Atomistic study on the interaction of nitrogen and Mg lattice and the nitride formation in nanocrystalline Mg alloys synthesized using cryomilling process

作者：Nezafati Marjan; Giri Anit; Hofmeister Clara; Cho Kyu; Schneider Matthew M; Zhou Le; Sohn Yongho^*; Kim Chang Soo^*

来源：Acta Materialia, 2016, 115: 295-307.

DOI：10.1016/j.actamat.2016.06.012

• Magnesium alloys
• Nanocrystalline alloys
• Powder processing
• Density functional theory (DFT)
• Transmission electron microscopy (TEM)
• Electron energy-loss spectroscopy (EELS)

Cryomilling is a broadly applied technique to synthesize nanostructured alloys and composites through powder metallurgy (PM) processing. Understanding the interactions between liquid nitrogen and the nanostructured metal powder is important as it can potentially impact the mechanical performance of these materials. In this study, we performed a series of ab initio density functional theory (DFT) computations to examine the interactions of liquid nitrogen and Mg-based matrices and the formation of Mg nitrides. The diffusion energy barriers of nitrogen in the Mg and/or Mg-Al alloys were systematically quantified by calculating the transition state (TS) for the displacement of nitrogen between two neighboring equivalent positions. The TS calculation results indicate that diffusion of N atoms is much easier than that of N-2 molecule in the Mg matrix. It is predicted that at least similar to 0.4 eV is required to overcome the diffusion energy barrier in the Mg matrix. We also quantified the formation energy of Mg nitride in the matrix. The presence of Mg nitride was demonstrated experimentally using transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). In conjunction with the DFT computations and TEM/EELS analysis, we performed analytical calculations for the strain energy introduced during cryomilling to examine the impacts of processing parameters.

• 出版日期2016-8-15