喷丸处理对高强度7150铝合金弯曲形变的影响EI北大核心CSCD

采用X射线衍射残余应力分析和衍射峰半高宽研究喷丸残余压应力和塑性变形对7150铝合金薄壁试样弯曲形变的影响.结果表明：喷丸时间0～60s时,由于喷丸残余应力的引入和塑性变形的累积,试样弯曲形变速率较大,对于喷射压力为0.05MPa的试样,其值可达10.3μm/s;喷丸时间超过60s后,残余压应力场饱和,试样形变主要依靠喷丸表面的塑性变形,而试样弯曲形变速率降低到1.3μm/s.增大喷射压力将使试样的弯曲形变速率和相对弯曲形变总量增大.     

基于激光加工和自组装技术硅基底超疏水表面的制备

利用激光在硅基底上加工具有规则点阵结构的表面纹理,采用自组装技术在此硅表面制备全氟辛烷基三氯硅烷自组装分子膜。采用扫描电子显微镜和表面形貌仪对硅试样表面进行形貌分析,采用接触角测量仪测量试样的接触角。结果表明,激光加工后的硅试样表面纹理深度和表面粗糙度均随激光加工间距的增加而逐渐变大,试样表面的去除量随光照时间的增加而增大。通过激光加工和沉积自组装分子膜,硅试样表面的水接触角显著增大,最大可达到156°,且试样的水接触角随激光加工间距的减少而增大。试样接触角测量值与Cassie模型预测值相一致,当点阵直径与加工间距比0.510时,硅试样表面为超疏水表面。     

成形角度对选区激光熔化4Cr5MoSiV1钢组织和性能的影响EI北大核心CSCD

选区激光熔化(SLM)成形4Cr5MoSiV1钢具有良好的强/硬度以及耐磨性是提高其使用寿命的重要保证,为优化SLM成形4Cr5MoSiV1钢的组织和性能,研究不同成形角度下4Cr5MoSiV1钢试样的显微组织、显微硬度、拉伸性能和耐磨性。结果表明:随成形角度的增加,试样熔道间的热量累积程度降低,晶粒尺寸减小,细晶强化作用增强,故试样的显微硬度升高。随成形角度的增加,拉伸试样的滑移搭接面数量增多,滑移程度增加,且熔道边界处分正应力值降低,故试样的抗拉强度和断裂伸长率均升高。磨损试样的磨损机制以黏着磨损和氧化磨损为主,且随成形角度增加,试样的耐磨性升高。同一成形角度下,试样底层表面经多次热量累积后,其细晶强化和固溶强化作用减弱,显微硬度和耐磨性均降低。SLM成形4Cr5MoSiV1钢试样的显微硬度、耐磨性和拉伸性能呈正相关,45°成形角度下试样的力学性能最高,抗拉强度最高为1576.5 MPa,断裂伸长率最高为17%,顶层表面的显微硬度最高为608.4HV,顶层表面的磨损率最低为4.95×10^(-9)kg·N^(-1)·m^(-1)。     

Ti6Al4V表面纹理制备及其润湿性

采用激光加工技术在Ti6Al4V表面分别加工直线、网格和具有规则点阵状结构的表面纹理,采用自组装技术制备自组装分子膜。采用扫描电镜、形貌分析仪和接触角测量仪对成膜后的钛合金表面进行形貌和接触角的表征与测量。结果表明,通过激光加工和沉积自组装分子膜,可显著增大Ti6Al4V的水接触角。其中直线纹理的试样表面水接触角可达124.8°,网格纹理的试样表面接触角可达126.1°,点阵状纹理的试样表面接触角可达151.6°。表面接触角与表面粗糙度相关,随着表面粗糙度值的增大,接触角呈增大趋势,当表面粗糙度>4μm时,接触角均>150°,形成超疏水表面。     

