The Effect of Pulse Energy on the Defects and Microstructure of Electro-Spark-Deposited Inconel 718
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INTRODUCTION
ELECTRO-sPARK deposition (ESD) is a process whereby material from a moving electrode is ejected towards the base metal as a result of the generation of pulsed electric arcs between the two which is also known as a spark. During the sparking process, the ejected material is heated up to a partially molten and subsequently solidifies on the substrate thus forming a thin alloying zone with the base material.[1] The deposition of the electrode materials often takes on a macro-structure commonly referred to as a splat. The short duration of the sparking events during ESD processing combined with the intermittent contact between the electrode and the substrate results in very low heat input, hence leading to a minimal alteration to the microstructure of the base metal.[2] Consequently, the ESD process generally results in a minimal impact on the substrate, thus minimizing changes in the microstructure and mechanical properties of the substrate.[3] More recently, the ESD process has also been adopted as a coating process for building up material onto a substrate. Considering
LORENZO MARZARI FELIX, CHARLES C.F. KWAN, and NORMAN Y. ZHOU are with the Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Ave W, Waterloo, ON N2L 3G1, Canada. Contact e-mail: [email protected] Manuscript submitted January 15, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
the nature of the material that can be deposited using ESD, it has been used to provide a coating to improve wear resistance, corrosion resistance of the substrate or even for dimensional restoration.[4] The use of ESD as a coating process has many advantages, including but are not limited to the excellent coating adhesion of the deposited electrode material to the substrate and the minimal effect the process has on the microstructure of the base metal.[2,3] Although using the ESD process as a coating process offers many benefits, the process also has some limitations regarding its applications, such as its low deposition rate and the reproducibility of the coating properties due to the irregular contact geometry.[1,4] Given the minimal effect of the ESD coating processing on the substrate, it is an ideal candidate for coating component and parts where the formation of a heat affected zone (HAZ) is detrimental to its performance. Better yet, a coating of the same material can be used to slowly build up a part back to its intended geometry in a manner similar to additive manufacturing. Precipitation-hardened Ni-base superalloys are a class of material that can benefit from such a process as a way to repair components with minor damages. Currently, damaged components are often repaired by welding a newly casted piece onto the damaged components to reduce the operational cost.[5] However, care must be taken during the welding process to control the formation of the HAZ which may lead to cracking and hence failure of the repaired part. On the other hand, it is theoretically possible to use the ESD process in the place of
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