Performance Assessment on Corrosion Resistance of Refractory Materials Based on High-temperature Machine Vision Technology

Refractory materials,as the crucial foundational materials in high-temperature industrial processes such as metallurgy and construction,are inevitably subjected to corrosion and penetration from high-temperature media during their service.Traditionally,observing the in-situ degradation process of refractory materials in complex high-temperature environments has presented challenges.Post-corrosion analysis are commonly employed to assess the slag resistance of refractory materials and understand the corrosion mechanisms.However,these methods often lack information on the process under the conditions of thermal-chemical-mechanical coupling,leading to potential biases in the analysis results.In this work,we developed a non-contact high-temperature machine vision technology by the integrating Digital Image Correlation(DIC)with a high-temperature visualization system to explore the corrosion behavior of Al2O3-SiO2 refractories against molten glass and Al2O3-MgO dry ramming refractories against molten slag at different temperatures.This technology enables realtime monitoring of the 2D or 3D overall strain and average strain curves of the refractory materials and provides continuous feedback on the progressive corrosion of the materials under the coupling conditions of thermal,chemical,and mechanical factors.Therefore,it is an innovative approach for evaluating the service behavior and performance of refractory materials,and is expected to promote the digitization and intelligence of the refractory industry,contributing to the optimization and upgrading of product performance.

Effect of chromium on hot corrosion behavior of arc-sprayed NiCr coatings

In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.

Protective Effect of the Sputtered TiAlCrAg Coating on the High-Temperature Oxidation and Hot Corrosion Resistance of Ti-Al-Nb Alloy

The effect of a sputtered Ti-48AI-8Cr-2Ag (at. pct) coating on the oxidation resistance of the cast Ti-46.5AI-5Nb (at. pct) alloy was investigated in air at 1000-1100℃. Hot corrosion in molten 75 wt pct Na2SO4+25 wt pct K2SO4 was investigated at 900℃. The scale on the cast TiAINb tends to spall in air, while the scale on coating is very adherent. The sputtered Ti-48AI-8Cr-2Ag coating remarkably improved high temperature oxidation resistance of the cast Ti-46.5AI-5Nb alloy because of the formation of an adherent Al2O3 scale. Due to the inward diffusion of Cr, Kirkendall voids were found at the coating/substrate interface. TiAICrAg coating provided excellent hot corrosion resistance for TiAINb alloy in molten 75 wt pct Na2SO4+25 wt pct K2S04 at 900℃ due to the formation of a continuous Al_2O_3 scale.

Hot Corrosion Resistance of TB8 Titanium Alloy after ECAP and Heat Treatment

The metastableβtitanium alloy TB8(Ti-12.76Mo-2.13Nb-2.73A1-0.16Si)was used as the original material,and the secondary processing method combining equal channel angular pressing(ECAP)and heat treatment was adopted.With the help of optical microscope(OM),scanning electron microscope(SEM)and X-ray diffractometer(XRD),the corrosion behavior of TB8 titanium alloy after different secondary processing(800℃/850℃solid solution-520℃aging,ECAP-800℃/850℃solid solution-520℃aging,and800℃/850℃solid solution-ECAP-520℃aging)was studied.The experimental results show that the hot corrosion products of the six samples are similar,mainly Na_(2)Si_(2)O_(5),MoS_(2),TiCl_(2),Ti(SO_(4))_(2),and TiS.Due to the grains of the TB8 titanium alloy treated by 850℃solid solution-ECAP-520℃aging are obviously refined,the surface structure is the most smooth and dense,forming a continuous Al2O3protective film,and the surface defects are the least after corrosion.Its corrosion layer thickness is the lowest(102.3μm),only 36.5%-81.4%of that of other secondary processing titanium alloys.In addition,the corrosion kinetics curves of the six materials all follow parabolic laws,and the minimum corrosion weight gain of the samples after 850℃solutionECAP-520℃aging treatment is 0.7507 mg·mm^(-2),showing better hot corrosion resistance.

