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Purpose: To clarify the effects of rice straw returning on the yield and quality of common buckwheat. Methods: Common buckwheat cultivar Fengtian 1 was used across two years and treated with no rice straw returning combined with no compound fertilizer (CK), no rice straw returning combined with normal fertilizer (NSNF), full rice straw returning with 20% (FSRF20%), 40%, (FSRF40%) and 80% (FSRF80%) reduction in compound fertilizer application, and full rice straw returning with no compound fertilizer (FSNF). Results: Compared with the CK treatment, the FSRF20% treatment increased the accumulation and transport rate of non-structural carbohydrate in leaves at full bloom and grain filling stages and the enzyme activity of rhizosphere soil. With decreased compound fertilizer application rate, the grain weight per plant, 100-grain weight, and yield initially increased and then decreased, reaching the maximum at FSRF20% treatment. Compared with that of the CK treatment, the NSNF, FSRF20%, FSRF40%, FSRF80%, and FSNF treatment increased the yield by 172.54%, 181.02%, 104.49%, 69.30%, and 22.33%, respectively. The proportion of essential amino acids was about half that of total amino acids of common buckwheat. The flavonoid and starch content in grains of FSRF40% treatment were the highest. The protein, total amino acids, and essential amino acids content in grains of CK treatment were the highest. Conclusions: For the sustainable development of farmland and improve the economic benefits of cultivating common buckwheat, 20% reduction in compound fertilizer can be considered when the total amount of rice straw was returned to the field.

In the precision machining of thin-walled planar components, the initial residual stress of the workpiece could lead to subsequent deformation after machining, which influences the geometrical accuracy of the final parts. Generally, conventional methods, such as stress-relief annealing and vibration stress relief, are implemented to reduce the magnitude of the residual stress. However, the distribution of the residual stress, which is more significant to the machining accuracy for thin-walled parts, is difficult to be adjusted in these methods. This article proposes a novel method to control the stress distribution and magnitude during the manufacturing process and thus reduce the machining-induced deformation for the thin-walled planar part of pure copper. In this method, symmetrical distribution of residual stress is introduced by multi-pass rolling, quenching, stress-relief annealing, and turnover turning. The stress field and deformation of the part are predicted by finite element modeling in the whole process. The part deformation after machining is verified by the experiments. The results show that compared with the traditional stress-relief annealing, this novel method could reduce the part deformation after machining and improve the geometrical accuracy for thin-walled parts.

The forming-induced residual stress of metallic parts could cause undesired deformation in the final machining process, especially for the thin-walled parts. Therefore, heat treatment is essential to release the residual stress prior to machining. This study investigates the residual stress change of a forged pure iron part in annealing heat treatment and material removal processes. A modified creep constitutive model with the consideration of microstructure evolution was established to describe the residual stress relaxation in the annealing. Stress relaxation tests were conducted to calibrate the material constants. This constitutive model was then implemented into the finite element model of annealing for the cold-forged semi-spherical shell. The residual stress and the grain size of the shell were predicted at different heating temperatures. The semi-spherical shells were machined to the final thin-walled parts, and the deformation owing to the residual stress release was measured and compared to the simulation results. The heating temperature was determined aiming to minimize the machining-induced deformation as well as to ensure the microstructure. This study could provide guidance to the elimination of the residual stress and the improvement of the geometrical accuracy for thin-walled parts in the machining process.

A novel electropolishing approach for Ti6Al4V was developed involving a zinc chloride (ZnCl2)-urea deep-eutectic polishing system, with current density of 0.6 A cm−2, temperature of 90 °C, stirring speed of 260 rpm, and polishing time of 10 min. The system achieved a polished surface with 73% reduction in surface roughness. Compared with other electropolishing processes, the system decreased material mass loss rate following electropolishing of titanium alloys, making it suitable for surface polishing of additively or conventionally melt-cast fabricated titanium alloys. Using the deep-eutectic solvent for electropolishing of Ti6Al4V not only improves surface hydrophobicity, but also enhances electrochemical corrosion resistance. Furthermore, compared with electropolishing behaviour in green nonaqueous solvents, a similar electropolishing mechanism occurred in deep-eutectic solvents, but the electropolishing efficiency in the ZnCl2-urea deep-eutectic system was higher, and its surface mass loss become lower than that of the sodium chloride-glycol electropolishing systems. The developed system provided a new approach for surface finishing of titanium alloys and has great potential for engineering applications.

In order to improve the wear resistance of titanium alloys, the potential of the plasma nitriding process with a cathode assiting discharge setup was examined. Ti6Al4V alloy was nitrided by the cathode assiting discharge nitriding (CAN) and conventional DC plasma nitriding (CPN) methods, respectively. The micro-topography, phase composition and cross-sectional microhardness distribution of two nitriding layers were studied comparatively. The sliding wear resistance of the nitriding layers was examined by a ball-on-disk test against Si3N4balls. The results indicated that the surface roughness Ra of the CAN layer was about 1 order less than that of the CPN layer. In addition, the CAN surfaces possessed significantly greater wear resistance than the CPN layer at higher loads, and increased the wear resistance of Ti6Al4V alloy by about 2 orders due to the higher loading bearing ability, higher rate of TiN phase, greater surface microhardness and bigger microhardness improving depth. This is because the double glow discharge effect in CAN strengthened the density of the active nitrogen atoms and the nitriding efficiency. Moreover, the ion bombardment effect on the surface of the nitriding titanium alloy was reduced obviously.