Enhanced pitting corrosion resistance of a Zr-based metallic glass by ultraviolet light irradiation

The influence of ultraviolet light irradiation on the pitting corrosion performance of a Zr_(2)Ni metallic glass was examined using electrochemical methods and immersion test in 0.05 mol/L NaCl solution.From the results of potentiostatic polarization,the pitting potential of the ultraviolet light-irradiated sample shifted positively with a value of~300 mV,revealing the enhanced pitting corrosion resistance of the samples.The corrosion morphology after the immersion test also demonstrated lower degree of corrosion damage and improved pitting resistance of the sample with ultraviolet light irradiation.X-ray photoelectron spectroscopy analysis revealed more zirconium enrichment in the passive film and no chloride ions adsorption for the samples with ultraviolet irradiation,accounting for the suppression of the pit generation and growth.Our findings indicate that ultraviolet light irradiation improves the pitting corrosion resistance of the Zr-based metallic glasses,which are promising structural materials to be used in corrosion environments with high ultraviolet irradiation.

Relationship of Corrosion Behavior Between Single-Phase Equiatomic CoCrNi,CoCrNiFe,CoCrNiFeMn Alloys and Their Constituents in NaCl Solution

The composition is a significant issue for corrosion resistance of metallic materials.To reveal the correlation of corrosion behavior between multiprinciple alloys and their constituents,a series of single-phase equiatomic alloys of CoCrNi,CoCrNiFe and CoCrNiFeMn was fabricated.The electrochemical and scanning electron microscope results demonstrated that corrosion resistance of the equiatomic alloys in 0.1 M NaCl solution is located in the range but not the average value of their constituents.X-ray photoelectron spectroscopy analysis indicated that the protective performance of passive film is mainly determined by the constituent with the highest corrosion resistance and the breakdown of passive film is mainly dominated by the elements with the highest corrosion rate.Our findings can guide the materials design of multiprinciple alloys with expected corrosion performance.

An effective approach for bonding of TZM and Nb-Zr system:Microstructure evolution,mechanical properties,and bonding mechanism

A novel method of liquid metallic film(LMF)bonding was developed to join titanium zirconium molybdenum alloy(TZM)and Nb-Zr alloy with a Ni interlayer.Using this method,a Ni-Zr liquid phase was formed by the eutectic reaction and then squeezed out from the gap due to a transient pressure,leaving an LMF.It not only achieved a reliable metallurgical bonding but also served as a transition layer between TZM and Nb-Zr alloy to reduce the mismatch between them thus further improving its performance.The bonding mechanism of the TZM and Nb-Zr system was discussed based on theoretical calculation and high-resolution microscopy analysis.The advantages of this method were established by comparing the microstructure and mechanical properties of LMF bonded joints with that of traditional contact-reaction brazing and direct diffusion bonding.Additionally,the feasibility of the LMF bonding method was also demonstrated by the reliable joining of other high-temperature and immiscible systems.

Effects of Nb content in Ti–Ni–Nb brazing alloys on the microstructure and mechanical properties of Ti–22Al–25Nb alloy brazed joints

Vacuum brazing was successfully used to join Ti-22Al-25Nb alloy using Ti-Ni-Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti-Ni-Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, ？3, and Ti2 Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached359 MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180？C for 20 min, and it was321, 308 and 256 MPa at 500, 650 and 800？C, respectively. Cracks primarily initiated and propagated in ？3compounds, and partially traversed B2＋O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2＋O region, which was favorable for the mechanical properties of the brazed joint.

Active metal brazing of SiO2–BN ceramic and Ti plate with Ag–Cu–Ti＋BN composite filler

SiO2–BN ceramic and Ti plate were joined by active brazing in vacuum with Ag–Cu–Ti＋BN composite filler.The effect of BN content,brazing temperature and time on the microstructure and mechanical properties of the brazed joints was investigated.The results showed that a continuous Ti N–Ti B2reaction layer formed adjacent to the SiO2–BN ceramic,whose thickness played a key role in the bonding properties.Four Ti–Cu compound layers,Ti2Cu,Ti3Cu4,Ti Cu2and Ti Cu4,were observed to border Ti substrate due to the strong affinity of Ti and Cu compared with Ag.The central part of the joint was composed of Ag matrix,over which some fine-grains distributed.The added BN particles reacted with Ti in the liquid filler to form fine Ti B whiskers and Ti N particles with low coefficients of thermal expansion（CTE）,leading to the reduction of detrimental residual stress in the joint,and thus improving the joint strength.The maximum shear strength of 31 MPa was obtained when 3 wt%BN was added in the composite filler,which was 158%higher than that brazed with single Ag–Cu–Ti filler metal.The morphology and thickness of the reaction layer adjacent to the parent materials changed correspondingly with the increase of BN content,brazing temperature and holding time.Based on the correlation between the microstructural evolution and brazing parameters,the bonding mechanism of SiO2–BN and Ti was discussed.