Hot Corrosion Resistance of TB8 Titanium Alloy after ECAP and Heat Treatment

The metastableβtitanium alloy TB8(Ti-12.76Mo-2.13Nb-2.73A1-0.16Si)was used as the original material,and the secondary processing method combining equal channel angular pressing(ECAP)and heat treatment was adopted.With the help of optical microscope(OM),scanning electron microscope(SEM)and X-ray diffractometer(XRD),the corrosion behavior of TB8 titanium alloy after different secondary processing(800℃/850℃solid solution-520℃aging,ECAP-800℃/850℃solid solution-520℃aging,and800℃/850℃solid solution-ECAP-520℃aging)was studied.The experimental results show that the hot corrosion products of the six samples are similar,mainly Na_(2)Si_(2)O_(5),MoS_(2),TiCl_(2),Ti(SO_(4))_(2),and TiS.Due to the grains of the TB8 titanium alloy treated by 850℃solid solution-ECAP-520℃aging are obviously refined,the surface structure is the most smooth and dense,forming a continuous Al2O3protective film,and the surface defects are the least after corrosion.Its corrosion layer thickness is the lowest(102.3μm),only 36.5%-81.4%of that of other secondary processing titanium alloys.In addition,the corrosion kinetics curves of the six materials all follow parabolic laws,and the minimum corrosion weight gain of the samples after 850℃solutionECAP-520℃aging treatment is 0.7507 mg·mm^(-2),showing better hot corrosion resistance.

Effect of pre-recovery on microstructure and properties of rolled Al-12.18Zn-3.31Mg-1.43Cu-0.20Zr-0.04Sr aluminum alloy

The independently designed and manufactured ultra-high-strength aluminum alloy Al-12.18 Zn-3.31 Mg-1.43 Cu-0.20 Zr-0.04 Sr was investigated via scanning electron microscopy observations, X-ray diffraction analysis, hardness tests, electrical conductivity tests, tensile tests, intergranular corrosion tests, and exfoliation corrosion tests. The effect of pre-recovery on the microstructure and mechanical properties of this aluminum alloy was also studied. The results show that the pre-recovery heat treatment releases deformation energy, inhibits recrystallization, and decreases the dislocation density. Although the pre-recovery heat treatment has little effect on the hardness, electrical conductivity, and elongation of this aluminum alloy, it can dramatically improve the alloy's tensile strength(the maximum tensile strength increased from 785.0 MPa to 809.2 MPa). Moreover, the tensile properties of this aluminum alloy have a certain degree of isotropy, and the pre-recovery heat treatment does not affect this property. In addition, the rolled aluminum alloy exhibits good corrosion resistance, but the effect of the pre-recovery heat treatment on the alloy's resistance to intergranular and exfoliation corrosion is negligible.

Bionics-Inspired Structure Boosts Drag and Noise Reduction of Rotating Machinery

As a global concern,environmental protection and energy conservation have attracted significant attention.Due to the large carbon emission of electricity,promoting green and low-carbon transformation of the power industry via the synergistic development of clean energy sources is essential.Rotating machinery plays a crucial role in pumped storage,hydropower generation,and nuclear power generation.Inspired by bionics,non-smooth features of creatures in nature have been introduced into the structure design of efficient rotating machines.First,the concept and classification of bionics are described.Then,the representative applications of non-smooth surface bionic structures in rotating machineries are systematically and comprehensively reviewed,such as groove structure,pit structure,and other non-smooth surfaces.Finally,conclusions are drawn and future directions are presented.The effective design of a bionic structure contributes toward noise reduction,drag reduction and efficiency improvement of rotating machineries.Green and ecological rotating machinery will remarkably reduce energy consumption and contribute to the realization of the“double carbon”goal.

Enhanced wetting and properties of carbon/carbon-Cu composites with Cr_3C_2 coatings by Cr-solution immersion method

A facile ammonium-dichromate solution immersion method was introduced to synthesize the copperwettable Cr3C2 coating on and inside the carbon-carbon （C/C） preform. The formation mechanism and the microstructures of the Cr3C2 coatings were studied. The contact angle between molten copper and the C/C decreased from 140°to 60°, demonstrating the significant improvement in the wettability. The Cr3C2- coated C/C-Cu composite with only 4.2% porosity and 3.69 gcm^-3 density was manufactured through copper infiltration. As a result, the thermal and electrical conductivity of the modified C/C-Cu increased significantly due to the infiltrated copper. Also the mechanical properties of the composites including both the flexural and compressive strengths were enhanced by over 100%. The modified C/C-Cu composite exhibited lower friction coefficients and wear rates for different load levels than those of the commercial C/Cu composite. These results demonstrate the potential of the modified C/C-Cu material for use in electrical contacts.

Macroscopic superlubricity of potassium hydroxide solution achieved by incorporating in-situ released graphene from friction pairs

Graphene(G),as a typical two-dimensional material,is often used as an additive for liquid lubricants.However,graphene is mostly added to liquid lubricants in a one-time manner in friction;it mainly exists in the form of multilayer agglomerated structures due to theπ–πstacking between graphene sheets,making it unable to fully exert the synergistic lubrication function.Herein,we propose a new macroscopic superlubric system of graphene/potassium hydroxide(G/KOH)solution;and the graphene additive involved is exfoliated in-situ from graphene/epoxy(G/EP)friction pair by friction,continuously providing freshly-peeled graphene into KOH solution and minimizing the adverse effects of graphene agglomeration.Moreover,the in-situ produced graphene additive has thinner thickness and better anti-aggregation ability,which provide more graphene to accommodate OH−,form more stacked sandwich structures of OH−/graphene/OH−between friction pairs(i.e.,equivalent to a moving pulley block with more wheels),and finally realize superlubricity.This study develops a new liquid superlubric system suitable for alkaline environments,and at the same time proposes a new way to gradually release graphene additives in situ,rather than adding them all at once,deepening the understanding to liquid superlubricity mechanism,and paving the experimental foundation for the practical application of macroscopic superlubricity.

模板遗传实现纳微双尺度有序化碳单元及其在紧凑电容储能中的应用

紧凑型超级电容器需要具有高体积能量和功率密度的高密度碳.然而,大多数传统的密度提升方案都是基于孔隙压缩,导致提高体积性能的同时过多地牺牲倍率性能.在此,本研究从碳单元有序堆叠的相反角度出发,提出了一种通过调节模板形貌在纳米和微米双尺度上压缩碳单元之间剩余孔隙的新策略(即一级碳纳米笼和二级由碳纳米笼组成的类碟状组装体的双尺寸排序).优化的纳微有序碳单元的电极密度高达1.08 g cm^(-3)(是商业活性炭的两倍);在离子液体中表现了创纪录的体积能量密度(79 Wh L^(-1))和功率容量(31 kW L^(-1)),以及出色的稳定性(>30,000次循环)和理想的库仑效率(~100%).即使在商业级电极厚度下,其可用的最大堆叠功率密度仍然高达12 kW L^(-1),远高于大多数报道的致密碳.如此出色的体积性能使其在同时需要高体积能量和功率密度的领域具有巨大潜力.