NdCeFeB快淬带相互作用与磁性能

采用感应熔炼制备名义成分为(Nd_1-xCe_x)_2.4Fe₁₄B (x=0, 0.2, 0.4, 0.6, 0.8, 0.8, 1.0)的快淬带,研究了Ce取代量对快淬带的相组成、磁性能和微观结构的影响。XRD结果表明,所有快淬带均呈现四方结构(Nd, Ce)₂Fe₁₄B相,当Ce取代量超过x=0.6时,快淬带中出现CeFe₂相并且CeFe₂含量随着Ce取代量的增加而增加。快淬带的剩磁、剩磁比（M_r/M_s）和晶格常数随着Ce含量的增加而减小,当Ce取代量为x=0.2时,快淬带的磁性能为矫顽力1.31×10⁶ A/m,最大磁能积103 kJ/m³。通过小回线和δM曲线研究了快淬带的矫顽力机理和晶粒间交换耦合,在每个样品中都观察到正的δM值,证实了交换耦合相互作用的存在。Ce含量为x=0.2时δM最大值达到0.76,说明快淬带晶粒间交换耦合效应最强,这一结果与剩磁比的变化一致。SEM观察发现,Ce取代量的增加恶化快淬带的柱状晶结构。     

腔室压力对Ce17Fe78B6合金磁性能及微观结构的影响

本文采用熔体快淬法制备了Ce17Fe78B6合金,研究了不同腔室压力对其磁性能和微观结构的影响。研究结果表明：在熔体快淬过程中,不同的腔室压力对Ce17Fe78B6合金的磁性能和微观结构有着很大的影响。随着腔室压力的增加,快淬条带的矫顽力逐渐增大,但是剩磁和最大磁能积却呈现先升高后下降的趋势。X射线衍射和透射电子显微镜的研究结果表明：当腔室压力为0.05 MPa时,Ce17Fe78B6合金中的硬磁相Ce2Fe14B的体积百分含量最高,而且晶粒细小且分布均匀,因而具有最佳的磁性能。     

Nd(FeTiNb)12N/α-Fe纳米复相永磁材料微观组织与磁性能

采用真空电弧熔炼和熔体快淬工艺分别制备了化学成分为Nd(FeTi)₁₂/ɑ-Fe与Nd(FeTiNb)₁₂/ɑ-Fe合金薄带,研究添加Nb元素以及不同氮化温度对合金微观组织和磁性能的影响。结果表明：Nb元素的添加可显著细化晶粒尺寸,同时提高了合金的非晶形成率。合金薄带经过晶化退火与渗氮处理后,磁性能有明显升高。Nd(FeTiNb)₁₂N/ɑ-Fe薄带的磁性能在渗氮温度为500 ℃时达到最佳,此时的剩磁(Br)和矫顽力(Hcj)分别为21.9 emu/g和700 Oe。     

腔室压力对快淬Ce_(17)Fe_(78)B_6合金磁性能及微观结构的影响

采用熔体快淬法制备了Ce_(17)Fe_(78)B_6合金,研究了不同腔室压力对其磁性能和微观结构的影响。结果表明:在熔体快淬过程中,不同的腔室压力对Ce_(17)Fe_(78)B_6合金的磁性能和微观结构有着很大的影响。随着腔室压力的增加,快淬条带的矫顽力逐渐增大,但是剩磁和最大磁能积却呈现先升高后下降的趋势。XRD和TEM的研究结果表明:当腔室压力为0.05MPa时,Ce_(17)Fe_(78)B_6合金中硬磁相Ce_2Fe_(14)B的体积分数最高,而且晶粒细小且分布均匀,因而具有最佳的磁性能。     

