Sintered Nd-Ce-Fe-B magnets were grain boundary diffused(GBDed) with Pr_(x)Tb_(80-x)Al_(10)Ga_(10)(at%)(x=0,20,40,60,80) alloys.The effect of Pr/Tb content in diffusion source on magnetic properties,microstructure and...Sintered Nd-Ce-Fe-B magnets were grain boundary diffused(GBDed) with Pr_(x)Tb_(80-x)Al_(10)Ga_(10)(at%)(x=0,20,40,60,80) alloys.The effect of Pr/Tb content in diffusion source on magnetic properties,microstructure and elements distribution of GBDed magnets was investigated.When Pr is used to substitute for 75% Tb in diffusion source,Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%,compared with the Tb_(80)Al_(10)Ga_(10) diffused magnet.Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains,resulting in substantial coercivity improvement.Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process.It can eliminate some sharp defects of main phase grains and make grain boundaries smooth,which provides diffusion channels for further diffusion of Tb element.Therefore,there are more diffusion channels for Tb and less Tb enriched at surface region,making Tb diffuse more deeply and improving Tb utilization efficiency.This method significantly improves the coercivity,and realizes the green,efficient and high-quality utilization of heavy rare earth(HRE)elements.展开更多
A homogenization treatment(1250 °C + 12 h) was carried out to minimize the micro-segregation of bulk 718H martensitic mold steel, as verified by advanced experimental characterization and kinetic model of diffusi...A homogenization treatment(1250 °C + 12 h) was carried out to minimize the micro-segregation of bulk 718H martensitic mold steel, as verified by advanced experimental characterization and kinetic model of diffusion. However, new research found that there are still limitations in the use of the homogenization process. The result indicates that the chemical heterogeneity can be significantly reduced after homogenization. The segregation ratio of Cr and Mo elements of sample decreased by 40.9% and 35.6% of the original level, respectively. Simultaneously, the test steel with higher strength and toughness is produced by controlling micro-segregation tempered from 540 °C to 650 °C. Importantly, it reveals that the impact energy is increased by up to 27.3%. The isotropy of impact energy in different directions can reach 0.89,resulting in an overall improvement in the isotropy. Toughness mainly depends on the orientation relationship between the crack propagation direction and the band segregation region. The chain carbides formed due to the decomposition of the micro-segregated region during tempering are considered the main source of cracks. The more evenly distributed the subsequent tempered carbides after homogenization, resulting in an increase in toughness. However, an abnormal phenomenon is found in which the yield strength after homogenization is lower than that of the untreated sample tempered at 700 °C. This result can be attributed to the combined influences of precipitation strengthening and fine grain strengthening by analyzing various strengthening mechanisms. The mutually restrictive strengthening effect leads to the limitations of the homogenization process of bulk martensitic mold steel.展开更多
基金Project supported by the National Key Research and Development Program of China (2022YFB3503303)。
文摘Sintered Nd-Ce-Fe-B magnets were grain boundary diffused(GBDed) with Pr_(x)Tb_(80-x)Al_(10)Ga_(10)(at%)(x=0,20,40,60,80) alloys.The effect of Pr/Tb content in diffusion source on magnetic properties,microstructure and elements distribution of GBDed magnets was investigated.When Pr is used to substitute for 75% Tb in diffusion source,Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%,compared with the Tb_(80)Al_(10)Ga_(10) diffused magnet.Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains,resulting in substantial coercivity improvement.Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process.It can eliminate some sharp defects of main phase grains and make grain boundaries smooth,which provides diffusion channels for further diffusion of Tb element.Therefore,there are more diffusion channels for Tb and less Tb enriched at surface region,making Tb diffuse more deeply and improving Tb utilization efficiency.This method significantly improves the coercivity,and realizes the green,efficient and high-quality utilization of heavy rare earth(HRE)elements.
基金The work was financially supported by the China Postdoctoral Science Foundation(No.2019M661153)The authors also appreciate the financial support by Young Talent Project by Shenyang National Laboratory for Materials Science(No.2020000358)+2 种基金Doctoral Research Startup Fund Guidance Program Project of Liaoning Province(No.2020-BS-004)Project to Strengthen Industrial Development at the Grass-roots Level(No.TC190A4DA/35)Guangdong Basic and Applied Basic Research Foundation(No.2019A1515110886).
文摘A homogenization treatment(1250 °C + 12 h) was carried out to minimize the micro-segregation of bulk 718H martensitic mold steel, as verified by advanced experimental characterization and kinetic model of diffusion. However, new research found that there are still limitations in the use of the homogenization process. The result indicates that the chemical heterogeneity can be significantly reduced after homogenization. The segregation ratio of Cr and Mo elements of sample decreased by 40.9% and 35.6% of the original level, respectively. Simultaneously, the test steel with higher strength and toughness is produced by controlling micro-segregation tempered from 540 °C to 650 °C. Importantly, it reveals that the impact energy is increased by up to 27.3%. The isotropy of impact energy in different directions can reach 0.89,resulting in an overall improvement in the isotropy. Toughness mainly depends on the orientation relationship between the crack propagation direction and the band segregation region. The chain carbides formed due to the decomposition of the micro-segregated region during tempering are considered the main source of cracks. The more evenly distributed the subsequent tempered carbides after homogenization, resulting in an increase in toughness. However, an abnormal phenomenon is found in which the yield strength after homogenization is lower than that of the untreated sample tempered at 700 °C. This result can be attributed to the combined influences of precipitation strengthening and fine grain strengthening by analyzing various strengthening mechanisms. The mutually restrictive strengthening effect leads to the limitations of the homogenization process of bulk martensitic mold steel.
