超声滚压装置设计及试验研究

设计了一种新的超声滚压装置,并利用该装置研究了超声滚压加工对18CrNiMo7-6齿轮钢表面性能的影响.首先对滚压装置进行了结构设计,应用ANSYS Workbench对装置进行了模态分析和谐响应分析,通过调整滚压装置结构,使该装置能够正常高效地工作;然后综合利用NPFLEX型三维表面形貌测量系统、Proto高速大功率...     

Effect of coating thickness on properties of Mo coatings deposited by plasma spraying

Plasma sprayed molybdenum coatings with different coating thicknesses (100, 200, 300 and 400 μm) were deposited on steel substrate. The variation in microstructural characteristics and properties of coatings with various thicknesses was investigated. The microhardness was measured using a Vickers’ indenter. The quantitative investigation of porosity is carried out with the help of computerised image analyser. The influence of coating thickness on wear resistance was estimated using pin on disc wear test rig. The worn surface of coated pin was characterised by scanning electron microscopy. The experimental results indicated that porosity of coating was increased with increased coating thickness. The enhanced coating thickness also resulted in decreasing microhardness and reduced wear resistance. In this study, the plasma sprayed thin coating with thickness of 100 μm possesses the lowest porosity, the highest hardness and better wear resistance.     

Investigation of roughness,topography, microhardness,white layer and surface chemical composition in high speed milling of Ti-6Al-4V using minimum quantity lubrication

Abstract

In this research, the effects of high speed milling on the main surface integrity characteristics, including surface roughness and topography, microhardness, white layer thickness, and surface chemical composition of Ti-6Al-4V were empirically studied. Totally, 18 experiments were carried out using a full factorial design of experiments method in the presence of minimum quantity lubricant. The results showed that by using high speed milling, it is possible to reach the surfaces with a higher quality and surface roughness of approximately 0.2?μm. Also, it was discovered that the microhardness variation with cutting speed has a dual nature. The maximum microhardness was obtained at the cutting speed of 375?m/min and the feed rate of 0.08?mm/tooth, which showed a 57% increase compared with the bulk material. In addition, by using the cutting speed of 450?m/min, the depth of heat-affected layer and work hardening effects declined up to 75% in comparison with the cutting speed of 300?m/min.     

Effect of Operating Temperature on Tribological Behavior of As-Plated Ni-B Coating Deposited by Electroless Method

The present work investigates the tribological behavior of electroless Ni-B coating in its as-plated condition at elevated operating temperatures. Ni-B coating is deposited using an electroless method on AISI 1040 steel specimens. Coating characterization is done using scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. Vicker's microhardness and surface roughness are measured. Friction and wear tests are carried out on a pin-on-disc tribological test setup at room and elevated temperatures of 100, 300, and 500°C. The tribological behavior deteriorates at 100°C compared to room temperature. Electroless Ni-B coating shows excellent wear resistance at 300°C, which again degrades at 500°C due to severe oxidation and softening of the deposits. The worn surface of the coatings is analyzed using optical microscopy and scanning electron microscopy. Within the temperature range considered, the wear mechanism changes from adhesion to a combination of adhesion and abrasion as the temperature rises from ambient condition to 100°C, following which the wear mechanism is predominantly abrasive. The formation of a tribochemical oxide film also affects the tribological behavior of the coatings at high temperature.     

入射角度对激光熔凝层组织及性能的影响

采用HL-1500型CO2激光加工机,以不同入射角度对40Cr钢进行激光熔凝处理,利用扫描电镜、X射线衍射仪、显微硬度计、恒电位仪及磨粒磨损试验机等对熔凝层进行显微组织观察和性能测试。结果表明:熔凝层分为表层、中间层及过渡层;随着入射角度的增大,熔凝层的组织变得粗大,显微硬度逐渐下降,耐磨性呈降低趋势;熔凝层的耐蚀性比基体有所提高。     

A Study of Tribological Phenomena in Friction Couple: Brake Composite Material—Steel

An investigation has been made of the mechanism of the iron layer formation on brake friction materials sliding over a steel surface. The nature of the metallization of specimens of friction materials, as well as changes in the surfaces as a result of sliding, were studied by optical and scanning-electron microscopy, electron-probe microanalysis, X-ray diffraction, thermogravimetric analysis, gas chromatograph analysis, and microhardness measurements. Based on this work and on reviews of some of the most recent results concerning the wear of friction materials, a hypothesis of the metallization of friction linings (iron layer formation) is presented. A model of a tribological system for a frictional brake as well as a model of the subsurface layers of composite brake materials is described.     

