diamond burnishing (DB) and low-temperature gas nitriding (LTGN) to optimally improve the fatigue strength of 304 steel. The essence of the proposed approach is to combine the advantages of the two processes (DB and LTGN) to create a zone of residual compressive stresses in the surface and subsurface layers—the enormous surface residual stresses (axial and hoop) introduced by LTGN, with the significant depth of the compressive zone characteristic of static surface cold working processes. DB (both smoothing and single-pass hardening), in combination with LTGN, achieves a fatigue limit of 600 MPa, an improvement of 36.4% compared to untreated specimens. Individually, smoothing DB, single-pass DB and LTGN achieve 540 MPa, 580 MPa and 580 MPa, respectively. It was found that as the degree of plastic deformation of the surface layer introduced by DB increases, the content of the S-phase in the nitrogen-rich layer formed by LTGN decreases, with a resultant increased content of the ε-phase and a new (also hard) phase: stabilized nitrogen-bearing martensite.

ПРИЧИНЫ СНИЖЕНИЯ КОРРОЗИОННОЙ СТОЙКОСТИ ДЕТАЛЕЙ МАШИН И ОБОРУДОВАНИЯ ПЕРЕРАБАТЫВАЮЩИХ ОТРАСЛЕЙ АПК

The fast-wearing parts of machinery and equipment of the processing branch of the agro-industrial complex are made of corrosion-resistant steels of various classes. There are many ways to restore them, but the most optimal way is electrocontact welding of corrosion-resistant steels of the appropriate class. This method has a number of advantages over other recovery methods, however, the effect of electrocontact welding of the tape on the corrosion resistance of the coating has not been practically studied. (Research purpose) The research purpose is theoretically substantiating the possible reasons for the decrease of corrosion resistance of coatings obtained by electrocontact welding of tape from corrosion-resistant steels, and experimentally proving the hypotheses presented. (Materials and methods) Were used as materials for the study of 0.5 mm thick tapes made of corrosion-resistant steels 12X18N10T, 20X13, 12X17, 15X28, 12X13. Tests were carried out for the formation of intercrystalline corrosion under various types of thermal influence according to the AM method (GOST 6032-2017). (Results and discussion) Laboratory tests have shown that welded tapes made of austenitic steels (12X18H10T) are not prone to the intercrystalline corrosion due to the presence of titanium in the tape and the austenization temperature of 1100-1200 degrees Celsius. In ferritic steels at a temperature of 1000 degrees Celsius in the welding zone, intercrystalline corrosion does not form according to the theory, but reheating (tempering zone) provokes its formation. The same pattern is observed with martensite steels (for example, 20X13). (Conclusions) The theory was confirmed that during electrocontact welding of tapes made of corrosion-resistant steels of martensit (20X13), martensit-ferritic (12X13), ferritic (12X17) steels are subjected to intercrystalline corrosion, with the exception of austenitic steels (type 18-10). It is recommended to take into account the results obtained to restore machine parts and equipment of the processing branches of the agro-industrial complex by electrocontact welding of the tape.

Effect of additional cooling during friction stir welding on structure and properties of aluminum alloy joints

The mechanical and corrosion properties of welded joints of sheets with a thickness of 5 mm made of the Al–Cu– Mg system alloy in the T state (hardening and natural ageing) and the 1565сhN116 alloy with a thickness of 3 mm, obtained by friction stir welding (FSW) in air and in water, are studied. It is established that additional cooling of the welded joint by water helps to increase the ultimate strength of the weld, slightly changing the properties of the welded joint. The destruction of the welded joint in both cases occurs along the thermo-mechanical affected zone. The strength of the welded joint of the Al–Cu–Mg system alloy and the 1565chN116 alloy is 0.8 and 0.95...0.99 of the strength of the base metal, respectively. When FSW of the Al–Cu–Mg system alloy in the T state in water, in comparison with welding in air, there is an increase in the microhardness of the mixing zone by 20 % and a decrease in the grain size in it from 9.8 to 4.8 μm. For the 1565chN116 alloy under the same conditions, an increase in the microhardness of the metal of the thermo-mechanical affected zone and the mixing zone by about 12 % and reduction of grain size in the mixing zone from 6 .8 to 4.5 μm is detected. At the same time, both for the Al–Cu–Mg system alloy in the T state and the 1565chN116 alloy during FSW in water, the length of the heat-affected zone decreases by about 1.6—2.2 times compared to FSW in air. For both alloys, an increase in the cooling rate during FSW leads to an increase in resistance against intercrystalline corrosion of all zones of the welded joint by about 1.5—2 times.

