超音速微粒轰击纳米化拉矫辊表面形貌与力学性能研究

采用超音速微粒轰击方法（USPP）对宝钢某机组拉矫辊进行了表面纳米化处理,利用扫描电镜（SEM）、粗糙度仪和显微硬度计对其表面形貌和力学性能进行了表征分析,结果表明,轰击后拉矫辊表面随机分布大量的冲击坑,表面粗糙度可在1.5-2.5之间调整;拉矫辊表层晶粒尺寸明显细化。纳米化处理后拉矫辊表层硬度可达到HV 920。工作气体温度和压力是影响酸洗拉矫辊表面粗糙度和显微硬度的主要因素。     

氮气流量对TiN 薄膜组织结构及力学性能的影响

采用磁控溅射方法在不锈钢表面沉积TiN薄膜,通过扫描电子显微镜、显微硬度计、CSPM5500扫描探针显微镜、X射线衍射仪、往复式摩擦磨损仪等分析测试手段,研究氮气流量对薄膜形貌、成分、结构、硬度、表面粗糙度、耐磨损等性能的影响.结果表明,随着氮气流量的增加,薄膜的显微硬度、膜厚都逐渐降低,膜基结合力逐渐增加,膜基结合力在16 mL/min时达到最大67.2 N;表面粗糙度和平均摩擦系数均在8 mL/min时最低.随着氮气流量增加,薄膜主要生长取向由(200)晶面转向(111)晶面生长;TiN薄膜的颜色也随氮气流量增大而加深,8 mL/min和12 mL/min时为金黄色,4 mL/min和16 mL/min时颜色较差.      

超声滚压处理7B85合金的显微组织和力学性能

采用不同压下量（0、0.1、0.2、0.3、0.4 mm）对7B85合金进行超声滚压处理，利用光学显微镜、表面粗糙度测量仪、显微维氏硬度计、拉伸实验、扫描电镜、X射线衍射和电子背散射衍射对经过超声滚压处理的7B85合金的微观组织和力学性能进行研究。结果表明，当下压量为0.2 mm时，超声表面滚压处理后7B85合金的表面粗糙度、显微硬度以及抗拉强度达到较优值。滚压处理后合金的断口形貌呈现出大量较深的韧窝，其主要以韧性断裂形式为主。同时，超声表面滚压处理后合金中大部分η析出相溶解到铝基体中，其表层晶粒的平均晶粒尺寸约为（25.22 ± 6.46）nm。滚压后合金力学性能的提高主要归因于合金表面细晶强化和应力强化的共同作用。      

Effect of Shot Blasting and Shot Peening Parameters on Residual Stresses Induced in Connecting Rod

This paper investigates the effect of shot blasting and shot peening parameters on residual stresses induced in connecting rod. Compressive residual stresses are induced using shot peening to increase fatigue life of connecting rod. Shot peening is also responsible for increase in surface roughness. Surface roughness is detrimental for fatigue life of the connecting rod. This necessitates shot blasting to reduce surface roughness. Shot peening and shot blasting processes are analysed to find optimum process parameters which will induce required value of compressive residual stress on the surface of connecting rod. Compressive residual stresses induced in the connecting rod specimen have been experimentally measured using X-ray stress analyser. The experimental results have been analysed using grey relational analysis to find optimum values of process parameters for target value of compressive residual stress and surface roughness. The experimental investigation and the analysis of it have resulted in achieving the desired value of compressive residual stress, which is 10.5% higher over the existing connecting rod. Surface roughness also decreases to 3.84 Ra which is 8.5% lesser than specified value to achieve better fatigue life.     

Effects of Burnishing Parameters on the Surface Characteristics,Microstructure and Microhardness in EN Series Steels

Surface finish and surface hardness of the components play vital role in quality of products/components, in general and failure resistance, in particular. One of the finishing process involving surface plastic deformation that introduces compressive residual stresses and thereby improves fatigue resistance is “Burnishing”. Even though the burnishing process is widely employed, its process parameters were not systematically studied till date and not fully established for various important structural materials. The burnishing process parameters include force, speed, feed, and number of tool passes. In the present study, the data obtained from systematically conducted burnishing experiments are correlated with theoretical design using Taguchi method in case of EN series steels (EN 8, EN 24 and EN 31). The surface characterization employed includes optical microscopy, microhardness and magnitude of residual stress. The study revealed a one-to-one correlation between burnishing depth, increase in average microhardness and magnitude of compressive residual stresses and a peak in all these three at intermittent extent of burnishing (either after first or second pass) in all the three alloy steels.     

Structural,Micromechanical and Tribological Analyses of Electrodeposited Nickel–Graphite Coatings with Different Fractions of Graphite Microparticles

Nickel–graphite composite coatings were electrodeposited on a steel substrate from typical watts bath and with specific operating conditions for different weight fractions of graphite microparticles. The weight percentage of particles in coatings and the microstructure were studied, respectively, by atomic absorption, scanning electron microscope and X-ray diffraction. The influence of graphite fraction on roughness and microhardness were also investigated. It was found that roughness increases with the increase of particle content while microhardness decreases. The tribological response was examined against high chromium steel ball using linear reciprocating tribometer. The results indicated that the friction coefficient decreases when graphite content increases. This was ascribed to the development of tribo-layer on the wear track and transfer film on the counterface. However, it was found that the improvement of wear resistance was obtained until an optimal value of graphite concentration, which provided the best condition that promoted the tribo-layer stability and maintained the matrix integrity.     

