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Dy-added Nd-Fe-B magnets are widely used for high-performance motors in battery electric vehicles (BEVs), hybrid electric vehicles (HEVs) and so on. The demand for these magnets is increasing due to the spread of BEVs and HEVs. However, Dy resources are scarce and unevenly located in the earth crust. Thus, it is necessary to develop an inexpensive and effective recovery/separation process of Dy from scraps of the Dy-added Nd-Fe-B magnet. From this background, we have been investigating a new recovery process of Dy and Nd from the magnet scraps using molten salt electrolysis and alloy diaphragms [1-3]. The key step in this process is the alloying and de-alloying of rare earth (RE) elements on both sides of the diaphragm in order to effectively separate them in the molten salt. So far, we have reported that Dy can be selectively alloyed with Ni by potentiostatic electrolysis in a molten LiCl-KCl-DyCl3(0.50 mol%)-NdCl3(0.50 mol%) system at 723 K [2]. The selective permeation of Dy through the RE-Ni alloy diaphragm from an anolyte containing DyCl3 and NdCl3 to a catholyte has been also confirmed [3]. However, the current density was of the order of 10 mA/cm2 or less, which is insufficient for industrial electrolysis. So, we focused on the CsCl system as a candidate melt to achieve a higher current density due to its high operation temperature. Since the alloying and de-alloying of REs in this system is unknown, the electrochemical formation of Dy-Ni alloys was investigated in a molten CsCl-DyCl3 system at 973 K as a first step in the investigation of this system. All experiments were conducted under a dry Ar gas atmosphere at 973 K in a glove box. Mo, Ni wires and Ni plates were used as working electrodes. A glassy carbon rod was used as a counter electrode. The reference electrode was a Ag wire immersed in a molten CsCl containing 1 mol% of AgCl. All the potentials are referred to the Cs+/Cs electrode potential. The alloy samples were prepared by potentiostatic electrolysis. After electrolysis, the samples were analyzed by XRD and were also observed by SEM-EDS. First, cyclic voltammetry was conducted with a Ni wire electrode in a molten CsCl-DyCl3(0.50 mol%) system. During the cathodic potential scan, a large cathodic current was observed from 0.50 V. Since this potential was more positive than that of Dy metal deposition on a Mo wire electrode, the cathodic current was suggested to correspond to the formation of Dy-Ni alloys. Then, open-circuit potentiometry was carried out with a Mo electrode after electrodepositing Dy metal at 0.11 V for 150 s. A potential plateau was observed at 0.26 V. Since Mo does not form any intermetallic compounds with Dy, the observed potential is interpreted as the Dy3+/Dy potential. Also, open-circuit potentiometry was performed with a Ni electrode after depositing Dy metal at 0.18 V for 90 min. As a result, four potential plateaus were observed at 0.29, 0.42 V, 0.52 V, 0.77 V and 0.90 V, which possibly correspond to the potentials of two-phase coexisting states of different Dy–Ni alloys. Based on these results, potentiostatic electrolysis was conducted at 0.38 V for 1 h with a Ni plate electrode. XRD analysis indicated the formation of DyNi2 on the Ni plate electrode. The thickness of DyNi2 layer was estimated to be 50 μm from cross-sectional SEM observations. The growth rate of this DyNi2 layer, 50 µm h-1, was higher than that obtained in a molten LiCl-KCl system at 700 K, 28 µm h-1 [4]. After the formation of DyNi2 on the Ni plate electrode, potentiostatic electrolysis was also conducted at 0.46 V, 0.66 V and 0.82 V for 1 h. These potential values were selected from the observed plateau potentials. The formed DyNi2 were transformed to other phases such as DyNi3 at 0.46 V, Dy2Ni7 at 0.66 V and DyNi5 at 0.82 V due to anodic dissolution of Dy, depending on the applied potentials. References [1] T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T. Usui, Kagaku Kogaku Ronbunshu, 36, 299 (2010). [in Japanese] [2] H. Konishi, H. Ono, T. Nohira and T. Oishi, ECS Transactions, 50, 463 (2012). [3] T. Oishi, M. Yaguchi, Y. Katasho, H. Konishi and T. Nohira, J. Electrochem. Soc., 167, 163505 (2020). [4] H. Konishi, T. Nohira and Y. Ito, Electrochim. Acta, 48, 563 (2003).

