Mechanics of advanced alloys: Prof. Vijay Vasudevan honours K.A. Padmanabhan @bhadeshia123

Uploaded April 2026 | Updated September 2026, 2 weeks ago

On April 6th, we celebrated the 80th birthday of Professor Kuppuswamy Anantha Padmanabhan and his distinguished contributions to science. To mark the occasion, Professor Vijay Vasudevan of the University of North Texas, USA, talded about the fundamental mechanisms of deformation and phase stability in pioneering alloys.

The presentation highlights the intersection of wonderful physical metallurgy and modern characterisation techniques. By exploring how microstructural features influence the mechanical properties of metals, the lecture honouurs Professor Padmanabhan’s foundational work in superplasticity and structural mechanics while looking toward the future of high-performance alloys.

Mechanics of advanced alloys: Prof. Vijay Vasudevan honours K.A. Padmanabhan

$Steels: overall transformation kinetics In calculating a volume fraction of transformation as a function of time, temperature and chemical composition, it is necessary to possess models for nucleation and growth of each of the product phases, based on their respective mechanisms of transformation. However, this is not sufficient to estimate the volume fraction, because growing particles will eventually collide and the nucleation of new particles cannot occur in already transformed regions. This hard impingment is taken into account in Avrami theory by calculating first, an extended volume where particles can grow into each other, and then correcting that by multiplying by the fraction of untransformed austenite. This theory is then generalised to multiple, simultaneous transformations and applied to continuous cooling transformation. A case study is presented at the end of how to use such knowledge to design a hydrogen-resistant steel. Associated teaching materials can be found on: http://www.phase-trans.msm.cam.ac.uk/teaching.html H. K. D. H. Bhadeshia$

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$Kinetics of niobium carbide precipitation in steels Kinetics and thermodynamics of niobium carbide precipitation in steels Welcome back to the channel! In this lecture, we take a deep dive into the physical metallurgy, thermodynamics, and kinetics of niobium carbide (NbC) precipitation in steels. Very often we think about niobium carbide purely in terms of equilibrium solubility products, but in real-world applications, we need to understand how fast it can precipitate and how it behaves over time. Whether you are a student, a researcher, or a professional metallurgist, this video breaks down the mathematical models and physical phenomena that control phase transformations in steel. Thermodynamics & the effect of Mmnganese: We begin by exploring thermodynamic calculations using databases and how empirical experimental data proves that adding manganese actually increases the solubility of niobium carbide in austenite. Ostwald ripening & coarsening: Discover the history of coarsening, tracing back to Ostwalds 1900 paper on interfacial energy (surface tension) and Geoffrey Greenwoods pioneering theory. Learn exactly why incredibly small particles dissolve while larger particles grow to maintain a constant volume fraction. Diffusion & particle growth: Understand the complexities of local equilibrium at the particle interface. We tackle a major problem in precipitation kinetics: how a particle can grow when carbon diffuses orders of magnitude faster than niobium, and how the ternary phase diagram provides a flat carbon concentration gradient to compensate. Nucleation & impingement: A look at the classic equations for nucleation rates, the crucial role of the number density of nucleation sites, and the beautifully simple Johnson-Mehl-Avrami-Kolmogorov theory for calculating how growing particles collide and impinge on one another. Software modelling & bold predictions: Learn the limitations of using commercial software like Dictra or MatCalc, the danger of simply fitting data without generalised parameters, and how to use these models creatively to make bold predictions—like predicting the formation of room-temperature bainite. Real-world engineering applications: We conclude with an exciting real-world application of phase transformation theory: the design of a brand new, highly resilient steel alloy for the shafts of Rolls-Royce civil aircraft engines. Free resource: Everything discussed in this video regarding phase transformations and kinetics is covered in depth in my book. You can download it entirely free of charge from my website! Also, check out the free biography of Geoffrey Greenwood available to download to learn more about the crazy, pioneering history of materials science. If you found this lecture helpful, please leave a like, subscribe for more materials science deep-dives, and let me know your thoughts in the comments below!$

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Mechanics of advanced alloys: Prof. Vijay Vasudevan honours K.A. Padmanabhan