邯钢2180mm连退平整机工作辊毛化参数的优化

简述了电火花毛化机的工作原理,分析了轧辊毛化程序中各参数对轧辊表面粗糙度 Ra和峰值密度Pc的影响,通过对连退平整机工作辊毛化参数的优化获得了带钢质量要求的表面粗糙度和峰值密度。     

Effect of rare earths on mechanical properties of plasma nitrocarburized surface layer of 17-4PH steel

The aim of this investigation is to reveal the influence of rare earths(RE) addition on mechanical properties of plasma nitrocarburized 17-4PH steel.The nitrocarburized layers were characterized by optical microscope,scanning electron microscope equipped with energy dispersive X-ray analyzer,X-ray diffractometer,microhardness tester and pin-on-disc tribometer.The results showed that RE atoms could diffuse into the surface layer of 17-4PH steel plasma nitrocarburized at 500 °C for 4 h and did not change the ...     

Effect of Black Plate on Corrosion Resistance of T5 Tinplate

The effect of black plate on corrosion resistance of T5 tinplate was studied by glow discharge spectrograph, X-ray diffractometer （XRD）, stress tester, roughness tester and metallographic microscope. The result shows that black plate influences corrosion resistance of T5 tinplate intensely. It also indicates that the increase of content of manganese, phosphorus, silicon and aluminum in black plate would reduce the corrosion resistance of T5 tinplate and the increase of degree of crystal orientation on （200） crystal face, ｜X-Y｜ value （internal stress difference within two orientation）, roughness and exposure degree of iron grain after the same acid wash of black plate would enhance the corrosion resistance of T5 tinplate and the grain number of black plate has small effect on corrosion resistance of T5 tinplate.     

压痕对车轴钢疲劳极限的影响

利用硬度计在光滑沙漏状车轴钢疲劳试样上制造压痕,同时利用电火花在试样上加工缺陷,通过疲劳试验研究两种缺陷尺寸与试样疲劳极限之间的关系.将两类试样的测试结果和基于材料硬度、缺陷投影面积的Murakami模型计算结果进行对比.利用扫描电镜观察试样疲劳断口.结果表明,与计算结果相比较,压痕局部塑性变形导致的加工硬化和残余应力对试样的疲劳强度没有影响,裂纹依然从应力集中最大的压痕底部起裂.电火花缺陷表面粗糙度较大引起二次缺口效应,表面硬脆的重铸白层上还有微孔和微裂纹存在,导致此类试样疲劳强度低于模型计算结果,裂纹从电火花缺口底部多处萌生.      

Response of Continuous System with Stochastically Varying Surface Roughness to Moving Load

The problem of calculating the second moment characteristics of the response of a general class of nonconservative linear distributed parameter systems with stochastically varying surface roughness, excited by a moving concentrated load, is investigated. The surface roughness is modeled as spatial Gaussian, stationary colored noise. The resulting initial/boundary value problem is transformed by eigenfunction expansion into the modal state space, where the second moment characteristics of the response are determined by direct integration using a Runge-Kutta method.     

Microstructure and Wear Behavior of Zircon Reinforced Copper Based Surface Composite Synthesized by Friction Stir Processing Route

Although copper has its use in many industrial and functional applications, but its low wear resistance limits its potential application. Hard particulates are generally reinforced in bulk copper to increase its wear resistance but it tend to decrease its toughness. Thus the present research focuses on synthesis of copper based surface composite by friction stir processing. Zircon sand was used as reinforcement in copper as it is hard and fairly inexpensive. To prepare the composites, a groove of defined dimension was machined in the copper plate for compaction of zircon sand (18 vol%) at the centre of the plate. After filling the zircon sand in grooves, friction stir processing technique was employed to reinforce it in copper. For microstructure analysis, XRD, microhardness and wear characterization, specimens were cut from the processed portion of the plate. The micrograph obtained by optical and scanning electron microscope revealed equiaxed and fine grain structure in stir zone with no sign of concentration gradient, aggregation and segregation of particles. XRD pattern revealed no peaks corresponding to intermetallics or interfacial reaction products. The microhardness and wear resistance of fabricated surface composite improved significantly as compared to pure copper. The micrograph of worn surface was also analysed to investigate the predominant wear mechanisms. Adhesion and delamination wear were predominant wear mechanisms in pure copper whereas these wear mechanism was not significant in Cu/Zircon composite.     

