study of corrosion resistance of alloy inconel 625 coatings deposited ...
STUDY OF CORROSION RESISTANCE OF ALLOY INCONEL 625 COATINGS DEPOSITED ON STEEL API 5LX70 THROUGH WELDING PROCESSES GMAW AND PTA-P A. X. Santos1*; T. M. Maciel1; R. A. C. Santana1 1 LabSol, Department of Mechanical Engineering, University Federal of Campina Grande, 59072-970, Campina Grande, PB, Brazil. e-mail: [email protected] Abstract The aim of this work, a comparative study of the corrosion resistance of the coatings of nickel base alloy Inconel 625 deposited by welding processes P-PTA (Plasma Arc Powder Transfered) and GMAW (Gas Metal Arc Welding) steel API 5L X70 . We used the factorial statistical experimental design for evaluation of process parameters on the corrosion resistance. Three overlapping ½ deposits by both welding processes, followed by cutting the samples and machining the surface of the coating were carried out, with leaving a height of 3 mm according to standard Petrobras coating. The electrochemical behavior of the coating surface (Inconel 625) was investigated at room temperature in a solution of NaCl using the technique of linear potentiodynamic polarization. To reveal the corrosion resistance of the coatings of both processes, some parameters relevant characterization were analyzed such as corrosion potential (Ecorr), corrosion current (Icorr) and polarization resistance (Rp), through the polarization curves. The results showed that the values of the parameters for the characterization of coatings deposited by PTA-P, showed higher values than applied for GMAW, indicating higher corrosion resistance of the coatings applied by this welding process.
Keywords: Coating, PTA-P, GMAW, Corrosion. Introduction The application of coatings for welding is very attractive to offer protection to the substrate and good metallurgical union. The PTA-P (Plasma Powder Transfered) and GMAW (Gas Metal Arc Welding) processes have great importance in the field of manufacture and repair through coatings, for providing a good quality of welds and high deposition rate and welding speed . For corrosion protection has been widely using nickel superalloys, Inconel 625, like coat, through deposition by welding [Alfaro; Carvalho; Melo Júnior]. The aim of this work, the comparison of the corrosion resistance of the coatings of nickel base alloy Inconel 625 deposited by PTA and PGMAW steel API 5L X70. Experimental part The PTA-P and GMAW were used for deposits in plate steel API5LX70, (145x60x19) mm, using a nickel alloy Inconel 625 was a factorial design 2³ used to check the influence of the process variables: voltage, current, feed speed and welding speed (Vs) the corrosion analysis performed using the technique of linear potentiodynamic polarization (PPL). This analysis was done in both welding processes, the samples with the same level of heat input (H). Results and discussion Corrosion resistance of the coatings for PTA-P and GMAW Table 1 shows the results of Experiments 2 and 3 in the PTA-P and GMAW 4 and 5.
Tabela 1 Experiment 2 4 3 5
Process PTA-P MIG PTA-P MIG
H(KJ/cm) 18,99 18,99 8,34 8,34
D% 15,33 24,88 5,02 12,77
%Fe 15,18 17,74 3,60 5,54
Rp (KΩ) 578,48 375,56 151,77 130,85
Ecorr(V) -0,1897 -0,2124 -0,2877 -0,3447
H- welding power;D%- Dilution;%F- Percentage of Iron;Rp- Resistance polarization e Ecorr- Corrosion potential
Figure 1(a) shows the curves PPL of experiments 2(PTA-P) and 4(GMAW) with welding energy, H, same 18.99 kJ/cm. Figure 1(b) shows the curves PPL of experimental 3 (PTA-P) and 5 (GMAW) with welding energy, H, same 8.34 kJ/cm.
(a)
(b)
Fig. 1- (a) Polarization curve of the experiments by 2-PTA- and 4 for GMAW e (b) Polarization curve of the experiments by 3-PTA- and 5 for GMAW.
