均匀化态GH3625合金熔化和凝固过程中的相变

使用差示扫描量热仪(DSC)、共聚焦激光扫描显微镜(CLSM)、扫描电镜(SEM)、和能谱分析仪(EDS)等手段研究了均匀化态GH3625合金在熔化和凝固过程中的组织演变以及主要相的溶解和析出。结果表明:定制的二段式均匀化工艺基本上消除了GH3625合金中的低熔点laves相和微观元素偏析;均匀化态GH3625合金的初熔温度明显提高,熔化先发生在晶界、表面、缩孔及碳化物(NbC)区域;GH3625合金的凝固过程分为三个阶段,主要发生了L→γ、L→γ+MC和L→γ+laves的结晶反应;γ相的形核属于非均匀形核,使溶质原子易偏聚于晶界,从而在枝晶间不可避免的形成了元素偏析和相偏析,其中低熔点laves相的析出类型主要与冷却速率有关。     

铸锭GH 3625合金微观偏析及均匀化热处理

为消除铸态GH 3625合金的显微偏析,改善其热加工性能,建立其均匀化动力学并制订均匀化处理制度,采用ImagePro Plus软件、扫描电镜(SEM)和能谱分析仪(EDS),对通过真空感应熔炼和电渣重熔双联工艺制备的GH 3625合金电渣锭的显微组织及元素偏析情况进行分析和研究.同时,对铸态GH 3625合金在不同温度下同一时间及同一温度下不同时间进行了均匀化处理.结果表明:GH 3625合金电渣锭存在明显的枝晶间微观偏析,主要偏析元素为Nb、Mo等,形成富Nb的Laves相、MC碳化物;不同元素的偏析程度为NbMoTiAlCr;Nb、Mo、Ti、Al在枝晶间大量富集,使得Laves等多种非平衡相在枝晶间析出;在均匀化过程中,随着均匀化温度的升高和时间的延长,偏析元素逐渐扩散均匀;当热处理制度为1 130℃×32 h时,元素偏析基本消除;Laves相体积分数随均匀化处理时间呈明显指数函数特征,V1 130℃=0.033 5exp(-0.163 1t).     

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%。     

热等静压/热处理工艺对激光选区熔化成形GH4169合金微观组织与拉伸性能的影响

采用激光选区熔化(SLM)成形技术制备GH4169合金,利用金相显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等分析热等静压/热处理工艺对SLM成形GH4169合金微观组织及拉伸性能的影响规律。结果表明:沉积态合金组织中,沿沉积方向的晶粒为柱状晶,晶粒内枝晶组织细小,枝晶间分布大量Laves相;经热等静压后,合金中的气孔及Laves相可被有效消除,沿沉积方向的晶粒转变为等轴晶;经980℃/1 h固溶处理后,合金中的晶界处析出大量短棒状δ相。热等静压/热处理后GH4169合金试样的室温及650℃拉伸性能均高于锻件标准要求的力学性能指标,且温度对断裂方式影响不大。     

热等静压/热处理工艺对激光选区熔化成形GH4169合金微观组织与拉伸性能的影响EI北大核心CSCD

采用激光选区熔化(SLM)成形技术制备GH4169合金,利用金相显微镜(OM)、扫描电子显微镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)等分析热等静压/热处理工艺对SLM成形GH4169合金微观组织及拉伸性能的影响规律.结果表明:沉积态合金组织中,沿沉积方向的晶粒为柱状晶,晶粒内枝晶组织细小,枝晶间分布大量Laves相;经热等静压后,合金中的气孔及Laves相可被有效消除,沿沉积方向的晶粒转变为等轴晶;经980℃/1 h固溶处理后,合金中的晶界处析出大量短棒状δ相.热等静压/热处理后G H4169合金试样的室温及650℃拉伸性能均高于锻件标准要求的力学性能指标,且温度对断裂方式影响不大.     

