Evaluation of the superplastic formability of SP-inconel 718 superalloy

The superplastic formability of SP- lnconel 718 superalloy was evaluated using the argon blowing method. Relationships among superplastic forming parameters (forming temperature, argon pressure, and forming time) and specific dome height (dome height/workpiece diameter) were investigated, as were changes in material properties after superplastic forming. Experimental results showed the optimum forming temperature range for SP- lnconel 718 to be between 975 and 995 °C. During the superplastic forming process, 5- phase precipitates formed at grain boundaries and limited the grain growth, which is considered beneficial for superplastic deformation. On the other hand, increasing the forming deformation also increased the formation of cavities, which can be attributed to the existence of niobium- rich inclusions. This degraded the superplasticity of the superalloy. Electrochemical tests showed that the corrosion resistance of SP- lnconel 718 after superplastic forming worsened because of the existence of both S- phase precipitates and niobium- rich inclusions.     

Friction welding of TiAl intermetallics and structural steel by applying Inconel 718 as interlayer

0IntroductionInterlayer metal is usually introduced while solidwelding heterogeneous metals with different chemical com-ponents and microstructures[1-3].The diffusion activationenergy(DAE)in both sides of interlayer and base metalcould be affected by the …     

G.718音频编码器核心层的一种低延时编码方案

语音编码器不仅要求提供高质量的语音,同时还要具有较低的编解码延时。较大的编码延时不仅会降低语音通信的服务质量,同时还可能减小系统容量。由于G.718编码器的延时主要由核心层算法引入,为了降低G.718编码器核心层的延时,提出了一种帧长为5ms的低延时编码方案,通过改变语音分类、开环基因搜索、线性预测系数的求解和量化方法,成功将编码延时在G.718基础上降低了25ms。主客观语音评测结果表明,该方案接近G.718核心层的重建语音质量。     

Feasibility study of the ultrasonic vibration assisted drilling of Inconel superalloy

The ultrasonic vibration assisted drilling of Inconel 718 superalloy is studied in this paper. The tool holder of a machining center is retrofitted so that axial resonant vibration can be provided. Experimental results show that the chip size is reduced, and the variation of torque in drilling becomes smaller. These phenomena are particularly apparent at the final stage of a drill's usable life. It is also found that there is little improvement in drilling performance when the frequency of the ultrasonic vibration is varied. On the contrary, a drill's life is greatly increased when the vibration with a smaller amplitude is applied. But too large a vibration amplitude, such as over 12 μm in this study, could lead to negative effects. For the testing conditions, the frequency of 31.8 kHz and the amplitude of 4 μm result in the best drill life and quality of the drilled hole in this study. Under this condition a drill's life is prolonged by as much as 2.7 times of that without vibration assisted drilling process. Concerning drilling efficiency, it is found that by applying ultrasonic vibration assisted drilling, lifting of the drill for chip removal as commonly employed in conventional drilling of a high aspect ratio hole is not necessary, and saving of the working time is obtained.     

An experimental study of tool wear and cutting force variation in the end milling of Inconel 718 with coated carbide inserts

Inconel 718 is a difficult-to-cut nickel-based superalloy commonly used in aerospace industry. This paper presents an experimental study of the tool wear propagation and cutting force variations in the end milling of Inconel 718 with coated carbide inserts. The experimental results showed that significant flank wear was the predominant failure mode affecting the tool life. The tool flank wear propagation in the up milling operations was more rapid than that in the down milling operations. The cutting force variation along with the tool wear propagation was also analysed. While the thermal effects could be a significant cause for the peak force variation within a single cutting pass, the tool wear propagation was believed to be responsible for the gradual increase of the mean peak force in successive cutting passes.     

Refrigerated cooling air cutting of difficult-to-cut materials

One approach to enhance machining performance is to apply cutting fluids during cutting process. However, the use of cutting fluids in machining process has caused some problems such as high cost, pollution, and hazards to operator's health. All the problems related to the use of cutting fluids have urged researchers to search for some alternatives to minimize or even avoid the use of cutting fluids in machining operations. Cooling gas cutting is one of these alternatives. This paper investigates the effect of cooling air cutting on tool wear, surface finish and chip shape in finish turning of Inconel 718 nickel-base super alloy and high-speed milling of AISI D2 cold work tool steel. Comparative experiments were conducted under different cooling/lubrication conditions, i.e. dry cutting, minimal quantity lubrication (MQL), cooling air, and cooling air and minimal quantity lubrication (CAMQL). For this research, composite refrigeration method was adopted to develop a new cooling gas equipment which was used to lower the temperature of compressed gas. The significant experimental results were: (i) application of cooing air and CAMQL resulted in drastic reduction in tool wear and surface roughness, and significant improvement in chip shape in finish turning of Inconel 718, (ii) in the high-speed milling of AISI D2, cooling air cutting presented longer tool life and slightly higher surface roughness than dry cutting and MQL. Therefore, it appears that cooling air cutting can provide not only environment friendliness but also great improvement in machinability of difficult-to-cut materials.     

TEM STUDY OF PRECIPITATED PHASES IN P／M INCONEL 718 ALLOY UNDER LONG TIME EXPOSURE

用透射电子显微镜研究了改型与常规粉末７１８合金长期时效过程中γ″，γ′，δ相的析出、粗化行为．结果表明：改型合金与常规合金中γ″，γ′的析出行为不同，前者γ″和γ′主要以包覆及复合组织析出，后者γ″和γ′则多以单独、分离形式析出．在６５０℃等温１００００ｈ时效过程中，改型合金的γ″粗化速率低于常规合金，表现出良好的稳定性．经过７５０℃，１０００ｈ时效，两种合金均发生δ相的大量析出，但δ相在两个合金中析出的形貌、数量不同．     

Friction welding of TiAI intermetallics and structural steel by applying Inconel 718 as interlayer

Inconel 718 with thickness ranged from 0. 1 - 1.7 mm was chosen as interlayer to promote weldability in friction welding of TiAl intermetallics and structural steel such as AIS14140, in which the welded joint presents single fin showing less welding deformation on TiAl side. The correlations between tensile strength and the interlayer thickness were analyzed and fitted to a model. It indicates an optimum interlayer thickness ranged from 0.9 - 1.1 mm where the tensile strength reaches as high as 360 MPa. Otherwise, while the interlayer thickness decreases to 0. 1 mm, brittle compounds of TiC, Al2Ti4C2 and MTC3 are formed in the welded zone so that the tensile strength decays. Thicker interlayer should be also avoided as double joints may occur at TiAl -lnconel 718 and lnconel 718 -AISI 4140, respectively, which lowers the tensile strength to some extent.     

激光退火对Inconel 718微观组织和硬度的影响

研究激光退火对Inconel718时效合金的显微组织和硬度的影响.一台2.5kW的CO2激光机被用来照射试样的表面.在激光能作用下,试样表面层被加热后空冷.通过控制激光工艺参数,在表面不发生熔化的前提下,能够使一定厚度表面层内的硬度降低到标准退火合金的水平,而不影响试样内部母材的硬度.显微组织观察显示表面层的基体强化相(γ″和γ‘)在激光照射过程中被固溶,而其它二次相没有变化.γ″和γ‘的固溶被确定是表面层硬度下降的原因.在其它试验条件不变时,确立了退火层生成时由激光散焦距离和扫描速度描述的工艺参数范围.