低能斜入射离子束诱导单晶硅纳米结构与光学性能研究

为了研究低能Ar+离子束在不同入射角度下对单晶硅表面的刻蚀效果及光学性能,使用微波回旋共振离子源,对单晶Si(100)表面进行刻蚀,采用原子力显微镜、非接触式表面测量仪和傅里叶变换红外光谱仪对刻蚀后硅片的表面形貌、粗糙度和光学透过率进行了测量.实验结果表明:当离子束能量为1000 eV、束流密度为265μA·cm-2、刻蚀时间为30min时,离子束入射角度从0°增加到30°,样品表面出现条纹状结构.入射角度在0°～15°,随着角度增加,样品表面粗糙度增加,条纹周期减小,光学透过率提高;而在15°～ 30°范围内,随着角度增加,粗糙度开始减小,条纹周期增大,同时光学透过率降低.继续增加入射角度,条纹状结构逐渐消失,入射角度到45°时,粗糙度和光学透过率达到最小值;增加入射角度到55°,样品表面出现自组织点状结构,表面粗糙度急剧增大,光学透过率随着角度增加开始增加;继续增加离子束入射角度到80°,表面粗糙度和光学透过率继续增加,样品表面呈现出均匀有序的自组织柱状结构;此后,随着入射角度的增加,表面粗糙度又开始减小,光学透过率降低.自组织条纹结构到柱状结构的转变是溅射粗糙化和表面驰豫机制相互作用的结果.     

磁致伸缩仪超声空化流的数值研究

基于CFD方法采用"Singhal完全空化模型"及动网格技术对磁致伸缩仪超声空化流进行数值计算。结果表明,变幅杆高频振动引起试样表面附近局部流场发生空化,且在试样表面形成脉冲压力;压力与空泡体积组分在试样表面近似呈环形分布,并随试样振动,二者周期性变化。试样表面中心区域空泡经两次振荡后溃灭产生强烈脉冲压力,峰值可达5 MPa;脉冲压力在试样表面按间隔环形区域分布,且随试样振动在相邻环形区域交替出现。随超声波在空化流场中传播声压快速衰减;压力只在距变幅杆端面约20 mm内波动明显,振幅从25μm增大到30μm时试件中心区域脉冲压力增大;振幅增大到35μm时空化效果增强,试件中心区域所受脉冲压力作用减弱。     

纸浆模制波状结构填充物的设计及缓冲性能

目的对纸浆模制波状结构形式的缓冲填充物进行结构设计与缓冲包装性能的测试。方法设计并加工制备2种纸浆模制品波状缓冲结构填充物,其中A组试样的高度均为30 mm,波状角度分别为5°,15°,30°;B组试样确定的波状角度均为5°,高度变化分别为10,20,30 mm。对2组试样分别进行了静态压缩、动态冲击和振动试验。结果高为30 mm,波状角度为5°,15°,30°的波状结构最大静载荷分别为1230,1430,1600 N,波状角度为5°,高为20和30 mm的波状结构最大静载荷分别为560,1380 N。结论静态压缩试验表明高度一定时,纸浆模制缓冲结构的波状角度越大,载荷能力越强,波状角度一定时,高度越高,载荷能力越强;动态冲击试验表明纸浆模制缓冲结构的波状角度、高度影响着结构体的缓冲应用范围;振动试验表明在给定的载荷条件下试样避开了公路运输的共振频率。     

时效热处理对选区激光熔化成形18Ni300摩擦磨损性能的影响

目的 通过研究选区激光熔化(SLM)成形18Ni300时效热处理前后摩擦磨损性能及磨损机制,为SLM技术在模具中易磨损部位的应用提供理论支撑。方法 采用扫描电镜对热处理前后试样进行微观组织观察,采用X射线衍射仪对原始粉末和试样进行物相分析,并测试试样时效热处理前后的硬度、密度和抗拉强度,采用球盘摩擦磨损试验机测试在不同载荷下时效热处理前后试样的摩擦磨损行为,采用3D轮廓仪和扫描电镜对磨损后试样和磨球表面进行观察,并对磨损区域进行能谱分析。结果 时效热处理后试样“鱼鳞状”熔道组织弱化,主要为板条状马氏体组织。原始粉末及成形后试样的物相主要为马氏体,原始粉末和时效热处理后试样中含有少量残余奥氏体。时效热处理后试样硬度由37.6HRC升高到54.4HRC,密度变化不大,抗拉强度由1 107 MPa升高到2 031 MPa,伸长率由14.4%降低至4.5%。随着摩擦磨损试验载荷的增大,时效热处理后试样摩擦因数降低,体积磨损率增大,但均低于热处理前试样。结论 当载荷为10 N时,磨损机制主要为磨粒磨损;当载荷为15 N时,磨损机制过渡到氧化磨损和黏着磨损;当载荷为20 N时,主要为黏着磨损。     

