Process parameter analysis of inertia friction welding nickel-based superalloy

A two-dimensional axisymmetric model for the inertia friction welding (IFW) of a nickel-based superalloy was developed. The influences from the axial pressure, initial rotational speed, and moment of inertia of the flywheel on the interface temperature and axial shortening were systemically examined. The analysis shows that the mechanical energy mainly depends on the initial rotational speed, and a relatively high axial pressure will increase conversion efficiency from mechanical energy to effective welding heat. The axial shortening is found to be approximately proportional to the square of initial rotational speed while logarithmical to the axial pressure. Based on this work, the weldability criteria for IFW nickel-based superalloy was established. Additionally, the approach for welding parameter optimization was performed considering the evolution of temperature profiles from various parameters. The results show that the axial pressure has a more obvious effect on the width of high-temperature zone than the rotational speed during the quick shortening stage.     

Research on sub-surface recrystallization of single crystal nickel-based superalloy in micro-milling

Journal of Mechanical Science and Technology - The micro-structure/parts of single crystal nickel-based superalloy materials are extensively used in high temperature environments. The...     

Evaluation of surface integrity in micro drilling process for nickel-based superalloy

This study focuses on the mechanical drilling of micro-holes in Inconel 718 alloy under wet cutting conditions. Qualitative and quantitative mechanical and metallurgical characterization of the surface and subsurface region was undertaken using nanoindentation, backscatter electron microscopy, electron backscatter diffraction microscopy and transmission electron microscopy. The analysis revealed three different zones, namely, a highly deformed nanostructured surface layer containing ultra-fine and high aspect ratio grains drawn out by large scale deformation, a deformed subsurface layer and finally the unaffected parent metal. The nano-hardness, plastic deformation, microstructure and crystal misorientation were assessed. The correlation between the modified surface and subsurface layers and the cutting conditions was established. The phenomena behind the formation of the different zones were investigated. The results suggest that subsurface alterations are driven by thermo-mechanical loading, causing plasticity and grain refinement by excessive shearing local to the cut surface.     

Experimental study of micro-milling mechanism and surface quality of a nickel-based single crystal superalloy

Micro-milling is widely used as a method for machining of micro-parts with high precision and efficiency. Taking the nickel-based single-crystal superalloy DD98 as the research object, the crystal characteristics of single-crystal materials were analysed, and the removal mechanism of single-crystal micro-milled parts was described. Based on molecular dynamics, a simulation model for nickel-based single-crystal superalloy DD98 micro-milling was established. Based on the response surface method of central composite design, the influences of spindle speed, feed rate, and milling depth on the surface roughness were examined, and a second-order regression model of the DD98 surface roughness was established. Using analysis of variance and the residuals of the model, a significant influence on surface roughness was found in the following order from large to small: Feed rate, spindle speed, and milling depth. Comparisons were conducted between the micro-milling experimental values and the predicted model values for different process parameters. The results show that the model fit is relatively high, and the adaptability is good. Scanning electron microscopy analysis of the micro-milling surfaces was performed to verify the slip and the removal mechanism of single-crystal materials. These results offer a theoretical reference and experimental basis for micro-milling of single-crystal materials.     

Single and multiobjective optimization of Inconel 718 nickel-based superalloy in the wire electrical discharge machining

Inconel 718 is widely used in high-temperature environments, high-performance aircraft, and hypersonic missile weapon systems; however, it is very difficult to machine using conventional techniques. This study employed an L9 Taguchi orthogonal array for the analysis of wire electrical discharge machining parameters when used for the machining of Inconel 718. Our aim was to determine the optimal combination of parameters to minimize surface roughness while maximizing the material removal rate. The Taguchi method is widely applied in mechanical engineering with the aim of identifying the optimal combination of processing parameters as they pertain to single quality characteristics. Unfortunately, Taguchi analysis often leads to contradictory results when seeking to rectify multiple objectives. To resolve this issue, this study implemented gray relational analysis in conjunction with Taguchi method to obtain the optimal combination of parameters to deal specifically with multiple quality objectives. For the dual objectives of surface roughness and material removal rate, the optimal combination of parameters derived using gray relational analysis resulted in a mean surface roughness of 2.75 μm. In L9 orthogonal array experiments, run 1 produced the best gray relational grade with mean surface roughness of 2.80 μm, representing an improvement of 1.8%. The material removal rate achieved after the application of gray relational analysis was 0.00190 g/s, whereas the L9 experiment achieved a material removal rate of 0.00123 g/s, representing an improvement of 54.5%.     

Influence of cutting speed on surface integrity for powder metallurgy nickel-based superalloy FGH95

Powder metallurgy (PM) nickel-based superalloy FGH95 has been widely used for components, which requires the greatest service performance. The surface integrity is becoming more and more important in order to satisfy the increasing service demands. However, the machined surface of FGH95 is easily damaged due to its poor machinability. The purpose of this paper is to investigate the effects of dry milling process parameters on the surface integrity of FGH95. Experiments were conducted on a CNC machining center under different cutting speeds. The machined surface is evaluated in terms of surface roughness, microhardness and white layer. Experiments results show milled surface integrity of FGH95 is sensitivity to the cutting speeds. The machined surface roughness decreases with increase of the cutting speed, but with further increase of cutting speed between 80?m/min to 100?m/min an increase in surface roughness appears. For microhardness, it can be seen that the machined workpiece surface hardens seriously. It can also draw the conclusion that cutting speed has the marginal effect on the white layer thickness generated in the machined subsurface.     

