Ni3Al-based Single Crystal Alloy Research Articles

Thickness debit effect and multi-factor coupling mechanism of Ni3Al-based single crystal alloy

With the continuous development of aircraft engine generations, single-crystal alloy blades with more complex shapes and reduced wall thickness are urgently requested. However, the deteriorated performance associated with the wall thickness reduction has not been effectively resolved until now. In this research, the creep behavior of a [001]-oriented Ni3Al-based single crystal alloy with a thin-wall thickness was explored under the environment of 980 °C/220 MPa. A multi-factor coupling mechanism was proposed to explain the premature failure of the thin-walled specimen, providing a comprehensive understanding of the reasons behind the occurrence of the thickness debit effect. The study elucidated the influences of surface oxidation, the stress state of TCP phases, pore growth, and crack propagation on the creep performance. The findings serve as valuable theoretical references for the design and related research of future blade materials.

Effect of temperature and stress on high temperature creep behavior of Ni3Al-based single crystal superalloy

The creep behavior and dislocations mechanism of the Ni3Al-based single crystal alloy IC6SX with [001] orientation were investigated under the testing conditions of 1100 ​°C/137 ​MPa, 1100 ​°C/120 ​MPa and 1070 ​°C/137 ​MPa. It was observed that the temperature and stress had a significant effect on the high temperature creep life of the single crystal alloy. As the temperature was reduced from 1100 ​°C to 1070 ​°C, the creep life increased from 65.07 ​h to 313.8 ​h. As the stress was reduced to 120 ​MPa, the creep life increased to 243.3 ​h. Under the high temperature and low stress condition the dislocations entered the γ′ phase by climbing caused by the atomic diffusion, instead of slipping.

Creep behavior and dislocation mechanism of Ni3Al based single crystal alloy IC6SX at 760°C

The creep behavior and dislocation mechanism of Ni3Al-based single crystal alloys IC6SX with crystal orientation [001] which was prepared by seed crystal method under the testing conditions of 760 ​°C/500 ​MPa,760 ​°C/540 ​MPa and 760 ​°C/580 ​MPa were investigated. The experimental results showed that the creep properties, dislocation morphology and mechanism of this alloy were different under different stress conditions. With the stress increasing from 500 ​MPa to 580 ​MPa, the creep life decreased from more than 1000h to 32.64h. The cubic degree of γ′ phase in single crystal alloy decreased obviously and the size of γ′ phase increased. The mechanism of dislocation movement also changed with the increasing stress. It was found that after the specimen was tested under the condition of 760 ​°C/500 ​MPa the dislocation network prevented the movement of dislocations and it was difficult for dislocations to enter the γ′ phase from the γ/γ′ interface. When the stress was 540 ​MPa, the dislocations cut into the γ′ phase by stacking fault. Furthermore, with the stress increasing to 580 ​MPa, the dislocation entered the γ′ phase in the form of extended dislocation and Lomer-Cottrell dislocation.

Effect of Stress on Creep Behavior of Single Crystal Alloy IC6SX at 980°C

Ni3Al-based single crystal alloy IC6SX was prepared by seed crystal method. The effect of different stress conditions on creep behavior of this alloy at 980°C was investigated. The results showed that the creep life of this alloy at 980°C decreased significantly with the increase of stress. When the stress increased from 180 MPa to 230 MPa, the creep life dropped from 245.5 h to 69.3 h, and the steady-state creep rate increased slightly but not significantly. Meanwhile, the morphology of γ ′ phase and dislocation after creep were studied. The results showed that with the increase of stress, the density of dislocations in the γ ′ phase increased gradually, the strength of this alloy decreased gradually, so the creep life decreased significantly. The Y-NiMo phase resolved from the γ phase decreased gradually as the creep life decreased. The creep experiment of the alloy was carried out at 980°C. Due to the higher temperature, the diffusion of atoms in this alloy became faster. Deformation was not only caused by the slippage of dislocations in the crystal but also by the diffusion of atoms. Therefore, the creep mechanism of single crystal alloy IC6SX at this temperature is a mixed mechanism of dislocation glide and diffusion.

