Wear of Bulk Metallic Glass Alloys for Space Mechanism Applications

Space-based mechanisms must operate under harsh environments, usually without access for maintenance; failure may result in a loss of a spacecraft. Therefore, space agencies support research on high-performance mechanism designs and materials, one key area being space tribology. Bulk metallic glasses (BMGs) are a class of alloy characterized by their amorphous structure, which results in a material with extremely high strength, corrosion resistance, high hardness, and high elastic limit. BMGs have demonstrated improved wear resistance when compared against traditional engineering materials in similar applications. Four BMG compositions, Zr(53)Al(1)6Co(23.25)Ag(7.75), Zr49Ti1.96Cu37.24Al9.8Y2, Zr60Ti2Nb2Al7.5Ni10Cu18.5, and Cu47Zr46Al5Y2 (at%), were selected from the literature as potential candidates for space-based mechanisms applications. Wear testing, hardness, profilometry, and scanning electron microscopy (SEM)/energy dispersive X-ray (EDX) spectroscopy analysis were performed on the selected alloys, and their results were compared. High-resolution 3D profilometry and detailed image analysis of wear tracks and volume loss resulted in a critical re-assessment of the Archard wear coefficient. For the compositions tested, the hardness was not a useful predictor of the wear performance as suggested by the Archard wear equation. Processing history and test configuration significantly influenced the wear behavior. The alloy Zr49Ti1.96Cu37.24Al9.8Y2 was found to be the best BMG candidate for space wear applications when taking manufacturability into consideration. BMG hardness and wear test results were compared with similar testing performed on conventional crystalline alloys commonly used in space applications: titanium alloy Ti-6Al-4V ELI, and cold-worked stainless steels AISI 303 and AISI 304.