Computation of synthetic surface heat transfer coefficient of 7B50 ultra-high-strength aluminum alloy during spray quenching

According to inverse heat transfer theory, the evolutions of synthetic surface heat transfer coefficient（SSHTC） of the quenching surface of 7B50 alloy during water-spray quenching were simulated by the Pro CAST software based on accurate cooling curves measured by the modified Jominy specimen and temperature-dependent thermo-physical properties of 7 B50 alloy calculated using the JMat Pro software. Results show that the average cooling rate at 6 mm from the quenching surface and 420-230 ℃（quench sensitive temperature range） is 45.78℃/s. The peak-value of the SSHTC is 69 kW/（m^2·K） obtained at spray quenching for 0.4 s and the corresponding temperature of the quenching surface is 160 ℃. In the initial stage of spray quenching, the phenomenon called ＂temperature plateau＂ appears on the cooling curve of the quenching surface. The temperature range of this plateau is 160-170℃ with the duration about 3 s. During the temperature plateau, heat transfer mechanism of the quenching surface transforms from nucleate boiling regime to single-phase convective regime.

Aging precipitation behavior and properties of Al-Zn-Mg-Cu-Zr-Er alloy at different quenching rates

The effect of quenching rate on the aging precipitation behavior and properties of Al-Zn-Mg-Cu-Zr-Er alloy was investigated.The scanning electron microscopy,transmission electron microscopy,and atom probe tomography were used to study the characteristics of clusters and precipitates in the alloy.The quench-inducedηphase and a large number of clusters are formed in the air-cooled alloy with the slowest cooling rate,which contributes to an increment of hardness by 24%(HV 26)compared with that of the water-quenched one.However,the aging hardening response speed and peak-aged hardness of the alloy increase with the increase of quenching rate.Meanwhile,the water-quenched alloy after peak aging also has the highest strength,elongation,and corrosion resistance,which is due to the high driving force and increased number density of aging precipitates,and the narrowed precipitate free zones.

Large-scale control of enhancement and quenching of photoluminescence for ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution

We investigated the optical properties of hybrid exciton–plasmon coupling ensembles composed of ZnSe/ZnS quantum dots and Ag nanoparticles in aqueous solution. We modulated their average interval by changing the ratio of quantum dots and Ag nanoparticles. The transition from dramatic PL enhancement to PL quenching state was experimentally observed, according to the continuous decrease of the PL lifetime. The PL enhancement rate exceeded 10, with the Purcell factor of 3.5. Meanwhile, the proportion of fast decay increased from 0.3 to 0.6, corresponding to the proportion of slow decay decreased from 0.7 to 0.4. Our experiment is important for the hybrid exciton–plasmon coupling system to be practicable in optoelectronic application.

Machining the Integral Impeller and Blisk of Aero-Engines:A Review of Surface Finishing and Strengthening Technologies

The integral impeller and blisk of an aero-engine are high performance parts with complex structure and made of difficult-to-cut materials. The blade surfaces of the integral impeller and blisk are functional surfaces for power transmission, and their surface integrity has signif- icant effects on the aerodynamic efficiency and service life of an aero-engine. Thus, it is indispensable to finish and strengthen the blades before use. This paper presents a comprehensive literature review of studies on finishing and strengthening technologies for the impeller and blisk of aero-engines. The review includes independent and inte- grated finishing and strengthening technologies and dis- cusses advanced rotational abrasive flow machining with back-pressure used for finishing the integral impeller and blisk. A brief assessment of future research problems and directions is also presented.

