Phase Grain Research Articles

The effect of laser post-treatment on the microstructure and properties of Al coating on the PEEK substrate

To improve the bonding strength and electrical conductivity(σ) of cold-sprayed Al coatings on polyetheretherketone(PEEK) substrates, laser post-treatment was employed as an effective strengthening method without decomposition of the polymer substrates. Optical and electron microscopy observations were used to examine the microstructures and tensile fracture surfaces of the Al coatings fabricated with various laser powers. X-ray diffraction and electron backscatter diffraction were employed to investigate the phase composition and grain information of each coating. Hardness, pull-out adhesion, and electrical conductivity tests were performed to investigate the effect of laser power on the mechanical and physical properties of cold-sprayed Al coatings. The results revealed that despite the formation of several hundred micrometer-sized pores on the PEEK side, the porosity of the laser post-treated Al coatings significantly decreased, and the particle–particle interfaces were greatly healed with increasing laser power. The heat input induced large-scale recrystallization and significantly reduced the dislocation density in the samples. The XRD pattern revealed that no oxidation phase appeared following the laser treatment under the protection of Ar. The electrical conductivity and bonding strength of the Al coatings increased by up to 40 % and 167.4 %, respectively, after the laser post-treatment.

Synergistic influence mechanism of B-Ga content on microstructures and magnetic properties of Nd-Fe-B ribbons

To understand the influence mechanism of B and Ga content on magnetic properties of NdFeB ribbons, Nd29.89FebalGayCo5.93Bx (wt%, x = 0.80–0.98, y = 0.24–1.04) alloys were prepared and magnetic properties, phase composition, coercivity mechanism, and microstructure of these alloys were investigated systematically. The melt-spun ribbons exhibited 2:14:1 phase grains with varying grain sizes and amorphous grain boundary phases at a wheel speed of 25 m/s. By reducing the B content within a specific range, grain refinement was achieved, resulting in narrower triangular grain boundaries, more uniform and continuous thin grain boundaries. Meanwhile, further increasing the Ga content, the grain shape changes from elongated to equiaxed, and the grain size is greatly refined. However, for x = 0.89, y = 0.84 strip, the coercivity is still reduced due to the large number of directly contacted grains. Consequently, an alloy composition of Nd29.89FebalGa0.64Co5.93B0.89 yielded excellent comprehensive magnetic properties, including a remanence of 8.5 kGs and a coercivity of 18.01 kOe. The corresponding magnetic properties enhancement mechanism is further discussed.

Li‐Doping and Ag‐Alloying Interplay Shows the Pathway for Kesterite Solar Cells with Efficiency Over 14%

AbstractKesterite photovoltaic technologies are critical for the deployment of light‐harvesting devices in buildings and products, enabling energy sustainable buildings, and households. The recent improvements in kesterite power conversion efficiencies have focused on improving solution‐based precursors by improving the material phase purity, grain quality, and grain boundaries with many extrinsic doping and alloying agents (Ag, Cd, Ge…). The reported progress for solution‐based precursors has been achieved due to a grain growth in more electronically intrinsic conditions. However, the kesterite device performance is dependent on the majority carrier density and sub‐optimal carrier concentrations of 1014–1015 cm−3have been consistently reported. Increasing the majority carrier density by one order of magnitude would increase the efficiency ceiling of kesterite solar cells, making the 20% target much more realistic. In this work, LiClO4is introduced as a highly soluble and highly thermally stable Li precursor salt which leads to optimal (>1016 cm−3) carrier concentration without a significant impact in other relevant optoelectronic properties. The findings presented in this work demonstrate that the interplay between Li‐doping and Ag‐alloying enables a reproducible and statistically significant improvement in the device performance leading to efficiencies up to 14.1%.

The Role of Oxygen Vacancies in Phase Transition and the Optical Absorption Properties within Nanocrystalline ZrO2.

