Mechanical and tribological features of TaN(Ag-Cu) duplex nanocomposite coatings: their response to heat treatment

Abstract

AISI 420 martensitic stainless steel samples and silicon (100) were coated with tantalum nitride doped with copper and silver nanoparticles TaN(Ag-Cu) to improve their hardness and wear resistance. The coatings were deposited by unbalanced DC Magnetron Sputtering technique, using a tantalum target and other silver/copper composite target (50/50%at), confronted each other. The coated samples were subjected to an appropriate heat treatment at 250 ºC for 8 minutes to achieve a controlled diffusion of Ag-Cu nanoparticles to the TaN(Ag-Cu) surface. Due to their mechanical and tribological properties depend, not only on the content of Ag-Cu, but also on the size, shape and density of nanoparticles of Ag-Cu on the surface of the coating. The influence of the Ag-Cu content on the microstructure and mechanical and tribological properties of the composite coating were evaluated before and after the heat treatment was evaluated. In general terms, the microhardness and wear rate increased initially with Ag-Cu content, but then dropped down for contents higher to 0.71% at, exhibiting the lubricating effect of Ag-Cu nanoparticles in the compound before and after heat treatment. The heat treated C3 sample showed a microhardness of 15 GPa, very superior to the hardness of AISI 420 stainless steel, as well as a wear rate six orders of magnitude lower than the steel.Keywords: AISI 420, magnetron sputtering, silver and cooper nanoparticles, tantalum nitride, tribological properties. (100) coated samples. These parameters were studied in this as well. RESUMEN Se recubrieron muestras de acero inoxidable martensítico AISI 420 y de silicio EXPERIMENTAL METHODS TaN(Ag-Cu) coatings developmentTaN(Ag-Cu) coatings were deposited on AISI 420 steel plates (12.5x12.5x2.8 mm 3 ) and single crystalline silicon wafers (100) by unbalanced DC magnetron sputtering, using a tantalum target and an Ag/Cu (50-50%at) composited target, both with 99.9% purity and dimensions of 500x100x6 mm 3 . A rectangular vacuum chamber with dimensions of 500x500x800 mm 3 was used in this work.Silicon substrates were used for spectroscopic and X-ray diffraction measurements to reduce the signal from the alloying elements of steel. AISI 420 stainless steel samples were polished using SiC emery paper with grain sizes between 300 to 1200 and subsequently polished to a mirror finish until obtaining an average roughness of Ra= 0.05mm in alumina aqueous solution. The polished samples were cleaned in an ultrasonic bath with an alcoholacetone solution for 15 minutes and then subjected to argon ionic cleaning into the vaccum chamber during 30 minutes at a pressure of 1.7x10 -1 mbar and using a bias voltage of -500V applied to substrates.The nitriding process was performed into pulsed plasma conformed by Ar = 57 sccm, N 2 = 15 sccm and H 2 =27 sccm; the pressure, bias voltage and temperature of the process were fixed to 5.1x 10 -1 mbar, -600 V and 380 ºC, respectively. This process was performed for 7 hours. The low temperature of plasma nitriding was used to avoid the...