粉末冶金法制备La(Fe,Co,Si)_(13)磁制冷合金

La(Fe,Co,Si)_(13) Magnetic Refrigerant Alloy Prepared by Powder Metallurgy

用非自耗电弧炉熔炼制备了LaFe10.8Co0.7Si1.5C0.2铸锭,并将该铸锭在石油醚的保护中球磨制粉,粉末经过压制后在氩气气氛中高温烧结2～8 h。用XRD和SEM检测了LaFe10.8Co0.7Si1.5C0.2铸锭及烧结后样品的相和组织结构。结果表明,LaFe10.8Co0.7Si1.5C0.2合金铸锭主要由α-Fe(Co,Si)相和1∶1∶1相组成,仅含有极少量1∶13相。采用粉末冶金法制备的合金相比传统工艺下合金的成相时间有明显缩短,仅烧结2 h就有一定比例的NaZn13型1∶13相生成,而且在1100℃烧结4 h时合金的成相最好,形成了以1∶13相为主相的合金,温度过高或过低所形成的1∶13相的相对含量都会减少。烧结时间增加或缩短也会导致1∶13相的相对含量减少。此外,还对在LaFe10.8Co0.7Si1.5C0.2粉末中加入LaFe0.9Co0.27Si1.17作为烧结助剂对合金成相的影响进行了研究。结果表明,加入烧结助剂后有助于合金的成相,加入质量分数为25%的LaFe0.9Co0.27Si1.17作为烧结助剂在1100℃烧结4 h所形成的合金几乎是单一的1∶13相,仅含极少量点状分布的富含镧的杂相。而LaFe10.8Co0.7Si1.5C0.2块状铸锭在1100℃退火4 h后仍含有α-Fe相和1∶1∶1相。可以看出,用粉末冶金法制备La(Fe,Co,Si)13磁制冷合金的热处理时间得到极大缩短。

LaFe10.8Co0.7Si1.5C0.2 as-cast was prepared by arc melting furnace in argon atmosphere.The alloy powder was prepared from the as-cast using mechanical method in petroleum ether.The compacted green parts were sintered at high temperatures for 2~8 h under argon gas.The microstructure and composition were characterized by X-ray diffraction（XRD） with Cu Kα radiation and scanning electron microscope（SEM） with EDS attached.The results showed that LaFe10.8Co0.7Si1.5C0.2 as-cast mainly composed of α-Fe（Co,Si） phase and 1∶ 1∶ 1 phase in addition to very few 1∶ 13 phase.1∶ 13 phase was formed as the matrix phase when sintered at 1100 ℃ for 4 h.The content of 1∶ 13 phase would decrease if the sintering temperature was too high or too low and the sintering time was too long or too short.In addition,the phase formation of LaFe10.8Co0.7Si1.5C0.2 powder added with LaFe0.9Co0.27Si1.17 as sintering aid was investigated.A nearly single 1∶ 13 phase was obtained when LaFe10.8Co0.7Si1.5C0.2 powder added with 25% LaFe0.9Co0.27Si1.17 as sintering aid sintered at 1100 ℃ for 4 h,and very few La-rich impurity phase was present.Meanwhile,when bulk LaFe10.8Co0.7Si1.5C0.2 as-cast was annealed at 1100 ℃ for 4 h,α-Fe phase and 1∶ 1∶ 1 phase still existed.The results indicated that the heat treatment time for alloys prepared by powder metallurgy was significantly shortened.