Effect of Phosphorus on Microstructure and High Temperature Properties of a Cast Ni—base Superalloy

Effect of phosphorus on the microstructure and high temperature properties of a cast Ni-base superalloy M963 has been investigated.SEM observation and EDS analysis showed that P was mostly enriched in the interdendritic region,and the P-rich phase was formed in the front position of finally solidified eutectics in high P doped alloys.It was found that the P-rich phase,as preferred initiation and propagation site of cracks,could aggravate the fracture process at high temperature in high P doped alloys.Consequently,high P addition would reduce remarkably the ductility and creep life of M963 superalloy at high temperature.     

Transient Liquid Phase Bonding of Ni—base Single Crystal Superalloy

The Ni-base single crystal superalloy was bonded by the transient liquid phase(TLP) bonding,using a Ni-base flexible metal cloth as an insert alloy.TLP bonding of superalloy was carried out at 1473-1523K for 0.5-24h in vacuum.The [001] orientation of each test specimen was aligned perpendicular to the joint interface.The bonded region was observed by optical microscopy, and the microstructural and compositional analyses across the bonded interlayer were performed by using a scanning electron microscopy(SEM) .The electron back scattering diffraction(EBSD) method was applied to determine the crystallographic orientation.The resultsindicated that the chemical homogeneity across the bonded region can be achieved,and γˊphase both in the bonded interlayer and in the superalloy substrate is almost identical,while the bonded interlayer had almost matched the crystallographic orientation of the bonded substrates.     

Antiphase Boundary Strengthening in a Single Crystal Nickel—base Superalloy

An investigation has been made into strengthening mechanism in a single crystal nickel-base superalloy DD8 by transmission electron microscopy. The results show that the stress rupture strength of the alloy increases with decreasing misfit, and the antiphase boundaries (APBs) formed in the ordered γ' phase, rather than the misfits, play a dominate role in strengthening of the single crystal Ni-base superalloy DD8. There are three kinds of mechanisms for forming the APBs which were observed in the present materials. One is mis-arrangement of the local ordered atoms in the γ' precipitates due to the local strain; the second arises from the 1/2<110> dislocations cutting into the γ', and the third is the formation of the APBs induced by the 1/2<110> matrix dislocation network. The contribution of the antiphase boundary energy to the strength of the alloy can be expressed by: where τ is the resistance to deformation provided by the APB energy; S is the long-range order degree in γ'; Tc is the transition     

Effect of Phosphorus on Stress Rupture Properties of GH4133 Ni—Base Superalloy

The effect of phosphorus on the stress rupture property of GH4133 alloy has been investigated and is compared with that of IN718 alloy. The GH4133 alloy is crept by dislocation movement. Phosphorus has a tendency to prolong the rupture life of some wrought superalloys by inhibiting the dislocation movement. If the phosphorus addition is too high, its effect on impairing the grain boundary cohesion overwhelms that on inhibiting the dislocation movement,and the life of the GH4133 alloy can be shortened. The two functions of inhibiting the dislocation movement and impairing the grain boundary cohesion determine that the optimum phosphorus content in the GH4133 alloy is around 0.011 wt pct. Phosphorus exhibits a greater effect on prolonging the rupture life of IN718 alloy than that of GH4133 alloy. The two alloys are crept by different mechanisms. The intergranular phosphorus-bearing phase is precipitated in the IN718 alloy, while not in the GH4133 alloy. The precipitation of the phosphorus bearing phase can balance the phosphorus segregation at the grain boundaries and allows a more remarkable effect of phosphorus on extending the rupture life of IN718 alloy.     

K417G合金的环境致脆磨损机理

采用可控气氛磨损试验机测试含有Ni3Al相的K417 G合金在不同相对湿度空气、真空、氧气、氮气、二氧化碳、氢气和氩气下的摩擦磨损性能,用SEM观察磨损表面形貌,基于线弹性力学计算表面裂纹应力强度因子K1,依据能量学计算合金元素的环境敏感性,研究合金的环境致脆磨损机理.结果 表明:磨损工况下,高相对湿度空气中的水蒸汽是...     