Study on the Creep Behavior of a Ni3Al-Based Single Crystal Alloy at 850°C/450 MPa

The creep behaviors of Ni3Al-based single crystal alloy IC6SX with [001] and [111] orientations under the condition of 850°C/450 MPa were investigated. The effect of crystal orientation on the creep lives, fracture morphology, fracture mechanism, and dislocation evolution of the alloys with different orientations was analyzed systematically. The results showed that the creep lives of the alloy were closely related to the crystal orientation under the condition of 850°C/450 MPa. The creep lives of the single crystal alloys with [001] and [111] orientations were 56.3 h and 126.9 h, respectively. Moreover, the fracture morphologies of the two alloys with [001] and [111] orientations were different. The results showed that some holes formed at the fracture surface of the alloy with [111] rather than [001] orientation. Furthermore, the surface near the fracture of the two alloys with [001] and [111] orientations was serrated. Therefore, the fracture mechanism of the single crystal alloys with [001] and [111] orientations was ductile fracture. In addition, a large number of dislocations cut into the γ ′ phase. Therefore, the cutting mechanism of dislocations in the alloys with [001] and [111] orientations was the creep deformation mechanism.

Microstructure and heat treatment for Ni3Al-based single crystal alloy with different crystal orientations

Ni3Al-based single crystal alloy IC6SX with different crystal orientations were prepared by seed crystal method. The microstructure and heat treatment of the alloy were investigated. The results showed that the microstructure of the alloy was in dendrite structure, and the crystal orientation had significant effect on the dendrite morphology of this alloy. The precipitated phases of (MoNi)6C and NiMo appeared in the microstructure of the three alloys with different crystal orientations during solidification process. Compared with other two alloys, the volume fractions of precipitated phases of both (MoNi)6C and NiMo was the most in the alloy with [111] orientation and the least in the alloy with [001] orientation. The solidus and liquidus temperatures of the alloy IC6SX tested by differential scanning calorimetry (DSC) were 1356 °C and 1387 °C, respectively. Meanwhile, the effect of different solution temperatures on the microstructure of the alloy with different orientations was studied. The results showed that the precipitated phases of (MoNi)6C and NiMo were eliminated with the solid solution treatment under the condition of 1300 °C/10 h. However, the incipient melting of the alloys occurred due to the dissolution of low melting point phases. As the temperature dropped to 1280 °C, the area of incipient melting in the alloy with different orientations decreased gradually. However, there was no incipient melting appearing in the three alloys with different orientations when the solution treatment temperature dropped to 1260 °C.

Cyclic oxidation behavior of Ni3Al-based single crystal alloy IC21

In this study, the cyclic oxidation tests of the Ni3Al-based single-crystal superalloy IC21 were carried out at 800, 900, 950, 1000, 1050 and 1100 °C in air. The present study shows that the complex oxide scale on the surface of the alloy is made up of an outer columnar NiO layer, an intermediate mixture of NiO and NiAl2O4 layer with a small amount of Mo oxides and an inner continuous layer of α-Al2O3. The cyclic oxidation kinetics curves show that oxidation resistance at 800, 900, 950, 1000 and 1050 °C seems to follow a similar law and is better than that at 1100 °C. The overall weight changes at 1100 °C follows a parabolic law. Spallation and severe rumpling of the oxide scale are observed on the surface of the alloy at 1100 °C, revealing the occurrence of disastrous oxidation.

Rotating bending fatigue behaviour of a Ni3Al-based single crystal alloy IC6SX at 760°C

The high cycle fatigue behaviour at 760°C of a Ni3Al-based single crystal alloy IC6SX has been studied in the present investigation. The specimens for the fatigue tests were prepared by screw selection crystal method in a directional solidification furnace. The rotating bending fatigue tests of the specimens was carried out at the temperature of 760°C in air, the stress ratio of R (σmax/σmin) was − 1, and the rotating speed of the fatigue tests was 6500 r min− 1 (108 Hz). The stress–fatigue life cycle (S − Nf) curve was obtained based on the fatigue tests, and the fracture surfaces were examined using scanning electron microscopy (SEM). The results showed that the fatigue cracks initiated from the surface defects of the specimens and the cracks propagated along the (111) crystal plane. The fatigue fracture was composed of three different characteristic regions corresponding to the three fatigue stages, including fatigue crack initiation stage, steady-state propagation stage and the fast propagation stage. The research results also showed that the rotating bending fatigue performance of alloy IC6SX is superior to that of the second-generation single crystal nickel-based superalloys containing 3 wt-% Re.

