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℃/120 MPa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℃/300 MPa和1 150℃/120 MPa条件下的持久性能呈现各向异性。合金在2种条件下的持久寿命都按[011]、[001]、[111]取向的顺序增加,伸长率按[111]、[011]、[001]取向的顺序升高。随着试验温度的降低,合金持久各向异性增强。在980℃/300 MPa条件下,[001]和[111]合金持久呈现韧窝断裂特征,而[011]合金持久呈现类解理与韧窝混合断裂特征;在1 150℃/120 MPa条件下,不同取向合金持久都呈现韧窝断裂特征。不同取向合金断裂后的γ′相具有明显不同的形貌或筏排化程度。[001]取向合金的γ′相筏排与应力轴方向垂直,而[011]和[111]取向合金的γ′相筏排与应力轴呈一定夹角,筏排化程度按[011]、[001]和[111]的顺序增加。     

980℃/230 MPa下IC6SX单晶合金蠕变行为的各向异性研究

研究了[001]和[111]不同取向的IC6SX单晶合金在980℃/230MPa下的蠕变性能,探明了蠕变性能与取向的相关性,研究了蠕变组织的演变,确定了合金蠕变断裂机制.不同取向IC6SX单晶合金的蠕变性能研究表明:单晶合金的蠕变寿命存在显著的各向异性.在980℃/230MPa条件下,[001]和[111]取向的蠕变寿...     

一种单晶高温合金的组织和持久性能

研究了一种第二代单晶高温合金的显微组织和不同条件下的持久性能.研究结果表明合金铸态组织由γ相、γ′相和共晶相组成.完全热处理后,无共晶和初熔,γ′相立方化较好.合金不同条件下持久性能良好.在760 ℃/800 MPa条件下持久断裂为类解理断裂,而合金980 ℃/250 MPa、1 100 ℃/140 MPa的高温持久断裂显示出韧窝断裂特征.持久断裂组织分析表明,在760 ℃/800 MPa条件下,γ′相仍保持立方状.在980 ℃/250 MPa条件下,γ′相发生筏排化.在1 100 ℃/140 MPa条件下,γ′相筏排化更严重.      

涂层扩散热处理工艺对DD6单晶高温合金组织和力学性能的影响

研究了870℃/6 h涂层扩散热处理工艺对第二代镍基DD6单晶高温合金(简称DD6合金)组织和性能的影响。研究结果表明,采用870℃/6 h涂层扩散热处理工艺处理后,DD6合金的显微组织、760℃拉伸性能、980℃/250 MPa持久性能、700℃高周疲劳性能无明显变化。DD6合金760℃拉伸断裂类型为准解理断裂,980℃/250 MPa持久断裂类型为韧窝断裂,700℃高周疲劳断裂类型为准解理断裂。涂层扩散处理没有改变DD6合金的断裂机制。     

喷砂处理对定向凝固镍基高温合金DZ406组织及持久性能的影响

对定向凝固镍基高温合金DZ406分别进行强度为0.3MPa、0.5MPa的1min表面喷砂,研究喷砂对合金组织及980℃/275MPa持久性能的影响。结果表明,不同强度喷砂处理后的合金表面均存在变形层。喷砂明显降低DZ406合金980℃/275MPa的持久性能,且随喷砂强度的增加而进一步下降。喷砂后的合金在随后的热处理及持久过程中产生了再结晶层,再结晶晶粒均为等轴状,且厚度随喷砂强度的增大而增加。喷砂导致合金产生的再结晶横向晶界在持久过程中成为裂纹萌生区,是造成DZ406合金持久性能降低的主要原因。     

固溶处理对DSM11合金显微组织和力学性能的影响

研究了固溶处理制度对DSM11合金组织和性能的影响.结果表明,固溶热处理可明显降低合金元素的偏析,减少枝晶组织偏析及共晶数量,提高γ'相的尺寸均匀性.随着固溶处理温度的提高,该合金室温和980℃的拉伸性能变化不大,但816℃、483 MPa和980℃、190 MPa下固溶处理后合金的持久寿命显著提高.     

