Improving corrosion resistance of additively manufactured WE43 magnesium alloy by high temperature oxidation for biodegradable applications

Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples were built with the relativity density reaching 99.9%.High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations.The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface,a transition layer in the middle and the matrix.The oxide layer consisted of rare earth(RE)oxides,and became dense and thick with increasing the holding duration.The matrix was composed ofα-Mg,RE oxides and Mg_(24)RE_(5) precipitates.The precipitates almost disappeared in the transition layer.Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation.The original L-PBF samples lost 40%weight after 3-day immersion in Hank’s solution,and broke into fragments after 7-day immersion.The casted and solution treated samples lost roughly half of the weight after 28-day immersion.The high temperature oxidation samples,which were heated at 525℃ for 8 h,kept the structural integrity,and lost only 6.88%weight after 28-day immersion.The substantially improved corrosion resistance was contributed to the gradient structure at the surface.On one hand,the outmost dense layer of RE oxides isolated the corrosive medium;on the other hand,the transition layer considerably inhibited the corrosion owing to the lack of precipitates.Overall,high temperature oxidation provides an efficient,economic and safe approach to inhibit the corrosion of WE43 L-PBF samples,and has promising prospects for future clinical applications.

Enhanced corrosion resistance of epoxy resin coating via addition of CeO_(2) and benzotriazole

The use of fillers to enhance the corrosion protection of epoxy resins has been widely applied.In this work,cerium dioxide(CeO_(2))and benzotriazole(BTA)were introduced into an epoxy resin to enhance the corrosion resistance of Q235 carbon steel.Scanning electron microscopy results indicated that the CeO_(2) grains were rod-like and ellipsoidal in shape,and the distribution pattern of BTA was analyzed by energy dispersive spectroscope.The dynamic potential polarization curve proved the excellent corrosion resistance of the composite epoxy resin with CeO_(2) and BTA co-addition,and electrochemical impedance spectroscopy test analysis indicated the significantly enhanced long-term corrosion protection performance of the composite coating.And the optimal protective performance was provided by the coating containing 0.3%(mass)CeO_(2) and 20%(mass)BTA,which was attributed to the barrier performance of CeO_(2) particles and the chemical barrier effect of BTA.The formation of corrosion products was analyzed using X-ray diffraction.In addition,the corrosion resistance mechanism of the coating was also discussed in detail.

High corrosion resistance 21%Cr-0.4%Cu ferritic stainless steel contributing to resource conservation

With prices for metal resources such as nickel and molybdenum soaring,there is a heightened sense of crisis concerning resource scarcity.While Type304,the most common stainless steel,offers excellent corrosion resistance,its price is affected significantly by the cost of nickel because of its 8%nickel content.The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required.JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel,the world's first ferritic stainless steel,which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum,two rare metals.The newly developed steel contains 21%chromium with the addition of 0.4% copper.The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition.Copper addition enriches the chromium content in passive films after field exposure.Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304,including commercial kitchenware,building materials and industrial machinery.The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.

Microstructure evolution and corrosion resistance in simulated CGHAZ of X80 high-deformability pipeline steel

In this study, the microstructure evolution and corrosion resistance in O. 5 M Na2CO3 - 1 M NaHCO3 solution of X80 high-deformability （ X8OHD ） pipeline steel coarse-grained heat-affected zone （CGHAZ） with several heat input levels were investigated. It is shown that the microstructure of CGHAZ changes from bainite ferrite to granular bainite as the heat input increasing. In addition, the corrosion resistance and the stability of passive film of base material are better than those of CGHAZ with several heat input levels. Too small or too big heat input is inadvisable and better corrosion resistance of CGHAZ is attained when heat input is 30 kJ/cm.

Improvement of the Corrosion Resistance of High Alloyed Austenitic Cr-Ni-Mo Stainless Steels by Solution Nitriding

Characteristic features of austenitic steel grades combine a good corrosion resistance with a low hardness, wear resistance and scratch resistance. An interesting possibility for improving the wear behaviour of these steels without loss of their corrosion resistance lies in enriching the near surface region with nitrogen. The process of a solution nitriding allows the rise of the solution of nitrogen in the solid phase. On this state nitrogen increases the corrosion resistance and the tribilogical load-bearing capacity. The aim of the study was, to investigate the improvement of the pitting corrosion behaviour by solution nitriding. A special topic was to observe the effect of nitrogen by different molybdenum content. So austenitic stainless steels (18% Cr, 12% Ni, Mo gradation between 0.06 to 3.6%) had been solution nitrided. The samples could be prepared with various surface content of nitrogen from 0.04 to 0.45% with a step-by-step grinding. The susceptibility against pitting corrosion of these samples had been tested by determination of the stable pitting potential in 0.5M and 1M NaCl at 25°C. For the investigated steel composition and the used corrosion system there is no influence of molybdenum on the effectiveness of nitrogen. The influence of nitrogen to all of the determined parameters can be described well by PRE = Cr + 3,3 * Mo + 25 *N. XPS analysis of the sample surfaces support the results of the pitting corrosion tests.Additionally surface investigations with an acid elektolyte (0,1M HC1 + 0,4M NaCl) were performed. In this case the passivation effective nitrogen content increases markedly with rising molybdenum concentration of the steel. Obviously an interaction of Mo and N is connected with a strongly acid electrolyte.

