影响NdFeB永磁合金磁性的微观结构分析

以N35TH烧结态NdFeB永磁合金为实验材料,进行时效态处理,系统分析了合金微观结构对磁性的影响。通过场发射扫描电镜观察了合金形貌,结果表明,影响NdFeB磁性的内在因素包括在主晶相Nd2Fe14B晶界处富稀土相的形态和分布、主晶相晶界的平直规整和Nd2Fe14B主晶相的数量增加,而且NdFeB永磁合金中具有001强织构和001取向的主晶相Nd2Fe14B晶粒明显增多,也是导致磁性改善的重要原因。     

纳米晶粉末添加对烧结NdFeB矫顽力的影响

以在传统速凝甩带、氢爆破碎工艺下制得的烧结NdFeB粉末为对象,通过添加粒度小于1μm的Dy2O3粉末、DyF3粉末或纳米级镓粉及铝粉,或者上述几种材料的混合粉末制备成烧结永磁体;系统研究了添加不同上述材料对烧结NdFeB永磁晶相结构及主要磁性能指标的影响。结果表明:添加上述纳米级粉末材料后,通过设置相应的制粉及烧结回火工艺可以促使该类材料均匀地富集在边界相当中,改善了原有材料的组织结构,可以大大提升NdFeB永磁材料的内禀矫顽力,从而使得烧结NdFeB磁体的热稳定性得到显著提升。     

Zr,Yb,Cr对Al-Zn-Mg-Cu合金组织、断裂和局部腐蚀行为的影响

研究复合添加稀土元素Yb和过渡元素Zr,Cr对Al-Zn-Mg-Cu超高强合金组织、强韧性和局部腐蚀(晶间腐蚀和剥落腐蚀)性能的影响。结果表明:单独添加Zr和复合添加Cr,Yb的合金均发生了再结晶现象,合金的强度、韧性和腐蚀抗力均较低。而在Al-Zn-Mg-Cu合金中复合添加Zr,Yb,Cr形成大量10~20 nm、共格的固溶部分Zn,Mg,Cu的(Al,Cr)3(Zr,Yb)弥散相,这些均匀分布于基体的细小共格弥散相能强烈钉扎位错和亚晶界,抑制基体再结晶,使合金亚晶界上的析出相与晶内近似,晶界无沉淀析出带(PFZs,precipitate-free zones)不明显。复合添加Zr,Yb,Cr的Al-Zn-Mg-Cu合金在保持高强度和塑性的同时,沿晶断裂抗力和局部腐蚀抗力显著提高。T6态Al-Zn-Mg-Cu-Zr-Yb-Cr合金的断裂机制主要为韧窝型断裂,剥落腐蚀等级降至EA。再结晶晶界成为超高强Al-Zn-Mg-Cu合金腐蚀和断裂的优先扩展路径。     

放电等离子体烧结NdFeB永磁材料力学性能的研究

采用传统烧结技术和放电等离子体烧绱技术（SPS）制备相同成分的烧结NdFeB水磁合金。研究了所制备合金的力学性能和断裂行为。利用扫描电子显微镜观察了合金的显微组织和断口形貌；测量了合金的抗弯强度并对磁体的力学性能进行评价。结果表明：SPS NdFeB磁体的抗弯渔度较传统烧结体有显著的提高，前者a bb=402．25MPa，后者abb=278．97Mpa；SPS NdFeB磁体显微绀织主相晶粒细小均匀、富稀土相细小弥散且彼此隔断，断口观察发现了较明显的撕裂棱及一些解理断裂；而传统烧结磁体主相晶粒粗大、富稀土相粗大且彼此连接。沿晶断裂特征明显。     

第二相对Ti-25V-15Cr-2Al-0．2C-x（x=0，2％Mo，2％Nb，0．02％Si）合金拉伸断裂行为的影响

研究了第二相对Ti—25V—15Cr—2Al—0．2C—x(x=0，2％Mo，2％Nb，0．2％Si)阻燃β钛合金拉伸断裂行为的影响。结果表明，β晶界上析出的。相增加了合金发生沿晶断裂的趋势，特别是热暴露后形成的连续晶界α膜是导致合金脆性沿晶断裂的主要原因。虽然粗大的碳化物颗粒是合金中的裂纹源之一，但细小、弥散分布的碳化物却能显著降低合金发生脆性沿晶断裂的趋势，其原因是细化了β晶粒和有效抑制了晶界α沉淀的析出。     

