Metallic Glass Film: A Novel Coating for Improving Fatigue Properties of Light-Weight Structural Materials

Metallic glasses (MGs), non-crystalline metals which lack long-range atomic periodicity, are non-equilibrium materials. MGs have many desirable properties including unusually smooth surfaces, high specific strengths, and excellent resistance to corrosion and wear. Because of their random atomic arrangement and lack of grain boundaries, MGs have been the subject of intense scientific research over the past several decades. Nevertheless, bulk MGs still suffer from poor workability at room temperature. Thus, thin film metallic glasses (TFMGs) have been investigated in recent years as a possible route for making use of unique MG properties while minimizing issues related to extreme brittleness.

In this presentation, the TFMGs have been shown to improve fatigue properties of light-weight structural materials (Al- and Ti-based alloys). Specifically, the four-point-bending fatigue life of Ti-6Al-4V is improved ~17 times from 2.2x10⁵ cycles of uncoated sample to 3.7x10⁶ cycles when a 200-nm-thick TFMG is coated, under a stress of 675 MPa. Furthermore, the fatigue life of TFMG-coated 7075-T6 Al alloy could be drastically improved 45 times at 250 MPa. On the other hand, the ceramic hard coating such as TiN with higher hardness than TFMG often could not offer better protections to the substrate due to its brittle nature and the thermal impact of the coating fabrication process. The significant improvements from TFMGs are largely attributable to improved ductility and flexibility as well as to good adhesion.