Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

Effects of precipitation phases on the hydrogen embrittlement sensitivity of Inconel 718

We investigated the effects of precipitation phases on the hydrogen embrittlement (HE) sensitivity of Inconel 718 by means of tensile tests. Hydrogen was charged into the test specimens via a cathodic charging process prior to the tensile tests. Various heat treatments were applied to conventionally aged specimens to fabricate specimens with different precipitation conditions for the γ″ phase and the δ phase. For each precipitation condition, we fabricated two specimens, one of which was charged with hydrogen before the tensile test. All specimens were tensioned under identical tensile conditions. The percent loss of the reduction of area (RA) caused by pre-charged hydrogen was used to assess HE sensitivity. Both the δ phase and the γ″ phase were found to play significant roles in altering HE sensitivity of Inconel 718. When these phases were totally dissolved, the HE sensitivity of the alloy was very low. The percent loss of RA decreased along with a decrease in the fractional volume of γ″. The δ-free aged alloy had greatly enhanced HE resistance, the same level as that of conventionally annealed alloy, and its strength was equal to that of the conventionally aged alloy. Fracture origins noted on the specimens were located on the surface layers and displayed brittle cleavage when pre-charged hydrogen was utilized. Local transgranular cleavages initiated from the δ/matrix were also observed in conventionally aged specimens, where there was a presence of pre-charged hydrogen. Therefore, the δ phase was considered to promote HE by initializing micro-cracks from δ/matrix interfaces. Since the d-free aged alloy has both good strength and good ductility, we propose that it is advantageous for fabricating some hydrogen-containing parts.     

Effect of δ Phase on Hydrogen Embrittlement of Inconel 718 by Notch Tensile Tests

The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.     

Grain size effect on precipitation behavior of nanostructured Inconel 718

To provide insight into the effect of grain size on the precipitation behavior of γ\"strengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000 ℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.No y\"precipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).For δ phase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700 ℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation of δ was suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000 ℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800 ℃.     

Inconel 600及Inconel 718合金晶界偏聚研究进展

高温合金中的溶质晶界偏聚是影响合金多方面性能的重要因素.以高温合金Inconel 600和Inconel718为研究对象,总结了合金中溶质晶界偏聚的研究现状,并对已有的研究成果进行了深入分析,结果发现:溶质在Inconel 600合金中的偏聚规律对舍金性能的影响还需要进一步研究晶界偏聚特性、基本物理参量以及晶间腐蚀抗力的作用;溶质在Inconel 718合金中的晶界偏聚对合金性能的影响依然有待于进一步研究其作用机理、偏聚动力学和共偏聚特性.同时,指出今后高温合金中溶质晶界偏聚的研究方向为溶质晶界偏聚动力学以及溶质问晶界共偏聚行为.     

Effects of precipitation phases on the hydrogen embrittlement sensitivity of Inconel 718

We investigated the effects of precipitation phases on the hydrogen embrittlement (HE) sensitivity of Inconel 718 by means of tensile tests. Hydrogen was charged into the test specimens via a cathodic charging process prior to the tensile tests. Various heat treatments were applied to conventionally aged specimens to fabricate specimens with different precipitation conditions for the γ″ phase and the δ phase. For each precipitation condition, we fabricated two specimens, one of which was charged with hydrogen before the tensile test. All specimens were tensioned under identical tensile conditions. The percent loss of the reduction of area (RA) caused by pre-charged hydrogen was used to assess HE sensitivity. Both the δ phase and the γ″ phase were found to play significant roles in altering HE sensitivity of Inconel 718. When these phases were totally dissolved, the HE sensitivity of the alloy was very low. The percent loss of RA decreased along with a decrease in the fractional volume of γ″. The δ-free aged alloy had greatly enhanced HE resistance, the same level as that of conventionally annealed alloy, and its strength was equal to that of the conventionally aged alloy. Fracture origins noted on the specimens were located on the surface layers and displayed brittle cleavage when pre-charged hydrogen was utilized. Local transgranular cleavages initiated from the δ/matrix were also observed in conventionally aged specimens, where there was a presence of pre-charged hydrogen. Therefore, the δ phase was considered to promote HE by initializing micro-cracks from δ/matrix interfaces. Since the δ-free aged alloy has both good strength and good ductility, we propose that it is advantageous for fabricating some hydrogen-containing parts.     

