Effect of partial replacement of carbon by nitrogen on intergranular corrosion behavior of high nitrogen martensitic stainless steels

The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M23C6 to M2N,furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.

Stern-Geary Constant for X80 Pipeline Steel in the Presence of Different Corrosive Microorganisms

The Stern-Geary constant(B value)is indispensable to measure the corrosion rate in the microbiologically influenced corrosion(MIC)systems.Linear polarization resistance(LPR)and weight loss methods were used to study the variation of B values for X80 pipeline steel in the presence of Pseudomonas aeruginosa,Acetobacter aceti and Desulfovibrio vulgaris.The results showed that B values in the presence of three different bacteria were 35.60±0.55 mV,33.00±1.00 mV and 58.60±0.55 mV,respectively,suggesting that the change of corrosion system significantly affected the B values of X80 pipeline steel.This work further indicated that the determination of B values is necessary to accurately measure the MIC rate by LPR method.

Antibacterial activities of a novel Cu-bearing high-entropy alloy against multi-drug-resistant Acinetobacter baumannii and Staphylococcus aureus

Acinetobacter baumannii and methicillin-resistant Staphylococcus aureus(MRSA)are two prevalent pathogens and have developed high resistant to most antibiotics.Therefore,it is a pressing need to develop a new method to inhibit the spread of drug-resistant bacteria.Copper containing high-entropy alloy(HEA,Al0.4CoCr-CuFeNi)is a new kind of alloy material,which shows extensive antibacterial activity and mechanical properties in our previous research.This study further develops another HEA(CoCrCuFeNi)and evaluates its resistance against gram-negative A.baumannii and Gram-positive MRSA.The antibacterial tests show that the antibacterial rate of the HEA toward both bacteria reached nearly 99%,far better than the traditional copper-bearing 304 stainless steel(304 Cu-SS).The biofilm observation shows that the HEA could not only kill the planktonic bacteria,but also effectively inhibit the formation of biofilm.These data demonstrate that CoCrCuFeNi HEA possesses effective antibacterial and antibiofilm activities,making it a potential candidate for using in hospital,food industry,and domestic kitchens.

A Synergistic Acceleration of Corrosion of Q235 Carbon Steel Between Magnetization and Extracellular Polymeric Substances

In this work, surface characterization and electrochemical measurement were employed to investigate the effects of magnetic field（MF） on the corrosion of Q235 carbon steel in a NaCl solution containing sulphate-reducing bacteria（SRB） or extracellular polymeric substances（EPS）. Results demonstrated that a 150 mT MF enhanced steel corrosion in a SRB-containing NaCl solution by 202% calculated from weight loss with pitting corrosion as the main corrosion type.Either EPS or MF rendered steel corrosion, but a synergistic interaction between MF and EPS boosted up steel corrosion.This synergistic enhancement could be referred to the alteration in orientation of EPS induced by MF. The presence of higher percentage of chloride ions on the carbon steel surface manifested that MF initiated the erosion of chloride ions on the carbon steel coupon.

Antibacterial property of a gradient Cu-bearing titanium alloy by laser additive manufacturing

Streptococcus mutans(S.mutans)is the most common cariogenic bacteria and causes caries by forming biofilms.A novel gradient Cu-bearing titanium alloy(TC4-5Cu/TC4)was manufactured using selective laser melting(SLM)technology for dental applications,which is anticipated to inhibit the formation of biofilm.In this study,the released concentration of copper ions in both minimum inhibitory concentration(MIC)and minimum bactericidal concentration(MBC)was tested in order to assess the antibacterial property of the alloy against planktonic S.mutans,and the antibacterial and antibiofilm efficiencies of TC4-5Cu/TC4 alloy against sessile S.mutans were evaluated via quantitative antibacterial tests and biofilm determination.Reverse transcription polymerase chain reaction(RT-PCR)was performed to analyze the expression of biofilm-related genes(gtfB,gtfC,gtfD,ftf and gbpB)and acid production-related gene(ldh).The results suggested that the MIC and MBC of Cu^(2+)were much higher than the release concentration of copper ions of the alloy,which was consistent with the lack of antibacterial effect against planktonic bacteria.On the contrary,TC4-5Cu/TC4 alloy exhibited significant bactericidal property against the sessile bacteria and efficient biofilm-restrained ability,and all genes detected in this research were down-regulated.The results indicated that the TC4-5Cu/TC4 alloy suppressed biofilm formation and the sessile bacterial viability by down-regulating biofilm-related genes.

A New High-Efficiency Experimental Design for Optimizing Various Flow Velocities Testing in Extremely Aggressive Formation Water

Compared to the traditional one-by-one method,a new high-efficiency method is used to characterize large numbers of regulations varying samples.Accordingly,bump-shaped electrodes are designed using the computational fluid dynamics model,and the effect of the height and placement of these electrodes is discussed.The experimental feasibility is certified by weight loss measurement.Results indicate that flow velocities of different bump-shaped electrode surfaces are significant differences.Thus,each surface can be analyzed independently;the thickness loss of each electrode surface is consistent with that using one-by-one method,which can effectively improve the experimental efficiency 12 times.