磨削表面损伤对RBSiC弯曲强度的影响

借助X射线衍射方法测量了反应烧结碳化硅(RBSiC)材料的磨削表面的残余应力状态,并根据断裂力学评价了磨削引入的裂纹尺寸,分析了RBSiC的弯曲强度受磨削引入裂纹和残余应力的影响.研究表明,由于磨削过程中与磨削方向有关的机械载荷占主导作用,使磨削后的表面残余应力具有方向依赖性.砂轮轴向进给从0.90μm/s增加到1.35μm/s,磨削表面的残余压应力数值降低,计算得到的磨削引入的裂纹尺寸增大,导致强度下降.     

轴向超声振动辅助磨削的表面残余应力建模EI北大核心CSCD

以单颗磨粒为对象,分析了轴向超声振动下磨粒的运动特性;在此基础上,将磨削力分为切削变形力和摩擦力两部分,分别分析了轴向超声振动对切屑变形力和摩擦力的影响。在切削变形力方面,轴向超声振动改变了磨粒的运动方向和运动轨迹;在摩擦力方面,轴向超声振动降低了磨粒与工件间的摩擦因数;结合切向磨削力与热源强度的关系,以及温升是磨削表面残余应力产生的主要因素,建立了轴向超声振动辅助磨削的表面残余应力模型。进行轴向超声振动辅助磨削45钢的表面残余应力实验,确定了模型的常数,并验证了所建模型的正确性。     

轴向超声振动辅助磨削的表面残余应力建模

以单颗磨粒为对象,分析了轴向超声振动下磨粒的运动特性;在此基础上,将磨削力分为切削变形力和摩擦力两部分,分别分析了轴向超声振动对切屑变形力和摩擦力的影响。在切削变形力方面,轴向超声振动改变了磨粒的运动方向和运动轨迹;在摩擦力方面,轴向超声振动降低了磨粒与工件间的摩擦因数;结合切向磨削力与热源强度的关系,以及温升是磨削表面残余应力产生的主要因素,建立了轴向超声振动辅助磨削的表面残余应力模型。进行轴向超声振动辅助磨削45钢的表面残余应力实验,确定了模型的常数,并验证了所建模型的正确性。     

固定短芯棒拔管残余应力分布规律研究

为了研究固定短芯棒拔管残余应力的产生机理和分布规律,采用弹塑性有限元法模拟拉拔过程,讨论模具形状参数、拉拔变形参数、摩擦条件对残余应力的影响.结果表明,当模具半锥角α较小时,随着α的增加,残余应力增大;在减径率εs一定的条件下,随着减壁量ΔS的增加,钢管内外表面的残余应力逐渐减小,在ΔS一定而εs增加时,内外表面上残余应力呈先增大后减小变化趋势;同时,轴向残余应力随着拉拔速度v和摩擦系数μ的增加而增大.     

超声振动辅助磨削马氏体不锈钢表面粗糙度研究

针对强韧性材料铣磨、小孔磨削等工艺中,因磨削速度低所引起的磨削表面粗糙度不易改善的问题,提出采用轴向超声振动辅助磨削工艺进行加工的方法。从几何层面对轴向超声振动辅助磨削表面创成进行理论分析,并对9Cr18马氏体不锈钢开展磨削试验,对比了轴向超声振动辅助磨削与普通磨削条件下的磨削表面粗糙度及表面形貌。结果表明,轴向超声振动辅助磨削可有效改善磨削表面粗糙度,且改善效果受磨削参数的影响,其中磨削速度对轴向超声振动效果影响最大,进给速度及磨削深度影响相对较小。磨削速度及磨削深度的增加对轴向超声振动效果具有弱化作用;增大进给速度,轴向超声振动效果略有增强。     

石英玻璃微流道超声振动磨削加工及流动阻力特性研究

石英玻璃微流控芯片在医学诊断、生化分析和药物筛选等领域具有广阔的应用前景,高性能石英玻璃微流道的加工质量直接决定微流控芯片的使用性能。本工作采用超声振动磨削加工技术对石英玻璃微流道进行高效精密加工,首先研究了主轴转速N、进给速度v_f、磨削深度a_p和超声功率P对微流道表面质量和形状精度的影响,然后对超声振动磨削工艺参数进行优化,最后测试微流道的水流阻力,研究微流道水力直径对其流动阻力特性的影响。超声振动磨削加工实验结果表明：石英玻璃微流道的表面粗糙度R_a可达较小值0.191μm,形状精度RMS值和PV值分别达到3.332μm和23.783μm,并且微流道表面形貌完整,底部微观表面光滑,边缘整齐无明显崩边。流动性测试实验结果表明：石英玻璃微流道内流动摩擦阻力系数随雷诺数和水力直径的增大而减小,因此设计微流道时应尽量选择较大的水力直径,并且适当增大流速。     