Fe-P-C-Cu-Mo系粉末合金的组织、性能及断口

研究了Fe-P-C-Cu-Mo系铁基粉末冶金材料中合金元素、烧结温度对合金组织及性能的影响,以及不同回火温度下磷的分布及其对合金断裂方式的影响。
通过研究得出:Fe-0.60%P-0-44%C-1.0%Cu-0.50%Mo合金在1160-1240℃烧结,保温1-2小时,可以获得较好的性能;若进一步经过850-900℃淬火,200℃或600℃回火,则合金的综合机械性能可以显著提高。通过试验发现:合金在200℃回火后,固溶在基体中的铝能抑制磷向晶界偏聚,使合垒断裂时呈现为穿晶断裂;400℃回火后,由于钼以碳化物形式析出,磷主要偏聚在晶界,造成合金沿晶断裂;600℃回火后,磷主要偏聚在孔隙表面,合金断口呈韧窝状。     

DyAl合金薄膜在NdFeB基体上真空热扩渗行为的研究

采用直流(DC)磁控溅射的方法,在烧结NdFeB磁体表面制备了DyAl合金薄膜,镀膜样品经真空热扩渗(800℃×6h)和时效处理(900℃×2.5h+490℃×5h),研究了样品的微观结构组织与磁性,并对Dy、Al元素在基体中的真空热扩渗行为进行了探讨。结果表明,随着DyAl合金薄膜厚度的增加,磁体的内禀矫顽力Hcj相应提高,内禀矫顽力Hcj提高176kA/m(2.2kOe)。通过对样品微观组织结构观察发现,Dy和Al元素沿晶界富Nd相优先扩散,大量集中分布在主相晶粒表层和富Nd相交界处,不仅改善了晶界表面浸润性,也改变了主相晶粒表层合金成分和微结构,这种晶粒表面与晶界相的改性导致烧结NdFeB磁体的内禀矫顽力Hcj提高。     

第二相对Ti-25V-15Cr-2Al-0.2C-x(x=0,2%Mo,2%Nb,0.2%Si)合金拉伸断裂行为的影响

研究了第二相对Ti 2 5V 15Cr 2Al 0 .2C x (x=0 ,2 %Mo,2 %Nb ,0 .2 %Si)阻燃β钛合金拉伸断裂行为的影响。结果表明 ,β晶界上析出的α相增加了合金发生沿晶断裂的趋势 ,特别是热暴露后形成的连续晶界α膜是导致合金脆性沿晶断裂的主要原因。虽然粗大的碳化物颗粒是合金中的裂纹源之一 ,但细小、弥散分布的碳化物却能显著降低合金发生脆性沿晶断裂的趋势 ,其原因是细化了β晶粒和有效抑制了晶界α沉淀的析出     

Co—Ni钢长期回火脆性的研究

用透射电镜、扫描电镜及俄歇能谱研究了１６ＮｉＣｏ钢和２３ＮｉＣｏ钢长时间回火后韧性降低及冲击韧性断口出现沿晶断裂的原因。产生脆性的原因主要是由于杂质元素Ｐ、Ｓ及合金元素Ｎｉ在晶界偏析所致。已经变脆的试样，经６００℃保温处理可消除脆性及沿晶脆断。     

GH3535高温合金的蠕变断裂机理和寿命预测

钍基熔盐堆中构件与高温熔融的氟化盐、核燃料及其裂变产物直接接触,这导致材料要同时处于高温、受力、强中子辐照和强熔盐腐蚀等交互作用的多重极端环境中。GH3535合金作为熔盐堆构件的候选材料之一,其力学性能的研究对熔盐堆的设计和安全性评估具有重要意义。以GH3535高温合金为研究对象,开展了650、700、750、800℃不同应力条件下的蠕变试验,采用SEM、EDS、EPMA等表征方法分析了合金微观组织与蠕变断裂机理。结果表明,GH3535合金在650℃时,其断裂方式为沿晶断裂,随着温度的升高,该合金的断裂方式由沿晶断裂转变为韧性断裂。GH3535合金一次析出相富含Mo、Si和C元素,其既存在于晶界又存在于晶内,蠕变过程中有二次析出相在晶界处析出。蠕变裂纹起源于晶界交汇处,裂纹处存在C元素富集。利用蠕变试验数据,建立了GH3535合金的Norton蠕变模型,获得了同一温度下的蠕变速率与应力关系式,得到了GH3535合金的蠕变极限。在此基础上,建立了基于时间温度参数法的Larson-Miller(LM)模型和基于蠕变曲线的修正θ参数模型。相比于LM模型,修正θ参数法可以充分利用蠕变曲线信息,...     