直流电场作用对K 41 7G镍基高温合金凝固组织的影响

研究了直流电场作用下K417G镍基高温合金凝固组织的变化。实验结果表明：电场作用改变了枝晶组织的生长形态和碳化物的形貌,并引起了凝固组织择优生长取向的变化及第二相的分布和形态的变化。提出了电场作用造成上述结果的机理。     

n-Al2O3/Ni复合电刷镀层的接触疲劳行为

为研究纳米颗粒复合电刷镀层的接触疲劳行为,通过在镍盐溶液中加入纳米氧化铝(n-Al2O3)颗粒,采用电刷镀技术制备了含n-Al2O3颗粒的镍基复合镀层(n-Al2O3/Ni),采用接触疲劳试验机评价了镀态和热处理态的n-Al2O3/Ni复合镀层的抗接触疲劳性能,并与纯镍刷镀层进行了性能对比.借助SEM和TEM对复合刷镀层的组织进行了分析,探讨了复合刷镀层的接触疲劳失效过程以及纳米颗粒等对刷镀层疲劳失效过程的影响.研究表明:n-Al2O3/Ni复合镀层在镀态下的接触疲劳寿命超过100万周次,明显高于纯镍镀层;退火后n-Al2O3/Ni复合镀层接触疲劳寿命为45.9万次,为纯镍镀层的1.62倍;复合镀层的接触疲劳失效过程分为裂纹萌生、裂纹扩展和镀层断裂3个阶段;纳米颗粒在复合镀层接触疲劳失效过程中起到阻碍位错滑移的作用,从而抑制塑性变形和裂纹扩展,使复合镀层具有较高的接触疲劳寿命.     

镍基高温合金K417热机械疲劳行为

主要研究了Ｋ４１７高温合金在不同实验条件下的热机械疲劳（ＴＭＦ）行为。在计算机辅助控制伺服液压疲劳实验机上进行了同相和反相热机械疲劳实验。实验结果表明，与等温低周疲劳性能相比较，无论是同相和反相的热机械疲劳均使寿命大大降低，不同相位对ＴＭＦ性能产生不同的影响，此外，对于热机械疲劳过程中的塑性应变分量中的时间相关相（蠕变）和非时间相关相（纯塑性变形）应当分别进行考虑，这样才能对该合金的热机械疲劳行为有更加准确的认识。最后用ＳＥＭ对不同试验条件下的断口进行了详细观察，并对其微观断裂机制进行了分析和探讨。     

Investigation of Solidification and Segregation Characteristics of Cast Ni-Base Superalloy K417G

Differential scanning calorimetry(DSC) analysis, isothermal solidification experiment and Thermo-Calc simulation were employed to investigate solidification characteristics of K417 G Ni-base superalloy. Electron probe microanalysis(EPMA) was employed to analyze the segregation characteristics. Liquidus,solidus and the formation temperatures of main phases were measured. In the process of solidification,the volume fraction of liquid dropped dramatically in the initial stage, while the dropping rate became very low in the final stage due to severe segregation of positive segregation elements into the residual liquid. The solidification began with the formation of primary γ. Then with solidification proceeding, Ti and Mo were enriched in the liquid interdendrite, which resulted in the precipitation of MC carbides in the interdendrite. Al accumulated into liquid at the initial stage, but gathered to solid later due to the precipitation of γ/γ’ eutectic at the intermediate stage of solidification. However, Co tended to segregate toward the solid phase. In the case of K417 G alloy, combining DSC analysis and isothermal solidification experiment is a good way to investigate the solidification characteristics. Thermo-Calc simulation can serve as reference to investigate K417 G alloy.     

Tensile and Fracture Behavior of DZ68 Ni-base Superalloy

The tensile and fracture behavior of DZ68 directionally solidified Ni-base superalloy was studied in the temperature range of room temperature (RT) to 1000°C. The fracture mode was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show the tensile strength and yield strength of DZ68 alloy increase slightly with increasing temperature, so that at 760°C its reach maxima value: 1214 and 1019 MPa, respectively. When the experimental temperature is higher than...     