Wear and corrosion resistance of Al1.2CoCrFeNiScx high entropy alloys with scandium addition

The present study focuses on investigating the microstructure, hardness, wear, and corrosion resistance of Al1.2CoCrFeNiScx high entropy alloys, where the Sc content (x) varies between 0, 0.1, 0.2, and 0.3. The results indicate that the addition of Sc promotes the formation of the FCC phase and improves the hardness and wear resistance, but reduces the corrosion resistance of the alloy. The alloy's evolution can be observed as a transition from a single BCC phase to a combination of Fe, Cr-rich BCC phase, Al, Co, Ni-rich BCC phase, and Ni, Sc-rich FCC phase. As the Sc content increases from 0 to 0.3, the hardness increases from 438 HV to 581 HV, representing a 32.6 % increment. This increase can be mainly attributed to grain size strengthening and solid solution strengthening. Additionally, the average friction coefficient experiences a notable reduction from 0.999 to 0.574, indicating a 42.5 % decrease. With respect to wear resistance, the Al1.2CoCrFeNiSc0.3 alloy exhibits superior performance, demonstrated by its lower friction coefficient, reduced wear rate, and smaller volume, width and depth of wear marks. Furthermore, the addition of Sc to the Al1.2CoCrFeNiScx alloys leads to an overall decrease in corrosion potential, accompanied by an increase in corrosion current density, suggesting that Sc has a detrimental effect on the corrosion resistance of the alloy. Moreover, the Al1.2CoCrFeNi alloy displays pitting corrosion, while the Al1.2CoCrFeNiScx alloys demonstrate intercrystalline corrosion, which preferentially occurs on the Ni, Sc-rich phase due to the high electrochemical activity and low equivalent chemical potential.

Study of the corrosion mechanism of Mg–Gd based soluble magnesium alloys with different initial texture states

Abstract In order to clarify the influence of different initial texture states on the corrosion mechanism of soluble Mg alloy materials, the as cast and after extruded + perforated (EP) deformed Mg–Gd based soluble magnesium alloys are investigated by the microstructure, surface morphology, surface volta potential, immersion test and electrochemical measurement separately. The results indicate that: the rate of corrosion of the as cast Mg–Gd based soluble magnesium alloy can reach 43.85 mg/cm2/h at 93 °C in a 3 wt% KCl solution, while after EP deformation the rate of corrosion is greatly reduced to only 8.37 mg/cm2/h. Combined with the microstructure analysis, it is concluded that the EP deformed destroyed the coarse reticulated second phase in the as cast structure, which reduced the micro-electrocouple corrosion effect of the second phase. Finally, the corrosion mechanism models for different initial texture states are established through the analysis of microstructure and corrosion morphology, respectively. It is found that the microscopic corrosion mechanism of the as cast Mg–Gd based soluble magnesium alloy is mainly intercrystalline corrosion, which is a superposition of micro-electrocouple corrosion and Mg matrix dissolution. While the microscopic corrosion mechanism of the EP deformed is mainly intracrystalline corrosion, which is manifested as pitting corrosion.

Corrosion Resistance of the Welded Joints from the Ultrafine-Grained Near-α Titanium Alloys Ti-5Al-2V Obtained by Spark Plasma Sintering

A solid-phase diffusion welding of coarse-grained and ultrafine-grained (UFG) specimens of titanium near-α alloy Ti-5Al-2V used in nuclear power engineering was made by Spark Plasma Sintering. The failure of the welded specimens in the conditions of hot salt corrosion and electrochemical corrosion was shown to have a preferentially intercrystalline character. In the case of the presence of macrodefects, crevice corrosion of the welded joints was observed. The resistance of the alloys against the intercrystalline corrosion was found to be determined by the concentration of vanadium at the titanium grain boundaries, by the size and volume fraction of the β-phase particles, and by the presence of micro- and macropores in the welded joints. The specimens of the welded joints of the UFG alloy are harder and have a higher resistance to hot salt corrosion and electrochemical corrosion.

