A researcher with Sandia National Laboratories (Albuquerque, New Mexico) explains the process for creating ultrafine-grained ceramic coatings as submicron particles splatting onto a surface. That splatting action is a key part of a project to lay down ceramic coatings kinetically. By making high-velocity submicron ceramic particles slam onto surfaces at room temperature, the high temperatures otherwise required to process ceramics such as alumina (Al2O3) and barium titanate (BaTiO3) are avoided.
Coating at room temperature makes microelectronics design and fabrication more flexible and could someday lead to better, less expensive microelectronic components that support modern technology. The kinetic process produces nanocrystalline films that are very strong and could be used as protective coatings against wear, corrosion, and oxidation.
Because ceramic components are processed at temperatures of about 1,300 °F (700 °C) or more, it can be difficult to combine them with similar hard materials and then integrate them into devices with materials that have relatively low melting temperatures. The ability to put down ceramics at room temperature means that ceramics and lower-melting temperature materials can be processed at the same time.
The coatings are created with an aerosol deposition process that uses kinetic energy instead of heat and draws on special material properties found at the micro- and nanoscale. A nozzle accelerates submicron particles suspended in a gas toward a surface. When a particle impacts the substrate or another layer, it plastically deforms and changes shape by a process known as dislocation nucleation and slip. The researchers discovered the particles have nanofractures that make them “lay down onto a substrate like splatting cookie dough, forming a pancake-shaped grain.”
As the next particle hits and deforms, it tamps down the original layer to create an even tighter bond. This mechanism makes many layers possible, so coatings that are tens of microns thick can be created.
The process also spans the microscale gap between two established technologies: thin films and thermal spray technology. Thin films are coating layers, ranging in size from nanometers to a few microns. Thermal spray technology can produce coatings starting at about 50 µm up to a few centimeters.
Source: Sandia National Laboratories, sandia.gov.