Effect of γ' formation and strengthening elements on microstructures and stress rupture property of single crystal super-alloys

An investigation was carried out to study the effects of γ' formation and strengthening elements (Al, Ti and Ta) on the microstructure and stress rupture properties of nickel base single crystal super-alloys.The results show that with the increase of γ' formation and strengthening elements, the percentage of γ-γ' eutectic and the misfit degree of γ/γ' increases.Detailed microstructural analysis revealed that with the increase of γ' forming element content, the morphology of γ' changed from spherical to cubic, then irregular shape; and the size of γ' increases gradually.Excessive γ' formation and strengthening elements will lead to the precipitation of μ phase during stress rupture tests.The alloy with 5wt.%Al, 1wt.%Ti and 6wt.%Ta has the best stress rupture property.

Single crystal growth and characterization of 166-type magnetic kagome metals

Kagome magnets were predicted to be a good platform to investigate correlated topology band structure,Chern quantum phase,and geometrical frustration due to their unique lattice geometry.Here we reported single crystal growth of 166-type kagome magnetic materials,including HfMn_(6)Sn_(6),ZrMn_(6)Sn_(6),GdMn_(6)Sn_(6)and GdV_(6)Sn_(6),by using the flux method with Sn as the flux.Among them,HfMn_(6)Sn_(6)and ZrMn_(6)Sn_(6)single crystals were grown for the first time.X-ray diffraction measurements reveal that all four samples crystallize in HfFe6Ge6-type hexagonal structure with space group P6/mmm.All samples show metallic behavior from temperature dependence of resistivity measurements,and the dominant carrier is hole,except for GdV6Sn6 which is electron dominated.All samples have magnetic order with different transition temperatures,HfMn_(6)Sn_(6),ZrMn_(6)Sn_(6)and GdV_(6)Sn_(6)are antiferromagnetic with TN of 541 K,466 K and 4 K respectively,while GdMn_(6)Sn_(6)is ferrimagnetic with the critical temperature of about 470 K.This study will enrich the research platform of magnetic kagome materials and help explore the novel quantum phenomena in these interesting materials.The dataset of specific crystal structure parameters for HfMn_(6)Sn_(6)are available in Science Data Bank,with the link.

Purification of copper foils driven by single crystallization

High-purity copper(Cu) with excellent thermal and electrical conductivity, is crucial in modern technological applications, including heat exchangers, integrated circuits, and superconducting magnets. The current purification process is mainly based on the zone/electrolytic refining or anion exchange, however, which excessively relies on specific integrated equipment with ultra-high vacuum or chemical solution environment, and is also bothered by external contaminants and energy consumption. Here we report a simple approach to purify the Cu foils from 99.9%(3N) to 99.99%(4N) by a temperature-gradient thermal annealing technique, accompanied by the kinetic evolution of single crystallization of Cu.The success of purification mainly relies on(i) the segregation of elements with low effective distribution coefficient driven by grain-boundary movements and(ii) the high-temperature evaporation of elements with high saturated vapor pressure.The purified Cu foils display higher flexibility(elongation of 70%) and electrical conductivity(104% IACS) than that of the original commercial rolled Cu foils(elongation of 10%, electrical conductivity of ~ 100% IACS). Our results provide an effective strategy to optimize the as-produced metal medium, and therefore will facilitate the potential applications of Cu foils in precision electronic products and high-frequency printed circuit boards.

Single crystal growth and transport properties of narrow-bandgap semiconductor RhP_(2)

We report the growth of high-quality single crystals of RhP_(2),and systematically study its structure and physical properties by transport,magnetism,and heat capacity measurements.Single-crystal x-ray diffraction reveals that RhP_(2) adopts a monoclinic structure with the cell parameters a=5.7347(10)A,b=5.7804(11)A,and c=5.8222(11)A,space group P2_(1)/c(No.14).The electrical resistivityρ(T)measurements indicate that RhP_(2) exhibits narrow-bandgap behavior with the activation energies of 223.1 meV and 27.4 meV for two distinct regions,respectively.The temperaturedependent Hall effect measurements show electron domain transport behavior with a low charge carrier concentration.We find that RhP_(2) has a high mobilityμ_(e)~210 cm^(2)·V^(-1)·s^(-1)with carrier concentrations n_(e)~3.3×10^(18)cm^(3) at 300 K with a narrow-bandgap feature.The high mobilityμ_(e) reaches the maximum of approximately 340 cm^(2)·V^(-1)·s^(-1)with carrier concentrations n_^(e)~2×10^(18)cm^(-3)at 100 K.No magnetic phase transitions are observed from the susceptibilityχ(T)and specific heat C_(p)(T)measurements of RhP_(2).Our results not only provide effective potential as a material platform for studying exotic physical properties and electron band structures but also motivate further exploration of their potential photovoltaic and optoelectronic applications.

