SYNTHESIS AND PROPERTIES OF A MAGNETICALLY HARD SM5(FE,CO,TI)17 PHASEIN SINTERED MAGNETS

Magnetically hard Sm5(Fe,Co,Ti) 17 phases have been synthesized by the conventional powder metallurgical method. A representative magnet of composition Sm5(Fe0.94Ti0.06)17 shows a room-temperature coercivity, ( i)H(c), approximately 21.5 kOe, remanence, B(r), approximately 3.5 kG, and Curie temperature, T(c) approximately 300-degrees-C. The main pha se of the magnets has the hexagonal Nd5Fe17 Structure with a=20.146 an gstrom, c=12.310 angstrom. The magnets contained minor amounts Of Sm2( Fe,Ti)17 and Sm(Fe,Ti)3, as detected by thermomagnetic analyses (TMA). When Fe is partially substituted by Co, T(c) increases, by approximat ely 40-degrees-C for the magnet of composition SM5(Fe0.74Co0.20Ti0.06) 17. ThiS magnet exhibits (i)H(c) approximately 4.0 kOe and B(r) approx imately 3.4 kG at room temperature. It consists of 2:17,5:17, and 1:2 phases. The effects of heat treatment procedure on the phase formation and magnetic properties of the magnets have been studied. The best si ntering temperature for forming the 5:17 phase, as well as for develop ing the highest (i)H(c), is approximately 700-850-degrees-C. Above 850 -1000-degrees-C the 2:17 and 1:2 or 1:3 phases become dominant, the 5: 17 hard phase almost disappears, and the coercivity of the magnets dec reases substantially.