A study on microinjection moulding using moulding blocks by additive micromanufacturing

Microinjection moulding is one of the most efficient replication methods for polymeric components in microsystems. The manufacturing of moulding blocks for complex geometries is resorting increasingly to the techniques of rapid prototyping. This development on the use of additive microtechnologies can promote the massification of microsystems within a shorter tooling development cycle time. However, the microinjection moulding process itself has mechanical and thermal demands that must be addressed and require specific consideration of the selection of the tool material. This constrains the selection of the best-suited additive manufacturing process. The current state of the art of additive manufacturing technologies at the micrometric scale favours laser sources to process layer by layer the media contained in a vat. The media type, the laser power and the laser spot size are parameters that can influence the replication tool tolerances and physical properties. This work explores the possibilities of two additive technology tooling approaches for microinjection moulding, using different materials. The research parameters included replication detailing onto the plastic part, surface roughness, microtool integrity and wear. The evaluation of these parameters was carried out using both optical and hybrid microscopy, a laser perthometer as a non-contact solution for surface roughness evaluation, scanning electron microscopy and X-ray spectroscopy. The results of this research work showed that the processed material and technology play an important role both on surface quality and tool life, enabling criteria definition for technology selection.     

增材制造成形方向对冲蚀磨损性能的影响*

增材制造的零部件由于逐层制造而具有各向异性,为研究成形方向对冲蚀磨损性能的影响,采用激光同轴送粉工艺制备逐层堆积的铁基合金熔覆层,并对其显微硬度、金相组织、微观组织及冲蚀后表面形貌进行分析。水平表面(XY)、横截面(YZ)和纵截面(XZ)的显微观察表明:各方向的微观组织结构与热流方向、熔合线密切相关,进而显著影响了细晶区的分布和数量;堆积熔覆层水平上表面的平均显微硬度最大,横截面的平均显微硬度次之,纵截面的平均显微硬度最低;由于冲蚀过程中的加工硬化,弱化了各成形方向之间冲蚀磨损性能的差异,进而导致各成形方向上相似的冲蚀磨损形貌。冲蚀磨损试验表明,堆积熔覆层的冲蚀机制以微切削和犁削为主,堆积熔覆层水平表面的抗冲蚀磨损性能最好,纵截面的抗冲蚀磨损性能最差。     

INVESTIGATING THE EFFECTS OF EDM PARAMETERS ON SURFACE INTEGRITY,MRR AND TWR IN MACHINING OF Ti–6Al–4V

Ti–6Al–4V is a kind of difficult-to-cut material with poor machinability by traditional machining methods, while electrical discharge machining (EDM) is suitable for machining titanium alloys. In this paper, three input machining parameters including pulse current, pulse on time and open circuit voltage were changed during EDM tests. To investigate the output characteristics; material removal rate (MRR), tool wear ratio (TWR) and different aspects of surface integrity for Ti–6Al–4V samples such as topography of machined surface, crack formation, white layer (recast layer) thickness and microhardness were considered as performance criteria. The variations of MRR and TWR versus input machining parameters were investigated by means of main and interaction effect plots and also verified by ANOVA results. The effect of pulse energy based on pulse on time and pulse current variations against recast layer thickness and microhardness was studied. The possibility of forming different chemical elements and compounds on the work surface after EDM process was investigated by EDS and XRD analyses. The experimental results revealed that general aspects of surface integrity for machined samples are mostly affected by pulse current and pulse on time. The approximate density of cracks, micro holes and pits on the work surface is intensively dependent on pulse energy variations. Although increase of pulse energy improves the material removal efficiency but leads to increase of average thickness and microhardness of recast layer.     

Tribological phenomena in steel-composite brake material friction pairs

The mechanism of the formation of iron layers on brake friction materials sliding over a steel surface has been investigated. The nature of the metallization of friction material specimens and the changes in the surfaces as a result of sliding were studied by optical and scanning electron microscopy, electron probe microanalysis, X-ray diffraction, thermogravimetric analysis, gas Chromatographic analysis and microhardness measurements. A mechanism for the metallization of friction linings (iron layer formation) is proposed. Models of a tribological system for a frictional brake and of the subsurface layers of composite brake materials are described.     

Structural and mechanical properties of (Cr,Ni) N single and gradient layer coatings deposited on mild steel by magnetron sputtering

Ternary single and gradient layer (Cr, Ni) N thin films were deposited on the mild steel substrate by unbalanced magnetron sputtering technique in order to evaluate mechanical properties for machine tools and automotive applications. Microstructure, chemical composition, surface morphology and phase analysis were carried out using field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy and X-ray diffraction, respectively. Both single and gradient layer of (Cr, Ni) N coatings show a significant increment in mechanical properties such as hardness, adhesion strength and surface roughness along with the reduction of friction coefficient. Mechanical tests revealed that the hardness of the gradient layer increased up to 3.1 times due to the formation of Cr₂N and Ni phase whereas single layer showed the least friction. Single layer CrNiN layer exhibited 27.2% less surface roughness (R_a) in comparison with gradient layer. High values of surface roughness, hardness, thickness and friction could be correlated with high film-to-substrate adhesion (L_c2) for the gradient layer.     

