Influence of powder-mixed EDM on surface morphology and metallurgical alterations of Inconel 625

ABSTRACT

Current research work aims at improving the surface integrity characteristics of Inconel 625 (a nickel-based super alloy) during electric discharge machining (EDM) process. Powder particles such as graphite, aluminium and silicon were added to kerosene dielectric during the EDM process to enhance the surface integrity characteristics. A specially designed and fabricated dielectric recirculating system was attached to the EDM setup to carry the experiments. Design of experiments was carried out using response surface methodology. Influence of process variables such as powder material, particle concentration in dielectric, peak current, pulse on time, duty cycle and gap voltage was investigated on surface integrity characteristics of machined specimens. Mixing of powder particles with dielectric resulted in reduced surface cracking, recast layer thickness and surface microhardness. While EDM with conventional dielectric primarily demonstrated FCC structure of γ-phase of Inconel 625 along with some δ(Ni₃Nb) phase, powder-mixed EDM has promoted formation of carbides of Ni, Cr and Mo along with Ni₃Nb from Inconel 625. Addition of powder with dielectric also caused reduction in crystallite size as well as lattice strain due to enlargement of crater while maintaining uniform discharge over a large area.

KEYWORDS:

• Inconel 625
• microstructure
• powder-mixed EDM
• recast layer
• surface crack density
• surface morphology

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

Data available on request from the authors.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Notes on contributors

Gangadharudu Talla

Dr. Gangadharudu Talla is an Assistant Professor of Engineering at National Institute of Technology Warangal, India. He received his B.E. from Andhra University Visakhapatnam, India in 2007, M.Tech from Visvesvaraya National Institute of Technology Nagpur, India in 2010 and his Ph.D. degree from National Institute of Technology Rourkela, India in 2016. He had taught at National Institute of Technology Andhra Pradesh from 2016 to 2019, before joining as Assistant Professor at National Institute of Technology Warangal, India in 2019. His research contributions are in the field of unconventional machining of high strength materials, powder metallurgy and hybrid machining. He is currently working on dry-EDM and additive manufacturing of advanced materials.

S. Gangopadhyay

Dr. S Gangopadhyay is an Associate Professor of Mechanical Engineering at Indian Institute of Technology Bhilai, India. He received his B.E. from Jawaharlal Nehru College of Engineering, Aurangabad, India in 2002, M.Tech from West Bengal University of Technology, India in 2000 and his Ph.D. degree from Indian Institute of Technology, Kharagpur, India in 2009. He had taught at National Institute of Technology Rourkela from 2009 to 2017, before joining as Associate Professor at Indian Institute of Technology Bhilai, India in 2017. He was a BOYSCAST Fellow at University of Leoben, Austria from 2011 to 2012. His research contributions are in the field of Advanced PVD coatings for cutting tools, Metal cutting, Non- traditional machining, Micromachining, Surface texturing and Thin film tribology. He is currently working on advanced PVD coating for machining Ni-based superalloys and additive manufacturing of a functionally graded coating for environment-friendly application.

Chandan Kumar Biswas

Dr. Chandan Kumar Biswas is a Professor of Mechanical Engineering at National Institute of Technology Rourkela, India. He received his B.Tech. from National Institute of Technology Rourkela, India in 1984, M.Tech and Ph.D. degrees from Indian Institute of Technology, Kharagpur, India in 1985 and 1998 respectively. He has been teaching at National Institute of Technology Rourkela, India since 1986. He was also an Associate Professor at Universiti Teknologi Petronas, Ipoh, Malaysia from 2013 to 2016. His research contributions are in the field of Non Conventional Machining and Micro Manufacturing. He is currently working on manufacturing of biomedical implants and biopolymer coatings.