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The effect of boron (B) on stress corrosion resistance of S31254 in the presence of residual stresses has been studied. The microstructure and corrosion resistance of S31254 containing B at different levels of cold deformation are analyzed in this study. In the results, it is shown that B favors the improvement of deformation uniformity of S31254. The grain boundary (GB) and slip bands have better corrosion resistance at 5% deformation, and the overall corrosion resistance is better than that of the undeformed state, with smaller passivation current density and narrower width of GB corrosion grooves, especially for the 40B samples. At 30% deformation, the overall corrosion resistance of 40B S31254 is better than 0B due to improved deformation uniformity. [ABSTRACT FROM AUTHOR]

The occupation tendencies of Cr, Cu, Mo, Nb, Ni, Ti and V in Fcc-Fe stacking fault containing vacancy were studied by the first principles calculations. The effects of C, N and Nb, Ti co-segregation in the region of vacancy is discussed. The results are as follows: the substitutional elements Cr, Cu, Mo, Ni, Nb, Ti and interstitial elements C, N have no segregation tendency at the stacking fault of Fcc-Fe (111) plane. When the stacking fault contains vacancy, the above elements have the tendency to segregate around the vacancy, and C, N tend to occupy vacancy and their segregation tendency is the stronger than that of substitutional elements. C, N are easily co-segregated with Nb, Ti in the region of vacancy. It is difficult for Mo to aggregate around the carbonitride precipitates, which is conducive to the use of nano-scale carbide and nitride precipitation strengthening in high Mo austenitic steel, and simultaneously improves corrosion resistance. Nb and Ti tend to aggregate around the vacancy where occupied by C, N. [ABSTRACT FROM AUTHOR]

In order to reduce the segregation of Cr and Mo and inhibit the precipitates, we added a small amount of B and Ce to traditional S31254 steel. Using an air-cooling and low-temperature diffusion treatment, the purpose was to control B and Ce at the grain boundary. The heat-treatment process could prompt co-segregation of B, precipitate-forming elements, and Ce at the grain boundary at 950 °C. After aging at 950 °C for different amounts of time, the diffusion treatment had an obvious inhibitory effect on the precipitates that caused them to become discontinuous, fine, and serrated. The B-containing serrated precipitates were only rich in Mo, while Cr was homogeneously distributed in the probed volume. A uniform distribution of Cr reduced the Cr-depleted zone in the area adjacent to the phase interface. Ce was observed to be segregated at the grain boundary. This showed that Ce could inhibit the formation of precipitates at the grain boundary. The serrated precipitates had an obvious resistance to intergranular corrosion. [ABSTRACT FROM AUTHOR]

S is a common corrosion medium for austenitic stainless steels. The severe intergranular fracture of austenitic stainless steels occurs in sulfur environments. In this paper, the permeation of S at different atomic positions for three symmetric tilt grain boundary types, i.e., Σ5(210), Σ5(310), and Σ9(114) have been computed using first-principles calculations. S has the strongest segregation tendency in the Σ5(210) grain boundary. A high content of S at the grain boundary indicates harm to the grain boundary. Sulfur segregation in the grain boundaries can weaken the strength of the metallic bond. When Mo and Cr are present at the Σ5(210) grain boundary, the sulfur-induced embrittlement is inhibited. With increased S concentration at the grain boundary, the coexistence of Mo and Cr can suppress the intergranular fracture of S on the grain boundary. The reason why high-Mo stainless steel has excellent sulfur-induced intergranular corrosion resistance is explained at the atomic level. [ABSTRACT FROM AUTHOR]