The Influence of Heat Treatments in Corrosion Resistance of Austenitic Steels

Abstract This paper presents the results of laboratory research on the influence of heat treatment on the corrosion resistance of austenitic steels (Cr-Ni, Cr, Mn, Cr-Mn-Ni), research that may extend under certain conditions and ferrites steels and semi-ferrites chrome steels.This type of intercrystalline corrosion was observed in other alloy systems due to media containing chloride ions.The experimental results consist in comparing structural changes and corrosion rate for different types of austenitic steels that were made experimental research.

Effect of electromagnetic forming–heat treatment process on mechanical and corrosion properties of 2024 aluminum alloy

The 2024 aluminum alloys are used in a wide range of industrial applications, and improvement in their formability and serviceability is key in the manufacturing process. Electromagnetic forming (EMF) has proven to be an effective means of improving the formability of aluminum alloys. By combining EMF and heat treatment process, three samples of 2024 aluminum alloy were designed: Sample A (annealing + EMF + solid-solution + aging), Sample B (solid solution + EMF + aging), and Sample C (solid solution + pre-aging + EMF + aging). The effects of three heat treatment regimens on the properties and microstructure of 2024 aluminum alloy were studied by hardness test, intercrystalline corrosion, and exfoliation corrosion, as well as by microscopic characterization techniques including scanning electron microscopy and transmission electron microscopy. The results show that the dislocations-induced deformation could shorten the time to peak aging and led to the increase in peak strength. Sample C exhibited the highest strength and sample A exhibited the highest elongation and corrosion resistance. The microscopic results show that the differences in properties were mainly influenced by the distribution of precipitated phases and the width of the precipitation-free zone. The discrete and coarse grain boundary precipitations make sample A have excellent corrosion resistance. The fine and dense precipitated phases provide good strength for samples B and C, but also reduces the elongation. This research has important implications for rational formulation based on the combination of EMF and heat treatment processes for the fabrication of Al–Cu–Mg alloys. Conclusionsmay be made more concise. They should focus on the mechanisms responsible for high strength or corrosion resistance rather than the values obtained that are shown in results.

Analysis of structural and deformation characteristics in localized plastic shear of iron-based heterophase materials

Studies have been carried out to identify the conditions of protection against intercrystalline corrosion of metals and iron-based alloys. A method is proposed and a technological regulation of deformation-structural transformations in the metal-pore(liquid) system is developed-metal" in the implementation of thermomechanochemical reactions and implantation of hydrogen ions in the form of an atomic-molecular reducing (protective) film with localized shift of structurally heterogeneous heterophase mechanical mixtures.

Effect of post-weld heat treatment on inhomogeneity of mechanical properties and corrosion behavior of rotary friction welded 2024 aluminum alloy joint

The effects of different aging treatment conditions on inhomogeneity of mechanical properties and corrosion behavior of rotary friction welded (RFWed) AA2024 joints were studied by artificial and natural aging treatment. The sliced samples at the center, 0.25R, 0.5R and 0.75R positions were taken along the radius of RFWed joint. After artificial aging and long-term natural aging treatment, the tensile strength and corrosion resistance in different positions of joint tended to be homogeneous. Furthermore, the distribution of elements existed in the interior of grain and grain boundary was homogeneous after artificial aging, which reduced the tendency of intercrystalline corrosion. And pitting corrosion occurred at dynamic recrystallization zone (DRZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM). The order of corrosion resistance of each region was inferred from the electrochemical parameters as BM > TMAZ > HAZ > DRZ. With the prolongation of natural aging time, the best corrosion resistance occurred in BM, while the corrosion types of DRZ, TMAZ and HAZ gradually changed from pitting and intergranular corrosion to pitting corrosion mainly.

The effect of forced cooling during friction stir welding on the structure and properties of 1565ChN116 aluminium alloy joints

This paper describes the results of a study that looked at mechanical and corrosion performance of joints between 3 mm thick 1565ChН116 aluminium alloy sheets produced by friction stir welding in atmosphere and in water. It was established that a higher in-water cooling rate resulted in a higher tensile strength of the weld joint and slightly impacted its properties. It is the thermomechanical impact zone of the joint that sees fracture during tensile testing when aluminium alloy 1565ChН116 is friction stir welded in atmosphere and in water. The strength of such joint is 95 to 99% of the strength of the base metal. When conducting friction stir welding in water, the thermal impact zone is approximately 1.6 to 2.2 times shorter than when the process takes place in atmosphere. For the alloy 1565ChН116, friction stir welding conducted in water is associated with a 10 to 12% higher microhardness of metal in the thermomechanical impact zone and the stirring zone. The grain size in the stirring zone was observed to decrease from 6.8 to 4.5 μm. In this zone (the core of the joint), small angle boundaries account for approximately 15% of the total number of boundaries. This suggests that the structure mainly consists of equiaxed grains with large angle boundaries. A transmission electron microscopy study of foil obtained in the joint core area confirmed the results of phase and microtexture analysis (carried out by means of the EBSD technique) indicating that a recrystallized structure formed in the centre of the joint. A higher cooling rate during friction stir welding increases the intercrystalline corrosion resistance of all areas of the joint by approximately 1.4 to 1.7 times. The biggest increase in the intercrystalline corrosion resistance was observed in the thermal impact zone.

Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

There were studied structures and properties of welded joints of laboratory melted austenitic steels: Fe-0.04C-18Cr-9Ni-0.2N and new-developed Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu. Correct choice of composition and deformation-heat treatment leads the new-developed steels are high-strength corrosion-resistant ones with stable austenite. Computer simulation shows that enough quality of welded seam can be provided by laser welding of plates of up to 4 mm in thick at the room temperature. For bigger thicknesses preliminary heating is necessary. Microstructure, phase compositions, lattice periods, X-ray diffraction peak broadening, microhardness, bending strength and ductility, resistance against intercrystalline, pitting and total corrosion was studied for bulk metal and laser welded joints of high-temperature thermomechanically treated hot-rolled plates, including tests after 1000 thermal cycles in range –163…+20 °C were investigated. It was shown that welded seams are 300…1000 μm in wide and have no porosity and no thermal affected zone. The welded seam strength is the same as for bulk metal, 180° bend test shows no cracks in the seam. The resistances of welded seam and bulk of Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu steels against total corrosion in the sea water (3 % NaCl) and in acid environment (0,5M H2SO4, including additional blowdown by H2S), pitting and intercrystalline corrosion in standard environments are practically equal. The structures, phase compositions, hardnesses and corrosion resistances of welded joints of both new-developed steels are constant after the thermocycling.

Influence of full-scale climatic tests on the properties of aluminum alloys in zones of river and marine water mixture

Within nine months, comprehensive studies were conducted on the effect of full-scale climatic tests on the properties of samples of aluminum alloy AMg6 when fully submerged in the estuary region of the Don River (the basin of the Sea of Azov) at two stations. The features of the formation of micro- and macro-fouling communities on experimental plates at one, three, six and nine months after the start of the experiment are shown. It is shown that microfouling communities on the experimental plates begin to form within a month of exposure. Diatoms were the background-forming species during the entire practical period of the study. Single macrozoobenthos organisms begin to appear on the samples after three months and only at second station. After six months, macro-fouling organisms are fixed on plates at both stations. As the exposure period increases, the number and biomass of macro-foulers increases. The corrosion resistance assessment of the samples revealed the absence of intercrystalline corrosion during the entire test period in water, at both stations, as well as pitting corrosion during the first six months of exposure.

Effect of phosphonate functional group on corrosion inhibition of imidazoline derivatives in acidic environment

In the present study, ({2-[2-(7-Isopropyl-1,4-dimethyl-9,10-octahydro-phenanthren-1-yl)-4,5-dihydro-1-yl]-ethylamino}-methyl)-phosphonicimidazole (GSIM) was synthesized by introducing phosphonate (–PH2O3) group into imidazoline derivatives and its corrosion inhibition performance was studied for Q345 steel in acidic medium along with SIM using potentiodynamic polarization, EIS and SECM analysis. Surface analysis of steel samples was also performed by optical microscopy and SEM-EDS analysis after polarization tests. XPS was used to detect chemical composition of the surface passive films. It was observed that introducing -PH2O3 group not only improved the adsorption capacity on the metal surface by coordinating with iron ions, but also inhibited the interference of hydrogen bond formed by –NH2 group and water molecules on the adsorption. GSIM not only inhibited intercrystalline corrosion and pitting corrosion, but also reduced uniform corrosion. Thermodynamics studies demonstrated that GSIM followed the Langmuir adsorption isotherm and had a larger adsorption equilibrium constant than SIM, which indicated that it had a stronger adsorption capacity. XPS and UV confirmed that the coordination between GSIM and Fe3+ and hydrogen bonding between SIM and water molecules. The quantum chemical study further clarified that the site and strength of hydrogen bond between SIM and H2O and the dominant configuration and coordination stability of GSIM with Fe3+.

