Boundary Microstructure Research Articles

Effects of irradiation plus thermal aging on the phase boundary microstructure of austenitic stainless steel welds

Irradiation damage and thermal aging greatly affect the phase boundary microstructure and stress corrosion cracking of austenitic stainless steel weld metals (ASSWMs) in water-cooled nuclear reactors. However, the effects of irradiation plus thermal aging (I + A) on the phase boundary segregation and phase changes remain unclear. Phase changes and elemental segregation at the carbide and carbide-free phase boundaries of 308 L ASSWMs after I + A treatment were investigated using atom probe tomography and transmission electron microscopy. The I + A treatment induced Si depletion at the phase interfaces of δ-ferrite/austenite (δ/γ) and δ-ferrite/carbide (δ/C) and also induced Ni enrichment and Cr depletion with concentrations having the order Ni/Cr(δ/γ) > Ni/Cr(δ/C) > Ni/Cr(γ/C). The solute-defect binding model and the vacancy mechanism were applied to explain the phase boundary segregation. Furthermore, the I + A treatment affected microstructural evolution near the phase boundaries; this reduced spinodal decomposition and inhibited G-phase and Ni/Si-rich-cluster formation. The phase separation of δ-ferrite near δ/γ and δ/C phase boundaries differed with the distance from the boundary, forming a gradient microstructure from phase boundaries to δ-ferrite internally. The gradual precipitation of the G-phase was observed beyond about 15 and 10 nm from the δ/γ and δ/C interfaces, respectively; moreover, the growth of α'-phase in the δ-ferrite was accelerated with increasing distance from the δ/γ and δ/C interfaces.

Effect of aging treatment on microstructure and corrosion properties of Al-Cu-Mn-Si-Mg-Er-Zr alloy

The microstructure, mechanical properties and intergranular corrosion resistance of Al-Cu-Mn-Si-Mg-Er-Zr alloy with squeeze casting in the peak aging state at different temperatures were studied. The alloy was aged at 165 °C, 175 °C and 185 °C, and reached peak aging at 18 h, 12 h and 8 h respectively, among them, the alloy treated with 175 °C/12 h aging has the highest hardness, reaching 149 HV, and the yield strength is also the highest, which is 387 MPa. It is because the Q phase precipitated during the aging process of the alloy provides a heterogeneous nucleation site for the θ′ phase, the average size of the θ′ phase is 73.38 nm. The intergranular corrosion depth of the alloy after aging treatment at 175 °C/12 h was the deepest, reaching 284.91μm. At this time, the width of precipitation-free zone(PFZ) is the widest in the grain boundary microstructure, which is 92.21 nm, and the grain boundary precipitation phase is continuously distributed.

Near-surface self-resistance hydrogen effect of eutectic high-entropy alloy AlCoCrFeNi2.1

A series of engineering application studies related to hydrogen damage has been carried out for the eutectic high-entropy alloy (HEA) AlCoCrFeNi2.1 with excellent comprehensive properties. This work mainly introduces the element segregation and microstructure evolution phenomenon near the surface phase boundary and around the precipitated phase found in the hydrogen damage experiment of the material. Studies have shown that the evolution of the near-surface phase boundary microstructure of HEAs caused by hydrogen charging has a great influence on the hydrogen trap density inside the alloy. The “self-resistance hydrogen effect” is produced, that is, hydrogen-induced microstructure evolution causes the effect of delayed hydrogen diffusion. In this phenomenon, the synergy between hydrogen atoms and vacancies and dislocations on the alloy surface is crucial.

Grain boundary microstructure engineering of Li1.3Al0.3Ti1.7(PO4)3 electrolytes with a low-temperature-prepared nanopowder and Bi2O3 additive

All-solid-state lithium batteries have great potential applying to the fields of transportation and portable devices because of their high safety and energy density as the power source. As a critical component of device, solid-state electrolyte has been paid much attention. Given the excellent physical and chemical stability, Li1+xAlxTi2-x(PO4)3 (LATP)-based electrolyte has been considered as one of the most promising electrolytes for the next generation batteries. However, a further promotion of its ionic conductivity becomes extremely difficult, originating mainly from the poor connection of grains and a low relative density of LATP. Here, the nanosized and homogenous LATP (x = 0.3) powders were synthesized through reducing the agglomeration of precursor powders and preparing at low temperatures. It is revealed that uniformly superfine LATP powders are able to improve the microstructure of grain boundaries during the pellet sintering process, thereby reducing the grain boundary resistance. Furthermore, as-synthesized nanosized powders mixed with Bi2O3 additive present a better enhancement on the connection of grains and the relative density in LATP. On the basis of this understanding, we prepared LATP electrolytes with 0.5 wt% Bi2O3 exhibiting a high ionic conductivity of 8.56 × 10−4 S/cm, a high relative density of 94.4 % and a low activation energy of 0.27 eV, which is demonstrated as a prospective electrolyte in all-solid-state lithium battery LiFePO4/PEO/LATP/PEO/Li.

