Processing effects on the magnetostrictive and physical properties of SmFe2/metal composites

Hot pressed SmFe2/Fe and SmFe2/Al composites combine the large magnetostric tion of SmFe2 with the mechanical robustness of the Fe or Al matrix. Here w e report the dependence of the magnetostriction, density, and mechanical ha rdness on processing parameters, specifically on the SmFe2 volume fill frac tion and the consolidation temperature. The magnetostriction increases mono tonically with increasing SmFe2 content, but both the density and hardness decrease; low fill fraction composites are within 10% of theoretical densit y and have hardnesses of 40-85 Rockwell B, whereas hot pressed SmFe2 powder alone has high porosity (exceeding 30%) and is too soft to register on the Rockwell B hardness scale. The best combination of properties lies in the range of 40%-60% SmFe2. Similar competition between magnetostriction and ph ysical properties is observed as a function of the temperature used to cons olidate the samples. The magnetostriction falls slowly as the hot press tem perature increases, probably as a result of chemical reaction between the S mFe2 phase and the matrix metal. On the other hand, higher temperature impr oves the consolidation, resulting in higher density and hardness. These res ults demonstrate that the magnetostrictive and physical properties of SmFe2 composites can be tailored by adjusting the fill fraction and processing t emperature. (C) 1998 American Institute of Physics. [S0021-8979(98)34311-X] .