Effect of cold working and sandblasting on the microhardness,tensile strength and corrosion resistance of AISI 316L stainless steel

The aim of this work is to investigate the effect of cold working and sandblasting on the microhardness, tensile strength and corrosion rate of AISI 316L stainless steel. The specimens were deformed from 17% to 47% and sandblasted for 20 min using SiC particles with a diameter of 500-700 μm and an air flow with 0.6-0.7 MPa pressure. The microhardness distribution and tensile test were conducted and a measurement on the corrosion current density was done to determine the corrosion rate of the specimens. The result shows that the cold working enhances the bulk microhardness, tensile and yield strength of the specimen by the degree of deformation applied in the treatment. The sandblasting treatment increases the microhardness only at the surface of the specimen without or with a low degree of deformation. In addition, the sandblasting enhances the surface roughness. The corrosion resistance is improved by cold working, especially for the highly deformed specimen. However the follow-up sandblasting treatment reduces the corrosion resistance. In conclusion, the cold working is prominent to be used for improving the mechanical properties and corrosion resistance of AISI 316L stainless steel. Meanwhile, the sandblasting subjected to the cold worked steel is only useful for surface texturing instead of improving the mechanical properties and corrosion resistance.     

Laser Texturing of Rolled Surfaces

To reduce friction and improve clarity of steel surfaces, laser texturing was used to produce known surface roughness profile on rolled surfaces using a Nd:YAG laser. Laser texturing process was analyzed to select the laser parameters. The surface roughness hardness and abrasion resistance were then measured and analyzed. The results show that the surface roughness is harder than the matrix, which fits for the requirements of laser texturing. The surface roughness also has good abrasion resistance. The intensity and distribution of the single pulse are the key points affecting the surface roughness profile.     

Effects of heat treatment on the intermetallic compounds and mechanical properties of the stainless steel 321-aluminum 1230 explosive-welding interface

The effects of heat treatment on the microstructure and mechanical properties of intermetallic compounds in the interface of stainless steel 321 explosively bonded to aluminum 1230 were investigated in this study. Experimental investigations were performed by optical microscopy, scanning electron microscopy, and microhardness and shear tensile strength testing. Prior to heat treatment, increasing the stand-off distance between samples from 1 to 2.5 mm caused their interface to become wavy and the thickness of intermetallic layers to increase from 3.5 to 102.3 μm. The microhardness increased from HV 766 in the sample prepared at a stand-off distance of 1 mm to HV 927 in the sample prepared at a stand-off distance of 2.5 mm; in addition, the sample strength increased from 103.2 to 214.5 MPa. Heat treatment at 450℃ for 6 h increased the thickness of intermetallic compound layers to 4.4 and 118.5 μm in the samples prepared at stand-off distances of 1 and 2.5 mm, respectively. These results indicated that increasing the duration and temperature of heat treatment decreased the microhardness and strength of the interface of explosively welded stainless steel 321-Al 1230 and increased the thickness of the intermetallic region.     

Influence of Dispersion of Nano-Zn0 Particles in Polymer Matrices on Properties of Relevant Nano Composite Fibers

The surface-passivated and non-surface-passivated zinc oxide nano-particles （marked as s-nanoZnO and ns-nanoZnO respectively） were evenly dispersed in polymer solutions with the aid of ultrasonic vibration to prepare nanocomposite film by free casting and to prepare nanocomposite fibers by wet spinning and to prepare nancomposites coating by surface smearing. The dispersion of s-nanoZnO and nsnanoZnO in PAN matrix were observed by transmittance electron microscopy, the mechanical properties of the relevant compesite samples were studied by INSRTON tensile strength tester. It was found that s-nanoZnO behaves a well-dispersed morphology in PAN films and fibers when its concentration was 2 wt% but ns-nanoZnO nano particles agglomerate into larger congeries in PAN films. It means that the surface-passivated process oft zinc oxide nano. particles was effective to disperse. The relative intensity and elonsation at break of s-nanoZnO-PAN composite fibers show maximum values with the increase of nano particle content in compesites （from 0 wt% to 2 wt% of s- nanoZnO）. The elasticity of the composite fibers increases whereas their modulus declines. Balanced the changes of the properties mentioned above, 2 wt% s-nanoZnO in PAN matrix is a proper content for the composite fibers spun by wet spinning. The result of surface smearing test means that the reactim between s-nanoZnO and polymer can be indicated by the color of nanocomposite surface coat on fibers.     

Effect of Electrospark Alloying Process on Microstructure and Properties of the coating

Using electrospark alloying machine, a series of experiments were carried out to investigate the effect of electrospark surface strengthening process on the microstructure and the properties of the coatings with ultrafine cemented carbide as electrode material and white cast iron as substrate material. The results indicated that the optimum process parameters to be used reached a satisfying coating surface. Wear test results showed the coatings had a high wear-resistance.     