Effect of Fusion Boundary Microstructure on Flow-Accelerated Corrosion Cracking.

Flow-accelerated corrosion (FAC) preferentially attacks the downstream heat-affected zone of the root-pass weld in steam pipe systems. A detailed characterization identifies the fusion boundary as the initiation location for the attack. Alloying elements are found depleted along the weld fusion boundary, and multiple welding thermal cycles and repetitive austenite-to-ferrite phase transformations result in an increased proportion of grains with Goss {110}<001> texture along the fusion boundary. The synergistic effects of chemical segregation and the Schmid factor may contribute to the preferential initiation of FAC cracks along the root weld fusion boundary, making it the weakest link for FAC attack in steam pipe girth welds.

Microstructure analysis of 7050 aluminum alloy joint fabricated by linear friction weld

The microstructure of a linear friction welded joint of 7050 aluminum alloy was investigated through optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The analysis focused on grain boundary types, microstructure, and mechanical properties of the joint. The results reveal that fine equiaxed crystals are generated in the welded zone through dynamic recrystallization. The average grain size is 6.8 μm, with a volume fraction of large angle grain boundaries reaching 69.5%. The microstructure primarily consists of Cube {001}<100> texture, {111}<110> Brass recrystallization texture, and a small amount of copper {112}<111> deformation texture. The thermo-mechanically affected zone (TMAZ) presents a linear structure with an average grain size of 15.8 μm and a volume fraction of 36.1% at large grain boundary, resulting in a deformed Brass {011}<211> texture and a small amount of {236}<385> as well as {111}<110> Brass recrystallization texture. The welded joint exhibits a tensile strength of 492 MPa and a yield strength of 380 MPa, which represents 94.2% and 78.5% of the base material, respectively. Furthermore, the elongation of the joint is 10.2% and 98% of the base material, respectively. The fracture of the tensile sample is observed in the TMAZ, showing good mechanical properties with a mixed fracture mode with some degrees of ductility and brittleness.

Impact behaviour of Al 2014 wrought alloy using Split-Hopkinson pressure bar (SHPB): Its influence on mechanical and microstructural properties

The deformation behaviour of Al 2014 alloy under high strain rate dynamic load experienced in the actual service condition of aero-structural components is scarce in the literature. Therefore, Split Hopkinson Pressure Bar (SHPB) based high strain rate compressive behaviour (dynamic loading) of Al 2014 is investigated in this work. The wrought (WAR) form of Al 2014 alloy has been chosen to examine its deformation behaviour with varying high strain rate compressive loading, generated through 4 different pressure ranges (1 bar, 1.5 bar, 1.75 bar, and 2 bar) at striker bar end in SHPB technique. These pressure ranges induced high strain rates 5536/s, 6236/s, 6576/s, and 7783/s in separate WAR specimen, correspondingly, which were recorded as flow stress curves. Also, the WAR Al 2014 alloy was heat treated with standard Tempered-6 (T6) condition to homogenize its microstructure. The T6 condition was exposed further with the same pressure values, which induced high strain rates 5303/s, 6139/s, 6977/s, and 7861/s in T6 specimens. The SHPB-based flow stress responses for both WAR and T6 conditions were compared to understand high strain rate deformation behaviours. The WAR specimen exposed at 7783/s strain rate has shown superior Peak Stress (P.S., ∼765 MPa) and %contractionP.S. (∼15%) compared to its T6 counterpart (at 7861/s). Prior to the dynamic studies, the quasi-static responses were also explored through tensile, compressive and hardness measurements (with WAR and T6) to realize the overall materials' behaviour. These dynamic responses under high strain rate compressive loading were correlated with in-process microstructural evolution, explored through SEM and XRD techniques. Exhaustive EBSD analysis quantified the excellent peak stress and % contraction in WAR conditions due to presence of huge amount of low angle grain boundaries (∼85%), ultrafine grains, relatively textured microstructure ({111} 〈100〉, {101} 〈001〉, etc), and significant strain hardening phenomena, whereas large amount of high angle grain boundary (∼88%), equiaxed and uniform microstructure contributed for higher hardness (∼22%) and tensile strength (∼2%) in T6 conditions.