Effect of Ni on the corrosion resistance of bridge steel in a simulated hot and humid coastal-industrial atmosphere

The corrosion resistance of weathering bridge steels containing conventional contents of Ni(0.20 wt%, 0.42 wt%, 1.50 wt%) and a higher content of Ni(3.55 wt%) in a simulated hot and humid coastal-industrial atmosphere was investigated by corrosion depth loss, scanning electron microscopy–energy-dispersive X-ray spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical methods. The results showed that, with increasing Ni content, the mechanical properties of the bridge steel were markedly improved, the welding parameters were satisfactory at room temperature, and the corrosion resistance was enhanced. When the Ni content was low(≤0.42 wt%), the crystallization process of the corrosion products was substantially promoted, enhancing the stability of the rust layer. When the Ni content was higher(~3.55 wt%), the corrosion reaction of the steel quickly reached a balance, because the initial rapid corrosion induced the formation of a protective rust layer in the early stage. Simultaneously, NiO and NiFe_2O_4 were generated in large quantities; they not only formed a stable, compact, and continuous oxide protective layer, but also strongly inhibited the transformation process of the corrosion products. This inhibition reduced the structural changes in the rust layer, thereby enhancing the protection. However, when the Ni content ranged from 0.42 wt% to 1.50 wt%, the corrosion resistance of the bridge steel increased only slightly.

Anisotropy in mechanical properties and corrosion resistance of 316L stainless steel fabricated by selective laser melting

The corrosion behavior and mechanical properties of 316 L stainless steel(SS) fabricated via selective laser melting(SLM) were clarified by potentiodynamic polarization measurements, immersion tests, and tensile experiments. The microstructural anisotropy of SLMed 316 L SS was also investigated by electron back-scattered diffraction and transmission electron microscopy. The grain sizes of the SLMed 316 L SS in the XOZ plane were smaller than those of the SLMed 316 L SS in the XOY plane, and a greater number of low-angle boundaries were present in the XOY plane, resulting in lower elongation for the XOY plane than for the XOZ plane. The SLMed 316 L was expected to exhibit higher strength but lower ductility than the wrought 316 L, which was attributed to the high density of dislocations. The pitting potentials of the SLMed 316 L samples were universally higher than those of the wrought sample in chloride solutions because of the annihilation of MnS or(Ca,Al)-oxides during the rapid solidification. However, the molten pool boundaries preferentially dissolved in aggressive solutions and the damage of the SLMed 316 L in FeCl3 solution was more serious after long-term service, indicating poor durability.

Influence of mill scale and rust layer on the corrosion resistance of low-alloy steel in simulated concrete pore solution

Electrochemical impedance spectroscopy, cyclic potentiodynamic polarization measurements, and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy were used to investigate the influence of mill scale and rust layer on the passivation capability and chloride-induced corrosion behaviors of conventional low-carbon（LC） steel and low-alloy（LA） steel in simulated concrete pore solution. The results show that mill scale exerts different influences on the corrosion resistance of both steels at various electrochemical stages. We propose that the high long-term corrosion resistance of LA steel is mainly achieved through the synergistic effect of a gradually formed compact, adherent and well-distributed Cr-enriched inner rust layer and the physical barrier protection effect of mill scale.

Antibacterial properties and corrosion resistance of AISI 420 stainless steels implanted by silver and copper ions

Silver or copper ions are often chosen as antibacterial agents. But a few reports are concerned with these two antibacterial agents for preparation of antibacterial stainless steel （SS）. The antibacterial properties and corrosion resistance of AISI 420 stainless steel implanted by silver and copper ions were investigated. Due to the cooperative antibacterial effect of silver and copper ions, the Ag/Cu implanted SS showed excellent antibacterial activities against both Gram-negative Escherichia coli （E. coli） and Gram-positive Staphylococcus aureus （S. aureus） at a total implantation dose of 2~ 1017 ions/cm2. Electrochemical polarization curves revealed that the corrosion resistance of Ag/Cu implanted SS was slightly enhanced as compared with that of un-implanted SS, The implanted layer was characterized by X-ray photoelec- tron spectroscopy （XPS）. Core level XPS spectra indicate that the implanted silver and copper ions exist in metallic state in the implanted layer.