Phase Transforming Cellular Material (PXCM) exhibits transformation by loading and maintains the deformed shape even after unloading after compression and restores the original shape by deforming in the opposite direction. Conventional PXCM needs to be stressed reversely to restore its original shape. Bimetals, i.e., clad sheets of metals with large differences in the coefficient of thermal expansion, can spontaneously bend in response to temperature changes because of thermal stress. In this study, we designed a lattice structure that not only deforms when a compressive/tensile load is applied but also changes its shape by heating/cooling by using bimetal for the curved beam of PXCM. A newly created PXCM is named thermally induced PXCM. The TI-PXCM exhibited a large recovery strain of 20% or more with a temperature hysteresis of 302 K in the temperature range of − 190 to 200 °C. Graphical abstract

Kubo J., Koizumi Y., Ishimoto T., et al. Modified cellular automaton simulation of metal additive manufacturing. Materials Transactions 62, 864 (2021); https://doi.org/10.2320/matertrans.MT-M2021009., Metal additive manufacturing (AM) technologies are attracting attentions not only as a fabrication process of complicated threedimensional parts but also as microstructure controlling processes. In powder bed fusion (PBF)-type AM, crystallographic texture can be controlled by scanning strategies of energy beam. To optimize microstructures, computer simulations for predicting microstructures play very important roles. In this work, we have developed simulation programs to explain the mechanism of the crystal orientation control. First, we simulated the shape of melt pool by analyzing the heat transfer using apparent heat conductivity when the penetration of laser beam through keyholes was taken into consideration because of the evaporation and accompanying convections. It was assumed that the primary crystal growth direction can be determined by the temperature gradient, and the crystals grow keeping the growth direction as generally recognized. The shapes of simulated melt pools agree well with experimental observations. The modified cellular automaton simulations successfully reproduced two typical textures with different preferential orientations along the building directions of (100) and (110) when the bidirectional scanning with and without a rotation of 90°, respectively, was accomplished between the layers.

Powder bed properties affect the quality of the parts manufactured by powder bed fusion (PBF). On PBF with laser, researchers had thoroughly studied the impact of powder layer on consolidation. In terms of interaction mechanisms with materials, electron beam is different from laser. Thus, an in-depth discussion is required for PBF with electron beam. In this study, numerical simulations were performed to reconstruct the powder bed and analyze the subsequent consolidation. The powder layer's presence altered the emissivity and thermal conductivity to be different from those of a solid. Concerning the powder with different particle size distributions, the differences in thermal properties led to an alteration in the molten pool formation. The emissivity increased, and the thermal conductivity decreased as the fraction of fine powders increased. With the increased fraction of fine powders under a given layer thickness, relatively high energy should be input to ensure exceptional forming quality.

Al alloy parts fabricated by powder bed fusion (PBF) have attracted much attention because of the degrees of freedom in both shapes and mechanical properties. We previously reported that the Si regions in Al-Si alloy that remain after the rapid remelting process in PBF act as intrinsic heterogeneous nucleation sites during the subsequent resolidification. This suggests that the Si particles are crucial for a novel grain refinement strategy. To provide guidelines for grain refinement, the effects of solidification, remelting, and resolidification conditions on microstructures were investigated by multiphase-field simulation. We revealed that the resolidification microstructure is determined by the size and number of Si regions in the initial solidification microstructures and by the threshold size for the nucleation site, depending on the remelting and resolidification conditions. Furthermore, the most refined microstructure with the average grain size of 4.8 µm is predicted to be formed under conditions with a large temperature gradient of Gsol = 106 K/m in the initial solidification, a high heating rate of HR = 105 K/s in the remelting process, and a fast solidification rate of Rresol = 10−1 m/s in the resolidification process. Each of these conditions is necessary to be considered to control the microstructures of Al-Si alloys fabricated via PBF.