Grain boundary migration behavior and microstructure evolution during multilayer additive hot-compression bonding

Multilayer additive hot-compression bonding (MAHCB) was a new technology to prepare large-size homogeneous materials, the strain hardening at the bonding interface was an urgent issue for its application. In this paper, the effect of grain boundary migration on strain hardening was studied by the MAHCB process of pure copper. The results show that prolonging the holding time can significantly promote both interfacial grain boundary migration (IGBM) and matrix grain boundary migration (MGBM). The bonding interface became tortuous due to the promotion of IGBM, accompanied by the reduction in dislocation density at the interface and the gradual elimination of interfacial defects. It occurred mainly by the evolution of the triple junction grain boundary from T-type to equal type, which was driven by the decrease in the interface energy. On the other hand, the growth of dynamic recrystallization (DRX) grains was improved with MGBM, and enlarged the low dislocation density region. With the combined effect of both, strain hardening was completely eliminated, when the strain was 0.15 and the holding time was 3 h. Then the optimal bonding properties were obtained, the average tensile-shear strength and elongation were 191.2 MPa and 212 %, and the recovery rates were 99.7 % and 98.9 %, respectively, compared to the as-cast pure Cu samples.

Microstructure and mechanical properties of highly dense Si3N4 ceramics with ZrN–AlN–Re2O3 (Re=Yb, Y, Nd, Ce, La) additives

The Si3N4 ceramics with ternary ZrN–AlN–Re2O3 (Re=Yb, Y, Nd, Ce, La) and ZrN–AlN system as sintering additives were prepared by hot-pressed sintering with vacuum environment at 1750°C-30min–30MPa. Subsequently, the effect of the ternary additives system with 2 wt% Re2O3 on phase transformation, grain boundary phases, microstructure, and mechanical properties of the Si3N4 ceramics were investigated firstly. All samples achieved the high β-Si3N4 phases transformation (≥98.86%), while the grain boundary phases RexZr1-xO(4-x)/2 and Yb2Si2O7 were detected in the sintered Si3N4 ceramics with Re2O3 additives. Additionally, compared with Si3N4 ceramic not contain Re2O3 additives, the Si3N4 ceramics added Re2O3 additives presented the textured microstructure with more elongated rodlike β-Si3N4 grains based on the XRD and SEM results. Consequently, the sample S-Ce with added CeO2 additive shows the highest relative density of 99.85% and optimal fracture toughness of 8.75 ± 0.36 MPa m1/2. The sample S–Nd with added Nd2O3 additive presented a highest bending strength of 1061.78 ± 41.76 MPa. Sample S–Yb with added Yb2O3 additive presented the maximum Vickers hardness of 16.35 ± 0.07 GPa. The results of this study can provide a helpful reference for the preparation of high-performance Si3N4 ceramics.

Impacts of different designed microstructures on creep performance of a Ni-based wrought superalloy

The creep behavior of a novel Ni-based wrought superalloy with varying aging states, classified as large under-aged (UA), little UA, and little over-aged (OA) states, was investigated at a temperature higher than the intra-grain/grain-boundary iso-strength temperature (750 ​°C/250 ​MPa). In the samples before creep test, there are spherical γ′ precipitates homogeneously dispersed within the γ matrix and carbides precipitated at grain boundaries (GBs). After creep tests, precipitate-free zones (PFZs) appear on grain boundaries, with a large block-like γ′ phase present between carbides and PFZs, potentially serving as initiation sites for cracks. Little UA state samples exhibit the strongest creep resistance and intergranular fracture. The dominant creep deformation mechanism in the intra-grain is a combination of Orowan process involving slip and climb of matrix dislocations and shearing of γ′ precipitates. The results indicate that the optimizing the grain boundary microstructure may be more important than the change of intragranular microstructure when the creep temperature exceeds the iso-strength temperature.

