Ni3Al-based Alloy Research Articles

Influence of aging heat treatment on microstructure and mechanical properties of a novel polycrystalline Ni3Al-based intermetallic alloy

A novel polycrystalline Ni3Al-based intermetallic alloy was prepared using the vacuum induction melting process. Subsequently, the alloy was subjected to the solution-treatment underwent two different aging processes: 870 °C for 24 h in air cooling, referred to as AT 1, and 1060 °C for 4 h in air cooling followed by 870 °C for 24 h in air cooling, referred to as AT 2. The effects of different aging processes on the microstructure and mechanical properties of the polycrystalline Ni3Al-based intermetallic alloys were analyzed. Results indicated the cubicity of the primary γ′ phase within the dendritic γ+γ′ structure of the AT 2 sample was significantly enhanced, yielding the best overall mechanical properties for the alloy. The percentage elongation increased from less than 3 % for the AT 1 sample to about 4.5 %, highlighting a notable enhancement in room temperature tensile plasticity. The creep rupture time at 1100 °C/30 MPa reached 113 h. The α-Cr particles in the As-cast and solid solution alloy gradually transformed into Cr23C6 during the aging process, exhibiting the orientation relationships of (020)Cr23C6||(010)γ' and [103]Cr23C6||[103]γ'. High-temperature aging treatments resulted in Cr23C6 particles that provided enhanced precipitation strengthening effects, thereby improving the creep rupture performance of the Ni3Al-based intermetallic alloys. Following high-temperature aging, a four-layer interface structure formed around the blocky γ′ matrix phase, which altered the alloy's fracture mechanism from a brittle intergranular fracture to a ductile transgranular fracture.

Studying the Effect of the Period of Mechanical Activation on the Formation of Ni3Al-Based High-Legered Alloys Obtained via Spark Plasma Sintering

Studying the Effect of the Period of Mechanical Activation on the Formation of Ni3Al-Based High-Legered Alloys Obtained via Spark Plasma Sintering

High-temperature thermal fatigue of Ni3Al-based single crystal alloy affected by wall thickness and peak temperature

Complex thin-walled structures are commonly employed in turbine components to improve cooling efficiency. However, thin-walled blades are prone to thermal fatigue failure due to the high thermal stress induced by frequent and abrupt temperature fluctuations during duty cycles. The thermal fatigue behavior of Ni3Al-based single crystal alloy with thin-walled structure during 25 °C ↔ 1000 °C/1100 °C was investigated by combining thermal fatigue tests and finite element simulation. The thermal fatigue demonstrated a significant thickness debit effect, with thermal fatigue property dropping as peak temperature and wall thickness increased. Wall thickness had a more pronounced effect than peak temperature. Visible slip traces were found on the wall thickness surface, and their density was positively correlated with wall thickness. Further investigation revealed that thermal fatigue is primarily driven by the octahedral slip system ({111}<110>), with significant contributions from (111)[101‾] and (1‾1‾1)[101]. Simulations of thermal stress distribution and J-integral at the crack tip during crack initiation and propagation stages indicated that wall thickness influences thermal fatigue properties by affecting thermal stress concentration at the notch and crack tip. Higher peak temperatures increased thermal stress and reduced yield strength, thus diminishing thermal fatigue performance. A thermal fatigue crack propagation prediction model was constructed incorporating Paris' law and the J-integral. The model revealed an unfavorable correlation between material Cj/ nj and both peak temperature/wall thickness, indicating that both factors adversely affect thermal fatigue resistance.

Preparation of the close cross-section component of NiAl-based alloy by a novel combined sintering method

In this study, to overcome the bottleneck of forming NiAl for aerospace applications, a novel combined sintering method based on hot-press sintering, which divides the components into various parts and compacts them gradually, is proposed and studied. Two typical close cross-sectional components (tube-like components and conical tube components with flanges), which are highly demanding and more challenging to obtain for NiAl intermetallic, were prepared and analyzed in detail. Based on these results, both prepared components were fully dense. In addition, as shown by the bending tests, the interfacial strength is between the strengths of the base alloys on the two sides, which confirms the reliable bonding ability achieved by this method. For the conical tube component with flange, the ultimate tensile strength of the combined-sintered part in 1000 ℃ is 406.7±3.2 MPa, and the ultimate strength of the pre-sintered part is 368.6±2.7 MPa, which are 39% and 26% higher than the strength of blade-like component prepared by casting and hot isostatic pressing (292 MPa). The proposed method discussed in our study can overcome the uneven density defects in HPS and achieve collaborative control of both the shape and performance when preparing a high height-to-thickness ratio or a complex-shaped close cross-section component.

