The plastic deformation behaviors of crystalline materials are usually determined by lattice dislocations. Below a certain particle or grain size, focus is placed on the grain-boundary-mediated ...mechanisms (e.g., grain rotation, grain boundary sliding, and diffusion), which has been observed during recrystallization, grain growth, and plastic deformation. However, the underlying mechanisms of grain rotation remain to be studied. In this article, we review the theoretical models, molecular dynamics simulations, and experimental investigations on grain rotation. The development of in situ transmission electron microscopy (TEM) and X-ray characterization methods for probing grain boundary processes during plastic deformation provides a better understanding of the mechanisms of grain rotation. Especially, the ability to acquire high-quality X-ray diffraction patterns from individual nanograins is expected to find broad applications in various fields such as physics, chemistry, materials science, and nanoscience.
The study utilizes a multi-directional compression (MDC) process on a basal-textured ZK60 alloy with the aim of inducing extensive twinning, which is followed by an aging treatment on the ...pre-deformed sample. The mechanical response and corrosion behavior of the deformed and aged samples are systematically investigated. The MDC process effectively generates numerous {10 1‾ 2} twins with increased compression passes, resulting in the enhanced grain refinement. The interplay between twins and numerous dislocations formed during pre-deformation plays a crucial role in altering both the distribution and morphology of the second phase precipitated during aging. During the aging process, the alloy exhibits a higher concentration of dense rod-like β′ phase and disk-like β″ phase. Remarkably, the compressive yield strength and ultimate strength of aged ZK60 alloy along the rolling direction are significantly improved without obvious compromise of ductility by pre-compression. Notably, the yield strength of the sample after 12-passes compression and aging (APD-12) is approximately 45 % higher than that of the sample without pre-compression (APD-0). Furthermore, the corrosion resistance of ZK60 alloy displays notable improvement upon pre-compression treatment. Specifically, the hydrogen evolution in the APD-12 sample is halved compared to the APD-0 sample. Electrochemical assessments were conducted on both pre-compressed and non-pre-compressed samples, revealing their distinct behaviors. Furthermore, an in-depth exploration has also been undertaken into the underlying mechanisms contributing to the enhancement of mechanical properties and corrosion resistance resulting from the pre-compression.
The corrosion behaviour of Nd alloyed magnesium alloy AZ80 in three simulated concrete pore solutions (SCPs) was studied using corrosion immersion tests and electrochemical tests. The study ...investigated the effects of the composition and pH of the SCPs on the corrosion properties of AZ80 and AZ80-1.0Nd using aluminum alloy AA6061 as a reference. The SCP1, SCP2, and SCP3 solutions were the simulated concrete pore solutions with different carbonation stages at pH 13.5, 12.5, and 9.7 respectively. The corrosion mainly in the form of localized corrosion, developed significantly along the transverse direction, and less in the vertical direction. AZ80 and AZ80-1.0Nd exhibited the best corrosion resistance in the SCP2 solution, which was attributed to the formation of a dense protective film on the surface. The corrosion in the high alkalinity SCP1 solution was first enhanced within 12 h and then somewhat decreased within 72 h attributed to the destruction and re-formation of the surface film. AA6061 corroded severely in the SCP1 solution and suffered significantly less corrosion in the SCP2 and SCP3 solutions. Nd alloying contributed to the reduced corrosion rates of AZ80 in the simulated concrete pore solutions, attributed to changes in the microstructure and electrochemical properties.
Due to the good biocompatibility and tensile yield strength, magnesium alloys are promising in degradable prosthetic implants. The objective of this study is to investigate the corrosion behavior of ...surgical AZ91 magnesium alloy treated by aluminum, zirconium, and titanium plasma immersion ion implantation and deposition (PIII&D) at 10 kV in artificial physiological fluids. The surface layers show a characteristic intermixed layer and the outer surface are mainly composed of aluminum, zirconium or titanium oxide with a lesser amount of magnesium oxide. Comparing the three sets of samples, aluminum PIII&D significantly shifts the open circuit potential (OCP) to a more positive potential and improves the corrosion resistance at OCP.
Magnesium alloys are potential materials in biodegradable hard tissue implants. However, their fast degradation rates in a physiological environment constitute the main limitation for their ...applications. In this work, a ZrN/Zr bilayered coating is deposited on AZ91 magnesium alloy using a filtered cathodic arc deposition system. The ZrN/Zr bilayered structure buffers the serious mismatch between the substrate and ZrN coating thus improving film adhesion. The composition of the coating is evaluated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrochemical behavior of the coated alloy is systematically studied by means of potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). Our results disclose that the corrosion resistance of the coated alloy is significantly improved.
