Effects of microstructure, porosity and interface on thermal properties of titanium, aluminum-silicon, and brass coated AISI 410 stainless steel

There have been many attempts to change not only the mechanical properties but also physical properties of a material through common material processing. One such property of interest is the thermal conductivity (TC), which is driven by the need for improved materials and composites to conduct heat away from crucial components of a given system. It is important to know what influences TC. Some of the important factors include: matrix microstructure, the reinforcement distribution as well as amount of reinforcement, the strength of the interfacial bond between the matrix and the reinforcement and finally the porosity level. In this work, the feasibility of enhancing the inherent TC of a given material through various methods has been studied. Three main methods were implemented using laser processing; porosity, microstructure, and surface modification or coating. All of these can be accomplished utilizing Laser Engineered Net Shaping, a rapid prototyping technique in conjunction with optimized processing parameters. In the first part of this work porosity was introduced into Ti-6Al-4V alloy samples to study the effect it has on TC and thermal performance. The porosity level of laser processed samples varied from 0.5 to 22%. Laser processed samples showed an increase of TC as the porosity decreased. Next, attention was turned to modifying microstructural features of Al-12Si and studying the effect this had on TC. Comparison of microstructural features of laser processed samples with cast Al-12Si alloy showed significant refinement in Si, which improved the TC and compensated for the detrimental effect of porosity on TC. The TC of cast alloy was ∼21--76% lower than the values exhibited by laser processed samples. Finally, surface modification of AISI SS410 was accomplished by coating it with a high TC brass alloy. The influence of laser treatment on interfacial microstructure and thermal performance was evaluated as a function of coating thickness. Laser deposition resulted in a diffused and metallurgically sound interface between metallurgically incompatible brass coating and the AISI SS410 substrate. Depending on the coating thickness the TC of AISI410 steel increased from 27 W/mK to a maximum of 37 W/mK.