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1. PREDICTIVE MODELING OF INORGANIC 3C-SiC FRICTION MATERIALS USING MOLECULAR DYNAMICS SIMULATION

   https://doi.org/10.1615/IntJMultCompEng.2022043612  

   Zhang, Yizhan; LeNeave, Cortney; Yi, Yun-Bo (January 2023, International Journal for Multiscale Computational Engineering)

   Metallic friction materials currently used in industry may adversely impact the environment. Substitutions for metals in friction materials, on the other hand, can introduce operational safety issues and other unforeseeable problems such as thermal-mechanical instabilities. In this work, a molecular dynamics model has been developed for investigating the effects of material composition, density, and surface asperities on the tribological properties of inorganic 3C-SiC under various contact conditions at the atomic level. Predictions on the following results have been made: (1) elastic modulus, (2) tensile strength, (3) thermal conductivity, and (4) friction coefficient. The research findings can help improve the design of metal-free friction materials against thermal-mechanical failures. Parametric studies were performed by varying a number of conditions including (1) ambient temperature, (2) sliding speed, (3) crystal orientation, (4) asperity size, (5) degree of asperity intersection, (6) types of loading, and (7) surface contact. Plastic deformation and material transfer were successfully modeled between two sliding pairs. Some of the computational results were validated against existing experimental data found in the literature. The evaluation of wear rate was also incorporated. The model can easily be extended to deal with other nonmetallic friction composites. 

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2. Computational Predictions and Microwave Plasma Synthesis of Superhard Boron-Carbon Materials

   https://doi.org/10.3390/ma11081279  

   Baker, Paul; Catledge, Shane; Harris, Sumner; Ham, Kathryn; Chen, Wei-Chih; Chen, Cheng-Chien; Vohra, Yogesh (August 2018, Materials)

   Superhard boron-carbon materials are of prime interest due to their non-oxidizing properties at high temperatures compared to diamond-based materials and their non-reactivity with ferrous metals under extreme conditions. In this work, evolutionary algorithms combined with density functional theory have been utilized to predict stable structures and properties for the boron-carbon system, including the elusive superhard BC5 compound. We report on the microwave plasma chemical vapor deposition on a silicon substrate of a series of composite materials containing amorphous boron-doped graphitic carbon, boron-doped diamond, and a cubic hard-phase with a boron-content as high as 7.7 at%. The nanoindentation hardness of these composite materials can be tailored from 8 GPa to as high as 62 GPa depending on the growth conditions. These materials have been characterized by electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, and nanoindentation hardness, and the experimental results are compared with theoretical predictions. Our studies show that a significant amount of boron up to 7.7 at% can be accommodated in the cubic phase of diamond and its phonon modes and mechanical properties can be accurately modeled by theory. This cubic hard-phase can be incorporated into amorphous boron-carbon matrices to yield superhard materials with tunable hardness values. 

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3. Modeling Fretting Wear Resistance and Shakedown of Metallic Materials with Graded Nanostructured Surfaces

   https://doi.org/10.3390/nano13101584  

   Yang, Ting; Venkatesh, T. A.; Dao, Ming (May 2023, Nanomaterials)

   In applications involving fretting wear damage, surfaces with high yield strength and wear resistance are required. In this study, the mechanical responses of materials with graded nanostructured surfaces during fretting sliding are investigated and compared to homogeneous materials through a systematic computational study. A three-dimensional finite element model is developed to characterize the fretting sliding characteristics and shakedown behavior with varying degrees of contact friction and gradient layer thicknesses. Results obtained using a representative model material (i.e., 304 stainless steel) demonstrate that metallic materials with a graded nanostructured surface could exhibit a more than 80% reduction in plastically deformed surface areas and volumes, resulting in superior fretting damage resistance in comparison to homogeneous coarse-grained metals. In particular, a graded nanostructured material can exhibit elastic or plastic shakedown, depending on the contact friction coefficient. Optimal fretting resistance can be achieved for the graded nanostructured material by decreasing the friction coefficient (e.g., from 0.6 to 0.4 in 304 stainless steel), resulting in an elastic shakedown behavior, where the plastically deformed volume and area exhibit zero increment in the accumulated plastic strain during further sliding. These findings in the graded nanostructured materials using 304 stainless steel as a model system can be further tailored for engineering optimal fretting damage resistance. 

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4. Layered 2D Nanomaterials to Tailor Friction and Wear in Machine Elements—A Review

   https://doi.org/10.1002/admi.202101622  

   Marian, Max; Berman, Diana; Rota, Alberto; Jackson, Robert_L; Rosenkranz, Andreas (December 2021, Advanced Materials Interfaces)

   Abstract Recent advances in 2D nanomaterials, such as graphene, transition metal dichalcogenides, boron nitride, MXenes, allow not only to discover several new nanoscale phenomena but also to address the scientific and industrial challenges associated with the design of systems with desired physical properties. One of the great challenges for mechanical systems is associated with addressing friction and wear problems in machine elements. In this review, the beneficial properties of layered 2D materials that enable the control of their tribological behavior and make them excellent candidates for efficient friction and wear reduction in dry‐running and boundary lubricated machine components are summarized. The recent studies highlighting the successful implementation of 2D structures when used as solid lubricant coatings or reinforcement phases in composites for various machine components including sliding and rolling bearings, gears, and seals are overviewed. The examples presented in the studies demonstrate the great potential for 2D materials to address the energy‐saving needs by friction and wear reduction. 

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5. Surface property study of additively manufactured Inconel 625 at room temperature and 510 °C

   https://doi.org/doi.org/10.1016/j.mfglet.2020.10.001  

   Tripathy, Manisha; Munther, Michael; Davami, Keivan; Beheshti, Ali. (October 2020, Manufacturing letters)

   null (Ed.)

   Various mechanical systems are subjected to inherent oscillatory motions often paired with extreme, high-temperature environments resulting in fretting wear. In this work, the fretting wear resistance of additively manufactured Inconel 625 was studied at room and elevated temperatures. In-situ temperature-controlled nanoindentation was employed to further elucidate mechanical property evolution as a function of temperature. The results showed a 30% decrease in near-surface mean hardness at 510 °C compared to room temperature. However, the material exhibited significantly lower wear and coefficient of friction values at high temperatures, attributed to the formation of a compacted, intermediate oxide layer preventing excessive friction and wear. 

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