Analysis of Pitting Corrosion on an Inconel 718 Alloy Submitted to Aging Heat Treatment

Abstract

Inconel 718 is one of the most important superalloys, and it is mainly used in the aerospace field on account of its high mechanical strength, good resistance to fatigue and creep, good corrosion resistance and ability to operate continuously at elevated temperatures. In this work the resistance to pitting corrosion of a superalloy, Inconel 718, is analyzed before and after double aging heat treatment. The used heat treatment increases the creep resistance of the alloy, which usually is used up to 0.6 T m . Samples were subjected to pitting corrosion tests in chloride-containing aqueous solution, according to ASTM-F746-04 and the procedure described by Yashiro et al. The results of these trials show that after heat treatment the superalloy presents higher corrosion resistance, i.e., the pitting corrosion currents of the as received surfaces are about 6 (six) times bigger (~0.15 mA) than those of double aged surfaces (~0.025 mA). Keywords: Double aging heat treatment; Pitting corrosion; Inconel 718. ANÁLISE DE CORROSÃO POR PITE NA LIGA INCONEL 718 SUBMETIDA A TRATAMENTO TÉRMICO DE ENVELHECIMENTOResumo O Inconel 718 é uma das superligas mais importantes, sendo utilizada principalmente no setor aeroespacial devido a alta resistência mecânica, boa resistência a fadiga e fluência, boa resistência a corrosão e capaz de operar continuamente em temperaturas elevadas. Neste trabalho a resistência à corrosão por pite da superliga Inconel 718 é analisada antes e após o tratamento térmico de duplo envelhecimento. O tratamento térmico utilizado aumenta a resistência à fluência desta superliga, que normalmente é utilizada até 0,6 T m . Amostras foram submetidas ao teste de corrosão por pite em solução de cloreto de sódio, de acordo com a norma ASTM-F746-04 e o procedimento descrito por Yashiro et al. Os resultados mostram que a superliga apresenta maior resistência a corrosão após o tratamento térmico, isto é, a corrente de corrosão por pite da condição como recebida é 6 vezes maior (~0,15mA) do que a envelhecida (~0,025 mA). Palavras-chave: Duplo envelhecimento; Corrosão por pite; Inconel 718. *Dedicated to the memory of Prof. Carlos de Moura Neto.

Corrosion fatigue crack growth behavior of oil-grade nickel-base alloy 718. Part 2: Effect of aging treatment

“…Pedron and Pineau [25] performed fatigue crack growth tests on alloy 718 at 650°C under air Page 15 of 44 A c c e p t e d M a n u s c r i p t 15 and vacuum environments to investigate the influence of microstructure and environment.…”

“…Moreover it was shown that the i corr of Alloy718-TSA is higher than the one of Alloy 718-SA, confirming the lower corrosion resistance due to the bigger grain size and formation of new  phases. It should be pointed out that Alloy 718-OSA shows lower i corr values than Alloy718-SA, which might be ascribed to the formation of the nano-size γ′/ γ″ precipitates [15]. respectively, which shows the same trend of corrosion resistance of three alloy 718 specimens in 3.5 wt.% NaCl solution.…”

“…It has been reported by Jing et al [3] that the fatigue life of alloy 718 in air was significantly increased by the two-step aging treatment, while the pitting corrosion behavior in chloride solution at RT did not change in spite of different heat treatment processes. Felipe et al [15] have studied the pitting corrosion behavior of Inconel 718 in 3.5 wt.% NaCl solution before and after double aging heat treatments. Their results have shown that the pitting corrosion potential of solution annealed specimen was higher than the one of double aged condition, while the pitting corrosion current of solution annealed specimen was about six times bigger than the double aged specimen.…”

“…Felipe et al[15] have also compared the pitting corrosion behavior of solution treated and double aged Inconel 718 in 3.5 wt.% NaCl solution at RT by using cyclic voltammetry and chronoamperometric experiments. Their results have confirmed that the double aged Inconel 718 specimens were more susceptible to pitting formation then the solution treated ones, however, when pit formation started it was more severe in the solution treated samples than in the double aged ones.…”

Surface engineering of IN-718 by low-temperature carburisation: properties and thermal stability

“…IN-718 is a precipitation-hardenable austenitic Ni–Cr–Fe superalloy (Figure 1) with excellent oxidation- [1] and corrosion resistance [2]. It combines high strength and good ductility up to temperatures of K ( ) and it possesses good phase stability, weldability, castability, and machinability.…”