Surface strengthening and grain refinement of AZ31B magnesium alloy by ultrasonic cavitation modification

Ultrasonic cavitation modification(UCM)employs cavitation effect to induce strong plastic deformation on the material surface and improve surface properties.To explore the surface strengthening and grain refinement of materials by UCM,the UCM orthogonal experiments of AZ31 B magnesium alloy were carried out in water and kerosene,respectively.The effects of ultrasonic amplitude,distance from the sample,and processing time on Vickers hardness and grain size of the material were studied.The results showed that the Vickers hardness of samples increased to1.5–3 times after UCM in water,which was 23.77–48.19%higher than that in kerosene.The metallographic observation indicated the grains on the surface of AZ31 B were refined after UCM.The maximum fluctuation of grain size on the material surface was not more than 10 lm after UCM in water,and most of them were concentrated between 1.5 lm and 2.5 lm,while the former was more than 40 lm and the latter were concentrated between 2 lm and 10 lm in kerosene.This reflected that the grain refinement effect of UCM in water was better than that in kerosene.Ultrasonic cavitation can be used as a benign means to improve the surface properties of materials.

Influence of varying forms of bionic units on repairing remaining quenching surface of gray cast iron

In order to repair and reuse remaining quenching surface(RQS)divided into severely worn surface(SWun-S)and mildly worn surface(MWun-S)of abandoned gray cast iron guide rail,inspired by the bionic theory,varying forms of bionic units such as spot(Sp-S),striation(St-S),and reticulation(Re-S)were fabricated on RQS of gray cast iron through laser processing technology.Firstly,the microstructure,phase composition,and microhardness of bionic units and RQS were analyzed by optical microscopy as well as X-ray diffraction instrument and scanning electron microscopy,respectively.Secondly,the oil lubrication wear experiment was performed on homemade line reciprocating wear machine.The results demonstrated that the bionic units had a significant effect on improving wear resistance of RQS of abandoned guide rail due to the microstructure and higher hardness.In addition,the weight loss ratios of MWun-S,Sp-S,St-S,and Re-S samples were decreased by 36.72%,36.78%,62.26%,and 80.39%,respectively,compared with that of SWun-S sample.The mechanism of wear resistance enhancement was also discussed.

Luster Polish Strengthening Treatment for Raceway Surface of Aeroengine Bearings

A new surface strengthening technology, luster polish strengthening treatment, was proposed to treat the raceway surface of aeroengine bearings （9Cr18Mo） with the centrifugal strengthening machine exclusively designed for luster polish strengthening treatment. The experimental results showed that luster polish strengthening treatment produced a compressive residual stress layer with a depth of over 80 μm below the surface of the bearing raceway, and thus effectively removed the metamorphic layer in the raceway surface. After luster polish strengthening treatment, the average surface hardness of the aeroengine bearing raceway was increased from 61.02 HRC to 63.01 HRC, the surface roughness was reduced from 0.06 μm to 0.03 μm, and the contact fatigue life of the aeroengine bearings was improved by about 90%, with the dispersion of fatigue life being reduced remarkably. Theoretical calculation result agrees with that obtained by experiment.

O2（1△g） Deactivation on O2-adsorbed Metal Surfaces

A flow system was set up to measure the quenching probability ~ of O2（1△g） on various O2- adsorbed metal surfaces including Cu, Cr, Ni, and Ag. increased with both the duration of the experiment and the O2（1△g） concentration. After several hours evacuation to a few Pa, γ can return to its original value. A deactivation mechanism of O2（1△g） is suggested by considering first the weak chemisorption of O2（1△g） on the surface adsorption sites, followed by the near resonant energy transfer between the gas phase O2（1△g） and surface O2（1△g）. A phenomenological model in accord with the experimental fact has been proposed together with relevant kinetic equations.

