Strain hardening recovery mediated by coherent precipitates in lightweight steel

We investigated the effect of κ-carbide precipitates on the strain hardening behavior of aged Fe–Mn-Al-C alloys by microstructure analysis. The κ-carbides-strengthened Fe–Mn-Al-C alloys exhibited a superior strength-ductility balance enabled by the recovery of the strain hardening rate. To understand the relation between the κ-carbides and strain hardening recovery, dislocation gliding in the aged alloys during plastic deformation was analyzed through in situ tensile transmission electron microscopy (TEM). The in situ TEM results confirmed the particle shearing mechanism leads to planar dislocation gliding. During deformation of the 100 h-aged alloy, some gliding dislocations were strongly pinned by the large κ-carbide blocks and were prone to cross-slip, leading to the activation of multiple slip systems. The abrupt decline in the dislocation mean free path was attributed to the activation of multiple slip systems, resulting in the rapid saturation of the strain hardening recovery. It is concluded that the planar dislocation glide and sequential activation of slip systems are key to induce strain hardening recovery in polycrystalline metals. Thus, if a microstructure is designed such that dislocations glide in a planar manner, the strain hardening recovery could be utilized to obtain enhanced mechanical properties of the material.

HIGHLY RESPONSIVE AND ACCURATE TEMPERATURE MEASUREMENTS IN ORTHOGONAL CUTTING THROUGH INNOVATIVE SINGLE LEG THERMOCOUPLE

During machining, most of the thermal sources are resulting from the conversion of mechanical energy during the chip shearing mechanism and the intense frictions between the tool, the chip, and the machined surface. Thermal gradients are high and localized, especially for low thermal diffusivity material like titanium alloys. Moreover, heat rates come close to few million degrees per second in the shearing zones. Even though several authors performed thermography techniques to determine the temperature distribution into the machined material, their results remain underestimated due to experimental limitations. In this research, a new temperature measurement technique has been developed based on a single wire thermocouple to measure at one exact location both the temperature and the heating rate during orthogonal cutting test. The tests are performed with uncut chip thicknesses of 0.020 mm and 0.100 mm and with a cutting speed of 120 m/min with two different cutting angles. Results are discussed and compared to prior studies.

Design and Testing of a Shearing and Breaking Device for Mulch Film and Cotton Stalk Mixtures

HighlightsThis article presents a shearing and breaking device for mulch film and stalk mixtures after mechanized recovery.The focus is on a curved V-shaped mechanism with three-dimensional precompression and shearing functions.The device can efficiently and continuously perform film crushing, stalk crushing, and entanglement breaking.The crushed film and stalk mixture is conducive to material separation, further treatment, and recycling.Abstract. Because the mixture of mulch film and stalks collected in harvested cotton fields in Xinjiang, China, cannot be separated mechanically, a technical solution for shearing and breaking is proposed. This study designed a shearing and breaking device for film and stalk mixtures that can continuously perform film crushing, stalk crushing, and entanglement breaking. The design focuses on a curved V-shaped shearing mechanism, which provides three-dimensional shearing and improves the crushing of film and stalks. The linear speed of the conveying rollers (x1), the working angle of the shearer (x2), and the speed of the shearer spindle (x3) were selected as influencing factors, and the crushed film rate (Ph), crushed stalk rate (Gh), and broken entanglement rate (Kh) were used as evaluation indexes in quadratic orthogonal rotation combination tests. The test results were analyzed with Design-Expert software, and a regression model between each factor and the evaluation indexes was established to analyze the significance of each factor’s influence. The results showed that the influences of the three factors on Ph in descending order were x3, x2, and x1. The order of influence on Gh and Kh was x3, x1, and x2. The optimization module in the software was used for parameter optimization, and the optimal combination of working parameters of the device was x1 = 0.98 m s-1, x2 = 153°, and x3 = 753 r min-1. The optimized parameter combination was tested and verified, and the results were Ph = 77.28%, Gh = 87.78%, and Kh = 85.30%. The test results are basically consistent with the predicted values, and the optimized working parameters are reliable and can meet the requirements for the shear fracture of film and stalk mixtures. This research provides a technical reference for the cutting and crushing of complex mixed solid materials. Keywords: Agricultural machinery, Curved V-shaped moving knife, Design, Film and stalk mixture, Parameter optimization.

TEM observation of precipitates and their role to mechanical properties in Ti-5553 alloy heated to some temperatures up to 923 K

A Ti-5553 specimen was continuously heated to 923 K and simultaneously in-situ HEXRD profiles were taken. In addition, specimens heated at the same rate to several temperatures up to 923 K and further quenched were observed by transmission electron microscopy. Based on both results obtained, transformation sequence was clarified, precipitations of ω-, α”iso- and α-phases were confirmed, and size and density of these precipitates were measured. Hardness values of those specimens were also measured. The hardening mechanism was considered as shearing-mechanism for specimens aged at lower temperatures and by-pass one for specimens aged at higher temperature. An attempt of distinction between α”iso - and α-precipitates was also tried. Both precipitates were in needle-like shape and a possibility was suggested by measuring angles between two needle-shape precipitates on {110} of the matrix and comparing with each other.

Detailed investigation of the shearing mechanism of β" precipitates in Al-Mg-Si alloys

The mechanism behind shearing of β11 precipitates in Al-Mg-Si alloys during deformation is investigated by applying advanced transmission electron microscopy (TEM) techniques and frozen phonon multislice TEM image simulations on a selection of shearing configurations. In particular, the results indicate that the needle-like precipitates are sheared several times in single matrix Burgers vector steps. The multislice image simulations suggest that shearing events are most likely achieved in single Burgers vector steps, and there are some experimental evidence that the shearing planes are the matrix glide planes.