In recent times, there has been widespread research on nanocrystalline materials (Figure 1) due to their unique physical and mechanical properties, and their exciting potential for industrial applications. However, corrosion of these materials has received very limited research attention.
This prompted Rajiv Kumar, a research scholar with the IITB-Monash Research Academy, to work on a project titled, 'Nanostructured Alloys for Corrosion Resistance', under the supervision of Prof S Parida and Prof V S Raja (IITB), and Prof Raman Singh (Monash University, Australia)
The Academy, which operates a graduate research program in Mumbai, is a Joint Venture between IIT Bombay and Monash University. Research is conducted by scholars in both countries, whilst studying for a dually-badged PhD from both organisations.
Fig 1 : TEM image of nanocrystalline Fe-20Cr-5Al alloy powder
[R. Kumar et al., J. Alloys Compd., 671, 164-169, (2016)]
Metals corrode rapidly at high temperatures, and corrosion resistant alloys are required to arrest this. Ferrous alloys are the most widely used engineering materials, says Rajiv, as they are easy to process and not very expensive. "Ferrous alloys comprising chromium, and aluminium (i.e., Fe-Cr-Al alloys) are used widely for high temperature applications such as heating element wire, furnace tube, and gas turbines. The nanocrystallisation of Fe-Cr-Al alloys has been shown to improve their mechanical and anti-corrosion properties. Such nanocrystalline alloys also have the potential to rein in their cost as they may require considerably less amounts of expensive alloying elements such as chromium."
Stainless steels are the most commonly used corrosion-resistant materials for moderate temperature applications because they instantaneously develop a protective layer of chromium oxide. Common stainless steels require 18-20% chromium for effective development of the protective layer. Chromium content required for the formation of a complete layer of chromium oxide is considerably lower in nanocrystalline materials than for their conventional/microcrystalline counterparts. As a result, stainless steel with a nanocrystalline structure is much more economical.
Expanding on the work he has done so far, Rajiv says, "After oxidation of nanocrystalline and microcrystalline Fe-Cr-Al alloys at high temperature, we found that the oxide layer formed on a microcrystalline alloy was remarkably thicker than that on its nanocrystalline counterpart, suggesting greater oxidation resistance of the latter. Therefore, it can be said that the nanocrystalline alloys exhibit better corrosion resistance at high temperatures than microcrystalline alloys." Rajiv's work has specifically demonstrated the beneficial role of nannocrystalline structure in the case of Al-containing alloys.
"The IITB-Monash Research Academy was conceived as a unique model for how two leading, globally focused academic organisations can come together in the spirit of collaboration to deliver solutions and outcomes to grand challenge research questions facing industry and society," says Prof Murali Sastry, CEO, IITB-Monash Research Academy
What better place to start than helping arrest corrosion?
Research scholar: Rajiv Kumar, IITB-Monash Research Academy
Project title: Nanostructured Alloys for Corrosion Resistance
Supervisors: Prof S Parida and Prof V S Raja (IITB), and Prof Raman Singh (Monash University)
Contact details: firstname.lastname@example.org
This story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.