熔体温度对快淬法制备纳米晶复合Nd_(8.5)Fe_(77)Co_5Zr_3B_(6.5)合金微观结构和磁性能的影响

将Nd_(8.5)Fe_(77)Co_5Zr_3B_(6.5)(at%)合金熔化至不同温度后,以18 m/s的甩带速度快淬,对淬态条带进行了退火处理,分析了其微观结构和磁性能的变化。结果表明,熔体温度对淬态及其退火态合金的微观结构和磁性能可以产生重要影响,熔体温度为1210℃时制备的快淬条带由Nd_2Fe_(14)B相和部分非晶相组成,具有一定的硬磁性;随着快淬时熔体温度的升高,淬态条带中非晶相的质量分数逐渐增加,其磁性逐渐转变为软磁性。几种合金经退火处理后均由大量Nd_2Fe_(14)B相与少量软磁相组成,熔体温度较低的合金退火后其晶粒尺寸较小,磁性能较好。熔体温度为1210℃时制备的合金退火后磁性能最佳,内禀矫顽力Hci为559.2 kA/m,剩余磁化强度Br为0.98 T,最大磁能积(BH)_(max)为127.8 kJ/m~3。     

快淬速度对Nd2Fe14B/α-Fe纳米复合永磁材料结构和磁性能的影响

利用熔体快淬法制备了(Nd0.9Dy0.1)9(Fe0.9Co0.1)85.5B5.5快淬薄带,研究了快淬速度对晶化过程、晶化后薄带的结构及磁性能的影响.研究发现,快淬速度不同,薄带的非晶程度不同,晶化过程存在很大差异;在快淬速度为12m/s时,快淬薄带中已存在一定的晶态相,晶化后的晶粒细小均匀,磁性能较高;而当快淬速度达到18m/s和25m/s时,合金晶化后的晶粒粗大且不均匀,磁性能较低.     

Pd71.5Cu12Si16.5金属玻璃的氢相关性能

钯基金属玻璃在氢相关工业中具有潜在的应用价值。在本工作中,我们通过电弧熔炼、铜辊甩带的方法制备了Pd_71.5Cu₁₂Si_16.5 金属玻璃的宽带样品。通过常规X射线衍射仪和短波长X射线应力分析仪的X射线衍射谱确定了样品的完全非晶态结构。在室温、100kPa压力条件下,对样品进行了多次的吸、放氢循环实验。经过10次以上的循环后,样品没有发生破坏,表现出良好的抗氢脆性能。通过气体直接渗透的方法进一步测试了Pd_71.5Cu₁₂Si_16.5 金属玻璃及其同成分晶态合金的氢渗透性能。在金属玻璃的过冷液相区温度范围内,其氢渗透率明显高于晶态相,这一结果由金属玻璃在该区间内的等温保持引入了更多的自由体积进行解释。     

NdFe12永磁材料中的相转变研究

Nd-Fe系稀土过渡族化合物包含有很多种不同的类型,其中大部分化合物的结构可以在一定条件下相互转化。在稀土永磁材料制备过程中存在的各相之间的转变对永磁材料磁性能有很大的影响。然而之前的研究对Nd-Fe系化合物中相变过程的分析较少,本文制备了NdFe₁₂铸锭并使用EDS能谱分析了冷却过程中铸锭中的相变过程,同时使用熔体快淬法制备了前驱体的薄带,通过X射线衍射分析了薄带中相的组成。研究发现铸锭与薄带中的相组成均受冷却速度的影响。控制NdFe₁₂系化合物中相组成及相变过程对之后制备NdFe₁₂N_x低稀土新一代永磁材料具有很重要的意义。     

