Cobalt-rich ductile permanent magnet alloys with molybdenum additions
- PDF / 294,642 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 242 Views
W } R E S of permanent m a g n e t alloys with low s t r e s s sensitivity have become interesting for a n u m b e r of switching and m e m o r y applications in the electronic industry. The requirements for c o e r c i v e f o r c e and energy product are moderate, about Hc = 10 to 100 oe and (B × H)max = 200,000 to 400,000 G - o e , resulting in the designation of " s e m i h a r d " for t h e s e alloys. However, a square hysteresis loop ( B r / B s > 0.90) is desirable. Ductile permanent m a g n e t alloys have been known for a long t i m e , produced e . g . on the b a s i s of C o - F e - V , with a C o : F e ratio of about 1:1 and a vana d i u m content of 5 to I0 pct (Vicalloy). I The 50 pct Fe content results in high values for saturation and residual induction, but also in large magnetostriction, and, therefore, high sensitivity to stresses. Since the magnetostriction of Co-Fe alloys goes through zero at about 15 pct Fe,2 an 85 pct Co-15 pct Fe composition is desirable for these newer electronic applications. The permanent magnet properties are obtained by precipitation of intermetallie phases. (Au,3 Be,4 Nb, s and Ti6 compounds with cobalt and iron, or related phases.) All these alloys require over 90 pct cold reduction and subsequent heat treating at 600° to 800°C for the development of the best permanent magnet properties. Molybdenum forms an intermetallic compound with cobalt which is similar to, though not isomorphous with, that of titanium.7 Its solubility in fcc cobalt at 600° to 800°C is much larger than that of titanium (15 wt pct against 4 wt pct), but little of either element remains dissolved at low temperatures. This should hold true also for the ternary system, analogous to Co-Fe-V.s Therefore, a larger amount of precipitate should form in molybdenum-containing alloys during heat-treatment, and a higher coercive force should be obtained. This was proven correct by this study, which was performed to develop wires with Hc close to 100 oe. The depletion of the matrix in cobalt by the precipitation of the intermetallic compound was expectedto be lower for molybdenum-containing alloys than for those with titanium, if compared for the same coercive force, resulting in higher B r values. Simultaneous precipitaROBERT STEINITZ is Research Metallurgist, Research Department, Wilbur B. Driver Co., a subsidiary of GTE Sylvania, Inc., Newark, N.J. Manuscript submittedMay 18, 1971. METALLURGICAL TRANSACTIONS
tion of titanium and molybdenum compounds was also investigated. EXPERIMENTAL The desired compositions were prepared from electrolytic cobalt, A r m c o iron, molybdenum-powder pellets, and titanium-sponge. About 5 lb. were melted in magnesia crucibles under a cover of 90/10 N2/H2, and cast into graphite molds. The protective cover proved to be quite effective, since the oxygen content even of the alloys containing titanium was less than 500 p p m (TiO2 < 0.15 pct). The alloys were chemically analyzed, and the composition was always found to be very close to the intended one. The cast rods (about ~-in.
Data Loading...
