Y合金化对电热丝用镍基高温合金显微组织与性能的影响

采用Y合金化的方法制备了电热丝用镍基高温合金,研究了Y含量对合金显微组织、高温力学性能和高温氧化性能的影响。结果表明,未添加Y的镍基高温合金的平均晶粒尺寸约为113μm,且在合金基体组织中出现较多孪晶,在晶界处存在不连续分布的链状析出物;当向镍基高温合金中添加Y后,晶粒尺寸有所减小;随着镍基高温合金中Y含量的增加,抗拉强度、屈服强度和显微硬度呈现先上升而后降低的趋势,且Y合金化的镍基高温合金的强度和显微硬度都要高于未添加Y的合金,而断后伸长率和断面收缩率相比未添加Y的镍基合金变化幅度不大;添加Y的镍基高温合金的氧化质量增加和氧化膜脱落要相对未添加Y的镍基高温合金较轻。     

微观组织结构对镍基825合金力学性能和硫化物应力腐蚀开裂的影响

目的 揭示微观组织结构对镍基825合金硫化物应力腐蚀开裂的影响规律及机理。方法 利用金相显微镜(OM)、扫描电子显微镜(SEM)和背散射电子衍射(EBSD)分析了2种镍基825合金的金相组织、夹杂物种类及等级、晶界类型以及残余应变和晶粒尺寸分布。通过显微维氏硬度计评价了合金的力学性能,同时采用氢微印、动态充氢慢应变速率拉伸试验和三点弯曲试验,评估了合金的氢脆倾向和硫化物应力腐蚀开裂敏感性。结果 2种镍基825合金的夹杂物均以B类和D类TiN为主。2种合金中B类夹杂物均以晶界分布为主,D类夹杂物在合金1#中集中分布,在合金2#中随机分布。合金1#中B类夹杂物等级为0.91,D类夹杂物等级为1.4,合金2#中2种夹杂物等级分别为0.54和1.33。氢微印试验发现氢在合金1#的晶内、晶界处均大面积存在,而在合金2#中则分布稀疏。EBSD发现2种合金均为等轴奥氏体,合金1#晶粒尺寸稍大,晶界以随机大角度晶界为主且存在较高的残余应变集中,而合金2#晶粒细小且尺寸分布更均匀,随机大角度晶界和低Σ界面为其主要晶界类型,残余应变分布均匀。合金1#的硬度为184.67HV,屈服强度为285.30 MPa,而合金2#的硬度和屈服强度分别为207.75HV和300.03 MPa。在动态充氢慢应变速率拉伸试验中,2种合金均出现了氢脆倾向,合金1#的断裂延伸率降低了2.6%,而合金2#只降低了1.6%。三点弯曲试验中合金1#表面发生严重均匀腐蚀,出现了以穿晶为主的宏观裂纹,裂纹萌生部位的基体元素显著降低,在其周围还发现了夹杂物及其脱落留下的微孔,而合金2#表面仍有金属光泽,只有微米级的裂纹萌生于应力集中处。结论 大量夹杂物的存在降低了合金1#的屈服强度并导致晶界残余应变集中,同时作为有效氢陷阱增加了镍基825合金硫化物应力腐蚀开裂的敏感性。此外,夹杂物与金属基体之间形成微电偶,促进周围金属阳极溶解,进一步增加了合金的开裂敏感性。     

精铸用镍铜合金熔炼工艺的改进

精密铸造镍铜合金M-35-1／Mone中，镍与铜的熔点相差较大，满足镍的熔炼要求时，铜在高温下熔炼时间太长，导致氧化严重，形成氧化铜夹杂存在于铸件晶体之间，使内部组织不致密，不能通过气压测试。经过改变加料顺序及脱氧方法，减轻了铜的氧化，铸件经外观及内在质量检查，完全符合要求，气压测试合格率达97％以上。     

