Influence Of Melt Treatment And Structural Readjustment On The Properties Of FeBYMo Bulk Amorphous Invar Alloys

Iron-based amorphous alloys possess good glass forming ability(GFA), relatively low material cost, unique soft magnetic, mechanical properties and good corrosion resistance,which is considered to have potential engineering applications as structural and functional materials. In recent years, invar effect has been investigated in numerous iron-based amorphous ribbons, these alloys are characteristic of the small thermal expansion coefficient in the order of 10-6K-1 below the Curie temperature, analogous to the traditional invar alloys.Developing new bulk Invar metallic glasses is essential to the practical application for the new kind of material.In this paper(Fe73.2B22Y4.8)95Mo5 amorphous alloys were fabricated by copper mold casting method, the invar effect of amorphous alloys are investigated through cyclic thermal dilation. The influence of melt heating treatment on the invar effect and structure of amorphous alloys were also studied. The crystallization activation energy have been calculated by Kissinger method. The crystallization behaviors of the alloys were studied by in-situ XRD. The nano-hardness and Young,s modulus of the samples have been measured by nanoindentation.The main results indicate that(Fe73.2B22Y4.8)95Mo5 amorphous alloys present clear invar effect, this effect is absent in the crystalline state alloys. The local Fe-Fe atomic pairs at the amorphous state are essential to the invar transition. The structure of the alloys can be turned through the melt heating treatment, which has influence on the invar effect, however cannot be distinguished by the XRD and DSC. When the alloys were cast at 1393K~1673K melting temperature, the amorphous samples cast from 1563 K have strongest invar effect due to thespecial local structure, which is inherited from the melt at 1500 K and disappeared at the temperature above 1640 K. Different holding time of melt no more than 2 min has little influence on the invar effect of samples, however the holding time longer than 2 min will weaken the Invar effect due to the change of composition.The nano-hardness and Young,s modulus of the samples are not sensitive to the melt heating treatment. The values of Young,s modulus are in the range of 201.2~216.1GPa, while the values of nano-hardness are in the range of 14.28~14.7GPa. The initial and main crystalline phase for the annealed(Fe73.2B22Y4.8)95Mo5 alloy is Fe2 B, and the other two minor crystalline phases are B6Fe23 and Mo2 Fe B4. Amorphous alloys cast from different melt temperature possess different values of Ex and Ep, and the values of Ex and Ep are in the range of 382~488k J/mol and 407~526k J/mol, respectively. All the samples, values of Ep are bigger than that of Ex. It means amorphous alloys need more energy in the growth stage than it in the nucleation stage, which indicates that the alloys are stable against crystallization at room temperature.