Enhancing the surface hardness and roughness of engine blades using the shot peening process

The effects of shot peening on the mechanical properties of steel 1070 were studied to enhance the material's properties and surface characteristics. In this study, pressure and exposure time were the main parameters governing surface hardness and surface roughness. The optimal time duration and pressure were determined after several experimental trials. Changes in hardness and surface roughness were monitored as the pressure of the shot and the exposure time were varied. Furthermore, the microstructure was evaluated by scanning electron microscopy (SEM) and the images were enhanced by image processing techniques to evaluate the surface changes. Pareto charts were constructed to estimate the effects of pressure and time on both surface hardness and surface roughness. The novelty of this study is the concentration on engine blades which are frequently used in aircrafts to determine the optimal time-pressure combination for shot peening to achieve suitable mechanical and surface properties. The results show that shot peening pressure (up to 482.6 kPa for 7 min) has positive effect on enhancing the surface and mechanical properties for steel 1070 blades; however, an increase in either pressure or time above that level adversely affected both surface hardness and surface roughness.     

Effect of PLA Knitted Structure on the Mechanical Properties of Composite Vascular Scaffold

A new entire biodegradable scaffold has been developed which does not require precelluiarization before transplantation. This new kind of vascular scaffold prototype made from porous poly- e-caprolactone （PCL） membrane to provide three-dimensional environment for cell growth, and embedded with weft-knitted polylactic acid （PLA） fabric to support mechanics. The aim of this paper is to study the variation tendency of mechanical properties with the fabric spacing changing. The basic geometrical parameters were measured to characterize properties of the samples. The tensile and compressive elastic recovery of the samples were tested by the universal mechanical tester and radial compression apparatus, respectively. Both tensile and compressive properties enhanced when reducing the fabric spacing of the composite vascular scaffold.     

FFT and Wavelet-Based Analysis of the Influence of Machine Vibrations on Hard Turned Surface Topographies

With hard turning, which is an attractive alternative to existing grinding processes, surface quality is of great importance. Signal processing techniques were used to relate workpiece surface topography to the dynamic behavior of the machine tool. Spatial domain frequency analyses based on fast Fourier trans- form were used to analyze the tool behavior. Wavelet reconstruction was used for profile filtering. The re- sults show that machine vibration remarkably affects the surface topography at small feed rates, but has negligible effect at high feed rates. The analyses also show how to control the surface quality during hard turning.     

Morphology observation for surface orange peel and fracture in tension sample of aluminum alloy sheet and characterization of nano hardness

The tension property of aluminum-alloy sheet with different microstructures is measured,and the surface and tension fracture morphology of tension sample with and without orange peel are observed by using scanning electron microscope(SEM).Surface roughness and nano hardness of tension sample are measured.The results show that the average elongation of the samples with orange peel is lower than that without orange peel;especially the r value of perpendicular to the rolling direction is much lower than that without orange peel.The tension surface of the orange peel samples is very rough;various parameters of surface roughness are higher.Under the observation of SEM,a wider sliding band with a micro crack on the surface of orange peel sample can be found.The various parameters of surface roughness without orange peel sample are near to zero,the sliding band is narrow and without micro cracks.The dimple width in tensile fracture of orange peel sample is larger than that without orange peel sample,but shear lip is narrower.The nano hardness testing results show that samples with orange peel behave high elastic modulus,high hardness,and high maximum load,but low plastic deformation depth.These mentioned features can completely describe surface and fracture morphology of tension samples with orange peel.     

Effect of rolling geometry on the mechanical properties,microstructure and recrystallization texture of Al–Mg–Si alloys

The effect of rolling geometry on mechanical properties, microstructure, and recrystallization texture of Al–Mg–Si alloys was studied by means of tensile tests, microstructural observations, and electron backscatter diffraction measurements. The results reveal that the elongation and the average plasticity strain ratio(r) values of the T4P(pre-aging plus natural aging)-treated alloy sheet with a rolling geometry value between 1 and 3 are somewhat higher than those of the T4P-treated sheet with a rolling geometry value between 3 and 6. The deformation and recrystallization microstructures of the sheet with a rolling geometry value between 1 and 3 are more uniform than those of the sheet with a rolling geometry value between 3 and 6. The former also possesses somewhat higher surface quality. H {001}110 and Goss {110}001 orientations are the main recrystallization texture components for the former case, whereas the latter case only includes H{001}110 orientation. Texture gradients are present in the two alloy sheets. Shear texture component F on the surface of the sheet with a rolling geometry value between 3 and 6 and its higher texture gradients have revealed that non-uniform deformation occurred during cold rolling. The effects of texture on the yield strength and r value were also discussed.     

