Investigation of the Relation between Rolling Contact Fatigue Property and Microstructure on the Surface Layer of D2 Wheel Steel

Through the rolling contact fatigue experiment under the condition of the lubricating oil, this article investigated the relation between contact fatigue property and microstructure on the surface layer of D2 wheel steel. The results showed that although the roughness of the original specimen induced by mechanical processing would diminish to some extent in the experiment, the 0.5 - 1.5 μm thick layer of ultrafine microstructure on the original mechanically-processed specimen surface would still become micro-cracks and small spalling pits due to spalling, and would further evolve into fatigue crack source. Additionally, even under the impact of the load that was not adequate to make the material reach fatigue limit, the ferrite in the microstructure underwent plastic deformation, which led the refinement of proeutectoid ferrite grains. During the experiment, the hardening and the refinement caused by plastic deformation consisted with the theory that dislocation gave rise to plastic deformation and grain refinement. The distribution laws of hardness and ferrite grain sizes measured could be explained by the distribution law of the shearing stress in the subsurface.

Microstructure of Ni /WC Surface Composite Layer on Gray Iron Substrate

The surface infiltrated composite （Ni/WC） layers on gray iron substrate were fabricated through a vacuum infiltration casting technique （VICT） using Ni-based composite powder with different WC particles content as raw materials.The microstructures of surface infiltrated composite layer,the interface structures between surface composite layer and the substrate,the changes of macro-hardness with the increasing of WC content and the micro-hardness distribution are investigated.The infiltrated composite layer includes a surface composite layer and a transition layer,and the thickness of the transition layer decreases with the increasing content of WC.The thickness of transition layer with 20%WC content in the surface infiltrated composite layer was 170 μm which was the thickest for all transition layers with different WC content.The surface composite layer was mainly composed of WC,W2C,FeB and NiB,along with Ni-Cr-Fe,Ni （Cr） solid solution,Ni （Si） solid solution and Ni （Fe） solid solution.The transition layer was composed of Ni （Cr） solid solution,Ni （Fe） solid solution,Ni （Si） solid solution,Fe （Ni） solid solution and eutectic.The surface macro-hardness and micro-hardness of the infiltrated layer had been evaluated.The macro-hardness of the surface composite layer decreases with the WC content increasing,and the average macro-hardness is HRC60.The distribution of micro-hardness presents gradient change.The average micro-hardness of the infiltrated layer is about HV1000.

Mg,Ti-base surface integrated layer and bulk doping to suppress lattice oxygen evolution of Ni-rich cathode material at a high cut-off voltage

The Nickel-rich layered cathode materials charged to 4.5 V can obtain a specific capacity of more than 200 m Ah g^(-1).However,the nickel-rich layered cathode materials suffer from the severe capacity fade during high-voltage cycling,which is related to the phase transformation and the surface sides reactions caused by the lattice oxygen evolution.Here,the simultaneous construction of a Mg,Ti-based surface integrated layer and bulk doping through Mg,Ti surface treatment could suppress the lattice oxygen evolution of Nirich material at deep charging.More importantly,Mg and Ti are co-doped into the particles surface to form an Mg_(2)TiO_(4) and Mg_(0.5–x)Ti_(2–y)(PO_(4))_(3) outer layer with Mg and Ti vacancies.In the constructed surface integrated layer,the reverse electric field in the Mg_(2)TiO_(4) effectively suppressed the outward migration of the lattice oxygen anions,while Mg_(0.5–x)Ti_(2–y)(PO_(4))_(3) outer layer with high electronic conductivity and good lithium ion conductor could effectively maintained the stability of the reaction interface during highvoltage cycling.Meanwhile,bulk Mg and Ti co-doping can mitigate the migration of Ni ions in the bulk to keep the stability of transition metal–oxygen(M-O)bond at deep charging.As a result,the NCM@MTP cathode shows excellent long cycle stability at high-voltage charging,which keep high capacity retention of 89.3%and 84.3%at 1 C after 200 and 100 cycles under room and elevated temperature of 25 and 55°C,respectively.This work provides new insights for manipulating the surface chemistry of electrode materials to suppress the lattice oxygen evolution at high charging voltage.

