Temperature-Dependent Small Strain Plasticity Behavior of 304L Stainless Steel

Glass-to-metal seals are used extensively to protect and isolate electronic components. Small strains of just a few percent are typical in the metal during processing of seals, but generate substantial tensile stresses in the glass during the solidification portion of the process. These tensile stresses can lead to glass cracking either immediately or over time, which results in a loss of hermiticity of the seal. Measurement of the metal in the small strain region needs to be very accurate as small differences in the evolving state of the metal have significant influence on the stress state in the glass and glass-metal interfaces. Small strain tensile experiments were conducted over the temperatures range of 25–800 °C. Experiments were designed to quantify stress relaxation and reloading combined with mid-test thermal changes. The effect of strain rate was measured by directly varying the applied strain rate during initial loading and reloading and by monitoring the material response during stress relaxation experiments. Coupled thermal mechanical experiments were developed to capture key features of glass-to-metal seal processing details such as synchronized thermal and mechanical loading, thermal excursions at various strain levels, and thermal cycling during stress relaxation or creep loadings. Small changes in the processing cycle parameters were found to have non-insignificant effect on the metal behavior. The resulting data and findings will be presented.