MoSi2/Mo5Si3 eutectic composites have been considered as one of the promising candidates for ultra-high temperature structural applications owing to their high melting point, good oxidation resistance, and low mass density. Their mechanical properties can be improved by controlling the eutectic structure (i.e. script lamellar structure) in directional solidification. It is important to elucidate the dominant factors underlining the unique pattern formation. We conducted a comprehensive phase field study to examine the influence of various factors on the MoSi2/Mo5Si3 eutectic microstructure with complicated morphology. First, the inclined lamellae have been attributed to the minimization of elastic strain energy due to the lattice mismatch between MoSi2 and Mo5Si3, which are partially relaxed by forming semi-coherent phase boundaries. Second, the maze-like pattern on the horizontal cross-section appeared when a two-fold anisotropy of interfacial energy is superimposed on the MoSi2/Mo5Si3 boundary. Third, the random and intersected lamellae have been obtained by assuming the instability of the solid-liquid interface and introducing successive nucleation of Mo5Si3 phase. These findings provide guidance for manipulating the eutectic structure and act as footsteps for further theoretical investigation.

Powder bed fusion with electron beam (PBF-EB), allows Co-Cr-Mo (CCM) implants with patient-customization to be fabricated with high quality and complex geometry. However, the variability in the properties of PBF-EB-built CCM alloy, mainly due to the lack of understanding of the mechanisms that govern microstructural heterogeneity, brings limitations in extensive application. In this study, the microstructural heterogeneity regarding the γ-fcc → e-hcp phase transformation was characterized. The phase transformation during PBF-EB was analyzed depending on the thermal history that was elucidated by the numerical simulation. It revealed that isothermal γ → e transformation occurred during the fabrication. Importantly, the difference in γ/e phase distribution was a result of the thermal history determining which method phase transformation was taking place, which can be influenced by the PBF-EB process parameters. In the sample with a low energy input ( E a r e a = 2.6 J/mm2), the martensitic transformation was dominant. As the building height increased from the bottom, the e phase fraction decreased. On the other hand, in the sample with a higher energy input ( E a r e a = 4.4 J/mm2), the e phase formed via diffusional-massive transformation and only appeared in a short range of the lower part away from the bottom.

Masayuki Okugawa, Yuta Ohigashi, Yuya Furishiro, Yuichiro Koizumi, Takayoshi Nakano, Equiaxed grain formation by intrinsic heterogeneous nucleation via rapid heating and cooling in additive manufacturing of aluminum-silicon hypoeutectic alloy, Journal of Alloys and Compounds, Volume 919, 2022, 165812, ISSN 0925-8388, https://doi.org/10.1016/j.jallcom.2022.165812., The high strength of Al-Si hypoeutectic alloys additively manufactured by powder-bed fusion is of great scientific interest. To date, the mechanism of grain refinement near the fusion line, which contradicts conventional Hunt's columnar–equiaxed transition criteria, remains to be elucidated. Here we present the first report on the mechanism of grain refinement. When a laser was irradiated on cast Al-Si alloy consisting of coarse α-Al grain and α-Al/Si eutectic regions, grain refinement occurred only near the eutectic regions. This strongly suggests that the Si phase is crucial for grain refinement. Multi-phase-field simulation revealed that rapid heating due to the laser irradiation results in unmelted Si particles even above the liquidus temperature and that the particles act as heterogeneous nucleation sites during the subsequent re-solidification. These results suggest the feasibility of a novel inoculant-free grain refinement that is applicable to eutectic alloys comprising phases with a significant melting point difference.

The influence of various laser powder bed fusion (LPBF) process parameters on the crystallographic textures and mechanical properties of a typical Ni-based solid-solution strengthened alloy, Hastelloy-X, was examined. Samples were classified into four groups based on the type of crystallographic texture: single crystalline-like microstructure with &lt, 100&gt, //build direction (BD) (&lt, SCM), single crystalline-like microstructure with &lt, 110&gt, //BD (&lt, SCM), crystallographic lamellar microstructure (CLM), or polycrystalline microstructure (PCM). These four crystallographic textures were realized in Hastelloy-X for the first time here to the best of our knowledge. The mechanical properties of the samples varied depending on their texture. The tensile properties were affected not only by the Schmid factor but also by the grain size and the presence of lamellar boundaries (grain boundaries). The lamellar boundaries at the interface between the &lt, //BD oriented main layers and the &lt, //BD-oriented sub-layers of CLM contributed to the resistance to slip transmission and the increased proof stress. It was possible to control a wide range of crystallographic microstructures via the LPBF process parameters, which determines the melt pool morphology and solidification behavior.