Effects of Mo and Ta in Ni3Al based single crystal alloys on their stress–rupture properties at intermediate temperatures

The effects of the addition of Mo and Ta elements to Ni3Al based single crystal (SC) alloys on their microstructures and stress–rupture properties were investigated. The results of this research indicate that in a Ni3Al based SC alloy with an added 3%Ta, the volume fraction, mean size and cubical degree of the γ′ phase increased and the segregation ratios of the refractory elements were not totally altered, compared to the effects seen after the addition of 3%Mo, as analysed using scanning electron microscopy (SEM) and energy dispersive spectroscopy. Moreover, the lattice mismatch of the γ/γ′ phase in the Ni3Al based SC alloy became smaller, as observed using X-ray diffraction. The stress–rupture lives of the Ni3Al based SC alloys were ∼330 and 260 h respectively. The results suggest that Mo promotes an increase in the stress–rupture property and that the effect of Ta is less than that of Mo. Analysis through transmission electron microscopy illustrated that, in the alloy with Mo, a multiple slip of <011> [111] dislocations was developed to form dense dislocation networks and a few of the dislocations sheared into γ′ by short <112> [111] stacking faults ribbons. In the alloy with Ta, the dislocations sheared into the γ′ precipitates by coupled dislocation pairs without dense dislocation networks. These differing results are mostly due to larger lattice mismatch and denser dislocation networks formed through the addition of Mo.

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.

Heat Treatment of a Ni&lt;sub&gt;3&lt;/sub&gt;Al-Based Single Crystal Alloy IC32

C32 is a new type of Ni3Al-based single crystal alloy, which has been designed to serve at 1200. The effect of heat treatment on the microstructure of single crystal superalloy IC32 was investigated. The microstructure after heat treatment under different solution and aging temperature was examined by using optical microscope (OM), scanning electron microscopy (SEM) and electron probe microscopic analyzer (EPMA). The as-cast microstructure of IC32 consisted of a two-phase γ/γ microstructure, and primary bulky γ phase which priciptated in the interdendritic region. The incipient melting temperature of IC32 is 1360, and the heat treatment window is about 40. Considering high contents of refractory elements Re and Ta, a complicated 18 hours solution heat treatment at different temperatures was conducted to elimate the segregation and dissolove the primary bulky γ phase. The optimum heat treatment of IC32 alloy is 1325/4h+1335/4h+1345/10h, ac + 1165/2h, ac + 870/32h, ac.

Effects of boron and carbon contents on long-term aging of Ni3Al-base single crystal alloy IC6SX

Abstract: Effects of contents of boron and carbon on microstructure and mechanical properties of Ni3Al-base single crystal alloy IC6SX after long-term aging at 1070°C were investigated. It was found that, stress rupture life of samples with lower contents of boron and carbon was longer than that of higher contents of boron and carbon prior to long-term aging, but decreased much faster after aging at 1070°C.Microstructure of samples with higher contents of boron and carbon after standard heat treatment contained bulky γ’ and borides besides γ’+γ, and less carbides and Y-NiMo phases precipitated after aging at 1070°C.

Effect of yttrium on oxidation behavior of Ni3Al-based single crystal alloys

The influence of ∼0.18 wt.%Y addition on the oxidation behavior of Ni3Al-based single crystal alloy IC6SX at 1000 and 1100 °C was investigated, and the structure of oxidized surface was analyzed by X-ray diffraction. The research on the microstructure and composition of the oxides was conducted by means of a scanning electron microscope with EDAX unit. The results show that the addition of yttrium significantly improves the oxidation resistance of this alloy including reducing the oxidation rate and the spallation of oxide scale. The positive effects are probably due to finer grain size of surface oxide improving the scale plasticity, and thinner depth of oxide scale which allows greater critical strain energy of the scale to reduce the intrinsic growth stress. Meanwhile, a small amount of yttrium enhances the selective oxidation of Al and retards the formation of MoO3 which is detrimental to the oxidation resistance of alloys.

