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The effects of electrolyte ratio, voltage, and polishing time on the surface quality and corrosion resistance of the Ti6Al4V crowns fabricated by selective laser melting were analyzed in this paper. The results show that, the surface roughness of the Ti6Al4V crowns is large, and there are a large number of powder particles on the sample surface. At the same time, the undulating molten pool boundary and steps can be observed and the initial roughness is about 30 μm. For the electrochemical polishing performed with the volume ratio of perchloric acid and acetic acid as 1:8, when the voltage is low (10 V), the adhered powder particles are removed, the surface roughness changes little, the polishing effect is not obvious. Meanwhile, when the voltage is high (50 V) or the volume ratio of perchloric acid and acetic acid is high, the surface is locally uneven, the surface roughness increases, the polishing effect is excessive. The surface quality of the Ti6Al4V crowns is significantly optimized by polishing in the electrolyte with the volume ratio of perchloric acid and acetic acid as 1:8 at 30 V for 30 min, the surface roughness is about 1 μm after polishing, satisfying the requirements for application. The corrosion resistance of the Ti6Al4V crowns after electrochemical polishing is greatly improved, which is nearly an order of magnitude compared with the crowns without the surface treatment.

The mechanical properties and corrosion resistance of selective laser melted high-strength martensitic stainless steel were enhanced by cryogenic treatment. The microstructure of the martensitic stainless steel contained fine martensite lath due to fast cooling rate. Simultaneously, there were bulk austenite formed at the boundary of molten pool and thin austenite film distributed at martensite laths. After cryogenic treatment, the content of austenite decreased from 25 to 19.2%, and Cu-rich precipitates were refined to 1-3 nm during subsequently aging due to decreasing of lattice constant, which were benefit for the hardness and tensile strength of the selective laser melted 15-5PH martensitic stainless steel without negatively influencing on the plasticity. Simultaneously, the electrochemical tests showed that the pitting potential and passivation film stability gradually increased after cryogenic treatment. Finally, the effect of cryogenic treatment on microstructure for selective laser melted high-strength martensitic stainless steel was discussed. [ABSTRACT FROM AUTHOR]

• The microstructure of Nickel-rich Custom 465 steel is significantly changed by various tempering temperatures. • Passive film stability first reduces and then increases with increasing tempering temperatures. • The Volta potential of the interface between nanoscale ɳ-Ni 3 Ti and the matrix is the lowest. • The Volta potential of reversed austenite is higher than that of martensite. The multiple effects of ɳ-Ni 3 Ti precipitates and reversed austenite on the passive film stability of nickel-rich Custom 465 steel were studied. The results showed that with an increase in tempering temperature, the η-Ni 3 Ti precipitates gradually coarsened. The Volta potential of the ɳ-Ni 3 Ti/matrix interface was approximately 30 mV lower than that of the precipitates, which decreased the passive film stability. The volume of reversed austenite gradually increased at higher tempering temperatures. The Volta potential of the reversed austenite was 14 mV higher than that of the martensite, which enhanced the passive film stability and slightly increased the pitting corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract In this study, plasma electrolytic nitriding technology and an annealing treatment are used to modify titanium bipolar plates. Subsequently, the surface topography, corrosion resistance, and interfacial contact resistance of the nitrided samples are characterized. The results show that the nitrided layer consists of porous volcano-like micro-nano structure surface layer and the dense inner layer. Compared to the blank sample (87.9°±1.7°), the contact angle between the nitrided samples with annealing and deionized water significantly increases (104.7°±1.4° (nitrided for 15 min), 114.3 ± 3.0° (nitrided for 30 min)). The results of the electrochemical and atomic force microscopy analysis indicate that the nitrided samples with annealing have good corrosion resistance. The corrosion potential and corrosion current density of the nitrided samples with annealing are −0.016 V (Ag/AgCl) and 0.275 μA cm−2 (nitrided for 15 min) and 0.04 V (Ag/AgCl) and 0.195 μA cm−2 (nitrided for 30 min), respectively, which satisfy the requirement of DOE 2020 target (<1 μA cm−2). After potentiostatic polarization at 600 mV (SCE) in the simulated environment, the contact resistance of the samples remains very low (6.47 mΩ cm2 (nitrided for 15 min) and 3.91 mΩ cm2 (nitrided for 30 min)) and also satisfies the requirement of the DOE (≤10 mΩ cm2). Highlights • Plasma electrolytic nitriding technique was used to modify titanium bipolar plates. • Nitriding and annealing treatment improved significantly the corrosion resistance. • ICR of nitrided samples with annealing met the goal of DOE. [ABSTRACT FROM AUTHOR]

