Inconel 625合金堆焊金属开裂机理研究

针对Inconel 625合金焊接热裂纹问题，文中基于大厚度堆焊裂纹敏感性评价方法对采用GTAW工艺、ERNiCrMo-3焊丝堆焊的金属进行了开裂机理研究.结果表明，堆焊金属的微观组织主要由柱状树枝晶组成，堆焊金属组织中析出相主要有Laves(Ni,Fe,Cr)₂(Nb,Ti,Mo)相、MC型碳化物和针状δ(Ni₃Nb)相.大厚度堆焊金属组织局部存在位于一次枝晶间、沿柱状晶方向的结晶裂纹.在裂纹附近的组织及断口发现存在大量密集分布的δ相，裂纹的形成主要与结晶终了阶段形成的共晶δ(Ni₃Nb)有关.Inconel 625合金堆焊金属存在以共晶Laves、共晶δ分别为终凝析出相的(1)、(2)两种凝固模式.相比较而言，结晶终了阶段发生L→γ+δ共晶反应的模式(2)热裂纹敏感性较大，从而造成Inconel 625合金开裂.创新点：(1)研究了625合金堆焊金属开裂的机理.(2)提出了625合金堆焊金属存在以共晶Laves、共晶δ分别为终凝析出相的两种凝固模式.     

镍基合金焊丝GTAW熔敷金属凝固偏析行为

采用OM,SEM,EDS,EPMA等分析手段对试制的镍基合金焊丝GTAW熔敷金属开展了凝固偏析行为研究.结果表明,熔敷金属中主要包括γ相、（Nb,Ti） C碳化物、Laves相等,金相组织主要为柱状晶,在枝晶间存在宽度约为5~10 μm的偏析区域;按照Scheil公式对EPMA分析结果进行了偏析系数计算,估算的Nb,Mo,Ni,Cr,Fe偏析系数分别为k_Nb=0.23,k_Mo=0.68,k_Ni=1.07,k_Cr=1.05,k_Fe=1.23,在结晶过程中Nb,Mo更倾向于分配在残余液相,Nb的偏析倾向最大,Mo次之,Fe更倾向于分配在固相中,Ni,Cr基本为固液平均分配.文中试验用镍基合金焊丝GTAW熔敷金属凝固结晶路径为L→L+γ→L+γ+MC→L+γ+MC+Laves相→γ+MC+Laves相.     

铸态GH742合金的凝固特点及枝晶偏析

高合金化GH742合金存在严重的枝晶偏析,Nb、Ti大量偏聚于枝晶间,导致MC碳化物、(γ+γ′)共晶、Laves相、δ相等析出;高Mo含量及其枝晶间偏析是析出σ相的重要原因;La、Ce在枝晶间的富集促使含氧硫稀土相和Ni5Ce相的析出。与一般合金凝固特点不同,高含量Al、Ti、Nb导致GH742合金凝固过程中先后发生(γ+γ′)和(γ+Laves)两种类型的共晶反应。结合差热分析技术和凝固组织特点确定了合金的凝固温度区间为1346-1190℃,凝固顺序为γ、MC、(γ+γ′)、Laves、Ni5Ce。     

Si对K325铸造高温合金的凝固行为和拉伸性能的影响

采用扫描电镜、电子探针和差热分析等方法研究Si含量对铸造高温合金K325凝固行为、组织特征和拉伸性能的影响。结果表明:Si添加粗化枝晶、加重Nb元素偏析且偏析程度随Si含量增加呈增大趋势。不含Si合金的凝固路径为L→L+γ→L+γ+MC→γ+MC,铸态相组成为γ+MC。含Si合金的凝固路径为L→L+γ→L+γ+MC→L+γ+MC+γ/Laves→γ+MC+γ/Laves,铸态相组成为γ+MC+γ/Laves。此外,随着Si含量的升高,γ/Laves共晶相的尺寸明显增大且量明显增加,形貌由半连续状向连续致密筛网状和花瓣状转变。固溶处理后含Si合金中的γ/Laves共晶消失,相组成为γ+MC+Laves相,Laves相为具有尖锐棱角的块状。随Si含量增加,块状Laves相含量明显增多,Si含量为1.5%(质量分数)时,形成Laves相团簇区。Si对拉伸强度的影响与Si含量密切相关,小于1.0%的Si对合金抗拉强度无明显影响,然而Si含量为1.5%,抗拉强度明显降低。     

