The current situation of study on erosion-corrosion mechanism and the influence of different environmental factors and alloy properties on erosion-corrosion is reviewed in this paper. The erosion-corrosion is mainly composed of two parts: erosion wear and electrochemical corrosion, of which the contribution to the total erosion-corrosion rate may depend upon the environmental factors. To protect metallic materials from erosion-corrosion the following measures may be effective: i.e. proper selection and addition of alloying elements, proper heat treatment and applied surface coatings as well. Meanwhile, the paper discusses the development of erosion-corrosion research in the future.
A molten salt reactor (MSR) is a kind of nuclear fission reactors using a molten salt mixture as the primary coolant and fuel. As one of the generation IV reactors MSR has received an increasing attention. The corrosion of materials is one of the technical obstacles to the development of MSR, and thus has been investigated extensively. Up to now, great progresses have been achieved<br>in the study of the corrosion of materials in MSR environments. This paper presents a comprehensive review of the progress in research work on the corrosion of materials for MSR.
Oxidation of Super 304H steel after two different surface preparations was studied in steam of pure water at 700~900 ℃. The two preparations are grinding with emery paper down to 1000 grit and polishing with diamond paste down to 1 μm. Oxidation kinetics was measured continuously for 24 h by thermo gravimetric analyzer (TGA) connected with a steam generator. After oxidation, the surface and cross sectional morphology, the chemical composition and the phase constituent of all oxide scales were examined by means of scanning electron microscopy (SEM), X-ray energy dispersive analysis (EDS), and X-ray diffraction (XRD) respectively. The results showed that oxidation kinetics of Super 304H steel in steam followed an near-parabolic rate law, however, parabolic rate constants were significantly dependent on the exposure temperature and surface state. As a consequence of rising temperature or polishing the steel surface, the parabolic rate constants could remarkably be increased and the formation of iron oxide nodules as well as the internal oxidation beneath them could be facilitated for the oxidation of Super 304H steel in steam.
The effect of frequency of the applied alternating current (AC) on corrosion behavior of X80 steel in an artificial liquid aiming to simulate the acid soil medium of Yingtan area was studied by means of electrochemical measurement, immersion test and surface characterization technique. The results showed that with the increasing AC frequency, the corrosion rate and the corrosion degree of X80 steel decreased gradually. The corrosion product of X80 steel under the applied AC was loose with many cracks thus could not offer proper protection to the substrate. The offset of corrosion potential of X80 steel decreased as the AC frequency increases. With the increase of AC frequency, the oscillation amplitude of anode and cathode polarization curve gradually receded. In the range of the test frequency, the applied AC to X80 steel not only induced the increase of the current density for both anode and cathode, but also the change of cathode reaction from mixing control to activation control.
With an autoclave the environment of submarine gathering system was simulated, then in which the influence of concentration of H2S and pH value on the corrosion behavior of weld joints of X65 pipeline steel was investigated by electrochemical techniques, immersion test, SEM and XRD analysis technique. The results show that the free corrosion potential of different portion of the X65 pipeline steel weld joint exhibited a tendency of decrease, but the corrosion density of increase, corresponding to the following order as: the weld seam, the heat affected zone and the base material. The average corrosion rate of the steel weld joints is in the range of 0.1~0.25 mm/a, the increase of the concentration of H2S and the reduction of the pH value can both lead to the increase of corrosion rate. The corrosion mode of weld seam of X65 steel is mainly the uniform corrosion in the simulated environment, and the corrosion of weld seam is slighter than that of the heat affected zone.
The resistance to hydrogen induced corrosion cracking (HIC) of the weld joint of X100 pipeline steel prepared by gas shielding metal arc welding was studied. OM and SEM with EDS were adopted to characterize the microstructure of the X100 weld joint and the non-metallic inclusions. The experimental results presented that the X100 weld joint exhibited a microstructure consisted of acicular ferrite, bainite and M/A islets, MnS, Al-oxide, Si-oxide and Al-Mg-O, Ca-Al-O-S mixed inclusions were also found in the weld joint. The weld joint had a high susceptibility to HIC due to the large amounts of non-metallic inclusions, furthermore, the interfaces and stress between the matrix and brittle M/A islets as well as inclusions might play an important role in the initiation of HIC cracks and then the cracks propagated along the grain boundaries of the coarse bainite.