激光辅助热喷涂NiCoCrAlYTa/ZrO2/BaF2·CaF2涂层的组织及性能∗

高温耐磨涂层是航空发动机关键摩擦副可靠使用的重要保障,鉴于其服役环境日益严苛复杂,进一步提高涂层的高温耐磨性能是十分必要的。利用激光辅助热喷涂技术制备 NiCoCrAlYTa / ZrO₂ / BaF₂·CaF₂ 高温耐磨涂层,利用 SEM、EDS 分析高温耐磨涂层的横截面微观组织及化学成分,研究 ZrO₂ / BaF₂·CaF₂质量分数、激光功率及扫描速度对耐磨涂层微观组织、力学性能及高温耐磨性能的影响。结果表明：激光辅助处理可以诱导耐磨涂层表面形成具有树枝状结构的 ZrO₂陶瓷层; 当激光功率为 80 W,扫描速度为 8 mm / s,喷涂粉末为 75 wt.% NiCoCrAlYTa+25 wt.% ZrO₂ / BaF₂·CaF₂时,制备涂层的微观组织、综合力学性能及高温耐磨性能达到最好;在此工艺参数下,涂层顶部的 ZrO₂ 陶瓷层最为致密均匀,其平均纳米硬度为 13.6 GPa,平均弹性模量为 182.5 GPa,800 ℃时的磨损率为 2.7×10^?5 mm³ ·N^?1 ·m^?1 。将高温耐磨涂层的组分设计与激光辅助热喷涂工艺相结合,可为提高涂层综合性能的提供解决途径。     

Mn1-xZnxFe2O4 (0≤x≤1)纳米粉体的模板辅助溶胶凝胶法制备及其磁性能研究

通过模板辅助溶胶-凝胶法制备了一系列的Mn_1-xZn_xFe₂O₄(0≤x≤1,步长为0.2)纳米粉体。利用XRD和VSM对材料的物相和磁性能进行了表征,主要研究了Mn_1-xZn_xFe₂O₄分子式中Zn含量的变化对样品的微观结构和磁性能的影响。实验结果表明,具有不同Zn含量的Mn_1-xZn_xFe₂O₄样品均为尖晶石结构;随着Zn含量的增加,样品的晶面间距d、平均晶粒尺寸D、饱和磁化强度M_s和居里温度T_c都呈现出下降的趋势,而样品的矫顽力H_c则呈现出先升高后降低的趋势。分析认为,M_s的下降可以用Yafet-Kittel倾角理论解释,T_c的降低归因于晶格中反铁磁性耦合的降低,而H_c的变化则主要是由于材料的磁晶各向异性常数K₁的变化引起的。     

Microstructural characteristics of Nd2Fe14B/α-Fe nanocomposite ribbons bearing Nb element

The effects of Nb on the microstructure and magnetic properties of (Nd_0.9Dy_0.1)_9.5Fe_79-xCo₅Nb_xB_6.5 (x = 0, 1) nanocomposite magnets were investigated. A fine and uniform microstructure was achieved for the ribbons annealed at 710°C for 4 min, enhancing the interaction coupling between grains and improving the magnetic properties. The results of three-dimensional atom probe (3DAP) indicated that Fe-Nb-B intergranular phase existed at the grain boundaries, suppressing the grain growth during the crystallization process. The coercivity was improved from 224 to 643 kA/m for the modification of the microstructure.     

Phase formation, microstructure and magnetic properties investigation in Cu and Fe substituted SmCo5 melt-spun ribbons

Magnetic properties and microstructure were investigated in Sm_17.24Co_66.20Cu_8.28Fe_8.28 ribbons melt-spun at different wheel speeds of 5, 15, 30, 40 and 50 m/s. X-ray diffraction studies revealed that the ribbons melt-spun at lower wheel speed (<15 m/s) were comprised of three phases viz. SmCo₇, Sm₂Co₇ and SmCo₅, while higher wheel speed ribbons exhibited single phase SmCo₅. The coercivity was found to increase with increase of the wheel speed. A high coercivity of 33 kOe was obtained in ribbon prepared at 50 m/s.     