Corrosion evolution of high-temperature formed oxide film on pure Sn solder substrate

The evolution of morphology, composition, thickness and corrosion resistance of the oxide film on pure Sn solder substrate submitted to high-temperature aging in 150 °C dry atmosphere was investigated. The results indicate that high-temperature aging accelerates the dehydration of Sn(OH)_(4)in the pre-existing native oxide film to form SnO_(2)and facilitates the oxidation of fresh Sn substrate, resulting in the gradual increase in oxide film thickness and surface roughness with prolonging aging time. However, the corrosion resistance of the film initially is enhanced and then deteriorated with an extending aging time. Besides, the formation and evolution mechanisms of the oxide film with aging time were discussed.

High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants

High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.

Surface destructive mechanism on high-temperature ablation, supersonic-erosion, dreg-adherence and corrosion

The exhaust and flame from a supersonic airborne missile high-energy smoke-born engine (SAMHSE) may lead to high-temperature ablation, supersonic-erosion, dreg-adherence (HTASED) and corrosion on the launcher slide track, causing serious problems to the operation and decreasing the lifetime of the launcher. Therefore, it is imperative to study the destructive mechanism so as to guarantee the smooth operation and increase the lifetime of military equipments. Accordingly, HTASED and corrosion were systematically observed and analyzed with the emphasis placed on the mechanism investigations making use of a series evaluation tests, typical missile engine simulation tests, national military standard methods, scanning electron microscopy and electrochemical corrosion tests. It is found that the thermal impact of high-temperature flame and supersonic erosion of corrosive melting particle jet of the SAMHSE lead to surface defects of micro-cracks, denudation and corrosive residue. Some defects reach to metal base becoming to "corrosive channels". Repetitive HTASED may cause ablation-adhesion fatigue stress, which enhances the surface corrosion and destruction. HTASED and corrosion are related to the type of a SAMHSE fuel and experience of the launcher. Surface destruction is related to synergistic effects of the HTASED. The ablated and failed Al or steel surface is liable to electrochemical corrosion characterized by pitting in humid and salt-spray environment.

Hot corrosion behavior of Ni-xCr-6.8Al based alloys

The hot corrosion behaviors of as-cast and preoxidized Ni-xCr-6.8Al based alloys in the mixture of Na2SO4＋25% NaCl at 873 K were studied. The results show that the mass loss of Ni-xCr-6.8Al based alloys decreases with the increase of Cr content. Preoxidation improves the resistance to corrosion regardless of the concentration of Cr. The kinetics of as-cast Ni-12Cr-6.8Al and Ni-16Cr-6.8Al based alloys fits the parabolic law well, while that of the as-cast Ni-20Cr-6.8Al based alloy fits the power law. The kinetics of all the preoxidized samples obey the logarithmic law. The mechanism of the as-cast alloys can be well explained by the acid-base melting model. The behavior of the preoxidized alloys is found to be mainly determined by the properties of the oxide layer formed during the preoxidation to a large extend.

Hot corrosion characteristics of Ni-20Cr-18W superalloy in molten salt

The hot corrosion behavior of a Ni?20Cr?18W (mass fraction, %) superalloy in the mixture of 75%Na 2 SO 4?25%NaCl melts at 700 and 800 °C was studied. The results demonstrate that the alloy suffers from serious hot corrosion attack in the mixture molten salt. Meanwhile, the degradation of the substrate accelerates with increasing the corrosion temperature. The corrosion layer has an obvious duplex microstructure, and the Cr-depletion zone is detected obviously nearby the inner corrosion layer. The main corrosion products at 700 and 800 °C are almost the same and mainly include NiO, Cr2O3and Ni3S2, but a trace amount of NiCrO2 is detected at 800 °C for 20 h. The hot corrosion mechanism and formation mechanism of corrosion scales of the Ni?20Cr?18W superalloy in the molten salt are proposed.