The Effect of Laser Power on the Microstructure and Wear Resistance of a Ni3Al-Based Alloy Cladding Layer Deposited via Laser Cladding

A coating prepared via laser cladding has the advantages of a high-density reinforced layer, a low matrix dilution rate, and combination with matrix metallurgy. In this study, Ni3Al-based alloy cladding layers with Cr7C3 were prepared via laser cladding, and the corresponding microstructures and wear resistance were studied in detail. The results show that the Ni3Al-based cladding layer prepared using laser cladding technology had good metallurgical bonding with the matrix, and there were no pores, cracks, or other defects on the surface. The microstructures of the laser cladding layer were mainly γ′-Ni3Al, β′-NiAl, and in situ C7C3. As the laser power increased, the heat input increased, resulting in an increase in the dilution rate. Simultaneously, the carbide size in the laser cladding layer increased. With the increase in laser power, the hardness of the laser cladding layer of the Ni3Al-based alloy decreased, and the wear resistance of the laser cladding layer first strengthened and then weakened. When the laser power increased to 2.0 kW, the wear rate of the laser cladding layer decreased to 0.480 × 10−5 mm3/N·m. When the laser power increased to 2.4 kW, the wear rate of the laser cladding layer increased to 0.961 × 10−5 mm3/N·m, which was twice the rate at 2.0 kW. This could be attributed to small Cr7C3 particles, which could not effectively separate the wear pairs, resulting in more serious adhesive wear. Large Cr7C3 particles caused the surface of cast iron material with lower hardness to be damaged, which suffered more serious particle wear. The generation of short rod-shaped carbides should be avoided because, in the process of friction and wear, carbides with these shapes are easy to break, thus leading to crack initiation.

Microstructure, Phase Composition, and Mechanical Properties of Intermetallic Ni-Al-Cr Material Produced by Dual-Wire Electron-Beam Additive Manufacturing

Electron-beam additive manufacturing is one of the most promising methods for creating complex metal parts and structures. Additive manufacturing has already gained wide acceptance in the creation of various constructions from aluminum, copper, titanium, and their alloys as well as different classes of steels and other metallic materials. However, there are still many challenges associated with the additive manufacturing and post-production processing of intermetallic alloys. Thus, it is currently an urgent task for research. In this work, heat-resistant intermetallic alloys based on nickel, aluminum, and chromium were produced by dual-wire electron-beam additive manufacturing using commercial NiCr and Al wires. The microstructure, phase composition, and microhardness of the intermetallic billets are strongly dependent on the ratio of NiCr and Al wires, which have been fed during the additive growth of the material (NiCr:Al = 3:1 and NiCr:Al = 1:3). A metal-matrix composite material (Al3Ni-based intermetallide in Al-based matrix) was fabricated using the NiCr:Al = 1:3 ratio of the wires during the deposition. In tension, it fractures in a brittle manner before the plastic deformation starts, and it possesses a high microhardness of 6–10 GPa with a high dispersion of the value (the mean value is 8.7 GPa). This is associated with the complex phase composition of the material and the high fraction of a brittle Al3Ni intermetallic phase. In the material, obtained with the ratio NiCr:Al = 3:1, the ordered Ni3Al(Cr) and disordered Ni3Cr(Al) intermetallides are the dominating phases. Its microhardness turned out to be lower (4.1 GPa) than that in Al + Al3Ni-based composite, but intermetallic Ni3Al-based alloy demonstrates good mechanical properties in a high-temperature deformation regime (650 MPa, more than 10% elongation at 873 K). Microstructural studies, analysis of phase composition, and tensile mechanical properties of additively produced intermetallic materials show the perspective of dual-wire electron-beam additive manufacturing for producing intermetallic compounds for high-temperature applications.

