不锈钢复合板热疲劳性能分析

利用冷热疲劳试验机模拟分析了冷热循环对不锈钢复合板热疲劳性能的影响,并采用扫描电镜、电子探针和电子背散射衍射仪对热疲劳试样V形缺口及裂纹区域的形貌和成分进行了深入分析。结果表明,不锈钢复合板热疲劳试样经 20~550 ℃ 7 500次冷热循环后,结合界面处V形缺口区出现微裂纹,且微裂纹起裂于V形缺口尖端基层侧。随着冷热循环的继续进行,微裂纹向基层内扩展,但并非沿着结合界面处扩展,而是沿着基层侧扩展。此外,热疲劳裂纹的起裂和扩展与氧化和应力作用有关,微裂纹起裂于热疲劳试样 V 形缺口区域基层侧表层局部氧化孔洞,并在冷热循环的应力作用下向基层内扩展,同时加剧氧化。随着冷热循环的继续进行,晶界氧化逐渐加剧,导致微裂纹扩展成更为明显的裂纹。     

Importance of initial surface film in the degradation of stainless steels by atmospheric exposure

The surface compositions of stainless steels types 304, 316, 430, and 444 combined with four types of surface finishes, 2B finish, hairline polishing, mirror polishing, and bright annealing, were measured by ICP-AES, EPMA, and XPS before exposure. The surface finish that most enriched the chromic species in the surface film was mirror polishing, followed by bright annealing, 2B finish, and hairline polishing. The order of corrosion-resistance was type 444, type 316, type 304, and type 430. The surface compositions were correlated with the rating number and pitting depth after exposure to atmospheric environments. The rating number had a high positive correlation with the concentration of Cr in the surface film, and had a slight correlation with the near-surface composition measured by EPMA at 12 kV, but did not show any correlation with bulk composition within the composition range covered in the present work. This same trend was observed for pitting depth. It was concluded that the cationic concentration of Cr in the surface film before atmospheric exposure is the prime factor in controlling the resistance of stainless steels to atmospheric corrosion.     

Preparation of self-healing protective films on a zinc electrode treated in a cerium(III) nitrate solution and modified with sodium phosphate and cerium(III) nitrate

Self-healing protective films were prepared on a zinc electrode previously treated in a Ce(NO₃)₃ solution by modification with Na₃PO₄ and Ce(NO₃)₃. The protective and self-healing abilities of the films were examined by polarization measurements and observation of pit formation after the electrode was scratched with a knife-edge crosswise and immersed in oxygenated 0.5 M NaCl at 30 °C for many hours. Mechanisms of the protective and self-healing activities were discussed using X-ray photoelectron spectroscopy and electron-probe microanalysis. The protective and self-healing abilities of the films prepared on the zinc electrode by treatment in the Ce(NO₃)₃ solution and modification with Na₃PO₄ plus Ca(NO₃)₂, Mg(NO₃)₂, Zn(NO₃)₂ or Ce(NO₃)₃ were summarized.     

High temperature corrosion mechanisms and effect of alloying elements for materials used in waste incineration environment

Corrosion products on two typical materials, SA213-T12 steel and alloy 625 exposed to the actual combustion gas, were analyzed in addition to laboratory tests for penetration of corrosive matter. It has been clarified that corrosion products of oxides containing a little chlorides and sulphides show lamellar structures and that at the alloy-scale interface, chlorination, sulphidation, and oxidation occur under a low P_O2-high P_Cl2 condition. The formation of scale structures and the effect of corrosion-resistant alloying elements can be explained according to the stability tendencies of metals, chlorides, and oxides in the M-Cl-O equilibrium diagrams. The severity of corrosion environments at the interface is influenced by the penetration extent of corrosive matters through deposits and scales, and the protective effects of oxide films derived from alloying elements play an important role in preventing the corrosion. On the other hand, it has been shown that thermal fluctuation characterized in this kind of environment makes the lamellar scale structures and sometimes breaks and peels off the scale, and thus accelerates the corrosion. On the basis of the above mentioned knowledge, a new corrosion model is presented.     

Determination of phase equilibria in the Ni-Ta-Zr system at 1223 K

The phase equilibrium relations of the ternary Ni-Ta-Zr system at 1223 K were investigated by means of diffusion triple and electron probe microanalysis (EPMA) techniques. Two ternary compounds were found and a series of tie lines and tie triangles have been determined. The maximum solubility of Ta in NiZr2 is about 13.5% (atom fraction). The corresponding tentative isothermal section at this temperature was constructed based on current experimental information.     