Pure copper, tin copper and beryllium copper were exposed to a harsh marine environment, and the effects of tin and beryllium addition on copper corrosion were systematically investigated and compared. The corrosion rate for pure copper was similar with that for tin copper, but significantly higher than that for beryllium copper, indicating an improvement in corrosion resistance due to the addition of beryllium. Pitting corrosion occurred in all investigated materials and the extent of pitting damage was in the order of pure copper > tin copper > beryllium copper. Flaking corrosion was prominent on tin copper plate after long-term exposure and the primary corrosion products in all materials were Cu 2 O, CuCl and Cu 2 Cl(OH) 3 . The tin content in the inner corrosion layer was higher than in the outer layer for tin copper, whereas beryllium accumulated at the outer layer of beryllium copper, confirmed by auger electron spectroscopy, and related corrosion mechanisms were proposed. [ABSTRACT FROM AUTHOR]

The semiconducting properties of passive films formed on copper, in anaerobic alkaline sodium chloride solution, were studied using Mott-Schottky analysis and electrochemical impedance spectroscopy, based on the point defect model. Results showed that the corrosion resistance increased with increasing potential, which was attributed to a well crystallised, refined grain structure, and a thicker passive film at higher potential. P-type semiconducting characteristics were obtained with or without chloride. The density of copper vacancies was approximately 1020 cm−3, and increased with the increasing chloride concentration, which was attributed to faster film-formation in a higher chloride environment. The diffusion coefficient of the defects, a key dynamic parameter for passive film breakdown, was in the range of 10−16-10−15 cm2 s−1, and increased with increasing chloride concentration, thus leading to a greater probability of pitting. [ABSTRACT FROM AUTHOR]

The electrochemical behavior and passive film properties of Co-Cr-Mo ultrahigh-strength stainless steel in neutral and acidic chloride solution were evaluated by potentiodynamic polarization curves, electrochemical impedance spectroscopy and x-ray photoelectron spectroscopy. The results indicate that the steel exhibited good passivation behavior in neutral NaCl solution. Both the film formation potential and the applied potential time showed great effects on the open-circuit potential value and stability of the passive film. Furthermore, the oxides and hydroxides of Fe, Co, Mo and Cr were the primary components of the passive film, and the composition of the passive film was changed with a change of pH environment. [ABSTRACT FROM AUTHOR]

Inspired by the porous morphology of anodized Ti and the adhesive versatility of polydopamine (PDA), which can induce apatite mineralization, we fabricated a novel interface by coating a porous anodized TiO 2 layer with PDA to rapidly immobilize HA on Ti-based substrates. It was found that the as-prepared PDA/anodized (HD) surface exhibited nanoscale roughness, which possessed an excellent ability to form apatite when immersed in 1.5× simulated body fluid (SBF), as observed by AFM and FE-SEM. The morphology and composition of each layer were further confirmed by XPS, XRD and FTIR. The corrosion resistance of the multilayer was investigated using potentiodynamic polarization curve and electrochemical impedance spectra (EIS) measurements in a 0.9 wt% NaCl solution, the results suggested that the HA/PDA/anodized (HDA) layer increased the corrosion resistance of pure Ti with higher corrosion potential and lower passive current, the surface wettability was also enhanced with the incorporation of HA. In vitro cellular assays showed that the HDA layer stimulated cell attachment and improved the alkaline phosphate (ALP) activity. Overall, the PDA/anodized treatment provided a viable method to quickly integrate HA, and the obtained HDA layer improved both corrosion resistance and biocompatibility of the Ti surface. [ABSTRACT FROM AUTHOR]

H 2 O 2 usually develops after implanting an implant of biomedical material in human body. Our study showed that H 2 O 2 has dual effects on degradation behaviour of biomedical material depending on its concentration. As for a SLMed CoCrMo alloy, a critical concentration of H 2 O 2 exists, below which the corrosion potential shifts positively as the concentration increases, facilitating the passive film formation; and above which, the film becomes less protective due to the change in composition of the film. The corrosion resistance of XOZ plane of the alloy is better than that of XOY plane due to less grain boundaries and secondary precipitates. • A critical concentration of H 2 O 2 exists, below which the formation of passive film was facilitated with increasing concentration, and above which the change of passive film composition results in lower corrosion resistance. • The passive film formed in 9 g/L NaCl + 30 mM H 2 O 2 mainly consist of oxide/hydroxide of Co, which is less protective than Cr 2 O 3 formed in solutions without H 2 O 2. • Corrosion resistance of XOZ plane of the tested SLMed CoCrMo alloy is larger than that of XOY plane due to less grain boundaries and secondary precipitates. [ABSTRACT FROM AUTHOR]