Studying Corrosion Resistance of Weld Joints of Ultrafine-Grained Titanium Alloys

Ultrafine-grained (UFG) samples of PT-3V near-α titanium alloy were subjected to diffusion welding using the Spark Plasma Sintering system. It has been shown that the destruction of welded UFG samples under hot salt corrosion (HSC) is two-staged – first, intercrystalline corrosion is manifested, which then graduates to pitting corrosion. It has been established that the corrosion resistance of weld joints is determined by vanadium concentration at the grain boundaries, the size and volume ratio of β-phase particles and the presence of pores in the weld joints. It has been shown that welded UFG samples possess higher hardness and corrosion resistance than coarse-grained samples.

Corrosion resistance of ultrafine-grained pseudo-α titanium alloy PT-3V

Ultrafine-grained (UFG) samples of PT-3V pseudo-α titanium alloy were subjected to diffusion welding through spark plasma sintering. It has been shown that the destruction of welded UFG samples under hot salt corrosion (HSC) is two-staged: first, intercrystalline corrosion (ICC) is manifested, which then graduates to pitting corrosion. It has been established that the corrosion resistance of the weld joints is determined by the concentration of vanadium at the grain boundaries, the size and volume ratio of the β-phase particles, and the presence of pores in the weld joints. It has been shown that welded UFG samples possess a higher hardness and resistance to ICC than coarse-grained samples.

Increasing the corrosion resistance of aluminum alloys when modified

The corrosion properties of aluminum alloys of AI-Mg, AI-Mg-Sc and Al-Ѕi systems before and after modification were studied. Tests were made for intergranular, layered corrosion and corrosion cracking of AMg6, AL4 alloys. The results showed the modification efficiency of aluminum alloys AL4 by silicon carbide. In order to stabilize the structure, increase the corrosion resistance and the performance properties of aluminum alloys, experiments were conducted on the treatment of liquid melts with nanosized compositions based on silicon carbide. The research materials were foundry and deformed aluminum alloys of AI-ЅI, AI-Mg-Ѕс, AI-Mg systems. Promising directions of modification of aluminum alloys in the world are conducted in the field of application of powder modifiers. The use of such modifiers facilitates the technological process, is environmentally safe, leads to a uniform distribution of the introduced nanocompositions over the crosssection of the casting, which increases the strength, plastic properties of the alloys and their stability. Іndustrial enterprises of Ukraine apply modification of foundry aluminum alloys with sodium salts. To increase the complex of physical and mechanical properties and to achieve the required technological characteristics, including weldability, a complex modifier was used to provide grinding of the structure of aluminum alloys Processing of aluminum melts was performed by a nanosized tablet modifier based on silicon carbide using the developed technology. A modifier with a particle size of up to 100 nm was obtained by the method of plasma chemical synthesis. The initial and modified alloys were tested for general intercrystalline and stratification corrosion by standard methods. In modified alloys found intercrystalline corrosion. Corrosion cracking did not even occur after 55 days of testing

ВПЛИВ ТЕМПЕРАТУРИ ТЕРМІЧНОЇ ОБРОБКИ НА СТІЙКІСТЬ ДО МІЖКРИСТАЛІТНОЇ КОРОЗІЇ ЗВАРНИХ З'ЄДНАНЬ

Welded joints with corrosion-resistant steels and heat-resistant alloys requiring different modes of heat treatment to achieve the level of mechanical properties specified in the design documentation are used to manufacture parts and components of the rocket engine turbo-pump unit.For the manufacture of parts and assemblies of liquid-propellant rocket engines at the machine-building enterprises of Ukraine there was a necessity of replacement of half-finished products because of certain difficulties at delivery of materials from EU countries.First of all, it was necessary to replace flat products from high-alloy ХН67МВТЮ and 06Х15Н6МВФБ with one alloy that would possess the necessary set of physicomechanical characteristics. In the work, as a replacement for the used heat-resistant alloys, the Inconel 718 alloy welded to 316L steel was chosen. As a result of comparative studies of the intercrystalline corrosion resistance of welded joints of the heat-resistant Inconel 718 alloy with stainless steel, after testing various heat treatment conditions, the low-temperature heating conditions were recommended for soldering at a temperature of 950°C. Samples of welded joints, processed according to the recommended mode, showed increased corrosion resistance.