多弧离子镀NiCrAlY涂层与搪瓷基复合涂层的抗热震行为对比研究

以K444镍基高温合金为基体,采用多弧离子镀法制备了NiCrAlY涂层、喷涂-烧结法制备了搪瓷基复合涂层,并对比研究了2种涂层的抗热震性能。热震实验高温段温度为900℃。高温段保温1.5h后经水或空气冷却为一个热震循环。结果表明,NiCrAlY涂层的抗热震性能较差。当冷却介质为水时,水淬热震30cyc后,涂层表面氧化膜开裂明显,且有个别裂纹已穿透氧化膜,扩展至涂层内部;而搪瓷基复合涂层的抗热震性能非常优异。热震后,涂层表面及内部均未发现裂纹,涂层和基体界面结合良好。经分析,其优良的抗热震性能源于:(1)搪瓷釉热膨胀系数与高温合金基体匹配度高;(2)纳米Ni和NiCrAlY金属颗粒的加入进一步增大涂层热膨胀系数的同时,还提高了搪瓷的韧塑性。     

单晶合金中夹杂物形状对蠕变行为的影响

通过对不同形状夹杂物缺陷的单晶镍基合金蠕变性能测试、组织形貌观察及采用有限元对近夹杂物区域的应力场进行分析,研究了不同形状夹杂物缺陷对单晶合金蠕变行为及组织演化的影响.结果表明:夹杂物缺陷可明显降低单晶镍基合金的塑性和蠕变寿命.在高温蠕变期间,近夹杂物区域的应力等值线具有圆弧形分布特征.蠕变期间,在夹杂物的两侧极点处具有最小应力值,而在夹杂物缺陷的上、下区域具有较大的应力值,随蠕变时间延长,应力值增大,促使裂纹在该处长大,并且裂纹将沿平行于应力轴方向扩展是降低合金蠕变寿命的主要原因.     

《中国表面工程》2010年第5期

高Al＋Ti含量镍基高温合金激光、微弧火花表面熔焊处理研究进展及解决熔焊裂纹的途径Al、Ti是镍基高温合金主要沉淀强化元素,随着Al＋Ti含量的增加,镍基高温合金γ-Ni,（Al,Ti）相体积百分数增加,高温强度增加,但是热裂纹敏感性也随之增加,如何利用熔焊工艺实现高Al＋Ti镍基高温合金材料的表面无损伤熔焊处理一直是高Al＋Ti镍基高温合金叶片与热端部件制造与再制造面临的难题。     

PREP工艺制造的镍基高温合金粉末中夹杂物

夹杂物是影响粉末冶金产品质量的主要因素之一。采用SEM、XRD、EPMA等手段通过对等离子旋转电极制粉工艺(PREP)制取的镍基高温合金粉末中夹杂物的形貌特征、化学组成的研究,将不同工序处理后粉末中的夹杂物进行分类,统计分析其存在形式、尺寸、数量及分布。结果表明:粉末中的夹杂物按产生机制和来源主要分为陶瓷、熔渣、有机物、粉末粘连夹杂物或升华物形成的异常颗粒。经过筛分和静电处理后,残留在成品粉末中的陶瓷占夹杂物总数量的7%,熔渣占53%,有机物占40%。筛分和静电分离去除各类夹杂物的能力主要与成品粉末的粒度和夹杂物的密度、介电常数及其尺寸、形态有关。     

金属铁熔融过程中镁脱氧产物的特性

在高温钼丝炉内向铁液中分别加入NiMg和SiMg合金进行脱氧,分析过程中溶解氧、全氧、残镁量及夹杂物随时间的变化,并与铝脱氧进行对比。结果表明:加入0.05%的SiMg合金处理后,铁液中溶解氧含量(质量分数)为1.5×10-6,全氧含量为1.9×10-5;经SiMg与NiMg合金处理的试样中夹杂物变化基本相同;加入镁合金并保温15min后凝固试样中夹杂物尺寸明显减小,约为2μm,其成分由Mn-Si-Al复合氧化物转变为Mg-Al尖晶石类夹杂物;加入Al并保温15min后,凝固试样中夹杂物尺寸较大,约为5μm,成分为纯Al2O3夹杂物;SiMg合金处理的试样中单位面积上夹杂物数量最少,钢中夹杂物最为细小、分散。     

