Q & A with Prof. Anup Keshri from IIT Patna (India)

The plasma spray coatings laboratory (Link) at Indian Institute of Technology, Patna, headed by Prof. Anup Kumar Keshri is a pioneer in plasma sprayed 1-D & 2-D nanomaterials, specifically CNT's and graphene reinforced composite coatings for wear, corrosion and thermal barrier applications. 

In this interview with Prof. Anup Kumar Keshri, he shares his experience and novel findings on developing nano-composite coatings using thermal spray processing.

Q1 What are the research challenges that you are working on ?

We are working to develop stronger and tougher 1-D & 2-D nanomaterials (CNT, GNP, BNNT etc.) reinforced plasma sprayed ceramic (TiN, CeO₂, Al₂O₃, etc.) composite coatings that minimize wear while still offering a low coefficient of friction (CoF) at high temperatures (< 873 K), something that is an Achilles heel for conventional ceramic coatings. In our latest work, we were able to produce single and multi-layer graphene from a low cost graphite raw powder based on in-situ exfoliation in a thermal spray process. This technique can significantly reduce costs and drive technology adoption.

Figure 1. TiN-GNP composite coating synthesis using plasma spray

Q2 Can you share some major findings and insights ?

The most recent finding includes, graphene nanoplatelets (GNPs: 1–2 wt. %) reinforced TiN composite coating fabricated over titanium alloy using a reactive shroud plasma spraying technique. The addition of GNP in TiN matrix reduced the wear rate and friction of the coatings upto 873 K. GNP was present on the wear track even at 873 K and their multi-layer structure imparted long term lubricity to the coating. This phenomena was also observed in GNP-reinforced CeO₂ coatings, with maximum reduction in wear rate (260%) and COF (26%) at 873 K. Our technologies could pave a new path for designing coatings operating at high temperature.

Figure 2. As deposited and high temperature tested coatings

Q3 What are the gaps and development needs in evaluating tribological characteristics ?

"Tribology testing of composite materials for high temperature needs substantial advancement in instrumentation and in-situ techniques. " (Link)

Though, we tested composite coatings upto 800°C, instrumentation capabilities should allow testing temperature ≥ 1000°C. In-situ characterization of the wear volume and simultaneous measurement of flash temperature at the contact will better assist understanding the high temperature interactions.

"To address gaps in the current market technologies,  UniTest was developed as an open platform with 3D profilometry and insitu sensors for tribology research." (Link)

Figure 3. UniTest with Profilometer and embedded sensors for in-situ tribology research

Q4 What is your experience with Ducom high temperature tribometers ?

We are very happy with the Ducom high temperature tribometer (Link), which helped to evaluate our novel materials and their characteristics. The friction data was quite repeatable (< 10 % variation) over a wide ranges of temperatures and helped us differentiate and optimize the chemistry and % of nanomaterials. The ability to cover different load ranges (loads 1N or lower) for thin graphene coatings and higher (200N or more) for thicker wear resistant coatings while still offering accurate friction is appealing for material scientists for diverse research.

The group's work has been funded by the Govt.of India (DST, NRB, DRDO, others) and supported by the industry (Tata Steel, Carborundum Universal Limited, Associate Plasmatron).

References -

1. Microstructure, mechanical and high temperature tribological behaviour of graphene nanoplatelets reinforced plasma sprayed titanium nitride coating, Journal of the European Ceramic Society, 40, (2020) 660-671, Shreshtha Ranjan, Biswajyoti Mukherjee, Aminul Islam, Krishna Kant Pandey, Rohit Gupta, Anup Kumar Keshri*
   
2. Peculiar high temperature tribological behaviour of plasma sprayed graphene nanoplatelets reinforced cerium oxide coatings, Ceramics International, 47 (2021) 17809-17812, Dipak Kumar Shukla, Biswajyoti Mukherjee, Aminul Islam, Anup Kumar Keshri*
   
3. Ultra-Fast, Chemical-Free, Mass Production of High Quality Exfoliated Graphene ACS Nano (2021), 15, 1, 1775–1784, Aminul Islam, Biswajyoti Mukherjee, Krishna Kant Pandey, and Anup Kumar Keshri*