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Combined with digital image correlation （DIC）， infrared thermal imaging （IRT）， electron backscatter diffraction （EBSD）， and microhardness distribution， the plastic instability behavior of medium-Mn steel processed by inter-critical quenching during uniaxial tension was analyzed. The results show that the strain-induced martensite transformation of experimental steel mainly occurs in the early stage of uniaxial tension. The Portevin-Le Chatelier（PLC）bands are obviously formed and propagated during this process， accompanied by thermal fluctuations. Moreover， the type of the PLC bands has transitioned from type A to type B and then to type A. The PLC bands are formed by the interaction between dislocation multiplication and interstitial solute atoms， i.e.， dynamic strain aging （DSA）. In the early stage of deformation， the dislocation will preferentially move to the low-density dislocation area， i.e.， propagate unidirectionally along the axis （the type A band）. Then， in the middle stage， the dislocation multiplication and initial interaction leads to the jumping （type B） PLC band formation. Finally， dislocation density and interactions increase in the later stage of deformation， leading to the formation of the type A PLC band again.

7A85-T74 forged aluminum alloy was chosen as the experimental material, and the microstructure, tensile properties and impact energy of the alloy were investigated after 5 h of thermal exposure at room temperature to 240℃. The mechanism of the influence of the microstructure on the mechanical properties of 7A85-T74 aluminum alloy was also analyzed by transmission electron microscopy. The results show that the grain size of 7A85-T74 aluminum alloy does not change much in the temperature range of 80-240℃, but the precipitation phase changes significantly with the increase of temperature. Below 120℃, the precipitate size, tensile properties and impact absorption energy do not change significantly with increasing thermal exposure temperature, and the precipitation strengthening mechanism is a mixture of dislocation cutting precipitates and dislocation bypassing precipitates. With the increase of the thermal exposure temperature from 120℃ to 240℃, the precipitate average radius increases from 3.8 nm at room temperature to 12.3 nm, and the precipitate changes from η' phase to η phase. The yield strength and tensile strength of the alloy decrease significantly by 45.7% and 33.5% respectively compared with that of room temperature and the elongation, reduction of area and impact energy of the alloy increase significantly. The precipitation strengthening mechanism changes to dislocation bypassing precipitates, and the fracture mode changes from mixed fracture consisting of intergranular fracture and dimple transgranular fracture to dimple transgranular fracture. The effect of precipitate size on the strength and impact energy of the alloy discusses based on the precipitation strengthening theory, and the results of the theoretical analysis are consistent with the experimental results.

Al-Cu alloy samples with 5%-20% (mass fraction) Cu were prepared by die-casting process. The hardness of the samples was measured on a Brinell hardness tester. The wear experiments with three kinds of load (1-5 N) were carried out with a ball-disk reciprocating wear tester. The wear mechanism of the samples with different Cu contents was analyzed by SEM and EDS. The results show that as the Cu content increases from 5% to 20%, the volume fraction of θ phase in Al-Cu alloy increases from 2.00% to 25.80%, and the size of θ phase increases gradually; the hardness increases from 59HB to 170HB. The coefficient of friction changes within the range of 0.4-0.85; with the increase of Cu content, the specific wear rate of Al-Cu alloy samples decreases sharply at first and then tends to be gentle. When Cu content is more than 15%, the specific wear rate of alloy samples does not change much, and the lowest specific wear rate is about 4.1×10-4 mm3·N-1·m-1. The specific wear rate of samples with lower Cu content changes significantly with the load, and the specific wear rate difference decreases with the increase of Cu content. The main wear mechanisms of Al-Cu alloys are adhesive wear and abrasive wear. For samples with low Cu content, adhesive wear is dominant; while for samples with high Cu content, abrasive wear is dominant. With the increase of load, the adhesive wear degree of the samples with low Cu content increases, and the abrasive wear degree of the samples with high Cu content increases.

ABSTRACT Understanding the reciprocal interaction between root development and coadapted beneficial microbes in response to elevated CO2 (eCO2) will facilitate the identification of nutrient‐efficient cultivars for sustainable agriculture.Here, systematic morphological, anatomical, chemical and gene expression assays performed under low‐nitrogen conditions revealed that eCO2 drove the development of the endodermal barrier with respect to L‐/S‐shaped lateral roots (LRs) in rice.Next, we applied metabolome and endodermal‐cell‐specific RNA sequencing and showed that rice adapts to eCO2 by spatially recruiting diazotrophs via flavonoid secretion in L‐shaped LRs. Using the rice Casparian strip mutant Oscasp1‐1, we confirmed that reduced lignin deposition selectively recruits the diazotrophic family of Oxalobacteraceae to confer tolerance to low nitrogen availability. [ABSTRACT FROM AUTHOR]