基于原位拉伸的ERNiCrFe-13焊丝熔敷金属断裂机制分析

针对ERNiCrFe-13焊丝熔敷金属拉伸过程中的微观组织演变规律和微裂纹的萌生扩展机制，采用SEM原位拉伸结合扫描电子显微镜(scanning electron microscope,SEM)观察和能谱(energy dispersive spectrometer,EDS)分析对熔敷金属组织及断裂行为等进行分析.结果表明，ERNiCrFe-13焊丝熔敷金属组织主要由柱状晶γ相(NiCrFe固溶体)、枝晶间富Nb和Mo元素的Laves相(Cr,Fe,Ni)₂(Nb,Mo)、MC碳化物与共晶组织组成，Laves相的形成主要与凝固过程中Nb和Mo元素的偏析有关，且具有尺寸效应，水平方向Laves相尺寸大于4μm易发生开裂，断裂机制为枝晶间析出相在切应力作用下本体断裂萌生微裂纹，在轴向拉应力的作用下进一步沿晶界扩展连通至断裂失效，断口呈韧性断裂，碳化物偏析(NbC、TiC)和大尺寸Laves相是晶界裂纹产生的主要原因.     

核电用新型镍基合金焊丝熔敷金属组织研究

采用OM、SEM、EDS等方法针对试制的新型镍基合金焊丝GTAW熔敷金属开展组织、凝固偏析行为等研究,结果表明:1#、2#焊丝熔敷金属金相组织较为相似,主要为柱状晶,在枝晶间存在偏析区域,不同的是2#焊丝熔敷中未发现Laves相+γ共晶组织;Nb、Ta、Mo的初凝平衡分配系数小于1,在结晶过程中更倾向于分配在残余液相,Fe的初凝平衡分配系数大于1,倾向于分配在固相中,Ni、Cr基本为固液平均分配;2#焊丝中Ta加入对各元素的初凝平衡分配系数影响不明显,但对组织有显著影响,避免了低熔点Laves相+γ共晶组织的形成,减小了熔敷金属的结晶温度区间。     

高铬镍基合金熔敷金属的组织和性能

采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等分析手段研究了一种高铬镍基合金焊丝熔敷金属的显微组织和力学性能。结果表明:试验用焊丝熔敷金属显微组织具有明显的柱状枝晶形态;在凝固过程中,除Cr元素外,Fe,Nb,Mo,Si等主要添加元素均表现出明显的偏析行为;γ基体上的析出物主要是TiC和γ/Laves共晶组织,其中TiC呈块状,分布较为均匀,而γ/Laves共晶组织呈层片状,主要分布于枝晶间区域。熔敷金属的强度较高,其冲击断口形貌为典型的韧窝状,在韧窝附近的γ/Laves共晶组织对熔敷金属的塑性和韧性有不良影响。     

一种铸造镍基高温合金的凝固行为

M963合金的凝固顺序为：L→L γ→L （γ‘ MC） γ→（γ γ‘) （γ MC） γ→（γ γ‘） （γ MC） γ γ‘；凝固组织呈树枝状结构，由γ固溶体基体。γ‘析出组及分布在枝晶间区的骨架状MC碳化物和（γ＋γ‘）共晶组成；碳降低合金的液相线温度和（γ＋γ‘）共晶温度，提高MC碳化物的形成温度，增加MC碳化物的体积分数，降低（γ＋γ‘)共晶的体积分数；高熔点元素W和Co在枝晶干偏聚，Al,Ti,Nb,Cr和Mo在枝晶间偏聚。     

GH742y合金凝固偏析行为

采用组织分析和差热分析相结合的方法系统研究GH742y合金的凝固偏析行为和铸态组织形成规律。GH742y合金枝晶偏析严重,组织析出复杂:Cr、Co、W、V和Al偏析于枝晶干,而Nb、Ti和Mo等元素在枝晶间的富集导致一次和二次γ′相、(γ γ′)共晶、MC碳化物、M6C碳化物、Laves相和δ相的析出;稀土元素La和Ce的偏析导致Ni5Ce相和富氧硫稀土相的枝晶间析出。相分计算表明,严重的元素偏析以及大量富Nb和Ti相的析出是σ相和μ相等有害TCP相析出的主要原因。GH742y合金的凝固顺序为:γ基体、MC碳化物、一次γ′相、(γ γ′)共晶、Laves相、Ni5Ce相和M6C碳化物。     