Oxidation behavior of 4774DD1 Ni-based single-crystal superalloy at 980℃ in air

The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain methods.The phase constitution and morphology of surface oxides and the characteristics of the crosssection oxide film were analyzed by XRD,SEM and EDS.Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law,indicating its weak oxidation resistance at this temperature.As the oxidation time increases,the composition of the oxide film evolves as following:One layer consisting of a bottom Al_(2)O_(3)sublayer and an upper(Al_(2)O_(3)+NiO)mixture sublayer after oxidized for 25 h.Then,two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h.This internal layer is consisted of the bottom Al_(2)O_(3)sublayer,an intermediate narrow CrTaO_(4)sublayer,and an upper(Al_(2)O_(3)+NiO)mixture sublayer.Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h.This internal layer is composed of the upper(Al_(2)O_(3)+NiO)mixture sublayer,an intermediate continuous(CrTaO_(4)+NiWO_(4))mixture sublayer,and a bottom Al_(2)O_(3)sublayer.Finally,three layers consisting of an outermost(NiAl2O_(4)+NiCr2O_(4))mixture layer,an intermediate(CrTaO_(4)+NiWO_(4))mixture layer,and a bottom Al_(2)O_(3)layer for 200 h.

Analysis of deformation mechanisms in magnesium single crystals using a dedicated four-point bending tester

In this study,we explored the deformation mechanisms of Mg single crystals using a combination of scanning electron microscopy and electron backscattered diffraction in conjunction with a dedicated four-point bending tester.We prepared two single-crystal samples,oriented along the<1120>and<1010>directions,to assess the mechanisms of deformation when the initial basal slip was suppressed.In the<1120>sample,the primary{1012}twin(T1)was confirmed along the<1120>direction of the sample on the compression side with an increase in bending stress.In the<1010>sample,T1 and the secondary twin(T2)were confirmed to be along the<1120>direction,with an orientation of±60°with respect to the bending stress direction,and their direction matched with(0001)in T1 and T2.This result implies that crystallographically,the basal slip occurs readily.In addition,the<1010>sample showed the double twin in T1 on the compression side and the tertiary twin along the<1010>direction on the tension side.These results demonstrated that the maximum bending stress and displacement changed significantly under the bend loading because the deformation mechanisms were different for these single crystals.Therefore,the correlation between bending behavior and twin orientation was determined,which would be helpful for optimizing the bending properties of Mg-based materials.

Synergistic effect of orientation and temperature on slip behavior and precipitation behavior of Al−Cu−Li single crystals

The slip behavior and precipitation behavior of four Al−Cu−Li single crystals with varying orientations at different temperatures were investigated using electron backscattering diffraction(EBSD)and transmission electron microscopy(TEM).The maximum differences in yield strength and ductility of the single crystals at room temperature are 41.6%and 14.7%,respectively.This indicates that the mechanical properties are strongly influenced by the crystal orientation.Moreover,grains with varying orientations exhibit distinct slip characteristics,including slip homogenization,slip localization,and multiple slip.In single crystal SC1,slip localization primarily contributes to its inferior ductility compared to other grains.Nevertheless,during deformation at 250℃,the distinct morphology and distribution of precipitates in the crystals are also correlated with orientation,which causes the increase in the maximum elongation difference to 20.8%in all selected single crystals.Notably,SC1,with a precipitate volume fraction of 2.65%,exhibits more severe slip localization compared to room temperature conditions,while SC2,with a precipitate volume fraction of 4.79%,demonstrates cross-slip characteristics,significantly enhancing the plastic deformation capacity of the Al−Cu−Li alloy.