The corrosion characteristics of 15CrMoG steel a supercritical unit water-wall tube material in two kinds of waters were studied by means of metallography, SEM/EDS, and XRD etc. The two waters aim to simulate the boiler water after the all-volatile treatment (reduction) and the oxygenated treatment, i.e. all-volative treatment (reduction) (ATV(R)) water and oxygenated treatment (OT) water respectively. The results showed that a much uniform oxide scale with much uniform particles size distribution grew on the steel surface under the AVT(R) condition rather than that under OT condition. The corrosion degree of the steel increased in the OT water with addition of Cl- or Cl-/SO42- with increasing ion concentrations. At the same ion concentration, the corrosion of the steel under the simulated OT condition was more severe than that under AVT(R) condition and the Cl-/SO42- was more corrosive than Cl- under the same condition. Due to autocatalytic effect of pitting corrosion, serious local corrosion occurred on the steel in the simulated AVT(R) and OT waters. It is noted that Cl- was not detected but an obvious S content was detected by EDS in the pits on the steel surface under the two conditions with different ion in waters.
The effect of Zn addition on the composition of oxide scales formed on 316L stainless steel has been studied in high-temperature and high pressured waters, which aim to simulate the primary loop water environment of pressurized water reactor (PWR). Then, the formed oxide scales on the steel are analyzed by X-ray photoelectron spectroscopy (XPS). The results show that after soaked in water with 10 μg/kg Zn addition at 320 ℃ for 1000 h, compact oxide scales formed on the steel, which consist mainly of (Zn, Fe, Ni)(Cr, Fe)2O4, with an inner portion rich in Cr. However, the Cr rich portion extends gradually outwards to lead the whole oxide scale to become the same with the increasing exposed time.
A method of Pt deposition on a pre-oxidized 316LN steel surface was developed in an artificial environment, which aims to simulate hydrogenated water chemistry (HWC) condition of the primary loop of PWR and then its effect on the electrochemical behavior in the same environment of the structural material 316LN steel was studied by SEM, XPS, XRD, ICP-AES and linear dynamic polarization etc. At first, all the test steel samples were exposed in 320 ℃water with less than 100 μg·kg-1 oxygen for 400 h in order to form an oxide scale on the steel surface. Next, the pre-oxidized steel were immersed for 48 h at 150 ℃ to the water with addition of Na2Pt(OH)6 to deposit Pt (0, 10, 50 and 100 μg·kg-1, respectively) on the pre-oxidized steel. Finally, the samples were exposed to 300 ℃ high temperature water with <100 μg·kg-1 oxygen, 200 μg·kg-1 hydrogen while measuring the linear polarization curve of the treated steel. The result showed that a two layered oxide scale with the Ni-rich outer layer and Cr-rich inner layer were form on the steel, which is similar to the oxide scale formed during PWR service; the amount of the deposited Pt on the pre-oxidized steel was from 4.37 to 7.37 μg·cm-2 while the water containing Pt from 10 to 100 μg·kg-1. With the increase of the Pt concentration of the treated solutions, Ecorr decreased sharply while current density slightly changed, which revealed that the pre-oxidized steel samples with Pt deposit exhibit a better corrosion resistance.
Superhydrophobic complex coatings of mesoporous carbon/silica on stainless steel were prepared by a sol-gel spin cast method. The morphologies, anticorrosion property and hydrophobicity of the coatings were characterizd by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM), electrochemical test technique-Tafel curve and electrochemical impedance spectroscopy, as well as water contact angle measurement (CA) respectively. The coatings exhibited varied surface morphologies with bump-like and nipple-like protrusions on the stainless steel substrate. The coatings had a high water contact angle larger than 163°, indicating its strong hydrophobicity. The corrosion current density of the superhydrophobic complex coating coated steel was 8 order of magnitude lower than the bare steel, while its charge transfer resistance (Rct) was 6 order of magnitude higher as well, implying an excellent corrosion protectiveness. Besides, an electrochemical equivalent circuit was proposed to interpret the relevant anti-corrosion mechanism for the superhydrophobic coatings.
