Role of Surface Cracking and Recast Layer Deposition …
85
Ay et al. [11] experienced micro-cracks on the EDMed surface during microdrilling of Inconel 718 using a copper-tungsten (Cu-W) electrode. The occurrence of
micro-cracks was reduced by decreasing the peak current as well as pule duration.
The authors concluded that the existence of globules, pockmarks and micro-cracks
caused inferior surface integrity of the EDMed specimen. Moreover, the aforementioned machining-induced surface irregularities greatly depend on EDM process
conditions. Rajesha et al. [12] studied EDMed surface integrity in the context of
machining of Inconel 718 using a hollow copper electrode. The authors investigated the influence of process parameters on surface micro-cracks and the depth of
the recast layer. The recast layer exhibited higher hardness as it contained carbide
compounds. Carbide formation was due to the decomposition of dielectric media.
Rajendran et al. [15] investigated mechanisms involved in the formation of surface
cracks as well as recast layer on the EDMed surface of the steel. Authors concluded
that tool/work material properties, electrode wear and recast layer significantly influenced surface cracking. Çayda¸ s and Hasçalik [9] conducted EDM experiments on
Ti–6Al–4V using a graphite electrode and evaluated the influence of EDM parameters
on the occurrence of electrode wear and recast layer formation. The authors noticed
that the peak current was the most influential parameter affecting EDM responses.
Pradhan et al. [14] found that higher values of peak current as well as pulse duration
damaged topographical features of EDMed surface, including the formation of thick
recast layer while machining of Ti–6Al–4V with a brass electrode. Yilmaz et al. [16]
reported ill-EDMed surface morphology as described by craters, pockmarks, surface
cracks, and globules of debris during EDM of Ni and Ti-based superalloys. Microhardness profile exhibited a decreasing trend of hardness values as moving away from
the machined surface due to the alteration in microstructure of the heat-affected zone
(HAZ). According to Newton et al. [10], EDMed/Wire-EDMed surface consisted of
three different zones, just beneath the machined surface: recast layer, HAZ and base
material. HAZ might contain micro-cracks, impurities, altered microstructure due to
the quenching effect, and other unwanted features, which in turn degrade the life of
the machined product when the part product is put in service. Therefore, in-depth
investigation is indeed required to minimize the severity of surface cracking along
with recast layer formation on the EDMed work surface. According to D’Urso et al.
[4], thermal conductivity, melting point and electrical resistivity of the electrode,
as well as the workpiece, play crucial roles during the EDM process. From the
literature, it was noticed that a substantial volume of work was reported on EDM
performance while exploring copper, brass, graphite and tungsten carbide electrodes.
Electrode material also influences machined surface integrity. Therefore, the current
work examines the performance of copper–nickel (90% Cu and 10% Ni) electrodes
during EDM on Inconel 825 workpiece. EDM performance is assessed in the purview
of topographical features of the machined surface, including crack density, recast
layer thickness and microhardness. Finally, the study compares the obtained results
with that of the traditional copper electrode.
85
Ay et al. [11] experienced micro-cracks on the EDMed surface during microdrilling of Inconel 718 using a copper-tungsten (Cu-W) electrode. The occurrence of
micro-cracks was reduced by decreasing the peak current as well as pule duration.
The authors concluded that the existence of globules, pockmarks and micro-cracks
caused inferior surface integrity of the EDMed specimen. Moreover, the aforementioned machining-induced surface irregularities greatly depend on EDM process
conditions. Rajesha et al. [12] studied EDMed surface integrity in the context of
machining of Inconel 718 using a hollow copper electrode. The authors investigated the influence of process parameters on surface micro-cracks and the depth of
the recast layer. The recast layer exhibited higher hardness as it contained carbide
compounds. Carbide formation was due to the decomposition of dielectric media.
Rajendran et al. [15] investigated mechanisms involved in the formation of surface
cracks as well as recast layer on the EDMed surface of the steel. Authors concluded
that tool/work material properties, electrode wear and recast layer significantly influenced surface cracking. Çayda¸ s and Hasçalik [9] conducted EDM experiments on
Ti–6Al–4V using a graphite electrode and evaluated the influence of EDM parameters
on the occurrence of electrode wear and recast layer formation. The authors noticed
that the peak current was the most influential parameter affecting EDM responses.
Pradhan et al. [14] found that higher values of peak current as well as pulse duration
damaged topographical features of EDMed surface, including the formation of thick
recast layer while machining of Ti–6Al–4V with a brass electrode. Yilmaz et al. [16]
reported ill-EDMed surface morphology as described by craters, pockmarks, surface
cracks, and globules of debris during EDM of Ni and Ti-based superalloys. Microhardness profile exhibited a decreasing trend of hardness values as moving away from
the machined surface due to the alteration in microstructure of the heat-affected zone
(HAZ). According to Newton et al. [10], EDMed/Wire-EDMed surface consisted of
three different zones, just beneath the machined surface: recast layer, HAZ and base
material. HAZ might contain micro-cracks, impurities, altered microstructure due to
the quenching effect, and other unwanted features, which in turn degrade the life of
the machined product when the part product is put in service. Therefore, in-depth
investigation is indeed required to minimize the severity of surface cracking along
with recast layer formation on the EDMed work surface. According to D’Urso et al.
[4], thermal conductivity, melting point and electrical resistivity of the electrode,
as well as the workpiece, play crucial roles during the EDM process. From the
literature, it was noticed that a substantial volume of work was reported on EDM
performance while exploring copper, brass, graphite and tungsten carbide electrodes.
Electrode material also influences machined surface integrity. Therefore, the current
work examines the performance of copper–nickel (90% Cu and 10% Ni) electrodes
during EDM on Inconel 825 workpiece. EDM performance is assessed in the purview
of topographical features of the machined surface, including crack density, recast
layer thickness and microhardness. Finally, the study compares the obtained results
with that of the traditional copper electrode.