第二代单晶高温合金DD6长期时效后的拉伸性能

研究了第二代单晶高温合金DD6长期时效后的拉伸性能.结果表明:980℃长期时效后,[001]取向DD6合金760℃条件下保持了良好的高温拉伸性能;时效1000 h,抗拉强度仍然大于1000MPa,屈服强度接近900MPa;γ'相的变化对DD6合金760℃条件下的拉伸性能没有明显影响.     

单晶高温合金DD6拉伸性能各向异性

研究了[001],[011],[111]取向第二代单晶高温合金DD6的拉伸性能与断口组织。结果表明:DD6单晶高温合金存在拉伸各向异性,850℃以上[001]取向DD6单晶高温合金的抗拉强度与屈服强度分别高于[011],[111]取向合金的强度,[001],[011],[111]取向DD6单晶高温合金的拉伸断口具有类解理断裂与韧窝断裂的特征。     

喷丸对DD6单晶高温合金拉伸性能的影响

采用扫描电子显微镜(SEM)、X射线(X-ray)和透射电子显微镜(TEM)等手段研究铸钢丸喷丸对第二代单晶高温合金DD6在500,600,650℃拉伸性能的影响。结果表明:500,600,650℃时,喷丸对DD6合金抗拉强度影响不大,略微提高屈服强度,显著降低伸长率和断面收缩率。喷丸DD6合金在流变应力上升到最高点后断裂,试样拉伸断裂后的横截面为圆形;未喷丸DD6合金拉伸曲线呈现双重阶段特征,试样拉伸断裂后的横截面为椭圆形。     

小角度晶界对单晶高温合金DD6拉伸性能的影响

采用两个籽晶制备了第二代单晶高温合金DD6小角度晶界试样,在800,850,900,950℃的条件下,进行了拉伸实验研究.结果表明:小角度晶界对合金仲长率有显著影响;在850℃,小角度晶界试样具有最大的伸长率:高于850℃,随着温度的升高小角度晶界试样伸长率具有明显下降倾向.小角度晶界对合金抗拉强度的影响较小;除角度大于约9°的小角度晶界外,相同实验温度条件下小角度晶界试样的抗拉强度大致相当.随着温度的升高和晶界角度的增大,小角度晶界强度降低而成为相对较为薄弱部位,从而导致拉伸性能的降低.     

[011]取向DD6单晶高温合金薄壁持久性能

采用薄壁试样研究了760,980,1070℃条件下[011]取向第二代单晶高温合金DD6的持久性能.结果表明:与标准试样(直径5mm)相比,DD6单晶高温合金薄壁试样的持久寿命与之相当.对合金760℃/590MPa,980℃/270MPa及1070℃/270MPa条件下组织分析发现:760℃合金γ’相局部发生变形,98...     

第二代单晶高温合金DD6的横向拉伸性能

在800-950℃的条件下,研究了第二代单晶高温合金DD6的横向拉伸性能。结果表明：随着温度的升高,横向拉伸强度下降,横向伸长率先增加然后明显下降;与合金的纵向性能即[001]取向性能相比,在较高温度下横向伸长率明显小于纵向伸长率;随着温度的升高,沿枝晶界面易于形成显微裂纹,导致塑性降低。     

长期时效对 DD4 单晶高温合金组织稳定性的影响EI

在８５０℃和９５０℃（ＴＣＰ相析出的敏感温度）对ＤＤ４单晶高温合金进行了１０００ｈ的长期时效，并采用定期取样的方法进行分析。结果表明：ＤＤ４单晶合金具有良好的组织稳定性，经过长期高温时效后未出现ＴＣＰ相，与理论计算的结果相符。在８５０℃下，γ相的尺寸和形态无明显变化，持久性能也未发生明显变化。在９５０℃下，γ相的尺寸和形态有一定变化，导致持久性能下降。     

抽拉速率对DD6单晶高温合金凝固组织的影响

研究了不同的抽拉速率对第二代单晶高温合金DD6凝固组织的影响.结果表明,随抽拉速率的增加,DD6合金凝固界面由粗枝状组织向细枝状组织演变,枝晶干和枝晶间的γ'相尺寸减小,且枝晶间γ'相的形状越来越趋向于规则的立方体形状,γ-γ'共晶含量增加,粗大的初生γ'相减少.     

