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Due to their high theoretical energy density, lithium metal batteries have generated great research interest. However, the development and utilization of lithium metal batteries is mainly hindered by the key issues (e.g., large volume change, dendrites growth, safety issues) from the Li anode. Therefore, it is of great significance to develop a protective layer with hydrophobic and high elastic properties for stable Li metal anode. Herein, a hydrophobic styrene–isoprene–styrene block copolymer protective layer with high elasticity for stable Li anode has been fabricated. Under the protection of the highly elastic water-repellent protective layer, Li anode showed 'dendrite-free' characteristics and exhibited a long cycle life of 1000 h in Li/Li symmetric batteries and a significant capacity retention rate enhancement of 23% in Li/LiFePO4 full batteries. [ABSTRACT FROM AUTHOR]

The components made out of hypereutectic high-chromium cast iron (HCCI), featured with high abrasion resistance and hardness, are usually subjected to destabilization treatment before use, to improve their hardness and wear resistance by destabilizing the retained austenite which transforms to martensite. This study investigates the effects of destabilization and tempering heat treatment on the microstructure and mechanical properties of an HCCI with and without modification of primary carbides. For the unmodified HCCI, the destabilization simultaneously increased both hardness and the transverse rupture strength (TRS). Increasing the destabilization temperature from 970 to 1090 °C led to a marginal decrease in hardness and slight increase in TRS. Destabilization at 1090 °C increased the transverse rupture strength (TRS) by 54% compared to the as-cast HCCI without reduction in wear resistance due to the coarsening of the secondary carbides. In addition, tempering within a temperature range from 200 to 280 °C after destabilization at 1090 °C led to a slight decrease in hardness, but an increase in TRS and wear resistance. Further increasing the tempering temperature to 310, 340 and 400 °C did not vary the properties. Tempering at 280 °C after destabilization at 1090 °C enabled more than 85% increase in TRS compared to the as-cast HCCI. The influence of destabilization temperature on the TiB2-modified HCCI is similar to the unmodified alloy. But, tempering after destabilization at 1090 °C decreased both hardness and TRS without significant variation of wear resistance even though a TRS peak was obtained at 310 °C tempering. Hence, to achieve the best performance an optimized heat treatment for the unmodified HCCI is destabilization at 1090 °C followed by tempering at 280 °C. For the TiB2-modified HCCI, tempering is not needed. Rationalizations of the mechanical properties are also discussed in terms of microstructure. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of different solutes on the formation of primary carbides in high chromium cast irons (HCCI) through thermodynamic modeling. Growth restriction factor, Q, for the growth of primary carbide in a multicomponent HCCI is evaluated with the assistance of the CALPHAD method. Thermodynamic modeling indicates that modification of the primary carbide by growth restriction through solute addition is ineffective because commonly used solutes in ferrous alloys such as Ti, Nb, and Mn, form carbides or other intermetallic compounds in the melt prior to the formation of primary carbide and non-reactive solutes, such as Cu, Ni, Si, and Co, cannot lead to the formation of sufficient constitutional undercooling zone at the front of the growing carbide to enable the new nucleation event. Hence, it is suggested that external addition or in-situ formation of inoculants to promote heterogeneous nucleation of primary carbides is a more effective approach to refine or modify the primary carbides in HCCIs. [ABSTRACT FROM AUTHOR]

A hypereutectic high chromium cast iron (HCCI) is featured with high abrasion resistance and hardness, making it one of the most widely used materials in mining, minerals and cementation industries. However, the alloy is also naturally brittle partially due to the coarse needle-shaped primary M7C3 carbides. The present work challenges one of the long-term issues associated with HCCIs to modify the primary carbide through addition of a newly discovered additive, TiB2. Addition of 300 ppm such particles led to a significant decrease in the fraction of needle-shaped primary carbides by 35% and reduction in average size of the carbide by 32% in length for the needle-shaped carbide and by 32% in diameter for the equiaxed carbide. As a result, the transverse rupture strength (TRS) of the alloy after heat treatment was increased by 37% together with no noticeable loss in wear or hardness. Although excess TiB2 addition up to 8000 ppm continued reducing the amount of needle-shaped carbide, the improvement in TRS was annulled by the embrittlement of TiB2. Detailed microstructural examination showed that upon addition, TiB2 decomposed in the melt, leading to the formation of TiN particles with fresh surfaces, which acted as M7C3 carbide refiner through promotion of the heterogenous nucleation of the carbide. [ABSTRACT FROM AUTHOR]