Influence of Ultrasonic Surface Rolling Process and Shot Peening on Fretting Fatigue Performance of Ti-6Al-4V

At present,there are many studies on the residual stress field and plastic strain field introduced by surface strengthening,which can well hinder the initiation of early fatigue cracks and delay the propagation of fatigue cracks.However,there are few studies on the effects of these key factors on fretting wear.In the paper,shot-peening(SP)and ultrasonic surface rolling process(USRP)were performed on Ti-6Al-4V plate specimens.The surface hardness and residual stresses of the material were tested by vickers indenter and X-ray diffraction residual stress analyzer.Microhardness were measured by HXD-1000MC/CD micro Vickers hardness tester.The effects of different surface strengthening on its fretting fatigue properties were verified by fretting fatigue experiments.The fretting fatigue fracture surface and wear morphology of the specimens were studied and analyzed by means of microscopic observation,and the mechanism of improving fretting fatigue life by surface strengthening process was further explained.After USRP treatment,the surface roughness of Ti-6Al-4V is significantly improved.In addition,the microhardness of the specimen after SP reaches the maximum at 80μm from the surface,which is about 123%higher than that of the AsR specimen.After USRP,it reaches the maximum at 150μm from the surface,which is about 128%higher than that of AsR specimen.It is also found that the residual compressive stress of the specimens treated by USRP and SP increases first and then decreases with the depth direction,and the residual stress reaches the maximum on the sub surface.The USRP specimen reaches the maximum value at 0.18 mm,about−550 MPa,while the SP specimen reaches the maximum value at 0.1 mm,about−380 MPa.The fretting fatigue life of Ti-6Al-4V effectively improved after USRP and SP.The surface integrity of specimens after USRP is the best,which has deeper residual compressive stress layer and more refined grain.In this paper,a fretting wear device is designed to carry out fretting fatigue experiments on specimens with different surface strengthening.

Study on microstructure of Fe-Cr-C-Ni-B-Si coating formed by plasma jet surface metallurgy

The technical connotation of surface metallurgical technology by DC-Plasma-Jet is a kind of rapid, non- equilibrium metallurgical process which is similar to powder metallurgy. Accordingly the specialized equipment is developed all by ourselves, which is not subjected to limitation of solubility, melting point, density of constituents, therefore pre-alloy powders are not needed. The plasma surface metallurgical coating using Fe-Cr-C-Ni-B-Si mixed alloy powders has good wettability with substrate material. The metallurgical coating has apparent characteristics of rapid and layered crystallization from planar crystal-cell to dendritic transition zone at the interface, from dendritic crystal to equiaxed crystal in the midst, from equiaxed crystal to spike crystal on the surface. Its metastable microstructure is complex phase of supersaturated γ- （ Fe, Ni ） dendritic crystal solutioning great amount of alloy element and interdendritic eutectic structure （ Cr, Fe） γ （ C, B） 3 and T-（Fe,Ni）.

Quasi-plane-hypothesis of strain coordination for RC beams seismically strengthened with externally-bonded or near-surface mounted fiber reinforced plastic

The application of fiber reinforced plastic（FRP）,including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement（EBR） and near-surface mounted（NSM） strengthening techniques.This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods,including externally-bonded and near-surface mounted FRP,to study the strain coordination of the FRP and steel rebar of the RC beam.Since there is relative slipping between the RC beam and the FRP,the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis;that is,the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height（h 0） of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of the FRP and steel rebar satisfies the equation：ε FRP =βε steel,and the value of β is equal to 1.1-1.3 according to the test results.

Analysis of Orientation Relationships,Carbon Partitioning and Strengthening Mechanism of a Novel Ultrahigh Strength Steel

The orientation relationships,carbon partitioning and strengthening mechanism of a novel ultrahigh strength steel were analyzed in depth during the complex process of heat treatment.The experimental results reveal that the(011)α//()γ,[100]α//[011]γ orientation relationships can be drawn between martensite and retained austenite.The position and angle of martensite and retained austenite are shown more clearly from the stereographic projections.Moreover,the calculated results show that the carbon content near the austenite interface is the highest in the shorter carbon allocation time.With the further increase of time,its carbon content gradually decreases.Furthermore,a model of the relationship between yield strength and strengthening mechanism was established.It was proved that the main strengthening components contributing to the yield strength include Orowan strengthening,grain-size strengthening and dislocation hardening.The main strengthening mechanism of steel in this experiment is dislocation strengthening.