An experimental investigation of affected layers formed in grinding of AISI 52100 steel

A systemic experimental investigation involving scanning electron microscopy, Vickers microhardness tester, X-ray diffraction, three-axis piezoelectric dynamometer, and thermocouple was carried out to analyze the affected layers formed in grinding of AISI 52100 steel. The formation mechanisms and properties of affected layer at different grinding conditions were investigated. It is found that the phase transformation, as well as retained austenite and white layer, can be formed at the grinding temperature below the nominal phase transformation temperature of the workpiece material. Mechanical effect associated with plastic deformation also can influence the white layer formation, and play an important role for the phase transformation of the ground workpiece. Furthermore, higher hardness and residual tensile stress are observed on the ground surface of hardened steel, but it shows residual compressive stress on the ground surface of annealed steel.     

Surface layer microhardness changes with high-speed turning of hardened steels

In high-speed cutting of hardened steels, the surface layer is strongly affected by thermal effects and mechanical forces. Due to this, the surface layer of the machined material changes noticeably. Microhardness, one parameter of the surface integrity, is the most important. This paper deals with an investigation of microhardness. Measuring results are presented, and reasons for the sometimes significant changes in microhardness are analysed. It is proved on which part of the cutting edge the material removal will not take place but the cutting edge deforms the material plastically and how this part of the cutting edge can be reduced. With the measurement of the cutting force, the hypothesis is proved that the values of the cutting force components related to each other are different compared to the traditional turning. The passive force is 1.88?C2.25 times higher than the main cutting force. Hence, the force taking place on the flank face of the cutting tool is very high and the friction power significantly influences the cutting temperature. The friction taking place on the flank face of the cutting tool generates 2.8?C3.9 times higher heat than the cutting force. Due to the changes that occur in the surface layer, the hardness of this layer is higher with 100?C150?HV in depth of 0.1?mm than the original hardness or the hardness prescribed in the technical drawings. This phenomenon can be observed not only in internal hard turning but also machining of external and conical surfaces. Microhardness is compared after hard turning and after grinding. According to the measurements, the ground surface has not become a harder surface layer but softer. As an average result of many measurements, it has been proven that the original hardness (700?HV) after case hardening will increase to 800?C850?HV after hard turning and will decrease to 500?C550?HV after grinding. Microhardness changes are analysed considering the typical chip removal characteristics of hard turning. In this article, the focus is on how changes in microhardness influence the functional behaviour of the components and may affect their lifetimes. In this article, it has been proven that independently from the surface of the machined gear (bore, conical or face surface) the changes in the surface layer regarding microhardness do not differ.     

Study of surface integrity of ground bearing steel using Barkhausen noise technique

An experimental study was undertaken to compare the role of process parameters on the grindability of bearing steel (unhardened and hardened) in conventional grinding domain with particular emphasis on surface integrity. Surface residual stress on the ground specimens has been assessed using X-ray diffraction technique and Barkhausen noise analysis. The aim of this article was to compare the applicability of Barkhausen noise analysis technique to assess the state of residual stress with simultaneous change in microstructure along with the formation of white layer, microhardness, the incorporation of plastic deformation, etc. The results indicate a significant effect of downfeed and work speed on surface integrity parameters like residual stress, microstructure, and microhardness. Residual stress varied in the present work over a domain of 50–700 MPa. Despite simultaneous variation in the microhardness, microstructure, and residual stress during grinding, a linear correlation could be established between Barkhausen noise parameters and residual stress.     

Effect of shot peening parameters on microhardness of AISI 1045 and 316L material: an analysis using design of experiment

Shot peening is widely used to improve the fatigue properties of components and structures. Residual stresses, surface roughness, and work hardening are the main beneficial effects induced in the surface layer from shot peening, which depend on the correct choice of the peening parameters. In this investigation, experiments were designed using the full factorial design of experiment (DOE) technique and an air blast type of shot peening machine. Effects of process parameters such as pressure, shot size, stand-off distance, and exposure time on surface microhardness for AISI 1045 and 316L materials were investigated. An ANOVA was carried out to identify the significant peening parameters. In the case of 316L material, the maximum surface hardness was found to be in the range of 450–824 Hv, whereas it was found to be in the range of 314–360 Hv for AISI 1045. A critical assessment was made so as to understand the variation of microhardness in the direction of peening. Empirical equations between the peening parameters and the surface microhardness for both materials were developed, which are useful in predicting the surface microhardness. It is believed that this technique could prove beneficial in industries for reduction of performance variation and cost and to increase productivity.     