循环热处理对定向凝固DZ417G高温合金组织和力学性能的影响

研究了镍基定向凝固高温合金DZ417G经多次循环热处理后的微观组织、力学性能和断裂方式的变化规律.随着循环热处理次数的增加,基体上较大的γ'强化相的数量降低,弥散的γ'相间距减小,合金室温硬度随之提高,900℃抗拉强度略微增大,拉伸塑性在3次循环热处理后有所下降.合金在980℃、216 MPa条件下的持久寿命随循环热处理次数的增加而延长,但循环热处理超过4次后,合金的持久寿命迅速下降.     

Re对耐腐蚀镍基定向高温合金组织及持久寿命的影响

优化设计了4种不同Re含量的耐腐蚀定向镍基高温合金,含Re分别为0%,1%,2%和3%(质量分数)。对比了不同Re含量合金的铸态枝晶、γ’相形貌及持久性能试样的断口筏排化组织,测试了不同Re含量合金热处理态的980℃/200 MPa持久寿命,研究了Re对耐腐蚀镍基定向合金组织及持久寿命的影响。研究表明:随着Re含量的增加,合金的一次枝晶间距减小;γ’相尺寸减小,立方化程度增加;蠕变试样的筏排组织更加细化、完善与稳定,因此,合金持久寿命提高。     

热处理工艺对真空冶炼GH871合金性能的影响

研究了15种热处理工艺对采用VIM配合ESR双联工艺冶炼的GH871合金力学性能的影响。结果表明:在保持高强度高持久寿命的同时提高该合金650℃持久塑性的最佳热处理工艺为980℃×1h固溶,油冷+720℃×16h时效,空冷。经此热处理后,该合金在保持室温抗拉强度为1130MPa、650℃抗拉强度为890MPa的同时,650℃持久塑性达5%以上。     

C含量对一种单晶高温合金组织和持久性能的影响

研究了C含量对一种单晶高温合金组织和持久性能的影响。研究结果表明,随着C含量的增加,合金中γ/γ′共晶组织含量和尺寸减小,碳化物含量增加,其形貌由块状向骨架状和发达骨架状转变,Ta偏析程度降低,Re,W,Mo和Nb偏析程度增加。C含量对热处理后碳化物的形貌几乎无影响。随着C含量的增加,合金在980℃/250 MPa条件下的持久寿命先增加后降低,C质量分数为0.048%时达到最大值。持久过程中,未溶碳化物作为裂纹源缩短了合金的持久寿命。     

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.     

Structure–phase characteristics and the mechanical properties of single-crystal nickel-based rhenium-containing superalloys with carbide–intermetallic hardening

Single crystals of rhenium-containing ZhS32-VI, ZhS32U nickel superalloys with the 〈001〉, 〈011〉, and 〈111〉 crystallographic orientations have been produced by directional solidification. The alloying element segregations and the thermal stability of the microstructure consisting of a γ solid solution and hardened by precipitates of the γ′ phase and MC carbides are studied. The crystal lattice parameters of the γ′ and γ phases; the γ/γ′ misfit; and the liquidus, solidus, and γ′-solvus temperatures of the alloys have been found. The temperature dependence of the γ′-phase solubility has beeisn determined. The temperature–orientation dependences of the tensile strength characteristics in the range 20–1150°C and the low-cycle fatigue at 850°C of the alloy single crystals with the 〈001〉, 〈011〉, and 〈111〉 orientations are presented.     

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.     

铸型温度对单晶高温合金叶片凝固组织的影响

在高温度梯度真空定向凝固炉中,采用螺旋选晶法通过3种不同铸型温度分别制备了[001]取向的DD6单晶高温合金叶片,利用光学显微镜和扫描电镜观察了不同工艺条件下合金的铸态组织,研究了铸型温度对单晶高温合金凝固组织的影响。结果表明,随着铸型温度的升高,合金的一次枝晶间距和二次枝晶间距变小,合金元素的偏析程度降低,枝晶干和枝晶间的铸态γ′相尺寸减小,共晶的尺寸和含量稍有减小,显微疏松的尺寸和体积分数稍有减小。     

贝氏体铁素体和残余奥氏体取向关系

 用分析电镜和高分辨电镜确定了贝氏体钢中贝氏体铁素体和残余奥氏体之间存在3种取向关系。其中一种为K-S关系,即［110］γ′//［111］α,（111）γ′//（110）α;一种为N-W取向关系,即［110］γ′//［001］α,（111）γ′//（110）α;还有一种为G-T关系,即［112］γ′//［110］α,（111）γ′//(110)α。高分辨像显示,贝氏体铁素体-奥氏体相界面不平直,α和γ′两相内有系列刃型位错和结构小台阶,两相界面未显示出连续的严格共格关系。     

