Microstructure, Mechanical Properties, and Corrosion Resistance of Ag-Cu Alloys with LaO Fabricated by Selective Laser Melting.

Ag and its alloys, when prepared by a selective laser melting (SLM) process, have a low density and poor overall performance due to their high reflectivity when the most commonly used laser ( = 1060 nm) is used, and they have exorbitant thermal conductivity. These characteristics lead to the insufficient melting of the powders and severely limit the applications of additive manufactured silver alloys. To improve the absorption of the laser, as well as for better mechanical properties and higher resistance to sulfidation, Ag-Cu alloys with different LaO contents were prepared in this work using the SLM process, via the mechanical mixing of LaO nanoparticles with Ag-Cu alloy powders. A series of analyses and tests were conducted to study the effects of LaO in Ag-Cu alloys on their density, microstructure, mechanical properties, and corrosion resistance. The results revealed that the addition of LaO particles to Ag-Cu alloy powders improved the laser absorptivity and reduced defects during the SLM process, leading to a significant rise from 7.76 g/cm to 9.16 g/cm in the density of the Ag-Cu alloys. The phase composition of the Ag-Cu alloys prepared by SLM was Silver-3C. LaO addition had no influence on the phase composition, but refined the grains of the Ag-Cu alloys by inhibiting the growth of columnar grains during the SLM process. No remarkable preferred orientation existed in all the samples prepared with or without LaO. An upwards trend was achieved in the hardness of the Ag-Cu alloy by increasing the contents of LaO from 0 to 1.2%, and the average hardness was enhanced significantly, from 0.97 GPa to 2.88 GPa when the alloy contained 1.2% LaO due to the reduced pore defects and the refined grains resulting from the effects of the LaO. EIS and PD tests of the samples in 1% NaS solution proved that LaO addition improved the corrosion resistance of the Ag-Cu alloys practically and efficaciously. The samples containing LaO exhibited higher impedance values and lower corrosion current densities.