气膜孔分布对DD6单晶高温合金持久性能及断裂行为的影响

研究在980℃/300MPa条件下不同气膜孔分布对DD6单晶气冷叶片模拟试样持久性能及断裂行为的影响。结果表明:在相同的温度和应力条件下,气膜孔的分布是影响模拟试样持久寿命的主要因素;随着气膜孔排数的增加,持久寿命呈规律性下降,而带1排孔、2排孔试样的持久寿命与不带孔的持久寿命略长。通过断口微观和金相组织观察发现,不带孔试样的断裂方式为微孔聚集型断裂,断口上分布着大量方形小平面特征,断口附近纵剖面上可见明显的心部裂纹;而带气膜孔试样的持久变形主要出现在气膜孔区域,断口整体氧化较严重,方形小平面特征减少,韧窝特征明显增加,断口附近纵剖面上气膜孔处均可见裂纹及氧化形貌。基于晶体塑性理论分析了不同孔分布下孔边应力的分布规律,模拟结果显示在气膜孔周边存在应力集中和应力重分布,数值模拟分析结果与试样的断裂位置及形貌吻合。     

Hf含量对第二代单晶高温合金拉伸性能的影响

在室温、760℃和980℃下,研究了Hf含量对第二代单晶高温合金DD6拉伸性能的影响,采用扫描电镜和透射电镜研究了合金拉伸断口和拉伸断裂显徽组织.结果表明,在本试验研究范围内,Hf含量对DD6合金的拉伸性能影响较小;不同Hf含量DD6合金室温下和760℃的拉伸断裂为类解理断裂,980℃的拉伸断裂为韧窝断裂.     

再结晶对DD6单晶高温合金轴向高周疲劳性能的影响

为了研究再结晶对二代单晶高温合金DD6高周疲劳性能的影响,对标准热处理的DD6合金进行表面吹砂处理,然后分别在1120℃和1315℃保温4h,以获得不同类型的再结晶组织。在疲劳试验机上分别测试了光滑和含再结晶的DD6合金试样在1070℃的轴向高周疲劳寿命。采用SEM观察DD6合金再结晶组织及疲劳断口。结果表明:胞状再结晶和等轴再结晶降低了DD6合金的轴向高周疲劳性能,胞状再结晶作用小于等轴再结晶;含再结晶的DD6合金试样的轴向高周疲劳断裂机制为类解理断裂和枝晶间的局部韧窝断裂共存的混合断裂;再结晶使DD6合金试样变为多源疲劳断裂。高温条件下,再结晶晶界的存在加快合金试样的氧化损伤,显著缩短早期疲劳裂纹的萌生和扩展时间,降低合金的轴向高周疲劳性能。     

Effect of long term aging on mechanical properties and microstructure of nickel base weld

Abstract

The mechanical properties of a Ni base weld have been examined after long term aging in the temperature range 600–900°C. Impact testing revealed a substantial decrease in toughness after heat treatment at 600 and 700°C. In particular, after aging at 700°C there was a marked loss of ductility, which was associated with elongated particles appearing in the fracture surfaces. The concomitant microstructural changes occurring have been investigated using analytical electron microscopy. In material heat treated at 600°C for 10000 h, seven phases were identified: M₂₃C₆, MC, η, γ′, γ″, G, and δ. At 700°C, the following phases were distinguished after 3000 h: M₂₃C₆, MC, and η. After longer testing times G, γ′, and γ″, were formed. Whereas G, γ′, and γ″ formed intragranular needles, η formed intragranular laths or plates at 700°C. The minimum in ductility observed in material aged at 700°C can be explained in terms of copious intragranular precipitation of γ′, γ″, and η.

MST/1131     

Ru对第四代镍基单晶高温合金DD22长期时效组织演化的影响EI北大核心CSCD

利用透射电镜和场发射扫描电镜研究了两种不同Ru含量(3%和5%,质量分数)的第四代镍基单晶高温合金DD22在1130℃长期时效过程中γ′相形貌演化、TCP相析出和界面位错网的演化情况。研究结果表明:在完全热处理后5Ru合金比3Ru合金的γ′相尺寸更小,形状更规则,γ/γ′相界面的错配度更大,高Ru含量使合金Re,Mo等元素出现反分配现象;5Ru合金在1130℃长期时效过程中γ′相粗化速率、溶解速率和形筏速率均低于3Ru合金;5Ru合金在长期时效1000 h后仍没有TCP相析出,而3Ru合金在时效50 h后便析出TCP相,随着长期时效时间延长,TCP相数量增多,尺寸增大;与3Ru合金相比,长期时效1000 h后5Ru合金γ′/γ界面位错网更加致密和规则;综上所述,Ru的元素反分配作用和低的扩散系数使5Ru合金比3Ru合金表现出更高的组织稳定性。     

Effect of thermal exposure on the microstructure and creep properties of a fourth-generation Ni-based single crystal superalloy

