FRECKLE FORMATION AND CHARACTERIZATION OF A Ni-Cr-Mo-Fe-W ALLOY

The freckle formation and their phase characterization in freckle areas were investigated by means of microstructure analysis approaches and a thermodynamic equilibrium phase calculation method in a Ni-Cr-Mo-Fe-W alloy. These results show that in freckle areas a large number of M6 C, u and P phases precipitate in grain boundaries even within grain due to the enrichment and segregation of Mo and C during solidification, which results in small grains in freckle areas. Equilibrium phase and liquid segregation calculation can give an reasonable interpretation of the freckle feature for this alloy.     

热丝脉冲TIG堆焊Inconel625成型质量优化与性能

基于中心复合试验设计方法,采用热丝脉冲TIG工艺在AISI 4130基体上堆焊Inconel 625合金。借助响应面法建立了焊缝几何特征与工艺参数之间的数学模型。根据优化后的工艺参数,获得了平坦、连续、无缺陷的多道两层堆焊层。堆焊层微观组织主要由柱状晶组成,在融合界面附近存在少量的平面晶与胞状晶,其顶部组织为等轴晶与转向晶。利用动态极化曲线法对基体与堆焊层的耐腐蚀性能进行了评价。结果表明：堆焊层的耐腐蚀性随着Fe含量的增加而降低,但增加堆焊层的层数可以显著提高耐腐蚀性能。而且,两层堆焊层试样与铸态Inconel 625的耐腐蚀性能基本相当。     

Nucleation mechanisms of dynamic recrystallization in Inconel 625 superalloy deformed with different strain rates

The effects of strain rates on the hot working characteristics and nucleation mechanisms of dynamic recrystallization (DRX) were studied by optical microscopy and electron backscatter diffraction (EBSD) technique. Hot compression tests were conducted using a Gleeble-1500 simulator at a true strain of 0.7 in the temperature range of 1000 to 1150 °C and strain rate range of 0.01 to 10.00 s-1. It is found that the size and volume fraction of the DRX grains in hot-deformed Inconel 625 superalloy firstly decrease and then increase with increasing strain rate. Meanwhile, the nucleation mechanism of DRX is closely related to the deformation strain rate due to the deformation thermal effect. The discontinuous DRX (DDRX) with bulging of original grain boundaries is the primary nucleation mechanism of DRX, while the continuous DRX (CDRX) with progressive subgrain rotation acts as a secondary nucleation mechanism. The twinning formation can activate the nucleation of DRX. The effects of bulging of original grain boundaries and twinning formation are firstly gradually weakened and then strengthened with the increasing strain rate due to the deformation thermal effect. On the contrary, the effect of subgrain rotation is firstly gradually strengthened and then weakened with the increasing strain rate.     

偏析对DZ483镍基高温合金糊状区内液相密度的影响

为研究DZ483合金在凝固过程中的元素偏析行为对糊状区内液相密度的影响,采用等温凝固结合水淬法对合金进行不同温度下的凝固实验.利用OM和SEM观察试样的凝固组织,利用EDS测量固相和剩余液相的元素含量,并根据剩余液相的成分计算其密度.结果表明,DZ483合金的开始凝固温度略低于1335℃,在1325℃液相中开始析出富含Ta和Ti的MC;W和Co为负偏析元素,Mo,Ta和Ti为正偏析元素,而Al和Cr几乎不发生偏析;剩余液相的密度随温度降低基本呈下降趋势,但在1325至1315℃之间有所回升.计算结果表明,温度对液相密度的影响很小,合金元素的偏析对液相密度的影响占主要地位.其中,Mo和Ta的偏析导致液相密度增加,而Ti和W的偏析导致液相密度明显降低.备合金元素的偏析对密度变化的贡献由大到小顺序为:Ti>Ta>W>Cr>Mo>Al>Co.MC的形成消耗了大量的Ti和Ta,对合金元素的偏析造成一定的影响,从而导致液相密度在1325至1315℃之间有所增加.     

