Evaluation of the DOS by DL−EPR of UNSM Processed Inconel 718

Abstract

In this work, influence of ultrasonic nanocrystal surface modification (UNSM) on the degree of sensitization (DOS) in Inconel 718 has been studied and correlated with the resulting microstructure. The UNSM processed samples decreased their grain size from 11.9 µm to 7.75 µm, increasing the surface of grain boundaries, and thus enhancing the area where δ phase and niobium carbides precipitate. The effect of the UNSM process on the DOS of Inconel 718 was studied by the double loop electrochemical potentiokinetic reactivation (DL−EPR) test. The DL−EPR showed that for UNSM processed samples with no thermal treatment, the DOS increased up to 59.6%, while for UNSM treated samples that were post-annealed at 1000 °C for 10 min and water quenched the DOS decreased down to 40.9%. The increase of grain boundaries surface area and triple junctions after the UNSM process enables the formation of twice the amount of δ phase compared to the as-received Inconel 718 bulk sample. The area fraction of the grain boundary covered by δ phase was of 9.87% in the UNSM region while in the bulk the area fraction was 4.09%. In summary, it was found that after UNSM process, the annealing at 1000 °C for 10 min and water quenching promoted the transformation of γ″ to form δ phase on the grain boundaries, which reduces the intergranular corrosion susceptibility.

Effect of Laser Peening on the Corrosion Properties of 304L Stainless Steel

“…Corrosion properties by surface modification have recently been studied as follows: Shot peening on the corrosion of aluminum alloy [ 19 , 20 ] and the corrosion properties of stainless steel [ 21 , 22 ]; laser peening on the corrosion of Alloy 600 [ 23 ], the corrosion of 304 stainless steel [ 24 ], the corrosion of stainless steels [ 25 , 26 , 27 , 28 , 29 ], the corrosion of aluminum alloy [ 30 ], and the corrosion of magnesium alloy [ 31 ]; UNSM on the corrosion of nickel base alloys [ 32 , 33 , 34 ] and the corrosion of stainless steels [ 35 , 36 , 37 , 38 ]; and comparison between laser peening, shot peening, and ultrasonic peening [ 8 ]. Most recent research efforts on surface modification methods have shown beneficial effects on the corrosion of various alloys [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. In some cases, detrimental effects of surface modification methods can be induced.…”

Passivation of precipitation-hardened UNS N07718 in a shallow sour aqueous solution

“…[1][2][3][4] The UNS N07718 alloy is corrosion-resistive in oil elds, such as fasteners, bolts, and nuts, where a shallow sour (sweet) condition is associated with the localised corrosion. 5,6 The sweet wells are mildly corrosive to Ni-based alloys due to the passive lm on the alloy surfaces, which governs the localised corrosion resistance during service in the environments. For these reasons, the precipitation-hardened UNS N07718 alloy provides the desired mechanical properties 7,8 and localised corrosion resistance in sour environments.…”

Effect of the Thermomechanical Treatment on the Corrosion of UNSM Processed Inconel 718: An Electrochemical Study

“…The UNSM promoted a high twin and dislocation density region on Inconel 718, preventing the fatigue crack to nucleate by creating barriers for the dislocation to move forward, delaying the failure of the samples [16]. Concerning the corrosion performance, the UNSM treatment has also positively influenced the corrosion behavior; among the techniques used to test it, electrochemical impedance spectroscopy (EIS) is one of the most common [12,17,18]. The combination of UNSM and nitriding enhanced the impedance by five times compared to the control sample, improving the pitting corrosion protection [19].…”