The severe local corrosion behavior was triggered by the Cr-depleted zone presented in stainless steel, entailing the enormous economic losses and casualties. Resultantly, how to understand the phenomena of Cr-depleted zone systematically was arising topic. This paper presents a review of two kinds of local corrosion emerged commonly in stainless steel and the effect of Cr-depleted zone on the local corrosion from three aspects, including the location where Cr-depleted zone comes up, the method of studying Cr-depleted zone and the existing problems currently. The results show that the characteristics of smaller size, higher Cr content or distributing along the grain boundary possessed by inclusions, precipitates or secondary phases may be favorable to the occurrence of Cr-depleted zone. If the Cr-depleted zone around the secondary phases be eliminated by adjusting the compositions of stainless steel in smelting process and process parameters in subsequently rolling and heat treatment or field processing, the local corrosion resistance of stainless steel should be greatly enhanced.

The doping effect of single, binary and ternary rare earth oxides respectively on the hot corrosion resistance of ZrO₂ ceramic coatings in molten Na₂SO₄+NaVO₃ salts was systematically summarized and discussed in this paper. The hot corrosion behavior of the top ceramic coating, thermal grown oxide scale and bond coat of the TBCs in molten Na₂SO₄+NaVO₃ and the relevant hot corrosion mechanisms were summarized. The research direction of improving the hot corrosion resistance of ZrO₂ ceramic coating against the Na₂SO₄+NaVO₃ salts was suggested, too.

The present research on technologies for intelligent self-healing coatings, including liquid core/hollow fiber technology, microcapsule self-healing technology, reversible reaction technology as well as shape memory technology, is discussed. Based on that, the different principle and key issue of self-healing technologies were pointed out. Synergistical combination of various self-healing techniques would become the direction of further research.

In order to improve high temperature oxidation resistance of γ-TiAl based alloys, TiAlSiN coatings were deposited on two alloys of Ti-46Al-2.5V-1Cr-0.3Ni and Ti-48Al-2Cr-2Nb using arc ion plating, while the cyclic oxidation behavior at 800 ℃ was comparatively assessed for the bare and coated alloys. The tested samples were characterized by means of scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). After cyclic oxidation at 800 ℃ for 300 h, the formed oxide scales composed of TiO₂ and α-Al₂O₃ on the bare Ti-48Al-2Cr-2Nb and Ti-46Al-2.5V-1Cr-0.3Ni alloys. The oxide scale formed on the Ti-46Al-2.5V-1Cr-0.3Ni alloy was very thick and spalled seriously, and that on the Ti-48Al-2Cr-2Nb alloy was thinner and spalled slightly. Application of the TiAlSiN coatings with different Al and Si content significantly decreased the oxidation rate of the bare alloy. After oxidation at 800 ℃ for 300 h, the oxide scales formed the Ti_0.5Al_0.4Si_0.1N and Ti_0.5Al_0.45Si_0.05N coatings were very thin and dense, while that on the Ti_0.6Al_0.3Si_0.1N was thicker. The oxide scales formed on the coatings also composed of TiO₂ and α-Al₂O₃. After oxidation the degradation of Ti_0.5Al_0.4Si_0.1N and Ti_0.5Al_0.45Si_0.05N coatings was not apparent, however, the consumption of the Ti_0.6Al_0.3Si_0.1N coating was obvious. Interdiffusion between the coatings and the γ-TiAl based alloys was very limited. So it can be concluded that the oxidation resistance of the Ti_0.5Al_0.4Si_0.1N and Ti_0.5Al_0.45Si_0.05N coatings is superior to that of the Ti_0.6Al_0.3Si_0.1N coating, and the application of the Ti_0.5Al_0.4Si_0.1N and Ti_0.5Al_0.45Si_0.05N coatings can significantly improve the oxidation resistance of the γ-TiAl-based alloys at 800 ℃.

Nb₂N coating was deposited onto TC4 (Ti-6Al-4V) substrates via a double cathode glow discharge plasma method. The microstructure of the coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The adhesive property of Nb₂N coating to the substrate was assessed by scratch test. While the electrochemical behavior in 3.5% (mass fraction) NaCl solution of the coating was investigated with electrochemical techniques, such as open circuit potential (OCP) measurement, potentiodynamic polarization and EIS. Result shows that the as-deposited coating of 21 μm in thickness is dense with a homogeneous microstructure without obvious voids or micro-crack. Compared with TC4 matrix, the open-circuit potential of Nb₂N coating can reach a higher steady-state value within a shorter time interval, in other words, the coating presents higher corrosion potential (E_corr) and lower corrosion current. The data of EIS show that the Nb₂N coating shows a single capacitive reactance arc with higher capacitive reactance, larger phase angle maximum, as well as wider phase angle plateau, in the contrary to those of the bare TC4 Ti-alloy.

