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Nanocrystalline multi-main-phase (MMP) Nd-Ce-Fe-B magnet can effectively suppress the magnetic dilution effect of Ce. However, its low coercivity and poor thermal stability have not been adequately overcome. In this work, a novel low-melting-point Gd 60 Y 10 Cu 15 Al 15 alloy was introduced into MMP Nd-Ce-Fe-B magnet through intergranular addition for simultaneously enhancing its coercivity and thermal stability. The results show that the intrinsic coercivity H cj is obviously improved, and its maximum increment is ∼12.3 % at 4 wt% Gd 60 Y 10 Cu 15 Al 15 alloy. Especially, the increase in H cj is more significant, and an abnormally increase in the maximum energy product (BH) max occurs at high temperature of 150 °C. Meanwhile, the reversible temperature coefficients of H cj (β) and B r (α) are improved simultaneously. These findings imply the enhanced thermal stability for the MMP magnet with Gd 60 Y 10 Cu 15 Al 15 addition. The microstructural characterizations, compositional analyses and micromagnetic simulations reveal that the competitive effects of the formed non-ferromagnetic grain boundary (GB) phase and Y or Gd diffusion into the main phase lead mainly to a synergistic improvement in the coercivity and thermal stability of the magnet. This work is expected to provide a promising cost-effective approach for developing the high-performance thermally-stable Nd-Ce-Fe-B magnet and explore more possibilities for effective utilization of Y or Gd rare-earth resources. • The Research Highlights in this paper are as follows: • A novel low-melting-point Y-Gd based alloy was developed and used to modify the nanocrystalline MMP Nd-Ce-Fe-B magnet. • H cj and thermal stability of nanocrystalline MMP magnet are synergistically enhanced. • Microstructure evolutions and composition distributions are revealed. • The enhanced mechanisms for H cj and thermal stability are systematically analyzed. [ABSTRACT FROM AUTHOR]

This paper aims to improve the magnetic properties of sintered Nd Fe B magnet. Ni powders were added to the Nd Fe B magnet through intergranular addition, and their effects on the microstructure and magnetic properties of the magnet were investigated. By adding a proper amount of Ni (0.3 wt%), the intrinsic coercivity H cj of Nd Fe B magnet is significantly improved with only a slight decrease in the remanence B r and the maximum energy product ( BH ) max . The microstructural and compositional analyses reveal that Ni atoms not only enter the matrix phase but also concentrate in the intergranular regions either as Ni-containing Nd-rich phase or as Ni particles. This is consistent with the thermodynamic calculation results. Furthermore, a sintering mechanism of magnet with intergranular addition of Ni powders is tentatively proposed. These results may provide a reference for improving the magnetic properties of sintered Nd Fe B magnets. [ABSTRACT FROM AUTHOR]

The microstructure and chemical heterogeneity play critical roles in the magnetic performance of nanocrystalline multi-main-phase (MMP) Nd–Ce–Fe–B magnets. In this work, we report a strategy to synergistically tailor the microstructure and chemical heterogeneity of MMP magnet through optimizing sintering temperature (T s). An optimum T s of 700 °C has been obtained for nanocrystalline MMP Nd–Ce–Fe–B magnets. When sintered at T s = 700 °C, the nanocrystalline MMP magnet exhibits the maximum intrinsic coercivity H cj , the preferable remanence B r , and the resultant optimum maximum energy product (BH) max , which is attributed mainly to the appreciable density, controlled grain size, and better chemical heterogeneity. Comparably, lower or higher T s leads to the inferior magnetic properties. At lower T s below 700 °C, the poor magnetic properties are mainly due to the insufficient densification. However, at higher T s above 700 °C, the decreased H cj originates mainly from the excessive grain growth and gradual chemical homogenization. The above findings deepen our understanding on the relationship among the microstructure, chemical heterogeneity, and T s , concurrently providing an effective approach for fabricating low-cost high-performance nanocrystalline MMP Nd–Ce–Fe–B magnets. • Microstructure and chemical heterogeneity of nanocrystalline MMP Nd–Ce–Fe–B magnet are synergistically tailored. • H cj , B r , and (BH) max are simultaneously enhanced at optimum T s of 700 °C. • Dependences of microstructure and composition on T s are revealed, and an evolution model is proposed. • Mechanisms underlying changes in magnetic properties with T s are systematically analyzed. [ABSTRACT FROM AUTHOR]

