粉末冶金法制备La(Fe_(11.05)Co_(0.85)Si_(1.1))B_(0.25)化合物的磁热效应

Magnetocaloric Effect of La(Fe_(11.05)Co_(0.85)Si_(1.1))B_(0.25) Compounds Prepared by Powder Metallurgy Method

用非自耗电弧炉熔炼制备了La（Fe11.05Co0.85S i1.1）B0.25铸锭,并将该铸锭在氩气保护中球磨制粉,采用SPS（放电等离子烧结技术Spark P lasma S intering）将该粉制成La（Fe11.05Co0.85S i1.1）B0.25合金,在高温（1070℃）下对其进行20 h热处理;空冷之后用XRD及SEM检测了铸锭热处理样品、SPS烧结样品及SPS热处理后样品的相及组织结构,利用VSM和磁热效应直接测量仪测量了这3种状态下合金的等温磁熵变和绝热温变。结果表明,铸锭合金的基相组织结构中晶粒大小规则较均匀,晶界清晰明显,在0~1.5 T的变化磁场下测得其等温磁熵变达到-5.22.J（k.gK）-1,绝热温变也达到2.3 K,而采用SPS技术制得的样品的基相组织结构中没有明显晶界且夹杂较多,其等温磁熵变为-3.90.J（k.gK）-1,绝热温变为1.9 K（0~1.5 T）;经过热处理的SPS样品基相组织结构中,有少量晶界形成,但晶粒大小不规则,测得其等温磁熵变为-3.72.J（k.gK）-1,绝热温变为1.5 K（0~1.5 T）;与铸锭相比较,SPS技术制得的合金样品和经过高温热处理之后的SPS样品的绝热温变值和等温熵磁变值均降低,同比之下这两种样品较铸锭样品的居里点和半峰宽却发生了改变,均显著提高;可以看出采用SPS技术制备的室温磁制冷材料La（Fe11.05Co0.85S i1.1）B0.25能够在较宽的温度范围内制冷,但其磁热效应却相对降低。

La（Fe11.05Co0.85Si1.1）B0.25 as-cast was prepared by arc melting furnace in argon atmosphere.The alloy powder was prepared from the as-cast using mechanical method in argon atmosphere.The alloy bulk prepared from the alloy powder using spark plasma sintering method was heat-treated at 1343 K for 20 h and was cooled in air.The samples of the three different types（the as-cast alloy,the alloy prepared using SPS and SPS alloy after heat treatment） were investigated by means of XRD and SEM analysis apparatus.And the magnetocaloric effect（MCE） of the different samples were measured with the MCE direct measurement device and VSM equipment.The results showed that： The grain size of as-cast sample was symmetrical and the crystal boundary was obvious,the isothermal entropy change and the adiabatic temperature change of as-cast sample under a magnetic field change from 0 to 1.5 T was-5.22 J ·（kg · K）-1 and 2.3 K respectively.But the crystal boundary of SPS sample was not obvious and lots of impurities were found in its microstructure,the adiabatic temperature change and the isothermal entropy change of SPS sample under a magnetic field change from 0 to 1.5 T was-3.90 J ·（kg · K）-1 and 1.9 K respectively.The grain size of SPS sample after heat treatment was asymmetrical and few crystal boundary was obvious,the adiabatic temperature change and the isothermal entropy change of SPS sample after heat treatment under a magnetic field change from 0 to 1.5 T was-3.72 J ·（kg · K）-1 and 1.5 K respectively;Compared to as-cast sample,the adiabatic temperature change and the isothermal entropy change the samples prepared by SPS technology（whatever heat treatment was carried out） was decreased and its Curie temperature Tc and its value of peak breadth is increased.The results indicated that the La（Fe11.05Co0.85Si1.1）B0.25 MCE material prepared by SPS technology could be applied under a wide temperature range,but its MCE relatively decreased.