Nd60Fe30M10（M=Al，Si，Ga）系非晶永磁的性能与组织结构

采用真空快淬设备以辊速5m／s、10m／s、15m／s、20m／s、30m／s制备了Nd60Fe30M10（M=Al,Si,Ga）系的“非晶带”,研究了制备速度对“非晶带”永磁性能和结构的影响。实验结果表明：Nd60Fe30Si10和Nd60Fe30Ga10同经典合金Nd40Fe30Al10一样,也显示出非晶永磁性能,并且比相同条件下制备的Nd60Fe30Al10“非晶带”的永磁性能更好;三种“非晶带”的矫顽力随辊速的降低而提高。对Nd60Fe30Al10“非晶带”的TEM分析表明,以30m／s辊速制备的“非晶带”,有2～5nm的析出物弥散分布在非晶基体上;而以5m／s辊速制备的“非晶带”,有10nm左右和150-200nm的析出物分布在非晶基体上。析出物的生成,促进了矫顽力的提高。     

Planar Flow Casting of Fe71Si13.5B9Nb3Cu1Al1.5Ge1 Ribbons

In this study, the planar flow casting (PFC) technique for producing wide amorphous ribbons of Fe₇₁Si_13.5B₉Nb₃Cu₁Al_1.5Ge₁ alloy is investigated. Various ribbons of the mentioned alloy were produced through applying different values of wheel speed and ejection pressure. In addition, effects of wheel speed (13, 23, and 33 m/s) on the structure, degree of amorphicity, and surface quality of the ribbons were examined. The results showed that the trends of thickness variation with increasing wheel speed and ejection pressure for Fe₇₁Si_13.5B₉Nb₃Cu₁Al_1.5Ge₁ ribbons are in good agreement with what the Bernoulli equation in fluid dynamics predicts for the PFC process. Further, based on x-ray diffraction and differential scanning calorimeter results, it was shown that the degree of amorphicity increases by increasing the wheel speed. Besides, surface roughness measurements and scanning electron microscope micrographs of the ribbons revealed that the surface quality of the prepared ribbons improved by increasing the wheel speed.     

Effects of Cr on the early crystallization stages of Nd4.5Fe77-xCrxB18.5 amorphous ribbons

The effects of Cr on the early crystallization stages of Nd_4.5Fe_77-xCr_xB_18.5 amorphous ribbons were investigated. Nd_4.5Fe_77-xCr_xB_18.5 amorphous ribbons crystallize into (Fe·Cr)₃B (Fe₃B in Cr-free ribbon) initially and then Nd₂Fe₂₃B₃ forms. With increasing Cr content, the incubation period for the crystallization of (Fe·Cr)₃B and the time interval between (Fe·Cr)₃B and Nd₂Fe₂₃B₃ formation are shortened, and their decomposition is accelerated. (Fe·Cr)₂B, Nd₂Fe₁₄B and α-Fe form by the decomposition of (Fe·Cr)₃B and Nd₂Fe₂₃B₃. Thus, several reactions occur almost concurrently with the first reaction in the first exothermic peak of the ribbons with Cr above 3 at.%. Cr has been known to stabilize the (Fe·Cr)₃B and suppress the formation of Nd₂Fe₂₃B₃. However, the present result implies that Cr promotes both the formation and the decomposition of (Fe·Cr)₃B and Nd₂Fe₂₃B₃. Cr has no affect on the crystallization sequence itself but on the kinetics. Therefore, the crystallization sequence of Nd_4.5Fe_77-xCr_xB_18.5 amorphous ribbons is almost the same as those of Cr-free alloys, i.e., amorphous (Am)→Am+(Fe·Cr)₃B (Fe₃B in Cr-free ribbon)→Am+(Fe·Cr)₃B+Nd₂Fe₂₃B₃→(Fe·Cr)₃B+Nd₂Fe₂₃B₃→Nd₂Fe₁₄B+(Fe·Cr)₂B+α-Fe→ NdFe₄B₄+(Fe·Cr)₂B+α-Fe. The ambiguities for the early crystallization stages of high Cr ribbons arise from the fact that most of the studies so far have examined the ribbons annealed above the 60 sec where (Fe·Cr)₂B, Nd₂Fe₁₄B and α-Fe are detected in the 20 at.% Cr ribbons by the X-ray diffraction pattern.     