新型Ni-Co基高温合金中平衡析出相的热力学研究

利用热力学计算软件JMatPro和相应的镍基高温合金数据库,研究了U720Li合金以及在此基础上研发的新型Ni-Co基高温合金的化学成分对平衡相的析出行为、加工性能和γ/γ′晶格错配度的影响.结果表明:Ti/Al值(原子比)的增加提高了合金中γ/γ′相的晶格错配度,γ′析出相的含量随Ti+Al含量(原子分数)的增加而增加.因此,增加Ti/Al值和Ti+Al含量能提高合金的高温强度.Co含量的升高可以拓宽合金的加工窗口,改善合金的加工能力,并且还可以增加合金γ/γ′相的晶格错配度,提高合金错配强化的效果.同时,Ti/Al值的增加促进合金中η相析出,而Co含量的增加具有抑制η相的效果.因此,在Co含量较高的Ni-Co基高温合金中,适当提高Ti含量,增加Ti/Al值对提高合金高温强度有利.     

DYNAMICS OF PRECIPITATION AND TRANSFORMATION OF CARBIDES IN A Ni-BASE SUPERALLOY

The quantitative analytical method combining the electrolytic extraction with X-raydiffraction analysis to determine the carbides and TCP in a Ni-base superalloy wasdeveloped.The variation of decomposition of MC and precipitation of M_(23)C_6 and M_6C withhot exposure time at 850—1000℃ is shown to conform to hyperbolic law.The elemental con-stitution of M_(23)C_6 changes continutously during the hot exposure process.At the primarystage the constitution of the precipitates is(Cr_(0.67)Mo_(0.13)Ni_(0.13)Co_(0.07))_(23)C_6.Then with in-creasing Cr and decreasing Mo,Ni and Co it finally becomes(Cr_(0.88)Mo_(0.07)Ni_(0.03)Co_(0.02))_(23)C_6.The higher the hot exposure temperature,the faster the final constitution of M_(23)C_6 may beachieved.     

一种镍基高温合金的碳化物析出与转化动力学

采用化学分离联合衍射定量分析法,对多相镍基合金进行了定量相分析研究,得到了850—1000℃下MC的分解和M_(23)C_6,M_6C的析出与热暴露时间的双曲线型变化规律。热暴露过程中M_(23)C_6的元素组成一直在变化,刚析出时为(Cr_(0.67)Mo_(0.13)Ni_(0.13)Co_(0.07))_(23)C_6,其后Cr量增高,Mo,Ni和Co量减少,最终组成为(Cr_(0.88)Mo_(0.07)Ni_(0.03)Co_(0.02))_(23)C_6。热暴露温度愈高,M_(23)C_6达到最终组成状态愈快。     

INFLUENCE OF ASSOCIATED AND SEPARATE PRECIPITATION OF γ″ AND γ′ ON STRUCTURE STABILITY IN INCONEL718 AND MODIFIED ALLOYS

The precipitation behavior in Inconel 718 and modified alloys has been studied by means ofTEM.The structure of associated precipitation and compact morphology of γ″+γ′ were ob-tained by modifying the contents of Al,Ti and Nb.Experimental results show that the com-pact morphology of γ″+γ′ has the best structure stability at higher temperatures.Instead ofthe transformation γ″→δ in alloy 718 the dissolution of strengthening phases in modified alloyleads material degradation.     

Inconel 617镍基合金焊接接头热影响区组织和性能分析

采用钨极氩弧焊(TIG焊)对Inconel 617镍基合金(617合金)进行焊接,研究焊接热过程对接头热影响区(HAZ)组织和硬度的影响。采用光学显微镜(OM)和扫描电子显微镜(SEM)对接头的HAZ和母材(BM)的组织进行表征。结果表明:母材的基体为奥氏体,奥氏体晶粒大小不均匀。奥氏体晶粒内部和晶界间存在大量细小的M23C6碳化物。碳化物沿轧制方向呈带状分布。靠近母材的HAZ处奥氏体晶粒内部和晶界间M23C6碳化物粗化,在靠近熔合线的HAZ处奥氏体晶界处形成连续富Cr和Mo元素的片层状结构。对焊接接头进行维氏显微硬度测试,发现母材和HAZ的硬度值没有明显变化。实验结果表明:TIG焊过程对接头HAZ的性能影响不大,是一种适合617镍基合金的可靠的焊接方法。     