• Thermally-stable high-performance nanocrystalline MMP Nd-Ce-Fe-B magnet is fabricated by grain boundary engineering. • H cj and thermal stability are obviously improved with simultaneously enhanced (BH) max. • Microstructure evolution is revealed, and the Dy diffusion model is proposed. • The underlying mechanisms for enhanced magnetic properties and thermal stability are systematically analyzed. Low coercivity and poor thermal stability are still the main challenges for practical application of low-cost Nd-Ce-Fe-B magnet. To solve these challenging problems, a strategy to simultaneously improve the coercivity and thermal stability of Nd-Ce-Fe-B magnet through combining the nanocrystalline multi-main-phase (MMP) structure and grain boundary engineering is demonstrated. In this study, nanocrystalline MMP Nd-Ce-Fe-B magnet was grain boundary engineered by co-adding DyF 3 and Cu powders. The results show that the intrinsic coercivity H cj is significantly improved, and meanwhile optimum maximum energy product (BH) max is achieved at 2 wt% DyF 3 -Cu. Moreover, the superior reversible temperature coefficients of H cj (β) and B r (α) are both achieved, implying the improved thermal stability for the DyF 3 -Cu added magnet. Microstructural and compositional characterizations indicate that the modified RE-rich phase, the inhibited abnormal grain growth near the flake boundary, and the diffused Dy towards main phase grains are the main reasons for simultaneously enhanced magnetic properties and thermal stability. Thus, combining the nanocrystalline MMP structure and grain boundary engineering will be a promising approach for preparing thermally-stable high-performance Nd-Ce-Fe-B magnet. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxidation phenomenon in one laser spot on stainless steel surface is studied. [•] Compositions and morphologies vary from center to edge in one laser spot. [•] Hexagonal Cr2O3 distributes in the edge, while spherical Fe2O3 in the center. [•] Oxidation mechanism is proposed based on thermodynamics and kinetics. [Copyright &y& Elsevier]

Abstract: The butt welding of 304 stainless steel plates with thickness of 3mm and 6mm were achieved by YLR-6000 fiber laser under Ar protective gas. The weld appearance, microstructure, composition distribution and microhardness of welded joint were emphatically investigated. The results showed that the narrow and fully penetrated welded joint without marco-defects can be obtained with tightly focused 2kW fiber laser power and 20mm/s welding speed. The weld bead was smooth, and various microstructures typically formed at different zones of the welded joint. The fine columnar and equiaxed crystals existed in the edge and center of weld bead, respectively. Both were different with the microstructure of the stainless steel substrate. However, the composition distribution of the welded joint had no obvious changes. Furthermore, the superior microhardness of welded joint over the stainless steel substrate was mainly attributed to its finer microstructure. [Copyright &y& Elsevier]

Abstract: Different laser energy densities were utilized to treat AISI 304 stainless steel via Nd:YAG pulsed laser surface melting (LSM). The surface composition and microstructure of the stainless steel were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM). In particular, the corrosion behaviors of the stainless steel surface without and with LSM were evaluated by the electrochemical polarization measurement in 3.5wt.% NaCl aqueous solution at room temperature. The results showed that the stainless steel surface without LSM suffered severe localized pitting under the testing conditions. A thin surface oxide protective layer was produced on the stainless steel surface with LSM, which considerably improved the corrosion resistance properties of the stainless steel. The height differences of the corrosion regions on the stainless steel surface with LSM were measured to establish more corrosion resistant region, using scanning confocal laser microscopy. The underlying corrosion mechanism of the stainless steel with LSM was revealed. [Copyright &y& Elsevier]

Abstract: Experiments were conducted to study the microstructure and tensile properties of the sub-micro and nano-structured Al produced by the Nd:YAG pulsed laser surface melting (LSM). The surface and longitudinal section microstructures of the Al samples after LSM were analyzed. The solidification microstructures in the LSM region were very fine which was beneficial to improve the properties of the Al sample. The tensile behavior and the relevant fracture mechanism of the LSM layer on the Al surface were investigated based on the analyses of the tensile test results. The fracture morphologies in the LSM region were small and shallow dimples with the size of 0.4–1μm. It indicated that the Al sample showed the ductile behavior because the grains were refined effectively after LSM. Furthermore, the typical amorphous fracture morphology with the fish scale structure was also obtained at the strain rate of 1.0×10−4 s−1 after LSM with the laser power density of 3.65×109 W/m2. [ABSTRACT FROM AUTHOR]

