Ilaksh Adlakha

Hydrogen embrittlement limits the service life of various metallic components by causing a transition from a ductile to a brittle failure of inherently ductile alloys. In this work, using first-principles calculations, the effect of interstitial hydrogen on the ideal shear strength across various metals (Al, Ni, Fe, Nb, Ti, and Zr) and its implications on plasticity are discussed. The presence of hydrogen led to a volumetric expansion, which in turn had a key role in the observed shear strength response of cubic metals. However, in the case of HCP metals, the chemical contributions also have a significant part in the observed shear strength response. The interstitial hydrogen atom interacts strongly with valence d orbital metals (Ni, Fe, Nb, Ti, and Zr). Based on the Peierls-Nabarro framework, the presence of interstitial hydrogen reduces the Peierls stress across all the metals examined here. Finally, these findings provide insights to comprehensively understand hydrogen embrittlement.

Magnesium alloys have drawn considerable attention for several engineering applications, owing to their excellent properties like low density and high specific strength. The room temperature ductility and mechanical properties of Mg are usually enhanced by alloying additions. Based on the thermomechanical processing, the presence of critical concentration of alloying element typically leads to the formation of stable binary intermetallic phases with Mg, thereby distinctly altering the microscopic electrochemical properties of the alloy. However, the secondary intermetallic phases in Mg alloys are typically of sub-micron size; thus, accurate electrochemical characterization is a challenging issue. Using first-principles calculations, the electrochemical behavior of various Mg intermetallics was comprehensively quantified. The electrochemical polarization behavior of the intermetallics was strongly dependent on surface-mediated properties and chemical bonding characteristics. Finally, the computational framework provides an accurate screening tool that can assist in alloy design and development of coatings.

Here the electrochemical and mechanical behavior for different Mg based intermetallics (Mg17Al12, MgZn2, Mg3Nd, Mg2Si, Mg24Y5, Mg2Ca, Mg12Ce, Mg12La, Mg2Cu, and Mg2Sn) was comprehensively quantified. First, a robust thermodynamic framework was developed that utilized first-principles calculations to accurately predict the electrochemical polarization behavior of the Mg based intermetallics. Based on the predicted corrosion potential, apart from Mg2Ca which behaves as an anode to the Mg matrix, the rest of the Mg based intermetallics act as a cathode. The electrochemical polarization behavior of the intermetallics was strongly dependent on surface mediated properties (surface energy and work function) and chemical bonding characteristics. Furthermore, the electrochemical behavior was sensitive to the atomic arrangement on the surface. Based on Bader analysis, it was found that the direction of electron flow between the constituent elements of the intermetallic (towards or away from Mg) strongly influenced the electrochemical behavior. The accurate quantifications of elastic constants for the Mg based intermetallics conclusively clarified the mechanical behavior of Mg2Ca and Mg2Cu. Finally, the computational framework provides an accurate screening tool that can assist in alloy design and development of coatings.