Nickel-based Single Crystal Alloy Research Articles

Effect of mismatch degree on mechanical properties of Ni-based single crystal alloy under force-temperature coupling

Mismatch degree has an important effect on the mechanical properties of Ni-based single crystal alloys. However, the effect of mismatch degree on mechanical properties under force-temperature coupling is unclear. Thus, we used molecular dynamics method to study mechanical properties and microstructural evolution of Ni-based single crystal alloy. The interface dislocation network and mechanical properties under different positive mismatches are discussed respectively. We found that the lower the mismatch degree, the more regular the dislocation network is, which can effectively prevent the dislocation motion and increase the strength. Meanwhile, when the mismatch degree is less than 1.43, the yield strength gradually decreases with the increase of the mismatch degree. When the mismatch degree is 1.43, the yield strength reaches the minimum value. Moreover, the lower interface energy can increase the yield strength of nickel-based single crystal alloy, and the yield strength decreases with the increase of interface energy. To compare the influence of positive and negative mismatch on mechanical properties and microscopic evolution, the yield stress of Ni-based single crystal alloy increases with the increase of mismatch, but the change is not significant. At the negative mismatch degree, the yield stress decreases as the mismatch decreases. When the absolute value of the mismatch is the same, the yield stress at a positive mismatch of 0.33% is greater than the yield stress at a negative mismatch of −0.33%.

A united tension/compression asymmetry micro-mechanical model for nickel-base single-crystal alloys

In recent years, the micro-deformation mechanisms of the tension/compression behavior for nickel-base single-crystal superalloys have been studied extensively and general agreements have been derived. Based on these researches, a new model called united tension/compression asymmetry micro-mechanical model (UTCAM) has been proposed, which can effectively estimate the initial yield strength of nickel-base single-crystal (SC) superalloys under different loading directions. Considering the combined effects of octahedral slip system and cubic slip system, slip control factor is introduced in the UTCAM to determine the type of the open slip system of nickel-base single-crystal superalloys during deformation, thus making this model cover a rather wide range of application. Furthermore, the UTCAM is applied to hot tension and compression tests of three typical nickel-base SC superalloys (PWA1480-593 °C, RENE N4-760 °C and DD407-760 °C). The predicted initial yield strengths of the nickel-base SC superalloys are in good agreement with the experimental results, and the UTCAM proves to be effective.

Dislocation Structure in a Single Crystal Nickel Base Superalloy During High Cycle Fatigue at 870 °C

Abstract Dislocation structure and its impact on the mechanical behavior of a γ′ strengthened nickel base single crystal alloy under high cycle fatigue (HCF) at 870 °C was studied. The results indicate that HCF lifetime declines with increase of applied stress amplitude. In the early stages, the fatigue deformation occurs by forced bowing of dislocations through the narrow γ matrix channels on {111} planes. During mid-term fatigue stages, most of the dislocations formed in the matrix are located in the γ/γ′ interfaces, whose intersection and reaction produce new dislocation segments and three-dimensional dislocation networks. The Burgers vectors of the dislocations in the network are 1/2 . The interaction of cyclic stress with high temperature induces the precipitation of homogeneous globular γ′ particles, which is beneficial to fatigue strength. At the end of fatigue test, the cyclic stress leads to the formation of persistent slip bands moving through the γ matrix channels and γ′ particles. Dislocation shearing through the γ′ phase is found occasionally. The extrinsic stacking faults is also observed.

Crystallographic Orientation Dependence of Corrosion Behavior of a Single Crystal Nickel-Based Alloy

Crystallographic orientation dependence of corrosion behavior of a nickel-based single crystal alloy IN738 was studied. Potentiodynamic polarization and electrochemical impedance spectroscopy show that corrosion performance of the single crystal alloy varies with crystallographic orientation. The dependence of passivation behavior on crystallographic orientation is influenced by environmental concentration. Potentiostatic polarization, scanning probe microscopy, and X-ray photoelectron spectroscopy were performed to understand the variation in passivation of different crystallographic orientations. The crystallographic orientation dependence of corrosion performance of the alloy can be explained by the difference of passive films in terms of chemical compositions, compactness, and porosity properties, as well as surface roughness.

Transient Liquid Phase Bonding of Nickel-Base Single Crystal Alloy with a Novel Ni-Cr-Co-Mo-W-Ta-Re-B Amorphous Interlayer

AbstractA novel Ni-Cr-Co-W-Mo-Ta-Re-B alloy consisting of plate γ and M23B6 phases was prepared as interlayer for the transient liquid phase (TLP) bonding of Rene’ N5 nickel-base single crystal superalloy. The molten Ni-Cr-Co-W-Mo-Ta-Re-B alloy exhibited an excellent wettability on the nickel-base superalloy. The TLP bonding experiment has been carried out in vacuum furnace at 1,240 ℃ for 12 h and followed by post-weld heat treatment (PWHT) at 1,305 ℃ for 4 h. PWHT eliminated the intermetallic compounds and promoted the formation of γ´ precipitates in the bonding region. A more uniform microhardness profile of TLP joint was found after PWHT. The shear strength of the joint after PWHT significantly increased to 533.4 MPa compared with the value of 437.2 MPa without PWHT.