Abstract: The laser surface melting (LSM) technique was adopted to modify the surface layer microstructure of the AISI 304 stainless steel in this paper. The results showed that the hexagonal morphologies have been successfully fabricated on the surface after LSM. These hexagons had side lengths of about 0.5–1μm and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). It was proved by the XRD that the stainless steel surface mainly consisted of γ-Fe, Cr2O3, Fe2O3 and some manganese oxides. The FESEM micrographs showed that the hexagonal oxides were regular hexagons in geometry. The HRTEM micrographs also indicated the presence of the hexagons on the surface of the stainless steel. The spacing values were calculated from the HRTEM micrograph and the SAED pattern, and the hexagonal oxide phases determined by these spacing values were consistent with those verified by the XRD. After LSM, the microhardness of the stainless steel was significantly improved. [Copyright &y& Elsevier]

Abstract: To improve the magnetic properties and corrosion resistance of magnet, SiO2 nanopowders were added into Nd28.25Dy2.75FebalAl0.15Ga0.1Nb0.1B0.98-sintered magnets as grain boundary modifiers. It was found that the intrinsic coercivity (H cj), remanence (B r) and corrosion resistance were all improved with addition of certain amount of SiO2 nanopowders. The optimum addition amount of SiO2 nanopowders was found to be 0.01wt%. Thermodynamic calculation in combination of energy dispersive X-ray spectroscopy (EDX) analyses indicated that SiO2 nanopowders reacted with Nd of Nd-rich phase. As a result, the intergranular phase was modified, and the grain growth of main phase was restrained. It led to the optimization of microstructure. [Copyright &y& Elsevier]

Nanostructured multi-main-phase (MMP) Nd-Ce-Fe-B magnet produced by melt-spinning powders has great potential for achieving high performance. However, the inferior intrinsic properties of the Ce 2 Fe 14 B phase lead to the low coercivity and thermal stability of this magnet. In this study, low-melting-point Pr 68 Cu 32 powders were introduced into nanostructured MMP magnet through intergranular addition to further improve its coercivity and thermal stability. When only 2 wt% Pr 68 Cu 32 was added, the intrinsic coercivity H cj and thermal stability were significantly improved with a slight reduction in the remanence B r and the maximum energy product (BH) max. The microstructure evolution of MMP magnet with adding Pr 68 Cu 32 was revealed by microstructural and compositional characterization and thermodynamic calculation, and a schematic model was proposed. Furthermore, mechanisms underlying changes in magnetic properties were systematically analyzed by combining micromagnetic simulation. ● Grain boundary modification is adopted for fabricating high-performance nanostructured MMP Nd-Ce-Fe-B magnet. ● H cj and thermal stability are significantly improved with a slight reduction in B r and (BH) max. ● Microstructure and microchemistry evolution are investigated and a corresponding model is proposed. ● Mechanisms underlying changes in magnetic properties are systematically analyzed. [ABSTRACT FROM AUTHOR]