Controlled forming quality and solidification microstructure are crucial issues for the application of additive manufactured metal. The local heat accumulation through a line order hatching strategy was considered when a Co-28Cr-6Mo alloy was fabricated by powder bed fusion with electron beam. The study revealed that by weakening the local heat accumulation, overheating as a source of unevenness was easily avoided. Transient geometry of the molten pool and associated temperature gradient direction were determined by the local heat accumulation, which subsequently alters the solidification microstructure. The numerical simulations were performed to clarify the mechanisms involved.

Li Q., Qi Q., Li J., et al. Low springback and low Young’s modulus in Ti-29-Nb-13Ta-4.6Zr alloy modified by Mo addition. Materials Transactions 60, 1755 (2019); https://doi.org/10.2320/matertrans.ME201912., Deformation-induced higher Young’s modulus can satisfy the contradictory requirements of Ti alloys for spinal-fixation applications, which demand a high Young’s modulus to reduce springback during operations and a low Young’s modulus to prevent stress shielding effect for patients after surgeries. In this study, TNTZ-(1, 3, 5)Mo are designed by adding Mo and Ti to Ti-29-Nb-13Ta-4.6Zr (TNTZ) in order to maintain low initial Young’s modulus and achieve low springback. All the solutionized alloys show single β phase with increasing the β stability by Mo addition. They show low Young’s moduli less than 65 GPa, similar ultimate tensile strength of 650 MPa and elongation around 20%. The springback of TNTZ-3Mo and TNTZ-5Mo is lower than that of TNTZ and TNTZ-1Mo owing to their more stable β phase. After cold rolling, TNTZ-3Mo shows the largest increasing ratio of 25% in Young’s modulus and the highest ultimate tensile strength owning to the appearance of deformation-induced ω phase. With the low initial Young’s modulus of 59 GPa, TNTZ-3Mo is a potential candidate to make the spinal rods in spinal fixation devices.

The electron beam melting (EBM), a layer-by-layer additive manufacturing (AM) technique, has been recently utilized for fabricating metallic components with complex shape and geometry. However, the inhomogeneity in microstructures and mechanical properties are the main drawbacks constraining the serviceability of the EBM-built parts. In the present study, we found remarkable microstructural inhomogeneity along build direction in the EBM-built Co-based alloy, owing to the competitive grain growth and subsequent isothermal γ-fcc → e-hcp phase transformation, which affects the corresponding tensile properties significantly. Then, we succeeded in eliminating the inhomogeneities, modifying the phase structures and refining grain sizes via comprehensive post-production heat treatment regimes, which provides a valuable implication for improving the reliabilities of AM-built metals and alloys. The Co-based alloy can be selectively transformed into predominant e or predominant γ phase by the regime, and the grains were refined to 1/10 of the initial sizes by repeated heat treatment. Finally, we investigated the tensile properties and fracture behaviors of the alloy before and after each heat treatment. The γ → e strain-induced martensitic transformation is the major deformation mode of the γ phase, meanwhile the formation of stripped e phase at {111}γ habit planes contributed to a good combination of strength and ductility. Nevertheless, the e phase was deformed mainly by (0001)e 2 ¯ 0 >e basal and {1 1 ¯ 00 }e 2 ¯ 0 >e prismatic slip systems, exhibiting very limited ductility and strength. In addition, the e grains act as secondary hardening factor in the samples consisting of dual γ/e phase, leading to a non-uniform deformation behavior.

Niinomi M., Akahori T., Nakai M., et al. Quantitative and qualitative relationship between microstructural factors and fatigue lives under load- And strain-controlled conditions of Ti-5Al-2Sn-2Zr-4Cr-4Mo (Ti-17) fabricated using a 1500-ton forging simulator. Materials Transactions 60, 1740 (2019); https://doi.org/10.2320/matertrans.ME201904., The fatigue lives of forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment were evaluated under both load- and strain-controlled conditions: high and low cycle fatigue lives, respectively. Then, the tensile properties and microstructures were also examined. Finally, the relationships among fatigue lives and the microstructural factors and tensile properties were examined. The microstructure after solution treatment at 1203 K, which is more than the β transus temperature, and aging treatment exhibits equiaxed prior β grains composed of fine acicular ¡. On the other hand, the microstructures after solution treatment at temperatures of 1063, 1123, and 1143 K, which are less than the β transus temperature, and aging treatment exhibit elongated prior β grains composed of two different microstructural feature regions, which are acicular α and fine spheroidal α phase regions. The 0.2% proof stress, σ₀.₂, and tensile strength, σB, increase with increasing solution treatment temperature up to 1143 K within the (α + β) region, but decrease with further increasing solution treatment temperature to 1203 K within the β region. The elongation (EL) and reduction of area (RA) decrease with increasing solution treatment temperature, and it becomes nearly 0% corresponding to a solution treatment temperature of 1203 K. The high cycle fatigue limit increases with increasing solution treatment temperature up to 1143 K, corresponding to the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the β region. The fatigue ratio in high cycle fatigue life region is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the β transus temperature. The low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range of low cycle fatigue testing.