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ КРЕМНИЯ, ФОСФОРА И СЕРЫ МЕТОДОМ НАПРАВЛЕННОЙ КРИСТАЛЛИЗАЦИИ РАСПЛАВА С ВЕСЬМА НИЗКОЙ СКОРОСТЬЮ ПЕРЕМЕЩЕНИЯ ФРОНТА

РАФИНИРОВАНИЕ МОНОКРИСТАЛЛИЧЕСКИХ НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ ОТ ПРИМЕСЕЙ КРЕМНИЯ, ФОСФОРА И СЕРЫ МЕТОДОМ НАПРАВЛЕННОЙ КРИСТАЛЛИЗАЦИИ РАСПЛАВА С ВЕСЬМА НИЗКОЙ СКОРОСТЬЮ ПЕРЕМЕЩЕНИЯ ФРОНТА

镍基单晶高温合金滑移系剪应力集中分析

为了完善晶体滑移理论及基于该理论而发展起来的低周疲劳寿命模型、蠕变寿命模型在工程中的应用及评价，提出了镍基单晶合金滑移系剪应力集中系数的相关定义。通过理论推导和有限元方法分析了镍基单晶高温合金的滑移系应力集中系数，得到以下结论：1） 各向同性材料与镍基单晶合金的应力集中效应有着明显的差异，采用各向同性材料应力集中系数处理镍基单晶合金材料是不合适的；2） 对于平面问题，滑移系剪应力集中系数只决定于构件的形状、晶体方向、而与材料的弹性常数无关；3）对于镍基单晶合金材料，应力集中系数具有晶体取向各向异性。形状与载荷条件相同下，[111]取向具有最大的应力集中系数，[011]取向次之，[001]取向最小。 In order to perfect the crystal slip theory and its engineering application and evaluation of the low cycle fatigue and creep life model that developed on the crystal slip theory, the related definition of slip system shear stress concentration factor for nickel-based single crystal alloy was proposed .Through theoretical derivation and finite element method, the slip system stress concentration factor of nickel base single crystal superalloy was analyzed, it can be deduced that: 1) There exists obvious difference in stress concentration effect between isotropic alloy and nickel-based single crystal alloy. So it would be inappropriate to use the stress concentration coefficient of isotropic alloy to handle nickel-based single crystal alloy; 2) For plane problem, the shear stress concentration coefficient in slip system only determined by component’s shape and crystal orientation, and has nothing to do with the material elastic constants; 3) For nickel-based single crystal alloy, stress concentration coefficient is anisotropic with crystal orientation. Under the same shape and load conditions, stress concentration coefficient in [111] orientation takes its maximum, in [011] orientation second, and in [001] orientation the minimal.

Microgravity Material Research in China:2016

Firstly, recent research works of high undercooling and rapid solidification of metallic alloys under ground simulation conditions in Northwestern Polytechnical University are reviewed. Secondly, under normal gravity and microgravity of binary to quinary Nickel-base single crystal alloys with different contents of W, Ta, Al and Ti elements are comparatively investigated by Institute of Metal Research using drop tube. Thirdly, solidification and crystal growth of SJ10-Recoverable Scientific Experiment Satellite by Institute of Semiconductors is introduced.

Regular γ/γ′ phase interface instability in a binary model nickel-based single-crystal alloy

In this paper, long-term thermal treatment of a binary Ni–Al model nickel-based superalloy was performed at 1000°C for 50h, 100h and 200h. The evolution of the γ/γ′ interface was studied. As the treatment time increased, the γ′ precipitates coarsened and grew. Regular interface instability was observed that the shape of the γ/γ′ interface changed from flat to wavy. This interfacial instability was caused by the dynamic balance of strain energy and surface energy at the interface between the two phases. In addition, secondary γ′ precipitates were observed after long-term treatment and some of the larger ones took on pillow-like shapes. The pillow-shaped distortion was because that the growth rate of the cube vertices was faster than that of other locations due to the different strain states at different locations.

