Influence of grain size on precipitation hardening in melt-spun Sm(Co, Fe, Cu, Zr)$_{\mathrm{z}}$ alloys*

In this work, we have investigated the influence of grain size on precipitation hardening that takes place in 2:17 Sm-Co magnets. An alloy with a nominal composition of Sm(Co$_{0.72}$Fe$_{0.12}$Cu$_{0.13}$Zr$_{0.03})_{7.6}$ was prepared by arc-melting and subsequently melt-spinning. The grain size was controlled by varying the wheel speed from 5 m/s to 50 m/s. The melt-spun ribbons were subsequently isothermally aged at 850 $^{\circ}$C for 3 h followed by slow cooling at 0.7 K/min to 400 $^{\circ}$C. A single 1:7 phase was detected in the as-spun ribbons and the grain size of ribbons estimated by Scherrer's formula was found to decrease gradually with the increasing of the wheel speed from 5 m/s to 50 m/s. After aging, the 1:7 phase was decomposed into Sm$_{2}$(Co,Fe)$_{17}$ and Sm(Co,Cu)$_{5}$ phase. For the 5 m/s ribbon, the coercivity increased drastically form 0.8 kOe to 11.2 kOe. On the other hand, the coercivity of the 35 m/s ribbon showed a little increase from 4.7 kOe to 6.3 kOe. TEM studies are currently under way to study the microstructure as a function of grain size and the results will be reported.