一种新型镍铁基焊丝熔敷金属组织及性能研究

对一种700℃先进超超临界锅炉用新型镍铁基高温合金焊丝熔敷金属进行了研究。根据热力学模拟计算,其热力学稳态相包括γ基体、γ'、Ti C、硼化物、M23C6相。根据模拟计算的熔敷金属连续冷却转变曲线和等温转变曲线,结合热物性分析,存在少量γ'相在冷却过程中形核。对焊丝钨极氩弧焊的熔敷金属进行表征,结果表明:凝固过程中由于C、Ti元素强烈向枝晶间偏析,导致凝固末期在枝晶间形成了一次Ti C相,其他合金元素则无显著偏析,且焊丝熔敷金属中并无有害相析出。焊丝熔敷金属室温及高温力学性能较好,且相对较低的热膨胀系数能降低结晶裂纹的敏感性。     

Effect of Phosphorus on Solidification Behavior of IN783 Alloy

Phosphorus plays an important role in the solidification, segregation and as-cast microstructure of superalloys. In order to control the as-cast microstructure and homogenization of IN783 alloy, the effect of phosphorus on the as-cast microstructure and the solidification sequence of IN783 alloy was investigated and analyzed. The as-cast microstructure of IN783 alloy is constituted by γ matrix mainly located in dendrite core and segregation zone, together with β phase, blocky Laves phase and P-enriched phas...     

Element Segregation and Solidification Behavior of a Nb,Ti, Al Co-Strengthened Superalloy ЭК151

The as-cast microstructure, element segregation and solidification behavior of a multi-alloyed superalloy ЭК151 have been investigated. The results show that the severe element segregation leads to the complicated precipitations at the inter-dendritic region, including η-Ni_3(Ti, Nb), eutectic(γ + γ') and Laves, which shows the characteristics of both Ti, Al-strengthened and Nb-strengthened alloys. Differential thermal analysis, heating and quenching tests reveal the solidification sequence as follows: Liquids →γ matrix →(Nb, Ti)C →η-Ni 3(Ti, Nb) →eutectic( γ+γ') → Laves. The melting points are between 1250 and 1260 °C for(Nb, Ti)C, between 1200 and 1210 °C for η phase, between 1180 and 1190 °C for eutectic(γ+γ') and Laves. γ' initially precipitates from matrix at 1150 °C and achieves the maximum precipitation at 1130 °C. According to the microstructure evolution captured during solidification and composition analysis by an energy dispersive spectrometer and electron probe microanalyzer,(Nb, Ti)/Al ratio is put forward to explain the formation of η-Ni_3(Ti, Nb) and eutectic( γ+γ'). The solidification of γ matrix increased the Nb, Ti concentration in the residual liquids, so the high(Nb, Ti)/Al ratio would result in the formation of η-Ni_3(Ti, Nb); the precipitation of the phase consumed Nb and Ti and decreased the(Nb, Ti)/Al ratio in the liquid, which led to the precipitation of eutectic(γ + γ'). Laves formed by the sides of η-Ni_3(Ti, Nb) and in front of the eutectic( γ + γ') after Al, Ti were further depleted by the two phases and Cr, Co, Mo were rejected to liquids.     

一种核电用镍基合金焊丝熔敷金属的组织与性能

通过采用JMatPro软件，OM，SEM，TEM等手段分析了试制镍基合金焊丝GTAW熔敷金属的组织与力学性能. 结果表明:试验焊丝熔敷金属金相组织主要由柱状树枝晶γ相(NiCrFe固溶体)、枝晶间富Mo和Nb的偏析γ相以及枝晶间分布的(Nb,Ti)C碳化物、(Ni,Cr,Fe)₂(Nb,Mo)型Laves相、MoCrFe型σ相等组成. Mo，Nb等元素在组织中存在偏析现象，相比于焊丝化学成分，熔敷金属中枝晶干γ相Fe含量较高，Mo，Nb含量较低，而枝晶间Mo，Nb含量较高、Fe含量较低. 熔敷金属室温、350 ℃高温抗拉及屈服强度较高、塑性较好，室温拉伸断口形貌以沿晶分布的韧窝为主，在韧窝底部存在密集的析出相.     

Solidification behavior of Pt-containing 718Plus superalloy

Solidification behaviors of Pt-containing 718Plus superalloyswere studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), differential scanning calorimetry (DSC) and simulation calculations. It is found that Pt increases solidification range and decreases solidus temperature of the alloy and precipitation temperature of Laves + γ eutectic phase since Pt enlarges the region of γ phase by increasing Nb solubility. In addition, Pt segregates to the interdendritic region and increases the segregation of Nb and Tiin the interdendriticregion due to the strong attractive interactions between Pt and Nb/Ti. As a result, Pt promotes the precipitation of the Laves + γ eutectic phase and η phase around eutectic phase. The increase of solidification range and segregation degrees of Nb and Al caused by Pt also promotes the precipitation and growth of γ’ + γ” phase around eutectic phase. These results provide experimental bases for understanding the mechanism of Pt in solidification behavior of superalloys.     