Localization effect in single crystal of RuAs_(2)

We report the magnetotransport and thermal properties of RuAs_(2) single crystal.RuAs_(2) exhibits semiconductor behavior and localization effect.The crossover from normal state to diffusive transport in the weak localization(WL)state and then to variable range hopping(VRH)transport in the strong localization state has been observed.The transitions can be reflected in the measurement of resistivity and Seebeck coefficient.Negative magnetoresistance(NMR)emerges with the appearance of localization effect and is gradually suppressed in high magnetic field.The temperature dependent phase coherence length extracted from the fittings of NMR also indicates the transition from WL to VRH.The measurement of Hall effect reveals an anomaly of temperature dependent carrier concentration caused by localization effect.Our findings show that RuAs_(2) is a suitable platform to study the localized state.

Mitigating kinetic hindrance of single-crystal Ni-rich cathodes through morphology modulation,nickel reduction,and lithium vacancy generation achieved by terbium doping

Single crystallization has proven to be effective in enhancing the capacity and stability of Ni-rich LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(SNCM)cathode materials,particularly at high cut-off voltages.Nevertheless,the synthesis of high-quality single-crystal particles remains challenging because of severe particle agglomeration and irregular morphologies.Moreover,the limited kinetics of solid-phase Li^(+)diffusion pose a significant concern because of the extended diffusion path in large single-crystal particles.To address these challenges,we developed a Tb-doped single-crystal LiNi_(0.83)Co_(0.11)Mn_(0.06)O_(2)(SNCM-Tb)cathode material using a straightforward mixed molten salt sintering process.The Tb-doped Ni-rich single crystals presented a quasi-spherical morphology,which is markedly different from those reported in previous studies.Tb^(4+)oping significantly enhanced the dynamic transport of Li^(+)ions in the layered oxide phase by reducing the Ni valence state and creating Li vacancies.A SNCM-Tb material with 1 at%Tb doping shows a Li^(+)diffusion coefficient up to more than 9 times higher than pristine SNCM in the non-diluted state.In situ X-ray diffraction analysis demonstrated a significantly facilitated H1-H2-H3 phase transition in the SNCM-Tb materials,thereby enhancing their rate capacity and structural stability.SNCM-Tb exhibited a reversible capacity of 186.9 mA h g^(-1)at 5 C,retaining 94.6%capacity after 100 cycles at 0.5 C under a 4,5 V cut-off.Our study elucidates the Tb^(4+)doping mechanisms and proposes a scalable method for enhancing the performance of single-crystal Ni-rich NCM materials.

High cycle fatigue behavior of the second generation single crystal superalloy DD6

The second generation single crystal superalloy DD6 with 0.10%Hf and 0.34%Hf （in mass fraction） was subjected to high-cycle fatigue （HCF） loading at temperatures of 700 ℃ in ambient atmosphere. SEM was used to determine the initiation site and the failure mechanism. Evolution of the microstructure was investigated by TEM observation. The results show that fatigue limit of DD6 alloy with 0.34%Hf is a little smaller than that of the alloy with 0.10%Hf. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along { 111 } octahedral slip planes, rather than perpendicular to the loading axis of specimen. Typical fatigue striation formed in steady propagation of fatigue crack. The fracture mechanisms of the high cycle fatigue of DD6 alloys with 0.10%Hf and 0.34%Hf are quasi-cleavage fracture. Different types of dislocation structures were developed during high cycle fatigue deformation.

Temperature dependence of anisotropic stress-rupture properties of nickel-based single crystal superalloy SRR99

In order to reveal the temperature dependence of anisotropic stress？rupture behavior of SRR99 single crystal superalloys under conditions of temperature ranging from 650 to 1 040 °C and typical stresses,fracture morphologies and microstructure evolution were investigated by SEM and TEM.From the Larson-Miller curves,it is found that single crystal with [001] orientation has the optimum stress rupture property in comparison with [011] and [111] orientations at lower and intermediate temperature.With increasing temperature to 1 040 °C,stress-rupture properties of single crystals with three principal orientations tend to be equivalent.Based on the fracture surface and microstructural observations,superior stress？rupture behavior of single crystal with [001] orientation was rationalized and the effect of misorientation of single crystal on stress rupture property was also discussed.

