Influence of filler metals and welding techniques on the structure–property relationships of Inconel 718 and AISI 316L dissimilar weldments

In the present investigation, an attempt has been made to weld the precipitation hardened Nickel based super alloy Inconel 718 and austenitic stainless steel AISI 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process employing ER2553 and ERNiCu-7 fillers. Microstructure examination using optical and SEM analysis clearly witnessed the formation of unmixed zone at the Heat Affected Zone (HAZ) of Inconel 718 for all the joints. The studies showed the absence of deleterious phases in the CCGTA and PCGTA weldments employing ERNiCu-7. Tensile studies corroborated that the fracture occurred at the parent metal of AISI 316L in all the cases. It was inferred from the present study that PCGTA weldments employing ERNiCu-7 exhibited better metallurgical and mechanical properties. This study articulated the effect of filler metals on the structure–property relationships of the weldments.     

Si3N4陶瓷/Nb/Cu/Ni/Inconel 600界面反应层形成机制研究

观察分析了Si3N4陶瓷/Nb/Cu/Ni/Inconel600界面处反应层的形貌、元素分布、反应层中的相结构、界面反应以及反应层的生长规律,研究了Si3N4陶瓷/Nb/Cu/Ni/Inconel600界面处反应层的形成机制.研究结果表明:在连接过程中,Cu层首先熔化,Nb、Ni向液态Cu中扩散溶解形成Cu-Nb-Ni合金,液态合金中的Nb和Ni向Si3N4表面扩散聚集并与Si3N4反应形成反应层;Si3N4侧的反应层主要物相是NbN和Nb、Ni的硅化物,Ni基合金侧反应相主要是NbNi3和Cu-Ni合金;在连接温度为1403 K的条件下,随着连接时间的增加,界面反应层厚度先快速增加,再缓慢增加.     

阴极电弧沉积多元合金膜层的织构及其形成

采用阴极电弧沉积方法，制备了与靶材成分基本相同的多元合金Inconel625膜层[1]。用XRD，SEM，TEM研究了不同入射角下所获膜层中的织构分布及其成因。     

CTOD‐R curves of the metal‐clad interface of API X52 pipes cladded with an Inconel 625 alloy by welding overlay

Crack‐tip opening displacement resistance curves (CTOD‐R) of the substrate/cladding interface of an API 5 L X52 steel pipe internally coated with Inconel 625 applied by TIG (GTAW) welding were experimentally evaluated. A small pipe section with 168 mm of outer diameter and 22.5 mm of thickness was internally coated with a 15 mm thick layer of Inconel 625 corrosion resistant alloy. Tension test specimens were obtained from both substrate and cladding, as well as compact tension test specimens (C(T)) for the evaluation of CTOD‐R curves. The fracture testing specimens were notched at the interface in RL orientation. In addition to fracture and tensile testing, microstructural characterization was conducted at the interface using optical microscopy (OM) and scanning electron microscopy (SEM). Qualitative chemical composition scanning and microhardness determination were also performed. The results indicated high fracture toughness for the substrate/cladding interface and the absence of low toughness regions at the interface of the tested samples.     

Oxidation of Inconel 718 in Air at High Temperatures

Experiments were conducted with Inconel 718 at high temperatures to evaluate the rate of oxidation of the material over as wide a temperature range as possible, as well as to determine the high-temperature failure limit of the material. Samples of Inconel 718 were inserted into preheated furnaces at temperatures ranging from 973 to 1620 K and oxidized in air for varying periods of time. After being oxidized in air at a constant temperature for the prescribed time and then being allowed to cool, the samples were reweighed to determine their mass gain due to the uptake of oxygen. From these mass-gain measurements, it was possible to identify three regimes of oxidation for Inconel 718: a low-temperature regime in which the samples behaved as if passivated after an initial period of transient oxidation, an intermediate-temperature regime in which the rate of oxidation was limited by diffusion and exhibited a constant parabolic rate dependence, and a high-temperature regime in which material deformation and damage accompanied an accelerated oxidation rate above the parabolic regime.     

Effect of weld cooling rate on Laves phase formation in Inconel 718 fusion zone

Inconel 718 (2 mm thick) was welded using argon and helium gas shielded tungsten arc welding process with a filler metal. Both constant current and compound current pulse modes were applied and the cooling rates calculated. The dependence of Laves phase formation, dendrite arm spacing and niobium segregation ratios in fusion zone on the nature of shielding gases and current was studied. The maximum instantaneous weld cooling rate was achieved for the combination of Helium shielding gas and compound current pulse mode. This ultimately resulted in reduction of laves phase, segregation of niobium and dendrite arm spacing in the fusion zone.     

Fatigue strength of Inconel 718 at elevated temperatures

The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long-life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix ( phase) and the surface oxidation at elevated temperatures.     

Plasma enhanced machining of Inconel 718: modeling of workpiece temperature with plasma heating and experimental results

A numerical and experimental analysis of plasma enhanced machining (PEM) of Inconel 718 is presented in this paper. Surface temperatures due to plasma heating are systematically characterized through numerical modeling and experimental investigation using infrared radiation thermometry. A three-dimensional finite difference model is established to determine the temperature distribution in a cylindrical workpiece subjected to intense localized heating. The results are compared with experimental results obtained with a radiation pyrometer. A sensitivity analysis is presented to examine the effects of machining parameters on the temperature distribution. Benefits of PEM are also demonstrated through the reduction of cutting forces and improved surface roughness over a wide range of cutting conditions. In addition, improvement of productivity in machining Inconel with PEM is illustrated.     

永磁电机转子护套用高温合金Inconel625切削性能仿真与试验研究

本文针对高速永磁电机转子保护材料镍基高温合金Inconel625的切削性能展开研究。采用仿真软件DEFORM-3D建立了该材料的三维有限元仿真模型,仿真模型采用了Johnson-Cook模型、Usui刀具磨损模型等关键技术。通过仿真得到了切削过程中切削力的变化趋势、温度场的分布特性、刀具磨损、切屑形状等。在结合试验分析的基础上,得到了切削参数对切削力、切削温度、刀具磨损的影响规律。研究结果对Inconel625合金车削过程切削条件的合理选择和刀具使用寿命的提高提供了理论依据,为深入研究Inconel625合金切削机理提供了理论依据。     

两种合金在氯化物熔盐中腐蚀行为研究

氯化物熔盐是太阳能热发电储热系统具有前景的储热介质,但其对金属材料具有很强的腐蚀性。研究了太阳能热发电系统两种常用材料316L不锈钢和Inconel 625合金在900℃的NaCl、KCl、MgCl2和CaCl2熔盐中的腐蚀行为,采用XRD、带有能谱分析系统的扫描电镜分析了腐蚀产物的相组成和形貌。研究结果表明:两种材料在氯化物熔盐中均腐蚀严重,但在碱土金属氯化物熔盐(MgCl2、CaCl2)中的腐蚀程度要比它们在碱金属氯化物熔盐(NaCl、KCl)中严重得多。与Inconel 625合金相比,316L不锈钢在同种氯化物熔盐中的腐蚀速度较快。造成这种现象的原因是316L不锈钢表面的腐蚀产物FeCr2O4和Fe3O4比Inconel 625合金表面的腐蚀产物更易在氯化物熔盐中溶解。研究结果将有助于太阳能热发电系统的选材和发展腐蚀防护技术。