Fractal Characteristics and Microstructure Evolution of Magnetron Sputtering Cu Thin Films

How to describe surface morphology characteristic and microstructure evolution are the hottest researches of current thin film researches. But in traditional characterization of surface morphology, the roughness parameters are scale related. And the microstructure evolution of thin film during post-treatment is usually not considered in detail, To give a better understanding of the roughness of thin films topography, fractal method is carried out. In addition, microstrueture evolution of thin films is analyzed based on the crystallography and energy theory. Cu thin films are deposited on Si （100） substrates by magnetron sputtering, and then annealed at different temperatures. Surface topography is characterized by atomic force microscope （AFM）. Triangular prism surface area （TPSA） algorithm is used to calculate the fractal dimension of the AFM images. Apparent scale effect exists between the surface morphology roughness and film thickness. Relationship between the fractal dimension and roughness is analyzed by linear regression method and linear relationship exists between fractal dimension and surface roughness root mean square （RMS）. Fractal dimension can be characterized as a scale independence parameter to represent the complex degree and roughness level of surface. With the increase of annealing temperature, surface roughness and fractal dimension decrease. But when the annealing temperature exceeds the recrystallization temperature, due to the agglomeration and coalescence of Cu grain, surface roughness and fractal dimension increase. Scale effect and changing regularity of grain growth and shape evolution for different film thickness under different annealing temperatures are analyzed. Based on minimum total free energy, regularity of grain growth and changing is proposed. The proposed research has some theory significance and applicative value of Cu interconnect process and development of MEMS.

Effect of Sliding Wear on Surface Microstructure and Wear Property of D2 Wheel Steel

In this paper, the surface microstructure and wear property of D2 wheel steel under sliding wear condition were studied by MRH-30 sliding wear tester. After testing, a transmission electron microscope (TEM), scanning electron microscope (SEM) with electron backscatter diffraction (EBSD), and micro-hardness testers were used to characterize the surface microstructure of samples with different cycles. The results show that the wear losss samples are increased as the increase of cycles, and the wear loss of wheel samples is higher than that of rail samples. The surface hardness and thickness of deformation layer of wheel samples are increased as the cycles increase. After sliding wear, the samples surfaces form the white etching layer with the thickness of several microns. Through the analysis of surface microstructure of sample with 12,000 cycles, the lamellar cementite in pearlite is fragment into cementite particles with the decrease of depth from surface, and the cementite is dissolved at surface to lead to the form of white etching layer. The ferrite grains are refined gradually and the fraction of high angle grain boundary is increased with the decrease of depth from surface. The nanosgrains layer of ferrite grains with 5 μm thickness is formed. According to the result of finite element simulation of contact surface temperature, the formation of surface nanograins and the dissolution of cementite are caused by the severe plastic deformation. The fiber structure of samples is formed after sliding wear, with direction of .

Microstructure and Mechanical Property of Ni Metal Treated by Surface Mechanical Attrition

A nanostructured surface layer can be formed in Ni metal treated by surface mechanical attrition (SMA). The microstructure was investigated by using optical microscope, X-ray diffractometer and transmission electron microscope, respectively. Mechanical property measurements indicate that the yield strength of the surface layer raises significantly while the tensile strength somewhat changes and the elongation percentage reduces severely compared with that of the inside layer. Meanwhile, yield-drop-like phenomenon occurs in the surface layer after SMA treatment. In order to compare the mechanical behavior of nanostructured materials with two phases, Fe-30Ni nanostructured alloy was also investigated.

Friction Stir Processing of Thixoformed AZ91D Magnesium Alloy and Fabrication of Surface Composite Reinforced by SiC_ps

The microstructural evolution characteristics of the thermomechanically affected zone （TMAZ） alloy during friction stir processing （FSP） of thixoformed （TF） AZ91D alloy were investigated. Simultaneously, a surface composite layer reinforced by SiC particles （SiCps） was prepared on the alloy by FSP and the corresponding tribological properties were examined. The experimental results indicate that dynamic recrystallization and mechanical separation （including splitting and fracture of the primary grains） are the main mechanisms of grain refinement for the TMAZ. A composite surface reinforced by uniformly distributed SiCps was prepared on the alloy. Compared with the corresponding permanent mould casting alloy and the TF alloy without composite surface, the TF alloy with composite surface has the highest wear resistance and lowest friction coefficient.

