Results in Physics (Mar 2022)
Adhesion strength of paraffin droplet impacted and solidified on metal substrate
Abstract
Debonding of solidified splats is a crucial issue for thermal sprayed coatings, which greatly influences the performance and lifetime of industrial components. The purpose of this study is to provide an in-depth understanding of the effects of impact parameters as well as residual stress on the debonding behaviors, and the related adhesion strength and driving forces of single splats. In this study, debonding behaviors of molten paraffin droplets which were impacted and solidified on stainless steel substrates, were observed considering the effects of substrate pre-set temperature, drop height (impact velocity), and droplet temperature. It was found that the debonding is prone to take place at lower substrate pre-set temperatures, lower drop heights, and lower droplet temperatures. A scraping method was then employed to measure the adhesion strength of splats formed under various conditions. The results showed good accordance with debonding behaviors in the drop impact test. The scraping tests also indicated that the residual tensile stress in splats reduces the scraping forces and prevents the complete removal of splats during the scraping processes. Peeling stress and shear stress along the splat-substrate interface, which are driving forces for debonding, were calculated using coupled thermomechanical finite element analyses. The calculated driving forces were larger for lower drop heights and lower droplet temperatures under which the debonding was more easily to occur. The results of numerical simulations coupled with scraping tests provide reasonable explanations for observed debonding behaviors of single splats. This study provides a comprehensive understanding of the effects of several droplet impact variables and residual stress on the debonding behaviors, and the related adhesion strength as well as driving forces of single splats.