冲蚀角度对建筑用钢化玻璃和普通玻璃喷砂磨损粗糙度的影响及三维分析

采用气流挟沙喷射法对钢化玻璃和普通玻璃在不同角度下进行冲蚀试验,利用激光共聚焦显微镜(LSCM)和扫描电子显微镜(SEM)表征玻璃表面微观结构和形貌的变化,对比研究了冲蚀角度对建筑用钢化玻璃和普通玻璃喷砂磨损粗糙度和损伤形貌的影响和机制.研究结果表明:随着冲蚀角度的增加,钢化玻璃和浮法玻璃的冲蚀率均逐渐增大,冲蚀损伤区域深度和宽度也逐渐增大,损伤区域形状由椭圆向圆形转变,冲蚀剖面轮廓由抛物线形向圆锥形转变.钢化玻璃的粗糙度随冲蚀角度增加逐渐增大,浮法玻璃粗糙度随冲蚀角度增加先增后减,冲蚀角度为45°时达到最大.相同冲蚀角度下,浮法玻璃的损伤程度远大于钢化玻璃.当冲蚀角度为15°时,材料的损伤由沙粒微切削作用引起,材料表面粗糙度较小;冲蚀角度为45°时,材料的损伤由沙粒切削和裂纹扩展共同引起,沙粒铲削作用明显,材料表面粗糙度大;冲蚀角度为90°时,材料的损伤由裂纹叠加引起,钢化玻璃的粗糙度达到最大而浮法玻璃的粗糙度达到最小.冲蚀角度为15°和45°时,浮法玻璃表面粗糙度参数均大于钢化玻璃,冲蚀角度为90°时,钢化玻璃粗糙度评价参数均大于浮法玻璃.钢化玻璃表面轮廓微观不平度平均间距在冲蚀角度15°时达到最大,在冲蚀角度45°时达到最小;浮法玻璃在冲蚀角度15°时达到最大,在冲蚀角度45°时达到最小.     

强流脉冲离子束辐照对45钢表面状态的影响

本文研究了强流脉冲离子（HIPIB）束辐照对45钢表面形貌、显微硬度及残余应力等影响。结果表明,经HIPIB辐照处理,45钢表面出现火山口状熔坑,5次脉冲处理时熔坑比较明显,试样表面也变得凹凸不平,随着脉冲次数的增加,熔坑之间会连成不规则的网状形貌且界限变得不明显,表面发生光化。试样的显微硬度随着脉冲次数的增加而提高,未辐照时,显微硬度为HV342,20次脉冲时达到HV911。经HIPIB辐照处理,试样表面产生残余拉应力,且随着脉冲次数的增加,样品表面残余应力增大,由未处理时的152 MPa提高到656MPa。     

Nichtmagnetisierbarer warmbeständiger nichtrostender Stahl für Wälzlager

Nonmagnetic heating‐resistant stainless steel for roller bearings A low cost austenitic chromium manganese steel with about 1 mass% of carbon and nitrogen was molten under normal pressure which reveals an amazing combination of properties. Starting from a yield strength of about 600 MPa it is cold work hardened to 60 HRC. This high hardness is brought about for the first time without a martensitic microstructure which is usual for roller bearings. In addition this steel is stainless, non‐magnetic and heating resistant up to about 500 °C, i.e. a material to serve under complex loading. Manufacturing by ingot metallurgy, ESR, hot working, solution annealing and machining was carried out on an industrial scale. The investigation of the structure was carried out on several scales, beginning with the electronic structure, the TEM structure, the light optical microscopy up to macro‐etchings. In this manner an extensive understanding of the outstanding combination of properties of the steel named CARNIT was derived.     

Surface integrity studies on abrasive water jet cutting of AISI D2 steel

This article investigates the 3D surface topography and 2D roughness profiles, and micrographs were analyzed in the abrasive water jet (AWJ) cutting of AISI D2 steel kerf wall cut surfaces by varying water jet pressures and jet impact angles. In 3D surface topography, roughness parameters such as Sq, Ssk, Sp, Sv, Sku, Sz, and Sa were improved by various jet impact angles with different water jet pressures. However, the roughness parameters Ssk and Sku strongly depend on the water jet pressure and jet impact angle. This is confirmed by kerf wall cut profile structures. Fine irregularities of peaks and valleys are found on the AWJ cut surfaces, as evident from 2D roughness profiles. The scanning electron microscope micrographs confirm the production of an upper zone not very much damaged and a lower striation free bottom zone, by using the jet impact angle of 70° with a water jet pressure of 200?MPa. Finally, the results indicate a jet impact angle of 70° maintaining the surface integrity of D2 steel better than normal jet impact angle of 90°. The results are useful in mating applications subjected to wear and friction. This has resulted in enhancement of the functionality of the AWJ machined D2 steel components.     

