磷对IN718合金蠕变性能的影响

研究了磷对ＩＮ７１８合金蠕变性能的影响,结果表明,磷显著提高蠕湾抗力。磷对应力指数没有明显的影响,掺杂０．０２％磷使表观蠕变激活能由６７８．５ｋＪ／ｍｉｌ提高至７４６．１ｋＪ／ｍｏｌ。磷的有益作用可能是抑制晶界扩散实现的。     

Role of P, S and B on Creep Behavior of Alloy 718

The doping of phosphorus, sulfur and boron in IN718 superalloy can remarkably influence the creep behavior. The modifications of the minor elements seem not to vary the stress exponent and the influences primarily concentrate on the effective diffusion coefficient. A pronounced beneficial interaction between P and B and a weaker detrimental interaction between P and S have been obtained. The preexponential frequency constant is proved to be strongly related with the creep activation energy because of the so-called compensation effectl The compensation temperature has been determined to be about 1080 K, which corresponds to the transformation temperature from rapidly coarsened γ“ phase to δ phase. It has been proposed that trace elements can influence the effective diffusion coefficient individually or cooperatively, which in turn either retard or speed the creep process.     

复合添加磷和硼对Inconel718合金的影响

研究了磷和硼对Ｉｎｃｏｎｅｌ７８１合金持和蠕变性能的影响,结果表明,单独添加０．０２％磷对性能明显有益,单独提高硼含量在０．０１％对性能有害,复合添加磷和硼的效果最佳,磷和硼复合作用显著有益的原国有磷与硼之间存在强烈有益的交互作用,其机制可能与磷,硼和其本原子晶界集团扩散有关。     

Effects of alloy 718 microstructure on hydrogen embrittlement susceptibility for oil and gas environments

The effects of alloy 718 microstructure on hydrogen embrittlement susceptibility and tensile fracture mode were assessed through slow strain rate tensile testing and fracture surface analysis. Alloy 718 was annealed and aged to produce microstructures with variations in grain size and amount of grain boundary precipitates. Furthermore, the different ageing conditions likely resulted in differences in volume fractions and sizes of γ′ and γ′′ precipitates. The extent of grain boundary precipitation had the strongest effect on hydrogen embrittlement susceptibility, while grain size did not have any significant effect. Hydrogen embrittlement susceptibility was also correlated with differences in strength level, which was primarily controlled by the γ′ and γ′′ precipitate populations.     

The simultaneous improvements of strength and ductility in additive manufactured Ni-based superalloy via controlling cellular subgrain microstructure

Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 min.With the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain structure.Moreover,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain boundaries.It was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic flow.Hence,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 alloy.These results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.     

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℃/h620℃×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,不同热处理的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没有发生应力腐蚀开裂迹象。综合考虑耐蚀性能和力学性能,确定Inconel718合金的最佳热处理工艺为:1000℃固溶1h+720℃×8h→50℃/h620℃×8h时效。     

一种GH4169镍基合金的组织结构与蠕变性能

通过对一种等温锻造GH4169镍基合金进行直接时效处理,蠕变性能测试及组织形貌观察,研究了该合金的组织结构与蠕变行为。结果表明,GH4169合金的组织结构由γ基体,γ′相、γ″相和δ相组成,且各相之间保持共格界面。测定出合金在660℃/700MPa条件下的蠕变寿命为123h。合金在680℃/700MPa的蠕变寿命为39h,在实验温度和应力范围内,计算出直接时效合金的蠕变激活能为588.0kJ/mol。合金在蠕变期间的变形机制是位错滑移和孪晶变形,其中,沿晶界析出的粒状碳化物,可抑制晶界滑移,是使合金具有较好蠕变抗力的主要原因。随蠕变进行,开动的滑移系中位错运动至晶界受阻,并塞积于该区域引起应力集中,当应力集中值大于晶界的结合强度时,可促使其在与应力轴垂直的晶界处发生裂纹的萌生与扩展,直至断裂,是合金在蠕变期间的断裂机制。     

Investigation and improvement on structural stability and stress rupture properties of a Ni–Fe based alloy

The structural stability and stress rupture properties of a Ni–Fe based alloy, considered as boiler materials in 700 °C advanced ultra-supercritical (A-USC) coal-fired power plants, was studied. Investigation on the structural stability of the existing alloy GH984 shows that the most important changes in the alloys are γʹ coarsening, the γʹ to η transformation and the coarsening and agglomeration of grain boundary M₂₃C₆ during thermal exposure. The stress rupture strength was found to be slightly lower than the requirement of 700 °C A-USC. The fracture mode of creep tested specimens was intergranular fracture. Detailed analysis revealed that η phase precipitation is sensitive to Ti/Al ratio and can be suppressed by decreasing Ti/Al ratio. The coarsening behavior of γʹ phase is related to Fe content. Adding B and P was suggested to stabilize M₂₃C₆ and increase grain boundary strength. Based on the research presented and analysis of the data, a modified alloy was developed through changes in composition. For the modified alloy, η phase is not observed and M₂₃C₆ is still blocky and discretely distributes along grain boundary after thermal exposure at 700 °C for 20,000 h. Moreover, the creep strength is comparable to the levels of Ni-based candidate alloys for 700 °C A-USC.     

