单晶高温合金DD6表面渗碳处理组织研究

对单晶高温合金DD6进行表面渗碳处理,采用SEM、TEM研究了DD6合金渗碳层组织,运用EDS与SAD分析了渗碳层内碳化物的类型。结果表明,表面渗碳处理后,在渗碳层γ相内析出大量细小的MC型碳化物,与合金名义成分相比,其化学成分富含铌、钽和钼,而铝和镍含量较低。该碳化物呈块状析出,尺寸约为0.1μm,弥散分布在渗碳层区域内。由于碳化物的析出,渗碳层区域内的γ′相不能保持完整的立方化形态。渗碳处理温度越高,渗碳层深度越大。MC碳化物与基体γ相之间存在[001]MC∥[001]γ,(200)MC∥(200)γ的晶体学取向关系。     

第二代单晶高温合金DD6的拉伸性能

研究了低成本的第二代单晶高温合金DD6的拉伸性能.结果表明[001]取向DD6合金的屈服强度与国外实际应用的第二代单晶高温合金的屈服强度相当;室温至760℃,DD6合金的屈服强度基本相同;在760～850℃范围内,随着温度升高,屈服强度提高;850℃时,合金的屈服强度达到最大值,即1030 MPa;当温度超过850℃后,随着温度的升高,DD6合金的屈服强度显著降低.     

第二代单晶高温合金DD6的薄壁持久性能

采用薄壁试样研究了760℃、980℃、1070℃条件下第二代单晶高温合金DD6的持久性能.结果表明与标准试样的持久应力-寿命曲线相比,DD6合金760℃薄壁持久性能高,980℃薄壁持久性能先高后低,1070℃薄壁持久性能略低;760℃、980℃和1070℃条件下,与标准试样相比,薄壁试样持久寿命随应力降低而增加的速度较慢.     

单晶高温合金DD6不同状态下的显微组织和力学性能

研究了低成本的第二代单晶高温合金DD6在铸态、固溶处理状态和完全热处理状态的显微组织、拉伸性能和持久性能.结果表明在铸态、固溶处理和完全热处理三种状态中,完全热处理状态下DD6合金拉伸强度和持久寿命最高,分别为铸态的1.1倍和2.5～3倍;采用适当的热处理工艺可提高DD6合金中γ'相的数量,改善γ'相的尺寸和分布,显著提高合金的综合力学性能.     

DD15单晶高温合金持久性能各向异性

研究了[001]、[011]和[111]3种不同取向的DD15单晶高温合金的热处理组织、980 ℃/300 MPa和1 150℃/120MPa的持久性能、持久断口和断裂组织.结果表明在与定向凝固方向垂直的截面上,3种取向合金具有明显不同的热处理组织形貌,γ'相的形状分别为规则的正方形、矩形和多边形.合金在980℃/30...     

氢化物发生-原子荧光光谱法测定DD6单晶镍基高温合金中砷

DD6单晶镍基高温合金中含有Ta、Re、W等合金元素,因此样品溶解较为困难,得到的样品溶液也不稳定。实验采用盐酸-硝酸体系溶解样品,以镍基体匹配法绘制校准曲线克服了基体镍的干扰,实现了氢化物发生-原子荧光光谱法对DD6单晶镍基高温合金样品中As含量的测定。对溶样方法进行了探讨,结果表明,采用20mL盐酸-5mL硝酸、加热(100℃左右)溶解样品后,虽然会有少量不溶物存在,但待测元素As已完全溶出,即不溶物中未夹带元素As,因此实验选择该溶样方法进行溶样。对仪器的负高压、灯电流进行了优化试验,确定负高压为280V,灯电流为60mA。根据样品中镍的含量,分别采用无基体匹配和镍基体匹配法建立校准曲线,结果表明,对于同样质量浓度的As标准溶液,有基体镍存在时的测定结果均较无基体镍时明显偏低,说明镍基体的干扰对测定不可忽略,故实验采用镍基体匹配法绘制校准曲线。方法线性范围为0.00005%~0.001%,方法检出限为2×10^-5μg/mL。按实验方法对6个DD6单晶镍基高温合金样品进行测定,测得结果与高流速辉光放电质谱法基本一致,测得结果的相对标准偏差(RSD,n=8)为2.3%~8.7%。     