Investigations on hard machining of Impax Hi Hard tool steel

In this paper, experimental investigations are carried out by end milling process on hardened tool steel, Impax Hi Hard (Hardness 55 HRC) a newly developed tool steel material used by tool and die making industries. Experiments are performed with an aim to study performance investigations of machining parameters such as cutting speed, feed, depth of cut and width of cut with consideration of multiple responses viz. volume of material removed, tool wear, tool life and surface finish to evaluate the performance of PVD coated carbide inserts and ball end mill cutters. It has been observed through scanning electron microscope, X-ray diffraction technique (EDX) that chipping and adhesion are active tool wear mechanisms and saw-toothed chips are formed while machining of Impax Hi Hard steel. It is also noticed out that tool life is not enhanced while machining with minimum quantity lubricant than dry machining. From the investigations, it is observed that hard machining can be considered as an alternative to grinding and EDM, traditional methods of machining difficult-to-machine materials i.e. hardened steel with hardness greater than 50 HRC with a scope of improved productivity, increased flexibility, decreased capital expenses and reduced environmental waste.     

Machinability study of abrasive aqua jet parameters on hybrid metal matrix composite

The present work involves investigation of the abrasive aqua jet (AAJ) machining of hybrid metal matrix which consists of Al 6063 reinforced with boron carbide (B₄C) and zirconium silicate (ZrSiO₄) in the form of particulates in the proportion of 5% B₄C and 5% ZrSiO₄. The Response surface method using a central composite design was adopted for conducting experiments by changing the aqua jet pressure, abrasive flow rate, and traverse rate. The results were taken with different types of abrasives of various mesh sizes in this study, which were analyzed using response surface graphs. The striation effect on the bottom-machined surfaces was also examined using the striation length and its frequency. Surface topography and morphology were analyzed on the AAJ-machined composite kerf wall cut surfaces. The machined surface exhibited the inherent characteristics of AAJ which included wear tracks, and contamination generated in the metal surface. The experimental results revealed that higher abrasive flow rate (400 g/min), lower traverse rate (30 mm/min), and higher aqua jet pressure (300 MPa), the production of a higher material removal rate, lower surface roughness and kerf taper angle.     

An Investigation on Turning Hardened Steel Using Different Tool Inserts

Turning of hard materials usually presents poor machinability. However, for high productivity, it is desirable to employ turning of hard materials rather than grinding. In this work, turning of hardened 16MnCrS5 steel with hardness of 43 HRC was explored to judge machining performance with plain and wide-groove-type chip-breaking TiC-coated carbide inserts under dry and wet environmental conditions, different cutting velocity, and feed. Tool wear tests were also done in dry and wet conditions. Satisfactory tool performance was observed under wet condition using TiC-coated plain and wide-groove carbide inserts even at 268 m/min cutting velocity, when dry machining could not be done effectively.     

Investigation of process parameters influence in abrasive water jet cutting of D2 steel

In the present experimental study, abrasive water jet (AWJ) cutting tests were conducted on D2 steel by different jet impingement angles and abrasive mesh sizes. The experimental data was statistically analyzed using the simos–grey relational method and ANOVA test. In addition, the outcome of influencing cutting parameters, namely jet pressure, jet impingement angle, and abrasive mesh size on the different response parameters, namely, the jet penetration, material removal rate, taper ratio, roughness, and topography, were studied. Micro-hardness test and surface morphology analysis were employed to examine the D2 cut surfaces at different AWJ cutting conditions. The chemical element study was performed to determine the abrasive particle contamination in the AWJ kerf wall cut surfaces. The ANOVA test result indicated the jet pressure and jet impingement angle as the influencing process parameters affecting the various performance characteristics of AWJ cutting. The overall AWJ cutting performance of the D2 steel has been improved through proper identification of the optimal process parameter settings, namely jet pressure 225?MPa, abrasive mesh size #100, and jet impingement angle 70° by the simos–grey relational analysis.     

