Effect of two-step solid solution on microstructure andδphase precipitation of Inconel 718 alloy

Inconel 718 is the most popular nickel-based superalloy and is extensively used in aerospace,automotive,and energy indus-tries owing to its extraordinary thermomechanical properties.The effects of different two-step solid solution treatments on microstructure andδphase precipitation of Inconel 718 alloy were studied,and the transformation mechanism fromγ″metastable phase toδphase was clarified.The precipitates were statistically analyzed by X-ray diffractometry.The results show that theδphase content firstly increased,and then decreased with the temperature of the second-step solid solution.The changes in microstructure andδphase were studied by scanning electron microscopy and transmission electron microscopy.An intragranularδphase formed in Inconel 718 alloy at the second-[100]_(δ)[011]γ step solid solution temperature of 925℃,and its orientation relationship withγmatrix was determined as//and(010)_(δ)//(111)γ.Furthermore,the Vickers hardness of different heat treatment samples was measured,and the sample treated by second-step solid solution at 1010℃ reached the maximum hardness of HV 446.84.

High temperature tensile properties of laser butt-welded plate of Inconel 718 superalloy with ultra-fine grains

For successfully forming multi-sheet cylinder sandwich structure of Inconel 718 superalloy, high temperature tensile properties of laser butt-welded plate of Inconel 718 superalloy were studied. The experiment results show that tensile direction has great effect on elongation of the laser butt-welded plate. Under conditions of transverse direction tension, the maximum elongation reaches 458.56% at 950 °C with strain rate of 3.1-10-4 s-1, in which the strain rate sensitivity value m is 0.352 and the welding seam is not deformed. Under conditions of longitudinal direction tension, the maximum elongation is 178.96% at 965 °C with strain rate of 6.2-10-4 s-1, in which m-value is 0.261, and the welding seam contributes to the deformation with the matrix. The microstructure in as-welded fusion zone is constituted of austenite dendrites and Laves phase precipitated in interdendrites. After longitudinal direction tension, a mixed microstructure with dendrite and equiaxed crystal appears in the welding seam due to dynamic recrystallization. After high temperature deforming, many δ-phase grains are transformed from Laves phase grains but a small part of residual Laves phase grains still exist in the welding seam. The deformation result of multi-sheet cylinder sandwich structure verifies that high temperature plasticity of the laser butt-welded plate can meet the requirement of superplastic forming.

Effects of P and B addition on as-cast microstructure and homogenization parameter of Inconel 718 alloy

The effects of phosphorus and boron addition on the as-cast microstructure and homogenization parameters of Inconel 718 were studied. The results indicate that the addition of phosphorus and boron promotes the formation of blocky Laves phase. Due to the strong segregation behavior of boron in the final residual liquid, a low melting B-bearing phase enriched in Nb, Mo and Cr is observed. According to the differential scanning calorimeter results and electron probe micro-analysis characterization, the solidification sequence of Inconel 718 with phosphorus and boron addition in best combination is determined as L→L＋γ→L＋γ＋MC→L＋γ＋MC＋Laves→γ＋MC＋Laves＋MC＋Laves＋B-bearing phase. Accordingly, the homogenization temperature is recommended to be adjusted at least 40°C lower than that of standard Inconel 718 due to the existence of low melting B-bearing phase.

新型热处理方法制备超高强度Inconel 718合金

为改善Inconel718合金的组织并优化性能,提出一种980℃,1 min高温超短退火和随后的双时效相结合的新型热处理方法。结果表明,超短退火处理产生了部分再结晶组织,KAM图表明即使在变形晶粒中也形成了再结晶晶核。因此,高温超短退火克服了再结晶势垒,使得后续的再结晶过程可以在较低温度的时效处理过程中完成,从而获得了均匀细化的组织(~3.59μm)。980-1min-aged样品具有优异的拉伸性能,室温极限强度和总伸长率分别为1600 MPa和19%。650℃热拉伸条件下的极限强度和伸长率分别约为1350 MPa和26%。因此,高温超短退火能有效提高Inconel718合金的性能。