均匀化过程中铸态GH742合金的组织转变

铸态GH742合金中存在复杂的第二相组织和严重的枝晶偏析,Nb、Ti大量富集于枝晶间和MC碳化物、Laves相、δ相、(γ γ′)等析出相中.本文确定了γ基体的熔化温度为1160℃,并通过不同的均匀化处理确定了γ′相、(γ γ′)共晶、MC碳化物、Laves相、δ相、Ni_5Ce相及含氧硫稀土相等析出相的溶解温度.由于稀土相在1120℃发生熔化,提出一种GH742合金低温预处理加高温扩散的二次均匀化制度来扩大其均匀化温度区间,提高扩散退火温度,从而获得均一的组织.元素扩散计算结果表明,提高均匀化温度可以提高元素的扩散系数;Nb的偏析系数比Ti的小得多,达到完全均匀化需要很长的时间.     

固溶温度对等离子快速成形Inconel625合金组织的影响

为了优化快速成形零件组织和力学性能,利用脉冲等离子焊接快速成形工艺制备了Inconel625合金薄壁零件.采用扫描电镜、透射电镜研究了固溶温度对成形零件组织的影响规律.结果表明:沉积态组织以胞状枝晶为主,具有较强生长取向性的外延枝晶组织特征,同时,在枝晶间隙析出大量的Laves相和少量的MC碳化物.经过720℃/1 h的固溶处理,金相组织没有发生明显变化,但导致γ″(Ni3Nb)相的析出.经850℃固溶处理,组织中的Laves相部分被溶解,生成了针状δ相.当固溶温度升高到980℃,Laves相几乎完全溶解,δ相发生了部分回溶.而经过1 080℃固溶处理,消除了元素的偏析和Laves相,但再结晶导致晶粒严重长大.980℃是最佳的固溶处理温度.     

Al-4.5%Cu合金自由凝固过程固相率变化及枝晶间液相流动

本文设计了测试金属自由凝固过程的液淬装置和枝晶间液相流动性的实验装置,并在这些装置上,针对Al—4. 5％Cu合金,研究了温度(T)、冷却速度(V_c)、合金元素对凝固过程固相率(f_s)的影响以及枝晶间液相流动性与固相率的关系。     

Cu对Mg-7Zn-0.6Zr合金流动性的影响

使用流动性模具研究了Cu含量对Mg-7Zn-x Cu-0.6Zr(x=0,1,2,3)合金流动性的影响。用双电偶差热分析法分析了合金凝固过程中的凝固区间和枝晶相干温度等参数,根据TEM鉴别了合金的微观物相,并结合SEM和EPMA观察了合金的显微组织。基于理论预测和流动性实验测试研究了Mg-7Zn-x Cu-0.6Zr(x=0,1,2,3)合金的流动性。结果表明,随着Cu的加入在Mg-7Zn-0.6Zr合金中析出MgZnCu共晶组织,使晶粒细化、凝固区间减小、枝晶相干温度降低、枝晶生长速率降低和合金流动性提高。     

Nb含量对625合金带极堆焊层耐晶间腐蚀性能的影响

研究了不同Nb含量对625合金带极堆焊金属的组织转变及耐晶间腐蚀性能的影响。结果表明,Nb含量的增加导致堆焊层耐腐蚀性能显著下降。Nb含量较低时,合金中析出相以MC为主,Laves相很少,具有较好的耐腐蚀性能。Nb含量增加后,在枝晶间产生强烈偏析,促进合金中富Nb、Mo、Si的Laves相的析出和长大。块状形态的Laves相本身贫铬并造成枝晶间区域较大的成分差异,导致析出相附近成为晶间腐蚀的薄弱区,明显加快合金的腐蚀速率。     

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...     

