Effect Of Heat Treatment And Al Addition On The Microstructure And Properties Of TbDyFe Alloy

In the thesis , <110> oriented rods of TbDyFe giant magnetostrictive alloy have been prepared by zone melting directional solidification method. The effect of heat treatment and the effect of Al addition on the preferred orientation, microstructure, magnetostriction and mechanical properties of TbDyFe has been studied, the optimal heat treatment process and the optimal addition of Al content is selected for the alloy maintain high magnetostriction and has well mechanical properties.<110> oriented rods of TbDyFe alloy are heat-treated at different temperature for 2 h and 4h.It is show by the result that the axially preferred orientation of TbDyFe alloy remains unchanged after annealing. Annealing for 2 h, the net-shaped rare earth phase becomes discontinued and spheroidal, when the heat treatment temperature reach the 1000°C, the matrix lamellar microstructure are degradation; After 4 h heat treatment, the net-shaped rare earth phase changes obviously, the matrix lamellar microstructure are all degradation. The magnetostriction is improved the extent of 300×10-6 or so. Its mechanical properties is obviously improved, compressive strength become 256 MPa.The comprehensive performance of TbDyFe giant-magnetostrictive alloy is the best when it is heat-treated at temperature 930°C for 2 h and followed the furnace cooling.A small amount of Al are added in the TbDyFe alloy, the composition of the alloy is Tb0.3Dy0.7(Fe1-xAlx)2(x=0.05,0.10,0.15). Results show that the axially preferred orientation remains unchanged after a small amount of Al are added in the alloy. Some impurity phase are present after adding Al, with the increase of Al content, precipitation phase increases. The magnetostriction is improved by adding trace elements Al at the low magnetic field. At the high magnetic field, the magnetostriction increase, when the substitution amount x≤0.05, with the addition of Al increases, The magnetostriction decrease,when the substitution amount x=0.15, the magnetostriction decreased greatly. The addition of Al can improve the mechanical properties, with the Al content increases, the compressive strength increase.The TbDyFeAl alloy at the 930°C for 2 h annealing, it is found that the axially preferred orientation remains unchanged after annealing.The matrix lamellar microstructures of Tb0.3Dy0.7(Fe1-xAlx)2(x=0.05,0.10,0.15) alloy are degradation after annealing, the second phase grain refined, the crystal defects are present, with the Al content increase, the defects increase. After annealing,when the substitution amount x=0.10, the magnetostriction is improved the 80×10-6, its mechanical properties improved, when the substitution amount x=0.05,0.15, the magnetostriction is decreased, mechanical properties have little changes. So when the substitution amount x=0.1, the comprehensive performance of TbDyFeAl giant-magnetostrictive alloy is the best after annealing.