STIR: Computational and Experimental Investigation to Understand the Adaptation Mechanisms of 'Chameleon' Coatings

摘要

Double oxide phases that combine a transition metal and a noble metal have recently become a subject of investigation as potential lubricious materials for high temperature tribological applications. Two selected double metal oxide phases, namely silver molybdates and tungstates, were produced in thin film and powder forms using magnetron sputtering and hydrothermal methods, respectively. The lowest frictional properties of these materials were measured at 600 degrees C to be 0.1 and 0.4 for the Ag2Mo2O7 and alpha-Ag2WO4 phases, respectively. Changes in the chemistry and crystal structure of these materials were investigated with increasing the temperature up to 600 degrees C using in- situ Raman spectroscopy, X-Ray diffraction and a differential scanning calorimeter. These tools revealed that the coatings went through a phase transition accompanied by a phase segregation of silver. Simulations performed to investigate the structural and thermal properties of these materials using ab-initio molecular dynamics (AIMD) method were in agreement with the experimental results. The structural and chemical information obtained using computational and experimental studies was correlated to their high temperature tribological performance. Moreover, a new double metal oxide based on the Ag-V- O system was created and tested at very high temperatures. This system was found to be lubricious (friction coefficient of 0.1) at temperatures as high as 1000 degrees C. This is a significant result given that this is the first solid lubricant that was found to perform well at these extreme temperatures. This finding will enable the design of new military machinery that operates at these high temperatures. Potential applications include solid lubrication for small caliber barrel and weapon action components, EM Gun rail materials, and helicopter engines.