Adrian Mościcki

Effect of Artificial and Inflammatory Saliva on Desulfovibrio desulfuricans Growth and Biofilm Formation on NiTi Alloy

NiTi alloys are used for both medical and veterinary purposes, and also for production of surgical instruments. Sulphate-reducing bacteria (SRB) colonize various anaerobic environments, including human oral cavity. Desulfovibrio desulfuricans is the SRB species responsible for corrosion of many metals including highly alloyed steels as well as titanium and its alloys. The aim of this work was to compare growth of D. desulfuricans biofilms on NiTi alloy submerged in artificial saliva or in inflammatory saliva. The results of investigations showed differences between D. desulfuricans biofilms formed on NiTi alloy in the presence of artificial saliva and inflammatory saliva. The growth medium influenced biofilm structure; inflammatory saliva promotes its formation. The biofilms grown on samples immersed in inflammatory saliva were much thicker as compared with samples emerged in artificial saliva. After 28 days of incubation in inflammatory saliva, plentiful mature biofilm was present on alloy surface.

Investigation of Stress Corrosion Cracking in Magnesium Alloys

The paper organises the current state of knowledge concerning the effect of hydrogen on stress corrosion of magnesium alloys. This review describes phenomena and mechanisms connected with stress-corrosion cracking (SCC) in commonly used magnesium alloys from Mg-Al-Zn system. In addition, some information about SCC in alloys from Mg-Y-RE-Zr and Mg-Al-RE systems is described. It seems that microstructural factors (e.g., matrix α-Mg and intermetallic phases) related to the presence of Y, Zr and rare earth elements (RE) plays an essential role in hydrogen-induced cracking (HIC).

Characteristics of Fusion-Welded Joints Made Using Martensitic Steel after 100,000 Hours in Service

The paper presents the results of tests of mixed fusion-welded joints consisting of superheater pipes of grades T91 and HCM12A(T122) after 100,000 hours in service in a BB-1150 boiler welded to new pipes (in “as-delivered” condition) of grades T91 and VM12-SHC. The state of the microstructure and properties of the used tube material after long term service are characterized. The paper describes fusion welding conditions and parameters, and evaluates the quality of the created butt joints. The results of tests of the macro-and microstructure of the joints and their mechanical properties are presented. It was determined that the welding process intensifies further degradation of the tested materials to a small extent only. This work was performed under the Strategic Research Project No SP/E/1/67484/10 supported by the National Centre for Research and Development.

The Influence of Heat Treatment on the Microstructure and Hardness of Mg-5Si-7Sn-5Mn Alloy

The microstructure and hardness of as-cast Mg-5Si-7Sn-5Mn alloy after solution and ageing treatments is presented in this paper. It was found that the microstructure of as-cast alloy. is composed of primary dendrites crystals of Mg2Si phase, α-Mg matrix, long needle-like precipitates of Mn5Si3, Chinese script particles of Mg2Si phase and irregular Mg2Sn phase. The solution treatment at 500°C causes the dissolution of the Mg2Sn phase in the α-Mg magnesium solid solution, whereas the remaining intermetallic compounds are stable in this temperature. The hardness of alloy increases from 73 HV2 to 96 HV2 at 250°C. The increase in hardness is a result of the formation of the lath-like precipitates of Mg2Sn phase within the α-Mg matrix.

Application of Electron Microscopy to Investigation of Corrosion of Mg-Al Alloys in Various Electrolyte Solutions

The Mg-Al alloys are the best-known and most commonly used magnesium alloys (especially AZ91 alloy). However, the AZ91 alloy offers insufficient corrosion resistance. Many investigations show that hydrogen is the main corrosive factor appearing during chemical reactions between magnesium and water in electrolyte solution. The main intermetallic phase in the AZ91alloy is the Mg17Al12 (β phase), which is a hydrogen trap. During corrosion, magnesium hydride forms inside the β phase, and this phase is brittle fractured when the inner stress caused by hydrogen pressure and expansion stress due to the formation of magnesium hydride is higher thanthe fracture strength. We examined the corrosion behaviour of AZ91 and AE44 magnesium alloysin 0.1M Na2SO4 solution and 3.5% NaCl solution. We analysed two Mg-Al alloys in order todetermine the various effects of hydrogen on these materials.

Effect of Hydrogen on the Corrosion of Rare Earth-Containing Magnesium Alloys in Sodium Sulfate Solution

Modern magnesium alloys containing rare earth (RE) elements from the Mg-Y-RE-Zr and Mg-Al-RE systems are characterized by low density and good mechanical properties. Therefore, these alloys are used in the automotive and aerospace industries. However, magnesium alloys offer insufficient corrosion resistance in environments containing electrolyte solutions. Hydrogen is themain corrosive factor appearing during chemical reactions between magnesium and water in anelectrolyte solution. The results showed that when samples were immersed in 0.1M sodium sulfate solution, some cracks were observed inside the Al11RE3 and Al8CeMn4 intermetallic phases. Phase identification was performed by electron backscatter diffraction (EBSD) analysis. The microstructure of the alloys before and after corrosion was observed using a scanning electron microscope (SEM).

Corrosion of WE43 and AE44 Magnesium Alloys in Sodium Sulfate Solution

Magnesium alloys have low density densities and high specific strengths that are comparable to steels and titanium alloys. Therefore, they are widely used as structural materials in the automotive and aerospace industries. However, the use of magnesium alloys is hindered by the fact that they offer insufficient resistance against corrosion, even in diluted electrolyte solutions. We examined alloys from the Mg-Y-RE-Zr and Mg-Al-RE systems (WE43 and AE44) that are used in the domestic and international automotive and aerospace industries. In these applications, the alloys are exposed to corrosion in environments containing electrolytes. It is commonly known that hydrogen is the main corrosive factor, appearing during chemical reactions between magnesium and water in an electrolyte solution. Selecting rare earth-containing magnesium alloys allows us to analyse the various effects of hydrogen on these materials. Hydrogen interacts with the selected alloys in a manner that depends strongly on alloy structure and chemical composition—these factors cause variations in the concentration, solubility, and diffusion rate of hydrogen in the host material. After hydrogen uptake, the cracking velocity of each alloy phase is different and is related to cracking micromechanisms. Our results show that when samples were immersed in 0.1M sodium sulfate solution, hydrogen atoms diffused into the material and enriched the intermetallic phases. With increased immersion time, magnesium hydride fractures in a brittle manner when the inner stress caused by hydrogen pressure and the expansion stress due to the formation of magnesium hydride are higher than the fracture strength.