Electro-Spark Treatment with Low-Melting Al–Si and Al–Ca Electrodes in Order to Improve Wear and Oxidation Resistance of EP741NP Alloy Prepared by Selective Laser Melting

Abstract

In order to improve the oxidation resistance at 870°C of workpieces made of ÉP741NP alloy grown using selective laser melting (SLM) technology, electric spark treatment by near-eutectic Al–12%Si, Al–7%Ca–1%Mn and Al–6%Ca–0.6% Si electrodes is conducted. The effect of electrode composition on the microstructure, phase composition, mechanical and tribological properties of the modified layers before and after oxidation annealing is studied. It is shown that electro-spark treatment of EP741NP alloy with near-eutectic Al–Si and Al–Ca electrodes as a result of reaction phase formation leads to formation of intermetallic phases β-NiAl and γ′-Ni3Al. The modified layer formed by an Al–7%Ca–1%Mn electrode demonstrates the slowest wear rate (8.29 ⋅ 10–5 mm3/N/m), which is 4.4 times slower compared with ÉP741NP (36.50 ⋅ 10–5 mm3/N/m). Annealing treated samples at 870°C for 10 hours in air leads to formation of a dense and homogeneous barrier layer of Al2O3 or CaAl2O4 and an increase in the proportion of the β-NiAl phase that prevents oxidation of an SLM nickel sample, increases its hardness to 8.9 GPa, and wear resistance by a factor of 1.8.