The addition of B can inhibit the precipitation of σ phases at the grain boundary to improve the hot workability and corrosion resistance for super austenitic stainless steel with high Cr and Mo content. This study focused on the interaction between B and Mo at the Fe–Cr(111)/Cr2O3(0001) interface and its effect on interfacial adhesion by employing the first-principles method, especially the effect of B on the segregation behavior of Mo. The most stable O-terminated Fe/Cr2O3 interface was chosen as the basic configuration. The segregation energy and the work of separation were calculated for the metal/chromia interface with Fe–Cr as the substrate. It has been demonstrated that B can promote the diffusion of Mo atoms into the oxide layer to increase the content of Mo in the passive film. In addition, the interfacial adhesion is higher at the most segregated sites. However, it is more difficult for two or more Mo atoms than a single Mo atom to diffuse into the oxide part with the effect of B, indicating that B can only improve the Mo content of the passive film to a small extent. The electronic properties were also further discussed to analyze the interactions and the binding characters between doped atoms and their surrounding atoms and to explain the underlying reasons for the variation of interfacial adhesion. [ABSTRACT FROM AUTHOR]

The second phases in the S31254 super austenitic stainless steel is easily precipitated, and the solution treatment plays an important role on the microstructure and performance. In this work, the solution treatment is performed on S31254 steel at 1180, 1200, and 1220 °C for 1, 2, and 4 h, respectively. Given the grain size and precipitation of second phase, the 1200 °C for 4 h or 1220 °C for 2 h may be suitable as the solid‐solution parameters. The corrosion resistance and impact toughness of the steel after solution treatment at 1200 °C are further investigated by means of microstructural analysis and electrochemical experiments. The sample after solution treatment for 4 h, where no second phase can be observed, exhibits a lower corrosion rate and a better mechanical properties, compared to that after annealed for 1 or 2 h. The electrochemical impedance spectroscopy, Mott–Schottky, and XPS results indicate that the passive films of the samples, with a significantly decreased donor and acceptor densities and increased Cr2O3 and Mo‐riched oxides, may be responsible for the improvement of corrosion resistance. The impact toughness results show that the samples after solution treatment for 4 h has the highest impact energy among the studied samples. [ABSTRACT FROM AUTHOR]

• B addition of S31254 stainless steels promotes the redissolution of σ phases. • B addition of S31254 stainless steels improves the pitting corrosion resistance. • B addition of S31254 stainless steels improves the intergranular corrosion resistance. • The optimum solid solution condition for B-containing S31254 is at 1200 °C for 2 h. • The passive films of S31254 with B have increased Cr 2 O 3 and Mo-riched oxides. The effects of B on microstructure, pitting and intergranular corrosion in solution-annealed S31254 super austenitic stainless steels were systemically investigated. After solid solution treatment at 1200 °C for different time, the precipitation and grain size of S31254 with and without B steels were analyzed. Addition of B to S31254 promotes the redissolution of detrimental sigma (σ) phases, and the optimum solid solution condition for B-containing S31254 is at 1200 °C for 2 h. The S31254 steels with B after solid solution treatment exhibited much better corrosion resistance than that without B, which is relative to the elimination of destructional σ precipitates and the decrease of chromium-depleted region near the grain boundary. Moreover, the passive films of samples with B have increased Cr 2 O 3 and Mo-rich oxides, which may be responsible for the improvement of corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract: A Mg phosphate coating was prepared on home-developed Mg–Zn–Ca alloy to improve its anticorrosion performance in simulated body fluid (SBF, Kokubo solution). The coating was prepared by micro-arc oxidation (MAO) method at the working voltage of 120–140V. Evident improvement of anticorrosion was obtained even through the surface was porous. To further diminish the contact with SBF, a TiO2 layer was coated on the porous MAO layer by sol–gel dip coating followed by an annealing treatment. The coatings were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The electrochemical performance of the MAO and TiO2/MAO coated alloys was evaluated by anodic polarization measurements. The pores on Mg phosphate layer provided accommodation sites for the subsequent TiO2 sol–gel coating which sealed the pores and hence significantly enhanced the anticorrosion while single MAO coating only improve anticorrosion within a limited range. The present result indicates that fabrication of composite coatings is a significant strategy to improve the corrosion resistance of Mg–Zn–Ca alloy and other alloys, thus enhancing the potential of using Mg alloys as bio-implants. [Copyright &y& Elsevier]