The advanced electron backscatter diffraction (EBSD) technique was used to examine the microstructure of a widely used A517GrQ low-carbon low-alloy steel after different heat treatments. Three distinguishable microstructures were studied. Slow cooling in the furnace after austenitization led to the formation of a granular structure that consisted of massive ferrite and randomly distributed M–A constituents. Medium rate cooling in air produced granular bainite that was composed of lath ferrite, and M–A constituents were distributed between the laths. Lath martensite was formed by fast cooling into ice brine. EBSD analysis revealed that, in one austenite grain, the massive ferrite in the granular structure and the lath ferrite in the granular bainite were predominately separated by high-angle boundaries, whilst the ferrite laths in the martensite were separated by low-angle boundaries. The specimens with granular bainite formed by medium rate cooling had higher strength (both yield strength and tensile strength), and also almost 5 times higher Charpy impact energy than that of the specimens containing granular structure obtained at the slow cooling. The strength of the specimens with lath martensite after quenching into ice brine was slightly higher than the granular bainite but were associated with much lower Charpy impact energy. The present work indicates that it is critical to control the cooling rate after austenitization in order to simultaneously achieve high strength and high toughness of low-carbon low-alloy steels. [ABSTRACT FROM AUTHOR]

As a category of crucial wear-resistant alloys, high-chromium cast irons (HCCIs) are widely used in mining, minerals and cementation industries. The large volume fraction of coarse primary M7C3 carbides (PC) imparts excellent wear resistance. However, coarse carbides also induce brittleness, resulting in high cracking susceptibility, and early failure of components, particularly under impact. To minimize the brittleness and increase the service life of HCCI parts, different techniques have been developed through modifying the carbide morphology and refining its size. This paper comprehensively reviews the currently available methods that have either been used in industry production or in laboratory development to modify the primary M7C3 carbides in various HCCIs. The possible mechanisms that govern the refinement of primary carbides are also discussed in-depth. Based on previously published work, the mechanical performance of HCCIs is correlated with the microstructure of the matrix, and with the size, shape, volume fraction and distribution of primary carbides. This may provide solid fundamental to develop more effective techniques and/or new alloys to further improve the properties of this type of materials, increasing their engineering service life and to tailor their wider applications. In addition, the present work also seeks theoretical feasibility to apply the recently well-established theories/models of grain refinement for cast metals to refinement of the primary carbides in HCCIs. [ABSTRACT FROM AUTHOR]

Eutectic modification through minor addition of boron was firstly proposed to improve the malleability of brittle eutectic high-entropy alloys (EHEAs). The proposed approach involves adding small amounts of eutectic modifier, boron (0.2–1.6 at.%), to a brittle dual-phase [face centred cubic (FCC) and σ phase] Fe35Ni25Cr25Mo15 EHEA. Here, we report the role of boron additions in improvement of the mechanical properties of a Fe35Ni25Cr25Mo15 EHEA. It was found that with the increase in boron additions up to 1 at.%, the lamellar eutectic structure consisting of FCC and σ intermetallic phase gradually transited to a dendrite-like eutectic structure. As a result, the compressive fracture strain of the alloy was increased about 3 times with a slight reduction in strength. The mechanisms of eutectic morphology transition induced by boron additions in the Fe35Ni25Cr25Mo15 EHEA and their effects on mechanical properties were studied through microstructural characterization and thermodynamic analyses. The transition of eutectic morphology from lamellar eutectic to dendrite eutectic is believed to be resulted from the increased constitutional undercooling caused by B additions. The solute redistribution of B in the liquid ahead of the solid/liquid interface resulted in a B concentration gradient, which led to the formation of a constitutionally undercooled zone at the front of the σ phase, which destabilized the coupled growth conditions necessary for the formation of the lamellar eutectic structure. As a result, the eutectic morphology was transformed from lamellar eutectic to a dendritic-like eutectic structure. This type of structure exhibits a lower fraction of phase boundaries leading to improved malleability of the brittle EHEA. This insight can be used to design new advanced EHEAs through adjustment of the eutectic morphology. [ABSTRACT FROM AUTHOR]