Effect of Solidification Interface Morphologies on Microstructures of a Ni-base Superalloy

A cast Ni-base superalloy K5 wasdirectionally solidified and various solidification in-terfaces including plane front,cellular,cellular-dendritic and dendritic were obtained in awider range of G/R ratio by using improved highwithdrawal device and liquid metal cooling experi-mental sets.The precipitation pattern of some prin-cipal phases of the alloy and correlation of the vari-ous interfaces with microstructure were studied sys-tematically.It was indicated that the morphology ofsolidification interface of superalloy K5 varied withG/R ratio and that the solidification interfacemorphologies have a considerable effect on the fea-tures of phases both precipitated duringsolidification and post-solidification.Plane frontand cellular directional solidification of superalloyK5 lead to a substantial decrease of MC carbideand elimination of γ-γ'eutectic,but makeneedle-shape M_6C carbide precipitate easily duringageing treatment.The finer dendritic structuressolidified under the condition of higher cooling ratehave less dendritic segregation and idealmicrostructure.     

Multisheet structure of Inconel 718 superalloy processed by LBW/SPF technology and its microstructure

Abstract

Multisheet structure of Inconel 718 superalloy will be widely used in vehicles as heat resisting and heat shielding structure due to its lightweight, high strength and stiffness. Multisheet structure of Inconel 718 superalloy was processed by laser beam welding and superplastic forming (LBW/SPF) technology in the present paper. Multisheet structure of Inconel718 superalloy processed by LBW/SPF technology exhibits good configuration and uniform thickness distribution. Laser beam welding parameters for multisheet structure were as follows: pulse frequency was 32 Hz; pulse duration 3 ms; peak power per pulse 4500 W; welding speed 180 mm min^–1; SPF parameters were as follows: temperature T_f=965°C; forming pressure P _f=4·2 MPa; forming time t _f=130 min. Microstructure of multisheet structure was studied carefully. Microstructure in weld fusion zone was constituted of austenite dendritics and Laves phase precipitated in interdendritics. After SPF process, austenite dendritics in the weld fusion became coarser and most of Laves phases were dissolved and turned into δ precipitated phase but a few of Laves phases were still reserved. And Nb concentration in dendritics increased to 5·42% compared to 2·82% under as welded condition. Weld metal hardness increased from 331·63 under as welded condition to 391·74 under post-SPF condition which was closed to the base material hardness of post-SPF. Grain size of base material grew slightly and an amount of precipitated phase appeared in the base material undergoing SPF process. The tensile test results of base material show that tensile strength increased obviously and the ductility decreased slightly after SPF process. Therefore, LBW/SPF technology is an appropriate forming technique for multisheet structure of Inconel 718 superalloy.     

Microstructural analysis of fusion and heat affected zones in electron beam welded ALLVAC 718PLUS™ superalloy

The fusion zone and heat affected zone (HAZ) microstructures of electron beam welded superalloy 718PLUS™ (718 Plus) that has been newly developed by ATI ALLVAC were examined. The microsegregation pattern during solidification of the fusion zone indicated that while Fe, Co, W, and Cr segregated to the core of the gamma dendrites, Nb, Ti, and Al were extensively rejected into the interdendritic liquid. Electron diffraction and X-ray microanalysis using transmission electron microscopy (TEM) of the fusion zone showed that the major secondary phases that formed from the interdendritic liquid were gamma/MC type carbide eutectic and gamma/Laves eutectic constituents. HAZ microstructure showed partially melted zone immediately adjacent to the fusion zone and intergranular microfissuring associated with resolidified products which suggested that HAZ cracking in this alloy occurred by liquation cracking. Microstructural examination of the HAZ using analytical scanning electron microscope showed resolidified gamma/Laves eutectic on the cracked and backfilled grain boundaries. Fine resolidified MC type carbide particles were also observed in the HAZ. Causes of grain boundary liquation were identified and the solidification of intergranular liquid in the HAZ was discussed.     