MICROSTRUCTURE CHARACTERISTICS AND CRYSTALLOGRAPHIC ORIENTATION OF TRANSIENT LIQUID PHASE JOINT OF NI-BASE SINGLE CRYSTAL SUPERALLOY

采用Ni-15Cr-3.5B非晶合金箔带作为中间层合金对镍基单晶高温合金进行瞬态液相(TLP)连接. 利用光学显微镜、扫描电镜、透射电镜对接头的微观结构进行观察和分析, 利用电子背散射衍射(EBSD)方法测定了连接区域和基体之间的结晶学取向. 结果表明, 接头区域由连接区、中间金属/基体金属界面扩散区和基体金属区组成, 连接区中心形成M23B6+γ和MB+γ 共晶, 扩散区形成细小的M3B2颗粒; 均匀化处理后接头与基体的γ'相的尺寸趋于一致; TLP接头等温凝固过程中, 固/液界面向液相移动中外延生长, 连接层与所连接的基体金属的结晶学取向一致.     

镍基高温合金粉末颗粒的凝固组织研究

本文按粒度分级研究了PGH95镍基高温合金粉末颗粒的显微组织和析出相。随着粉末颗粒尺寸减小,冷却速度增加,颗粒的凝固组织从树枝晶为主的方式逐渐转变为胞状晶为主方式。主要析出相为MC型碳化物,其形态随颗粒尺寸不同而呈多样性。还发现少量硼化物,Laves相和一次γ′相,它们往往与MC碳化物伴生存在,粉末颗粒中相析出特征与其成分,凝固条件、显微组织密切相关。     

STUDY OF TCP PHASE PRECIPITATING IN GH4199 SUPERALLOY

The precipitating regulation and mechanism of TCP phase (μ phase and σ phase) are studied, using electron hole number (EHN) theory, phase analysis technology and TEM observation. The results indicate that the EHN in studied alloy is 2.311-2.348 which is higher than that of critical EHN of μ phase precipitate (2.30), so μ phase could precipitate if there is enough thermo-expasition. In contrast, the calculated EHN is less than that of critical EHN of σ phase precipitate (2.52). However the σ phase is also observed by TEM.Enrich of Cr and Mo around γ phase after γ‘ phase precipitated leads to σ phase precipitated.     

M91镍基铸造高温合金的组织和凝固特性SCIEI

研究了M91合金的组织及凝固过程,发现该合金和常规合金相比,铸态组织无碳化物相析出而有大量(γ+M_3B_2)及(γ+γ’)共晶,合金有极好的组织稳定性;在凝固过程中剩余液体量少而且能互相补充,其疏松倾向性很小。     

镍基单晶高温合金瞬态液相连接接头的微观结构和结晶学取向

采用Ni-15Cr-3．5B非晶合金箔带作为中间层合金对镍基单晶高温合金进行瞬态液相（TLP）连接．利用光学显微镜、扫描电镜、透射电镜对接头的微观结构进行观察和分析,利用电子背散射衍射（EBSD）方法测定了连接区域和基体之间的结晶学取向．结果表明,接头区域由连接区、中间金属／基体金属界面扩散区和基体金属区组成,连接区中心形成M23B6＋γ和MB＋γ共晶,扩散区形成细小的A4382颗粒;均匀化处理后接头与基体的γ＇相的尺寸趋于一致;TLP接头等温凝固过程中,固／液界面向液相移动中外延生长,连接层与所连接的基体金属的结晶学取向一致．     

MICROSTRUCTURE AND SOLIDIFICATION CHARACTERISTICS OF AS-CAST Ni-BASE SUPERALLOY M91

In comparison with conventional superalloys,no carbide but significant amount of γ+M_3B_2 and γ+γ′ eutectics were revealed to precipitate in the stable as-cast structure of Ni-base superalloy M91 which is abundant in B and minfied in C.During solidification of the superalloy,the residual liquid is much less and the tendency to porousness is inconsiderable.This superalloy seems to be available for turbine blade and other integral cast- ings under intermediate temperature and long-term services.     

