Nd-Fe-B包晶合金高梯度定向凝固试验研究

Directional Solidification of Nd-Fe-B Alloys with High Temperature Gradient

在定向凝固试验中,采用全熔和区熔两种加热方式分别获得了180K/cm和250～360K/cm的温度梯度,在5～500μm/s的抽拉速率范围内对过包晶Nd13.5Fe79.75B6.75合金进行了定向凝固试验,考察了温度梯度和抽拉速率对此合金凝固组织及相含量的影响。结果表明,合金的凝固组织包含初生α-Fe枝晶、包晶Nd2Fe14B相及少量的富Nd相。随着抽拉速率的增加,包晶相含量先增加后减少;而在同一抽拉速率下,提高温度梯度可增加铁磁性Nd2Fe14B相的含量。当抽拉速率为50μm/s时,区熔试样中(G=300K/cm)Nd2Fe14B相的含量可达约90%,而相同速率下全熔试样(G=180K/cm)中其含量约为60%。

Directional solidification experiments were performed on peritectic Nd13.5 Fe79.75 B6.75 alloy with temperature gradient of 180 K/cm and 250-360 K/cm obtained from total melting and zone melting,respectively,at pulling velocity ranging from 5 to 500μm/s to investigate the effects on microstructure and phase constituent in the alloy.The results indicate that the microstructure of the alloy is composed of primary α-Fe dendrites,peritectic Nd2Fe14B phase and minor Nd-rich phase.The volumetric fraction of ferromagnetic Nd2Fe14B phase is firstly increased and then decreased with rising the pulling velocity,and is improved with increasing temperature gradient.Grown at 50μm/s,the volumetric fraction of ferromagnetic Nd2Fe14 B phase reaches up to 90% in the zone melting specimens(given a temperature gradient at 300 K/cm),which is about 30% higher than that in the total melting specimens(given a temperature gradient at 180 K/cm).