Microstructure and mechanical properties of an inertia friction welded INCOLOY alloy 909 – INCONEL alloy 718 joint for rotating applications

Abstract

Inertia welding is a common practice to join axially symmetrical parts for aero-engine applications. The shaft for a new advanced high-pressure compressor will be produced by joining the high strength superalloys INCOLOY® alloy 909 (Incoloy909) and INCONEL® alloy 718 (IN718). IN718 is the work-horse nickel-iron-chromium alloy for a variety of parts for aero-engine applications due to a good combination of relevant mechanical properties, good corrosion resistance and easy fabricability. Incoloy909 is a nickel-iron-cobalt alloy used in aero-engines due to an interesting combination of a nearly constant low coefficient of thermal expansion combined with a constant modulus of elasticity and high strength over a wide range of temperatures. Both alloys are strengthened by precipitationhardening through additions of niobium and titanium. Ring shaped specimens of fully heat-treated Incoloy909 and IN718 are joined by inertia welding. The microstructure in the welded zone is investigated by optical microscopy and transmission electron microscopy with the focus on the Incoloy909 side. Post-weld heat-treatments (PWHT) are evaluated by microstructural investigations and by hardness measurements. The chosen PWHT is characterized by its tensile, creep and load controlled fatigue properties. The results of the mechanical tests are described in terms of the microstructural changes observed in the welded zone.     

固溶处理的热连轧GH4169合金的组织与蠕变特征

通过对热连轧GH4169合金进行固溶和时效处理、组织形貌观察和蠕变性能测试,研究了固溶和时效处理合金的组织结构和蠕变特征。结果表明,经固溶和时效处理合金由较大尺寸晶粒组成,并具有明显的孪晶特征,且细小γ′、γ″相在晶内弥散析出,可提高合金的蠕变抗力;在实验应力和温度范围内,测得该合金的蠕变激活能为537.8kJ/mol,且对施加应力和温度具有敏感性;在蠕变期间,热连轧GH4169合金的变形特征是位错的单双取向滑移和孪晶变形,随着蠕变进行,裂纹沿晶界萌生和扩展到发生沿晶断裂是该合金的蠕变断裂机制。     

The effect of Re and Ru on γ/γ′ microstructure, γ-solid solution strengthening and creep strength in nickel-base superalloys

A new in-house designed series of Ni based superalloys with stepwise increased Re and Ru additions has been investigated, to systematically determine the influence of Re and Ru on γ/γ′-microstructure and high temperature creep properties. Improved creep resistance and thus also a higher alloy temperature capability of up to 87 K/at.% was found for additions of Re. Additions of Ru revealed a lower temperature capability improvement of up to 38 K/at.% for low Re-containing second generation alloys. However, in third and fourth generation alloys with higher Re-contents, no significant influence of Ru on creep rupture strength was observed. The creep properties are discussed with respect to the γ′-volume fraction, γ′-size and γ′-coarsening rate, as well as the γ/γ′-lattice misfit and the γ/γ′ partitioning coefficient of the different Re and Ru containing alloys. The presented data shows, that these microstructure parameters are strongly influenced by additions of Re, but only marginally by additions of Ru. A further influence on creep rupture strength is given by the solid solution hardening of the γ-matrix, which is discussed based on solid solution hardener concentrations either experimentally derived or calculated from ThermoCalc data.     

Effect of processing conditions and heat treatments on mechanical properties of single-crystal superalloy CMSX-2

Abstract

It is shown that the mechanical properties of single-crystal superalloys can be optimized through appropriate solidification conditions and heat treatments. A comparison of the creep behaviour of low- and high-gradient processed single crystals of CMSX-2 alloy shows that minimizing porosity improves the creep strength at intermediate temperatures. The optimum creep resistance is achieved by aligned γ′-precipitates, about 0·5 μm in size. It is shown that in high-cycle fatigue the solidification conditions have a dramatic effect on the fatigue strength. The improvement in fatigue behaviour is attributed to the extremely low density and small size of pores achieved by using a very high-gradient process. The strain–controlled low–cycle fatigue properties of CMSX-2 at intermediate temperatures are also greatly improved by using the high-gradient process. Elimination of porosity in ‘industrial’ single crystals by hot isostatic pressing restores their creep and especially their fatigue performance to the level of the high-gradient solidified material.

