Effects of Ti-bearing inclusions on intragranular ferrite nucleation

The effect of Ti-bearing inclusion characteristics, such as size and marginal composition, on intragranular ferrite (IGF) nucleation has been explored in single sample through SEM and EDS. It can be seen that Ti-bearing inclusions can induce IGF nucleation, and this nucleation ability was scaled by the number of its induced lathes. Statistical analysis suggested that this ability may be correlated with inclusion size, and independent of Ti2O3 content in inclusion. The former can be attributed to the classical theory of heterogeneous nucleation. The latter can be explained by the relationship between the diffusion quantity of Mn and its solubility in Ti2O3 based on the theory of an Mn-depletion zone. Moreover, a probabilistic feature was observed in the nucleation phenomenon which may be due to a small difference in formation energy between the ferrite side plate and the IGF. These results may be helpful to clarify the nature of oxide metallurgy of a Ti-bearing inclusion.

Extruded Mg-Sn-Al-Zn Alloys with Superior Tensile Properties

This study investigated the microstructure and tensile properties of three indirectly extruded Mg-Sn-Al-Zn alloys: Mg-11Sn-1Al-1Zn (TAZ1111), Mg-8Sn-4Al-1Zn (TAZ841), and Mg-8Sn-1Al-4Zn (TAZ814). The investigation results revealed that in all the alloys, Mg2Sn particles formed during solidification were not fully dissolved by homogenization treatment. These undissolved particles enhanced the dynamic recrystallization behavior through a particle-stimulated nucleation phenomenon. As a result, all the extruded alloys exhibited a fully dynamically recrystallized microstructure. The tensile yield strength (TYS) of the extruded alloys was in the following order: TAZ1111 > TAZ841 > TAZ814. In contrast, the elongation of the alloys was in the opposite order: TAZ814 > TAZ841 > TAZ1111. The highest TYS of the TAZ1111 alloy was attributed mainly to the smaller grain size and more abundant Mg2Sn precipitates resulting from a higher Sn content. However, the ultimate tensile strengths of all the extruded alloys were nearly the same because the Al or Zn atoms dissolved in the TAZ841 and TAZ814 alloys improved the strain hardening rate during plastic deformation.

Effect of Pitting Corrosion on Strength of AISI 410 Stainless Steel Compressor Blades

In the present paper, effects of pitting corrosion on the strength of members made of AISI 410 Martensitic stainless steel were investigated. Stainless steel compressor blades in power generation industries commonly suffer from pitting corrosion. Pits geometry analysis and strength tests have been conducted. Pits geometry analysis established the maximum pit depth of 0.26 mm along with the maximum diameter of 1 mm. In addition, strength and elongation of the pitted tensile specimen gradually decrease with the increase of the area lost due to pitting corrosion. A damage nucleation phenomenon at the initial load values is also postulated.

Effect of Aluminum on the Nucleation of Intragranular Ferrite in Ti-Added Carbon Structural Steel

The features of inclusion and microstructure for Ti-added carbon structural steel were studied through the scanning electron microscope (SEM) and Energy Dispersive Spectrometer (EDS). From the SEM-EDS mapping images, two kinds of titanium-contained oxides are observed. The type I is the Al-Ti-O phase, in which the elements of Al and Ti coexist. The type II is the titanium-contained oxides, which precipitate on the Al2O3. Through the statistical analysis, it can be seen that the former type is dominating in number and smaller in size. After etching, the microstructure of intragranular acicular ferrites (IAF) is observed, which is totally different from that in the comparison sample without Ti addition. Furthermore, it’s found that the type I inclusion can act as nucleation sites for the IAF. However, the similar nucleation phenomenon is complex for the type II inclusion. This complexity is attributed to the diversity of precipitation of Ti and Mn.

A Theoretical Model to Fracture in Cell Membrane

A new stress function modelling the fails in biological tissue is here proposed. Under the assumption that the cell membrane may be modelled as neo-Hookean materials, we develop the problem in the framework of non-linear elasticity. We attempt to model the ice nucleation phenomenon when freezing and thawing occurs in cellular cryo-preservation. The ice seed generated surface can be either soft or wrinkled and, when the latter emerges a punch contact against the cell membrane takes place. Restricting our attention on opportune mono-dimensional sub-set, we extend the multiple critical points theorem at our model. We find a particular solution in agreement to the classical fracture models besides a response function in accordance to the stress and strain field distribution in biological materials.

Evaporation Induced Cavitation in Nanochannels

Cavitation refers to a nucleation phenomenon that occurs at room temperature when the liquid pressure is below the corresponding saturation vapor pressure. Although water confined by a nanochannel and a liquid-air meniscus is under negative pressure, i.e. much smaller than the corresponding satraton vapor pressure, cavitation has not been observed in any nanochannels. In this work, we report our observation and studies of cavitations in nanochannels for the first time. 1-D confined nanochannels for this work were fabricated based on a sacrificial-layer-etching scheme. The unique cavitation phenomenon occurred when water started evaporation at the nanochannel entrances. Instead of meniscus recession, a bubble was present inside the nanochannel and two meniscii were pinned at the entrances. This bubble started growing along both directions until it totally occupied the whole channel. We found that the bubble grows linearly with time and the bubble growth rate decreases with the increasing channel height. A theoretical model was developed to study this dynamic process. It is found that the bubble growth rate is determined by the evaporation rate at the entrance. Since the total evaporation flux is a constant, the predicted bubble growth rate is reversely proportional to the channel height, quantitatively consistent with the experimental results. Since most current studies for caviation are theoretical studies, our studies provide a new experimental approach to study these phenomena in artificial transparent nanochannel devices.