超声振动方向对激光定向能沉积Inconel 718性能影响研究

目的面向激光定向能沉积表面改性及再制造发展需求,揭示超声振动方向对激光定向能沉积Inconel 718零件的影响机制,为超声辅助激光定向能沉积高质量成形提供参考。方法开展多方向超声振动辅助激光定向能沉积Inconel 718零件试验,结合原位熔池监测技术,研究沉积方向、搭接方向和扫描方向超声振动对熔池流动行为、微观结构和力学性能的影响。结果不同方向超声振动显著影响了熔池的动态流动行为,其中搭接方向超声振动使熔池润湿面积提高了86.4%,并且形状更为规则,拖尾现象得到改善。微观组织细化方面,扫描方向振动效果最佳,晶体直径细化了46.9%,水平方向的晶体等轴晶转变优于沉积方向,而在沉积方向振动下,Laves相点球化和减少最为明显。相较于对照组的显微硬度210.4HV0.2,添加沉积、搭接和扫描方向超声振动后分别提高到了232.5HV0.2、230.9HV0.2和233.9HV0.2,变化趋势与晶体直径变化趋势基本一致。水平方向超声振动影响下,特别是扫描方向的超声振动在提高材料强度的同时,还在一定程度上保持了材料的延展性;在搭接方向上,超声振动辅助显示出较好的各向异性消除能力,获得了优异的硬度、强度和塑性匹配。结论不同方向超声振动,通过不同方向的惯性力和热流改善了熔池的动态流动性,其中搭接方向超声振动在扩大熔池润湿面积和改善熔池动态形状方面具有优异的综合能力。由于超声强度方向性传播衰减和引起不同的声压梯度,微观组织细化和Laves相的细小点球状消减分别在扫描方向和沉积方向上最为显著,这些变化引起了显微硬度和拉伸性能的相关性提升。超声振动还均衡了材料的力学性能,提高了抗拉强度、屈服强度和延展性,尤其在搭接方向上,显示出较好的各向异性消除能力。可根据具体需求目标,选用相应的超声振动方向或者复合使用,以获得优异的Inconel 718零件熔池流动、微观形貌和力学性能匹配。

不同温度对Inconel 718合金微动磨损行为的影响研究

Inconel 718高温合金在航空航天、燃气轮机和核电能源等领域有着广泛运用,为评价其在实际服役工况下的微动磨损性能,采用自主研制的高温微动磨损试验机开展切向微动磨损试验,研究并揭示不同环境温度下材料的微动运行行为、材料损伤响应和磨损机理。结果表明:环境温度对Inconel 718合金微动磨损区域特性及其损伤机理有较大影响。在不同位移幅值下,随着环境温度的升高,微动磨损均向完全滑移的方向转变。微动部分滑移区的磨损机制主要为黏着磨损,且随着温度的升高黏着加剧并在600℃转变为混合区。对于微动混合区或滑移区,其损伤机制由较低温度(室温和200℃)下的疲劳磨损主导转变为较高温度(400和600℃)下的黏着磨损和磨粒磨损主导,同时氧化磨损加剧。此外,环境温度的升高将不同程度加剧材料的微动损伤,其磨损率约为室温工况下的1.76~18.60倍,不同位移幅值下所导致最大磨损率的温度阈值亦不尽相同。研究结果为不同服役温度下Inconel 718合金的抗微动损伤防护提供了理论数据和应用参考。

激光选区熔化成形Inconel 718合金的热处理研究现状

论述了激光选区熔化(SLM)成形Inconel 718合金的成形原理,介绍了SLM成形Inconel 718合金的残余应力、Nb元素偏析等常见缺陷的形成机理,及热等静压、热处理等工艺对其控制的研究现状。重点归纳了固溶+双时效、均匀化+固溶+双时效的热处理工艺对SLM成形Inconel 718合金的缺陷、组织、力学性能、耐腐蚀性能的影响,并对SLM成形Inconel 718合金的热处理工艺、热处理工艺参数、耐腐蚀性等方面的研究进行了展望。

晶界工程调控Inconel 718合金晶界处δ相的析出

目的针对镍基Inconel 718合金在高温服役时强化相转化为晶界δ脆性相从而降低服役性能的问题,通过热机械处理工艺调整晶界脆性相的析出和分布,以提升合金在高温环境下的耐用性和服役性能。方法通过晶界工程(GBE)技术提高样品中低Σ重位点阵(CSL)晶界的比例,调整晶界处δ相的分布规律。利用扫描电子显微镜(SEM)和电子背散射衍射(EBSD)技术分析样品的显微组织演化规律。结果GBE处理使样品中低ΣCSL晶界比例较固溶态的54.34%提高至81.43%,显著优化了晶界特征分布。通过SEM分析了δ相在不同类型晶界处的分布特征:较小的δ相沿平行于Σ3c晶界两侧分布、沿垂直于Σ3i晶界两侧分布,沿Σ9晶界一侧呈针状分布;较大的δ相沿Σ27晶界一侧呈短棒状或层片状分布,在随机晶界处杂乱分布。GBE处理后合金的塑性显著提升,其延伸率从固溶态的21.1%提升至GBE态的26.6%。结论通过晶界工程技术提升了镍基合金中低ΣCSL晶界的比例,调整了晶界处δ相的析出规律,优化了Inconel 718合金的微观结构,从而有望提高其在高温环境下的服役性能。

