Bulk glass forming and thermal stability in Fe_(67.0)Co_(9.5)Nd_(3.0)Dy_(0.5)B_(20) alloy

摘要

Bulk glass forming ability (GFA) of a multicomponent alloy of Fe_(67.0)Co_(9.5)Nd_(3.0)Dy_(0.5)B_(20), is studied by synthesizing it in shapes of thin ribbons, rods or cylinders, or pellets. The three samples are obtained with three different methods of melt spinning, copper mold casting, or mechanical attrition (of ribbons) followed by a hot compaction of derived alloy powder, respectively. A melt-spun ribbon of 50- to 100-pm thickness has a truly amorphous structure with two X-ray diffraction halos of wavevectors q_1 = 14.2 and q_3 =33.0 mn~(-1). A modified diffractogram consists of two halos q_1 = 14.5 and q_2 = 19.0 nm~(-1) in the rods(3.0-mm diameter)while of three halos q_1 = 13 .4, q_2 = 15.0 and q_3 = 24.0 q_3=24.0 nm~(-1) in the pellets (5- to 10-mm diameter and 3-to 5-nm thickness). A small value of coercivity H_c of 7.1 kA/m in the rods or almost zero in the ribbons reveals soft magnetic behaviors characteristic of an amorphous structure of the alloy. An improved value of H_c= 188.5 kA/m develops in the hot compressed pellets of the powder at approx 630 deg C temperature. The pellets have some recrystallized alpha-Fe, Fe_3B and R_2Fe_(14)B (R=Nd or Dy) nanocrystallites in a bulk amorphous composite structure. The results are analyzed with thermal analysis and microstructures of the samples.