ABSTRACT Adding 200 nm WC can dramatically increase the mechanical properties of laser powder bed fusion (LPBF) 420 stainless steel, whereas the evolution of the microstructure, corrosion resistance, wear resistance, and tensile performance in LPBF 420 + 2 wt% WC MMCs is not researched yet. WC increases the hardness of the LPBF MMCs. WC offers W and C to the matrix during laser scanning, with C diffusing to the matrix to form austenite and Cr‐rich carbides. The austenite content increases with higher tempering temperatures by up to 22% after heat treatment at 400°C. However, more numbers and large size Cr‐rich carbides are formed after being tempered at 600°C. Austenite increases pitting corrosion resistance by a higher critical pitting potential and lower pit growth kinetics. Wear resistance is linearly related to the hardness value, with smaller grain and more austenite improving ductility without sacrificing tensile strength. Overall, LPBF 420 + 2 wt% WC MMCs has the best corrosion in 0.1 M NaCl, with optimized mechanical properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • The type of GBs affects the diffusion of Mg and Zn atoms. • Under flow stress and heating, the precipitation rate of η/η' phase at the GBs is accelerated. • The distribution of η/η' phase lead to obvious differences in alloys strength and dislocation density. • A high-throughput algorithm screened potential 7xxx Al alloying elements that could lower SCC sensitivity. In this study, a high-throughput calculation algorithm was compiled for screening the potential alloying elements that can increase the resistance of Al alloy to stress corrosion cracking (SCC). Studies show that the precipitation rate of η/η' phase at the GBs increased by 53 times due to hot rolling. The η/η' phase distribution at GBs decreased the dislocation density by an order of magnitude, which makes the GBs sensitive to SCC. To compensate for these weak sites, the algorithm was utilized to determine the stabilities, diffusion energy barriers, and GB cohesive energy of all elements in the Al. [ABSTRACT FROM AUTHOR]

• Strain mainly concentrated within Mg 2 Si particles and at Al/α(Al-Fe-Cu) interface. • Volta potentials of Mg 2 Si and α(Al-Fe-Cu) decreased slightly in the elastic stage. • Volta potentials of Mg 2 Si and α(Al-Fe-Cu) increased in the plastic stage. • The pitting corrosion resistance was improved under elastic deformation. • The pitting corrosion resistance was degraded under plastic deformation. Micro-galvanic corrosion behaviors between two primary intermetallic particles (Mg 2 Si, α(Al-Fe-Cu)) and the Al matrix were investigated under elastic and plastic deformations in AA7075-T6. Strain localization was mainly concentrated within Mg 2 Si and at the interface of α(Al-Fe-Cu)/Al matrix under deformations. The experimental Volta potential differences between Mg 2 Si, α(Al-Fe-Cu) and Al decreased by 0–16 mV and 2–27 mV in the elastic stage but increased by 0–39 mV and 0–81 mV in the plastic stage, which were consistent with the calculation results. Accordingly, the pitting corrosion resistance was improved under elastic deformation but deteriorated under plastic deformation. [ABSTRACT FROM AUTHOR]

The cellular microstructure is a special phenomenon in many additively manufactured metals and alloys. This work provided a new way to achieve both high catalytic performance and superior corrosion resistance for additively manufactured 316L stainless steel by surface engineering. Results show that a well-organized cellular structure array is formed along the sub-grain boundary during the anodization process and an oxidation voltage of 15 V afforded the selective laser melted 316L (SLM 316L-A15) with the largest specific surface area. Compared with the traditional 316L plate, the SLM 316L-A15 plate deserves a superior corrosion resistance due to the enrichment of molybdenum and chromium at the sub-grain boundary. The SLM 316L-A15 plate surface loaded with Pt nanoparticles exhibited excellent catalytic effect, which is ascribed to the increased electrochemical surface area and the beneficial synergistic effect between iron/chromium oxide and platinum. • Anodized selective laser melted 316L SS has high corrosion resistance due to Mo and Cr enrichment at cellular boundary. • The Fe/Cr oxides formed by the cellular boundary after anodization increase the catalytic oxidation of methanol. • Selective laser melted 316L SS, oxidized under 15 V and loaded with Pt, exhibited the best catalytic performance. [ABSTRACT FROM AUTHOR]