在钢铁基体上制备化学镀Ni-P镀层后,分别采用γ-氨丙基三乙氧基硅烷 (3-APTS),硬脂酸和3-APTS/硬脂酸对镀层进行防腐蚀后处理,利用点滴法、贴滤纸法、接触角测量、盐水浸渍实验法和电化学测试研究了镀层耐蚀性的变化,比较了各工艺的后处理效果。结果表明：3种后处理工艺都能提高化学镀Ni-P镀层的抗氧化性和耐蚀性,经3-APTS/硬脂酸复合处理后的镀层耐蚀性要优于3-APTS和硬脂酸的单一处理,镀层外观都没有明显变化。同时对缓蚀机理进行了分析。
The inhibition effect of triethyl phosphate (TEP) and the synergistic effect of TEP and rare earth Ce4+ on the corrosion of copper in 0.5 mol/L hydrochloric acid solution were studied by electrochemical impedance spectra and potentiodynamic polarization curve. The result reveals that the inhibition efficiency of the mixed inhibitor increases with the increase of the concentration of Ce4+ until the critical concentration is reached when TEP concentration remains unchanged. When Ce4+ concentration remains unchanged, the inhibition efficiency increased with the increase of the concentration of TEP, reaching 80.6% at 1 mmol/L Ce4+ and 58.7 mmol/L TEP.
采用微弧氧化-碱热处理在纯Ti表面制备了含有羟基磷灰石 (HA) 的仿生陶瓷膜。利用SEM,XRD和电化学工作站等手段研究了膜层的形貌、物相及其耐蚀性。结果表明：在乙酸钙-磷酸二氢钙电解液体系中微弧氧化 (MAO),纯Ti表面形成一层含Ca和P的TiO2多孔陶瓷膜。经水热处理后,膜层表面的孔洞变小、致密性增加,膜层中还出现了鳞状、层片状以及针棒状的HA。在Hank's模拟体液中,MAO膜和微弧氧化-碱热处理 (MAOAH) 膜均表现出较好的耐蚀性。MAO膜经模拟体液腐蚀后,形成了缺钙型HA (Ca8.86(PO4)6(H2O2)2) 和CaTiO3；而模拟体液中的阴离子与MAOAH膜层的氧化物作用使膜层孔洞直径和深度增加。
A new idea was proposed in the present work, based on the principle for the balance of stress field strength, to judge qualitatively the surface residual stress trends, and it was verified by the experimental results in literatures. For the surface-strengthened sample with a surface residual compressive stress field, the proposed theory shows that, the cumulative stress relaxation rate leads to the sharp decrease in the rest of the residual compressive stress field intensity and residual tensile stress field intensity, the surface residual stress measurements within a certain depth range are slightly greater than the actual values, the depth of surface residual compressive stress field is larger than that of the actual residual compressive stress field.
Atmospheric corrosion behavior of U-bended aluminum alloy plates of LY12 and LC4 with/without Al cladding was investigated by field exposure in salt lake environment in Western China for 2 a. Then their surface and cross-sectional morphology was examined by metalloscope and SEM. The results showed that the corrosion behavior of the Al clad alloys LY12 and LC4 was mainly pitting corrosion within the cladding and no pits penertrating the cladding could be observed after 2 a exposure. For the bare alloys LY12 and LC4, severe stress corrosion cracking (SCC) was observed in the test. Both tensile- and compressive-stress could lead to SCC in for LY12, while only tensile stress could induce SCC for LC4 during the exposure. Exfoliation corrosion (EFC) of LY12 and LC4 occurred under compressive stress but not under tensile stress.