Изучение условий получения прекурсоров из жаропрочного сплава на основе NiAl, предназначенных для 3D технологий

This article is the second in a series of articles devoted to studying the possibilities of preparing high-quality powder materials from heat-resistant light alloys based on refractory monoaluminides of nickel (β-NiAl), ruthenium (β-RuAl) and the FeCrAl system (fechrals) for the production of compact samples/products of complex shapes using additive technologies with minimal final machining. Additive technologies are based on the use of spherical precursor micropowders with a regulated granulometric composition, good fluidity and an oxide-free surface. In the first article, the possibilities of obtaining precursors from RuAl-based alloys by plasma spheroidization of powders obtained by crushing mixtures from scrap samples of RuAl-based alloys with various additives were considered. This article examines the possibility of obtaining precursors from NiAl-based alloys by plasma spheroidization of powders obtained by crushing mixtures from scrap samples of NiAl-based alloys with various additives. It has been shown that grinding and subsequent grinding of scrap powders in an attritor makes it possible to obtain precursors using the “attrition + plasma spheroidization” scheme with characteristics that make them suitable for additive manufacturing (perfectly round shape, surface almost free of oxides, phase composition – solid solution grains on based on NiAl with thin layers of Ni3Al of nano-sized thickness). The non-uniform distribution of alloying elements in NiAl grains is caused by the short duration (5 hours) of grinding the initial powders of scrap ingots of various compositions obtained using foundry technology. This can be corrected by increasing the grinding duration to 15 hours, which will require the use of the “attrition + granulation + plasma spheroidization” scheme, since the proportion of dispersed powders that must be included in circulation will increase. It has been shown that preliminary reaction alloying in the liquid phase (vacuum arc melting), including the use of recycled materials (scrap alloy samples) as starting materials, allows one to vary the alloy compositions over a wide range, using small volumes of material, and does not require specialized equipment.

Effect of Platinum Addition on Microstructure and Oxidation Behavior of Ni3Al-Base Alloys

Effect of Platinum Addition on Microstructure and Oxidation Behavior of Ni3Al-Base Alloys

P phase precipitation and strengthening behavior of a novel polycrystalline Ni3Al-based intermetallic alloy at 1100 °C

The microstructural evolution and strengthening behavior of a polycrystalline Ni3Al-based intermetallic alloy were investigated during varying durations of thermal exposure at 1100 °C. The study focused on the topologically closed-packed orthorhombic P phase precipitate, which was found to form in the interdendritic γ channel and grow in the γ'-matrix after thermal exposure. The morphology of the P phase evolved from needle-like to lath-like and then to blocky-like. The crystal structure and composition of the precipitates were analyzed using scanning transmission electron microscopy (STEM) and electron probe X-ray microanalysis (EPMA). The chemical composition of the P phase changed continuously during thermal exposure and the P phase was related to the γ'-matrix by three sets of orientation relationships (OR). The alloy's tensile properties and creep fracture time were enhanced during thermal exposure at 1100 °C for 2000 h due to P phase precipitation at grain boundaries or within the grain. Based on the experimental evidence of this study and theoretical strengthening behavior reported in the literature, a novel mechanism for in-situ precipitation strengthening was proposed.

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.

Atomistic analysis of temperature-dependent dislocation dynamics in Ni3Al-based intermetallic alloys

In this study, we investigate the dynamics of superlattice edge dislocations composed of partial dislocations, complex stacking faults, and antiphase boundaries in binary and ternary Ni-based alloys (γ’ phase) with the L12 structure. In the case of Ni3Al, the dislocation velocity decreases with increasing temperature at low applied shear stress, mainly owing to the phonon drag effect. Meanwhile, in the case of ternary alloys constructed by exchanging Ni atoms with Co atoms in Ni3Al, the effects of temperature on dislocation motion are more complex. At low applied shear stress, the dislocation motion is disturbed by solute Co (i.e., solid-solution strengthening). In this case, the temperature promotes dislocation motion because the potential energy barrier dominates the thermally activated dislocation dynamics. In contrast, when the applied shear stress increases, the temperature suppresses dislocation motion owing to the phonon drag effect. The drag effect also increases with increasing Co concentration. The origin of the energy barrier due to solute atoms at low applied shear stress can be explained by the interaction between the partial dislocation and solute Co. Meanwhile, the origin of the drag effect on the superlattice dislocation dynamics is discussed on the basis of atomic vibrational motions and wavy dislocation behaviors. In this study, we propose and construct a map showing the dominant effects on complex superlattice dislocation dynamics. The map has energy-barrier-dominated, phonon-drag-dominated, and sound velocity-dominated regions, suggesting that the dominant factor changes depending on the applied shear stress, temperature, and strength of the solute–dislocation interaction.