Influence of Sintering Conditions on Anisotropy of Grain Boundary Networks and Microstructure Topology in Yttria-Stabilized Zirconia

The paper presents original data of 3D EBSD orientation maps collected for 13 Yttria-Stabilized Zirconia (YSG) samples, sintered at different temperatures for different times. The largest map contains 18,833 grains and 64,506 grain boundaries. These data allowed for the analysis of grain boundary networks, based on all 5 macroscopic parameters and some topological studies of microstructures. Grain boundaries having the (001) and (111) boundary planes are favored and disfavored respectfully in all YSZ samples. The anisotropy appears to be stronger if grains are larger. However, large grains themselves do not imply strong anisotropy. Symmetric boundaries are slightly more frequent in YSZ compared to random boundaries, but despite some premises, the evidence for over-representation of 180 deg-tilt boundaries is still too weak. Distributions of the number of faces per grain and mean number of faces per grain are similar to those reported for metals, and there is a close-to-linear correlation between the number of faces and grain size.Graphical

Quasi-in-situ observation and analysis of grain boundary evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation

A systematic study was conducted to analyze the grain boundary microstructure evolution of GH4169 nickel-based superalloy during the micro-strain stage of thermal deformation. A quasi-in-situ EBSD (electron backscatter diffraction) approach was used for observation. Moreover, at a temperature of 1100 °C and a strain rate of 0.1 s−1, a continuous strain uniaxial compression experiment was carried out. We observed the development of the grain boundary structure and the grain boundary deformation. The experimental findings revealed that GH4169 underwent locally inhomogeneous thermal deformation during the micro-strain stage, and the simultaneous occurrences of grain boundary slip, grain rotation, and grain boundary migration, exhibiting microstructural diversity. The grain boundary structure changed continuously as a result of the random movement of high-angle grain boundaries. Twin grains displayed a stable structure during the migration of grain boundaries, and their content indicated a considerable decrease as the strain increased. This provides a basis for directing the design of grain boundary engineering since it suggests that twin boundaries are easier to migrate during thermal deformation. In addition, no evidence of dynamic recrystallization was found throughout the entire micro-strain stage and a <101>/<111> micro-texture was observed, which is compatible with common dislocation slips in face-centered cubic crystals. Then, on the basis of the transmission electron microscope images of the microstructure, the numerous forms of grain boundary deformation were rationally explained from the standpoint of the relation mechanisms among grain boundaries and dislocations. Finally, the synergistic mechanism of grain boundary slip and migration is established as the primary mechanism of thermal deformation in the micro-strain stage.

Solving nonconvex energy minimization problems in martensitic phase transitions with a mesh-free deep learning approach

In this paper, we propose a novel mesh-free method for solving nonconvex energy minimization problems for martensitic phase transitions and twinning in crystals using the deep learning approach. These problems pose significant challenges to analysis and computation because they involve multiwell gradient energies with large numbers of local minima, each involving a topologically complex microstructure of free boundaries with gradient jumps. We use the Deep Ritz method, which represents candidates for minimizers using parameter-dependent deep neural networks, and minimize the energy with respect to network parameters. The key feature of our method is a newly proposed activation function called SmReLU, which captures the structure of minimizers where traditional activation functions fail. Our mesh-free approach allows for the approximation of free boundaries, essential to this problem, without any special treatment, making it extremely simple to implement. We demonstrate the success of our method through numerous numerical computations.

Modification of grain boundary microstructure by controlling dissolution behavior of θ particles in Cr-containing hypereutectoid steel

To overcome the brittleness of high‑carbon steels, it is necessary to develop the strategy to remove the carbides on the grain boundaries and strengthen grain boundaries. In this paper, we achieved them by simply controlling the heat treatment conditions and the microstructure before heat treatment. It was found the dissolution behavior of the θ-cementite particles is changed greatly with and without Cr in the high‑carbon steels. In the Cr-free hypereutectoid steel, dissolution of θ particles at high temperatures is remarkably fast, but the dissolution behavior is greatly affected by the microstructure in the Cr-containing hypereutectoid steel. In the Cr-containing hypereutectoid steel, the dissolution of θ particles into the γ-austenite phase was rapid in steel with smaller θ particles in fine α grains, but slow in steel with larger θ particles in coarse α grains. The θ particles on the grain boundaries preferentially dissolved and rapidly disappeared in the initial stage of the dissolution treatment owing to the contribution of grain boundary diffusion, since the grain boundary diffusion of Cr is fast as comparable to C. However, the θ particles inside the grains slowly dissolved and then remained until the later stage, owing to slow dissolution via the partition local equilibrium (PLE) mode controlled by the lattice diffusion of Cr. Owing to the preferential dissolution of θ particles on the grain boundaries in the initial stage, large amounts of Cr atoms dissociated from the θ particles diffused along the grain boundaries with grain boundary diffusion, forming Cr-enriched grain boundaries. Such grain boundary microstructure control is expected to lead to the suppression of intergranular fracture, resulting in the improvement of fracture toughness.

