Residual stresses in bulk metallic glasses due to differential cooling or thermal tempering

Due to their very low thermal conductivities and large thermal expansion values, bulk metallic glasses (BMGs) undergo differential cooling during processing. Large thermal gradients are generated across a specimen leading to residual stress buildup. A thin surface layer contains compressive stresses balanced by tension in the middle. Such stresses can not only influence the mechanical behavior of BMGs, but they can also lead to problems during manufacturing of large or intricate components. Analytical and finite element modeling was used to predict the values and distribution of such stresses as a function of processing conditions. Neutron diffraction measurements were then performed on model specimens which included crystalline phases as `strain gages'. It was shown that significant stresses, on the order of several hundred MPa, can be generated in BMGs. Modeling and diffraction results are presented and their implications discussed.