Zirconia (ZrO2) nanoparticles were synthesized using a solvothermal method under varying synthesis conditions, namely acidic, neutral, and alkaline. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were leveraged to investigate the phase evolution and topographical features in detail. The resulting crystal phase structures and grain sizes exhibited substantial variation based on these conditions. Notably, the acidic condition fostered a monoclinic phase in ZrO2, while the alkaline condition yielded a combination of tetragonal and monoclinic phases. In contrast, ZrO2 obtained under neutral conditions demonstrated a refinement in grain sizes, constrained within a 1 nm scale upon an 800 °C thermal treatment. This was accompanied by an important transformation from a monoclinic phase to tetragonal phase in the ZrO2. Furthermore, a rigorous examination of XPS data and a UV-visible spectrometer (UV-vis) analysis revealed the significant role of oxygen vacancies in phase stabilization. The notable emergence of new energy bands in ZrO2, in stark contrast to the intrinsic bands observed in a pure monoclinic sample, are attributed to these oxygen vacancies. This research offers valuable insights into the novel energy bands, phase stability, and optical absorption properties influenced by oxygen vacancies in ZrO2. Moreover, it proposes an innovative energy level model for zirconia, underpinning its applicability in diverse technological areas.

Suppressing hydrogen embrittlement of a CrCoNi medium-entropy alloy by triggering co-segregation of carbon, boron, and Cr

The CrCoNi medium-entropy alloy has drawn extensive attention due to its outstanding mechanical properties, yet it suffers severe gaseous hydrogen embrittlement (HE). Here we report that co-doping of carbon and boron could greatly suppress such embrittlement, resulting in a significant reduction in ductility loss from 71 % to merely 16 %. The minor doping has no significant influence on the phase structure, grain size, and grain-boundary character. However, the co-segregation of carbon, boron, and Cr was triggered, which not only improves the grain-boundary cohesive strength but also hinders the diffusion and accumulation of hydrogen at GBs, thereby leading to improved HE resistance.

Enhancing mechanical properties of high Cr dual-phase FeCrNi medium-entropy alloy through mutual phase transformation and grain refinement

A high Cr Fe40Cr40Ni20 (at.%) medium-entropy alloy was prepared through vacuum arc melting. The alloy exhibited a dual-phase structure comprising face-centered-cubic (FCC) and body-centered-cubic (BCC) phases in a solid solution state. After annealing and cold rolling, two different heterogeneous structures emerged from the original FCC and BCC phases through mutual phase transformation. Moreover, the alloy exhibited a yield strength, ultimate tensile strength, and total elongation of 1.18 GPa, 1.25 GPa, and 13 %, respectively. The high strength of the alloy was mainly attributed to boundary strengthening and heterogeneous deformation-induced (HDI) strengthening within the two heterogeneous structures. Notably, the effectiveness of HDI strengthening was enhanced owing to the complete encapsulation and constraint of soft zones by hard zones in the heterogeneous structure originating from the BCC phase. Additionally, the deformation ability of the alloy mainly depended on dislocation slips and deformation twinning in recrystallized FCC grains and FCC strip phases, thereby ensuring satisfactory ductility.

Micromechanical and microstructure evolution of leaded (SnPb) and lead-free (SAC305 and SnCu) mixed solder joints during isothermal aging

This paper studies how isothermal aging affects the micromechanical and structural properties of mixed solder joints made of 60Sn-40Pb (SnPb) with Sn-3.0Ag-0.5Cu (SAC305) and SnPb with Sn-0.7Cu (SnCu). The nanoindentation test was done to measure the micromechanical properties of SnPb/SAC305 and SnPb/SnCu mixed solder joints. These properties are hardness, reduced modulus, and stress exponent. Scanning electron microscopy (SEM) was used to look at the microstructure of a cross-section of mixed solder joints. The micrographs that were taken were then examined with open-source image processing software called ImageJ. It was found that the rate and distribution of intermetallic compound (IMC) formation and the reduction of Sn-rich phase grain size affect how the hardness and stress exponent values of mixed solder joints change after 1000 h of high temperature storage (HTS). ImageJ analysis shows that the Pb-rich phase particle count and distribution can be used to figure out how mixed solder joints respond to indentation creep and how that relates to isothermal aging. Using ImageJ, it’s clear that the indentation creep behavior of the GBS mechanism of an as soldered SnPb/SnCu mixed solder joint is caused by the highest number and size of Pb-rich phase particles that are not well distributed across the dendritic area of Sn-rich phase grain boundaries.