Effects of Rapid Quenching on Grain Boundary Microstructure and Mechanical Properties of an Al-Mg-Si-Cu Alloy.

Precipitate free zones (PFZs) near grain boundaries generally soften alloys. The quenching rate after solution treatment is an important factor influencing the width of PFZs in Al-Mg-Si-Cu alloy. This study explored the effects of high quenching rates on the grain boundary microstructures and mechanical properties of an Al-Mg-Si-Cu alloy. Samples of various thickness were quenched in water at room temperature and in ethylene glycol at -40 °C, respectively. The results showed that the rapidly quenched samples at -40 °C exhibited better comprehensive mechanical properties than the water-quenched samples. Transmission electron microscopy studies revealed the rapidly quenched samples had wider PFZs, shorter intragranular precipitates, and larger grain boundary precipitates (GBPs) than water-quenched samples. It is proposed that when the quenching rate exceeds the critical cooling rate, e.g., in water quenching or rapid quenching, the formation of PFZs is controlled by the solute depletion mechanism rather than the vacancy depletion mechanism. The nucleation and growth of GBPs thus lead to the depletion of solute atoms, resulting in wider PFZs rather than thinner PFZs according to previous knowledge. This research provides valuable insights into the application of rapid quenching technology for modifying alloys' microstructures and properties.

Optimizing the mechanical properties of dual-phase Ti-6242s titanium alloy at 550°C using the boundary architecture

In this work, a desirable combination of mechanical properties is achieved at 550 °C by tailoring the boundary microstructure between the primary α phase (αp) and the transformed β structure (βtrans) in a dual-phase Ti-6242s titanium alloy. The αp/βtrans boundary is displaced by a transition region that consists of β nano-plates or nanoprecipitates gradually penetrating into the αp in a particular semi-equiaxed microstructure (S-ES). The results show that the αp/βtrans boundary, where strain concentration easily occurs during deformation in the equiaxed microstructure (ES), induces recrystallization softening in the α phase. However, the transition region in the S-ES alleviates the strain localization and thus effectively inhibits the recrystallization softening that occurred in the α phase with concentrated strain. These β plates/precipitates in this region in turn enable an appropriate accumulation of dislocations. Significant improvement in the high-temperature strength, ∼240 MPa for the yield strength, is obtained for the S-ES relative to the ES. This work provides a new strategy for achieving outstanding strength at high temperature by designing special boundary architecture in dual-phase titanium alloys.

Significant coercivity enhancement of Ga-doped sintered Nd-Fe-B magnet by grain boundary diffusion perpendicular to the c-axis

Grain boundary diffusion (GBD) process is the most effective approach for enhancing coercivity of Nd-Fe-B magnets with minimal consumption of heavy rare earth (HRE). However, understanding of GBD mechanism is still limited, especially on the anisotropic diffusion behavior within sintered magnets. Grain boundary (GB) phase is the key factor in determining the diffusion process, which acts as diffusion channel for HRE atoms. The effects of doping Ga on the grain boundary microstructure and diffusion behavior of Tb in the sintered Nd-Fe-B magnet were investigated. Sintered magnets with different Ga content (0.15 wt%, 0.45 wt%) were prepared. It should be noted that Tb was diffused perpendicular to the easy axis (c-axis) of the magnets. The coercivity increased more significantly to 2.802 T (1.006 T higher than that of the post-sinter annealed state) in magnets with high Ga content than the low Ga content magnets (2.291 T, 0.669 T higher than the post-sintered annealed state). Such a huge coercivity increment almost reached the same value by diffusing Tb along the easy axis reported by other researchers. Chemical compositions and microstructure of the GB phase were found to be key factors in influencing the HRE diffusion process. A considerable amount of Nd6Fe13Ga phase was observed near triple junctions after post-sinter annealing in the high Ga content magnets, which markedly decreased Fe concentration in the intergranular phase. In addition, amorphous intergranular metallic Cu-rich phases provided smooth diffusion channels for HRE atoms. (Nd1-x, Tbx)2Fe14B shell was much more obvious in the high Ga content magnets. Ga dopping induced novel modifications in diffusion behavior of HRE atoms and strongly influenced the magnetic properties of permanent magnets. The present approach provide new path for the manufacture of high performance magnets, which is interesting both for technical applications and fundamental studies.