Tribological performance of TiN and TiCN coatings on a working tool steel

Although the applications of TiN and TiCN coatings are extensive, their mechanical and tribological properties are influenced by the substrates in which they are deposited. The present work is focused on the tribological performance of TiN and TiCN coatings on a working tool steel. Besides, adhesion and microhardness tests were carried out. The adhesion performance of both coatings resulted in class 1, according to CEN/TS 1071–8 standard, which allows observing the quality of adhesion. The composite microhardness was investigated by the analysis of relative indentation (β). Pin-on-disk tests were performed in dry and lubricated condition at 100 °C against tungsten carbide (WC). Low friction coefficients of μ_k = 0.08 for TiN and μ_k = 0.03 for TiCN were obtained in lubricated conditions. Wear mechanisms were analyzed by scanning electron microscopy (SEM). Abrasive wear was observed as the principal wear mechanism in dry condition, while in lubricated conditions wear signals seem to be scarcely noticeable.     

The hardening mechanism of tools in ultrasonic drilling — an investigation by an X-ray diffraction technique

The hardening mechanism of tools in ultrasonic drilling was investigated by studying the variation in the microhardness of the tools used and the X-ray diffraction patterns obtained. Various tool and work material combinations were used, and the extent of increase in microhardness of tool materials was analysed. In addition, the nature and extent of the residual stresses left on the surfaces of the tools used were investigated.     

Surface modification and characterization of zirconium carbide particulate reinforced C70600 CuNi composite fabricated via friction stir processing

In the present research work, Friction stir processing (FSP) technique has been applied to develop a C70600 graded copper-nickel (CuNi) Surface metal matrix composite (SMMC) reinforced with and without addition of ZrCp. Rotational and traverse speeds were set as 1200 rpm and 30 mm/min, respectively. The fabricated SMMC were metallurgically characterized by using Optical microscope (OM) and Field emission scanning electron microscope (FESEM). The homogeneous distribution of ZrC particles and good interfacial bonding between matrix/reinforcement were observed via OM and FESEM microscopes. The microhardness of the CuNi/ZrC surface composite was observed by using microhardness tester at the cross section of the sample. The average higher microhardness of 148 Hv at CuNi/ZrC SMMC and lower microhardness of 115 Hv at FSPed CuNi was found. The Ultimate tensile strength (UTS) value was measured by using micro tensile testing machine. The UTS value of CuNi/ZrC composite and FSPed CuNi were observed to be 310 MPa and 302 MPa, respectively. The mode of fracture was also observed via FESEM. The X-ray diffraction (XRD) test was carried out to confirm the presence of CuNi & ZrC in the SMMC layer.     

Experimental research material characteristics effect on white layers formation in grinding of hardened steel

Many studies have been performed on the formation of white layer. However, little study has been done to investigate the effects of material characteristics on the formation and thickness of white layer. In this study, grinding experiments are carried out by using four different steels (hardened and annealed) as workpiece material. The specimens are analyzed using a microhardness tester and an optical microscope. The experiments indicate the depth of white layer increases with the carbon content of workpiece materials. There is a critical carbon content (about 0.77 %) associated with thick white layer. Microhardness of white layer increases with the carbon content in hardened steel. A higher hardness is observed in the hardened steel than that in annealed steel, while there is not a softer transition zone in the annealed steel. White layer varies with the different combinations of grinding parameters. White layer thickness increases with the grinding depth and wheel speed. Based on experimental data, nonlinear regression statistical models are proposed to predict white layer thickness during grinding.     

轴类镀层结构材料力学性能声学表征方法研究

针对轴类镀层结构材料力学性能无损表征方法开展理论和实验研究,对于表面工程的质量检测与评价具有重要意义。利用自主开发的超声显微测量系统与PVDF线聚焦探头,对不同厚度的轴类镀层材料进行散焦测量。针对轴类试件表面波传播路径与散焦距离的非线性关系,分析了线聚焦探头几何尺寸与散焦距离和试件轴径间的匹配关系,优化检测参数,并在V(f,z)分析法的基础上,采用相位相关分析法获得轴类镀层材料的实验频散曲线。结合镀层材料声波传播特性,采用基于模拟退火的粒子群优化算法(PS-B-SA)将理论频散曲线与实验频散曲线相拟合,反演轴类镀层结构材料的声学参数,进而表征镀层材料的弹性常数。多个不同厚度轴类镀层结构材料弹性常数及镀层厚度的反演结果与实际值相吻合,表明该测量方法可靠、结果准确。该研究成果为轴类镀层结构力学性能无损检测提供了技术手段,也为工程材料表面工程加工性能的评价提供了新方法。