The equiatomic CoCrMnNiFe high-entropy alloy (HEA) has attracted much attention owing to its exceptional mechanical properties. Here, we designed novel face-centered cubic (fcc) phase Co-rich non-equiatomic CoCrMnNiFe HEAs with tensile properties superior to the counterparts, derived from lowering stacking fault energy (SFE) via modifying constituent concentrations. The decrease of Mn, Ni, Fe meanwhile increase of Co, Cr concentrations does reduce the SFE value, based on ab initio and thermodynamics calculations. Hereinto, Co35Cr20Mn15Ni15Fe15 and Co35Cr25Mn15Ni15Fe10 HEAs overcame the strength-ductility trade-off, contributing to twinning-induced plasticity (TWIP) or transformation-induced plasticity (TRIP) effects, respectively. The present study sheds light on developing high performance HEAs.

Selective electron beam melting (SEBM) is a type of additive manufacturing (AM) that involves multiple physical processes. Because of its unique process conditions compared to other AM processes, a detailed investigation into the molten pool behavior and dominant physics of SEBM is required. Fluid convection involves mass and heat transfer; therefore, fluid flow can have a profound effect on solidification conditions. In this study, computational thermal-fluid dynamics simulations with multi-physical modeling and proof-of-concept experiments were used to analyze the molten pool behavior and resultant thermal conditions related to solidification. The Marangoni effect of molten metal primarily determines fluid behavior and is a critical factor affecting the molten pool instability in SEBM of the Co–Cr–Mo alloy. The solidification parameters calculated from simulated data, especially the solidification rate, are sensitive to the local fluid flow at the solidification front. Combined with experimental analysis, the results presented herein indicate that active fluid convection at the solidification front increase the probability of new grain formation, which suppresses the epitaxial growth of columnar grains.

Controlling the orientation of crystal grains in metal additive manufacturing is an active field of research. Assuming that three-dimensional control of orthotropic metal crystal grain can be achieved, we numerically studied the effective performance of a topology-optimized lattice made of crystal grains with optimal directions in orientation. The objective function is maximized for an effective isotropic stiffness. The effective properties of the lattice are calculated using the homogenization method. Each discretized finite element is regarded as a crystal grain and its artificial density and orientation are optimized. Through several numerical studies using a single orthotropic crystal of Ni exhibiting large anisotropy in its single crystal stiffness, the optimization and the usefulness of the lattice structure composed of optimal orientation crystal grains is confirmed. In the design of a lattice with effective isotropic stiffness, an improvement in stiffness was observed compared with that using equivalent isotropic Ni as a material.

To understand the fundamentals of microstructure formation in an electron beam melting (EBM) additive-manufacturing process, which is classified as a type of electron beam powder bed fusion (EB-PBF) in ISO562910/ASTM-F42, single bead experiments were conducted by using an electron beam to scan an IN718 plate, using various combinations of power and scan speed, focusing on the relationship between (i) the beam irradiation level, (ii) the melt pool geometry, and (iii) the solidification microstructure. The width and depth of the melt pool increases almost linearly with the line energy. Elongated grains, which are generally called “columnar grains” were observed in almost the entire cross-section of the beads regardless of the process parameters. Temporal evolution of the temperature distribution for the single bead experiments was simulated by finite element analysis (FEA) with thermal conduction and recoalescence taken into account. The surface heat source model used in the simulation was modified to cause the geometry of the simulated melt pool to align with that which was observed experimentally. The distributions of the temperature gradient (G) and solidification rate (R) on the solidification interface were evaluated from the simulation results. The distributions of the microstructures were constructed from the distributions of G and R, as obtained from a solidification map in the literature. Contrary to the experimental observations, the constructed microstructure consisted mostly of equiaxed and mixed grains. The reasons for this contradiction are discussed.