Laser powder bed fusion of a Ni3Al-based intermetallic alloy with tailored microstructure and superior mechanical performance

Ni3Al-based alloys are excellent candidates for the structural materials used for turbine engines due to their excellent high-temperature properties. This study aims at laser powder bed fusion and post-hot isostatic pressing (HIP) treatment of Ni3Al-based IC-221 ​M alloy with a high γ′ volume fraction. The as-built samples exhibits unavoidable solidification cracking and ductility dip cracking, and the laser parameter optimization can reduce the crack density to 1.34 ​mm/mm2. Transmission electron microscope (TEM) analysis reveals ultra-fine nanoscale γ′ phases in the as-built samples due to the high cooling rate during rapid solidification. After HIP treatment, a fully dense structure without cracking defects is achieved, which exhibits an equiaxed structure with grain size ∼120–180 ​μm and irregularly shaped γ′ precipitates ∼1–3 ​μm with a prominently high fraction of 86%. The room-temperature tensile test of as-built samples shows a high ultimate tensile strength (σUTS) of 1039.7 ​MPa and low fracture elongation of 6.4%. After HIP treatment, a significant improvement in ductility (15.7%) and a slight loss of strength (σUTS of 831.7 ​MPa) are obtained by eliminating the crack defects. Both the as-built and HIP samples exhibit retained high σUTS values of 589.8 ​MPa and 786.2 ​MPa, respectively, at 900 ​°C. The HIP samples exhibita slight decrease in ductility to ∼12.9%, indicating excellent high-temperature mechanical performance. Moreover, the abnormal increase in strength and decrease in ductility suggest the critical role of a high γ′ fraction in cracking formation. The intrinsic heat treatment during repeating thermal cycles can induce brittleness and trigger cracking initiation in the heat-affected zone with notable deteriorating ductility. The results indicate that the combination of LPBF and HIP can effectively reduce the crack density and enhance the mechanical properties of Ni3Al-based alloy, making it a promising material for high-temperature applications.

Microstructure and mechanical properties of a novel polycrystalline Ni3Al-based intermetallic alloy

A polycrystalline Ni3Al-based intermetallic alloy was successfully prepared via vacuum induction melting processing. Next, the microstructural evolution and mechanical properties of the intermetallic alloy were investigated by solution treatments at temperatures ranging from 1230 to 1290 °C. The results showed that the as-cast polycrystalline Ni3Al-based intermetallic alloy consisted of dendrite γ+γ′ with interdendritic distribution, matrix γ′ phase, and eutectic γ–γ′, and the total volume fraction of γ′ phase was ∼83.2%. After solution treatment at 1270 °C, the size and morphology of the γ′ phase changed and the secondary γ′ phase precipitated in the γ channel. The maximum room temperature yield strength, tensile strength and elongation reached 488 MPa, 686 MPa, and 5.2%, respectively. At 1100 °C, the high-temperature tensile strength of sample subjected to solution treatment at 1250 °C reached 203 MPa. It was found that solution treatment did not eliminate the incipient γ′m, resulting in the weaker interdendritic boundary area in the alloy. Moreover, noteworthy, α-Cr particles were found in the γ′m of the polycrystalline Ni3Al-based intermetallic alloy, revealing an orientation relationship such as [123]α-Cr∥[123]γ' and (1–21)α-Cr∥(11–1)γ'. The α-Cr particles have the strengthening effect of second-phase particles through pinning dislocations, which can improve the high-temperature creep performance of the alloy.