DD6镍基单晶合金的纳秒及皮秒激光烧蚀和制孔研究

DD6镍基单晶合金的纳秒及皮秒激光烧蚀和制孔研究

DD6镍基单晶合金的纳秒及皮秒激光烧蚀和制孔研究

DD6镍基单晶合金的纳秒及皮秒激光烧蚀和制孔研究

Effects of temperature and stress on the creep behavior of a Ni3Al base single crystal alloy

The creep behavior and microstructure of a Ni3Al base single crystal alloy IC6SX with [001] orientation under the testing conditions of 760°C/593MPa, 980°C/205MPa, and 1100°C/75MPa were investigated. The experimental results showed that Alloy IC6SX had good creep resistance and its creep resistance at elevated temperatures was similar to the second generation nickel-base single crystal alloy containing Re. TEM analysis indicated that the dislocation configuration and movement pattern were different under different temperature and stress conditions. It has been found that under the test condition of 1070°C/137MPa the dislocations moved within the γ channel during the primary creep stage, and the motion of dislocations were prevented by the matrix of γ′ phase, which reduced the creep rate of the alloy. In the secondary creep stage, dislocations cut into the γ′ phase from the γ/γ′ interface. However in the third creep stage, the dislocation pileups were observed in both γ and γ′ phase, and dislocation multiplication occurred when the dislocations with different Burgers vector met and reacted each other.

Influences of Holes Arrangement on Creep Characteristic of Nickel-Base Single Crystal Alloy Blade Cooling Holes

Film cooling technology is developed to enhance the temperature resistant of nickel-base single crystal alloy blade. The shape, dimension, and arrangement of cooling holes impact the blade strength and life grievously. In this paper, the influences of holes arrangement on creep characteristic of cooling holes in the plate sample are investigated. The constitutive model for creep considering both cavitation and degradation damage is developed to predict the creep behavior of cooling holes. Results show that there are stress interferences among cooling holes. The distance and radius of the cooling holes impact the creep behavior of cooling holes seriously. Decreasing horizontal distance of the holes results in creep time reducing. On the contrary, increasing the vertical distance of the holes makes the creep time reduced.

Structure Evolution and Creep Behavior for a Nickel-Base Single Crystal Alloy along [011] and [001] Orientations

Abstract The morphology evolution and creep behavior of γ′ phase in [001] and [011] oriented specimens of a nickel-base single crystal superalloy during the tensile creep at 1253 K and 200 MPa were investigated. SEM and TEM observation shows that the direction coarsening of precipitates is highly dependent on the crystal orientation. In [001] orientation, the γ′ phase transits from original cuboids to the raft-shape along the perpendicular direction to the tensile stress axis while in [011] orientation the γ′ phase develops along the [010] and [100] and evolves into a raft with inclined 45° angle to the tensile stress axis. The strain rates for [001] and [011] orientations are almost equal at the earlier stage of creep. With the matrix channel broadening, the strain rate for [011] orientation increases gradually, while the creep strength decreases rapidly. Based on the evolutional rule of γ′ phase and the creep curves, the anisotropic creep behavior is obvious at the later stage of steady-state and the tertiary creep stage

The Oxidation Characteristics of the γ–γ′ Tie-Line Alloys of a Nickel-Base Superalloy

A novel family of bond coats designed to be in EQuilibrium with their nickel-base superalloy substrates has been developed. These coatings have hence been termed ‘EQ coatings’. The first step taken for EQ coating development was to examine the γ–γ′ tie-lines of several superalloys. In these superalloys, γ and γ′ are in equilibrium with each other, and elemental activities are thus equal in these two phases. With equal activities, there will be no chemical potential differences between the two phases, and there is thus no driving force for diffusion. Applying γ,γ′, or a combination of both as bond coat candidates will ensure that no inter-diffusion zone (IDZ) will form. This is desirable, as IDZ causes gross local mechanical property degradation.In this paper, the γ′ volume fraction was varied from 0 to 100% at 25% intervals along the γ–γ′ tie-line of a nickel-base single-crystal alloy, TMS-82+. Cyclic and isothermal oxidation tests were conducted at 1100°C in ambient atmosphere. The resultant oxide structures, and the element concentration profiles from around the oxide/substrate interface, through the depletion zone, into the sound substrate, were analyzed by SEM/EDX.All samples started with the same element activities; hence, at the onset of oxidation, all samples were expected to form the same oxide structure. However, experiments showed that the specimens formed vastly different oxide structures, and that γ′ had the best resistance against high temperature oxidation.