EFFECT OF ALUMINIUM AND BORON ON SURFACE MODIFICATION OF SOME MATERIALS

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激光熔凝处理对P20钢组织及性能的影响

目的提高P20模具钢的表面硬度和耐磨性能。方法采用激光熔凝技术对P20模具钢表面进行强化处理。通过硬度梯度检测和摩擦磨损测试,分别评价熔凝层的硬度分布特征和耐磨性能,并通过光学显微镜和扫描电子显微镜对熔凝层及磨痕形貌进行分析。结果使用激光输出功率为500W、光斑直径为2.5mm、聚焦透镜距离为40 mm、扫描速度为6 mm/s、搭接率为45%、氮气保护的激光熔凝工艺所得熔凝层的组织细小,无脱碳、畸变、裂纹等缺陷,熔凝处理质量高。熔凝过程中单道激光熔凝层呈半椭圆形分布,最大深度为610~620μm。熔凝处理后表面硬度提升显著,熔凝层的硬度分布与熔凝层的区域位置有关,具有较高硬度且硬度保持基本稳定的熔凝层深度约为400μm;单道激光熔凝层最高硬度可达460~480HV,重叠影响区即双熔凝区的最高硬度在540~560HV之间,即熔凝层硬度普遍较基体硬度提高了60%以上。此外,P20模具钢经过激光熔凝处理后耐磨性能提升明显,其平均摩擦因数约为0.85,熔凝处理的磨损失重较未处理的试样减少了约61%,其磨损机制主要表现为磨粒磨损和少量的黏着磨损或剥落脱离。结论激光熔凝处理能够显著提高P20模具钢的表面硬度和耐磨性能,试验采用的激光熔凝工艺可在P20钢表面获得硬度较高且稳定可靠的熔凝层深度在400μm左右,能将P20模具钢的表面硬度及耐磨性提高60%以上。

等离子弧熔覆Fe-C-B-V系耐磨堆焊层的组织及性能研究

以硼铁、高碳铬铁、钒铁为原料,采用等离子弧熔覆技术在Q345钢表面堆焊Fe-C-B-V系铁基合金。使用金相显微镜、扫描电镜和X射线衍射仪等研究了堆焊层的显微组织;分别使用维氏硬度计和冲击试验机测量堆焊层的显微硬度和冲击韧性。结果表明,堆焊层显微组织主要由马氏体、网格状Fe_(3)(C,B)和Fe_(2)B、弥散分布的碳化物及硼化物等(如VB_(2)、VC、Cr_(2)B)硬质相构成;堆焊层的平均硬度高达904.58 HV10、冲击功为68.5 J。堆焊过程中形成的硼化物、碳化物作为硬质相提高了堆焊层的硬度和耐磨性,形成的碳化钒使组织从鱼骨状变成网格状,细化了晶粒,提高了堆焊层的冲击韧性。

超声滚压表面复合强化研究综述

超声滚压技术通过位错的湮灭和产生将晶粒细化至纳米级,提高了材料硬度和耐磨损等性能。探讨了如何进一步提升材料的使役性能,通过将超声滚压与其他处理技术相结合形成复合加工工艺,克服单一超声滚压处理工艺的局限性,如超过塑性变形的极限或过度强化带来的起皱、开裂和压溃等。超声滚压表面复合强化技术作为特种复合加工工艺,在零件高性能表面制造中具有明显优势。根据超声滚压在复合工艺中的位置顺序,分别介绍了超声滚压前端强化、同步强化和后续强化3种加工类型。超声滚压前端复合加工技术主要包括超声滚压复合物理气相沉积技术和超声滚压复合离子注入技术等。在超声滚压同步强化方面,讨论了声电耦合和温度场辅助超声滚压对变形层厚度和摩擦磨损性能的影响。在超声滚压后续强化方面,介绍了涂层复合超声滚压技术,讨论了它对涂层裂纹、孔隙以及表面粗糙度的影响。此外,分析了超声滚压对复合强化过程中材料微观组织演化和塑性变形的作用机制,总结了这些技术在改善表面强化效果和满足复杂服役要求方面的研究现状。最后,展望了超声滚压复合强化技术的应用前景和发展方向,强调了它在提高材料使役性能方面的研究价值和目标。

Y_(2)O_(3)对等离子堆焊WC/Ni60堆焊层组织及性能的影响

利用等离子堆焊在Q235钢板上制备镍基复合堆焊层,研究了不同含量的Y_(2)O_(3)对镍基碳化钨堆焊层组织及性能的影响。采用SEM、XRD分析了堆焊层的微观组织;使用维氏硬度计和端面高温摩擦磨损试验机对堆焊层进行了硬度和磨损性能测试。结果表明:Y_(2)O_(3)的加入促使堆焊层中碳化物规则化,以WC为核心向周围生长。堆焊层检测出主要的物相为γ-Ni(Fe)、WC、W_(2)C、M_(23)C_(6)、M_(6)C、Cr_(7)C_(3)、FeNi_(3)相。添加1.2%Y_(2)O_(3)的堆焊层维氏硬度达到最大值970 HV0.5,比未加Y_(2)O_(3)的堆焊层硬度高283 HV0.5,在高温摩擦磨损条件下磨损量最小为2.8 mg,摩擦系数为0.32,此时磨损机制为轻微的磨粒磨损。