Toughness of Sintered NdFeB Magnets

The failure mechanism of sintered NdFeB magnets was studied from the view of fracture model and fracture mechanism, and the effect of alloying on strength and toughness of the magnets was researched too. The results showed that intercrystalline fracture was the main fracture model and cracks elongated along the interface between 2–14–1 phase and Nd-rich phase. Generally, the methods for improving toughness include enhancing bond strength of the interface between the two phases mentioned just, refining grains of 2–14–1 phase and increasing the amount of particles of Nd-rich phase localized at grain boundary. The fracture model of the Nd_15.5Fe_76.5Al₁Ti_0.5B_6.5 magnets was transcrystalline cleavage fracture, whose value of fracture toughness increased about 30% compared to that of the Nd_15.5Fe₇₈B_6.5 magnets. Otherwise, the value of fracture toughness of the magnets with a proper amount of addition of Ag increased about 70% compared to that of the Nd_15.5Fe₇₈B_6.5 magnets. Moreover, the two sorts of modified magnet mentioned just could be drilled successfully. In addition, development of the research about increasing the strength and toughness of sintered NdFeB magnets is reviewed in this article.     

低失重烧结钕铁硼磁体的研究进展

烧结钕铁硼永磁材料被发明以来,以其优越的磁性能得到了广泛的应用,目前成为永磁产业的支柱。但是其耐腐蚀性能差,大大限制了其使用范围。因此,近20多年来如何改善其抗腐蚀性能成为烧结钕铁硼材料生产和使用的重要问题。总结了烧结钕铁硼腐蚀失重的机制,制备低失重烧结钕铁硼的方法和工艺,对如何提高烧结钕铁硼磁体的耐腐蚀性,降低腐蚀失重进行了综述。从磁体成分设计和微观结构方面总结了几条提高烧结钕铁硼磁体耐蚀性的原则,其关键是对晶界相的成分和微观结构进行合理的控制。     

Effect of Copper and Titanium Addition on Microstructures and Magnetic Properties of Sintered Nd_(22) Fe_(71) B_7 Magnets

Ｉｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｔｈｅｉｎｔｅｒｇｒａｎｕｌａｒｍｉ ｃｒｏｓｔｒｕｃｔｕｒｅｏｆｓｉｎｔｅｒｅｄＮｄ Ｆｅ Ｂｍａｇｎｅｔｓｐｌａｙｓａｋｅｙｒｏｌｅｉｎｄｅｔｅｒｍｉｎｉｎｇｔｈｅｉｒｃｏｅｒｃｉｖｉｔｙａｎｄｔｈｅｒｍａｌｓｔａｂｉｌｉｔｙ[1,2 ] .Ｔｈｅｒｅｆｏｒｅ ,ｉｔｉｓｉｍｐｏｒ ｔａｎｔｔｏｆｕｒｔｈｅｒｍｏｄｉｆｙｉｎｇｔｈｅｉｎｔｅｒｇｒａｎｕｌａｒｍｉ ｃｒｏｓｔｒｕｃｔｕｒｅｖｉａａｌｌｏｙｉｎｇｏｒｏｔｈｅｒｐｒｏｃｅｓｓｉｎｇｍｅｔｈｏｄｉｎｉｍｐｒｏｖｉ…     

Comparative Evaluations and Microstructure: Mechanical Property Relations of Sintered Silicon Carbide Consolidated by Various Techniques

A comparative evaluation between pressureless or self-sintered silicon carbide (SSiC), hot-pressed silicon carbide (HP-SiC), and spark plasma-sintered silicon carbide (SPS-SiC) has been carried out with emphasis on examination of their microstructures and mechanical properties. The effect of sample dimensions on density and properties of SPS-SiC has been also examined. Elastic modulus, flexural strength, and fracture toughness measured by indentation or testing of single-edge notched beam specimens have been found to follow the following trend, HP-SiC > SSiC > SPS-SiC. The SPS-SiC samples have shown size-dependent densification and mechanical properties, with the smaller sample exhibiting superior properties. The mechanical properties of sintered SiC samples appear to be influenced by relative density, grain size, and morphology, as well as the existence of intergranular glassy phase. Studies of fracture surface morphologies have revealed the mechanism of failure to be transgranular in SSiC or HP-SiC, and intergranular in case of SPS-SiC, indicating the dominating influence of grain size and α-SiC formation with high aspect ratio.     