In situ small-angle neutron scattering investigation of theγ′ precipitation and growth in the nickel-based single-crystal alloy SC16

The precipitation of γ′ particles in the SC16 single-crystal nickel-based superalloy has been studied by insitu small-angle neutron scattering (SANS). On cooling from the one-phase fieldγ (temperaturesabove 1250 °C), the γ′ precipitates develop in different sizes and shapes at each temperature. Samples underwentsolutionizing and different ageing treatments below the solutionizing point in a saw-toothtemperature profile. Microstructural information, as well as relative volume fraction andsize of the particles, could be deduced from SANS patterns at each ageing temperature.They indirectly show that the precipitates have a cuboidal shape and are arranged(periodically) along the [100] crystallographic direction, only at temperatures below1180 °C. Between1180 and 1120 °C the transition from spherical to cuboidal shape seems to take place, driven by theprevalence of the strain energy over the other driving mechanisms of the reaction.More than one particle population is necessary to interpret the scattering profilesat each temperature. Nucleation of small particles seems to take place down to1050 °C. Morphology evolutions as a function of temperature as well as possible splitting of theprecipitates are discussed.

The Effect of Crystallographic Orientation on the Oxidation Behavior of a Single-Crystal Nickel-Base Superalloy

The oxidation kinetics of DD100 nickel-base single-crystal alloy, with (221) and (100) surface orientations were tested in this study by thermogravimetry. A pronounced anisotropy in both the cyclic and isothermal oxidation resistance of DD100 alloy was observed. The (221) crystallographic surface of DD100 had a slower oxidation rate than the (100) surface when isothermally exposed to stationary air at 950°C, whereas the opposite results were obtained at 1050°C. When cyclically oxidized at 1100°C, the weight loss of samples with (221) surfaces was significantly greater than that of (100) surfaces, so that the cyclic-oxidation anisotropy was more remarkable at 1100°C than at 950°C. The different spatial alignment of the γ′/γ interface is thought to be responsible for the anisotropic oxidation behavior of the nickel-base single crystal alloy.

Development and Turbine Engine Performance of Three Advanced Rhenium Containing Superalloys for Single Crystal and Directionally Solidified Blades and Vanes

Turbine inlet temperatures over the next few years will approach 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching 445 KN (100,000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, design technology for stresses and airflow, single crystal and directionally solidified casting process improvements, and the development and use of rhenium (Re) containing high γ′ volume fraction nickel-base superalloys with advanced coatings, including full-airfoil ceramic thermal barrier coatings. Re additions to cast airfoil superalloys not only improves creep and thermo-mechanical fatigue strength, but also environmental properties including coating performance. Re dramatically slows down diffusion in these alloys at high operating temperatures. A team approach has been used to develop a family of two nickel-base single crystal alloys (CMSX-4® containing 3 percent Re and CMSX®-10 containing 6 percent Re) and a directionally solidified, columnar grain nickel-base alloy (CM 186 LC® containing 3 percent Re) for a variety of turbine engine applications. A range of critical properties of these alloys is reviewed in relation to turbine component engineering performance through engine certification testing and service experience. Industrial turbines are now commencing to use this aero developed turbine technology in both small and large frame units in addition to aero-derivative industrial engines. These applications are demanding, with high reliability required for turbine airfoils out to 25,000 hours, with perhaps greater than 50 percent of the time spent at maximum power. Combined cycle efficiencies of large frame industrial engines are scheduled to reach 60 percent in the U. S. ATS programme. Application experience to a total 1.3 million engine hours and 28,000 hours individual blade set service for CMSX-4 first stage turbine blades is reviewed for a small frame industrial engine.

Identification of constants of a viscoplastic constitutive model for a single crystal alloy

In this paper uniaxial experiments conducted at 1033 K with specimens from the cubic face centered, nickel base single crystal alloy SRR99 are described. Specimens with 〈001〉-orientation and orientations deviating considerably form 〈001〉 have been used. We describe the results of tension tests with constant strain rate, relaxation tests and creep tests. From these tests the full set of material constants for a constitutive model by Choi and Krempl [1] is identified. We compare the experimental data with simulations by the model using the identified constants. The correspondence between simulations and experimental data is satisfactory until good depending on the type of the experiment. Finally, we describe a comparison between experimental data and simulations where the experiments have not been used for constant identification. The correspondence is very satisfactory. Therefore, we conclude that the model of Choi and Krempl is applicable on practical problems in the temperature range covered by our experiments.

The growth and elevated temperature stability of high refractory nickel-base single crystals

Additions of refractory alloying elements to single-crystal and polycrystalline nickel-base alloys are known to provide potent high temperature strengthening. However, high levels of elements such as Re, W and Ta can result in unexpected modes of degradation during solidification and subsequent long-term exposures at high temperatures. Here the contributions of refractory alloying additions to various mechanisms of high temperature strengthening are discussed. In addition, the results of experiments which have identified two new modes of degradation associated with the presence of high levels of refractory alloying elements in nickel-base single crystals will be presented. Nucleation and growth of isolated columnar grains during solidification and discontinuous reactions at defects in the single-crystal structure will be shown to be extremely sensitive to the level of refractory alloying additions in a number of nickel-base single-crystal alloys.