固溶处理温度对GH3625合金热挤压管材微观组织和力学性能的影响

采用SEM、EDS和XRD等手段研究了不同固溶处理温度对GH3625合金热挤压管材组织性能的影响。结果表明,1 120℃是合金组织和力学性能的一个转折点。当固溶处理温度为910~1 120℃时,由于晶界处NbC相的钉扎作用,使得晶粒长大缓慢,合金硬度和强度缓慢下降;当固溶温度超过1 120℃时,NbC相大量回溶,钉扎作用减弱或消失,晶粒急剧长大,合金硬度和强度的下降趋势明显增大。随着固溶温度的升高,合金断口中的韧窝变得大而深邃,塑性逐渐提高;当固溶温度超过1 120℃时,拉伸断口基本以韧窝为主。GH3625合金热挤压管材在固溶处理时间为1h时的最佳固溶处理温度为1 120℃。     

热处理工艺对GH909板材TIG焊缝析出相的影响

为改善GH909板材的焊接工艺及使用性能,采用扫描电镜和EDX分析研究了GH909板材在TIG焊后不同热处理工艺焊缝析出相的变化规律,对提高GH909板材TIG焊接接头质量具有重要的应用价值.研究结果表明：焊缝形成的相有针片状ε/ε″相、γ/Laves低熔点共晶相,且都在γ晶间分布;焊缝中心低熔点共晶相所占比例均比离焊...     

Study of grain refinement and eutectic transformation of undercooled IN718 superalloy

Abstract

A substantial undercooling up to 250 K was produced in the IN718 superalloy melt by employing the method of molten salt denucleating, and the microstructure evolution with undercooling was investigated. Within the achieved undercooling, 0–250 K, the solidification microstructure of IN718 undergoes two grain refinements: the first grain refinement occurs in a lower range of undercooling, which results from the ripening and remelting of the primary dendrite, and at a larger range of undercooling, grain refinement attributes to solidification shrinkage stress and lattice distortion energy originating from the rapid solidification process. A ‘lamellar eutectic anomalous eutectic’ transition was observed when undercooling exceeds a critical value of ～250 K. When undercooling is small, owing to niobium enrichment in interdendrite, the remaining liquid solidifies as eutectic (γ+Laves phase); whereas, if the undercooling achieves 250 K, the interdendrite transforms from eutectic (γ+Laves phase) to Laves phase, which results from the formation of divorced eutectic arising from the huge variance of the growth velocities of γ and Laves phases.     

长期时效对低膨胀高温合金GH2909性能的影响

将低膨胀高温合金GH2909分别在500℃、600℃和650℃时效2000 h,研究了长期时效对合金组织和性能的影响。结果表明：GH2909合金在550℃和600℃时效2000 h后其组织稳定性较高,强度略有提高,塑性基本不变。而在650℃时效2000 h后合金的拉伸强度明显降低,室温塑性下降,尤其是在室温下断面收缩率明显降低,但是高温塑性却显著提高。其原因是,GH2909合金在650℃长期时效过程中析出了大量贯穿晶粒且呈魏氏组织形貌的针状ε/ε″相,而强化相γ′相明显减少。同时,在该温度下γ′相明显长大且其稳定性下降。     

Numerical simulation of solidification and liquation behavior during welding of low-expansion superalloys

Low-expansion superalloys are susceptible to weld solidification cracks and heat-affected zone (HAZ) microfissures. To predict solidification cracking, QBasic procedures were developed and solidification reaction sequence, type, and amount of eutectic product were calculated. As manifested, primary solidification is followed by L → (γ+NbC) and L → (γ+Laves) eutectic reaction sequentially for GH903 and GH907; hence, the terminal eutectic constituents are made up of γ/NbC and γ/Laves. While for GH909, only reaction L → (γ+Laves) occurs and more γ/Laves eutectic forms. Therefore, GH909 is more sensitive to solidification cracking. To predict HAZ liquation, cracking Visual FORTRAN procedures were developed, and constitutional liquation of NbC was simulated. As shown, solid dissolution of NbC prior to liquation decreases, and initial liquid film increases with the rate of thermal cycle. Higher rate of thermal cycle promotes the melting of the matrix adjacent to the liquid film and postpones the solidification of the liquid by the liquid-to-γ mode. Thus, more residual liquid film remains at the eutectic point, which will promote HAZ microfissuring. The increase in original grain size and peak temperature also promotes liquation. Finally, these conclusions were verified indirectly by hot ductility tests.