高温环境下超声电机的机械性能测试

研制了一种在高温环境下测试超声电机机械性能的装置,该装置包含了温度环境试验箱、转速转矩测量仪以及连接轴,提出了在高温环境下测试超声电机机械性能的方法.通过该装置和试验方法,对超声电机进行了高温环境试验,其环境温度为50～150℃.试验结果表明:随着环境温度升高,超声电机的转速下降;当环境温度<70℃时,超声电机最大力矩随着温度的上升而增加;当环境温度>80℃时,最大转矩随着温度的上升而下降;当环境温度到150℃时,超声电机不工作,超声电机在高温环境下需要降低其性能使用.该试验装置和试验方法同样适用于低温环境.     

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding cast nickel-based superalloy

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding nickel-based superalloy K424 was investigated. Grinding force and temperature acting on the abrasive wheels were measured. Optical microscopy and scanning electron microscopy were utilized to detect grain protrusion and wheel wear morphology. The normal distribution of the protrusion height of the brazed CBN grains on the wheel surface was determined. The results show that, though the grinding zone temperature is merely about 180°C during creep-feed grinding nickel-based superalloy, the grinding heat still has an important effect on the grain wear owing to the high temperature of the individual grain up to 500–600°C. Wear patterns of brazed wheels are composed of mild wear (attritious wear and grain micro-fracture) and severe wear (grain macro-fracture, erosion of the bonding layer). Strong joining of brazed CBN grains and Ag–Cu–Ti bonding layer improves significantly the resistance to grain pullout.     

Improvement of tribo-mechanical properties of directionally solidified CM-247 LC nickel-based super alloy through laser material processing

Nickel-based super alloy was used in high mechanical stress applications due to their good creep resistance and oxidation behaviour. However, their undesir     

Effect of cutting speed on surface integrity and chip morphology in high-speed machining of PM nickel-based superalloy FGH95

High-speed machining is being recognized as one of the key manufacturing technologies for getting higher productivity and better surface integrity. FGH95 powder metallurgy superalloy is a kind of nickel-based superalloy which is produced by near-net-shape technology. With increasing demands for high precision and high performance of FGH95 components in aerospace industry, it is essential to recognize that the machined surface integrity may determine machined part service performance and reliability. Then, little is known about the machined surface integrity of this superalloy. Thus, the surface integrity in high-speed machining of FGH95 is investigated in this paper. Experiments are conducted on a CNC milling center with coated carbide tools under dry cutting conditions. The surface integrity is evaluated in terms of surface roughness, microhardness, and white layer. The influence of cutting speed on chip morphology is also investigated. Experiment results show that surface integrity and chip morphology of FGH95 are very sensitive to the cutting speed. When cutting speeds are below 2,400?m/min, the values of surface roughness have little variation, while when cutting speeds are in the range of 2,800–3,600?m/min, the values of surface roughness are higher than that of other cutting speeds. Severe work hardening is observed resulting from high-speed machining of FGH95 superalloy. The higher the cutting speed, the higher the surface hardness. When cutting speeds are in the range of 2,800–3,600?m/min, the white layer thickness is slightly higher than that of other cutting speeds. In high-speed machining of FGH95, the chip is segmented and has a typical sawtooth shape. The degree of serrated chip increases with the cutting speed. When the cutting speeds exceed 2,400?m/min, serrated chips change into fragment chips.     

新型高可靠性超声波流量测量系统

介绍一种工业用大口径超声式气体管道流量测量系统的电路设计。该系统是一种带有微机的全电子式仪器,它克服了带有转子式的气体流量计固有的时漂误差,这种误差的主要来源在于管道中的油污或锈蚀造成了转子的丢转现象。该流量测量系统不仅适于各工厂中大口径管道的各种工业气体的流量测量,也适于西气东输等大型工程项目,具有广泛的应用前景。     

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10⁻⁶ mm³/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS₂ composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS₂/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.     

Creep feed grinding induced gradient microstructures in the superficial layer of turbine blade root of single crystal nickel-based superalloy

The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer. This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions. Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer (DFL) with nano-sized grains (48–67 nm) at the topmost surface, a DFL with submicron-sized grains (66–158 nm) and micron-sized laminated structures at the subsurface, and a dislocation accumulated layer extending to the bulk material. The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process, which were as high as 6.67 and 8.17 × 107 s?1, respectively. In the current study, the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and, simultaneously, from one orientation of a single crystal to random orientations of polycrystals, during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.     

高精度超声波辅助珩齿装置设计

分析了超声波珩齿装置中轴承的径向误差造成的珩齿轮径向偏差的大小;列出了珩齿轮相对于被加工齿轮的几种偏差形式,并给出了这几种偏差造成被加工齿轮的径向误差、公法线长度的变化、接触线方向误差、齿轮螺旋线误差和齿的锥度误差的计算方法.