Inconel718合金扩散连接接头的组织与性能研究

对细晶Incone1718高温合金无中间层和加Ni箔中间层两种情况下的扩散连接进行了研究,分析了不同的连接温度、连接压力、连接时间等工艺参数对接头剪切强度的影响;通过SEM、EPMA和金相技术对接头微观组织和力学性能进行了分析.确定了获得优质接头的最佳工艺参数区间,即扩散连接温度T=1 050℃,连接压力P=20 MPa,连接时间t=45 min,选用Ni箔作为中间层,厚度为25 μm.     

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.     

Machining Characteristics of Inconel 718 by Sinking-EDM and Wire-EDM

Inconel 718 superalloy has wide applications in several industries due to its excellent mechanical properties. However, it is very difficult to machine using conventional cutting and grinding because of its high strength at elevated temperatures. Electrical discharge machining (EDM) is an alternative competitive process to machine Inconel alloys by electrical erosion. However, machinability and surface characteristics of EDMed Inconel surfaces are poorly understood. This study focuses on the machining characteristics of Inconel 718 by Wire-EDM and Sinking-EDM with a new Cu-SiC electrode, respectively. Material removal efficiency, surface roughness, surface topography, surface alloying, and electrode wear have been characterized. It is found that the high toughness of Inconel 718 would be the major contributing factor to the absence of microcracks on the EDMed surface. The new fabricated Cu-SiC electrode for Sinking-EDM has better performance in terms of material removal rate (MRR), surface roughness, and electrode wear. The higher melting temperature and fine microstructure of SiC contribute to the lower electrode wear of the new Cu-SiC electrode than the traditional Cu electrode.     

Steady State Creep Rate Equation of Inconel 718 Superalloy

The steady state creep rate equdtion ofa nickel base superalloy Inconel 718, strengthenedby coherent ordered disc-shaped bct γ~(11) phaseand coherent spherical fcc γ~1 phase precipitates,has been established in the stress and temperatureranges of 620-840 MN m~(-2) and 853-943K, respecti-vely. Constant stress tensile creep tests wereused to medsure the values of steady state creeprate, ε_s, and the consecutive stress reductionmethod was used to measure the back stress duringcreep deformation. The values of effective stressexponent, n_e, were detemined from the slopesof the lgε_s vs. lg(σ_a-σ_0)/G plots. The effectof grain size, d, on steady state creep rdtehas been also studied in this investigation,and the grain size sensitive exponents m weredetemined from the slopes of lgε_s vs. lg(b/d)plots. The creep rate equations of Inconel 718,in the above stress and temperature ranges,have been proposed to beε_s=1.6×10~(-5)(D_1Gb/KT) (b/d )~(0.19)[(σ_a-σ_0)/G]~(1.35)in diffusional creep region, andε_s =75(D_1Gb/KT) (b/d)~(-0.42)[(σ_a-σ_0)/G]~(5.5)in dislocation power law creep region.     

Effect of microstructure on electrical conductivity of Inconel 718 alloys

The microstructural evolution of Inconel 718 during aging processes has been studied through a combination of eddy current testing, X-ray diffraction analysis, and metallography and hardness measurements. Measurements were carried out in samples subjected to eight different heat treatment cycles, between 620 and 1035°C for 1–18 h. Different amounts of secondary precipitates were achieved, reaching 18% of delta phase for samples overaged at 900°C for 18 h. Results show that the different microstructures of Inconel 718 obtained have a distinguishable effect on electrical conductivity when this is measured through an appropriately sensitive technique (i.e. eddy current testing). The lowest conductivity values were observed for under aged samples (1·44% IACS). A clear increase in conductivity values was seen for all aged or overaged conditions, reaching a maximum of 1·63% IACS, when coarsening of intra granular precipitates, associated with an increase in density of globular precipitates at grain boundaries, was identified. The influence of microstructure on conductivity could be shown to be due to the competition between two effects on the scattering of electrons: matrix purification and precipitation characteristics. A combination of hardness values and electrical properties proved to be a fast and practical way of determining the stage of aging of the alloy.     