Effects of the deep rolling process on the surface roughness and properties of an Al-3vol%SiC nanoparticle nanocomposite fabricated by mechanical milling and hot extrusion

Deep rolling is one of the most widely used surface mechanical treatments among several methods used to generate compressive residual stress. This process is usually used for axisymmetric components and can lead to improvements of the surface quality, dimensional accuracy, and mechanical properties. In this study, we deduced the appropriate deep rolling parameters for Al-3vol%Si C nanocomposite samples using roughness and microhardness measurements. The nanocomposite samples were fabricated using a combination of mechanical milling, cold pressing, and hot extrusion techniques. Density measurements indicated acceptable densification of the samples, with no porosity. The results of tensile tests showed that the samples are sufficiently strong for the deep rolling process and also indicated near 50% improvement of tensile strength after incorporating Si C nanoparticle reinforcements. The effects of some important rolling parameters, including the penetration depth, rotation speed, feed rate, and the number of passes, on the surface quality and microhardness were also investigated. The results demonstrated that decreasing the feed rate and increasing the number of passes can lead to greater surface hardness and lower surface roughness.     

超声表面滚压加工参数对40Cr表面粗糙度的影响

研究了超声表面滚压加工各种加工参数对供货态40Cr轴表面粗糙度的影响。采用表面粗糙度分析仪对初始及加工表面进行测定,并使用显微硬度计测量该技术对40Cr表层沿深度方向的硬化作用。试验结果表明：超声表面滚压加工技术能显著降低车削的加工痕迹,改善金属材料的表面质量;各工艺参数对试样表面粗糙度均有一定影响,并产生不同程度的表层硬化作用;并且给出了各工艺参数的合理范围,试样的表面粗糙度值可降低至0.2μm以下。     

粉末的物理性能对热喷涂涂层的影响

在SUS316L不锈钢基体上,采用HVOF和DGS两种不同的工艺方法,分别喷涂WC-12Co和FeAl涂层,观察WC-12Co和FeAl粉末的颗粒形貌、粒度组成以及DTA,研究它们对热喷涂涂层质量的影响.通过表面粗糙度、显微硬度、形貌相以及X射线衍射谱等分析表明,球化程度高,颗粒大小均匀的粉末可使涂层的组织均匀,致密性好,结合强度高.采用HVOF方法喷涂WC-12Co涂层的质量最好,而采用DGS工艺喷涂FeAl涂层的工艺参数还有待于进一步优化.     

Processing and characterization of the microstructure and mechanical properties of Al6061–TiB2 composite

In the present research, aluminum metal matrix composites were processed by the stir casting technique. The effects of TiB2 rein-forcement particles, severe plastic deformation through accumulative roll bonding (ARB), and aging treatment on the microstructural charac-teristics and mechanical properties were also evaluated. Uniaxial tensile tests and microhardness measurements were conducted, and the micro-structural characteristics were investigated. Notably, the important problems associated with cast samples, including nonuniformity of the rein-forcement particles and high porosity content, were solved through the ARB process. At the initial stage, particle-free zones, as well as particle clusters, were observed on the microstructure of the composite. However, after the ARB process, fracturing phenomena occurred in brittle ceramic particles, followed by breaking down of the fragments into fine particles as the number of rolling cycles increased. Subsequently, com-posites with a uniform distribution of particles were produced. Moreover, the tensile strength and microhardness of the ARB-processed com-posites increased with the increase in the reinforcement mass fraction. However, their ductility exhibited a different trend. With post-deforma-tion aging treatment (T6), the mechanical properties of composites were improved because of the formation of fine Mg2Si precipitates.     

增材-微锻造加工工艺应力场数值模拟研究

激光熔丝增材制造过程中,材料快热快冷的特点使熔覆层产生不利于表面强度的残余应力,而增材-微锻加工工艺可提高增材制件的加工质量,改善增材制件微观组织及力学性能缺陷.以TC4为研究对象,通过超声微锻造工具头与熔池保持一定的相对距离做进给运动,对材料表面进行高频次冲击与滚压,使熔覆层表面得到改善和强化.对增材-微锻加工工艺进行顺序热结构耦合数值模拟研究,分析加工过程中熔覆层应力场变化情况.研究表明:对尚未冷却的增材熔覆层表面进行超声微锻造,熔覆层由于热源加载产生的残余拉应力转化为较为有益的残余压应力,降低了熔覆层表层缺陷发生的概率.不同的超声振幅、进给速度以及锻造温度参数对残余压应力及法向变形量有较大影响.     

