Unraveling and Mapping the Mechanisms for Near-Surface Microstructure Evolution in CuNi Alloys under Sliding

Abstract

The origin of friction and wear in polycrystalline materials is intimately connected with their microstructural response to interfacial stresses. Although many mechanisms that govern microstructure evolution in sliding contacts are generally understood, it is still a challenge to ascertain which mechanisms matter under what conditions, which limits the development of tailor-made microstructures for reducing friction and wear.Here, we shed light on the circumstances that promote plastic deformation and surface damage by studying several FCC CuNi alloys subjected to sliding with molecular 1 Page 1 of 33 ACS Paragon Plus Environment ACS Applied Materials & Interfacesdynamics simulations featuring tens of millions of atoms. By analyzing the depth-and time-dependent evolution of the grain size, twinning, shear, and the stresses in the aggregate, we derive a deformation mechanism map for CuNi alloys. We verify the predictions of this map against focused ion beam images of the near-surface regions of CuNi alloys that were experimentally subjected to similar loading conditions. Our results may serve as a tool for finding optimum material compositions within a specified operating range.

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

“…In all cases, the presence of 600 K leads to a reduction in s Figure 4d, independently of alloy composition or temperature, share the same pre-factor s 0 = 1800 nm introduced in Ref. [23] for 300 K, which is more evidence that this quantity, which corresponds to a typical grain boundary length, only depends on the grain structure, morphology, and size of the sample, but not on load, temperature, or composition.…”

“…Higher Ni contents lead to an increase in the normal pressure that is necessary to generate a certain number of GB or TB atoms, as was shown in detail in Ref. [23]. When comparing the results for the two different temperatures, the effect of temperature on the GB and TB fraction can be clearly seen.…”

“…Interactions within the fcc CuNiX samples, where X is the atomic percentage of Ni (0%, 5%, 25%, 60%, and 100%), are governed by an embedded atom potential from [30]. All alloy systems were initially prepared by heat treatment and cooling to 300 K as described in [23]. The systems were subsequently linearly heated to 600 K over 200 ps and then kept at 600 K for another 200 ps before sliding.…”

“…It was already demonstrated in the early 2000s that plastic deformation processes like dislocation generation can be reproduced with polycrystalline MD models [19][20][21], which have the advantage that they do not require parameters such as activation energies for structural changes like grain growth, or the assumption of constitutive material laws as in continuum mechanics [22]. High-performance computing nowadays allows us to analyze the dynamics of systems consisting of tens to hundreds millions of atoms over periods of some 10 ns, evolving them into tools for solving surface and production engineering problems [23,24].…”

“…In recent work, the authors have derived a deformation mechanism map for CuNi alloys at room temperature from MD simulations [23]. CuNi alloys have numerous applications such as in shipbuilding, offshore oil production, power plants [28], electrical sliding contacts [29], and they are used in a similar fashion as CuAl coatings in tribological interfaces of jet engine compressors [15].…”