Surface recrystallization of single crystal nickel-based superalloy

As-cast single crystal （SC） superalloy samples were shot peened and then annealed at different temperatures to investigate the effect of annealing temperature on the surface recrystallization behavior of the SC superalloy. The results show that the depth of recrystallized layers increases with the increase of annealing temperature. Below 1200 °C, the recrystallization depth climbs slowly with temperature rising. Above 1200 °C, the recrystallization depth increases sharply with the rise of temperature. The morphology of recrystallized grains is significantly affected by annealing temperature. Below the γ′ solvus, cellular recrystallization may be observed. Above the γ′ solvus, recrystallization occurs through the growth of well developed recrystallized grains. In addition, the microstructure evolution of recrystallized grains at the homogenization annealing temperature was studied. It is found that recrystallized grains first nucleate in the dendritic core areas on the shot-peened surface and then grow inwards along the dendritic core areas. With the dissolution of the coarse γ′ precipitates and γ/γ′ eutectics in the interdendritic areas, the recrystallized grain boundaries move through the interdendritic areas. Finally, the fully developed grains nearly have a uniform depth. The dissolution of primary γ′ precipitates is a critical factor influencing the recrystallization behavior of SC superalloys.

Influence of temperature on tensile behavior and deformation mechanism of Re-containing single crystal superalloy

Tensile properties of a Re-containing single crystal superalloy were determined within the temperature range from 20 to 1 100 ℃with a constant strain rate of 1.67 ×10^-4 s^-1.From room temperature to 600 ℃,the yield strength increases slightly with increasing temperature.The yield strength decreases to aminimum at 760 ℃,while a maximum is reached dramatically at 800 ℃.The elongation and area reduction decrease gradually from room temperature to 800 ℃.Above 800 ℃,the yield strength decreases significantly with increasing temperature.The γ＇ phase is sheared by antiphase boundary （APB） below 600 ℃while elongated SSF （superlattice stacking fault） is left in γ＇ as debris.At 760 ℃the γ＇ phase is sheared by a/3 112 superpartial dislocation,which causes decrease of yield strength due to low energy of SSF.Above 800 ℃dislocations overcome γ＇ through by-passing mechanism.

Effect of carbon addition on carbide morphology of single crystal Ni-based superalloy

Single crystal superalloys of AM3 with different carbon levels were prepared at withdraw rate of 50μm/s. The effect of carbon addition on the carbide morphology was investigated. It was found that there were four types of MC-type carbides, acicular, nodular, blocky, and Chinese script-type in the crystals. With an increase in carbon level, the volume fraction of carbide increased significantly while the volume fraction of eutectic decreased significantly. Furthermore, the size of carbide in high level carbon alloy became much larger.

Effect of Ru on stress rupture properties of nickel-based single crystal superalloy at high temperature

Two experimental single crystal superalloys, Ru-free alloy and Ru-containing alloy with [001] orientation, other alloying element contents being basically kept same, were cast in the directionally solidified furnace. The effect of Ru on the stress rupture properties of the single crystal superalloy was investigated at （980 ℃, 250 MPa）, （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa）. The results show that Ru can enhance high temperature stress rupture properties of single crystal superalloy. The improvement effect of Ru addition on stress rupture properties decreases with increasing test temperature. The γ′ coarsening and rafting directionally are observed in Ru-free alloy and Ru-containing alloy after stress rupture test. Needle shaped TCP phases precipitated in both of alloys after stress rupture test at （1100 ℃, 140 MPa） and （1120 ℃, 140 MPa） and no TCP phase was observed in both of alloys after stress rupture test （980 ℃, 250 MPa）. The precipitate volume fraction of TCP phases is significantly decreased by the addition of Ru. At last, the relationship between the microstructure change with Ru addition and improvement of stress rupture properties was discussed.

Effect of ruthenium on γ' precipitation behavior and evolution in single crystal superalloys

The effect of Ru on γ＇ precipitation behavior and evolution in single crystal superalloys with different Ru contents were investigated by scanning electron microscopy with energy dispersive spectroscopy,3D atomic probing,differential scanning calorimetry.The results show that the solvus of the γ＇ phase decreases gradually with increasing Ru content in the alloys by casting or by the same solution and aging treatments,the alloy with a larger Ru content yields a smaller γ＇ phase.The addition of Ru increases the growth rate and coarsening rate of the γ＇ phase.Ru mainly distributes in the γ phase,which causes more Re and Mo partition into the γ＇ phase,increasing the absolute value of mismatch and the rafting rate of the γ＇ phase.