Structure and magnetic characterization of amorphous and crystalline Nd–Fe–Al alloys

Glass formation has been studied in Nd₆₀Fe₃₀Al₁₀ alloy produced by melt-spinning, water quenching and copper mold chill casting. Partially amorphous alloys were obtained by melt-spinning at low wheel speeds of 5 to 15 m/s and by water quenching of a 1-mm diameter rod, while fully amorphous alloys were obtained by melt-spinning at higher wheel speeds of 20 and 30 m/s and chill casting of a 1-mm diameter rod. A high coercivity was observed in the partially amorphous ribbon melt-spun at 5 m/s and water quenched rod, and in the fully amorphous chill cast rod, while low values of coercivity were obtained in fully amorphous ribbons melt-spun at high speeds of 20 and 30 m/s. Crystallization of water quenched and chill cast samples after heat treatment at high temperature resulted in a substantial reduction of the high coercivity. Results of X-ray diffraction indicate that formation of Nd and a ternary Fe–Nd–Al phase with an unknown crystal structure were present after crystallization. TEM results and a magnetic study of the heat treated samples indicate that as long as there is an amorphous phase produced by low cooling rate, the high coercivity remains. The high coercivity of bulk amorphous samples is discussed. The unknown ternary Fe–Nd–Al phase is antiferromagnetic with a Neel temperature at about 260 K.     

Nd9.5Fe81Zr3B6.5纳米复相永磁材料的物相演变及磁性能

利用单辊快淬法制备Nd9.5Fe81Zr3B6.5合金条带,采用X射线衍射、差式扫描热分析、透射电子显微分析和振动磁强计等分析测试手段,对合金条带的物相演变和磁性能进行研究。结果表明：在不同快淬速度的条件下,合金条带的微观组织结构不同;在热处理过程中,合金的晶化过程分两步完成：α-Fe 首先析出,Nd2Fe14B 随后析出。随着快淬速度的增大,最佳热处理后合金的晶粒变粗,这使得软磁相和硬磁相之间的交换耦合作用减弱,进而导致合金磁性能的降低。     

快速凝固法制备Mg-Al-Ca合金薄带

通过单辊快淬法制备了Mg-8.2Al-4.7Ca合金薄带,采用XRF、XRD、金相显微分析、显微硬度测量等分析方法研究了其凝固组织及相结构,以及转速对镁合金条带厚度和显微硬度的影响。研究结果表明,急冷快速凝固条件下,合金形成非晶相 细小hcp-Mg(Al,Ca)相;镁合金薄带显微组织沿厚度方向分为近辊面细晶区、内部柱状晶和自由面粗晶区;随着辊速的提高,晶粒不断细化,薄带的硬度不断提高。晶粒细化是显微硬度提高的主要原因。     

Characterization of nanostructured Nd–Fe–Al permanent magnets

Rapidly solidified Nd₆₀Fe₃₀Al₁₀ alloys produced in the form or ribbons or 1 and 5 mm diameter rods were examined using transmission electron microscopy (TEM), XRD, magnetic measurements, and Mössbauer spectroscopy. Strong dependence of the structure and magnetic properties on cooling rate was proved. The present work concerns the microstructure on the nanometric level (HRTEM) of the Nd₆₀Fe₃₀Al₁₀ alloy.The specimens were in a form of 1 and 5 mm diameter rods and a rapidly solidified ribbons, prepared at a roll speed of 30 m/s. The high-resolution images shown large regions where the crystalline phase is present. The size of the crystallites depends on the quenching rate, which also influences the composition of the amorphous phase. In both, ribbon and rod samples, well defined boundaries of nanoscale grains of similar crystallographic orientations were observed. Basing on the observations in the dark field, we can say that the precipitates often form agglomerates whose components maintain the same crystallographic orientations. The studies revealed that the crystalline grains are frequently separated by a narrow layer of an intermediate phase.The EDS examinations reveal that the individual crystallites differ in their chemical composition, but in all nano-regions examined, all the components of the alloy occur simultaneously, in the proportions varying around the average composition of the alloy.