增材制造用新型镍基高温合金的设计与开发

为了满足增材制造专用镍基高温合金成分优化设计需求，采用机器学习(machine learning, ML)和抗裂因子筛选相结合的综合设计策略开发了新型镍基高温合金。热力学计算结果表明，该合金凝固温度范围窄，在临界温度区间内凝固速度快，且收缩总应变及最大应变速率很小，表现出良好的凝固特性。利用选区激光熔化技术制备了新型合金，在成形试样的纵截面和横截面金相中未发现明显裂纹，合金表现出良好的抗裂性能。通过热处理工艺优化，合金在900℃时效后γ′相分数达到44.6%，组织内未见任何TCP相析出，实现了镍基高温合金在增材制造中抗裂性与力学性能的平衡。提出的综合设计策略可为增材制造领域中新材料的快速研发提供新的思路。     

高Al、Ti含量镍基高温合金激光、微弧火花表面熔焊处理研究进展及解决熔焊裂纹的途径

Al、Ti是镍基高温合金主要沉淀强化元素,随着Al、Ti含量的增加,镍基高温合金γ'-Ni3(Al,Ti)相体积百分数增加,高温强度增加,但是热裂纹敏感性也随之增加,如何利用熔焊工艺实现高Al、Ti镍基高温合金材料的表面无损伤熔焊处理一直是高Al、Ti镍基高温合金叶片与热端部件制造与再制造面临的难题.文中从高温合金表面熔焊修复与强化问题出发,着重介绍了高温合金焊接冶金问题及焊接性改善途径、激光与微弧火花两种低热输入熔焊工艺在高温合金表面修复与强化领域的研究与应用进展.分析表明:高Al、Ti镍基高温合金表面熔焊处理的主要难题是其高的热裂纹敏感性,主要表现在焊接或焊后热处理过程中容易产生凝固裂纹、液化裂纹、应变时效裂纹,采用惰性气体保护、改变基体组织状态、使用低强度的合金焊料、降低热输入等措施可有效改善其焊接性;激光、微弧火花等低热输入焊接工艺在解决高Al、Ti镍基高温合金表面熔焊问题方面具有极大的潜力.     

A new approach to develop complicated superalloy castings

As a precision casting process, investment casting process has been used widely in casting industry because of its many advantages. For almost all alloys, complicated near-net-shaped components can be cast relative easily and both external and internal designed complex castings can be achieved using investment casting. Investment casting is usually required for making complex shape castings while other manufacturing processes are too costly and time-consuming [1]. Conventional investment casti…     

熔模铸钢件裂纹缺陷形成原因的模拟分析

针对熔模铸造方法生产某不锈钢变频法兰过程中部分产品经常出现裂纹的问题,建立了铸件三维实体模型。结合熔模铸造实际生产工艺,运用基于DFDM方法的JSCAST软件对铸件充型和凝固过程进行了数值模拟。模拟结果表明,当浇注位置偏离铸件浇口杯中心时,上层右侧两个法兰将首先被充填,导致这两个法兰在充型与凝固过程中温度下降较快,与其他部位温差较大,易产生热应力集中倾向,导致裂纹产生。该部分与实际生产中裂纹产生部位相吻合。     

Optimization of investment casting process for K477 superalloy aero-engine turbine nozzle by simulation and experiment

In order to reduce the shrinkage porosity of nickel-based superalloy castings in the investment casting process, the effects of different gating systems on mold filling, solidification process, and prediction of shrinkage porosity of aero-engine turbine nozzle castings were investigated by simulation and experimental methods. Results show that the design of the vertical runner would cause greater turbulence of the melt in the riser during the mold filling process, and the outer runner is not necessary. With the decrease in number of runners, the hot spot moves down towards the casting, and the shrinkage and porosity defects are formed in the casting below the riser. In the original designs, a certain tendency of shrinkage and porosity defect is found in the vanes, inner rings, and outer rings of the castings by both simulation prediction and experiment. Finally, based on the processing optimization, the aero-engine turbine nozzle casting with no shrinkage and porosity defects is obtained.