► Extension twinning can occur in grains nearly twinned totally during reloading. ► Dislocation by pre-strain can greatly enhance yield stress of reloading. ► Extension twinning can induce preferred ...distribution of prismatic plane.
Plastic deformation behavior of hot-rolled AZ31 Mg alloy under 6 passes plane strain compression along transverse direction (TD) and normal direction (ND) alternatively is systematically study in current paper. With 10% compression along TD, most grains are nearly twinned totally and extension twinning takes place during subsequent compression along ND. Yield stress rises with increased compression passes due to enhanced activation stress for extension twinning by dislocations generated in previous pass of compression. Preferred distribution of prismatic planes appears after each pass of compression besides of the rotation of basal plane poles toward compression axis, which is closely related with extension twinning.
The multiaxial deformation behavior of magnesium alloys is an important factor in understanding the service performance of structures. In the present research, the deformation mechanism of a Mg AZ31 ...sheet under biaxial tension with various stress ratios (σRD:σ45) along the rolling direction (RD) and the diagonal direction (45° direction) between the normal direction (ND) and transverse direction (TD) was systematically studied for the first time using cruciform specimens. The impacts of the stress ratio, σRD:σ45, on the mechanical response, twinning behavior, texture and slip behavior were investigated. The results showed that the contribution of twinning to plastic deformation was limited and governed by the Schmid law. The activation of twinning induced a twin texture component with c-axes largely parallel to the 45° between ND and TD. The deformation induced by biaxial tension was accommodated mainly by prismatic and basal slips under the stress ratio of σRD:σ45=4:1, and the fraction of grains favoring basal slip increased with lower stress ratio along the RD. The characteristics of flow stress can be effectively explained by the relative activities of twinning and slip with stress ratio.
In the present study, mechanical property, microstructure and texture of an extruded Mg–1.0Al–1.5Ca–1.0Mn (wt.%) flat-oval tube in both the flat and the oval regions were systematically studied. Our ...results show that there exists a great difference in microstructure and texture between the flat and the oval regions. Both the flat and the oval regions have fine DRXed grains of 3–4 µm, while more row stacked grains are observed in the flat region. A large number of fine particles with a size of about 0.5 µm are dispersed in both the grain boundary and grain interior. The particles exhibit a uniform distribution in the oval region, while they tend to aggregate into bands along the extrusion direction (ED) in the flat region. The texture in the oval region is similar to that in extruded Mg rods with a preferred distribution of prismatic planes and random distribution of (0002) poles around the ED, while that in the flat region is close to that in extruded sheets containing two texture components, //normal direction (ND) and //transverse direction (TD). A high fraction of //TD component, about 52–62%, is observed in the flat region. The flat region has a tensile yield strength of 254 MPa, an ultimate tensile strength of 290 MPa and an elongation to failure of 4.3%.
The microstructures of pearlitic steel wire rods and steel wires are commonly characterized by secondary electron imaging （SEI） technique using scanning electron microscopy （SEM）. In this work, a ...back-scattered electron imaging （BSEI） method is proposed to determine the microstructures of undeformed and deformed pearlitic steels with nanometer scale pearlite lamellae. The results indicate that BSEI technique can characterize the pearlite lamellas veritably and is effective in quantitative measurement of the mean size of pearlite interlamellar spacing. To some extent, BSEI method is more suitable than SEI technique for studying undeformed and not severely deformed pearlitic steels.
The use of porous silicon as an energy carrier is investigated. NaOH and solid Mg alloy are used to introduce OH
− in water to react with the porous silicon and the porous silicon treated with Mg ...alloy in water is converted to transparent silicon oxide hydride. The amount and release rate of hydrogen from the reaction between porous silicon and water are determined and the efficiency is also studied. The total amount of released hydrogen does not vary much with the pH value but the release rate is sensitive to the pH value. The average amount of hydrogen produced form porous silicon can reach 63.2
mmol per gram of porous silicon. A moderate rate of about 1.77
mol of H
2 per mol of porous silicon can be obtained per day with the aid of the Mg alloy. This technique is potential useful in supplying hydrogen to fuel cells at normal temperature.
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