Isothermal oxidation behavior of single crystal superalloy DD6

The isothermal oxidation behavior of the second generation single crystal superalloy DD6 was studied at 1050 ℃ and 1100 ℃ in ambient atmosphere.Morphology of oxides was examined by SEM and their composition was analyzed by XRD and EDS.The experimental results show that DD6 alloy obeys subparabolic rate law during oxidation of 100 h at 1050 ℃ and 1100 ℃.The oxide scale exposed at 1050 ℃ is made up of an outer NiO layer with a small amount of Al2O3 and an inner Al2O3 layer.The oxide scale exposed at 1100 ℃ is made up of an outer Al2O3 layer with a small amount of NiO,an intermediate layer,mainly composed of Cr2O3 and TaO2,and an inner Al2O3 layer.The γ＇-free layer was formed under the oxide scale at two temperatures.

Influence of spiral crystal selector on crystal orientation of single crystal superalloy

To increase efficiency and improve performance, reducing cost and emissions, advanced single crystal Ni-based superalloys are required in aerospace propulsion and power generating gas turbines. With the development of alloy, significant improvements in casting techniques have been achieved by introducing the directionally solidified （DS） casting process followed by single crystal （SX） technique. The deviation of preferred orientation of single crystal superalloys is one of the most important defects in casting. In directional solidification equipment with high temperature gradient, single crystal specimens of DZ417G alloy were prepared successfully by the modified Bridgeman method with spiral grain selector. The orientation was investigated by means of X-ray diffraction （XRD） and electron backscattered diffraction （EBSD）.The results show that the crystal selector with a smaller angle can effectively reduce the deviation of preferred orientation.

Creep properties and microstructure evolution of nickel-based single crystal superalloy at different conditions

The creep properties of nickel-based single crystal superalloy with [001] orientation was investigated at different test conditions. The microstructure evolution of γ′ phase, TCP phase and dislocation characteristic after creep rupture was studied by SEM and TEM. The results show that the alloy has excellent creep properties. Two different types of creep behavior can be shown in the creep curves. The primary creep is characterized by the high amplitude at test conditions of (760 °C, 600 MPa) and (850 °C, 550 MPa) and the primary creep strain is limited at (980 °C, 250 MPa), (1100 °C, 140 MPa) and (1120 °C, 120 MPa). A little change ofγ′precipitate morphology occurs at (760 °C, 600 MPa). The lateral merging of the γ′ precipitate has already begun at (850 °C, 550 MPa). Theγphase is surrounded by theγ′phase at (980 °C, 250 MPa). Theγphase is no longer continuous tested at (1070 °C, 140 MPa). At (1100 °C, 120 MPa), the thickness ofγphase continues to increase. No TCP phase precipitates in the specimens at (760 °C, 600 MPa), (850 °C, 550 MPa) and (980 °C, 250 MPa). Needle shaped TCP phase precipitates in the specimens tested at (1070 °C, 140 MPa) and (1100 °C, 120 MPa). The dislocation shear mechanism including stacking fault formation is operative at lower temperature and high stress. The dislocation by-passing mechanism occurs to form networks atγ/γ′interface under the condition of high temperature and lower stress.

Effects of Cr content on microstructure and mechanical properties of single crystal superalloy

Two experimental single crystal superalloys with 2% Cr and 4% Cr (mass fraction) were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Cr content on the microstructure, phase stability, tensile properties at 1100 °C and stress rupture properties at 1070 °C and 160 MPa of the single crystal superalloy were investigated. The results show that the size ofγ′ phase particles become small and uniform, and the cubic shape turns a little regular with the increase of Cr content. Theγ′ directional coarsening and rafting were observed in the 2% Cr and 4% Cr alloys after long term aging (LTA) at 1100 °C. The rafting rate ofγ′ phase increased with increasing Cr content. Needle-shaped topologically close packed (TCP) phases precipitated and grew along fixed direction in both alloys. The precipitating rate and volume fraction of TCP phases significantly increased with the increase of Cr content. The tensile property of the alloy increased and the stress rupture properties of the alloy decreased with the increase of Cr content at high temperature. The increase of Cr content increased the partition ratio of TCP forming elements, Re, W, and Mo, and the saturation degrees of these elements inγ phases increased. Therefore, the high temperature phase stability of the alloy decreased with the increase of Cr content.