Ni—Al系中γ,γ‘,β相平衡的实验与热力学分析

为了对Ｎｉ基高温合金的设计提供数据和理论依据,采用实验和热力学解析的方法对该体系中γ,γ＇,β之间的相平衡进行了研究。实验结果发现,γ＇相的存在区域有一定的成分范围,且在１０５０℃左右成分范围最宽。采用规则溶液模型和亚点阵模型对该体系的液相、γ,γ＇和β相进行了热力学分析和计算,与实验结果基本一致。     

MICROSTRUCTURES AND THE STRUCTURE STABILITY OF INCONEL 725,A NEW AGE—HARDENABLE CORROSION RESISTANT SUPERALLOY

INCONEL725 is a highly corrosion resistant nickel based alloy capable of being age-hardened to high strength levels. The micro structure observations and the phase identification after a standard heat treatment were investigated. The results show that the precipitation phases include the strengthening phasesγ', γ", and 8 phase, primary carbide phase TiC, as well as M6 C carbide and a little extent MC (mainly TiC) precipitates which nucleate mainly at grain boundaries. An isothermal aging study was carried out on this alloy for up to 10 000 hours at 593℃. This additional aging did not affect the tensile strength. However, micro structures show that the thermal exposure has a little additional effect. With increasing the exposure time, the size of γ" phase slightly increases, almost no change for γ' phase, while M6C carbides precipitated at grain boundaries have an increased and complex tendency on a few grain boundaries. The experimental results illustrate the excellent structure stability of the ag     

含稀土低膨胀高温合金片状沉淀相研究

在Ｆｅ－Ｎｉ－Ｃｏ基低膨胀高温合金中加入微量稀土元素Ｙ,晶内和晶界的片状沉淀相增多,合金对应力加速晶界氧化脆性的抗力和合金的缺口持久性能也获得提高,运用常规透射为微术,会聚束电子显微术和高分辨透射电子显微术研究了该相的晶体结构及其与基体的取向关系。     

Additive layer manufacture of Inconel 625 metal matrix composites,reinforcement material evaluation

While some high performing nickel based superalloys are difficult to process through additive layer manufacturing routes, it is considered that more dilute nickel superalloy (in this case Inconel 625) based metal matrix composite may improve high temperature properties, while retaining good weldability for use in laser melting deposition technologies. In this paper, the effect of 5 wt% additions of 3 differing ceramic reinforcement particles to an Inconel 625 matrix was observed when processed by high powered laser melting, and compared to the processing characteristics of the pure matrix alloy. It was found that while additions of silicon carbide increased material hardness by 130%, levels of porosity and cracking also increased. The addition of aluminium oxide had no appreciable effect upon material hardness, while also compromising the integrity of the material. However additions of titanium carbide resulted in samples of similar density and consistency as the matrix alloy but with 30% increased hardness. However comparison of the width of single laser melted tracks of both Inconel 625 and Inconel 625 with titanium carbide composite indicated a need to further characterise the process window for this proposed MMC system.     

一种新型变形高温合金的组织与性能分析

采用热力学相计算、光学显微镜、扫描电镜、透射电镜及化学相分析等手段研究了一种新型变形高温合金标准热处理状态的基本组织,并通过与Waspaloy合金组织的对比,揭示了这种合金既具有较高的高温蠕变强度,又具有良好的加工性能的内在原因.结果表明,标准热处理状态的实验合金由大小不均匀的等轴晶组成,平均晶粒尺寸约为80 μm.合金中除基体γ外,晶界和晶内还分布着颗粒状的Cr23C6和少量(Ti,Mo)C相;γ′强化相弥散分布于基体中,其平均尺寸约为25 nm,质量分数为16.9%.适当增大固溶强化元素Mo的含量,减少γ′形成元素Al或Ti的含量,可得到既具有较高蠕变强度又具有良好加工性能的镍基变形高温合金.