Search

Microstructure evolution via deformation‐induced martensitic transformation, void formation, and crack propagation is investigated in a metastable austenitic Cr–Mn–N stainless steel for up to 90° bending using a combination of electron backscattering diffraction and parent grain reconstruction. Stress–strain heterogeneity and stress triaxiality studied using finite‐element analysis reveal that the inner and outer radii are in approximately uniaxial compressive and tensile stress states, respectively, with the outer radius showing higher values for von Mises and principal stresses and equivalent strain. Voids are observed at both austenite/α′‐martensite and α′/α′‐martensite interfaces. Parent grain reconstruction applied to the 90° bending sample reveal that the cracks at α′/α′‐martensite interfaces tend to propagate predominantly along intergranular parent austenite grain boundaries. It is also found that both intragranular and intergranular cracks in parent austenite tend to propagate between α′‐martensite child–child grains comprising the same crystallographic packets. This is the first study of its kind to comprehensively show this phenomenon. A representative example of intergranular crack propagation within a ⟨110⟩‖normal direction (ND)‐oriented parent austenite grain is also demonstrated. [ABSTRACT FROM AUTHOR]

Due to the negative correlation between the frequency response and the rated flow of the servo valve, there remains challenge to achieve high dynamic response of large-flow servo valve-controlled hydraulic systems under extreme operating conditions. Although the effective bandwidth of such system can be extended via various control methods, the inherent performance limit of hardware limits further improvement of the system dynamic response. In this paper, a flow-reduced double valve actuation strategy is proposed to improve the performance of electro-hydraulic servo drives. By reducing the actually used flow, the frequency response of the servo valve is enhanced due to the decreased hydraulic spring force and transient flow force acting on the spool. Two flow-reduced servo valves are adopted in parallel to meet large flow along with the improved dynamic performance. Simulation research is conducted and a servo valve-controlled shaking table with a specially designed valve block is used for experimental validation. Simulation and experimental results prove that the proposed strategy possesses better dynamic performance than the conventional single valve actuation. [ABSTRACT FROM AUTHOR]

Thin strips with varying thicknesses (TSVTs) produced by micro flexible rolling have wide applications in diverse micro manufacturing areas such as micro electromechanical systems (MEMS) and micro system technologies (MST). TSVTs consist of three regions based on different thicknesses, i.e. the thicker, the transition and the thinner zones. Among them, the transition zone plays a key role in evaluating the quality of TSVTs. In the current work, thin 1060 aluminium alloy strips were flexibly rolled under various thickness ratios followed by annealing treatment. The influences of annealing temperature on the microstructural evolution and hardness variation of the transition zone of TSVTs were investigated. The results reveal that the recrystallisation has happened after annealing at 400 °C for 30 min, which induces fine and homogeneously-distributed grains in both of the thinner and transition zones. Only moderate increase in hardness is found from the thicker to the thinner zones after annealing treatment.

The significant development of catalytic biomass conversion has provided a large library of chemicals ready for subsequent upgrading to polymerisable monomers for the design and preparation of sustainable polymers. In this study, hydroxyethylation of eugenol by using green ethylene carbonate as alkylation reagent and cheap tetrabutylammonium iodide ionic liquids as green solvents and catalysts produced 2‐(4‐allyl‐2‐methoxyphenoxy)ethan‐1‐ol with a 85% yield, which could be used to construct an in situ CO2 capture and conversion system by taking the reversible chemistry of alcoholic compounds with CO2 in the presence of superbases, on which α,ω‐diene functionalized carbonate monomers were successfully prepared and were applied in thiol‐ene click and acyclic diene metathesis polymerisation (ADMET), producing a series of poly(thioether carbonate)s and unsaturated aromatic aliphatic polycarbonates with moderate molecular weights and satisfactory thermal properties. The structures of the formed CO2 reversible ILs, the polymerisable monomers and the corresponding polymers were fully characterized by various technologies. [ABSTRACT FROM AUTHOR]

The microstructure of Cr–Mn–Ni–N stainless steel is regulated by a combination of cold deformation and subsequent martensite reversed annealing. The yield strength and tensile strength of the tested steel are greatly improved to 1220 and 1357 MPa, respectively, by conventional heavy cold rolling (66% thickness reduction) and a subsequent annealing process (750 °C for 5 min) relative to those before cold rolling (austenized state); at the same time, the total elongation keeps an appropriate value. The results show that the grain refinement strengthening acts as the primary factor for the strengthening of the tested steels while the precipitation behavior from the M23C6‐type carbides is not quite effective. Additionally, different yield phenomena and microstructural evolution for tested steels with 66% thickness reduction annealed at 750 °C with different holding times are systematically analyzed and discussed. Lüders‐like deformation features noticeably appear but become weakening with the longer annealing time. The change in initial free mobile dislocation density is the core cause of the preyield plateau phenomenon. [ABSTRACT FROM AUTHOR]

Highly textured Heusler alloy Mn44.7Ni43.5Sn11.8 ribbons were prepared by melt spinning. The magnetocaloric properties were evaluated by the direction of the magnetic field along the ribbon surface and perpendicular (H∥ and H⊥, respectively) for the same sample with the field up to 10 and 15 kOe. While the maximum magnetic entropy changes only a little difference (5%), the hysteresis loss (HL) and net refrigerant capacity (RC) have been significantly affected by the crystallographic texture of the magnetic field of 10 kOe. The amount of the RC reduces about 10% (H⊥) and 30% (H∥) due to the HL, respectively. The highly textured Mn-Ni–Sn melt-spun ribbons can be potentially applied in industrial magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Micro flexible rolling aims to fabricate submillimeter thick strips with varying thickness profile, where the surface quality of products is mainly determined by initial workpiece surface roughness and subsequent surface asperity flattening process, which is affected by process parameters during rolling. This paper shows a 3D finite element model for flexible rolling of a 250 μm thick workpiece with reduction of 20 to 50%, and rolling phase with thinner thickness indicates a better ability to decrease the surface roughness. Four types of initial workpiece surface roughness are studied in the simulation, and the influences of process parameters, such as friction coefficient, rolling speed and roll gap adjusting speed, on surface asperity flattening of workpieces with different initial surface roughness have been numerically investigated and analysed.

Micro forming of metals has drawn global attention due to the increasing requirement of micro metal products. However, the size effects become significant in micro forming processes and affect the application of finite element (FE) simulation of micro forming processes. Dividing samples into small areas according to their microstructures and assigning individual properties to each small area are a possible access to micro forming simulation considering material size effects. In this study, a new model that includes both grains and their boundaries was developed based on the observed microstructures of samples. The divided subareas in the model have exact shapes and sizes with real crystals on the sample, and each grain and grain boundaries have their own properties. Moreover, two modelling methods using different information from the microstructural images were introduced in detail. The two modelling methods largely increase the availability of various microstructural images. The new model provides accurate results which present the size effects well.