The effect of thermal exposure on microstructure and creep properties of a fourth-generation nickelbased single crystal superalloy was investigated.The thermal exposure of samples after the full heat treatment was carried out at 1000℃,1100℃ and 1140℃ for 100 h and 200 h.The γ' coarsening,γ' rafting and γ channel widening were observed in samples after thermal exposure.When the thermal exposure time was constant,the morphology of γ' phase in the alloy evolved significantly with increasing aging temperature.The interracial dislocation networks in aged samples after creep ruptured gradually became irregular and sparse with the increase of exposure temperature.When the higher exposure temperature was used,enla rgement of the defect pores was observed in samples,the microcracks were more likely to initiate and propagate at the corner of these pores.After aging at 1000℃ for 100 h,the creep life at 1140℃/137 MPa was slightly longer than that of heat-treated sample,which could be attributed to the slightly coarsened γ' phase,homogenization of refractor elements.In contrast,the creep life of sample exposed at 1140℃ for 100 h was greatly decreased.The decrease of creep life was dominated by the rafting of γ'phase,the irregular interfacial dislocation networks as well as the enlargement of homogenization pores.     

抽拉速率对SRR99单晶高温合金组织和性能的影响

用螺旋选晶法制备镍基单晶高温合金 SRR99,研究了抽拉速率对其组织和性能的影响.随着抽拉速率的增大,SRR99单晶合金的铸态组织由粗枝状晶向细枝状晶演变,枝晶干与枝晶间的γ'相尺寸减小,且枝晶间γ'相的形状逐渐趋向于规则立方体形状,而γ-γ'共晶的含量增加.热处理后,在高抽拉速度下生成的共晶组织更容易固溶,形成更加均匀的组织.随着抽拉速率的增大,SRR99单晶合金的持久寿命延长.     

Effect of element Ru on microstructure and creep behaviour of single crystal nickel-based superalloy

By means of creep property measurement and microstructure observation, the influence of element Ru on the microstructure and creep behaviour of single crystal nickel-based superalloy is investigated. The results show that the plate-like μ phase is precipitated along {111} plane of the Ru-free alloy during thermal exposure at 1080°C and creep at 980°C. And the precipitation of μ phase in the alloy with 6(wt)%Mo and 6(wt)%W may be restrained by adding 2% Ru element. Compared to Ru-free alloy, the creep life of the 2% Ru single crystal alloy at 980°C200 MPa increases form 123 h to 333h. Compared to the 2% Ru alloy, the precipitated plate-like μ phase in the Ru-free alloy may promote the initiation and propagation of cracks along the γ matrix up to fracture, which is thought to be the main reason of the alloy having a lower creep resistances and shorter lifetime.     

Microstructure and tensile properties of DD32 single crystal Ni-base superalloy repaired by laser metal forming

In this work, the microstructure and tensile properties of DD32 single-crystal(SC) superalloy repaired by laser metal forming(LMF) using pulsed laser have been studied in detail. The microstructures of the deposited samples and the tensile-ruptured samples were characterized by optical microscopy(OM),transmission electron microscope(TEM) and scanning electron microscope(SEM). Due to high cooling rate, the primary dendrite spacing in the deposited area(17.2 μm) was apparently smaller than that in the substrate area(307 μm), and the carbides in the deposited samples were also smaller compared with that in the substrate area. The formation of(γ + γ') eutectic in the initial layer of repaired SC was inhibited because of the high cooling rate. As the deposition proceeded, the cooling rate decreased, and the(γ + γ') eutectic increased gradually. The(γ + γ') eutectic at heat-affected zone(HAZ) in the molten pool dissolved partly because of the high temperature at HAZ, but there were still residual eutectics. Tensile test results showed that tensile behavior of repaired SC at different temperatures was closely related to the MC carbides, solidification porosity, γ' phase, and(γ + γ') eutectic. At moderate temperature, the samples tested fractured preferentially at the substrate area due to the fragmentation of the coarse MC carbide in the substrate area. At elevated temperature, the(γ + γ') eutectic and solidification porosity in the deposited area became the source of cracks, which deteriorated the high-temperature properties and made the samples rupture at the deposited area preferentially.     

Stability of microstructure and mechanical properties of K17G cast nickel-base superalloy during prolonged aging

K17G cast nickel-base superalloy has an attractive combination of mechanical properties: high strength and good ductility as well as low density. In particular, after prolonged exposure at 750, 850 (both up to 10000 h) and 950°C (up to 1500 h), this alloy proved to have excellent phase stability and no sigma phase was found. The effects ofprolonged exposure on high temperature tensile and stress rupture properties were not serious and decreased gradually with aging time. The change in properties of specimens taken directly from the turbine blades followed those ofthe cast-to-size specimens. The rupture lives, tensile and rupture ductilities were approximately one third lower compared with those ofthe cast-to-size specimens, but still remained at reasonably high levels.