Comprehensive Study of the Deformation Behavior during Diffusion Bonding of 1.4301 (AISI 304) as a Function of Material Width and Aspect Ratio

In this paper, the impact of material width as well as aspect ratio on deformation during diffusion bonding of layered samples were investigated. For this, six annular samples with a constant cross-sectional area but an increasing diameter and thus decreasing material width were designed. In a first set of experiments, specimens of a constant height of h = 20 mm were examined. Each sample consisted of 10 sheets, 2 mm in thickness each. Diffusion bonding was performed at T = 1075 °C, t = 4 h and p = 15 MPa. Subsequently, additional samples with a constant aspect ratio of about three but different material width were diffusion bonded. For this, additional layers were added. It was expected that the deformation should be nearly constant for a constant aspect ratio. However, comparing the deformation to a sample possessing an aspect ratio of about three from the first batch, a much higher deformation was obtained now. Bonding a third sample, a deformation in the same range as for the other two samples of the second batch was obtained. It was found that due to the evaporation of metals, the thermocouples were subjected to aging, which was proven indirectly by the evaluation of heating power. Since the diffusion coefficient of the metals follows an exponential law, deformation changes considerably with temperature. This emphasizes that exact temperature measurement is very important, especially for bonding microprocessor devices at constant contact pressure. The experiments showed that the deformation depends strongly on geometry. Bonding parameters cannot be generalized. For layered setups, the contribution that thickness tolerances from manufacturing and leveling of surface roughnesses of sheets add to the overall deformation cannot be reliably separated. After diffusion bonding, thickness tolerances increase with a lateral dimension. Obviously, the stiffness of the pressure dies is crucial.