Enhancing the comprehensive performance of MgO–MgAlON composite refractories synthesized from natural minerals

Developing and designing carbon-free refractory materials is an effective alternative to MgO–C refractory materials to produce large-scale, high-quality, low-carbon special steels. Therefore, in this work, excessive MgO is introduced into MgAlON to prepare a series of MgO–MgAlON composite refractories. The enhancement mechanism of comprehensive performance is systematically evaluated, where MgO as a reinforcer features intergranular phase strengthening and grain boundary purification effects. Besides, the pore structure of MgO–MgAlON composite refractories is also optimized to regulate the molten slag wetting behavior. The results demonstrated that MgO–MgAlON composite refractories have apparent porosity of 13.86%–15.84 %, bulk density of 2.78–2.97 mg cm−3, and compressive strength of 204.17–253.97 MPa. When 42.8 % MgO is introduced, the sample strength retention ratio after thermal shock measurement and slag corrosion experiments are 64 % and 75 %, respectively. Consequently, a cost-effective and feasible reinforcement strategy for MgO–MgAlON composite refractories is proposed, paving the way for.

Unraveling the Hall-Petch to inverse Hall-Petch transition in nanocrystalline high entropy alloys under shock loading

The transition from Hall-Petch (HP) to inverse Hall-Petch (IHP) behaviors associated with grain size reduction has been recognized for over two decades. However, the underlying mechanisms for such transition in high entropy alloys (HEAs) under dynamic loading, in which abundant deformation mechanisms could be activated either sequentially or simultaneously, remain unclear. Here, we investigate the HP to IHP transition in nanocrystalline CoCrFeMnNi HEAs under shock loading by examining their deformation mechanisms and flow stresses using large-scale molecular dynamics (MD) simulations. It is found that this transition is strongly dependent on the shock pressure as a result of the complex interplay among multiple competing deformation mechanisms, including the hardening mechanisms such as dislocations interactions and grain boundary (GB) blocking, as well as the softening mechanisms like phase formation, amorphization, GB thickening, and grain rotation. Moreover, there exists a critical shock pressure, which corresponds to the largest critical grain size for the HP-IHP transition. Below the critical shock pressure, the critical grain size increases with pressure due to a stronger hardening effect in grain interior (GIs), while above the critical pressure, the critical grain size first decreases and then undergoes a pressure-insensitive plateau before further decrease due to softening effects in GIs. A theoretical model that includes different deformation mechanisms is proposed for the first time to capture the shock pressure-dependent HP-IHP transition. Our work provides valuable guidance for optimizing the grain size of nanocrystalline HEAs for applications involving dynamic loadings.

C54-TiSi2 formation using nanosecond laser annealing of A-Si/Ti/A-Si stacks

Low resistive Ti-based contacts are required to reach the targeted performances of 3D imaging devices. To fulfill this request, the C54-TiSi2 phase appears to be the most efficient. However, in view of monolithic integration, the temperature needed to form C54-TiSi2 must be drastically reduced by at least 100 °C in order to avoid damage in other parts of the device. Indeed, as these 3D imaging devices require the co-integration of Ti and Ni based silicides, it is crucial to develop a thermal treatment which allows to form the C54-TiSi2 phase without agglomerating the NiSi layer (i.e. at temperatures lower than 600 °C). In this work, a three-layer stack made of a Ti layer in between two amorphous Si thin films deposited on (100) Si substrate has been studied. Nanosecond laser annealing (NLA) followed by rapid thermal annealing (RTA) from 500 to 800 °C were performed on those stacks. Sheet resistance and X-Ray Diffraction measurements showed that the C54-TiSi2 phase could be formed with a RTA treatment at a temperature as low as 600 °C in this case. In line with some previous work, this was due to another phase sequence involving the C40-TiSi2 during the laser annealing. The most favorable microstructure to form C54-TiSi2 by a subsequent RTA treatment seemed to be a matrix made of amorphous titanium silicide containing grains of the C40-TiSi2 template phase. This hypothetical microstructure was formed by laser annealing at a lower energy density when layers of amorphous Si were used.