Effects of long-term aging at 1070 °C on microstructure of Ni3Al-base single-crystal alloy IC6SX

The effects of long-term aging at 1070 °C for periods of 100 h to 1500 h on microstructure of Ni3Al-base single-crystal alloy IC6SX were examined by SEM, EDX and TEM. Results show that alloy IC6SX undergoes following microstructure changes during long-term aging: a large number of rod-like Y-NiMo phases and carbides precipitate, and more of them appear in the interdendritic areas than in the dendritic arms; γ-phase aggregate and coarsen, and no longer show a continuous network-like distribution; adjacent γ′ phases grow bigger and become connected with each other; some larger sized γ′ phases are discovered in the dendritic arms; after aging for 300 h, γ phases amid a row of adjacent γ′ phases dissolve to form a γ′ band, and during further aging, γ phases beside the γ′ band grow wider and finally occupy the γ′ band, where a γ band is formed; a small portion of Y-NiMo phases are found to re-dissolve to form γ phases after aging for 1500 h.

Recrystallization of Ni 3Al Base Single Crystal Alloy IC6SX with Different Surface Mechanical Processes

The recrystallization behavior of Ni3Al base single crystal alloy IC6SX with different mechanical processes has been studied. The specimens of the alloy were treated by surface cleaning and cold working during the blades manufacture, and then heat treated in the temperature range of 800–1260°C for 1 h to 4 h. The microstrcture of the specimens were examined by optical and scaning electron microscopy, and the room temperature tensile property, stress rupture property under the test condition of 1100°C/130 MPa, and the thermal cycle fatigue resistance under 1100–20°C of the specimens with and without recrystallization were carried out. The experimental results showed that the initial recrystallization nucleation temperatures of the alloy by dry grit blasting, wet grit blasting, indentation, shot blasting and burnishing were 900–950°C/1 h, 1000–1100°C/1 h, 1200–1220°C/4 h, 1220–1240°C/1 h and 1220–1240°C/1 h, respectively and the primal recrystallization completing temperatures of the alloy by those mechanical processes mentioned above were 1200–1210°C/1 h, 1100–1200°C/1 h, 1220–1240°C/4 h, 1240–1260°C/1 h and 1240–1260°C/1 h, respectively. The results also indicated that the deformation amount of the specimens by burnishing and dry grit blasting was bigger than that by wet grit blasting and shot blasting according to their recrystallization temperature and the micro-hardness profile below the surface of specimens. It has been found that the recrystallization had no evident effect on mechanical properties of the alloy.

Effect of Heat Treatment on Microstructure and Mechanical Properties for a Ni&lt;sub&gt;3&lt;/sub&gt;Al Base Single Crystal Alloy DDIC6

The effect of heat treatment on microstructures and stress rupture property of a Ni3Al base single crystal alloy DDIC6 was studied in the present investigate. The single crystal specimens were produced by screw selection crystal method. The heat treatment for the alloy was 1300°C/10h+1120°C/4h+870°C/32h and 1300°C/10h+870°C/32h.The microstructures were examined by SEM, TEM and X-ray EDS techniques. The stress rupture tests were carried out in air by constant load creep machines under 1100°C/130MPa with the specimens size of φ5×25 mm. The experimental results showed that the as-cast large size γ′ phases entirely dissolved after 1300°C/10h, and secondary fine γ′ phases precipitated by following aging at 1120°C and 870°C for certain periods of time. The stress rupture life under 1100°C/130MPa increased from 20~30hrs for as-cast condition to 60~100hrs for heat treatment condition. The improvement of the creep resistance of the alloy may attribute to the decrement of the elements segregation at dendrite and interdendritic areas, and the proper size and distribution of γ′ phases.