铼对单晶高温合金DD32组织的影响

采用SEM、XRD以及金相显微镜等分析技术研究了单晶高温合金组织对铼的响应行为.研究结果表明铼对单晶高温合金的枝晶组织和γ'相形态都有显著影响.在相同工艺条件下,含铼单晶合金的一次和二次枝晶间距都大于无铼单晶合金,无铼单晶合金的枝晶生长非常发达,具有三次枝晶.经同样热处理后,含铼单晶合金的γ'相形态较无铼单晶合金更规则.     

长期时效对DD407单晶高温合金组织和中温性能的影响

研究了DD407单晶高温合金在900℃长期无应力时效过程中,组织的演变规律及其对中温性能的影响。研究结果表明：经长达3 000 h的时效后,合金的组织稳定,无有害相析出,7 6 0℃中温强度稳定,但伸长率显著提高。     

电场对DD3单晶高温合金显微偏析的影响

研究了直流电场对DD3单晶高温合金凝固显微偏析的影响.实验结果表明在定向凝固速度为5μm/s和电流密度为0～20 A/cm2的条件下,随电流密度增大,胞晶或树枝晶间距减小.与不施加电场时相比,电流密度为6A/cm2时,凝固偏析明显减轻;电流密度为20A/cm2时,凝固偏析恶化.DD3单晶高温合金定向凝固过程中,由于电场的加入,引起溶质有效再分配系数的变化,减轻了凝固偏析;胞晶或树枝晶间距减小,也有利于减轻凝固偏析;胞晶间的原子团簇向胞晶侧面集聚,造成凝固偏析增大.上述因素共同作用决定了最终凝固组织的偏析.     

1070℃热暴露对一种单晶高温合金组织的影响

研究了一种镍基单晶高温合金在1 070℃热暴露不同时间后的组织变化。结果表明:合金的热处理组织由立方化较好γ'相和基体γ相组成。经过1 070℃热暴露处理后,γ相基体通道宽度增加,γ'强化相合并长大;热暴露200 h后,合金没有析出不稳定相(TCP相)。热暴露400 h后,少量TCP相开始在枝晶干区域以细针状的形态析出。经过800 h处理后,显微组织呈现出明显的筏排结构。随热暴露时间增加TCP相析出量明显增多,并由枝晶干范围向枝晶间区域生长。TCP相含有Re、W、Mo和Co等合金元素,衍射分析为σ相,与合金基体取向关系为(110)_σ∥(220)_γ,[012]_σ∥[001]_γ。     

Effects of Dendritic Orientation on Stress Rupture Properties of DD6 Single Crystal Superalloy

 DD6 single crystal superalloy slabs were prepared with seed method in the directionally solidified furnace with high temperature gradient. The transverse stress rupture properties and fracture behaviour of the alloy at 760 ℃/758 MPa, 850 ℃/550 MPa and 980 ℃/250 MPa were investigated and compared with those of longitudinal specimens. The transverse stress rupture lives are corresponding with the longitudinal stress rupture lives at 760 ℃/758 MPa and 850 ℃/550 MPa. The transverse stress rupture lives are slightly less than the longitudinal stress rupture lives at 980 ℃/250 MPa. The fracture mechanism of the transverse stress rupture of the alloy at 760 ℃/758 MPa shows quasi-cleavage mode and the fracture mechanism at 980 ℃/250 MPa shows dimple mode, while the fracture mechanism at 850 ℃/550 MPa shows quasi-cleavage and dimple mixture mode. At higher temperature and lower stress, the microcracks are easier to initiate and interconnect in the transverse specimen than those in longitudinal specimen because there are interdendritic regions perpendicular to the axis of stress.     

