Microstructural evolution and thermal conductivity of diamond/Al composites during thermal cycling

The microstructural evolution and performance of diamond/Al composites during thermal cycling has rarely been investigated.In the present work,the thermal stability of diamond/Al composites during thermal cycling for up to 200 cycles was explored.Specifically,the thermal conductivity(λ)of the composites was measured and scanning electron microscopy of specific areas in the same samples was carried out to achieve quasi-in situ observations.The interface between the(100)plane of diamond and the Al matrix was well bonded with a zigzag morphology and abundant needle-like Al4C3 phases.By contrast,the interface between the(111)plane of diamond and the Al matrix showed weak bonding and debonded during thermal cycling.The debonding length increased rapidly over the first 100 thermal cycles and then increased slowly in the following 100 cycles.Theλof the diamond/Al composites decreased abruptly over the initial 20 cycles,increased afterward,and then decreased monotonously once more with increasing number of thermal cycles.Decreases in theλof the Al matrix and the corresponding stress concentration at the diamond/Al interface caused by thermal mismatch,rather than interfacial debonding,may be the main factors influencing the decrease inλof the diamond/Al composites,especially in the initial stages of thermal cycling.

轮状病毒性肠炎患儿肠道菌群与病情程度、肠道黏膜屏障功能及体液免疫的相关性

背景轮状病毒性肠炎(rotavirus enteritis,RVE)是全球范围内严重影响婴幼儿生命健康的重要疾病之一,近年来临床逐渐认为肠道菌群紊乱在其发生过程中扮演重要角色.但关于肠道菌群对RVE患儿病情程度、体液免疫的影响的验证数据尚少.目的探讨RVE患儿肠道菌群与病情程度、肠道黏膜屏障功能及体液免疫的相关性.方法选取我院2019-01/2021-05 RVE患儿131例,根据病情程度分为轻症组(39例)、中症组(58例)、重症组(34例).比较3组肠道菌群数量与失调分级分布情况,分析肠道菌群数量、失调分级与病情程度的关系,对比不同肠道菌群失调分级患儿肠道黏膜屏障功能指标[血清D-乳酸(D-lactic acid,D-LA)、二胺氧化酶(diamine oxidase,DAO)、内毒素(endotoxin,ET)]、体液免疫指标[血清免疫球蛋白A(immunoglobulin A,IgA)、免疫球蛋白G(immunoglobulin G,IgG)、免疫球蛋白M(immunoglobulin M,IgM)]水平,分析肠道黏膜屏障功能、体液免疫与肠道菌群失调分级的相关性.结果肠道双歧杆菌、乳酸杆菌数量与病情程度呈负相关,肠道大肠埃希菌数量、菌群失调分级与病情程度呈正相关(r=-0.727、-0.734、0.757、0.748,P均<0.05);血清D-LA、DAO、ET与肠道菌群失调分级呈正相关,血清IgA、IgG、IgM与肠道菌群失调分级呈负相关(r=0.752、0.717、0.748、-0.715、-0.703、-0.787,P均<0.05).结论RVE患儿肠道菌群数量、失调分级与病情程度、肠道黏膜屏障功能、体液免疫显著相关,为临床制定治疗方案提供借鉴依据.

Deformation treatment and microstructure of graphene-reinforced metal matrix nanocomposites: A review of graphene post-dispersion

Graphene/aluminum(Gr/Al)composites have attracted the attention of researchers all over the world due to their excellent properties.However,graphene agglomerates easily because of the van der Waals force between graphite sheets,thereby affecting the performance of the composites.Decreasing the agglomeration of graphene and dispersing it uniformly in the Al matrix is a key challenge.In the preparation process,predispersion treatment and deformation treatment can play important roles in graphene dispersion.Researchers have conducted a series of research and literature reviews of the graphene predispersion and consolidation of composites.However,they paid less attention to post-deformation processing.This review summarizes different deformation treatments involved in the preparation process of Gr/Al composites and the evolution of the microstructure during the process.Research on deformation parameters is expected to further improve the properties of Gr/Al composites and would provide a deep understanding of the strengthening effect of graphene.

Mechanical Property of M40J_f/5A06Al Composite at Elevated Temperatures

In this work, aluminum alloy with a high concentration of magnesium （5A06） was reinforced with 55 vol% unidirectional ultra-high modulus and highly graphitized carbon fiber （M40J） using pressure infiltration method. The effect of temperature on the bending strength of the Cf/A1 composites was investigated from room temperature to 500 ℃. The experimental results showed that the strength of M40Jf/5A06A1 composites was not affected by temperature from room temperature to 200 ℃. The bending strength of the composite at 300 ℃ was decreased by 30% compared with that at room temperature. In order to evaluate the extent of interface weakening, the length of fiber pullout was measured. The results showed that the pullout length reached the maximum at 300 and 500 ℃, which indicated weak interface at the corre- sponding temperature. The DSC curve presented obvious heat absorption peak at around 300 ℃, which may be attributed to the dissolution of the interfacial product （A13Mg2） phases at the C/A1 interface. The bending fracture surfaces of the composites after three-point bending tests were observed by SEM, plastic-viscous flow of the matrix were observed at the samples tested at 500 ℃. The predominant mechanisms for high-temperature damage of M40Jf/5A06A1 composites are matrix softening caused by dislocation recovery and interface weakening caused by the dissolution of interfacial products.

Electrical Discharge Machining of Al2024-65 vol%SiC Composites

In the present work, the wire electrical discharge machining（WEDM） process of the 65 vol% SiCp/2024 Al composite prepared by pressure infiltration methods has been investigated. The microstructure of the machined composite was characterized by scanning electron microscope, the average surface roughness（Ra）, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy（TEM） techniques. Three zones from the surface to the interior（melting zone, heat affected zone and un-affected zone） were found in the machined composites, while the face of SiC particles on the surface toward the outside was ‘‘cut＇＇ to be flat. Increase in Al and Si but decrease in C and O were observed in the core areas of the removed particles. Si phase, which was generated due to the decomposition of SiC, was detected after the WEDM process. The irregular and spherical particles were further observed by TEM. Based on the microstructure observation, it is suggested that the machining mechanism of 65 vol% SiCp/2024 Al composite was the combination of the melting of Al matrix and the decomposition of SiC particles.