Improved Mechanical Properties and Thermal Stability of Sm-Co High Temperature Magnets Resulting From Surface Modifications

Improved mechanical properties and thermal stability of Sm-Co high temperature magnets resulting from surface modifications are reported. Compared to un-modified magnets, the modification with 15 μm sulfamate-Ni plating improved the fracture toughness by 76% and the thermal stability by 143% in vacuum and 861% in air for aging at 500 °C for up to 3000 hours. Microstructures of some specimens with and without modification were studied using SEM with EDS, and showed different fracture patterns. The improvements in mechanical properties were resulted by closing the infinite crack-origin sites on the surface of the brittle magnets with ductile metal. The striking improvement in thermal stability was achieved by sealing the Sm-Co magnets with corrosion resistive metal to limit oxidation. The adhesive bond strength between the magnet and the modified surface plays an important role in these improvements.     

Effect of Binder and Additives on Properties of NdFeB Bonded Magnets by Injection Moulding

Properties of NdFeB bonded magnets by injection moulding lie on many factors. The study indicates that those such as coupling agents exterior covering, binder contents, antioxidant and the selection of lubricator have significant effects on the properties of NdFeB bonded magnets. The appropriate choice of additives can improve the properties of NdFeB bonded magnet.     

Investigation of deformation and heat treatment effects on properties of PM 92.5W–5Ni–2.5Fe heavy alloys

Abstract

This paper presents the effects of vacuum heat treatment under different cooling conditions on mechanical and structural properties of forged heavy alloys, such as 92.5W–5Ni–2.5Fe and 92.5W–5Ni–25Fe microalloyed with Co. The tungsten composition in the c phase has proved to be higher and more homogenous in the rapidly cooled alloys than in the slowly cooled ones. The effects of chemical composition inhomogeneity on mechanical and structural properties of alloys were also analysed and discussed. The results of tensile and toughness testing have shown an increase in ductility and toughness, while the strength of heat treated alloys decreased in comparison with the strength of forged alloys. The fracture analysis has shown that in the sintered and rotary forged alloys, intergranular fracture of the tungsten phase and transgranular fracture of the γ phase occurred, respectively. The fracture of these phases after heat treatment was characterised by transgranular morphology.     

Magnetic Properties and Intergranular Action in Bonded Hybrid Magnets

Magnetic properties and intergranular action in bonded hybrid magnets,based on NdFeB and strontium ferrite powders were investigated.The long-range magnetostatic interaction and short-range exchange coupling interaction existed simultaneously in bonded hybrid magnets,and neither of them could be neglected.Some magnetic property parameters of hybrid magnets could be approximately obtained by adding the hysteresis loops of two magnets pro rata.     

HDDR NdFeB磁粉两步法伴温磁场取向制备高性能柔性各向异性NdFeB黏结磁体

利用高性能吸氢-歧化-脱氢-再复合(HDDR)NdFeB各向异性磁粉,通过两步法伴温磁场取向工艺制备高性能柔性各向异性NdFeB黏结磁体,重点研究了两步法伴温磁场取向工艺制备出不同成分配比磁体的磁性能和力学性能.结果发现:制备出磁体的取向度有大幅度提高,当成分配比(质量分数)为96.5%磁粉+1%偶联剂+2.5%黏结体系的磁体在120℃加热保温30 min磁场取向后,磁能积达到97 kJ·m-3,而磁体的矫顽力最大降幅只有1.3%,论证了两步法伴温磁场取向工艺制备柔性各向异性NdFeB黏结磁体在实际生产的可行性.环氧树脂润滑剂的加入使得制备出磁体的延伸率和柔性均大幅度下降,并且加入量越多,下降幅度越大,因此环氧树脂润滑剂最大加入量不应超过1%(质量分数).      

Ni对热变形Nd-Fe-B磁体磁性能及力学性能的影响

为提高热压结合热变形工艺制备的各向异性Nd-Fe-B磁体的力学性能,向磁体中掺杂高熔点、弱磁性金属元素Ni,研究Ni含量对磁体的磁性能、力学性能以及微观结构的影响。掺杂Ni的质量分数在0~5%之间时,Nd-Fe-B复合磁体的抗弯强度先增大后减小,2%Ni含量的Nd-Fe-B复合磁体具有最高平均抗弯强度212 MPa,其最大磁能积保持在40 MGOe以上。从磁体断口形貌上看,Ni会在孔洞附近富集,强化增韧晶界相,从而提高晶界相的裂纹扩展阻力,使抗弯强度提高。