MST/224     

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.     

一种含4.5%Re/3.0%Ru的单晶镍基合金的高温蠕变行为

通过对含4.5%Re/3.0%Ru单晶镍基合金进行高温蠕变性能测试,并采用扫描电镜(SEM)、透射电镜(TEM)对不同蠕变期间的试样进行组织形貌观察,研究了该合金的高温蠕变行为。结果表明,本实验所选用的单晶合金在高温蠕变期间具有良好的蠕变抗力,在1040℃/160MPa的蠕变寿命达到725h。高温蠕变初期,合金中γ′相沿垂直于应力轴方向转变成筏状结构,其稳态蠕变期间的变形机制是位错在基体中滑移和攀移越过筏状γ′相。高温蠕变后期,合金的变形机制是位错在基体中滑移和剪切筏状γ′相。位错的交替滑移使筏形γ′相扭曲,并在γ/γ′两相界面发生裂纹的萌生与扩展直至断裂,是合金在高温蠕变后期的断裂机制。     

微量元素P、B对GH4169合金组织与蠕变性能的影响

通过对等温锻造合金进行直接时效、蠕变性能测试和组织形貌观察,研究了微量元素P、B对GH4169合金组织结构及蠕变行为的影响.结果表明:添加微量P、B可促使粒状δ相在合金中析出,且沿晶界不连续析出的δ相可抑制晶界滑移,提高合金的蠕变抗力;在试验温度和应力范围内,测定出GH4169G合金具有较高的蠕变激活能Q=594.7 ...     

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.     

Influence of surface modification and long-term exposure on mechanical creep properties of γ-TiAl G4

Abstract

An investigation of the corrosion processes were performed for coated and uncoated γ-TiAl G4, an alloy designed to work in the temperature range 750 – 800°C, where oxidation and corrosion phenomena occur. An aluminising pack cementation treatment was used to improve the oxidation resistance of this γ-TiAl G4 alloy. Cyclic corrosion tests were performed at 800°C in air for up to 800 1-hour cycles with a Na₂SO₄/NaCl mixture. The influence of both aluminisation and the corrosion phenomena on the creep behaviour was investigated. The cyclic corrosion resistance of the coated γ- TiAl G4 was shown to be improved by aluminising. The pack cementation treatment had no detrimental effect on the creep behaviour. Moreover, neither is creep affected by the corrosion of coated specimens. As corroded uncoated specimen exhibited good creep behaviour, it can be concluded that this alloy is suitable, even without coating, for turbine applications in hot corrosion atmospheres at least up to 800°C.     

The creep fracture characteristics of nickel-base superalloy sheet samples

Center notched sheet samples of INCONEL alloy 718 with thicknesses from 0.5 to 3.1 mm were creep tested in the 595–704°C temperature range. No significant effect of thickness was observed in terms of failure times, minimum stress intensities needed to initiate crack growth, or fracture mode. Flat, intergranular fractures with no shear lips and no detectable change in thickness were observed in all cases. The results indicate that with materials such as nickel-base superalloys tested at half their melting point, creep fractures can be analyzed by fracture mechanics techniques.     

The effect of hold-time on fatigue crack growth behaviors of WASPALOY alloy at elevated temperature

The effect of hold-time on fatigue crack growth behaviors of WASPALOY alloy was investigated. It was found that the role of hold-time depends on the competition between the harmful environmental effect and the beneficial effect of creep. If temperature is not higher than 705 °C, fatigue crack growth rate of WASPALOY alloy increases with hold-time. On the contrary, hold-time plays a beneficial role on steady state fatigue crack growth of WASPALOY alloy at 760 °C and lower stress intensity factor. The beneficial effect of hold-time was attributed to the creep caused stress relaxation during the hold-time. However, accumulated creep damages cause to cavity nucleation and growth at the grain boundaries, and then accelerate fatigue crack growth. Hold-time plays a harmful role during the final stage of fatigue crack growth.     

Investigation of the abnormal effects of phosphorus on mechanical properties of INCONEL718 superalloy

The effects of phosphorus on mechanical properties of the world’s most widely used superalloy INCONEL718 was examined. The results indicate that P has little effect on the tensile properties of INCONEL718 at room temperature, 500 or 650°C, but it increases stress rupture life and ductility. Phosphorus also improves the creep property and crack propagation resistance of INCONEL718. Further microstructure analysis by means of optical, SEM and TEM does not reveal the obvious effect of P on grain size and precipitation of INCONEL718. Some theoretical discussions were held aiming at further understanding the role of P in INCONEL718. It was suggested that the interaction of P–GB–M (metal element) complex might be responsible for this.