反应烧结碳化硅磨削参数优化及机理研究

针对反应烧结碳化硅(RB-SiC)的磨削工艺参数及其磨削机理进行研究.着重分析了磨削工艺参数对反应烧结碳化硅材料的表面粗糙度Ra、磨削效率和显微硬度以及磨削后陶瓷表面形貌的影响并确定最佳磨削工艺参数.最佳磨削条件为磨削深度0.47μm/s、工作台速度2.5 r/min和光磨时间5min.磨削后碳化硅Ra最低(Ra＜100 nm),加工硬化变质层较小,表面完整性较好.同时对反应烧结碳化硅的磨削机理进行研究,确定其是以脆性断裂为主的材料去除方式,其形式包括晶粒去除、材料剥落、脆性断裂等.     

冲击射流下旋转热管砂轮冷凝器传热特性

轴向旋转热管砂轮是用于强化磨削弧区换热的新型砂轮,其冷凝器换热性能的优劣直接影响整个热管砂轮的换热性能。本文结合冷凝器设计方法设计了热管砂轮冷凝器,并借助数值模拟的方法对轴向旋转热管砂轮冷凝器的换热性能进行分析,以优化旋转热管砂轮冷凝器的结构参数。研究不同的翅片高度(f=0～8 mm)、喷嘴到翅片顶部距离(d=3～11 mm)、低温空气射流速度(v_j=45～115 m/s)和砂轮转速(n=150～1 180 r/min)等对冷凝器换热性能的影响,结果表明：当翅片高度为6 mm时,获得最佳传热性能,对流换热表面传热系数约为459 W/(m²·K),与无翅片结构相比,对流换热表面传热系数提高36%;当喷嘴到翅片顶部距离为5 mm时,换热性能最好,传热系数为459 W/(m²·K);当低温空气射流速度提高时,对流换热表面传热系数随之提高,射流速度为115 m/s时对流换热表面传热系数最高,可达459 W/(m²·K),与射流速度为45 m/s时相比提高43%;当砂轮转速提高,对流换热表面传热系数也随之升高...     

双相Ti-48Al-2Cr-2Nb合金电解加工表面 微观形貌演变研究

针对各向异性合金材料电解加工过程中,加工表面形貌难以控制的问题,利用位置函数建立双相Ti-48Al-2Cr-2Nb合金微观材料模型,进而建立电解加工仿真微观物理模型,分析加工表面微观形貌随宏观工艺参数演变的规律。研究结果表明：电解液流速在14.7~23.4 m/s、进给速度在1.7~2.3 mm/min范围内,随着电解液流速和进给速度的增加,加工表面粗糙度Ry越低;当加工电压为21 V、进给速度为2.3 mm/min、电解液流速为23.4 m/s时,加工表面最光洁,Ry值达最小,为0.677 μm。从微观形貌演变仿真可以看出,获得最光洁加工表面经历了先粗化后抛光的过程。     

二硅化钼喷涂粉末的制备及其涂层组织结构

以粒度为1~2μm的MoSi₂粉末为原料,采用喷雾干燥和真空烧结制备了喷涂用MoSi₂团聚粉末. 分别用平均粒度为9.68μm的MoSi₂粉末和团聚造粒MoSi₂粉末(38~72μm)为喂料, 大气等离子喷涂制备了二硅化钼涂层,分析了涂层的微观组织结构. 研究结果表明,喷雾干燥造粒后的近球形粉末在1300℃真空烧结1h后,粉末流动性和松装密度分别为17.1s/50g和2.16g/cm³,比烧结前分别增加了57.0%和46.0%.平均粒度为9.68μm 的MoSi₂粉末制备的涂层主要是由Mo和Mo₅Si₃等富钼相组成. 团聚粉末制备的涂层主要由MoSi₂相组成,涂层较致密, 内部出现了类似“网状”的组织结构.     