Cyclic oxidation and hot corrosion of Al_2O_3 or Y_2O_3-dispersed low-temperature chromizing coating

Chromium coatings with and without Al_2O_3 or Y_2O_3 particles were prepared by chromizing the as-deposited Ni-film with and without Al_2O_3 or Y_2O_3 particles using a conventional pack-cementation method at 800 ℃. The cyclic oxidation at 800 ℃ and hot corrosion in molten 75% Na2SO4＋25% NaC1 at 800 ℃ of the three different chromizing coatings were investigated. The effects of Al_2O_3 or Y_2O_3 on the cyclic oxidation and hot corrosion behavior of the chromizing coatings were discussed. Microstructure results show that the codeposited Al_2O_3 or Y_2O_3 particles significantly retard the grain growth of the chromizing coating, which increases the cyclic oxidation and hot corrosion resistance of the chromizing coatings, due to the more rapid formation of purer and denser chromia scnle

Oxidation and hot corrosion of electrodeposited Ni-7Cr-4Al nanocomposite

A Ni-7Cr-4Al（mass fraction, %） nanocomposite was fabricated by co-electrodeposition of Ni with Cr（40 nm） and Al（100 nm） nanoparticles from a nickel sulfate bath, and its oxidation at 800 °C in air and hot corrosion under molten 75% Na2SO4 ＋ 25% Na Cl salts（mass fraction） at 750 °C were investigated. For comparison, Ni-11 Cr nanocomposite and Ni-film were also investigated in order to elucidate the effect of Cr nanoparticles. The results indicate that Cr and Al nanoparticles are dispersed in the electrodeposited nanocrystalline Ni grains（in size range of 20-60 nm）. Ni-7Cr-4Al nanocomposite exhibits a dramatically increased oxidation resistance compared with Ni-11 Cr nanocomposite and Ni-film due to the fast formation of alumina scale, which also improves its hot corrosion resistance under molten 75% Na2SO4 ＋ 25% Na Cl salts.

HOT CORROSION BEHAVIOR OF Ni-BASED SUPERALLOYS WITH HIGHER Cr CONTENTS -PART Ⅱ.MECHANISM OF HOT CORROSION BEHAVIOR

Based on the experimental results in the previous paper, the mechanism of the hot corrosion behavior of alloy system Ni-16Cr-gAl-2W- 1Mo-4Co-(0～4)Ti-f(0 ～ 4)Ta-(0～4)Nb (in at%) is investigated. In the Ti and Nb-rich corners, hot corrosion is controlled by the basic fluxing mechanism, and a dense and protective surface scale is formed which results in the better hot corrosion resistance for the alloys in these regions. While in the Ta-rich comer,the basic and acidic mechanisms function alternatively, which results in the catastrophic corrosion by forming the porous and non-protective scale, so the alloys in this region show poor hot corrosion resistance. In addition, the concept of 'effective chromium content' seemed to give a correct prediction of the hot corrosion resistance of such alloy systems.

HOT CORROSION BEHAVIOR OF Ni-BASED SUPERALLOY WITH HIGH Cr CONTENTS -PART 1.EXPERIMENTAL STUDY

A systematic study of the effects of Ti, Ta and Nb on the hot corrosion behavior of alloy system Ni-16Cr-gAl-2W-1Mo-4Co-(0～4)Ti-(0～4)Ta-(0～4)Nb (at%) was conducted. The results showed that, in certain compositional regions, the hot corrosion resistance in 75% NaiSO4+25%NaCl molten salt of the expermental alloys was similar to that of IN738LC alloy. The hot corrosion property balances with other properties, which provides the basis for selecting alloy compositions to develop single crystal superalloys of high performance hot corrosion resistance.

HOT CORROSION OF A PLASMA SPRAYED CoNiCrAlTaSiY COATING

Hot corrosion(HC) of the APS(atomospheric plasma spraying)CoNiCrAlTaSiY coating on a nickel-base superalloy GH864 has been studied. The effect of laser-treatment on hot corrosion resistance was also examined.It was shown that CoNiCrAlTaSiY coating had superior properties in resistance to hot corrosion due to the readiness of the formation of a protective Cr2O3 scale on the coating surface.A model for the mechanism of hot corrosion of this coating has been suggested. Hot corrosion resistance of this coating was significantly increased by the laser treatment simply because the surface of the as sprayed coating was densified by the high power laser beam.

