Comparison of corrosion behavior between fusion cladded and explosive cladded Inconel 625/plain carbon steel bimetal plates

doi:10.1016/j.matdes.2012.06.053

Materials & Design

Volume 43, January 2013, Pages 467-474

https://doi.org/10.1016/j.matdes.2012.06.053 Get rights and content

Abstract

One of the main concerns in cladding Inconel 625 superalloy on desired substrates is deterioration of corrosion resistance due to cladding process. The present study aims to compare the effect of fusion cladding and explosive cladding procedures on corrosion behavior of Inconel 625 cladding on plain carbon steel as substrate. Also, an attempt has been made to investigate the role of load ratio and numbers of fusion layers in corrosion behavior of explosive and fusion cladding Inconel 625 respectively. In all cases, the cyclic polarization as an electrochemical method has been applied to assess the corrosion behavior. According to the obtained results, both cladding methods aggravate the corrosion resistance of Inconel 625. However, the fusion cladding process is more detrimental to nonuniform corrosion resistance, where the chemical nonuniformity of fusion cladding superalloy issuing from microsegregation, development of secondary phases and contamination of clad through dilution hinders formation of a stable passive layer. Moreover, it is observed that adding more fusion layers can enhance the nonuniform corrosion resistance of fusion cladding Inconel 625, though this resistance still remains weaker than explosive cladding superalloy. Also, the results indicate that raising the impact energy in explosive cladding procedure drops the corrosion resistance of Inconel 625.

Highlights

► Both explosive and fusion cladding aggravate the corrosion resistance of Inconel 625. ► Fusion cladding is more detrimental to nonuniform corrosion resistance. ► Single-layered fusion coat does not show any repassivation ability. ► Adding more layers enhance the corrosion resistance of fusion cladding Inconel 625. ► High impact energy spoils the corrosion resistance of explosive cladding Inconel 625.

Introduction

Despite the fact that Inconel 625 as a nickel based superalloy possesses a great corrosion resistance [1], the high production cost has restricted the individual application of this alloy. As a result, cladding procedures are applied to cover economic materials by Inconel superalloy. Fusion cladding conducted by various methods such as fusion welding procedures are the most common method due to flexibility and availability. Besides fusion cladding methods, explosive cladding as a solid state process is a potential method to fabricate Inconel 625-substrate bimetal plates.

The whole procedure of explosive cladding can be summarized in following steps. As Fig. 1 depicts the parallel set up for explosive cladding of plates, the cladding plate (flyer plate) lies on the substrate (parent plate) with a uniform predetermined air gap called stand-off distance (d). Also, a uniform thickness of proper explosive by a known velocity of detonation (V_D = the velocity of advancement of explosion front) will be laid on the flyer plate. The mass ratio of explosive to the flyer plate is called load ratio (R) which plays an important role in the explosive cladding procedure. By detonating explosive, the flyer plate accelerates towards parent plate through great pressure released by explosion. The flyer plate collides with the parent plate obliquely by a collision angle of β and impact velocity of VF (Fig. 1). As a result of intense oblique impact, the contaminant surface layer of plates will be removed through formation of a jet. Higher load ratios and/or longer stand-off distances yield higher impact velocities at a fixed detonation velocity, and therefore raise the possibility of jet formation. A pure metallic contact surface issuing from the jet formation phenomenon along great impact pressure bringing the gap between free surface of plates to atomic distances results in metallic bonding of flyer and parent plates [2].

The main concern in cladding the Inconel superalloy is minimizing the deterioration of corrosion resistance through cladding procedure. The alternation of chemical composition and microstructure, formation of secondary phases and development of residual stresses are some of the commonly known causes which are detrimental in aggravating the corrosion resistance of all fusion and solid state cladding materials [3], [4], [5]. However, the level of this deterioration varies depending on cladding method and utilized parameters, and corrosion resistance must be evaluated for each specific cladding case by means of corrosion tests. The corrosion tests are based on mass loss or electrochemical behavior of materials. The electrochemical methods can characterize the localized corrosion attacks besides a precise evaluation of uniform corrosion rate [6], [7]. Also, the electrochemical methods are faster, and can be conducted on small selected surfaces. Tafel polarization and cyclic polarization are two main electrochemical methods utilized to study the corrosion behavior of materials, where the former one is usually carried out to probe the uniform corrosion attack, while the latter one is used to study localized corrosion attacks [8].

The present study aims to compare the corrosion behavior of multi-layered fusion cladded and explosive cladded Inconel 625/plain carbon steel bimetal plates along with providing logical reasons for observations. Due to the formation of a thin passive oxide layer on nickel based superalloys exposed to corrosive media, these alloys are prone to localized corrosion attacks, where local damage of a passive layer initiates the localized corrosion [6]. Therefore, the cyclic polarization has been chosen to investigate the corrosion behavior of Inconel 625 and evaluate the localized corrosion characteristics such as passivation current (IP) (at which the passivation layer forms, and corrosion current almost becomes independent of voltage), breakdown potential (at which the defects start to initiate in the protective layer) and protection potential (at lower potentials than protection potential the damage nuclei will heal). Also, an attempt has been made to probe the role of load ratio and numbers of cladding layers in corrosion behavior of explosive cladded plates and fusion cladded bimetals respectively. The outcomes can be useful in selecting the proper design and procedure for cladding of Inconel 625 on plain carbon steel.

Section snippets

Experimental details

In all explosive cladded samples, Inconel 625 plate with dimensions of 150 × 100 × 3 mm was clad on ASTM A517 low carbon steel plate with dimensions of 130 × 80 × 20 mm. The chemical composition of materials measured by quantometer is listed in Table 1. Also, both plates were chosen in annealed condition to avoid likely effect of material texture on results. In order to remove coarse contaminants from contact surfaces, the plates were grinded by emery papers up to 600 grade. The uniform blend of Anfo

Results and discussion

In electrochemical analysis for corrosion behavior of material, the passivation current density, the breakdown potential and repassivation potential (protection potential) play a primary role in evaluation of corrosion resistance. Formation of a protective layer at low passivation current densities hinders the severe loss of material at higher current densities, and consequently can be interpreted as a positive characteristic in uniform corrosion resistance. However, any damage to this layer

Conclusions

According to the obtained results, although the fusion cladding method and the explosive cladding process both spoil the uniform corrosion resistance of Inconel 625 superalloy, the fusion cladding is more detrimental to nonuniform corrosion resistance, where no protection potential exists for a single-layered fusion layer. Despite the fact that adding more fusion layers can make repassivation potential appear, the safe range of electrochemical potential in which damage nuclei on the passive

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Technical ReportComparison of corrosion behavior between fusion cladded and explosive cladded Inconel 625/plain carbon steel bimetal plates

Abstract

Highlights

Introduction

Section snippets

Experimental details

Results and discussion

Conclusions

J Nucl Mater

J Mater Process

Mater Sci Eng A

Mater Sci Eng

Mater Des

Mater Des

Mater Des

Mater Sci Eng A

Explosive welding, forming and compaction

Technical Report
Comparison of corrosion behavior between fusion cladded and explosive cladded Inconel 625/plain carbon steel bimetal plates