粉末烧结钕铁硼激光熔凝过渡区组织的研究  

Microstructures in Transition Zone of a Laser Remelting/Solidificaiton Pool of Sintered Nd-Fe-B Magnets

作　　者：潘晶[1] 刘新才[1] 

机构地区：[1]宁波大学工程力学与材料科学系

出　　处：《中国稀土学报》2004年第2期219-224,共6页Journal of the Chinese Society of Rare Earths

基　　金：浙江省自然科学基金(502166);江西省跨世纪学术带头人项目(CA99110901);宁波大学项目(471089和471079)资助

摘　　要：对粉末烧结Nd15Fe77B8永磁体表面激光熔凝池中过渡区的组织进行了研究。结果表明,过渡区由初生相α Fe和富Nd的Nd2Fe14B两相组成。离激光熔凝池与基体的分界面越远,α Fe二次枝晶间距越小,而Nd2Fe14B以胞状液固界面向上推进的速度逐步加快,最后越过了先析出的α Fe,导致在过渡区结束时α Fe相不再出现。当粉末烧结Nd15Fe77B8磁体易磁化轴的取向为z轴时,过渡区的α Fe体积百分数最大;Nd2Fe14B以与z轴夹角30°～50°的方向生长,直到进入胞状区,其生长方向才逐步调整到与z轴基本平行。当磁体易磁化轴取向为随机分布时,过渡区α Fe的体积分数最小;过渡区Nd2Fe14B选择在基体内易磁化轴在XOY面内的等轴晶Nd2Fe14B上生长。当磁体的易磁化轴取向分别为x或y轴时,过渡区Nd2Fe14B直接在基体的Nd2Fe14B上生长,并在过渡区结束前后,1个过渡区Nd2Fe14B上平均分化出3个胞状区Nd2Fe14B柱状晶。The effects of different arrangements of the easy magnetization axis of whole magnets on the microstructures in the transition zone of the melting/solidification pool of the surface of Nd_(15)Fe_(77)B_8 magnets were studied. Four kinds of magnets were used, including that the easy magnetization axis originally distributed randomly and parallel to x, y, z-axis respectively. The laser scanning is along y-axis, in XOY plane. The results show that there are two kinds of phases in the transition zone, primary α-Fe and Nd_2Fe_(14)B, which is richer in Neodymium than the stoichiometric compositions of Nd_2Fe_(14)B. Why α-Fe occurs at the zone is that the crystal growth velocity of Nd_2Fe_(14)B at the bottom of the pool is very low and the temperature gradient at the liquid/solid surface is very high (～10~4 K·cm^(-1)). The farther the distance to the interfacing between matrix and pool, the thinner the second arm spacing of α-Fe dendrites, and the greater the crystal growth velocity of Nd_2Fe_(14)B pushes upward in the way of the cellular liquid/solid surface. So cellular Nd_2Fe_(14)B finally occupies the whole liquid/solid surface, and α-Fe is outflanked by Nd_2Fe_(14)B. So α-Fe does not appear at both the cellular column zone and the cellular dendrite zone in the pool. If the easy magnetization axis of the sintered Nd_(15)Fe_(77)B_8 magnets is originally parallel to z-axis, the volume fraction of the α-Fe is highest in the transition zone of the melting/solidification pool of the four kinds of magnets. And the angle between the (Nd_2Fe_(14)B) columns in the transition zone and the z-axis is 30°～50°. Till entering the cellular column zone, the grain boundary of the cellular Nd_2Fe_(14)B is not approximately parallel to the z-axis. If the easy magnetization axis of the magnets is originally parallel to x or y-axis respectively, Nd_2Fe_(14)B in the transition zone directly grows on the Nd_2Fe_(14)B equal-axis grains in the matrix. Within the boundary area between the transition zone and cellular columns zon

关 键 词：金属材料 激光表面熔凝 过渡区 ND2FE14B a-Fe 易磁化轴 稀土 

分 类 号：TM273[一般工业技术—材料科学与工程]