Study on the corrosion behavior of 316H stainless steel in molten NaCl–KCl–MgCl_(2) salts with and without purification

The corrosion behavior of 316H stainless steel(SS)in the impure and purified Na Cl–KCl–Mg Cl_(2) salt was investigated at700°C.Results indicate that the main deleterious impurity induced corrosion in the impure salt was the absorbed moisture,present in the form of Mg Cl_(2)·6H_(2)O.316H SS occurred severe intergranular corrosion with a corrosion depth of 130μm for1000 h in the impure Na Cl–KCl–Mg Cl_(2) salt.In contrast,the purification treatment of molten chloride salt by the dissolved Mg metal can remove the absorbed moisture,and the corresponding reactions were also discussed.As a result,the corrosiveness of Na Cl–KCl–Mg Cl_(2) salt is reduced significantly.316H SS occurred slight uniform corrosion with a depth of less than 5μm for 3000 h in the purified Na Cl–KCl–Mg Cl_(2) salt.

Growth and corrosion behavior of rare earth film on hot-dip galvanized steel

Hot-dip galvanized(HDG)steel sheets were treated for 30 s?24 h by the rare earth aqueous solution containing 20 g/L Ce(NO3)3·6H2O,and the growth behavior and corrosion resistance of the rare earth film were investigated by SEM,EDS,AES and NSS.The results reveal that the rare earth film becomes thick while the mass gain of the samples does not distinctly change due to the zinc dissolution with the increase of treatment time.The film grows up more quickly and is apt to cracking in the vicinity of zinc grain boundaries,and eventually the film partly warps and flakes off with increasing film thickness.The NSS results show that the corrosion resistance of the film is dominated by both the film thickness and the cracks.With increasing treatment time,the corrosion resistance of the film increases within 1 h due to the increased film thickness and decreases after 1 h because the cracking and flaking off gradually become dominant factor.

STUDY OF HOT CORROSION RESISTANCE MECHANISMS OF ARC SPRAYING COATINGS

According to the working condition of boiler tubes of power station, hot corrosion tests were carried out at two temperatures (650℃ and 800℃) to simulate the environment of coal fired boiler. The hot corrosion resistance and mechanism of three arc spraying coatings (SL30, 45CT and FeCrAl) have been studied. The result showed that coating SL30 and 45CT have a better protection ability against hot corrosion. It indicated that a protective Cr 2O 3 scale formed on the surface of coating SL30 and coating 45CT.

CORROSION RESISTANCE OF HOT DIP GALVANIZED STEEL PRETREATED WITH BIS-FUNCTIONAL SILANES MODIFIED WITH NANOALUMINA

The corrosion behavior of hot dip galvanized steel pretrvated with bis-[triethoxysilylpropyl] tetrasulfide （BTESPT） modified with alumina particles was studied. The corrosion resistance of the passiving films was evaluated by Tafel polarization curve and electrochemical impedance spectroscopy. The films formed on the galvanized steel substrate were characterized by Fourier transform infrared spectroscopy and energy dispersive X-ray spectrometry. The surface morphology of the treated hot dip galvanized steel samples was observed by Field Emission Scanning Electron Microscope. The results show that the pretrvatments on the basis of silane films modified with nanoalumina particles have reduced both anodic and cathodic current densities, and increased total impedance in the measured frequency, consequently, improving corrosion protection for hot dip galvanized steel during immersion in NaCl solutions compared to chromate films and silane films.

Effect of Yttrium on Microstructure and Hot Corrosion Preformance of Laser Clad Co-Based Alloy

The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.

Effect of Co on oxidation and hot corrosion behavior of two nickel-based superalloys under Na_(2)SO_(4)-NaCl at 900℃

Nickel-based superalloys with and without Co by partial replacement of W were prepared using double vacuum melting.A comparison of the oxidation in air and hot corrosion behaviors under molten 75 wt.%Na2 SO4+25 wt.%NaCl at 900℃were systematically investigated.The results showed that partial replacement of W with Co promoted the formation of chromia scale and consequently decreased the oxidation rate.Besides,the addition of Co also retarded the internal oxidation/nitridation of Al and consequently promoted the growth of Al_(2) O3 scale,which further decreased the scaling rate and improved the adhesion of scale.Moreover,the addition of Co also further improved the hot corrosion resistance under molten Na2 SO4-NaCl salts.