《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。     

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.     

[例40]微弧火花沉积技术在涡轮叶片表面强化与修复中的应用

<正>涡轮叶片是航空发动机/燃气轮机的核心部件,在服役过程中容易产生磨损、腐蚀、开裂等早期损伤,由于叶片价格昂贵,换件修理成本很高。涡轮叶片通常由高Al、Ti含量的镍基高温合金制成,此类合金的特点是,高温强度髙,但可焊性差,通常认为是不可焊材料。微弧火花沉积是一种低热输入的显微焊接工艺,单层沉积厚度不过几十微米,沉积过程对基材的热影响很小,基本不会引起工件变形和组织改变。大量研究表明:微弧火花沉积可以实现很多髙强度镍基高温     

γ’相强化钴基高温合金成分设计与蠕变机理研究进展EI北大核心CSCD

近年来,随着航空发动机和地面燃机的持续发展,对其关键热端部件的环境抗力和承温能力的要求越来越高,γ′相强化钴基高温合金在抗热腐蚀性能和熔点温度等方面较镍基高温合金具有优势。为了促进此类合金的发展,本文基于国内外在合金开发和蠕变性能等方面的研究成果,结合本课题组的研究工作,总结了该类合金在合金化原理、合金设计方法和蠕变机理等方面的研究现状,凝练出了目前该类合金发展存在的关键基础科学问题,并对未来需要关注的研究方向进行了概述。     

用反应烧结和反应熔化法制取TiAl—TiB2复合材料

Ti Al基合金的优点是密度低、比强度高、刚度大、抗裂纹稳定性好 ,耐热可达90 0℃～ 10 0 0℃ ,Ti- Al的强力共价键可保证它有高的扩散激活能 ,从而能在 90 0℃以下阻止蠕变过程的发展。Ti Al的室温弹性模量为 16 0 GPa～ 175 GPa,高于一般钛合金(10 0 GPa) ,但低于镍基高温合金 (2 0 0GPa)。随温度的升高其弹性模量下降 ,至90 0℃～ 10 0 0℃时为 15 0 GPa,接近于镍基高温合金值。如以 Ti Al取代钛基、镍基和铁基材料并以 Ti Al为基做成复合材料 (KM)可减轻零件质量 2 0 %～ 5 0 % ,与传统的耐热合金相比 ,Ti Al复合材料在空气中…     

沉淀强化镍基高温合金熔化焊液化裂纹研究进展

沉淀强化镍基高温合金由于具有优异的高温强度和耐热腐蚀性而被广泛应用于航空发动机和工业燃气轮机的热端部件。但是这类合金在焊接过程中具有较高的液化裂纹敏感性,影响部件的使用寿命和性能。系统地阐述了沉淀强化镍基高温合金熔化焊液化裂纹的形成机理,介绍了几种控制液化裂纹的方法,包括增大焊接热输入、焊前预热、焊前热处理和添加中间层,最后指出了今后的主要研究方向。     

激光熔覆镍基高温耐磨合金的组织及性能

通过增加IN718合金中(Ti+Al)含量制备一种镍基高温耐磨合金,以满足超临界机组镍基合金阀门密封面再制造的需求。采用万能试验机、摩擦磨损试验机、XRD、SEM等仪器和JMatpro软件研究该合金激光熔覆试样的组织与性能。研究结果如下：当IN718合金的(Ti+Al)含量增加至7.6%时熔覆层会出现开裂;当IN718合金的(Ti+Al)含量增加至6.6%时,其激光熔覆试样初始平均硬度值为40 HRC,抗拉强度为998 MPa,延伸率为5.2%,室温摩擦因素为0.75左右,磨损量为0.327 5 mm³,主相为γ相和γ′相,700℃×10 h时效处理后平均硬度值为54 HRC,700℃摩擦因素为0.35左右,磨损量为0.024 mm³,主相γ′占53%。研究结果表明,IN718合金中(Ti+Al)含量增加至6.6%时具有良好的激光熔覆工艺性能和高温摩擦磨损性能,可应用于超临界/超超临界机组镍基合金阀门密封面的维修与再制造。     