Fabrication of superhydrophobic surfaces on aluminum substrates using NaNO<Subscript>3</Subscript> electrolytes

A superhydrophobic surface with a water contact angle of 166.0° and a tilting angle of 1.5° was fabricated on an aluminum substrate by electrochemical machining using neutral NaNO₃ electrolytes, followed by fluorination. The fabrication process is based on the fact that the grain boundaries and dislocations on aluminum are anodic dissolved before the grain itself by an applied electric field. Using scanning electron microscopy to analyze surface morphology, micrometer scale caves, and protrusions were found on the surface, with numerous nanometer mastoids contained in the protrusions. These binary micro-nano rough structures, which are similar to the micro-structures of a lotus leaf surface, play an important role in achieving superhydrophobicity. The effects of processing time, processing current, and electrolyte concentration on superhydrophobicity were also examined. The results show that electrochemical machining does not require rigid processing parameters, uses a simple device, and is highly efficient and environmental friendly. The optimum processing conditions are a processing time of 60 min, a processing current of 250 mA, and an electrolyte of 0.15 mol/L.     

Effects of the TiC and sintering process on the TiC-steel composite

In this paper, the composite of low alloy steel reinforced with TiC particles was prepared by conventional powder metallurgy process. The effects of the combined carbon content of TiC powder, sintering temperature and heating rate on the composite were studied. The results showed that the selected TiC powder has a combined carbon content of 17.91?wt-% and the optimal sintering process is heating from 600 to 1440°C at a rate of 1°C?min^?1 and holding for 1?h at 1440°C. The composite after heat treatment has excellent mechanical properties with density of 6.45?g?cm^?3, hardness of 68–69 HRC and TRS of 1763?MPa, respectively, and will be used as wear-resistant parts, assembly fixtures, moulds, etc.     

Structure and properties of solid state diffusion bonding of 17-4PH stainless steel and titanium

Abstract

Solid state diffusion bonded joint between titanium and 17-4 precipitation hardening stainless steel was carried out in the temperature range of 800–1050°C in steps of 50°C for 30 min and also at 950°C for 30–180 min in steps of 30 min under a uniaxial pressure of 3·5 MPa in vacuum. Bonded samples were characterised using light microscopy, field emission scanning electron microscopy and X-ray diffraction technique. Up to 850°C for 30 min, FeTi phase was formed at the diffusion interface; however, α-Fe+λ, χ, Fe₂Ti and FeTi phases and phase mixtures were formed above 850°C for 30 min and at 950°C for all bonding times. Maximum tensile strength of ～326 MPa, shear strength of ～254 MPa and impact toughness of ～24 J were obtained for the diffusion couple processed at 1000°C for 30 min and 30–180 min time interval at 950°C, and maximum tensile strength ～323 MPa, shear strength ～243 MPa and impact toughness of ～22 J were achieved when bonding was processed for 120 min. The residual stress of the bonded joints increases with the increase in bonding temperatures and times.     

High resistance boron treated steels for railway applications

Abstract

The present study analyses different boron contents (between 10 and 160 ppm) on the structure of a 0·2C–2Mn–1Si (wt-%) steel deformed at a starting temperature of 1050°C in a T. J. Pigott laboratory rolling mill. The steel was made in a laboratory open induction furnace using high purity raw materials and cast into metallic moulds. This experimental steel has proved to have tribological properties, under dry rolling/sliding contact, as good as those for the 0·8% pearlitic steels used in railway applications. Before thermomechanical processing, the steel ingots (70 × 70 × 70 mm) were homogenised at 1100°C for 1·5 h. The thermomechanical treatment was carried out by a reversed multipass process to reach a level of deformation of 60%. Plastic deformation was finished at ～920°C for all the rolled steels and the plates (70 × 150 × 20 mm) were then water quenched and/or air cooled to room temperature. Results show more bainitic structures as boron content increases in the air cooled steel after hot rolling. For the quenched steels, the structure becomes more martensitic as boron content increases. The best combination of mechanical properties was obtained for the air cooled 76 ppm boron containing steel, which had a lower bainitic structure. This steel had the yield strength of 750 MPa, 15% elongation and the hardness of 40 HRC. Materials characterisation was carried out by optical and transmission electron microscopy (TEM). Results are discussed in terms of the boron segregation towards grain boundaries, the effect of boron on the steel hardenability, as well as on the boron carbonitrides (CNB) precipitation.