Permanent magnet materials based on iron-rare earth-carbon and iron-titanium-rare earth alloys.

摘要

To develop two prospective alloy systems Fe-R-C and Fe-Ti-R for new permanent magnet materials, the evolvement of hard magnetic phases, i.e., Fe{dollar}sb{lcub}14{rcub}{dollar}R{dollar}sb2{dollar}C and (Fe,Ti){dollar}sb{lcub}12{rcub}{dollar}R, the effect of alloying and heat treatment on the magnetic properties were investigated. The high intrinsic coercivity often exceeding 15 kOe in the Fe-Dy-C ingots is attributed to both find cells ({dollar}<{dollar}10 {dollar}mu{dollar}m) of Fe{dollar}sb{lcub}14{rcub}{dollar}Dy{dollar}sb2{dollar}C transformed in the temperature range of 850{dollar}spcirc{dollar}C to below 1200{dollar}spcirc{dollar}C and a negligible amount of grain boundary phase. The thin grain boundary phase at which the domain walls are trapped (or pinned) has a composition near that of the Fe{dollar}sb{lcub}14{rcub}{dollar}Dy{dollar}sb2{dollar}C phase, but its structure is not that of a recognized binary Fe-Dy or ternary Fe-Dy-C compound.; The extremely retarded formation of Fe{dollar}sb{lcub}14{rcub}{dollar}Nd{dollar}sb2{dollar}C in Fe-Nd-C alloys is due to the difficulties in nucleation, and Fe{dollar}sb{lcub}14{rcub}{dollar}Nd{dollar}sb2{dollar}C is much less stable than Fe{dollar}sb{lcub}14{rcub}{dollar}Dy{dollar}sb2{dollar}C so that it forms only in the narrow temperature range between 800{dollar}spcirc{dollar}C and 900{dollar}spcirc{dollar}C. However, small additions of B, Cu, or both, into the Fe-Nd (or Pr)-C alloys promote the formation of Fe{dollar}sb{lcub}14{rcub}{dollar}Nd{dollar}sb2{dollar}C (or Fe{dollar}sb{lcub}14{rcub}{dollar}Pr{dollar}sb2{dollar}C). By these additions the production of practical quantities of magnetically hard Fe{dollar}sb{lcub}14{rcub}{dollar}Nd{dollar}sb2{dollar}C (or Fe{dollar}sb{lcub}14{rcub}{dollar}Pr{dollar}sb2{dollar}C) has become feasible, although the coercivities are in the low-kOe range mainly due to the different nature of grain boundary phase from the of Fe-Dy-C alloys.; The tetragonal (Fe,Ti){dollar}sb{lcub}12{rcub}{dollar}R compounds are crystallized from the melt via peritectic reaction. The extension of the primary Fe field in Fe-Ti-R is as same as that in Fe-R-C, i.e., it increases in the direction Dy {dollar}to{dollar} Ce. In Fe-Ti-Nd and Fe-Ti-Sm, the Ti-stabilized Fe{dollar}sb7{dollar}R phase (hexagonal Cu{dollar}sb7{dollar}Tb type) is newly observed. The phase Fe{dollar}sb{lcub}11{rcub}{dollar}TiR in these systems either is stoichiometric or has a negligible homogeneity range. In Fe-Ti-Nd Fe{dollar}sb{lcub}11{rcub}{dollar}TiNd is stable only above 1000{dollar}spcirc{dollar}C. Below 1000{dollar}spcirc{dollar}C, it decomposes according to Fe{dollar}sb{lcub}11{rcub}{dollar}TiNd {dollar}to{dollar} Fe{dollar}sb{lcub}17{rcub}{dollar}Nd{dollar}sb2{dollar} + Fe{dollar}sb2{dollar}Ti + Fe. In Fe-Ti-Sm the high-anisotropy phase Fe{dollar}sb{lcub}11{rcub}{dollar}TiSm does not undergo this decomposition down to 700{dollar}spcirc{dollar}C, but it is cut off from higher Sm alloys by the tie line between Fe{dollar}sb{lcub}17{rcub}{dollar}Sm{dollar}sb2{dollar} and Fe{dollar}sb2{dollar}Ti. A new phase Fe{dollar}sb{lcub}9.5{rcub}{dollar}Ti{dollar}sb{lcub}1.5{rcub}{dollar}Sm has the structure of tetragonal (Mn,Ni){dollar}sb{lcub}11{rcub}{dollar}Ce with a = 0.8253, c = 0.4825 nm; it has no permanent magnetic moment at room temperature.