Thermostat Influence on the Structural Development and Material Removal during Abrasion of Nanocrystalline Ferrite

Abstract

We consider a nanomachining process of hard, abrasive particles grinding on the rough surface of a polycrystalline ferritic work piece. Using extensive largescale molecular dynamics (MD) simulations, we show that the mode of thermostatting, i.e., the way that the heat generated through deformation and friction is removed from the system, has crucial impact on tribological and materials related phenomena. By adopting an electron-phonon coupling approach to parametrize the thermostat of the system, thus including the electronic contribution to the thermal conductivity of iron, we can reproduce the experimentally measured values that yield realistic temperature gradients in the work piece. We compare these results to those obtained by assuming the two extreme cases of only phononic heat conduction and instantaneous removal of the heat generated in the machining interface. Our discussion of the differences between these three cases reveals that although the average shear stress is virtually temperature independent up to a normal pressure of approximately 1 GPa, the grain and chip morphology as well as most relevant quantities depend heavily on the mode of thermostatting beyond a normal pressure of 0.4 GPa. These pronounced differences can be explained by the thermally activated processes that guide the reaction of the Fe lattice to the external mechanical and thermal loads caused by nanomachining.

Shear heating, flow, and friction of confined molecular fluids at high pressure

“…[7][8][9][10] In recent NEMD simulations, Langevin thermostats 59 with a range of coupling times (0.5-50 ps) were tested to reproduce the experimental thermal conductivity of α-Fe surfaces. 64 In the current simulations, the Langevin thermostat in the bottom slab was assigned a coupling time of 0.1 ps, by which a thermal conductiv-ity similar to α-Fe surfaces (as a model for steel) was simulated. 64 In the first set of simulations, the top slab was also given a coupling time of 0.1 ps, yielding symmetrical systems with relatively efficient thermal dissipation.…”

“…64 In the current simulations, the Langevin thermostat in the bottom slab was assigned a coupling time of 0.1 ps, by which a thermal conductiv-ity similar to α-Fe surfaces (as a model for steel) was simulated. 64 In the first set of simulations, the top slab was also given a coupling time of 0.1 ps, yielding symmetrical systems with relatively efficient thermal dissipation. 32 In the second set of simulations, unsymmetrical systems in which one of the surfaces had much lower thermal conductivity compared to steel (e.g.…”

“…This range is similar to that employed in ref. 64 for thermostat parameterisation (0.5-50 ps). Results from only the most extreme case (bottom 0.1 ps, top 100 ps) are shown in the main text, while intermediate results are shown in the ESI.…”

“…In this symmetrical system, both slabs have a thermostat coupling time of 0.1 ps, representing efficient thermal dissipation of α-Fe (as a model for steel). 64 For all of the symmetrical systems, the T profiles are parabolic with the maximum T f in the center of the film and the outer molecular layer of fluid at the same T as the thermostatted Both slabs thermostat coupling time of 0.1 ps (symmetrical system). Note that h is normalized.…”

Effect of Temperature on the Deformation Behavior of Copper Nickel Alloys under Sliding

“…CuNi is an ideal alloy system in which both constituents form an isomorphous system without phase precipitation, where the stacking fault energy varies by a factor of three between pure Cu and Ni, and a fast and reliable force field exists that allows a treatment using MD [30]. For the correctness and transferability of the deformation mechanism map, it is important to achieve temperature gradients that realistically reflect the macroscopic heat conductivity of the sample [31]. Due to the small size of the modeled systems (layer thickness of 40 nm), they can only self-consistently increase their temperature due to friction by 100-150 K at the surface.…”