反倾层状斜坡破裂面演化特征离心机模型试验与数值模拟

破裂面形成演化特征是反倾层状斜坡研究的重点之一,也是稳定性评价和工程设计治理的基础。利用室内大型土工离心机,获取坡体受力和变形参数,同时结合PFC数值模拟成果,展示斜坡破裂面的形成演化过程和特征,并讨论破裂面的形成机理。结果表明:(1)首先在坡体内部产生压剪裂隙,随后向中下部扩展,坡体压剪分区;(2)裂隙向中上部发展,破裂面初步形成,深部坡体发生弯折;(3)浅层裂隙完全贯通,形成由坡顶至坡脚的完整破裂面Ⅰ,内部潜在破裂面(Ⅱ、Ⅲ)中上部近似平行坡面,下部合并后至坡脚,而稳定受压区域与弯折区分界潜在破裂面Ⅳ呈阶梯形,同时浅层存在3条次级破裂面;(4)斜坡的变形破坏由于重力作用,使得岩层差异性受力,在压剪、拉剪及弯折作用下,裂隙由预制裂隙尖端萌生、扩展,最终贯通形成破裂面。重力是内在原因,而坡体结构特征是基础条件。研究成果可以为反倾层状斜坡进一步深入研究和实践提供参考。

A novel micro-rolling&incremental sheet forming hybrid process:Deformation behavior and microstructure evolution

Thin-walled metal parts with functional micro-featured surface have broad application prospects in the fields of resistance reduction,noise reduction,etc.In this study,a novel micro-rolling&incremental sheet forming hybrid process(μR-ISF)is proposed to fabricate thin-walled metal parts with microgroove arrays.An analytical model which relates the rolling force and microgroove depth in the micro-rolling stage was first established.Then,the formation mechanism of microgroove morphology during both micro-rolling stage and macro-shape forming stage are investigated.After the micro-grooved sheet being incrementally formed,a significant reduction(between 21%to nearly 60%)is occurred in the depth of both transverse and longitudinal grooves compared to the flat sheet.Meanwhile,the width of transverse grooves decreases slightly by about 10%on average,while the width of longitudinal microgrooves increases significantly by more than 30%on average.After micro-rolling,85°{102}tensile twins appear on the micro-grooved sheet and the percentage of 65°{112}compressive twins increases.After incremental forming,the percentage of low-angle grain boundaries and the density of geometrically necessary dislocations in the formed part increase significantly,and the grain size distribution becomes more uniform.The present work provides a new strategy for the fabrication of 3D metal thin-walled components with surface micro-features.

不同工艺参数MIG焊Inconel 625熔覆层微观组织研究

为了提高Q345钢的使用性能,采用商用Inconel 625实心焊丝以MIG沉积方法制备了镍基熔覆层,随后进行了OM、SEM、EDS、XRD分析和显微硬度测试试验,研究了熔覆层的微观组织、元素分布、不同焊接电流的稀释率、物相组成和表面硬度等。结果表明,采用MIG沉积方法制备的镍基熔覆层与基体结合良好,熔覆层无明显的宏观缺陷;熔覆层从顶部到底部依次产生等轴晶、柱状晶和胞状晶;熔覆层主要由单一的面心立方(fcc)结构γ-Ni固溶体相组成,由于熔覆层存在微观偏析,晶间Nb、Mo等元素浓度较高;随着焊接电流的增大,熔覆层稀释率逐渐变大,熔覆层底部柱状晶受热长大,平均硬度及沿熔覆层截面深度方向硬度均逐渐下降。