Plastic flow behavior of Inconel 718 under dynamic shear loads

The plastic deformation behavior of nickel–iron alloy Inconel 718 in shear was measured at strain rates of 0.01 s⁻¹ and up to 3000 s⁻¹ with a quasistatic torsion machine and a split torsional Hopkinson bar, respectively. The measurements were analyzed to determine Johnson–Cook parameters and obtain material constitutive information needed for finite element simulations.     

Microstructure and mechanical properties in the TLP joint of FeCoNiTiAl and Inconel 718 alloys using BNi2 filler

High entropy alloy(HEA) of Fe Co Ni Ti Al and Inconel 718 superalloy were firstly transient liquid phase(TLP) bonded by BNi2 filler due to the diffusion of Si and B in the filler to the base metals. The effects of bonding time on microstructure evolution and mechanical properties of the TLP joints were investigated.Owing to the complete isothermal solidification of the joints bonded for 30 min 120 min at 1100°C,no athermally solidified zones(ASZs) formed by eutectic phases were observed in the welded zone. Thus the TLP joints were only composed by the isothermally solidified zone(ISZ) and two diffusion affected zone(DAZ) adjacent to the dissimilar base metals and the negative effect of the ASZ on joint properties can be avoided. In addition, the increase of the bonding time can also make the Ti B2 borides precipitated in the DAZ near HEA and the brittle borides or carbides in the DAZ near IN718 alloy decrease and reduce the possibility of the stress concentration happened in the joints under loading. Therefore, the highest shear strength(632.1 MPa) of the TLP joints was obtained at 1100°C for 120 min, which was higher than that of the joint bonded for 30 min, 404.2 MPa. Furthermore, the extension of the bonding time made the fracture mechanism of the joint be transformed from the intergranular fracture to the transgranular fracture. However, as the brittle borides in the DAZ near IN718 can not be eliminated completely and refining of grains also happened in such region, all the TLP joints fractured inner the DAZ near IN718 alloy.     

Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions

Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650 °C. The main load cycle for such components is typically defined by the start-up and shut-down of the engine. It generally includes hold times at high temperatures, which have been found to have a potential for greatly increasing the fatigue crack growth rate with respect to the number of load cycles. However, these effects may be totally or partly cancelled by other load features, such as overloads or blocks of continuous cyclic loading, and the actual crack propagation rate will therefore depend on the totality of features encompassed by the load cycle. It has previously been shown that the increased crack growth rate found in hold time experiments can be associated with a damage evolution, where the latter is not only responsible for the rapid intergranular crack propagation during the actual hold times, but also for the increased crack growth during the load reversals. In this paper, modelling of the hold time fatigue crack growth behaviour of Inconel 718 has been carried out, using the concept of a damaged zone as the basis for the treatment. With this conceptually simple and partly novel approach, it is shown that good agreement with experimental results can be found.     

薄壁GH169合金端接接头焊接缺陷研究

研究了壁厚0．15mmGH169合金端接接头的焊接缺陷产生机理，认为焊接缺陷是焊接过程中焊缝金属被氧化造成的，由于金属被氧化导致了焊缝熔合不良。采用端接接头反面成型及加强背面保护等工艺措施可以极大地降低焊缝熔合不良的敏感性。     

Thermal conductivity of Inconel 718 and 304 stainless steel

The results of thermal conductivity measurements on Inconel 718 and 304 stainless steel by the comparative and flash diffusivity techniques are reported for the temperature range 0–700°C. For 304 stainless steel, excellent agreement with published data is found for the specific heat, thermal diffusivity, and thermal conductivity. In the case of Inconel 718, the measurements show that the conductivity depends critically on the sample thermal history and the metallurgical condition of the alloy. Measurements on a solution-treated sample indicated a conductivity function close to that reported previously, while precipitated samples showed a higher conductivity, similar to the conductivityvs-temperature function used for reduction of comparative thermal conductivity data with Inconel 718 references. These results indicate that Inconel 718 is not a suitable reference for high-accuracy comparative thermal conductivity measurements unless its thermal history and associated conductivity function are known.     

