The Effect Of Addition Elements On The Properties In Mg-based Amorphous Alloys

Since the development of techniques for rapidly cooling liquids, a large number of amorphous structures have been discovered. These materials have demonstrated outstanding mechanical properties compared with conventional metal materials. Mg-based metallic glasses are regarded as a new family of promising materials with high specific strength, low cost and density. This work focuses on analysis and studying of the effect of addition (substitution) in Mg-based amorphous alloys, including glass forming ability, thermal stability, and mechanical properties.1. The effect of substitution of Gd in Mg60Ni25Gd15 amorphous alloy with NdThe neighbor atomic substitution is an effective method for producing now type amorphous alloys. In this work, the substitution of Gd with Nd enhanced the glass forming ability and thermal stability,The formerly disadvantage of only caring about the improvement of glass forming ability and neglecting the thermostability was conquered. As a result, supercooled liquid region is also a good token of glass forming ability. The reasons of the effect are as follows. The first reason is that the substitution of Gd with Nd is well satisfy the Inoue empirical rules, Nd has larger negative heat of mixing against the main component elements, and larger Goldschmidt atomic radius than Gd. All of this can increase the degree of dense random packed structure, and make a high solid/liquid interfacial energy which is favorable for the suppression of nucleation of a crystalline phase. Also the new type of liquid can have the difficulty of atomic rearrangement, leading to a decrease of atomic diffusivity and an increase of viscosity. Therefore, it will enhance the glass forming ability and thermal stability of amorphous alloy.Another reason is that the melting point of Nd is 1289K which is lower than Gd (1585K), and that will effect the decrease of melting temperature and liquidus temperature with partial substitution of Gd with Nd, leading to the increasing of reduced glass transition temperature, and then glass forming ability.2. The effect of Co addition in Mg-Ni-Gd amorphous alloysThermal stability and glass forming ability decreased with the addition of Co. The amorphous alloys do not satisfy the three empirical rules because the heats of mixing are nearly zero for Co-Ni pairs (0 KJ/mol), and Mg–Co pairs (3KJ/mol), which can not suppress the formation of crystalline phases very well and then decreased the glass forming ability and thermal stability. As a result, supercooled liquid region is also a good token of glass forming ability.3. The effect of Fe addition in Mg-Ni-Gd amorphous alloysThermal stability and glass forming ability are decreased with minor Fe addition in Mg60Ni25Gd15. It may be result from the unsatisfied with the Inoue empirical rules, Mg has positive heat of mixing against Fe (18 KJ/mol), which will increase the long-region atomic diffusivity, and then decrease the thermal stability and glass forming ability.4. The effect of Fe addition on mechanical properties in Mg-Ni-Gd bulk metallic glass Mg₆₀Ni₂₅Gd₁₅ and(Mg₆₀Ni₂₅Gd₁₅)₉₇Fe₃ bars of 2mm were prepared by using copper mold casting techniques. The fracture stress is enhanced with the addition of Fe, which may be attributed to the positive heat of mixing between Fe and main components which results in the decrease of glass forming ability, and then form some Fe crystalline phases. From a mechanical point of view, the fracture stress is significantly enhanced by the Fe addition, which may be probably related to the interaction between the dendrites and propagating shear bands through the glass.Also, elasticity modulus of alloys increased with the Fe addition, these result from the elasticity modulus of alloys is relative to the elasticity modulus of components. Fe has a larger modulus than the main components, which would lead to the increase of elasticity modulus of alloys.