Wear and corrosion resistance of laser-cladded Fe-based composite coatings on AISI 4130 steel

The wear and corrosion resistance of Fe_（72.2）Cr_（16.8）Ni_（7.3）Mo_（1.6）Mn_（0.7）C_（0.2）Si_（1.2） and Fe_（77.3）Cr_（15.8）Ni_（3.9）Mo_（1.1）Mn_（0.5）C_（0.2）Si_（1.2） coatings laser-cladded on AISI 4130 steel were studied.The coatings possess excellent wear and corrosion resistance despite the absence of expensive yttrium,tungsten,and cobalt and very little molybdenum.The microstructure mainly consists of dendrites and eutectic phases,such as duplex（γ＋α）-Fe and the Fe–Cr（Ni）solid solution,confirmed via energy dispersive spectrometry and X-ray diffraction.The cladded Fe-based coatings have lower coefficients of friction,and narrower and shallower wear tracks than the substrate without the cladding,and the main wear mechanism is mild abrasive wear.Electrochemical test results suggest that the soft Fe_（72.2）Cr_（16.8）Ni_（7.3）Mo_（1.6）Mn_（0.7）C_（0.2）Si_（1.2） coating with high Cr and Ni concentrations has high passivation resistance,low corrosion current,and positive corrosion potential,providing a better protective barrier layer to the AISI 4130 steel against corrosion.

Data-mining and atmospheric corrosion resistance evaluation of Sn-and Sb-additional low alloy steel based on big data technology

Machine-learning and big data are among the latest approaches in corrosion research.The biggest challenge in corrosion research is to accurately predict how materials will degrade in a given environment.Corrosion big data is the application of mathematical methods to huge amounts of data to find correlations and infer probabilities.It is possible to use corrosion big data method to distinguish the influence of the minimal changes of alloying elements and small differences in microstructure on corrosion resistance of low alloy steels.In this research,corrosion big data evaluation methods and machine learning were used to study the effect of Sb and Sn,as well as environmental factors on the corrosion behavior of low alloy steels.Results depict corrosion big data method can accurately identify the influence of various factors on corrosion resistance of low alloy and is an effective and promising way in corrosion research.

Superior corrosion resistance-dependent laser energy density in(CoCrFeNi)95Nb5 high entropy alloy coating fabricated by laser cladding

(CoCrFeNi)95Nb5 high entropy alloy(HEA)coatings were successfully fabricated on a substrate of Q235 steel by laser cladding technology.These(CoCrFeNi)95Nb5 HEA coatings possess excellent properties,particularly corrosion resistance,which is clearly superior to that of some typical bulk HEA and common engineering alloys.In order to obtain appropriate laser cladding preparation process parameters,the effects of laser energy density on the microstructure,microhardness,and corrosion resistance of(CoCrFeNi)95Nb5 HEA coating were closely studied.Results showed that as the laser energy density increases,precipitation of the Laves phase in(CoCrFeNi)95Nb5 HEA coating gradually decreases,and diffusion of the Fe element in the substrate intensifies,affecting the integrity of the(CoCrFeNi)95Nb5 HEA.This decreases the microhardness of(CoCrFeNi)95Nb5 HEA coatings.Moreover,the relative content of Cr2O3,Cr(OH)3,and Nb2O5 in the surface passive film of the coating decreases with increasing energy density,causing corrosion resistance to decrease.This study demonstrates the controllability of a high-performance HEA coating using laser cladding technology,which has significance for the laser cladding preparation of other CoCrFeNi-system HEA coatings.

Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels(conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions(ordinary Portland cement(OPC) extract and alkali-activated slag(AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various Na Cl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.

Effect of microstructure and passive film on corrosion resistance of 2507 super duplex stainless steel prepared by different cooling methods in simulated marine environment

The effect of microstructure and passive film on the corrosion resistance of 2507 super duplex stainless steel(SDSS)in simulated marine environment was investigated by electrochemical measurements,periodic wet–dry cyclic corrosion test,scanning Kelvin probe force microscopy,atomic force microscopy,and X-ray photoelectron spectrometry.The results show that the occupation ratio ofγphase increases with the decrease in cooling rate,whereas the content ofαphase reduces gradually.In addition,theσprecipitated phase only emerges in the annealed steel.The pitting sensitivity and corrosion rate of 2507 SDSS reduce first and then increase as the cooling rate decreases.Theσprecipitated phase drastically reduces the protective ability of the passive film and facilitates micro-galvanic corrosion of the annealed steel.For various microstructures,the pits are preferentially distributed within theσandγphases.The corrosion resistance of 2507 SDSS prepared by different cooling methods is closely related to the microstructure and structure(stability and homogeneity)of the passive film.Normalized steel shows an optimal corrosion resistance,followed by the quenched and annealed steels.