Inconel 718合金粉末热等静压成形及其影响因素

采用无坩埚感应熔炼超声气体雾化法(Electrode induction melting gas atomization,EIGA)和真空惰性气体雾化法(Vacuum induction melting gas atomization,VIGA)制备Inconel 718预合金粉末,随后采用热等静压工艺制备Inconel 718合金。研究制粉工艺、粉末粒度及包套结构对Inconel 718合金显微组织和力学性能的影响。研究结果表明,EIGA粉末具有更好的球形度,成形合金力学性能优于VIGA粉末;综合考虑力学性能、得粉率等因素,选择15~106μm粒度范围的粉末作为热等静压用粉末;包套壁厚的增加对作用在粉末上的有效应力产生屏蔽作用,空腔体积变化对致密化过程影响较小;粉末填充过程的长时间振动会导致粉末发生粒度偏析,需要控制粉末填充过程的振动频率和振动时间。

Microstructural characterization of Inconel 718 alloy after pulsed laser surface treatment at different powers

An annealed Inconel 718 alloy was surface-treated by pulsed laser at three different powers（100, 50 and 25 W）. Microstructural changes induced by the laser treatments were characterized by use of electron backscatter diffraction and electron channeling contrast imaging techniques. Results show that both annealing twins and strengthening precipitates profusely existing in the as-received specimen are dissolved at elevated temperatures during the laser irradiation. Meanwhile, in the melting zone（MZ）, densities of low angle boundaries（LABs） are greatly increased with a large number of Laves phases preferentially distributed along such LABs. For different specimens, widths and depths of their MZs are found to be gradually reduced with decreasing the laser powers. Orientation analyses reveal that the columnar grains in the MZ of the 100 W specimen could inherit orientations existing in the matrix while lower laser powers promote the formation of more nuclei with scattered orientations to grow to be granular grains in the MZ. Hardness tests reveal that the MZs of all laser-treated specimens are softer than the matrix probably due to both precipitate dissolution and grain coarsening.

选区激光熔化制造Inconel 718合金的氢脆行为

后热处理可以有效改善选区激光熔化(SLM)制造的Inconel 718合金的强塑性匹配,但其氢脆断裂行为目前还尚不明确。为此,对SLM制造的Inconel 718合金进行了高温固溶+单级时效热处理,并采用扫描电镜的电子背散射衍射(EBSD)和背散射电子(BSE)成像对其显微组织进行了分析,通过预充氢前后的拉伸实验对合金的氢脆敏感性进行了评估,并采用EBSD和BSE对拉伸试样的断口表面形貌和裂纹扩展路径进行了分析。结果表明:热处理后,SLM制造的Inconel 718合金的抗拉强度可达1341 MPa,并保持24.5%的断后伸长率,但也具有较高的氢脆敏感性,充氢96 h后合金的强度损伤和塑性损失分别达到18.5%和52.3%。拉伸过程中晶界上由于δ相以及滑移带引起的应力集中促进了晶界上氢的局部富集,从而诱发沿晶氢脆裂纹的萌生及扩展。

Influence of magnetically constricted arc traverse speed (MCATS) on tensile properties and microstructural characteristics of welded Inconel 718 alloy sheets

The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.