• The microstructure was significantly changed by different heat treatments. • The samples after directly aging treatment had better corrosion resistance. • Better corrosion resistance was attributed to the presence of austenite. The microstructural optimization for selective laser melted 15-5PH stainless steel via heat treatment to enhance corrosion resistance was investigated. The results showed that after aging treatment, Cu-rich nanoparticles (about 10 nm) diffusely precipitated, and approximately 18∼25 % austenite was distributed near the molten pool boundary. The surface potential of the austenite was approximately 15 mV higher than that of martensite by scanning Kelvin probe force microscopy. However, the austenite phase disappeared and the new NbC-(Mn, Si)O duplex particles precipitated after solution treatment and aging treatment, which decreased the pitting corrosion resistance and passive film stability of the SLM 15-5PH stainless steel. [ABSTRACT FROM AUTHOR]

• High sub-grain boundary density increased the nucleation of passive film. • Micro-galvanic effect accelerated the rapid formation of passive film. • Re-passive ability of the SLMed 316L without pore was equal to the wrought. • Widely precipitated oxide and sulphide particles led to poor corrosion resistance for SA SLMed 316L. The passive film properties of as-received selective laser-melted 316L stainless steel (SLMed 316L SS) without obvious pores were studied and compared with those of wrought and solution-annealed (SA) SLMed 316L SSs. Among the samples, the as-received SLMed 316L SS had the lowest passive current density, which was attributed to two factors: the super high sub-grain boundary density increased the number of nucleation sites for passive film formation, and the micro-galvanic effect between the sub-grain boundary and the inner sub-grains also accelerated the rapid formation of a thick protective layer. The poor passivation and re-passivation abilities of the SA SLMed 316L SS were ascribed to the extensively precipitated nanosized oxide and sulfide particles, especially those at the grain boundary. [ABSTRACT FROM AUTHOR]

The effect of manufacturing parameters on mechanical and corrosion resistance is investigated using tensile tests and electrochemical experiments for selective laser‐melted 15‐5PH stainless steel. The results demonstrate that when laser power is decreased to 150 W and scanning speed increased to 1400 mm s−1, manufacturing defects increase. Plasticity and corrosion resistance reduce significantly. Cracks mainly originate from manufacturing defects and extend along the interface between molten pools. Corrosion occurs near manufacturing defects. Finally, the most suitable laser energy density is 130 J mm−3 for 15‐5PH stainless steel. [ABSTRACT FROM AUTHOR]

• Hastelloy X was fabricated with optimised parameters by selective laser melting. • The SLMed components deserved better ultimate strength but lower elongation. • The XOZ plane in SLMed parts had bigger elongation than that on the XOY plane. • Corrosion resistance for the SLMed components was compared with the wrought. Mechanical properties and corrosion behaviours of hastelloy X fabricated by selective laser melting (SLM) were investigated and compared with the wrought counterpart, and the anisotropy of the selective laser melted (SLMed) hastelloy X was also clarified in this work. Nano-inclusions (Mo-rich M 6 C) were widely distributed at the sub-grain boundaries in the SLMed hastelloy X alloy, whereas micron-scale precipitations existed in the wrought counterpart. The grain sizes of the hastelloy X fabricated by SLM on XOZ plane were slenderer than that on XOY plane (equiaxed grains), and the molten pool boundaries widely existed in the SLMed matrix, leading to poor plasticity and the XOY plane was worse due to the cracks perpendicular to the stretching direction. The corrosion resistance for the SLMed matrix was better than the wrought in the less aggressive solution due to the thicker oxide passive film, but the SLMed parts corroded faster in a severe environment once the voids and the molten pool boundaries started to dissolve. The corrosion depth for the SLMed hastelloy X was approximately three times larger than for the wrought and there was little difference on different planes for the SLMed matrix. [ABSTRACT FROM AUTHOR]