新型低铼第三代镍基单晶高温合金的设计

对通过d电子理论以及电子空位数理论在现有第三代镍基单晶合金基础上进行成分设计,控制合金中Cr、Mo、Al、Re、Hf元素含量不变,通过增加合金中W含量以及添加元素Nb、Ti强化γ′相,微调合金中Ta/(W+Mo)比值和Al/Ti比值,并对合金中TCP相的析出以及合金相稳定性进行预测,来提高合金的高温性能,得到一系列的合金成分范围。利用热模拟软件JMat Pro,并结合相图分析,获得一系列低Re合金成分,通过对已有镍基单晶合金在平衡状态下热处理窗口、糊状区间、TCP相含量、熔点、密度等热力学参数进行模拟,并依据这些参数制定合金设计判据,得到新型低铼第三代镍基单晶合金的组成。     

镍基单晶高温合金中Ru元素作用的研究进展

具有优异的高温抗蠕变、抗疲劳、抗氧化和耐热腐蚀等综合性能的先进镍基单晶高温合金，是当代先进航空发动机热端部件的首选材料。研究者发现，Ru元素的引入对镍基单晶高温合金的组织稳定性和高温蠕变性能有重大影响。但是相关研究开始较晚，不够充分，因此Ru元素具体作用机制尚不明晰。此外，Ru的添加提高了镍基单晶高温合金的制造成本，所以高代次单晶合金目前仍处于试验阶段，并未在实际生产中实现大规模应用。本文从Ru元素对镍基单晶高温合金铸态组织、热处理态组织、组织结构稳定性和蠕变性能的影响4个方面出发，总结了Ru元素在单晶高温合金中具体作用的研究进展。     

Ti含量对镍基高温合金抗热腐蚀性能的影响

采用涂盐方法研究了不同Ti含量的镍基高温合金的热腐蚀过程。研究发现,在900℃涂盐条件下,Ni基高温合金中加入质量分数为0.55%的Ti就可以显著提高合金自身的热腐蚀抗力,并且随着Ti含量增加,合金的热腐蚀抗力进一步增强。研究认为,合金中加入Ti后,能促使合金表层形成致密、连续的Cr2O3层,并且随着Ti含量增加,Cr2O3层厚度增加,Al2O3层逐渐向外腐蚀层迁移,从而提高了合金的热腐蚀抗力。     

ON THE PRIMARY η-PHASE IN A HIGH-Ti Ni-Fe-Cr BASED SUPERALLOY

The precipitation and dissolution together with their control of the primary η-phase in ahigh-Ti Ni-Fe-Cr base superalloy have been investigated.The precipitation of primaryη-phase was found to be closely related to Ti or Al content and solidification rate of the alloy.The aggregation of blocky η-phase may remarkably reduce the tensile strength,ductility andrupture life of the alloy.The temperature-time relation of dissolution of the primary η-phaseobeys T=1370-86.1 lgt for as-cast superalloy.The formation of primary η-phase may beprevented by the reasonable control of Ti or Al content and smelting process.The adoption oftreatment under large hot deformation and homogenization may be the remedy forunfavorable influence of η-phase.     

DZ40M钴基合金铝化物涂层的循环氧化

以新型定向凝固钴基高温合金ＤＺ４０Ｍ为基体,研究其低压化学气相沉积铝化物涂层的循环氧化行为,发现该涂层具有较高的抗循环氧化性能,涂层与基体结合良好。涂层退化主要是由外表面氧化膜的愈合消耗Ａｌ源所造成,沉积渗剂中加入Ｔｉ可加速涂层的退化。     

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异种金属1Cr18Ni9Ti和GH3044在点焊后X光检查时发现裂纹。通过对焊点进行金相检查、断口观察和电镜能谱分析后表面发现:焊缝组织为单相奥氏体组织,裂纹断口为典型焊接热裂纹形貌,焊点中镍含量较高。经过分析验证得出结论:由于焊接过程中GH3044熔入量大,导致焊缝中镍含量增大,形成单相奥氏体组织,产生焊接热裂纹。     

Emission mitigation potential of lightweight intermetallic TiAl components

An environmental comparison is made between two gamma titanium aluminide (γ-TiAl) alloys, Ti–46Al–8Nb and Ti–46Al–8Ta (at.%), and the standard nickel superalloy, INC713LC used for investment cast components in the low pressure (LP) turbine section of aero-engines. Over the complete lifetime, weight reduction by direct replacement could give significant reductions in CO₂ emissions, greatly outweighing the impact of other environmental emissions.     

