## 6 Conclusions  
Interfacial thermal conductance is an important parameter for industry, especially for fast thermal processes. During phase transformations of a melting sample, various mesoscopic effects take place at the interface between the sample and the substrate, which affect the interfacial thermal conductance. In this study, we focused on the various contributions to ITC and the changes in these contributions during pre-melting and melting of metal microparticles. The contribution of various mesoscopic effects to the total ITC strongly depends on the effective size of the interfacial gap \(d\) between the melting sample and the substrate. During melting, interfacial dispersion forces cause the sample to spread over the surface roughness of the substrate. Thus, the thickness \(d\) is significantly reduced. The distance \(d\) varies in the range from micrometers to nanometers when the sample is melted. We found that in experiments with metal particles melting on a solid, the main contribution to the ITC is made by the near-field photon tunneling and heat transfer through the gas (the phonon contribution to the ITC is usually not observed). It turns out that the interfacial thermal conductance \(G_{LS}\) of the liquid-solid interfaces is mainly due to the near-field thermal conductance \(G_{nf}\), while the interfacial thermal conductance \(G_{SS}\) of the solid-solid interfaces is due to the thermal conductance through the gas \(G_{g}\). In fact, a sharp jump in ITC by an order of magnitude from \(G_{SS}\) to \(G_{LS}\) occurs just at the beginning of melting due to the formation of a thin liquid layer on the surface of the sample. However, it was observed that in some metals, the ITC gradually increase upon heating in a certain temperature range below the melting point \(T_{melt}\). This unusual gradual change in ITC is observed in a certain temperature range below the melting point during the pre-melting process in samples of aluminum alloy 7075 and pure indium. This pre-melting process occurs in the volume of the samples with enthalpy consumption. Thus, during the pre-melting, the interfacial thermal conductance gradually changes by an order of magnitude from \(G_{g}(d)\) to \(G_{nf}(d)\) as \(d\) decreases from micrometer to nanometer scale. We studied the nature of the gradual change in the ITC during the pre-melting process. This gradual change in the ITC during the pre-melting process is associated with a gradual volumetric change in the microstructure of the melting materials. This change in the microstructure during the pre-melting determines the strength of the dispersion forces and, consequently, the effective distance \(d\), and the near-field thermal conductance \(G_{nf}(d)\). Thus, we have made progress in understanding the effect of pre-melting processes on the ITC of metals and alloys in contact with a solid. We believe our results are universal, at least for alloys in the temperature range between solidus and liquidus temperatures since the gradual change in microstructure upon heating is a natural property of alloys in this temperature range. It is interesting to extend such experiments to various alloys and pure metals, in which a gradual microstructure change occurs when heated in a certain temperature range below the melting point. Understanding mesoscopic effects and the processes that affect interfacial thermal conductance during the pre-melting and melting of metal microparticles can provide theoretical guidance for optimizing technologies such as laser additive manufacturing. Conceptualization, A.M.; formal analysis, A.M.; methodology, A.M.; supervision, C.S. ; visualization, A.M.; writing--original draft, A.M.; writing--review and editing, C.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.