Surface Integrity and Fatigue Behavior for High-Speed Milling Ti–10V–2Fe–3Al Titanium Alloy

Influence of cutting parameters on surface integrity when milling Ti–10V–2Fe–3Al is investigated based on high-speed cutting experiments. Surface integrity measurements, fatigue fractography analysis, and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that under given experiment conditions, surface roughness decreases linearly when increasing cutting speed or decreasing feed per tooth. The latter has a greater impact on surface roughness than the former. Compressive stress can be detected on all machined surfaces. With the increase of feed per tooth or cutting speed, respectively, residual stress presents a linear increase. Cutting parameters have no significant impact on micro-hardness. When the surface roughness ranges from 0.5 to 1.0 μm, the effect of surface residual stress on fatigue life is more than that of surface roughness. When the surface residual compressive stress increases, the fatigue life improves significantly. Compared with 60 m/min, when cutting speed is 100 or 140 m/min, the surface roughness decreases, the surface residual compressive stress increases, and the fatigue life improves by 124 and 59%, respectively. Under a tensile load, fatigue crack on machined surface of Ti–10V–2Fe–3Al titanium alloy originates at the cross-edge of the specimen surface. With the increase of surface roughness, the area ratio of fatigue crack propagation zone, and fatigue fracture zone decreases.     

Oberflächen‐ und Randschichtcharakterisierung von hochgeschwindigkeitsgefrästem Stahl

Surface and subsurface characterization of high speed milled steel Surfaces und subsurface regions of workpieces generated by high speed milling were studied to support the understanding of micro‐processes of deformation and cutting. Microstructure, crystal structure, residual stress, and topography of the workpiece, and microstructure and shape of the chips were characterized. With low carbon and low alloyed steel the materials state is significantly influenced by the cutting parameters. The surface topography is related to the microtopography of the cutting edge of the tool. A deformation of the microstructure happens down to 15 μm under the surface. Residual stress has been measured within a 60 μm thick surface layer. The curvature of the ships increases with the cutting speed.     

碳化硅晶须增强铝复合材料的精密切削研究

对挤压铸造法制造的碳化硅晶须增强铝复合材料(SiCw/Al)进行的精密切削研究结果发现;一方面这种复合材料对刀具磨损较为严重;另一方面复合材料切削表面质量主要取决于进给速度,随进给速度提高,复合材料表面质量下降。研究还发现由于复合材料切削过程中特殊的金属去除机制,使复合材料切削表面均产生残余压应力。     

Protein micro and nanoencapsulation within glycol-chitosan/Ca²+/alginate matrix by spray drying

Encapsulation of therapeutic peptides and proteins into polymeric micro and nanoparticulates has been proposed as a strategy to overcome limitations to oral protein administration. Particles having diameter less than 5 μm are able to be taken up by the M cells of Peyer's patches found in intestinal mucosa. Current formulation methodologies involve organic solvents and several time consuming steps. In this study, spray drying was investigated to produce protein loaded micro/nanoparticles, as it offers the potential for single step operation, producing dry active-loaded particles within the micro to nano-range. Spherical, smooth surfaced particles were produced from alginate/protein feed solutions. The effect of operational parameters on particle properties such as recovery, residual activity and particle size was studied using subtilisin as model protein. Particle recovery depended on the inlet temperature of the drying air, and mean particle size ranged from 2.2 to 4.5 μm, affected by the feed rate and the alginate concentration in the feed solution. Increase in alginate:protein ratio increased protein stability. Presence of 0.2?g trehalose/g particle increased the residual activity up to 90%. Glycol-chitosan-Ca(2+)alginate particles were produced in a single step operation, with resulting mean diameter of 3.5 μm. Particles showed fluorescein isothiocyanate labeled bovine serum albumin (BSA)-protein entrapment with increasing concentration toward the particle surface. Similar, limited release profiles of BSA, subtilisin and lysozyme were observed in gastric simulation, with ultimate full release of the proteins in gastrointestinal simulation.     

