In order to solve the contradiction found in the Hall-Petch behavior in the ultra-finegrained- and nano-grained- materials, reinvestigation of the physical meaning of Hall-Petch constants has become necessary. The present work is hence attempted to theoretically construct the Hall-Petch slope constant, KH-P. This was carried out based on the principle of image analysis and previous internal energy approach. After analyzing several influencing factors on the KH-P, a model was established with 95% accuracy in predicting the KH-P value. In other words, this model, for the first time, has related the KH-P value to grain boundary surface energy,γ , shear modulus, G, and lattice constant, a0, via 1/ 2 0 K β G(2a γ ) H P = − .
With the increase of interest in using ultra-fine and nano-grained metals for structural purposes, the need to build on the knowledge pool regarding the response and behaviour of those metals under a mechanical load becomes more vital. However, it is well known that, especially for this type of materials such as the ECAPed and ARBed materials, the thermo-mechanical history affects the mechanical behaviour of the product strongly. Although ECAP and ARB are different techniques under the category of severe plastic deformation, similarities in their cyclic deformation response is observed from time to time. Specifically, the microstructural mechanisms involved in accommodating cyclic plastic strain in these two types of materials is seemingly comparable. The similarities arise from the similar microstructures in the majority of the volume of the bulk. In this report, the cyclic deformation response, and the related microstructural mechanisms of ECAPed copper will be discussed first and those of ARBed second. A comparison between ECAPed copper and ARBed copper will then be performed. Furthermore, the differences due to the unique features of ARBed material will be discussed. Lastly, the reasons behind the observed similarities in cyclic deformation behaviour and the related micro-mechanisms for metals process with the two different techniques will also be explored.
Recently, the necessity to grade grain size to ultrafine and nano scale for understanding the mechanical behavior of these materials has been recognized. However, the nature of such classification has remained unclear. As an example, ultrafine (100 nm -1 μm) and nano (<100 nm) grained FCC metals, compared to their coarse grained counterparts, exhibit a grain size strengthening that may deviate from the Hall-Petch relationship. To explain the mechanism of such deviation, previous dislocation theories seem insufficient. To solve this problem, a critical grain size criterion governing the shift of deformation mechanism is proposed in this work. This model employs an energetic approach; it relates the grain boundary energy density to certain critical energy values; and it permits, for the first time, a quantitative grading of grain sizes. Predictions based on this model were evaluated. The prediction on copper polycrystals of various grain sizes showed a very good agreement with experimental results. It is thus wished that the grain size theory on plastic deformation mechanism could be unified with the dislocation theory. In this study, such unification is attempted by using a parameter defined as the defect energy density. The possibility of such generalization is further reasoned upon the fact that the defect energy approach should be a unique but common form applicable for both dislocations and grain boundaries.
A coagulation-anaerobic hydrolysis-aeration process was used to treat the waste cutting fluid which was discharged from a metalworking plant, and the operating conditions of each unit were optimized in this paper. The results showed that 9 g/L polyaluminum chloride and 0.3 g/L cationic polyacrylamide were added in the coagulation stage, the TOC was removed by 78.94% and the BOD5/COD of the waste cutting fluid increased from 0.046 to 0.312 before and after coagulation; The coagulation effluent was further treated by anaerobic hydrolysis-aeration, and the TOC removal efficiencies of the biological process and the whole chemical-biological process were 92.77% and 98.48% respectively; Adding glucose as a cosubstrate into the anaerobic hydrolysis can improve the TOC removal efficiency, when the TOC content ratio of coagulation effluent to glucose solution was 7:3, the TOC removal efficiencies of the biological process and the chemical-biological process reached 97.16% and 99.40%, and the total oil removal efficiency of the whole process reached 99.99%; The effluent quality parameters of the coagulation-anaerobic hydrolysis (with cosubstrate glucose)-aeration process met the Class C limits specified in the Wastewater Quality Standards for Discharge to Municipal Sewers (GB/T 31962-2015); that is, the effluent COD, TN, TP and total oil were below 300 mg/L, 25 mg/L, 5 mg/L and 110 mg/L respectively, and the effluent pH was between 6.5–9.5.
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