Investigation of thermal conduction in microcontacts created by indentation

Abstract

Thermal contact conduction has been investigated on different scales for many practical and scientific motivations in the literature. Demands for engineering the interfaces are increasing for accurately managing the contact mechanics and heat transfer with miniaturization of the electronics devices. In this study, microcontacts, that are created by indentation, have been investigated with experimental, simulation, and analytical works. The spreading resistance perspective of the disc constriction case has been extended for the studied highly plastic microcontacts of indentation. Creating the microcontacts and investigating the conductance through them had been realized by indentation of metallic surfaces by specially prepared diamond micro-particles/indenters. Thermal measurements had been realized by mounting thin thermocouples on diamond tips. The experimental setup is home-built with commercial piezo, motor, DAQ utilities, and other miscellaneous devices. PC User Interface and Intercessor Microcontroller Unit had been programmed to properly manage to conduct experiments. Furthermore, to measure the resistance, we employed an oscillatory experimental procedure and lumped analysis of transient heat transfer. The application of oscillations at different indentation depths has enabled us to extract the RC behavior of the microcontacts created by high plastic deformation. Therefore, the time constant of the contacts can be obtained. Additionally, we could find an effective measure of the thermal diffusivity of the contact through the diamond tip by fitting the change of time constant to depth with the proposed modified constriction models. Moreover, to analyze and predict the change of the time constant with respect to depth and load, several simulations and calculation work had been pursued. The increase in the contact area by indenter penetration into the sample has been concerned to be suppressed by gradient occurrence along the tip-sample contact. Moreover, with help of the simulations, we deduced the effect of plasticity such as pile-up on the improvement of the indentation contact for the heat transfer can be effective. Consequently, for the first time, we conducted the periodic contact procedure for the thermal contact of single micro asperity of indentation. The periodic experimental procedure and fin efficiency application to spreading cases for single microcontact are unique parts of this work. Results with the diamond tip on three different metallic samples showed that the gradient occurrence along the indentation contact can be analyzed with the fin solutions of the literature. Experimental results were fitted properly to a unified function of conic fin and spreading resistance functions. In addition, parameters of the fits can be deduced for the conductivity and interface conductance. However, state of the results are not sufficient to exactly determine the contact and material parameters due to need for exact parameters for transient analysis and, uncertainties in the properties of the tip and samples. With help of more precise thermal measurements and indenter systems, this experimental procedure may provide further advances and ease in the investigation of the thermal contacts of many different materials and scales. In addition, for the solid-state thermal interface materials solutions, we deduce that investigation of the geometry optimization for pressure and heat transfer as indicated in this thesis would provide insights into the bottlenecks of the contact heat transfer. Specifically, the gradient occurrence and its effectivity on the overall contact heat transfer should be taken into account for the indentation contacts while improving the contact by plasticity.