Aging response of transient liquid phase bonded wrought IN718 superalloy: influence of post-bond heat treatment

Aging response of transient liquid phase Nb bearing wrought IN718 nickel base superalloy is studied. The aging behaviour of the joint is influenced by low Nb+Al+Ti content of isothermal solidification zone (ISZ) and formation of Nb–Cr–Mo based boride precipitates in diffusion affected zone (DAZ). It was shown that applying a post-bond heat treatment which was able to eliminate the diffusion induced boride precipitates in DAZ and increase the Nb+Al+Ti content of the ISZ improved the aging response and shear strength of the joint.     

Modeling Interdiffusion Processes in CMSX-10/Ni Diffusion Couple

A diffusion couple between directionally solidified nickel and the single crystal Ni-base superalloy CMSX-10 was produced by hot pressing in vacuum. The diffusion couples were heat treated at temperatures between 1050 and 1250 °C. The exposed samples were characterized by SEM/EBSD/EPMA. The interdiffusion results in dissolution of the γ′-Ni₃Al in the superalloy and in growth of nickel grains towards CMSX-10. Rapid diffusion of aluminum from the superalloy into pure nickel leads to a significant formation of pores in the superalloy. The interdiffusion processes were modelled using the finite-element simulation software DICTRA with the databases TCNi5 and MobNi2, tailored specially for Ni-base superalloys. The effect of alloying elements on the interdiffusion profiles is discussed in terms of alloy thermodynamics. The calculated element concentration profiles are in good agreement with the EPMA measurements. The interdiffusion modeling correctly predicts the shapes of the concentration profiles, e.g. kinks on the Al and Ti profiles in the vicinity of the original interface in the joint. The calculation predicts with reasonable accuracy the extent and the location of the Kirkendall porosity.     

Microstructure and mechanical properties of tungsten inert gas welded–brazed Al/Ti joints

The tungsten inert gas welding–brazing process using Al-based filler metal has been developed for joining 5052 Al alloy to Ti–6Al–4V alloy in a butt configuration. The results indicated that heat input influenced the morphology and thickness of the interfacial reaction layer of Al/Ti joints, which played an important role in the mechanical properties of weldment. With the optimised tungsten electrode offset D of 1.0?mm from Al/Ti initial interface to Al side and welding current of 70?A, the thin cellular-shaped and club-shaped TiAl₃ reaction layers formed in the brazing zone, which contributed to suppressing crack initiation and propagation during tensile test. Eventually, the maximum tensile strength of 183?MPa was obtained and the optimised Al/Ti joint fractured at Al alloy base plate. Moreover, the power density characterisation and joining mechanism of Al/Ti joints were discussed.     

Effect of Ti on aluminide coating for DZ40M alloy

The effect of Ti on the aluminide coating has been investigated for a new Co‐base superalloy DZ40M. The results showed that the addition of Ti into aluminiser could reduce the permeation of Al into the substrate, and quicken the oxidation and degradation of the coating.     

Microstructural evolution of CoCrAlY bond coat on Ni-based superalloy DZ 125 at 1050 °C

CoCrAlY alloy has been widely used as metallic protective coatings or the bond coats in thermal barrier coatings (TBCs) to protect the underlying superalloy from oxidation and hot-corrosion. In this paper, the TBC consisting of yttria stabilized zirconia (7YSZ) ceramic top coat and CoCrAlY bond coat was deposited onto directionally solidified nickel based superalloy DZ 125 by electron beam physical vapor deposition (EB-PVD). The microstructural evolution of the bond coat on this superalloy was investigated after thermal exposure for 100 h at 1050 °C. Due to a significant inward diffusion of Al, Co and Cr from the coating and outward diffusion of Ni, Hf, W and Ti from the substrate, the phase transformation from the Co-based Al-rich β-CoAl phase to the Al-deficient γ-CoNi solid solution phase occurred in the bond coat. Simultaneously, a large amount of Ni-based β-NiCoAl phase was present in the bond coat. In addition, the particles containing substrate strengthening elements Hf and/or W are abundant in the thermally grown oxides (TGO) and within the bond coat. The mechanism for the microstructural evolution is discussed.