Tribological Behavior and Self-Healing Properties of Ni3Al Matrix Self-Lubricating Composites Containing Sn-Ag-Cu and Ti3SiC2 from 20 to 800 °C

As a high-temperature structural material, Ni3Al matrix composites are often used to manufacture basic mechanical components that need to be used in high-temperature conditions. To meet the increasing demand for metal matrix composites with an excellent tribological performance over a wide temperature range, Ni3Al matrix self-lubricating composites containing Sn-Ag-Cu and Ti3SiC2 (NST) were synthesized via laser-melting deposition. Dry sliding friction tests of NST against Si3N4 ball were undertaken from 20 to 800 °C to investigate the tribological behavior and wear-triggered self-healing properties. The results show that the tribological behaviors of NST are strongly dependent on the testing temperature and self-healing properties. At low and moderate temperatures from 20 to 400 °C, as the Sn-Ag-Cu flows into the cracks and is oxidized during sliding friction, while the cracks on the worn surface are filled with oxides consisting mainly of Al2O3, SnO2 and CuO. At higher temperatures of 600 and 800 °C, the cracks are filled by the principal oxides of Al2O3, TiO2 and SiO2 due to the partial decomposition and oxidation of Ti3SiC2. Compared with other testing temperatures, the recovery ratio relative to the Ni3Al base alloy of the cracks on the worn surface of NST is the highest at 400 °C, which is about 76.4%. The synergistic action mechanisms of Sn-Ag-Cu and Ti3SiC2 on the crack self-healing from 20 to 800 °C play a significant role in forming a stable solid lubricating film, improving the anti-friction and wear resistance of NST. The results provide a solution allowing for metal matrix composites to achieve excellent lubrication stability over a wide temperature range by virtue of the crack self-healing properties.

Microstructure and cracking behavior of Ni3Al-based IC21 alloy fabricated by selective laser melting

Microstructure and cracking behavior of Ni3Al-based IC21 alloy fabricated by selective laser melting

Non-uniform high-temperature oxidation behavior of twin wire and arc additive manufactured Ni3Al-based alloy

Ni3Al-based alloy fabricated by twin wire and arc additive manufacturing exhibited periodic remelting bands (RB) with unique microstructural characteristics. In this work, the deposited Ni3Al-based alloy was oxidized at 1100 °C for different times to investigate the high-temperature oxidation difference caused by RB. The differences in the microstructure, grain orientation, oxidation behavior, and oxidation mechanism between RB and non-RB were systematically studied. The results showed that these RB, epitaxially grown on the non-RB during each deposition layer, displayed similar Goss textures but a higher proportion of γ + γ′ dual-phase microstructure compared to non-RB. The oxidation of the deposited Ni3Al-based alloy obeyed parabolic growth kinetics at 1100 °C for 10 h and the oxidation scales were consisted of external NiO layer, intermediate NiAl2O4 layer with dispersed Al2O3 and TiO2 particles and internal Al2O3 layer. The outward diffusion of Al and Ti elements during the oxidation process led to the decomposition of γ′ precipitations and the formation of γ′-reduced layer beneath the Al2O3 layer. The cross-section microstructure of oxidation scales indicated that the RB displayed thicker scales and poorer oxidation resistance than non-RB. The oxidation rate of the deposited Ni3Al-based alloy was controlled by the outward transport rate of the total cations (Ni2+, Al3+, and Ti4+) through the Al2O3 layer. Initial oxidation and diffusion interface analysis demonstrated that the γ + γ′ dual-phase had a higher outward transport rate of the cations, which was responsible for the thicker oxide scales on the RB.

Influences of laser remelting treatments on microstructure and tensile properties of multiphase Ni3Al-based intermetallic alloy

The microstructure control of multiphase Ni3Al-based intermetallic alloy by traditional heat treatment is still limited, especially size and volume fraction of interdendritic β phase cannot be effectively reduced, due to the limitation of interdendritic β phase dissolution temperature close to the melting point of the alloy. In present work, the temperature gradient and solidification rate of the alloy under different laser remelting parameters were calculated by the Rosenthal equation. Afterward, the as-cast multiphase Ni3Al-based intermetallic alloy (19.4 vol% of interdendritic β phase) was remelted under different laser parameters of 3000–4500 W laser power and 5–20 mm/s laser scanning rate. And the effects of different laser remelting parameters on the microstructure, room temperature, and 980 °C high-temperature tensile properties of multiphase Ni3Al-based intermetallic alloy were studied. The results show that laser remelting treatment with the appropriate parameters (4000 W laser power and 10 mm/s laser scanning rate) can effectively reduce the size and volume fraction of interdendritic β phase and the morphology and size of γ′ phase in the γ′+γ dendrite, and significantly refine the microstructure of alloy, thus effectively improving the room temperature and 980 °C tensile properties of multiphase Ni3Al-based intermetallic alloy. Under the optimum laser remelting parameters of 4000 W-10 mm/s, the tensile strength at room temperature and 980 °C of the corresponding laser remelting alloy can reach 1215 MPa and 280 MPa, respectively, and the elongations after fracture of the corresponding alloy are 14.09% and 6.41%, respectively.