Corrosion behavior of Q345q bridge steel was studied by dry-wet alternating accelerated corrosion test method with three designed media, which aim to simulate three environmental conditions commonly encountered in the Northwest China, namely deicing-, industrial- and industrial with deicing-conditions respectively. While the corrosion kinetics curves of Q345q bridge steel were measured by weight loss method. The morphology, microstructure and phase composition, as well as the electrochemical properties of the rust scales of Q345q bridge steel corroded for different time were assessed by means of SEM, XRD and electrochemical workstation. Results show that although the corrosion rate is small in the deicing salt medium within 480 h, the corrosion product contains unstable and soluble compounds such as β-FeOOH and chloride, which results in loose rust scale, the corrosion current of the rust scale increases with time, thus which is poor in protectiveness. The corrosion rate in the sodium bisulfite medium is higher, but with the increase of corrosion time, the corrosion rate decreases rapidly, the anode corrosion current of the rust scale decreases, therewith, the rust scale is protective. In the mixed medium, the corrosion behavior is a coupling effect. Due to the existence of corrosion products such as chlorides, the compactness of the rust scale is poor, but which exhibits protectiveness to a certain degree in comparison with that in the deicing salt medium.

The effect of the existed oxide scales on the initial corrosion behavior of SPHC hot rolled steels was assessed via field exposure in tropical marine atmosphere with features of high temperature, humidity, salinity and strong irradiation in a test site at Zhanjiang district for 15, 30, 90 and 180 d. After exposure test, the steel samples were then characterized by means of XRD and SEM with EDS, while their polarization curves were also measured in 3.5% (mass fraction) NaCl solution by Autolab. The results show that the existed oxide scales on the rolled steel consist mainly of Fe₃O₄, which can obviously slow down the initial corrosive rate of the steel. As the corrosion progresses, the oxide scales will gradually transform into the rust layers and corrosion products are constantly generated, the corrosion behavior of the steel samples with and without the existed oxide scales tend gradually to be consistent, and the difference of their corrosion rates turn to be small. In sum, the existed oxide scales can slow down the initial corrosion rate of the rolled steel without changing the composition of corrosion products at all.

The acceleration effect of the concentration of pitting corrosion products on the metastable pitting initiation and the stable pitting growth of 304 stainless steel was studied by changing the concentration of pitting products on the surface of 304 stainless steel compulsively. There are three characteristic indexes of metastable pitting initiation process with the decreasing concentration of pitting products, namely the increase of pitting incubation period, the reduce of average peak current and average peak width, and the decrease of pits number. The volume and the transverse growth rate of pits decreases. With the decreasing ratio of pits width to depth and the growth of pits, the concentration of pitting products in pits increases again and the corrosion rate increases. The concentration of pitting products is certainly the key factor for metastable pitting initiation and steady pitting growth.

Plates of ultra-low carbon austenitic stainless steel 304L were welded by manual arc welding and argon arc welding respectively with 316L stainless steel as filler. The welded joints were characterized by means of electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Whilst the welded joints were chemically passivated in 10% and 20% hydrogen peroxide solutions respectively, then their corrosion behavior was examined via electrochemical means and X-ray photoelectron spectroscopy (XPS). Results showed that the pitting potential of the weld zone was the highest due to the incorporation of 316L stainless steel welding wire. The corrosion resistance of the matrix was relatively good because its inherent microstructure of relatively uniform and small grains. The heat affected zone has coarse grains and/or mixed grain structure, so that its pitting potential was the lowest, correspondingly its corrosion resistance was the worst. In a word, the welded joints of austenitic stainless steel 304L had the best corrosion resistance, when they were passivated in 10% hydrogen peroxide solution for 15 min.

The erosion wear performance of Cr30A high chromium cast iron in a simulated circulating pump operation condition with slurry related to wet desulfuration process for thermal power plant, was investigated by means of mass loss test and microstructure examination. The result shows that with the increasing rotation speed, the mass loss of the steel significantly increases. The wear component is the main fraction of the total amount of corrosion-wear. When the rotation speed is 400 r/min, there is no oxide scale on the surface of the test steel sample. The component of interaction for corrosion and wear may be accounted for 48.73% of the total corrosion-wear, implying that there existed synergistic effect of the two. When the rotation speed is 1200 r/min, there is a dense oxide scale on the steel surface, the component of corrosion-wear interaction is negative and it seems that the two processes are antagonistic. The interaction between corrosion and wear is an important factor affecting the wear resistance of materials.

The effect of two-stage ageing heat treatment on the mechanical performance and sensitivity to hydrogen embrittlement for 7075 Al-alloy was assessed by means of tensile tester, hardness tester and cross section morphology observation, as well as cathodic hydrogen permeability method, hydrogen meter, EDS and SEM. The results show that the double peak phenomenon emerged for the two-stage ageing heat-treated 7050 Al-alloy, and the elongation decreases basically with the ageing process, while the peak positions fluctuate to certain extend. The hydrogen content increases with the extension of hydrogen charging time. From the perspective of the same hydrogen charging time, the hydrogen content is the lowest at the peak of the second ageing, however the alloy presented strong toughness. Scanning electron microscopy (SEM) revealed that the improvement of the second peak strength and hardness is due to the increased amount of η', while the plastic toughness increase is mainly ascribed to that η' phase particles evenly dispersed in the matrix, leading to the uniformity in deformation.