Neutron Diffraction Study of Strain/Stress States and Subgrain Defects in a Creep-Deformed, Single-Crystal Superalloy

A single crystal superalloy with initial sample axis 10 deg deviated from [001] was creep deformed at 1273 K (1000 °C) 235 MPa and its triaxial strain/stress state and subgrain defects were studied by neutron diffraction. Normal internal stresses with their directions close to the loading axis and their scales smaller than those perpendicular to the axis were observed and attributed to a lattice rotation toward [001] pole. The internal stress at a level approaching to the loading stress and mostly in the state of interphase stress was induced during the first stage of creep prior to rafting and associated to lattice rotation, microstrain relaxation and line-up of misoriented γ′-precipitates. The internal stress was diminished and released at final stage of creep associated with a reduction in unit-cell volume and a transition of strain/stress state between the two phases. The observation was explained by development of dislocations and raft structure during creep.     

Hot Deformation Behavior of Ni3Al-based Alloy MX246A简

The hot deformation behavior of homogenized Nia Al-based alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1 150--1225 ℃ and strain rate range of 0. 001-0.1 s-1. Microstructural obser- vation revealed striped secondary γ＇ phase which was vertical to compression axis, and precipitation of fine ternary γ＂ phase. The amount of striped secondary γ＇ phase reduced and that of fine ternary γ＇ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controUed by dynamic recovery mechanism.     

DD407单晶高温合金760℃拉伸性能的各向异性

研究了具有[001]、[011]和[111]取向以及[001]附近取向的DD407单晶高温合金经过热处理后,在760℃温度下的拉伸性能。结果表明,该合金具有明显的拉伸性能各向异性：[001]取向上表现出了最高的屈服强度和抗拉强度;当取向逐渐偏离[001]时,强度开始降低,但在相同的偏离角度内,偏向[111]取向的试样具...     

Effect of thermal fatigue on the structure and properties of Ni3Al-based alloy single crystals

The effect of thermal fatigue during tests of 〈001〉 and 〈111〉 single crystals according to the schedules 100 ai 850°C, 100 ai 1050°C, 100 ai 1100°C at a peak-to-peak stress Δσ_tc = 700–1000 MPa (sum of the maximum tensile and compressive stresses in a thermal cycle) on the structure, the fracture, and the fatigue life of an Ni₃Al-based VKNA-1V alloy is studied. It is found that, at 10³ thermal cycles, the 〈111〉 single crystals have the maximum thermal fatigue resistance at the maximum cycle temperature of 850 and 1050°C, and the properties of the 〈001〉 and 〈111〉 samples are almost the same at the maximum thermal cycle temperature of 1100°C. After thermal cycling at the maximum temperature of 850°C, the γ layers in the two-phase γ′ + γ region in dendrites remain a single-phase structure, as in the as-cast material, and the layer thickness is 100–150 nm. When the maximum thermal cycle temperature increases to 1050 or 1100°C, the discontinuous γ-phase layers in the γ′(Ni₃Al) matrix change their morphology and become shorter and wider (their thickness is 300–700 nm). The nickel-based supersaturated solid solution in these layers decomposes with the formation of secondary γ′(Ni₃Al)-phase (γ′_sec) precipitates in the form of cuboids 50 and 100 nm in size at the maximum cycle temperature of 1050 and 1100°C, respectively. The alternating stresses that appear during thermal cycling cause plastic deformation. As in nickel superalloys, this deformation at the first stage proceeds via the slip of screw dislocations along octahedral {111} planes. Networks of 60° dislocation segments form at γ′/γ interfaces in this case. Fracture begins at the lines of intersection of the slip planes of the {111} octahedron with the sample surface. During fractional, a crack passes from one octahedral plane to another and forms terraces and steps (crystallographic fracture); as a result, the fracture surface bends and becomes curved. In all cases, the fracture surfaces have a mixed brittle-ductile character with a combination of crystallographic and ductile (dimple) fracture elements.