Abstract To improve the corrosion resistance and electrical conductivity of 316L stainless steel used as a bipolar plate, TiN and ZrN coatings are deposited on the surface through magnetron sputtering in this study. Subsequently, the surface topography, composition, corrosion resistance, and interfacial contact resistance of the coated samples are characterized. The results show that the TiN and ZrN coating can significantly enhance the corrosion resistance of the 316L stainless steel. The corrosion current density of the coated 316L stainless steel with TiN and ZrN in the simulated cathodic environment of a proton-exchange membrane fuel cell (PEMFC) is 0.099 μA/cm2 and 0.209 μA/cm2, respectively, which meets the U.S. DOE 2020 target (<1 μA·cm−2). The EIS and polarization curves show that the TiN coating has better corrosion resistance than that of the ZrN coating. Moreover, the contact angle results indicate that TiN and ZrN can also improve the hydrophobicity of the stainless steel. The interfacial contact resistance between the TiN-coated sample and carbon paper before and after polarization is the smallest, which satisfies the U.S. DOE requirement (≤10 mΩ·cm2). Highlights • Uniform TiN and ZrN coating are deposited by reactive magnetron sputtering. • TiN and ZrN coating improve obviously the corrosion resistance and conductivity. • ICR and corrosion current of TiN coated sample meet the goal of DOE. [ABSTRACT FROM AUTHOR]

The corrosion performance of WC-12Co after different post heat treatments (1100 °C, 1100 °C + 400 °C, 1100 °C + 500 °C, 1100 °C + 600 °C), were tested in 0.05 M H 2 SO 4 , 0.1 M Na 2 SO 4 , and 0.1 M NaOH. Heat treatments influence the corrosion performance of WC-12Co in acidic and neutral environments. However, the corrosion properties for WC-12CO in alkaline solutions are independent of the heat treatments. W and C diffuse to Co from the quenching process, dramatically improving corrosion resistance, with higher annealing temperature slightly reduces the corrosion performance. The rank of corrosion nucleation parameter tested by EIS and potentio-dynamic polarisation, with the corrosion expansion rate measured by potentio-static polarisation at +0.2 V SCE , + 0.5 V SCE , and + 0.8 V SCE for 30 min are not the same. The corrosion mechanism tested in different pH values is analysed using SEM, XPS, and DFT calculations. • Heat treatments are applied on WC-12Co to increase W/C and adjust fcc/hcp ratio in Co. • The selective dissolution phase is Co in H 2 SO 4 and Na 2 SO 4 , which is opposed in NaOH. • The corrosion rate is more related to the corrosion product. • The rank of corrosion nucleation potential and corrosion propagation rate is different. • Localised corrosion forms in WC-12Co in acidic and alkaline environments. [ABSTRACT FROM AUTHOR]

Efficiently designing lightweight alloys with combined high corrosion resistance and mechanical properties remains an enduring topic in materials engineering. Due to the inadequate accuracy of conventional stress-strain machine learning (ML) models caused by corrosion factors, a novel reinforcement self-learning ML algorithm combined with calculated features (accuracy R2 >0.92) is developed. Based on the ML models, calculated work functions and mechanical moduli, a Computation Designed Corrosion-Resistant Al alloy is fabricated and verified. The performance (elongation reaches ∼30 %) is attributed to the H trapping Al-Sc-Cu phases (-1.44 eV H−1) and Cu-modified η/η' precipitates inside the grain boundaries (GBs). • Machine learning models combining DFT calculation are established to improve the corrosion resistance of Al alloy. • An Al alloy with 450 MPa UTS, 30 % elongation, and −0.694 V SCE corrosion potential in 0.1 M NaCl is fabricated. • Cu-modification to MgZn 2 precipitated at the grain boundary ameliorate the intergranular cracking. [ABSTRACT FROM AUTHOR]

• The critical NaF concentrations of SLM Ti6Al4V are determined. • The compositions of repassive films are analyzed. • SLM Ti6Al4V exhibits worse corrosion resistance than wrought sample. The corrosion behavior of the SLM and wrought Ti6Al4V are comparatively investigated. The critical NaF concentrations of SLM Ti6Al4V in the three cases of pH = 2, 4 and 6 are 0.0020 M, 0.080 M and 0.10 M, respectively, which are similar to those of the wrought sample. The repassivation process occurs when NaF concentrations are much larger than the critical values. The crystallinity and the Al and F contents decrease when the NaF concentration and pH value rise. As compared to the wrought Ti6Al4V, the SLM sample exhibits significantly worse corrosion resistance in almost all the test solutions. [ABSTRACT FROM AUTHOR]