Selective electron beam melting (SEBM) is a type of additive manufacturing (AM), which is categorized into powder bed fusion (PBF) in ISO52900 as well as selective laser melting (SLM). SEBM is denoted by PBF-EB, meaning electron beam-based PBF. Formerly, SEBM was denoted by the term “E-PBF,” but currently “PBF-EB” is used. To emphasize that the process is for metal, the term “PBF-EB/M” is used to indicate SEBM. Overviews of SEBM and the characteristics of the metal microstructures of EBM-built parts have been already published in books [1, 2] and commentary articles [3, 4, 5, 6, 7, 8]. The term “electron beam melting (EBM)” is used for meaning SEBM by the company Arcam, which developed this technology. The type of manufacturing method employing an electric beam, where the material is added through a process similar to build-up welding, and a metal wire is used instead of metal powder (i.e., Sciaky Co. Electron Beam Additive Manufacturing: EBAM [9]), is not dealt with here.

The effectiveness of applying selective laser melting (SLM) to a CoCrFeNiTi-based high-entropy alloy was compared with that of using electron beam melting (EBM). The higher solidification rate during SLM promoted a fine uniform microstructure with no visible segregation, which led to superior tensile properties (yield strength: 773.0 ± 4.2 MPa, ultimate tensile strength: 1178.0 MPa, elongation: 25.8 ± 0.6%) and a higher pitting potential (0.88 ± 0.03 V versus Ag/AgCl in a 3.5% NaCl solution at 353 K) in comparison to the EBM specimens (743.4 ± 11.6, 932.2 ± 4.8 MPa, 4.0 ± 0.2%, and 0.50 ± 0.04 V versus Ag/AgCl, respectively). The effect of a solution treatment on the tensile properties and pitting-corrosion resistance of the SLM specimens was then examined. The effect of the solution treatment on these properties depended on the cooling method used during the treatment. In particular, the tensile properties and pitting-corrosion resistance improved as a result of water quenching. On the other hand, the properties of the solution-treated specimens depended on the size and volume fraction of very fine-ordered particles, with diameters of tens of nanometers that contained Ni and Ti. The as-built and solution-treated SLM specimens exhibited excellent tensile strength and exceptional pitting-corrosion resistance; they had higher tensile strength and pitting-corrosion resistance than the conventional high-corrosion-resistant alloys.

The effectiveness of applying an electron beam melting (EBM) additive manufacturing process to Ti–6Al–2Sn–4Zr–2Mo–0.1Si–1B alloy by comparing the EBM alloy with a corresponding wrought alloy was demonstrated. The EBM alloys exhibited microstructures that had much finer whisker-like TiB precipitates with nanometer width dispersed more uniformly than those of the wrought alloy formed due to the rapid solidification process. The EBM alloys had higher tensile strength than the wrought alloy at elevated temperatures up to 873 K. Furthermore, the oxidation resistance at 1073 K of the EBM alloys was significantly improved because of the dense oxide film formation.

We have investigated the spatial distribution of microstructures of a Co-Cr-Mo alloy rod fabricated by Electron Beam Melting (EBM) method along built height. The topside of the rod is rich in γ-fcc phase and consists of fine grains with high local distortion density. The bottom part has an e-hcp single phase and consists of relatively coarser grains with low local distortion density. The middle part of the rod consisted of the mixture of both phases. The mean grain size increases from 56 μm (at the top of the rod) to 159 μm (at the bottom), and is accompanied by a decrease in the γ-fcc phase fraction. On the other hand, a large number of precipitates including the main M23X6 phase and minor phases (η-phase and π-phase) were observed. The area fraction of the precipitates increases gradually from 5.26% (at the top) to 8.73% (at the bottom), and the relative proportion of each phase fluctuates at different positions. The hardness of the top side is lower than that of the bottom side. As a result, the hardness of the samples, as well as the area fraction of precipitates formed in the samples, increases gradually from top to bottom of the rod, while corrosion resistance is uniformly high throughout the rod almost independently of the location. The mechanism behind the formation of phase distribution is discussed in terms of thermodynamic phase stability and kinetics of phase transformation accompanying the thermal history during the post-solidification process.