Introduction of a New Method for Regulating Laves Phases in Inconel 718 Superalloy during a Laser-Repairing Process

The morphology,size,and distribution of Laves phases have important influences on the mechanical properties of laser-repaired Inconel 718(IN718)superalloy.Due to the deterioration of the substrate zone,the Laves phase in the laser cladding zone of IN718 superalloy cannot be optimized by a hightemperature solution treatment.In this study,an in situ laser heat-treatment method was proposed to regulate the morphology and size of the Laves phase in the laser cladding zone of IN718 superalloy without impacting the substrate zone.In the in situ laser heat-treatment process,a laser was used to heat previously deposited layers with optimized manufacturing parameters.A thermocouple and an infrared camera were used to analyze thermal cycles and real-time temperature fields,respectively.Microstructures and micro-segregations were observed by optical microscopy,scanning electron microscopy,and electron probe microanalysis.It was found that the in situ laser heat treatment effectively changed the morphology and size of the Laves phase,which was transformed from a continuous striplike shape to a discrete granular shape.The effective temperature range and duration were the two main factors influencing the Laves phase during the in situ laser heat-treatment process.The effective temperature range was determined by the laser linear energy density,and the peak temperature increased with the increase of the linear energy density.In addition,the temperature amplitude could be reduced by simultaneously increasing the laser power and the scanning velocity.Finally,a flow diagram was developed based on the in situ laser heat-treatment process,and the deposition of a single-walled sample with fine and granular Laves phases was detected.

KINETICS OF δ PHASE PRECIPITATION IN COLD ROLLED INCONEL 718 ALLOY

The volume fraction of δ phase in cold rolled Inconel 718 alloy aged at 910℃ for different times is measured by X ray diffraction techniques, and the influence of cold rolling on the kinetics of δ phase precipitation is investigated. It has been found that the relation between the volume fraction of δ phase and aging time follows the Avrami equation. With increasing cold rolling reduction, the value of n decreases and the value of a increases.

Forging Optimization and Microstructural Simulation of an Inconel 718 Alloy Used in Turbine Discs

Simulating microstructure evolution during forging of superalloys is of great interest for manufacturer of critical components, particularly in aerospace applications. In this research, a phenomenological approach using a mathematical model was employed into a commercial finite element code, i.e. Abaqus, to study recrystallization and grain growth of IN718 supperalloys during forging. Model validation was performed by compression testing. Results show that the measured recrystallized volume fraction and the grain size were in good agreement with the model predictions. Subsequently, the model was used to simulate the evolution of microstructure in a turbine disc. Finally, a technique based on Tagushi method was used to determine the influence of forging parameters such as forging temperature, ingot height to diameter ratio, and top die velocity on the resultant microstructure. Uniform and refined microstructure of final forging was considered into the objective function. Optimum as well as the poorest parameters combination was attained through analysis. As well the contribution of each parameter on microstructure development was determined through variance analysis.

直接时效工艺对INCONEL718合金组织的影响

采用XRD定量相分析法及SEM技术 ,研究了不同时效温度下Inconel718合金中析出相含量的变化和组织结构特点。确定了最佳时效工艺为 72 0℃× 8h +6 2 0℃× 8h。

Inconel718合金扩散连接接头的组织与性能研究

对细晶Inconel718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=1050℃,连接压力P=20MPa,连接时间t=45min,选用Ni箔作为中间层,厚度为25μm.

热处理对Inconel718合金组织及力学性能的影响

针对Inconel 718合金的不同用途,分析研究了4种常用热处理工艺对Inconel 718合金组织和力学性能的影响。结果表明:固溶温度超过1020℃时,奥氏体晶粒显著长大。合金中主要析出相有MC、δ、γ'和γ″相。δ相沿晶界分布,1025℃固溶时呈颗粒状少量析出;950℃固溶时呈块状大量析出;直接时效时呈网状不连续分布。同时,δ相对合金的晶粒度影响较大,且其析出数量和形态决定了合金的韧塑性,γ″、γ'相的析出量和尺寸与晶粒尺寸决定了合金的强度变化。

热处理对Inconel718合金组织与性能影响的研究进展

综述了热处理对Inconel718合金的组织、力学性能、氢脆特性及耐蚀性能的影响;并展望了Inconel718合金在高温高压湿H2S腐蚀环境下的应用前景。

镍基合金Inconel 718与抗硫油套管钢在模拟气田地层水中的电偶腐蚀

采用电化学方法研究了在模拟罗家寨气田地层水中镍基合金Inconel 718和抗硫管材VM80 SS之间的电偶腐蚀特征和电偶效应.结果表明,Inconel 718和VM80 SS的自腐蚀电位分别为-260 mV和-770 mV,当阴阳极面积比S=0.25,1,4,8时,电偶电位Eg处于-760 mV^-700 mV之间,随S增大,Eg正移,Ig/Aa的初始值、稳态值和平均值均增大;而Ig/Ac的初始值降低,稳态值变化不大.根据混合电位理论计算的VM80SS的电偶腐蚀效应γ随S增大而增大,γ=1.14~4.82.