Microstructure evolution and mechanical properties of a Fe, Cr-rich multiphase Ni3Al-based superalloy during transient liquid phase bonding process

In this paper, a Fe, Cr-rich multiphase Ni3Al-based alloy is joined through transient liquid phase bonding (TLP) technique. Different from typical γ+γ′ dual phase Ni3Al-based alloys, the joint can be divided into three distinct zones: isothermal solidification zone (ISZ), gamma prime zone (GPZ) and diffusion affected zone (DAZ). Interestingly, the massive fine grains with γ+γ′ dual phase are observed inside the ISZ, and the GPZ consists of blocky γ′ phase. The precipitation of Cr-rich borides in DAZ provides an advantageous compositional condition for the local coarsening of γ′ phase. In addition, hardness value of the bonded samples fluctuates from the centerline to the BM and reaches the peak at the DAZ. The bonded specimens share equivalent room-temperature tensile strength and elongation to failure with the parent metal after the weld thermal cycle. Moreover, the fracture path propagates along the base metal (BM), which indicates excellent tensile properties of the joint.

Microstructure and mechanical properties of twin wire and arc additive manufactured Ni3Al-based alloy

A Ni3Al-based alloy was prepared for the first time using a twin wire and arc additive manufacturing (T-WAAM) by adjusting the relative feeding speed of the Ni and Al wires, and the microstructure and mechanical properties of the deposited alloy were investigated. The results showed that the deposited Ni3Al-based alloy consisted of a dendritic γ + γ' dual-phase structure and an interdendritic γ' block. The interdendritic γ' block was partially transformed into a γ + γ' dual-phase structure owing to multiple thermal cycles during the deposition process. Thus, the proportion of the γ + γ' dual-phase structure gradually decreased with increasing building height. Meanwhile, the tensile strength and elongation of the deposited alloy exhibited a similar decline in the height direction. Fracture analysis revealed that the interdendritic γ' block hindered dislocation slip in the γ + γ' dual-phase structure, which caused dislocation stacking and stress concentration at the dendrite/interdendritic phase interface. The increase in the interdendritic γ' block was responsible for the decline in the tensile strength and elongation of the deposited alloy along the height direction. With the lowest proportion of interdendritic γ' block, the bottom deposited alloy had an optimal combination with a tensile strength of 817.3 MPa and elongation of 20.9%. Evaluation of the mechanical properties showed that the tensile strength and elongation of the T-WAAMed Ni3Al-based alloy were equivalent to those of commercial cast IC218 and IC221M Ni3Al-based alloys.

Microstructure and mechanical properties of directionally solidified Al-rich Ni3Al-based alloy under static magnetic field

The influence of a longitudinal static magnetic field on microstructures and mechanical properties of Ni3Al-based alloy during directional solidification at the growth speed of 25 µm/s and 100 µm/s has been experimentally investigated. Results reflected that the utilization of a 0.5 T magnetic field refines the NiAl dendrites at both speeds of growth. When applying a high magnetic field, the columnar-to-equiaxed transition (CET) occurred at growth speed of 25 µm/s and dendrite networks formed at growth speed of 100 µm/s. Tensile property results indicated that the refinement of dendrites enhanced both plasticity and ultimate tensile strength of Ni-Al alloy. The change of microstructures and mechanical properties should be attributed to the combined action of the thermoelectric magnetic convection (TEMC) in mushy zone together with the thermoelectric magnetic force (TEMF) acting on the solid. When applying a low magnetic field (0.5 T), the TEMF is too small to fragment the dendrites, and the refined dendrites is mainly due to the TEMC in the interdendritic regions. At a lower growth speed, the TEMF is supposed to strong enough to fragment the dendrites and induce the occurrence of CET under 2 or 4 T. When the growth speed increased to 100 µm/s, no obvious CET was observed, but a vertical secondary convection is induced by the circulation in the parallel plane, which promotes the growth of secondary and tertiary branches, leading to the formation of abnormally developed high order dendrites. The hierarchical dendritic structure was suggested to provide a channel for rapid crack propagation and thus degraded the mechanical properties.