Corrosion resistance of steel materials in LiCl-KCl melts

The corrosion behaviors of 304SS, 316LSS, and Q235A in LiCl-KCl melts were investigated at 450℃ by Tafel curves and elec- trochemical impedance spectroscopy （EIS）. 316LSS shows the best corrosion resistance behaviors among the three materials, including the most positive corrosion potential and the smallest corrosion current from the Tafel curves and the largest electron transfer resistance from the Nyquist plots. The results are in good agreement with the weight losses in the static corrosion experiments for 45 h. This may be attributed to the better corrosion resistance of Mo and Ni existing as alloy elements in 316LSS, which exhibit the lower corrosion current densities and more positive corrosion potentials than 316LSS in the same melts.

Corrosion resistance evaluation of highly dispersed MgO–MgAl2O4–ZrO2 composite and analysis of its corrosion mechanism: A chromium-free refractory for RH refining kilns

The corrosion resistance behavior of a highly dispersed MgO-MgAl2O4-ZrO2 composite refractory material is examined by testing with high-basicity and low-basicity RH(Ruhrstahl-Hereaeus)slags.The composite material exhibits greater resistance to the RH slags than the traditional MgO-Cr2O3 composite,MgO-ZrO2 composite,and MgO-MgAl2O4-ZrO2 composite.On the basis of the microstructural analysis and mechanisms calculations,the corrosion resistance behavior of the MgO-MgAl2O4-ZrO2 composite is attributable to its highly dispersed structure,which helps protect the high activity of ZrO2.When in contact with the slag,ZrO2 reacts with CaO to form the stable phase CaZrO3,which protects MgAl2O4 against corrosion,thereby enhancing the corrosion resistance of the composite.

Electrodeposition of multi-layer Pd-Ni coatings on 316L stainless steel and their corrosion resistance in hot sulfuric acid solution

Pd-Ni coating shows good corrosion resistance in strong corrosion environments.However,in complex aggressiveenvironments,the performance of the coatings is limited and further improvement is necessary.The effects of the applied platingcurrent density on the composition,structure and properties of Pd-Ni coatings were studied.By changing the current density in thesame bath,multi-layer Pd-Ni coatings were prepared on316L stainless steel.Scanning electronic microscopy,weight loss tests,adhesion strength,porosity and electrochemical methods were used to study the corrosion resistance of the films prepared bydifferent coating methods.Compared with the single layer Pd-Ni coating,the multi-layer coatings showed higher microhardness,lower internal stress,lower porosity and higher adhesive strength.The multi-layer Pd-Ni coating showed obviously better corrosionresistance in hot sulfuric acid solution containing Cl-.

Effect of Boron on Delayed Fracture Resistance of Medium-Carbon High Strength Spring Steel

The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.

Microstructure and corrosion resistance of 304 stainless steel electroslag strip cladding

The 304 stainless steel strips were deposited one layer on carbon steel base metal by electroslag strip cladding （ESC） and submerged arc cladding （SAC）, respectively. The solidification microstrueture of ESC metal was analyzed by the optical microscopy, scanning electron microscope and energy dispersive spectroscopy. The corrosion resistance studies of strip cladding metals were carried out in 10% oxalic acid electrolytic etching test. The results showed that the cladding metal obtained by ESC presented low content of C, high content of Cr and enough alloying element of Ni in the chemical composition. The transition zone of ESC with small width was almost parallel with the base metal, leading to a lower dilution. There are three types of solidification modes （ A→AF→FA ） occurred in the ESC metal due to the decrease of cooling rate and degree of dilution from the transition zone to the top of ESC metal. As a result, the microstructure of ESC metal exhibited mainly austenite with a small amount of ferrite, contributing to achievement of better corrosion resistance.

Microstructure and mechanical property of resistance spot welded joint of aluminum alloy to high strength steel with especial electrodes

Dissimilar material joining of 6008 aluminum alloy to H220 YD galvanized high strength steel was performed by resistance spot welding with especial electrodes that were a flat tip electrode against the steel surface and a domed tip electrode upon the aluminum alloy surface. An intermetallic compound layer composed of Fe2Al5 and FeAl3 was formed at the steel/ aluminum interface in the welded joint. The thickness of the intermetallic compound layer increased with increasing welding current and welding time, and the maximum thickness being 7. 0 μm was obtained at 25 kA and 300 ms. The weld nugget diameter and tensile shear load of the welded joint had increased tendencies first with increasing welding current （ 18 -22 kA） and welding time （ 50 - 300 ms）, then changed little with further increasing welding current （ 22 - 25 kA） and welding time （300 -400 ms）. The maximum tensile shear load reached 5.4 kN at 22 kA and 300 ms. The welded joint fractured through brittle intermetallic compound layer and aluminum alloy nugget.