Microstructure－properties relationship of transient liquid phase diffusion bonded a third generation single crystal superalloy joint

Microstructure of transient liquid phase( TLP) diffusion bonded a third generation single crystal superalloy joint was investigated using scanning electron microscopy( SEM),and mechanical properties test of joint was carried out,for obtaining relationship between microstructure and mechanical properties of joint. The results showed that the joint contained bonding zone and base metal. The diffusion zone was obviously observed. When it was not finished for isothermal solidification process,the bonding zone would contain isothermal solidification zone and rapid solidification zone. Metallographic examination revealed that isothermal solidification zone was consisted of γ and γ' phase. Rapid solidification zone was consisted of two different structures,which were ternary eutectic of borides,γ and γ' phase developing at the edge of joint,binary eutectic of γ and γ' phase appearing in the portion of joint. When it was not enough for homogenization process under the condition of finishing isothermal solidification process,the bonding zone would contain isothermal solidification zone and borides at the interface. Under the conditions of relatively high welding temperature and long welding time,average tensile strength of joint was equivalent to that of parent material.     

Microstructure characteristics of Ni-43Ti-4Al-2Nb-2Hf alloy prepared by conventional casting and directional solidification

To further investigate the microstructure characteristic and solidification mechanism,so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material,t...     

Influence of Gd and B on solidification behaviour and weldability of Ni–Cr–Mo alloy

Abstract

The influence of Gd and B on the solidification behaviour and weldability of Ni–Cr–Mo alloy UNS N06455 has been investigated by Varestraint testing, differential thermal analysis and microstructural characterisation. These alloys are currently being developed as structural materials for nuclear criticality control in applications requiring transportation and disposition of spent nuclear fuel owned by the US Department of Energy. The Gd containing alloys were observed to solidify in a manner similar to a binary eutectic system. Solidification initiated with a primary L→y reaction and terminated at ~1258°C with a eutectic type L→y+Ni₅Gd reaction. The solidification cracking susceptibility of the Gd containing alloys reached a maximum at ~1 wt-%Gd and decreased with both higher and lower Gd additions. Low cracking susceptibility at Gd concentrations below ~1 wt-% was attributed to a relatively small amount of terminal liquid that existed over much of the crack susceptible solid+liquid zone. Low cracking susceptibility at Gd concentrations above ~1 wt-% was attributed to a reduced solidification temperature range and backfilling of solidification cracks. The addition of B above the 230 ppm level leads to the formation of an additional eutectic type reaction at ~1200°C and the secondary phase within the eutectic type constituent was tentatively identified as Mo₃B₂. The B containing alloys exhibited a three step solidification reaction sequence consisting of primary L→y solidification, followed by the eutectic type L→y+Ni₅Gd reaction, followed by the terminal eutectic type L→y+Mo₃B₂ reaction. Boron additions had a strong, deleterious influence on solidification cracking susceptibility. The high cracking susceptibility was attributed to extension of the crack susceptible solid+liquid zone induced by the additional eutectic type L→y+Mo₃B₂ reaction and extensive wetting of the grain boundaries by the solute rich liquid. Simple heat flow equations were combined with solidification theory to develop a relation between the fraction liquid f _L and distance x within the solid+liquid zone. Information on the phenomenology of crack formation in the Varestraint test were coupled with the calculated f _L–x curves and were shown to provide useful insight into composition–solidification–weldability relations.     

磷硼复合添加对Inconel 718合金铸态组织及均匀化处理参数的影响(英文)

研究磷硼复合添加对Inconel 718高温合金铸态组织及均匀化处理参数的影响。结果表明:磷硼的加入促进块状Laves相的形成。由于硼在最后残余液相中大量富集,形成一种富含Nb、Mo和Cr的含硼相。根据DSC和电子探针分析结果,确定磷硼复合添加Inconel 718高温合金的凝固顺序为L→L+γ→L+γ+MC→L+γ+MC+Laves→γ+MC+Laves+含硼相。由于低熔点含硼相的存在,磷硼复合添加Inconel 718高温合金的均匀化处理温度应比标准Inconel 718合金低至少40°C。