Study on Strengthening of RC Slabs with Different Innovative Techniques

This paper presents a focused study on using different methods to enhance the ultimate capacity of flexural behavior in RC slabs. Four RC specimens were casted with common compressive strength and reinforced with steel mesh. Specimens were strengthened with different methods such as usage of GFRP sheets, carbon fibers laminate strips and near surface mounted steel rebars. All specimens were subjected to two-point loading setup. Load was increased from zero to failure load. First crack was recorded and crack pattern was observed. The behavior of strengthened specimens was compared to that of the control specimen to judge the efficiency of the used techniques. Test results showed that the used techniques were effective in enhancing the behavior of the strengthened slabs by noteworthy values.

H13热作模具钢表面强化层耐磨性能研究进展

H13钢被广泛用于铝合金、镁合金等金属的热挤压模和压铸模,服役环境恶劣,常规处理淬、回火后,耐磨性严重不足,易导致热疲劳裂纹的产生,从而影响模具使用寿命和产品质量。对H13热作模具钢表面进行强化是提高耐磨性及服役寿命的有效手段。综述了国内外关于H13热作模具钢表面强化的研究现状及进展,并对H13模具钢表面改性技术发展方向做出展望。

调质处理对1000 MPa级水电用钢组织性能的影响

利用扫描电镜、透射电镜、拉伸和冲击试验机等研究了不同调质处理工艺对1000 MPa级水电用钢微观组织和力学性能的影响。结果表明:淬火后的实验钢组织呈准等轴状,板条马氏体组织细小。在890~950℃淬火温度范围内,随着淬火温度的升高,马氏体板条束尺寸增加,经过620℃回火后组织转变为回火索氏体,回火过程中碳化物的析出及其与位错的交互作用提高了实验钢的强度。随淬火温度升高,实验钢的屈服强度和抗拉强度增加,伸长率基本保持不变,-60℃冲击吸收能量呈现先缓慢增加后急剧减小的趋势,冲击断裂方式由韧性断裂转变为脆性解理断裂。经920℃×30 min+620℃×60 min调质工艺处理后,实验钢的屈服强度、抗拉强度、伸长率及-60℃冲击吸收能量分别为970 MPa、986 MPa、15%和185 J,其综合力学性能达到最优,满足1000 MPa级水电用钢的性能要求。

基于超声强化研磨加工的GH4099合金耐磨服役性能提升研究

GH4099合金具有优异的高温热稳定性、高温力学性能和高温抗蠕变性能,用于航空发动机涡轮盘和涡轮叶片的制造,常处于高温、重载、高频的工作环境,但因耐磨服役性能差导致其使用寿命较短。通过超声强化研磨加工技术对GH4099合金分别进行0、3、6、9 min的加工,实现其耐磨服役性能提升。采用超声强化研磨加工技术对GH4099合金板表面进行不同时间的加工处理,并对加工前后的截面显微硬度、金相组织以及表面形貌进行分析。同时,通过往复式摩擦磨损试验对加工前后的试样耐磨性能进行对比分析。研究结果表明:随着加工时间的增加,材料表面显微硬度逐渐增大,最大为432.83 HV,比未加工试样增加43.8%。当加工时间为6 min时,GH4099合金试样的摩擦系数为0.47,磨损率为5.78×10^(-14)m^(3)/(N·m),与未加工试样相比,分别降低24.2%、68.59%,表明超声强化研磨可有效提升GH4099合金耐磨服役性能。

