Mechanical and fatigue properties of plasma sprayed (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20 and Fe56.04Co13.45Nb5.5B25 metallic glasses

Metallic glasses (MG) are unique materials with a continuous and homogeneous structure. Thermally sprayed deposits are characterized by a nonuniform microstructure, with numerous interparticle and intersplat interfaces. This paper addresses the difference between conventionally manufactured and thermally sprayed MG's by microstructural characterization of the MG coatings (MGC) and their mechanical testing using the unified bending methodology. Two thick coatings of (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20, and Fe56.04Co13.45Nb5.5B25 were prepared on steel substrates with atmospheric plasma spraying (APS) using gas atomized powders. The relative glassy phase content of 92 % was obtained for (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20 coating and 53 % for Fe56.04Co13.45Nb5.5B25 coating. The strain-stress curves for both coatings show brittle behavior without any plasticity. The tensile strength was 142 +/- 27 MPa for Fe56.04Co13.45Nb5.5B25, and 152 +/- 36 MPa for (Fe0.9Co0.1)76Mo4(P0.45C0.2B0.2Si0.15)20. In the comparison of both MGCs, the Fe56.04Co13.45Nb5.5B25 coating has a higher crack growth resistance (significantly in fatigue, less significantly in the fracture toughness test). The obtained fracture toughness is much higher than usually reported in the literature for Fe-based metallic glasses.