Phase Fraction Estimation in Multicomponent Alloy from EDS Measurement Data.

To perform quality assessments of both metal alloys and many other engineering materials, measurements of the volume fractions of phases or microstructure components are utilized. For this purpose, quantitative analysis of the evaluated components' distribution on metallographic specimens is often employed. Phases or components of the microstructure are identified based on the variation in signal received in the band of light seen. Problems with the correct identification of measurement results in this spectral band can be caused by the inhomogeneity of the etching when the alloy components are segregated. Additional uncertainty arises when the analyzed image pixel contains a boundary between grains of different phases. This article attempts to use the results of local chemical composition measurements as a source signal for quantitative evaluation of phase composition. For this purpose, quantitative maps of elemental concentration distributions, obtained with a Tescan Mira GMU high-resolution scanning electron microscope in QuantMap mode, were used as input data for the phase composition evaluation of an EN AC 46000 alloy sample. The X-ray microanalysis signal generation area may contain grains of more than one phase. Therefore, evaluation of the phase fractions in areas of individual measurements were calculated by looking for the minimum of the objective function, calculated as the sum of the squares of the deviations of the results of measurements of the concentration of individual elements from the weighted average values of solubilities of these elements in the phases.

Enhancing wear resistance of laser-clad AlCoCrFeNi high-entropy alloy via ultrasonic surface rolling extrusion

The AlCoCrFeNi high-entropy alloy (HEA) coating was synthesized by laser cladding and subsequently processed by ultrasonic surface rolling extrusion (USRE) with varying static loads of 100 N, 200 N, and 300 N. This study aimed to explore the effects of static load on the microstructure, mechanical properties, and tribological characteristics of the coatings. The findings indicate that increased static load results in the precipitation of martensitic phases, grain refinement, enhanced microhardness, and an elevated dislocation density. Specifically, after USRE with 300 N static load, the coating's microhardness reaches 753 HV, 1.4 times greater than the un-USRE coating. This enhancement is attributed to the synergistic effect of martensite phase transformation, grain refinement, and dislocation strengthening. The volume wear rate of the coating decreases to 1.31 × 10−4 mm3·N−1·m−1 following USRE at 300 N, demonstrating superior resistance to abrasive wear due to the high microhardness. Besides, the high-density dislocations facilitate rapid migration and diffusion of oxygen elements, thereby enhancing the oxide layer's protective properties and improving the coating's resistance to oxidation wear.

Effect of heavy Dy3+ doping on the magnetic, structural, morphological, and optical characteristics of CuDyxFe2-xO4 nanoparticles

The present study explored the impacts of dysprosium (Dy³⁺) doping on the structure, optical, and magnetic characteristics of CuDyxFe2-xO4 nanospinel ferrites synthesized via a hydrothermal method. X-ray diffraction revealed a tetragonal spinel matrix with increasing Dy³⁺ content, accompanied by a secondary Dy2O3 phase at higher dopant levels for x ≥ 0.1. Crystallite size and microstrain increased with doping, while infrared spectroscopy confirmed the spinel structure and distinct vibrational modes. Interestingly, saturation magnetization displayed a non-monotonic trend, first rising due to spin polarization and cation redistribution, then decreasing with higher Dy³⁺ content attributable to the Dy2O3 phase and larger grains. Coercivity exhibited a maximum at x = 0.2, reflecting the interplay between magnetocrystalline anisotropy, canting angles, and domain wall pinning. These findings highlight the complex interplay between Dy³⁺ doping and the resulting properties, paving the way for tailored CuDyxFe2-xO4 nanospinel ferrites functionalities. . Further research involving advanced techniques and targeted dopant levels holds promise for optimizing properties for diverse technological applications such as magnetic storage, microwave devices, sensors, and hyperthermia treatment.

