TABLE OF CONTENTS The unique mechanical properties exhibited by metallic glasses are connected to their structure. Table 3.1 lists the hardnesses, yield stresses, and Young s moduli for several metallic glasses. The unique compositions correspond to regions in the phase diagram that have a very low melting point. The low melting points aid in the retention of the liquid structure. Metallic glasses are primarily formed by rapid cooling from the molten state, so that the atoms do not have time to form crystals. The Metglas group is commercially produced in wire and ribbon form. Young s modulus for glasses varies between 60 and 70% of the Young s modulus of the equilibrium crystalline structure. Li [7] has proposed a relationship between the shear modulus of the glassy and crystalline states, namely,
where G g and G c are the shear moduli of the glassy and crystalline states, respectively, and ? is Poisson s ratio. The crystalline Young s modulus of glasses is recovered when the material is annealed and crystallinity sets in. The yield stresses of metallic glasses are high, as can be seen in Table 3.1. For Fe B metallic glasses, strength levels over 3.5 GPa were achieved. This is close to the highest yield strengths achieved in polycrystalline metals. (See Section 1.4.) The yield stresses of the metallic glasses are usually 10 to 30 times higher than the yield stress of the same alloy in the crystalline state.