Molecular surface sampling and chemical imaging using proximal probe thermal desorption/secondary ionization mass spectrometry

Proximal probe thermal desorption/secondary ionization mass spectrometry was studied and applied to molecular surface sampling and chemical imaging using printed patterns on photopaper as test substrates. With the use of a circular cross section proximal probe with a tip diameter of 50 μm and fixed temperature (350 °C), the influence of probe-to-surface distance, lane scan spacing, and surface scan speed on signal quality and spatial resolution were studied and optimized. As a compromise between signal amplitude, signal reproducibility, and data acquisition time, a surface scan speed of 100 μm/s, probe-to-paper surface distance of 5 μm, and lane spacing of 10 μm were used for imaging. Under those conditions the proximal probe thermal desorption/secondary ionization mass spectrometry method was able to achieve a spatial resolution of about 50 μm as determined by the ability to distinguish surface patterns of known dimensions that were printed on the paper substrate. It is expected that spatial resolution and chemical image quality could be further improved by using probes of smaller cross section size and by incorporating a means to maintain a fixed optimal probe-to-surface distance real time, continuously adapting to the changing topography of the surface during a lane scan.     

机械滚压对A473M钢疲劳性能的影响

采用机械滚压对A473M马氏体不锈钢轴套材料进行表面处理,研究滚压工艺对其力学性能的影响。采用SEM、白光干涉仪、X射线衍射仪、显微硬度计、EBSD、拉伸试验机和疲劳试验机分别对试样表面形貌、表面粗糙度、残余应力、显微硬度、拉伸性能和疲劳性能进行系统表征。结果表明:滚压加工试样表面的粗糙度明显降低,仅为车削加工的1/5;滚压加工在材料近表面引入残余压应力,其值最高可达946 MPa,沿深度方向逐渐减小,残余压应力层深度约为200μm,表面硬度提高30%左右,硬度影响层深度可达200μm;抗拉强度、屈服强度和伸长率分别提升了40%,22%和8%,疲劳寿命由基体材料的5.4×10^4周次提高到1×10^7周次。采用滚压加工后材料的力学性能明显提升,疲劳寿命显著增加。     

GRINDING OF NICKEL-BASED SUPER-ALLOYS AND ADVANCED CERAMICS

This paper studies grinding of Inconel 718, Hastelloy, and some advanced ceramics. A newly developed ultra-high-speed grinding machine and a conventional grinding machine were used for the experiments. The ultra-high-speed grinding machine is equipped with a specially designed and built spindle unit that can run up to 200 m sec^-1 and deliver a maximum output of 12 kW. The surface roughness and residual stress values of the ground super-alloys and advanced ceramics were measured using a profilometer and a residual stress analyzer, respectively. The ground surfaces were also assessed using a scanning electron microscope. The effect of h_m (undeformed chip thickness) on surface topography of the difficult-to-machine materials was also investigated. A higher grinding wheel speed produces a smaller cutting depth and undeformed chip thickness, and thus smaller grinding force, decreased residual surface stress, and better surface finish. High productivity and good surfaces with ductile streaks could be obtained by employing ultra-high-speed grinding, even at very large wheel depths of cut such as 400 μm, without cross feed.     

铝合金A356微弧氧化电解液配方的优化

利用扫描电镜（SEM）、表面粗糙度测量仪等分析手段,研究了铝合金A356微弧氧化电解液配方对膜层性能的影响规律,优化了电解液配方：主电解质NaOH的质量浓度为4g／L及Na2SiO3的质量浓度为14g／L,添加剂KF的质量浓度为6g／L。KF对膜层性能有很大的改善,随着KF的加入,耐蚀时间从28．7min增大至36min,粗糙度从0．9μm减少到0．55μm。     

Machining residual stresses

As part of an extended investigation into the effects of pre-and post-processing on shot peening residual stresses, residual stresses due to a controlled turning process were investigated in the aircraft alloy 817M40. Cylindrical specimens were produced on a centre lathe with all machine parameters fixed except for feedrate. A variation in the feedrate was used to produce different surface roughnesses varying from 1·2 to 6·6 μm R_a. The residual stress field resulting from the varying feedrate was established by the well known centre hole drilling method, albeit with a modification which assisted in determining the variation of residual stresses with depth. The results indicated a definite variation in axial residual stress distribution with surface roughness, with a rough surface showing higher tensile residual stresses. This variation was however not duplicated for hoop or circumferential stresses. Maximum tensile residual stress varied from 90 MN m^?2 in the 6·6 μm R_a surface to 50 MN m^?2 in the 1·2 μm R_a surface. Although residual stresses are generally ignored in design, either because of a lack of experimental results or for ease of application, the results indicate that some consideration must be given to machining residual stresses as these can enhance or reduce the fatigue life of engineering components. The study also indicates that turning operations associated with large plastic deformations are encountered during the machining process.

MST/3230