Coercivity enhancement and microstructure optimization of Nd-Fe-Co-B magnets by Dy70Al10Cu20 grain boundary diffusion

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy70Al10Cu20 alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (Hcj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

Investigation of ratcheting fatigue behavior and failure mechanism of 1Cr18Ni10Ti pressure pipe under different force amplitudes and internal fluid pressure

This work reports on the development of an improved testing system to examine the effects of force amplitude and internal fluid pressure on ratcheting behavior and failure mechanism of 1Cr18Ni10Ti aero-engine pipe. Experimental results indicate that the ratcheting displacement and its rate during steady stage increase with the increasing force amplitude or internal fluid pressure, exhibiting a reverse tendency to fatigue life. Continuous cyclic softening response until fatigue fracture was observed in all conditions. Furthermore, microstructural evolution was characterized by SEM, EDS, XRD, and EBSD. The critical force amplitude to trigger noticeable dislocation accumulation and transition from austenite to ferrite phase was evaluated to be around 1900 N. The results highlight the decreased high-angle grain boundary (HAGB) and increased dislocation density causing the sample with a higher force amplitude to be more inclined to fracture. The initiation of fatigue crack was accelerated by the accumulation of dislocation within ferrite phase grains. Similar fatigue fracture morphology with ovalization phenomenon was observed in all conditions. To predict the ratcheting fatigue life of aero-engine thin wall pipes, a validated fatigue life estimation model considering steady ratcheting displacement rate based on a finite element analysis (FEA) model was conducted, and all of the fatigue data are contained in a 1.1X scatter band.

Revealing the microstructure, texture evolution and mechanical properties along the whole wall of Mg-Gd-Y-Zn-Zr cylinders by tailoring rotary backward extrusion parameters

In this article, industrial-specification Mg-Gd-Y-Zn-Zr alloy cylinder parts were successfully prepared by rotary backward extrusion process. The microstructure distribution and mechanical properties evolution of the whole wall of different cylinder parts were investigated, and the effects of different rotation speeds on the microstructure and properties were also revealed. The results showed that the strain of the cylinder wall increased significantly with rotation speed increased, thereby generating a higher driving force for the microstructure refinement. The transformation of the inner wall progressed from the deformed zone (bulk-shaped long period stacking ordered (LPSO) phases, coarse deformed grains, and fine recrystallized grains) to the strongly affected zone (particle-shaped LPSO phases and fine recrystallized grains), with the latter expanding as rotation speed increased. Furthermore, there was a gradient distribution of strain in the cylinder walls, with the strain gradient intensifying alongside rotation speed. The transformation of the strongly affected zone into the deformed region from the inner to the outer wall suggested a diminishing effect of rotation speed on LPSO phases fragmentation and grain refinement. Notably, increasing rotation speed rendered improvements in the strength and ductility of the cylinder wall. And mechanical properties also displayed a gradient decrease from the inner wall to the outer wall. This variation in mechanical properties of different regions was closely associated with the contributions of grain boundary strengthening, texture strengthening and second phase strengthening.

Achieving high strength-ductility synergy in TiBw/near α-Ti composites by ultrafine grains and nanosilicides via low-temperature severe plastic deformation

The common problem of low strength-ductility matching prevails in near-α high-temperature titanium matrix composites (TMCs). In this work, the design strategy of ultrafine grains and dispersed (Ti, Zr)6Si3 nanoprecipitates in the microstructure of TiBw/near α-Ti composites via low-temperature isothermal multidirectional forging (IMDF), is expected to break the trade-off dilemma between strength and ductility. The results show that with the decrease in the temperature of IMDF, the grain scale decreased from 0.98 to 0.59 μm, and the location of silicide precipitation shifted from phase boundaries and grain boundaries to α-grain boundaries and intracrystalline regions. The experiments confirm that the local segregation of Si and the temperature of thermomechanical deformation are the key factors affecting the precipitation behavior of silicides. With the decrease of the deformation temperature, the precipitation mechanism of silicides changes from a single diffusion-controlled precipitation to the coupling of two mechanisms, namely, elemental diffusion and dislocation-assisted nucleation, which facilitates the successive precipitation of nanometer-sized silicides at the grain boundaries and in the inner regions. The ultimate tensile strength (UTS) and elongation of the composites were substantially increased after IMDF at 950 and 800 °C, especially the excellent performance at 800 °C, where the strength reached 1320.3 MPa and the elongation was 5.8 %. The room and high-temperature strengthening and failure mechanisms of the composites are analyzed and discussed, and the yield strength (YS) increments provided by various strengthening mechanisms at room temperature are quantified, aiming to provide a potential preparation strategy for the synergistic strengthening of near-α TMCs with ultrafine grains and nanoparticles.

