Characterization of NbTiCrFeMoX high entropy coating processed by laser cladding in pipeline: investigation of microstructural, tensile, creep, wear, and corrosion properties

Abstract

Refractory High entropy alloy (RHEA) is a potential material for coating gas turbine blades and pipeline due to its high-temperature mechanical and chemical properties. In this paper, a series of new NbTiCrFeMo_X (x = 0.2, 0.4, 0.6, 0.8, 1) RHEAs were coated on GTD-111 nickel base superalloy by the laser cladding method. The effects of the Mo amount on the microstructure and tensile, creep, corrosion, and wear properties were investigated. XRD results showed that the microstructure of all five coatings included the B2 regular phase, the BCC irregular phase, C14-Laves (FeTi₂), and C15-Laves (Cr₂Nb). However, with the increase of Mo from 0.2 to 1, the amount of the BCC phase increased from 24.1 to 29.5%, the C14 phase increased from 55.1 to 61.4%, and the amount of the C15 phase decreased from 11.2 to 1.8%. The yield strength increased by increasing the volume fraction of BCC and C14-Laves phases from 328 MPa for the Mo0.2 sample to 685 MPa for the Mo1 specimen. The same factor increased the creep life of RHEA from 43 to 54 h under a force of 450 N and temperature of 800 °C by increasing the places of dislocation locking. The simultaneous presence of the BCC solid solution and Laves phase was one of the factors that reduced the coefficient of friction during the wear test from 0.63 to 0.44 with increasing Mo. Electrochemical tests in 3.5 wt% NaCl solution showed that the RHEAs showed significant corrosion resistance. Specimen Mo1 with the smallest I_corr (1.6103 × 10^–6 A cm²) and the highest E_corr (− 1.2025 V) showed the best corrosion resistance.