Effect of Hf on Stress Rupture Properties of DD6 Single Crystal Superalloy After Long Term Aging

 The specimens of the second generation single crystal superalloy DD6 with different Hf contents were prepared in the directionally solidified furnace with a high temperature gradient. The long term aging of the specimens after full heat treatment was performed at 1040 ℃ for 800 h. The effect of Hf on the microstructure and stress rupture properties under 980 ℃/250 MPa of the alloy after long term aging was investigated. The results show that the γ′ coarsening and rafting and no topologically close packed phase (TCP) are observed in the microstructures of DD6 alloy with different Hf contents after aged at 1040 ℃ for 800 h. It indicates that DD6 alloy with different Hf contents all possesses good microstructure stability. With increasing Hf content the rupture life after long term aging turns shorter and the elongation represents the increasing first and decreasing afterwards. The fracture mechanism of the alloy with different Hf contents at 980 ℃/250 MPa all shows dimple model. The influence of the microstructures on the stress rupture properties of the alloy is also discussed.     

Influence of yttrium addition on high temperature oxidation resistance of single crystal superalloy

Two experimental single crystal superalloys Y-free alloy and Y-containing alloy were cast in the directionally solidified furnace, while other alloying element contents were basically kept unchanged. T...     

一种单晶合金的高温蠕变行为及其变形特征

通过测定一种单晶镍基合金的高温拉伸蠕变曲线及位错运动的内摩擦应力σ0,建立了综合蠕变方程,计算出稳态蠕变期间的表观蠕变激活能及相关参数.结果表明：在蠕变期间,位错运动的内摩擦应力σ0,随外加应力的提高略有提高,随温度的升高而明显降低.蠕变后期,由于缩径使样品不同位置承受不同的有效的应力,导致筏状γ＇相具有不同的粗化特征,在近断口处,载荷的有效应力增大,使筏状γ＇相扭曲且粗化加剧.界面位错网对形变硬化和回复软化具有协调作用,并减缓位错切入γ＇相,因此有利于合金蠕变抗力的提高.     

基于微观参数的镍基单晶合金CMSX-4蠕变寿命预测

摘要：对变截面CMSX-4试样进行了不同温度下的蠕变试验,对比研究了不同应力处的微观组织筏化情况。结果表明：CMSX-4在温度和应力较低时筏化速率极慢,而在温度和应力较高时会快速完成筏化,在合适的温度和应力范围内γ相通道宽度会与材料损伤程度有显著的关联。基于相关结果,提出了一种以γ相通道宽度预测镍基单晶合金CMSX-4剩余蠕变寿命有效方法,通过对比本试验和其他相关报道的结果,本方法的预测结果分散性较小,均位于±1.5倍分散带内。     

金相分析法标定铸态镍基单晶高温合金晶体取向

摘要：精确标定晶体取向对镍基单晶高温合金的制备与应用具有重要意义,研究了金相观察结合定向切割的金相分析法标定铸态镍基单晶高温合金晶体学方向的原理及标定误差。结果表明,采用3次金相观察结合定向切割可以精确标定任意形状的铸态镍基单晶高温合金试样的晶体学方向。EBSD测定和显微组织分析验证了金相分析法标定单晶取向偏差在2°以内,并分析了引起标定误差的主要原因。     

Surface recrystallization of a single crystal nickel-base superalloy

The recrystallization behavior of a single crystal nickel-base superalloy was investigated by shot peening and subsequent annealing. Two kinds of recrystallization microstructures, which are intensively dependent on the annealing temperature, are shown in the nickel-base superalloy after shot peening and subsequent annealing. Surface recrystallized grains are obtained when the superalloy is anparticles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the shot-peened alloy annealed at 1050℃ accords with the Johnson-Mehl-Avrami-Kolmogorov equation. The low Avrami exponent is caused by the inhomogeneous distribution of stored energy, the decreasing of stored energy during recovery, and the strong resistance of boundary migration yb γ' particles.