FV520B钢表面熔化极气体保护焊堆焊层及其激光淬火后的组织与性能

采用熔化极气体保护焊在FV520B钢板上进行单层单道、二层多道以及三层多道同质堆焊试验,并对单层单道堆焊层进行激光淬火处理,研究了不同堆焊层和激光淬火后堆焊层的显微组织、硬度和耐腐蚀性能。结果表明:堆焊层由板条状马氏体、少量δ铁素体和一些碳化物组成,显微硬度为350 HV,与母材相比提高了14.7%,层间和道间交界处的组织中δ铁素体减少,最高硬度分别为380.3,373.5 HV,相对于堆焊层提高了8.0%,6.7%左右;堆焊层的腐蚀速率低于母材,且随着堆焊层数的增加,腐蚀速率不变。激光淬火后堆焊层的马氏体组织更加细小,淬火区和热影响区的厚度分别为194.3,186.3μm,堆焊层的最高硬度提高至390.4 HV;随着距淬火表面距离的增大,硬度先升高后降低;激光淬火后堆焊层的腐蚀速率比未进行激光淬火的堆焊层低。

钛合金材料超声滚压加工的仿真分析与实验研究

采用普通滚压加工工艺对钛合金材料进行加工时,存在因低频冲击造成的工件残余应力分布不均匀和表面硬度低等问题,为此,开展了钛合金材料超声振动滚压工艺仿真及实验研究。首先,从理论层面分析了超声滚压加工的运动学及动力学特性,找出了影响超声滚压加工性能的相关因素;然后,采用ABAQUS有限元软件建立了钛合金材料的仿真模型,分析了超声滚压对残余应力的影响及强化机理;最后,设计了钛合金工件的超声滚压实验,研究了不同参数指标对工件加工质量的影响,并根据实验结果对仿真模型和残余应力结果进行了验证。研究结果表明:随着静载荷和超声振幅的增加,工件表面残余应力分布相对均匀且趋于平稳,表面粗糙度呈现先降低后增加的趋势,表面硬度随强化层深度的增加逐渐降低;在振幅为20μm时,工件表面质量和性能相对较好,此时残余应力均值为849 MPa,表面粗糙度均值为0.1μm。该实验结果与仿真分析结果一致,验证了所建模型的可靠性,可为滚压制造工艺参数的选取提供参考。

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。

喷丸强化对车辆传动齿轮裂纹扩展影响的研究综述

疲劳断裂是重载车辆传动齿轮的主要失效形式之一,齿轮底部疲劳裂纹的扩展将缩短车辆传动系统的服役寿命,严重时会导致车辆发生安全事故。延缓裂纹扩展的主要方法是在传动齿轮的表面引入一定大小的残余压应力。喷丸技术是一种冷加工表面强化处理工艺,该技术利用高速弹丸冲击材料表面,使零件表层产生塑性应变的同时,在表面和内部引入残余压应力,从而使裂纹闭合的能力得到强化,达到延缓裂纹扩展的强化效果。为了更好地揭示喷丸引入的残余压应力对疲劳裂纹扩展的影响,首先综述了传动齿轮表面疲劳裂纹产生的原因以及疲劳裂纹的扩展行为对重载车辆服役的影响。从强度因子、J积分以及裂纹闭合效应出发,介绍了传动齿轮表面疲劳裂纹扩展的理论以及残余压应力与疲劳裂纹扩展速率之间的关系。其次概述了目前国内外常用的新型有益于将残余拉应力转化为残余压应力的微粒子喷丸、激光喷丸、超声喷丸方法,并与传统机械喷丸技术相比较,阐述了新型喷丸表面强化技术的优缺点。此外,从数值模拟和试验结果两方面,论述了喷丸速度、喷丸角度、弹丸直径、弹丸材质和覆盖率5个工艺参数对在传动齿轮表面引入残余压应力的改善影响。最后对喷丸强化技术在传动齿轮上的多目标参数优化以及多尺度残余压应力与疲劳性能进行了展望,并结合重载车辆的使用需求,强调需要创新设计一种效率高、价格低、适用性广的喷丸技术,以进一步推动喷丸强化在延缓疲劳裂纹扩展方面的持续发展。