Mechanical Alloying Synthesis and Spark Plasma Sintering Consolidation of Al-Ti-Si-W Alloys

Al-Ti-Si-W quaternary powders were mechanically synthesized by planetary ball milling; and further consolidated by spark plasma sintering. The nominal compositions of the quaternary alloys were designed to be Al60Ti30Si5W5 and Al45Ti40Si10W5 (wt.%). The microstructural evolution of intermetallic compounds in Al-Ti-Si-W alloys included titanium aluminide, titanium silicide, and ternary alloys (AlxTiy, TixSiy, and TixAly,Siz), whereas W was embedded in the Al-Ti matrix as a single phase. The phase composition and grain size distribution were investigated using electron backscatter diffraction analysis, in which refined and uniform microstructures (less than 0.3 μm) were attributed to severe plastic deformation and rapid densification of the pre-alloyed powders. The mechanical properties were correlated with the Al content in the quaternary alloys; a high hardness of 1014.6 ±73.5 kg/mm2 was observed.

Endowing low fatigue for elastocaloric effect by refined hierarchical microcomposite in additive manufactured NiTiCuCo alloy

NiTiCu-based shape memory alloys have been considered as ideal materials for solid-state refrigeration due to their superb cycling stability for elastocaloric effect. However, the embrittlement and deterioration caused by secondary phase and coarse grains restrict their applications, and it is still challenging since the geometric components are required. Here, bulk NiTiCuCo parts with excellent forming quality were fabricated by laser powder bed fusion (LPBF) technique. The as-fabricated alloy exhibits refined three-phases hierarchical microcomposite formed based on the rapid cooling mode of LPBF, composed of intricate dendritic Ti2Ni–NiTi composite and nano Ti2Cu embedded inside the NiTi-matrix. This configuration endows far superior elastocaloric stability compared to the as-cast counterpart. The low fatigue stems from the strong elastic coupling between the interphases with reversible martensite transformation, revealed by in-situ synchrotron high-energy x-ray diffraction. The fabrication of NiTiCuCo alloy via LPBF fills the bill of complex geometric structures for elastocaloric NiTiCu alloys. The understanding of interphase micro-coupling could provide the guide for designing LPBF fabricated shape memory-based composites, enabling their applications for special demands on other functionalities.

Experimental and calculational analysis about the influence of the grain boundary diffusion depth on the magnetic properties of a sintered Nd-Fe-B magnet

The grain boundary diffusion process (GBDP) has been widely applied to increase the coercivity of Nd-Fe-B magnets. After GBDP with Dy/Tb-rich diffusion sources the thickness of the Dy/Tb-rich shell formed on the epitaxial layer of the 2:14:1 main phase grain decreases from the magnet surface to the center. However, the influence of the Dy/Tb-rich shell gradient distribution on magnetic properties has not been thoroughly studied. In this work, a sintered Nd-Fe-B magnet was subjected to GBDP with Pr60Tb10Cu30 alloy at 860°C for various diffusion times (3 h, 6 h and 9 h). The coercivity improves rapidly from 884 kA/m (without GBDP) to 1533 kA/m after GBDP of 3 h. The coercivity further increases to 1741 kA/m with increased diffusion time to 6 h. But only marginal coercivity enhancement (rising to 1803 kA/m) can be obtained by further prolonging the diffusion time to 9 h. Microstructure analysis indicates that the long diffusion time leads to the surface grain coarsening, which degrades the diffusion efficiency. Meanwhile, micromagnetic simulation indicates that if the thickness of the Tb-rich shell in magnet center is less than 4 nm, the coercivity increases significantly with the enhanced thickness uniformity of the Tb-rich shell. But if the thickness of the Tb-rich shell in magnet center is higher than 4 nm, the coercivity cannot be improved effectively by further increasing the thickness uniformity of the Tb-rich shell. The results in this work clarify the mechanism of the magnetic property dependence on the diffusion time and help to optimize the GBDP parameters in the future.