Electrodeposition of functionally graded Ni-W/Er_2O_3 rare earth nanoparticle composite film

Multi-layered functionally graded(FG) structure Ni-W/Er_2O_3 nanocomposite films were prepared by continuously changing the deposition parameters, in which the Er_2O_3 and W contents varied with thickness. The microstructure and chemical composition of the electrodeposited Ni-W/Er_2O_3 films were determined by scanning electron microscopy(SEM) and energy-dispersive X-ray spectroscopy(EDS). The anti-corrosion and wear properties of the electrodeposition films were investigated by electrochemical measurement and ball-on-disk friction test. The microhardness distribution of the cross section of nanocomposites was measured by nanoindentation. The results showed that with decreasing agitation rate or increasing average current density, the contents of Er_2O_3 nanoparticles and tungsten were distributed in a gradient along the thickness, and the contents on the surface were larger. By comparison, FG Ni-W/Er_2O_3 films had better anti-corrosion and wear properties than the uniform Ni-W/Er_2O_3 films. Atomic force microscopy(AFM) and profilometry measurements indicated that Er_2O_3 nanoparticles had an effect on the surface roughness.     

氧化锆陶瓷微尺度磨削表面质量试验研究

为提高氧化锆陶瓷零件微细加工过程中的加工表面质量,改善氧化锆陶瓷零件的使用寿命,采用0.9mm磨头直径、500#磨粒的微磨棒对氧化锆陶瓷进行微尺度磨削三因素五水平正交试验.首先通过极差和方差分析,研究了磨削参数影响氧化锆陶瓷表面质量主次因素;其次优化出获得较低表面粗糙度值的工艺参数组合;最后通过单因素试验研究氧化锆陶瓷磨削表面粗糙度随磨削参数的变化规律.结果表明,磨削参数对表面粗糙度影响顺序依次为:磨削深度、进给速度、主轴转速;当主轴转速v_○s=40000r/min,进给速度v_○w=20μm/s,磨削深度a_○p=3μm时,表面粗糙度最小;表面粗糙度随主轴转速增大呈先下降后上升的趋势,随进给速度和磨削深度的增大而增大.     

车削氟金云母陶瓷脆性破碎机理及表面粗糙度模型

基于脆性断裂力学和刀具-工件干涉原理,研究氟金云母陶瓷脆性破碎机理及表面成形机制,预测了脆性材料车削中的裂纹扩展角度与深度;建立氟金云母陶瓷车削表面粗糙度理论模型,用以评价精密车削陶瓷表面质量并提高加工效率.脆性材料车削表面粗糙度由几何干涉粗糙度和脆性崩碎粗糙度构成.刀具几何形状和进给量主要影响几何干涉粗糙度,工件力学性能、切削速度、切削深度和切削力主要影响脆性崩碎粗糙度.验证实验结果表明,氟金云母陶瓷车削表面粗糙度随切削速度的增大而减小,随进给量或切削深度的增大而增大.本模型的理论预测值与实验结果趋势一致,与传统的几何模型相比更接近实验值.     

不锈钢冷连轧板带的表面粗糙度建模

针对不锈钢冷连轧生产工艺的特点,在引入转印率和遗传因子概念的基础上,通过深入的理论分析,推导出带钢表面粗糙度理论模型.首先通过SUS430不锈钢冷轧润滑实验进行表面粗糙度研究,定量分析压下率、来料厚度、带钢变形抗力和乳化液工艺参数等对转印率和遗传因子的影响,给出了轧辊粗糙度衰减函数方程,并对末机架入口带钢表面粗糙度进行近似求解,最终建立了不锈钢冷连轧成品板面粗糙度数学模型,并将其应用到冷连轧生产实践中.统计结果表明,粗糙度模型计算值与实测值的相对误差小于634%,该模型具有较高的精度和较好的泛化能力.     

镍基单晶高温合金磨削表面质量及亚表面微观组织试验

采用正交试验的方法,研究了镍基单晶高温合金DD5表面质量影响因素和亚表面微观组织.进行DD5平面槽磨削正交试验,得到砂轮线速度、磨削深度和进给速度对表面质量的影响规律,优选出最优工艺参数组合,并对磨削亚表面微观组织和磨屑形貌进行观察.结果表明:砂轮线速度对磨削表面粗糙度R_○a影响最大;随着砂轮线速度的增大,表面粗糙度R_○a不断减小;随着磨削深度和进给速度的增大,表面粗糙度R_○a不断增大.选出的镍基单晶高温合金DD5平面磨削试验参数范围内的最优工艺参数组合:砂轮线速度为30m/s,磨削深度为20μm,进给速度为0.2m/min.磨削亚表面出现了塑性变形层和加工硬化层.磨屑主要呈现出一节一节的锯齿状特征.