The MoSi 2 coating is an ideal coating system for stainless steel due to its good wear resistance and oxidation resistance in the sea service environment. However, there are always some cracks in the MoSi 2 coating due to different thermal expansion coefficients compared with stainless steel, which has an important effect on the corrosion behaviors. In this paper, MoSi 2 coatings on laser powder bed fusion (LPBF) high-strength stainless steel prepared by laser cladding technology were optimized by the addition of a TiVAlZrNb high-entropy alloy. The results showed that the addition of a TiVAlZrNb high-entropy alloy could optimize the cracks in the MoSi 2 coating by refining the grain size and optimizing the expansion coefficient. The open circuit potential and corrosion potential of the MoSi 2 coating were − 158 mV and − 262 mV, respectively, which were lower than those of the composite coating (148 mV and − 225 mV, respectively). The electrochemical impedance value of the MoSi 2 coating was higher than that of the MoSi 2 + TiVAlZrNb composite coating. The obvious local corrosion originated from the cracks in the MoSi 2 coating. Therefore, the addition of TiVAlZrNb high-entropy alloy could optimize the cracking and corrosion resistance of MoSi 2 coating on LPBF high-strength stainless steel. • The crack and density of MoSi 2 coating was optimized by doping of TiVAlZrNb high-entropy alloy. • The obvious local corrosion originated from the cracks of MoSi 2 coating. • The corrosion resistance of MoSi 2 + TiVAlZrNb composite coating was higher than that of MoSi 2 coating. [ABSTRACT FROM AUTHOR]

• The a-C/(Ti:C)/Ti film with 300 nm thickness prepared by multi-arc ion plating. • Improved 316L stainless steel corrosion resistance in simulated cathode solution. • Current density reaches 0.076 μA·cm−2 after 4 h test at 0.6 V (vs. Ag/AgCl). • Low interfacial contact resistance and hydrophobicity for a-C/(Ti:C)/Ti film. To enhance corrosion resistance and electrical conductivity of metallic bipolar plates for proton exchange membrane fuel cells (PEMFCs), the film containing amorphous carbon (a-C) outer layer, titanium carbon compound (Ti:C) transition layer and titanium (Ti) seed layer has been deposited on the surface of 316L stainless steel (316L SS) by multi-arc ion plating method. Dense and uniform a-C/(Ti:C)/Ti nano-thin film is relatively hydrophobic and approximately 300 nm thick, presenting a clear multilayer structure. The interfacial contact resistance of 316L SS is effectively reduced from 124.97 mΩ·cm2 to 3.97 mΩ·cm2 at 1.4 MPa after modification. Electrochemical corrosion tests are investigated in the simulated cathodic PEMFCs environment (0.5 M H 2 SO 4 and 2 ppm HF at 70 ℃ bubbled with air). Potentiodynamic polarization results reveal that the corrosion potential of a-C/(Ti:C)/Ti film modified sample is 0.23 V (vs. Ag/AgCl) and the corrosion current density is only 0.14 μA·cm−2. The durability of the a-C/(Ti:C)/Ti film was assessed by conducting potentiostatic polarization tests at various applied potentials. After 4 h potential of 0.6 V and 0.8 V (vs. Ag/AgCl) holding tests, the current densities of the modified 316L SS have stabilized at 0.076 μA·cm−2 and 0.098 μA·cm−2, respectively. [ABSTRACT FROM AUTHOR]

The effect of hot isostatic pressing (HIP) on microstructure, corrosion resistance and passive film characteristics for heterogeneous martensite stainless steel (MSS) manufactured by laser powder bed fusion (LPBF) was studied. The microstructure was mainly typical original austenite grains and martensite laths and the high content of austenite disappeared after HIP. The average grain size (about 14.09 μm) was larger than that of sample before HIP (about 4.33 μm). When the laser power was 170 W and the scanning speed was 550 mm·s−1, the density of the samples after HIP increased to >99.99%. When the scanning speed increased to 1250 mm·s−1, the density of samples increased from 97.82% to 99.89%. After HIP treatment, the passivation trend of low density (97.8%) samples was more obvious and the pitting potential increased from −44 mV SCE to 179 mV SCE. The pitting potential of high density (99.77%) samples increased from 265 mV SCE to 291 mV SCE and the electrochemical impedance value increased. The sensitivity of the samples to chloride ions significantly decreases after HIP. The donor density for sample before HIP was 2.5546 × 1020 cm−3, which was higher than that of sample after HIP (2.001 × 1020 cm−3). Therefore, the corrosion resistance of LPBF high strength stainless steel was enhanced after HIP. • The microstructure was significantly changed by hot isostatic pressing. • The defects have been optimized by hot isostatic pressing. • Better corrosion resistance was attributed to densification of passive film. [ABSTRACT FROM AUTHOR]