Effect of rhenium on solidification of Inconel 718 alloy

Abstract

The effect of rhenium (Re) on the solidification of standard Inconel 718 (St-In718) has been investigated by using experimental alloys containing 2·4, 3·5, and 6·0%Re. Rhenium is one of the most powerful refractory elements that improve the high temperature mechanical properties of Ni base superalloys. Results indicate that solidification starts with precipitation of primary γ phase, which is followed by (γ+ NbC) eutectic and (γ+ Ni₂Nb)eutectic. The solidification temperature of the St-In718 is increased by 30 K with the addition of 6%Re. Moreover, the volume fraction of the primary γ is increased, while the volume fraction of eutectic (γ+ NbC) and (γ+ Ni₂Nb) are decreased by the addition of Re. Also, increasing Re content enlarges the secondary dendrite arm spacing (SDAS). Finally, the effects of Re on the partition coefficients k of alloying elements to primary γ and to eutectic γ+ NbC were evaluated and Re was found to segregate preferentially to the primary γ.     

热处理工艺对Inconel718合金组织、力学性能及耐蚀性能的影响

对高含H2S/CO2酸性油气田封隔器材料-Inconel718镍基合金进行固溶处理和时效处理,研究不同热处理工艺条件下合金的组织、力学性能、耐蚀性能之间的关系.结果表明:随着固溶温度的升高,δ相不断溶入基体.材料经时效处理后析出第二相γ相,硬度和强度明显高于固溶处理的样品,1000℃固溶+720℃×8h 50℃/h→620℃×8h时效处理的样品硬度和强度达到最大值.高温高压H2S/CO2介质中挂片实验的结果表明,不同熟处理的Inconel718合金均具有良好的耐腐蚀性能,经固溶处理的材料耐腐蚀性略优于经固溶+时效处理的材料.高温高压H2S/CO2应力腐蚀实验的结果表明,Inconel718没     

热处理工艺对Inconel718合金多层夹芯板结构的微观组织与力学性能的影响

采用LBW+SPF组合技术制造Inconel718合金多层夹芯板结构.为了增强多层夹芯板结构使用时的安全性,研究其热处理技术.结果表明:Inconel718合金在焊接过程产生了Nb含量较高的Laves沉淀相;超塑成形后焊缝中的Nb元素的偏析问题得了缓解;经980℃固溶30min处理后,焊缝中的δ相完全回溶母体γ相,焊缝...     

Al、Ti含量对Inconel 718合金铸造组织和凝固行为的影响

采用差热分析(DSC)、光学显微镜、扫描电镜(SEM)、电子能谱(EDS)和X射线衍射分析(XRD)测试手段,结合JMatPro模拟计算分析研究了Al、Ti含量对Inconel 718铸锭组织和凝固行为的影响。结果表明,不同Al、Ti含量Inconel 718合金的铸态组织均呈典型树枝状结构,枝晶间析出相主要由(γ+Laves)共晶相和少量M(C,N)构成。随着Al/Ti原子比的升高,铸态组织中黑色枝晶间区域数量明显增加,Laves相形态由块状向共晶筛网状转变,同时Laves相周围析出的针状一次δ相和枝晶间γ″相数量减少;Inconel 718合金的凝固次序没有改变,合金的液相线由1363.5℃(合金Ⅰ)降低至1358.7℃(合金Ⅲ),而Laves相初熔温度和MC相固溶温度变化不大(不超过1.4℃);Nb,Mo,Ti元素在枝晶间的偏析程度随着Al/Ti原子比的升高而减轻。热力学计算结果显示,增加Al/Ti原子比可以提高γ′相数量,降低γ″相的数量。改型合金的硬度值随着Al/Ti原子比的提高而增加,当Al/Ti=4.32且(Al+Ti)=3.1at.%时,硬度值达到了345HV,比Inconel 718母合金硬度提高了23.7%。