纯Sn焊料表面高温氧化膜的腐蚀演化行为

对150℃高温时效条件下纯锡焊料表面氧化膜形貌、组成、厚度及耐蚀性的演化行为进行研究。结果表明,高温时效加速焊料表面原有自然氧化膜层中的Sn(OH)_(4)向SnO_(2)转变,同时加速新鲜Sn基体的氧化,从而使纯Sn焊料表面氧化膜厚度和粗糙度随时效时间的延长逐渐增加。然而,表面氧化膜层的耐蚀性随时效时间的延长呈先增强而后减弱的趋势。此外,还对纯Sn焊料表面氧化膜层的成膜机制及膜层演化机制进行讨论。

Effects of Hydrogen Charging Time and Pressure on the Hydrogen Embrittlement Susceptibility of X52 Pipeline Steel Material

The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimens are observed by scanning electron microscopy.The HE susceptibility of the X52 pipeline steel material increases with an increase in both hydrogen charging time and hydrogen pressure.At a charging time of 96 h,the HE susceptibility index reaches 45.86%,approximately 3.6 times that at a charging time of 0 h.Similarly,a charging pressure of 4 MPa results in a HE susceptibility index of 31.61%,approximately 2.5 times higher than that at a charging pressure of 0.3 MPa.

Microstructure, Residual Strain and Stress Corrosion Cracking Behavior in 316L Heat-Affected Zone

Austenitic stainless steels are usually chosen to make many components of nuclear power plants （NPPs）. However, their microstructure in the heat-affected zone （HAZ） will change during the welding process. Some failures of the weld joints, mainly stress corrosion cracking （SCC）, have been found to be located in the HAZ. In this research, the microstructure, micro-hardness, residual strain and SCC behavior at different locations of the 316L HAZ cut from a safeend dissimilar metal weld joint were studied. However, traditional optical microscope observation could not find any microstructural difference between the HAZ and the base metal, higher residual strain and micro-hardness, and higher fraction of random high-angle grain boundaries were found in the HAZ than in the base metal when studied by using electron back-scattering diffraction scanning and micro-hardness test. What＇s more, the residual strain, the microhardness and the fraction of random grain boundaries decreased, while the fraction of coincidence site lattice grain boundaries increased with increasing the distance from the fusion boundary in 316L HAZ. Creviced bent beam test was applied to evaluate the SCC susceptibility at different locations of 316L HAZ and base metal. It was found that the HAZ had higher SCC susceptibility than the base metal and SCC resistance increased when increasing the distance from the fusion boundary in 316L HAZ.

Molecular regulation of telomerase activity in aging

The process of aging is mitigated by the maintenance and repair of chromosome ends(telomeres),resulting in extended lifespan.This review examines the molecular mechanisms underlying the actions and regulation of the enzyme telomerase reverse transcriptase(TERT),which functions as the primary mechanism of telomere maintenance and regulates cellular life expectancy.Underpinning increased cell proliferation,telomerase is also a key factor in facilitating cancer cell immortalization.The review focuses on aspects of hormonal regulations of telomerase,and the intracellular pathways that converge to regulate telomerase activity with an emphasis on molecular interactions at protein and gene levels.In addition,the basic structure and function of two key telomerase enzyme components—the catalytic subunit TERTand the template RNA(TERC)are discussed briefly.

Microstructure, Mechanical Properties, and Corrosion Behavior of MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi High-Entropy Alloys

The development of high-entropy alloys(HEAs)has stimulated an ever-increasing interest from both academia and industries.In this work,three novel MoNbFeCrV,MoNbFeCrTi,and MoNbFeVTi HEAs containing low thermal neutron absorption cross section elements were prepared by vacuum arc melting.The microstructure,mechanical properties,and corrosion behaviors were investigated.A dominant body-centered cubic(BCC)phase was present in all these three HEAs.In addition,an ordered Laves phase was found to be another major phase in both MoNbFeCrV and MoNbFeCrTi alloys,whereas an ordered BCC(B2)phase was observed in the MoNbFeVTi alloy.The phase formation in these three alloys was discussed.It is found that the formation of the secondary phase in these alloys is mainly ascribed to the large atomic size difference and electronegativity difference.All the three HEAs show high hardness,high yield strength but limited plasticity.Moreover,the MoNbFeCrV,MoNbFeCrTi and MoNbFeVTi alloys exhibit excellent corrosion resistance in both deaerated 1mol/L NaCl and 0.5 mol/L H2SO4 solutions at room temperature.However,further composition adjustment and/or thermomechanical processing is required to enhance the mechanical properties of the three alloys.

Effect of Hydrogen on Corrosion and Stress Corrosion Cracking of AZ91 Alloy in Aqueous Solutions

The effect of hydrogen on the corrosion and stress corrosion cracking of the magnesium AZ91 alloy has been investigated in aqueous solutions. Hydrogen produced by corrosion in water diffuses into, and reacts with the Mg matrix to form hydride. Some of the hydrogen accumulates at hydride/Mg matrix （or secondary phase） interfaces as a consequence of slow hydride formation and the incompatibility of the hydride with the Mg matrix （or secondary phase）, and combines to form molecular hydrogen. This leads to the development of a local pressure at the hydride/Mg matrix （or secondary phase） interface. The expansion stress caused by hydride formation and the local hydrogen pressure due to its accumulation result in brittle fracture of hydride. These two combined effects promote both the corrosion rate of the AZ91 alloy, and crack initiation and propagation even in the absence of an external load. Hydrogen absorption leads to a dramatic deterioration in the mechanical properties of the AZ91 alloy, indicating that hydrogen embrittlement is responsible for transgulanar stress corrosion cracking in aqueous solutions.

Oxidation and Electrochemical Behavior of MonolayerGraphene-Coated Copper in Simulated Primary Water

In high-temperature and high-pressure water, traditional anticorrosion approaches are not suitable to be used to protect structural materials from oxidation and corrosion. In this study, monolayer graphene was explored as a barrier to protect the materials from degradation. The oxidation and corrosion rate of the monolayer-graphene-coated copper is much lower than that of the bare copper, suggesting that the monolayer graphene can effectively protect the copper from oxidation and corrosion in the simulated primary water of pressurized water reactors.

Effects of Temperature on Fretting Corrosion Between Alloy 690TT and 405 Stainless Steelin Pure Water

In pressurized water reactor,fretting corrosion has become the main reason for the failure of 690TT heat exchanger tubes.The effect of temperature on the fretting corrosion behavior between 690TT tube and 405 stainless steel(SS)bar has been studied during 106 fretting cycles.The overall average coefficient of friction(COF)values descends with an increase in test temperature,while the width of worn scar becomes wider.The severest fretting corrosion happens when the test temperature is at 100℃.The wear mechanism differs at different test temperatures,from adhesive wear at room temperature to abrasive wear and delamination at 100℃,to abrasive wear at 200℃.Deformation slips,high residual strain concentration,and micro-cracks are found which are disadvantageous for the further service performance of the tubes.