Effects of electrical discharge surface modification of superalloy Haynes 230 with aluminum and molybdenum on oxidation behavior

The effects of the electrical discharge alloying (EDA) process on improving the high temperature oxidation resistance of the Ni-based superalloy Haynes 230 have been investigated. The 85 at.% Al and 15 at.% Mo composite electrode provided the surface alloying materials. An Al-rich layer is produced on the surface of the EDA specimen alloyed with positive electrode polarity, whereas, many discontinuous piled layers are attached to the surface of the EDA superalloy when negative electrode polarity is selected. The oxidation resistance of the specimen alloyed with positive electrode polarity is better than that of the unalloyed superalloy, and the effective temperature of oxidation resistance of the alloyed layer can be achieved to 1100 °C. Conversely, the oxidation resistance of the other EDA specimen alloyed with negative electrode polarity is even worse than that of the unalloyed superalloy.     

Influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank

This work investigated the influence of Sn and Mo on corrosion behavior of ferrite-pearlite steel in the simulated bottom plate environment of cargo oil tank. The results indicate that the corrosion rate of three ferrite-pearlite steels increased with extending the immersion time due to the continuous accumulation of the residual Fe_3C. However, the addition of Sn or the combined addition of Sn and Mo could reduce the corrosion rate of Sn containing steel and Sn-Mo containing steel to 37.5% and 20% of that of carbon steel, respectively. Moreover, the cathodic reaction of Sn containing steel and Sn-Mo containing steel was always controlled by the charge transfer step during the whole immersion test, while that of carbon steel was gradually transformed into the diffusion-controlled process. These results were mainly related with the deposition of metallic Sn and Mo on the steel surface. The metallic Sn and Mo with uniform distribution restrained the galvanic effect through suppressing both the anodic dissolution of ferrite and cathodic hydrogen evolution reaction on the residual Fe_3C.     

Kinetics of reactive diffusion between Au and Sn during annealing at solid-state temperatures

The reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures using Sn/Au/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were annealed at temperatures of T = 393 and 473 K for various times in an oil bath with silicone oil. After annealing, compound layers composed of AuSn₄, AuSn₂ and AuSn were recognized to form at the Au/Sn interface. The thickness of the AuSn₄ layer is about six and four times greater than those of the AuSn₂ and AuSn layers at T = 393 and 473 K, respectively. The ratio of the thicknesses of the compound layers is kept constant independently of the annealing time. The total thickness l of the compound layers is described as a function of the annealing time t by the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent n is nearly equal to 1/2 at T = 393 K but takes a value between 1/4 and 1/2 at T = 473 K. Such an intermediate value of n at T = 473 K indicates that the grain boundary diffusion contributes to the reactive diffusion and the grain growth occurs at certain rates. As the annealing temperature decreases, the contribution of the grain boundary diffusion should become more remarkable, but the grain growth will slow down. Consequently, n becomes close to 1/2 at T = 393 K. According to the constancy of the ratio of the thicknesses, it is concluded that the same rate-controlling process works in the AuSn₄, AuSn₂ and AuSn layers at a constant annealing temperature.     

Lateral sensitivity in electron probe microanalysis studied by Monte Carlo simulations involving fluorescence enhancements

In electron probe microanalysis, secondary fluorescence can occur leading to an increase of the volume analysed, degrading the lateral resolution of this technique. An adequate knowledge of the interaction volumes from where the different signals of interest are detected is determinant to estimate the minimum size of the zone that can be characterized. In this work, the size of the signal source volume is surveyed for a wide set of samples at different beam energies. To this aim, the PENELOPE software package was chosen to run Monte Carlo simulations for several experimental situations in order to produce the various lateral radiation distributions of interest. A comparison between the interaction volumes of the different signals was performed by taking into account the different fluorescence enhancement possibilities. An unexpected behaviour was found in the particular cases of aluminium and alumina, where the secondary photons signal exhibits a decreasing trend up to certain beam energy (～17 keV); this implies that lower beam energies may degrade the lateral resolution of the technique in these materials.     

Effects of strain on the corrosion behaviour of X80 steel

The effects of strain on the corrosion behaviour of X80 steel in 0.62 M NaCl aqueous solution were investigated in the present paper. An increase in strain causes the corrosion resistance of the specimen to present a down and up trend, with the lowest point at about 1.0 × 10⁻³. When the strain increases further, corrosion resistance decreases again until the strain reaches 5.5 × 10⁻³. After that, corrosion resistance improves with the increase in strain and tends to be relatively stable. The variation of corrosion resistance has much to do with the surface activity and behaviour of dislocation on the surface of the specimen.