     

镍基高温合金熔模铸件凝固过程宏/微观多尺度模拟

建立镍基高温合金熔模铸件凝固过程的宏/微观多尺度数理模型,基于射线追踪法处理热辐射,模拟铸件的温度分布,采用三维宏/微观网格嵌套和改进的CA方法模拟微观组织,并依据微观组织模拟结果处理结晶潜热,实现微观与宏观模拟的耦合.依据等效液面下降法、Niyama判据和Darcy定律预测铸件的宏观缩孔、宏观缩松和微观缩松缺陷分布位置,并浇注实际的高温合金叶轮铸件.结果表明:模拟获得的冷却曲线、微观组织及缺陷位置与实验结果吻合良好,模拟结果能够准确预测铸件中多种缺陷的分布.     

Research progress on refractory composition and deformability of shell molds for TiAl alloy castings

At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.     

高温合金薄壁铸件浇注系统设计

某高温合金调节片采用熔模精密铸造方法生产。该调节片尺寸为330mm×240mm,壁厚为0.8mm,并有多处纵横交错的加强筋,铸造成形难度较大,在铸造过程中铸件易产生欠铸、冷隔、疏松、裂纹等缺陷,其合格率较低。重点叙述了通过改进、优化铸件浇注系统的设计,有效消除了铸件的冷隔、欠铸缺陷,铸件的合格率大幅度提升,工艺出品率提高到原来的2倍左右。     

Precision Cast vs. Wrought Superalloys

The advancement of jet engine technology has traditionally given wrought superalloys eminence when design calls for both reasonable high temperature strength and dynamic fracture reliability. Despite the attractiveness of cast superalloys for their improved buy-to-fly ratios and higher strengthening γ volume fractions, the expansion of polycrystalline castings into the more critical of the superalloy applications has been prevented by a lack of sufficient micro structural control in casting technology. Recently, however, advances in casting technology are making possible the production of defect tolerant superalloy castings with improved fracture reliability. This new generation of superalloy castings now offers serious competition to wrought superalloys. Never before have wrought superalloys been so seriously threatened by their cast counterparts.     

高温合金大型薄壁件熔模精铸技术与发展

熔模铸造是制造大型高温合金薄壁铸件的重要手段，蜡模型壳的制作及高温合金的熔炼浇注是高温合金精密铸造缺陷控制的重要环节。阐述了制模、制壳、熔炼、晶粒细化等环节中的选材、过程控制对产品的影响，并指出调压技术的应用将是大型薄壁高温合金熔模铸件制造的新方向。     

INVESTIGATION OF SURFACE GRAIN REFINEMENT OF SUPERALLOY CASTINGS

本文对国内外关于高温合金铸件表面晶粒细化机理的几种观点作了验证;用X射线,显微镜和电子探针法对效果不同的型壳作了分析,发现铸件晶粒的细化与铝酸钴的分解以及合金中的活性元素有关;从浇铸后的型壳表面、铸件表面以及铝酸钴粉加不同活性元素的真空加热后的产物中均发现了Co(高温型)粒子。本文也做了铝酸钴加Al粉的真空差热分析并作了热力学计算,证明Co粒子的生成并不伴随着吸热,实际却是一个不大的放热效应。综合诸实验,作者认为铸件表面晶粒细化主要是由于Co粒子的核心作用;据此也探讨了合理的工艺,并巳用于工厂生产中,效果显著。     

Research on investment casting of TiAl alloy agitator treated by HIP and HT

Using TiAl alloy to substitute superalloy is a hot topic in aeroengine industry because of its low density, high elevated temperature strength, and anti-oxidization ability. In this research, Ti-47.5AL-2Cr-2Nb-0.2B alloy was used as the test material. By applying a combination process of ceramic shell mold and core making, vacuum arc melting and centrifugal pouring, and heat isostatic pressing (HIP) and heat treatment (HT) etc., the TiAl vortex agitator casting for aeroengine was successfully made. This paper introduced key techniques in making the TiAl vortex agitator with investment casting process, provided some experimental results including mechanical properties and machinability, and explained some concerns that could affect applications of TiAl castings.