This work studied the effects of Nd on the corrosion behavior of a SAC305 alloy. The results show that the undercooling in solidification process decreases to 1.5–2.5 ℃ with Nd addition. The corrosion resistance of the solder with Nd is markedly enhanced, which is reflected in the following aspects: (1) the potential difference between IMCs and Sn drops to 14.4 mV and lessens the galvanic corrosion sensitivity; (2) the thickness of the passivation film increases; and (3) the proportion of SnO 2 in corrosion product layer in the pseudopassivation region increases. Specifically, 0.05 wt% Nd addition can provide the best improvement effects. [Display omitted] • 0.05 wt% Nd addition can provide the best improvement effects. • Nd addition decreases the potential difference between the IMCs and Sn. • Nd addition increases the thickness of the passivation film on solder alloy surface. • Nd addition enhances the proportion of SnO 2 in corrosion products layer. [ABSTRACT FROM AUTHOR]

By conducting salt-spray tests, we studied the corrosion behaviour and mechanism of printed circuit boards with an immersion Ag surface finish (PCB-ImAg) in polluted environments that contain SO 2 and Cl − . The polluted environment was similar to the polluted marine atmosphere environment in Qingdao China. A comparison of micrographs of the test specimens revealed that the test specimens containing SO 2 and Cl − suffered more serious damage. The entire corrosion process resulted in unevenly distributed partial corrosion products at the initial stage. However, this distribution gradually became uniform. The Raman spectroscopic analysis results for the test specimens containing SO 2 and Cl − show that the corrosion products mainly comprised Cu 4 (OH) 6 SO 4 , Cu 2 Cl(OH) 3 , Cu 2 O, Ag 2 O, Ag 2 CO 3 , Ag 2 SO 3 and Ag 2 SO 4 . [ABSTRACT FROM AUTHOR]

• Nanoscale Co 3 (Mo,W) 2 Si precipitates uniformly dispersed on γ-Co matrix of low-carbon PBF-LB CoCrMoW alloy. • Volta potential difference between the Co 3 (Mo,W) 2 Si precipitate and γ-Co matrix was 14 mV. • Nano hardness of Co 3 (Mo,W) 2 Si precipitate was 16.4 GPa, about 1.6 times of that of the matrix. • PBF-LB CoCrMoW alloy exhibited better passive property than wrought high-carbon CoCrMo alloy in 0.9% NaCl solution. A CoCrMoW alloy with little carbon was manufactured through laser beam powder bed fusion technique. Nanoscale intermetallic Co 3 (Mo,W) 2 Si precipitates uniformly dispersed on the γ-Co phase matrix, and caused less segregation of Cr and Mo elements than the microscale carbides in the wrought CoCrMo alloy. Nanoindentation test results showed that the nano hardness of Co 3 (Mo,W) 2 Si precipitate was 16.4 GPa, about 1.6 times of that of the matrix. The Volta potential of nanoscale Co 3 (Mo,W) 2 Si precipitate was 14 mV more positive than the matrix. The corrosion resistance of the PBF-LB alloy in 0.9% NaCl solution was larger than that of the wrought alloy. [ABSTRACT FROM AUTHOR]

• The corrosion behavior between α and β phases of Ti6Al4V is compared. • The repassivation of Ti6Al4V in F−-containing solution is explained. • Al content play a critical role in the repassivation of titanium alloys. In this study, the different corrosion behaviors between α and β phases of Ti6Al4V in solutions with different NaF concentrations are investigated. When the NaF concentration changes from 0.15 to 0.20 M, α phases are more likely to suffer from corrosion than β phases. However, the formation of a repassive film makes α phases exhibit superior corrosion resistance than β phases as the NaF concentration reaches 0.50 M. The mechanism analysis reveals that the formation of a repassive film on the α phases depends on not only the Al content but also on the active dissolution rate of Ti. [ABSTRACT FROM AUTHOR]