Effect Of Heat-Treatment On Damping Capacity Of FE-CR-MO Alloys

In the present paper, the magneto-mechanical damping and magnetostrictive properties of Fe-16%Cr (wt.%) alloys containing from2.5to3.5%Mo were investigated after different annealing heat-treatments. The effects of microstructures and magnetic properties on magneto-mechanical damping capacity were analyzed. The relationship between magneto-mechanical damping and magnetostriction was explained in detail.The cantilever beam device was used to test the damping capacity of the alloys after different annealing heat-treatments. The results indicate that the annealing treatment enhances the damping capacity, but further annealing treatment decreases it drastically. As the annealing temperature rises from800℃to1100℃, the damping capacity of Fe-Cr-Mo alloys reaches a peak at900℃. As to Fe-16Cr-2.5Mo alloy, the highest damping value of0.062(η) is obtained at900℃for one hour followed by air cooling. Besides, the annealing time also affects the damping capacity of Fe-Cr-Mo alloys obviously. When annealed from1to4hours at900℃by air cooling, the damping capacity of Fe-Cr-Mo alloys drops gradually.A water-based magnetic fluid was used to observe the magnetic domain structure using an optical microscope. It is found that the domains arrange themselves orderly as the annealing temperature rises. There are many finer and dispersed90°domains in the alloys annealed at900℃. Wider domains and some wedge-shaped domains appear at higher annealing temperatures. Annealing time affects the domain morphology dramatically. When the alloys are annealed from1to4hours at900℃by air cooling, some wedge-shaped domains and many spike domains appear as the annealing time increases.The magnetostriction coefficient values of annealed Fe-Cr-Mo alloys were measured by an improved Michelson interferometer. The experimental results show that when the annealing temperature is900℃, the saturation magnetostriction coefficient of the alloys reaches a maximum value which is about43.2ppm for the Fe-16Cr-2.5Mo alloy. However, the coefficient drops with the annealing time from1to4hours at900℃.It is found that the variation of saturation magnetostriction coefficient λs is in agreement with that of the loss factor η. The loss factor η increases with the increase of the saturation magnetostriction coefficient As and there is a liner relationship between them. From the point of view, the saturation magnetostrictiingon coefficient λs reflects the nature of the magneto-mechanical effect.