Figures 1(a) and (b), the curves of the experiments 2 e 3 obtained by PTA-P, shift the corrosion potential to more positive potentials by comparing the GMAW. This shift to the right indicates that the more positive the corrosion potential, Ecorr, is more delayed the onset of corrosion. Results also show that the lower the corrosion current (Icorr), the lower the dissolution of the coating, it confirms the higher values of the polarization resistance of the experiments 2 and 3 deposited by PTA-P shown in Table 1. Experiments with lower dilution and iron, are less susceptible to corrosion, as well as the main responsible for the start of iron corrosion. Conclusions The results of the analysis of corrosion of coatings, it was found that the deposited by PTA-P showed higher values than applied for GMAW, indicating higher corrosion resistance of the coatings applied by this process, welding. References [1]Alfaro S.C. A, Carvalho G.C., Melo Junior, S.A. Stand off’s indirect estimation in GMAW. Journal of Materials Processing Technology. 157–158 (2004) 3–7.
Keywords: Coating, PTA-P, GMAW, Corrosion. Introduction The application of coatings for welding is very attractive to offer protection to the substrate and good metallurgical union. The PTA-P (Plasma Powder Transfered) and GMAW (Gas Metal Arc Welding) processes have great importance in the field of manufacture and repair through coatings, for providing a good quality of welds and high deposition rate and welding speed . For corrosion protection has been widely using nickel superalloys, Inconel 625, like coat, through deposition by welding [Alfaro; Carvalho; Melo Júnior]. The aim of this work, the comparison of the corrosion resistance of the coatings of nickel base alloy Inconel 625 deposited by PTA and PGMAW steel API 5L X70. Experimental part The PTA-P and GMAW were used for deposits in plate steel API5LX70, (145x60x19) mm, using a nickel alloy Inconel 625 was a factorial design 2³ used to check the influence of the process variables: voltage, current, feed speed and welding speed (Vs) the corrosion analysis performed using the technique of linear potentiodynamic polarization (PPL). This analysis was done in both welding processes, the samples with the same level of heat input (H). Results and discussion Corrosion resistance of the coatings for PTA-P and GMAW Table 1 shows the results of Experiments 2 and 3 in the PTA-P and GMAW 4 and 5.
Tabela 1 Experiment 2 4 3 5
Process PTA-P MIG PTA-P MIG
H(KJ/cm) 18,99 18,99 8,34 8,34
D% 15,33 24,88 5,02 12,77
%Fe 15,18 17,74 3,60 5,54
Rp (KΩ) 578,48 375,56 151,77 130,85
Ecorr(V) -0,1897 -0,2124 -0,2877 -0,3447
H- welding power;D%- Dilution;%F- Percentage of Iron;Rp- Resistance polarization e Ecorr- Corrosion potential
Figure 1(a) shows the curves PPL of experiments 2(PTA-P) and 4(GMAW) with welding energy, H, same 18.99 kJ/cm. Figure 1(b) shows the curves PPL of experimental 3 (PTA-P) and 5 (GMAW) with welding energy, H, same 8.34 kJ/cm.
(a)
(b)
Fig. 1- (a) Polarization curve of the experiments by 2-PTA- and 4 for GMAW e (b) Polarization curve of the experiments by 3-PTA- and 5 for GMAW.
Figures 1(a) and (b), the curves of the experiments 2 e 3 obtained by PTA-P, shift the corrosion potential to more positive potentials by comparing the GMAW. This shift to the right indicates that the more positive the corrosion potential, Ecorr, is more delayed the onset of corrosion. Results also show that the lower the corrosion current (Icorr), the lower the dissolution of the coating, it confirms the higher values of the polarization resistance of the experiments 2 and 3 deposited by PTA-P shown in Table 1. Experiments with lower dilution and iron, are less susceptible to corrosion, as well as the main responsible for the start of iron corrosion. Conclusions The results of the analysis of corrosion of coatings, it was found that the deposited by PTA-P showed higher values than applied for GMAW, indicating higher corrosion resistance of the coatings applied by this process, welding. References [1]Alfaro S.C. A, Carvalho G.C., Melo Junior, S.A. Stand off’s indirect estimation in GMAW. Journal of Materials Processing Technology. 157–158 (2004) 3–7.