The Influence of Superimposed Creep Loadings on the Thermal-Mechanical Fatigue Behaviour of the Ni-Base Superalloy IN 792 CC

The effect of superimposed creep loadings on the cyclic deformation andthe lifetime behaviour of the Ni-base superalloy IN 792 CC underout-of-phase TMF loadings is presented and discussed. The mean stressand the stress amplitude are not affected significantly by the creeploading. A slight cyclic hardening is observed even for cycles withsuperimposed creep loadings at a maximum temperature of 920°C whichmeans that the work hardening processes occurring under TMF loading arenot fully compensated by recovery during the creep phase. The plasticstrain amplitude increases with increasing creep stress. Using theManson–Coffin relationship, it is possible to calculate the influence ofthe superimposed creep loadings on the lifetime behaviour in goodaccordance with the experimental results.     

高Cr铸造镍基高温合金K4648的母合金净度研究

对两炉冲击韧性存在明显差异的高Cr铸造镍基高温合金K4648进行了对比研究,通过分析两炉母合金的主量元素和气体含量,采用电子束纽扣锭(EB锭)实验观察合金内夹杂物和对母合金用原材料金属Cr的显微组织分析等方法研究了K4648母合金净度.结果表明:1 #与2#炉批母合金主量元素无明显差别.1 #母合金由于气体元素O含量高达(20.5±7.5)×10-6,远高于2#合金的6×10-6,造成其室温冲击韧性(aku)不及2#合金的一半,低于技术条件要求的19.6J/cm2.电子束纽扣锭(EB锭)实验可有效地将K4648中的夹杂物汇聚,经分析主要是富Y,Ce的氧化物和富Al氧化物.证明高Cr铸造镍基高温     

Thermomechanical Fatigue Behaviour of a Nickel Base Superalloy

The isothermal low cycle fatigue (LCF)and thermomechanical fatigue (TMF) behaviourof a Ni-base superalloy was investigated. Theresults show that temperature plays an importantrole in both LCF and TMF. The alloy shows thelowest LCF fatigue resistance in the intermediatetemperature range (～760℃). For strain-controlledTMF, in-phase (IP) cycling is more damagingthan out-phase (OP) cycling. The high tempera-ture exposure in the TMF cycling influencesthe deformation behaviour at the low temperature.LCF lives at different temperatures, and IPand OP TMF lives are successfully correlatedby using the hysteresis parameter Δσ·Δε_p.     

C和B的含量对K417G镍基高温合金的凝固行为和高温持久性能的影响

对不同C、B含量的K417G合金进行DTA分析、等温淬火实验和950℃/235 MPa持久性能测试,并观察其组织形貌,研究了C、B含量对K417G镍基高温合金的凝固行为和高温持久性能的影响.结果 表明,在合金的凝固期间C含量影响碳化物的析出温度和初生碳化物的含量,且随着C含量的提高而提高;共晶组织的析出温度主要受B元素...     

直流电位法检测高温合金的疲劳裂纹扩展性能

介绍了在高温下使用直流电位法测定疲劳裂纹长度的基本原理、试验方法及所需配置的仪器,并对有关影响因素进行了分析;并利用Johnson的分析型关系式,研究了一种适用于自动测定材料高温疲劳裂纹长度的直流电位法,该方法已成功应用于高温合金疲劳裂纹扩展试验,其测得的疲劳裂纹扩展速率da/dN-ΔK数据与长焦聚显微镜法测得的数据完全一致。     

应变比对定向凝固高温合金DZ125低循环疲劳行为影响的研究

对定向凝固镍基高温合金DZ125在850℃和980℃应变控制的低循环疲劳(LCF)行为进行研究。对比分析应变比R=-1和R=0情况下的应力-应变迟滞环、循环平均应力以及断裂循环次数(寿命)的差异。结果表明:在所研究的两个温度水平下,相同应变范围条件下应变比R=-1和R=0的低循环疲劳寿命差别不大。利用扫描电子显微镜对不同应变比作用的试样断口进行观测,初步分析裂纹萌生机理。