Nanostructure Cu–Cr alloy with high dissolved Cr contents obtained by mechanical alloying process

Abstract

A nanostructural solid solution of Cu–Cr was prepared by the mechanical alloying process. Three mixtures of Cu powders with 1, 3 and 6 wt-%Cr powders were milled under 250 rev min^?1 for different milling times of 4, 12, 48 and 96 h. The mixtures were subsequently compacted and sintered at 450, 600 and 750°C for half an hour. Milled powder mixtures were examined by X-ray diffraction technique, which showed the presence of nanoscale crystallites in the samples and the decrease of lattice parameter of Cu crystals. Sintered powders were investigated by optical microscope and their hardnesses were measured by microhardness. Results showed increasing trends in hardness of the compacted powder mixtures with increasing milling time. Sintering temperature had also evident effects on the behaviour of powder mixtures. As sintering temperature increased, microhardness increased and a peak appeared then a decreasing trend was observed.     

A comparative Study on the Wear Behavior of Al2O3 and SiC Coated Ti-6Al-4V Alloy Developed Using Plasma Spraying Technique

This paper reports the wear characteristics of the ceramic coatings made with Al₂O₃ and also with SiC which were performed using atmospheric plasma spraying technique on the Ti-6Al-4V biomedical alloy with the aim of improving their tribological behavior. The wear behavior of the coatings was evaluated using reciprocatory wear tester with coated substrate as the flat and alumina ball as a friction partner in simulated body fluid (Hank’s solution) environment. The microstructure and phase composition of the ceramic powders and as-sprayed coatings have been characterized using scanning electron microscope and X-ray diffractometer. Porosity, microhardness, adhesion strength and roughness of the coatings were measured as they have a bearing on wear and friction behavior. The results indicate that plasma sprayed Al₂O₃ coating exhibits higher wear resistance compared to that of plasma sprayed SiC coating. The higher wear resistance of Al₂O₃ coating is attributed to the improved melting and spreading of the alumina particles onto the substrate yielding increasingly bonded splats, resulting in compact and dense microstructure with lower porosity and higher microhardness.     

Surface Modification of AISI 1045 Carbon Steel by the Electrolytic Plasma Process

The electrolytic plasma process (EEP) was employed for surface modification of 1045 carbon steel for the first time, which resulted in a harder surface. Surface composition of the samples at different depths was evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), which revealed diffusion of Cr from the bath to ~15 μm beneath the surface of the samples during the test time of 10 minutes. The effects of applied voltage, test duration, and electrolyte concentration on the hardness and microstructure of the samples were investigated by microhardness measurements and optical microscopy. It was concluded that surface hardness as well as depth hardness of the samples increased with the applied voltage, test duration, and electrolyte concentration.     

Investigation of Tribological Properties and Characterization of Borided AISI 420 and AISI 5120 Steels

In the present study, tribological and characterization properties of borides formed on AISI 420 martensitic stainless and AISI 5120 cementation steels have been investigated. The boride layer was characterized by optical microscopy, X-ray diffraction technique and the micro-Vickers hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed the existence of FeB, Fe₂B and CrB compounds. The wear tests were carried out in a ball-disc arrangement under a dry friction condition at room temperature with an applied load of 10 N and with a sliding speed of 0.3 m/s at a sliding distance of 1,000 m. The wear surfaces of the steels were analyzed using a SEM microscopy and X-ray energy dispersive spectroscopy EDS. The results were compared with each other. It was observed that the friction coefficient of unborided and borided steels ranged from 0.42 to 0.63. The wear rate of the borided steels was found to be approximately five times lower the wear rate of the unborided steels.     

高Nb-TiAl合金α2→α等温相变中的组织演变

采用热膨胀法结合金相显微镜(OM)、X射线衍射仪(XRD)和显微硬度等测试手段,系统研究了固溶处理后Ti-45Al-8.5Nb-(W,B,Y)合金在等温过程中的显微组织演变规律。结果表明:高Nb-TiAl合金α2→α相变温度区间为1140~1209℃;α2→α等温相变过程中,α相的形成呈“S”形曲线,合金在等温过程中显微组织主要由α2、γ相和少量β相形成的片层结构组成,随保温时间的延长,晶界处存在的β相逐渐减少;沿晶界产生的细小等轴γ晶粒逐渐增大;显微硬度随保温时间延长呈先增大后减小的趋势。     

Coatings of nanocrystalline metallic wires on steel substrate: mechanical characteristics of coating layer

Coatings are produced by wire arc spraying on a steel surface and the effect of coating thickness on the coating characteristics in terms of microhardness, residual stress and friction coefficient are examined. The wire used during coating is composed of FeCrBMnSi, which comprises nanocrystalline and amorphous phases. The twin wire arc spray system was incorporated to generate different coating thicknesses on steel substrate. The analytical tools including three-dimensional imaging optical and scanning electron microscopes, energy dispersive spectroscopy and X-ray diffraction (XRD) are used to assess the coating characteristics. It is found that the surface texture and surface roughness of the coatings change with coating thickness. Thus, reducing the coating thickness results in slightly increased texture height and surface roughness. Microhardness is almost 15% higher for the thin coating (300?μm) than the thick coating (550?μm). The residual stress developed in the coatings is tensile and it changes with coating thickness, such that it reduces for thick coating.