氧化物陶瓷颗粒对铜基熔覆层组织演变及性能的影响

为了提高铜基熔覆层的硬度以及耐磨性能,向药芯焊丝中添加不同成分比例的氧化物陶瓷颗粒并采用TIG熔覆方法制备了Cu基熔覆层,利用OM、SEM、EDS、XRD和显微硬度测试等方法,研究了不同成分比例的氧化物陶瓷颗粒对铜基熔覆层的组织及性能的影响。研究发现,随着Al_(2)O_(3)/TiO_(2)的降低,合金液的流动性有所提高,从而释放了部分的残余应力,并且Cu (311)逐渐转变为Cu (200)峰,促进了铜基熔覆层顶部的晶粒细化,同时向铜侧扩散的铁数量逐渐减少,界面处的树枝晶也产生了明显细化,并且三种熔覆层界面处硬度过渡平缓,熔覆顶部的硬度随着TiO_(2)的增加逐渐升高;在3#熔覆层顶部出现了Al13Fe4金属间化合物,提高熔覆层的表面性能;磨擦磨损结果中磨损量随着TiO_(2)的增加,磨损量也逐渐降低,但明显细化晶粒的3#熔覆层摩擦系数保持稳定,有较少的犁沟效应。

人工淹没空化射流喷丸强化7075铝合金性能分析

目的利用喷丸强化技术提高材料的性能,延长零件的使用寿命。方法在人工淹没空化射流喷丸中,利用由2个具有大速度差的同心共流射流产生的剪切层引起的空化,在承受疲劳载荷或腐蚀环境的金属部件的表面层中引入压缩残余应力,从而实现冲击性能显著提高的新型喷丸强化技术。为了进一步验证人工淹没空化射流的强化性能,采用人工淹没空化射流喷丸对7075铝合金(Al7075)进行表面强化处理,研究不同扫描速度的人工淹没空化射流喷丸对其微观组织和力学性能的影响。观测不同扫描速度人工淹没空化射流喷丸下Al7075的表面形貌和粗糙度。结果在扫描速度为3.0mm/min时,粗糙度值约为1.27μm;在扫描速度为2.0 mm/min时,粗糙度值约为4.08μm;在扫描速度为1.0 mm/min时,粗糙度值约为12.35μm。测量了人工淹没空化射流喷丸冲击前后Al7075的残余应力和显微硬度沿深度方向的分布,研究并讨论了Al7075在人工淹没空化射流喷丸过程中的微观结构演变。结论人工淹没空化射流喷丸会在Al7075表面发生塑性变形,增加了表面粗糙度,且产生加工硬化。揭示了Al7075在塑性变形过程中的晶粒细化机制,旨在为获得高性能的Al7075提供一种新的表面强化方法。

Enhanced Surface Mechanical Properties and Microstructure Evolution of Commercial Pure Titanium Under Electropulsing-Assisted Ultrasonic Surface Rolling Process

The effects of electropulsing-assisted ultrasonic surface rolling process on surface mechanical properties andmicrostructure evolution of commercial pure titanium were investigated. It was found that the surface mechanical prop-erties were significantly enhanced compared to traditional ultrasonic surface rolling process （USRP）, leading to smallersurface roughness and smoother morphology with fewer cracks and defects. Moreover, surface strengthened layer wasremarkably enhanced with deeper severe plastic deformation layer and higher surface hardness. Remarkable enhancementsof surface mechanical properties may be related to the gradient refined microstructure, the enhanced severe plasticdeformation layer and the accelerated formation of sub-boundaries and twins induced by coupling effects of USRP andelectropulsing. The primary intrinsic reasons for these improvements may be attributed to the thermal and athermal effectscaused by electropulsing treatment, which would accelerate dislocation mobility and atom diffusion.

Carbon-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions:Optimization strategies and mechanistic analysis

Electrocatalysts are one of the essential components for the devices of high-efficiency green energy storage and conversion,such as metal-air cells,fuel cells,and water electrolysis systems.While catalysts made from noble metals possess high catalytic performance in both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),their scarcity and expensiveness significantly limit large-scale applications.In this regard,metal-free/non-noble metal carbon-based catalysts have become competitive alternatives to replace catalysts made of noble metals.Nevertheless,low catalytic ORR/OER performance is the challenge of carbon-based catalysts for the commercial applications of metal-air batteries.To solve the problem of poor catalytic performance,two strategies have been proposed:(1)controlling the microstructure of the catalysts to expose more active sites as the channels of rapid mass and electron transfer;and(2)reducing the reaction energy barrier by optimizing the electronic structures of the catalysts via surface engineering.Here,we review different types of bifunctional ORR/OER electrocatalysts with the activated surface sites.We focus on how the challenge can be overcome with different methods of material synthesis,structural and surface characterization,performance validation/optimization,to outline the principles of surface modifications behind catalyst designs.In particular,we provide critical analysis in the challenges that we are facing in structural design and surface engineering of bifunctional ORR/OER catalysts and indicate the possible solution for these problems,providing the society with clearer ideas on the practical prospects of noble-metal-free electrocatalysts for their future applications.