Tensile Strength and Fracture Characteristics of Heat Treated GRCop-84 Copper Additively Manufactured by Selective Laser Melting
Recent advances in powder bed Selective Laser Melting (SLM) of Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, produces a fully dense high conductivity alloy with tensile strength (470 MPa yield and 710 MPa ultimate tensile strength (UTS)) superior to other competing copper alloys. The high thermal stability of the Cr2Nb precipitate in the copper matrix reduces coarsening and maintains a 310 MPa yield and 520 MPa UTS after a 900°C, 5-hour heat treatment. The increased cooling rate of small diameter gas atomized powder used as an additive manufacturing feed-stock is shown to suppress agglomeration of primary precipitates during the atomization process and increase tensile strength of the final SLM material. Anisotropy of tensile strength was attributed to internal stress and based on print direction. Void nucleation during fracture was initiated by brittle fracture of precipitate particles. Fracture cusps contain matching precipitate fragment geometry on opposing sides located near the cusp center. An optimal precipitate size of 100-200 nm is predicted for maximum tensile strength.