Reducing stress corrosion cracking susceptibility of high-strength aluminum alloy and its fastener by a novel electromagnetic shocking treatment

A novel electromagnetic shocking treatment (EST) is put forward to reduce the stress corrosion cracking (SCC) susceptibility of high-strength aluminum alloys and its fasteners by selectively modifying grain boundary (GB) microstructure. The effect of EST on the microstructure, mechanical properties and SCC susceptibility of T73-Al7075 alloy and its high-lock nuts has been investigated. Mechanical properties, electrochemical performance and constant strain SCC test have been carried out for T73-Al7075 alloy, microhardness test and SCC test under wet-dry cyclic condition have been carried out for its high-lock nuts, as well as microstructure characterizations via SEM, EBSD and TEM have been carried out for T73-Al7075 alloy. Comparing to the received sample, the strength of EST sample basically keep consistent while the elongation increases slightly, besides, the electrical conductivity and electrochemical corrosion performance improves. The SCC susceptibility of T73-Al7075 alloy and its high-lock nuts have been reduced after EST. Microstructure characterization shows that the grain morphology and matrix intragranular precipitate distribution of the EST sample keep almost the same as those of the received sample, which is consistent with the almost unchanged mechanical properties of alloy sample. However, EST induces the transformation of grain boundary precipitates (GBPs) and the formation of stripy/wavy GB as observed experimentally, which indicates that EST promotes nonlinear GB wetting or pre-melting and even grain bridging. The phase transformation and GB complexion transition induced by EST are main factors attributing to the obvious improvement of SCC resistance of T73-Al7075 alloy and its high-lock nuts. It can be deduced that anodic dissolution cracking will be relieved because of the dissolution and coarsening of GBPs. Hydrogen induced cracking and crack propagation can be relieved with the occurrence of grain bridging. They are both beneficial to improve SCC resistance of Al7075 alloys. This work provides a novel EST method to targetedly embellish GB microstructure, optimize GB complexion and connectivity, and then enhance the service performance of solid alloys and even finished parts.

Study of fusion boundary microstructure and local mismatch of SA508/alloy 52 dissimilar metal weld with buttering

A SA508/Alloy 52 dissimilar metal weld (DMW) mock-up with double-sided Alloy 52 butterings, which is fully representative of Ringhals pressurizer surge nozzle DMW repair solution, was studied. The microstructure, crystal structure, elemental diffusion, carbide formation and macro-, micro- and nano-hardness of the SA508/nickel-base Alloy 52 buttering fusion boundary (FB) were investigated. Three types of FBs were analyzed, i.e., narrow FB (∼80–85% of whole FB), tempered martensitic transition region (∼15%) and wide partially mixed zone (∼1–2%). The different FB types were induced by the local heat flow and respective elementary diffusion, which significantly influence the local hardness mismatch across the DMW interface and the local brittle fracture behavior.

Magnetic properties, crystalline and magnetic microstructures of dual-main-phase (Nd, Ce)-Fe-B sintered magnets

The (Nd, Ce)-Fe-B sintered magnets were prepared by a dual-main-phase (DMP) process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and (Nd, Ce)-Fe-B strips. The crystalline and magnetic microstructures of DMP (Nd, Ce)-Fe-B magnets with the remanence of 11.92–12.68 kGs, the intrinsic coercivity of 3.97–5.31 kOe, and the maximum energy product of 23.08–32.99 MGOe have been investigated. Magnetic force microscope (MFM) investigations reveal that the DMP (Nd, Ce)-Fe-B magnets show maze-like patterns, which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large. However, much finer domain structures mixing with coarse ones can be observed obviously in DMP (Nd, Ce)-Fe-B sintered magnets. The size distribution of the domain width of the DMP (Nd, Ce)-Fe-B magnet is not uniform obviously. The average domain width is W = 0.912 μm, and the fine domain width has only 0.216 μm. The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets. This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity. Furthermore, it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM, indicating their ferromagnetism. Obvious correlations between the crystalline microstructure, chemical composition of phases, and magnetic structure were demonstrated for the DMP magnets.