Composition and structure of nitrogen-containing dispersoids in trimodal aluminum metal–matrix composites

Quantification of nitrogen impurity and estimated Orowan strengthening through secondary ion mass spectroscopy in aluminum cryomilled for extended durations

“…According to the aluminum-nitrogen equilibrium phase diagram, there is negligible solubility of nitrogen in aluminum [15], therefore it is not unreasonable to assume that all of the nitrogen incorporated is in the form of either a crystalline aluminum nitride (AlN) or an amorphous domain rich in nitrogen. In previous studies it was found that nitrogen concentration increases with milling time up to 26 hours [9,13]. If nitrogen resides in the aluminum powders as several nanometer-sized dispersoids of crystalline and/or amorphous phases, an increase in milling time would increase the volume fraction of nanoscale dispersoids, and consequently contribute to the Orowan strengthening.…”

“…(hexagonal, hP4 or cubic, cF8), and nitrogen-rich amorphous regions [2,[8][9][10][11][12][13]. Oxide dispersoids form by the breakup of the native oxide on the aluminum powder [10,14].…”

“…In this study, an analytical approach was devised, utilizing secondary ion mass spectrometry (SIMS), to determine the atomic and weight percent of nitrogen in cryomilled aluminum with an assumption that nitrogen resides in AlN or an amorphous domain of equivalent density. This approach was applied to determine nitrogen concentration from 8 to 72 hours cryomilling time using data from previous work with the aluminum and boron carbide (B 4 C) composites [13] and current work utilizing 100% cryomilled nanocrystalline aluminum. The Orowan strengthening contribution was then estimated as a function of cryomilling time.…”

Solid State Processing of Aluminum Matrix Composites Reinforced with Nanoparticulate Materials

“…In addition to the inclusion of aluminum oxide, aluminum carbide is a reaction product remaining after high‐energy milling with most common Process Control Agents (PCAs) − for example, stearic acid or toluene. If the content of aluminum carbides needs to be minimized (hydrophilic nature of these could promote fatigue crack growth of the composite), alternative milling agents can be used, mainly being liquid nitrogen . Although cryomilling is widely studied for dispersion of nanoparticles into aluminum alloys, its industrialization remains challenging.…”

DFT study on the adsorption and absorption behaviors of liquid nitrogen in the Mg nano alloys synthesized from powder metallurgy

“…In addition, it is believed that the liquid nitrogen can lead to the formation of nitrides or other nitrogen-rich phases (i.e., nitrogen-rich dispersoids), which can act as a source for the Orowan strengthening. It has been observed that concentration of nitrogen in the metal increases with increasing mixing time at cryogenic temperature and also that coarsening of the grains decreases with increasing nitrogen concentration during the higher temperature degassing and consolidation processes [15]. It is, therefore, thought that the production of nitrides or other nitrogen-rich phases in the matrix nanograins could be very instrumental in improving the strength of these types of nano alloys/MMNCs as it has been shown that grain size controls the yield stress, ultimate tensile and compressive stress, strain hardening behavior, and strain to failure of bimodal nano alloys [16].…”