Lightweight refractory high-entropy alloy coatings (RHEAcs) of Nb x Mo 0.5 Ti 1.5 Ta 0.2 Cr (where x = 1, 1.3, 1.5, and 2) were fabricated on the surface of 316L stainless steel using pre-placed powder laser cladding (LC) technology. A comprehensive study was conducted to elucidate the effect of Nb content on the microstructure, microhardness and wear resistance of Nb x Mo 0.5 Ti 1.5 Ta 0.2 Cr RHEAcs before and after annealing at 900 °C for 10 h. The results show that the grains are gradually refined with the increase of Nb content. The coating consists mainly of a body-centered cubic (BCC) solid solution, C15-Laves phase, and a small amount of hexagonal close-packed (HCP) solid solution containing Ti. The microhardness of RHEAcs is significantly higher compared to the base material. Notably, at Nb 1.3 , due to the possibility of dislocation, the microhardness reaches a peak of 1066.5 HV, which is about 7.11 times higher than that of the base material. On the contrary, at Nb 2 , the microhardness is at its lowest point, averaging 709.31 HV, but 4.72 times that of the base material. After annealing, an increase in microhardness is observed at all Nb concentrations, up to 31.2% at Nb 2. Before annealing, the wear resistance of RHEAcs was slightly better than that of 316L stainless steel at different Nb contents. However, after annealing, the coefficient of friction (COF) and wear rate of the coatings are lower than those of annealed 316L stainless steel, highlighting their excellent wear resistance. It is noteworthy that the loss of wear properties after annealing at Nb1 is at a minimum, obtaining the most balanced wear resistance before and after annealing. The enhanced wear resistance after annealing can be attributed to the presence of ultra-fine grain oxide friction layers, mainly composed of TiO 2 and Ta 2 O 5. The main mode of wear is oxidative wear, with a small amount of wear from abrasive wear. • Compositional design of a new non-equimolar-ratio lightweight refractory high-entropy alloy. • Preparation of high-performance coatings by laser cladding technology and careful analysis of the micro-morphology and elemental distribution of the coatings. • Comprehensive testing of coating microhardness, abrasion resistance, and mechanical properties after annealing. [ABSTRACT FROM AUTHOR]

Microstructural evolution and mechanical properties of an aging 6061 Al alloy subjected to laser shock processing treatment (post-aging LSP treatment) were investigated by transmission electron microscopy (TEM) and mechanical tests. Results showed that the precipitates formed during aging treatment still remained, and the grain was refined by the ultra-high plastic strain plastic deformation during subsequent LSP treatment. Moreover, the precipitates effectively interacted with the dislocations induced by LSP. These typical microstructures contributed to the improvement in mechanical properties of the Al alloy. Relatively higher microhardness and strength were observed for the post-aging LSP Al sample. Furthermore, the synergistic strengthening mechanism involving the interaction of precipitate with dislocation, dislocations, and refined grains were clearly revealed. • The Research Highlights in this paper are as follows: • Novel process combining aging and LSP, i.e., post-aging LSP treatment, is reported. • Grain refinement, interaction between dislocation and precipitate, are discussed. • Synergistic strengthening mechanisms during post-aging LSP treatment are revealed. [ABSTRACT FROM AUTHOR]

A facile approach to fabricate a surface nanocomposite structure by embedding SiC nano-particles (NPs) via laser micro-melting is reported. A high fidelity model is adopted to reveal transient temperature distributions and the embedding of the SiC NPs into an Al molten pool during laser micro-melting. Special attention is paid to the embedding dynamic behaviours within the molten pool affected by Marangoni convection. Fluid flow and migration characteristics of the SiC NPs into the molten pool, as well as the resultant bubble motion and pore defects formation, are considered. Simulation results show that the temperature distribution is basically symmetrical with respect to the laser beam, and the Marangoni convection in the molten pool tends to embed the SiC NPs into the Al surface layer together with gas bubbles. This phenomneon is well validated by the experimental study on the surface morphology and the SiC NPs distribution in the Al surface layer. Microstructural characterizations indicate that a relatively flat reinforced SiC/Al surface can be formed at an optimized laser energy of 0.6 J. These studies may provide a new strategy for constructing nanocomposite structure on metal alloy surface. [ABSTRACT FROM AUTHOR]

Abstract: The effects of laser shock processing (LSP) on tensile property of LY2 aluminum (Al) alloy were investigated, and strain rate sensitivity of the untreated and treated samples by LSP was studied at the strain rates ranging from 0.00001s−1 to 0.1s−1. In both conditions, fracture morphologies were observed by field emission scanning electron microscope (FESEM), and the microstructure in the near-surface region was characterized by transmission electron microscopy (TEM), respectively. Experimental results showed that LSP can obviously improve the ultimate tensile stress and elongation of LY2 Al alloy, and the strain rate sensitivity of the treated sample appeared to be remarkable. The improvement of tensile properties may be explained by the fact that the grain in the LSP-shocked region was obviously refined. Dynamic strain aging was found in the treated sample at the strain rate ranging from 0.00001s−1 to 0.0001s−1, and the underlying formation mechanism was revealed. [Copyright &y& Elsevier]