Journal of Materials Science, Vol.56, No.3, 2572-2583, 2021
Effects of annealing temperature and heating rate on microstructure, magnetic, and mechanical properties of high-B(s)Fe(81.7-x)Si(4)B(13)Nb(x)Cu(1.3)nanocrystalline alloys
The effects of annealing temperature and heating rate on the microstructure, magnetic, and mechanical properties of melt-spun Fe81.7-xSi4B13Cu1.3Nbx(x = 0-4) alloy ribbons have been investigated. With increasing the annealing temperature, a ductile-brittle transition occurs during amorphous structure relaxation, the brittleness becomes severe with more alpha-Fe precipitation, and the hardness rises continuously. After annealing at respective optimum temperatures under the heating rate of 20 K/min, as the Nb content increases from 0 to 4 at.%, average grain size (D alpha-Fe) and volume fraction (V alpha-Fe) of the alpha-Fe in the nanocrystalline alloys decrease gradually from 53.3 nm and 52% to 8.7 nm and 42%, respectively; the strain at fracture (epsilon(f)) representing ductile level increases from 1.33 to 1.72%; and the coercivity (H-c), saturation magnetic flux densities (B-s), and Vickers hardness (H-v) all decrease gradually. As the heating rate rises from 10 to 400 K/min, theD(alpha-Fe)of the Fe(81.7)Si(4)B(13)Cu(1.3)alloy decreases from 45.7 to 28.4 nm without considerable variation of theV(alpha-Fe); theH(c)lowers from 235 to 25 A/m, the epsilon(f)increases from 1.10 to 1.66%, and theB(s)andH(v)change slightly. Enriching of Nb weakens the dependence of nanostructure, magnetic softness, and annealing embrittlement on the heating rate. A correlation of epsilon(f) proportional to D(alpha-Fe)(n)is found for the nanocrystalline alloys, where thenrises from - 1 to - 1/2 with enriching of Nb from 0 to 4 at.%. The mechanisms by which nanostructure affects magnetic and mechanical properties have been discussed.