Metal matrix nanocomposites in tribology: Manufacturing, performance, and mechanisms

Metal matrix nanocomposites(MMNCs)become irreplaceable in tribology industries,due to their supreme mechanical properties and satisfactory tribological behavior.However,due to the dual complexity of MMNC systems and tribological process,the anti-friction and anti-wear mechanisms are unclear,and the subsequent tribological performance prediction and design of MMNCs are not easily possible:A critical up-to-date review is needed for MMNCs in tribology.This review systematically summarized the fabrication,manufacturing,and processing techniques for high-quality MMNC bulk and surface coating materials in tribology.Then,important factors determining the tribological performance(mainly anti-friction evaluation by the coefficient of friction(CoF)and anti-wear assessment with wear rate)in MMNCs have been investigated thoroughly,and the correlations have been analyzed to reveal their potential coupling/synergetic roles of tuning tribological behavior of MMNCs.Most importantly,this review combined the classical metal/alloy friction and wear theories and adapted them to give a(semi-)quantitative description of the detailed mechanisms of improved anti-friction and anti-wear performance in MMNCs.To guarantee the universal applications of these mechanisms,their links with the analyzed influencing factors(e.g.,loading forces)and characteristic features like tribo-film have been clarified.This approach forms a solid basis for understanding,predicting,and engineering MMNCs’tribological behavior,instead of pure phenomenology and experimental observation.Later,the pathway to achieve a broader application for MMNCs in tribo-related fields like smart materials,biomedical devices,energy storage,and electronics has been concisely discussed,with the focus on the potential development of modeling,experimental,and theoretical techniques in MMNCs’tribological processes.In general,this review tries to elucidate the complex tribo-performances of MMNCs in a fundamentally universal yet straightforward way,and the discussion and summary in this review for the tribological performance in MMNCs could become a useful supplementary to and an insightful guidance for the current MMNC tribology study,research,and engineering innovations.

Effects of metal binder on the microstructure and mechanical properties of Al2O3-based micro-nanocomposite ceramic tool material

The Al_2O_3-（W,Ti）C composites with Ni and Mo additions varying from 0vol% to 12vol% were prepared via hot pressing sintering under 30 MPa. The microstructure was investigated via X-ray diffraction（XRD） and scanning electron microscopy（SEM） equipped with energy dispersive spectrometry（EDS）. Mechanical properties such as flexural strength, fracture toughness, and Vickers hardness were also measured. Results show that the main phases A12O3 and（W,Ti）C were detected by XRD. Compound Mo Ni also existed in sintered nanocomposites. The fracture modes of the nanocomposites were both intergranular and transgranular fractures. The plastic deformation of metal particles and crack bridging were the main toughening mechanisms. The maximum flexural strength and fracture toughness were obtained for 9vol% and 12vol% additions of Ni and Mo, respectively. The hardness of the composites reduced gradually with increasing content of metals Ni and Mo.

Effects of SiC Nanoparticle Content on the Microstructure and Tensile Mechanical Properties of Ultrafine Grained AA6063-SiC_(np) Nanocomposites Fabricated by Powder Metallurgy

Ultrafine grained AA6063-SiCnpnanocomposites with 1, 5 and 10 vol.% SiCnphave been fabricated by a novel powder metallurgy process. This process combines high energy ball milling of a mixture of 6063 alloy granules made from machining chips and Si C nanoparticles and thermomechanical powder consolidation by spark plasma sintering and hot extrusion. The microstructure and tensile mechanical properties of the samples were investigated in detail. Increasing the Si C nanoparticle content from 1 to 10 vol.%,the yield strength and ultimate tensile strength increased from 296 and 343 MPa to 545 and 603 MPa respectively, and the elongation to fracture decreased from 10.0%, to 2.3%. As expected, a higher Si C nanoparticle content generates a stronger inhibiting effect to grain growth during the thermomechanical powder consolidation process. Analysis of the contributions of various strengthening mechanisms shows that a higher Si C nanoparticle content leads to a higher contribution from nanoparticle strengthening, but grain boundary strengthening still makes the largest contribution to the strength of the nanocomposite.When the Si C nanoparticle content increased to 10 vol.%, the failure of the nanocomposite was initiated at weakly-bonded interparticle boundaries(IPBs), indicating that with a high flow stress during tensile deformation, the failure of the material is more sensitive to the presence of weakly-bonded IPBs.

Chemical, mechanical, and thermal expansion properties of a carbon nanotube-reinforced aluminum nanocomposite

In the present study,the chemical and mechanical properties and the thermal expansion of a carbon nanotube（CNT）-based crystalline nano-aluminum（nano Al） composite were reported.The properties of nanocomposites were tailored by incorporating CNTs into the nano Al matrix using a physical mixing method.The elastic moduli and the coefficient of thermal expansion（CTE） of the nanocomposites were also estimated to understand the effects of CNT reinforcement in the Al matrix.Microstructural characterization of the nanocomposite reveals that the CNTs are dispersed and embedded in the Al matrix.The experimental results indicate that the incorporation of CNTs into the nano Al matrix results in the increase in hardness and elastic modulus along with a concomitant decrease in the coefficient of thermal expansion The hardness and elastic modulus of the nanocomposite increase by 21%and 20%,respectively,upon CNT addition.The CTE of CNT/A1 nanocomposite decreases to 70%compared with that of nano Al.

Effect of Nano-sized B4C Addition on the Mechanical Properties of ZA27 Composites

In order to understand the influence of nano-sized B4C additive on ZA27 alloy, mechanical and physical properties of ZA27-B4C nanocomposites were investigated in terms of B4C content. While physical properties were determined in terms of microstructural studies, density and porosity tests, mechanical properties were determined in terms of ultimate tensile strength（UTS） and hardness experiments. Morphological and microstructural studies were carried out with scanning electron microscopy（SEM）. The experimental results indicate that nano-sized B4C can be used to enhance the mechanical properties of ZA27 alloy effectively. The highest mechanical performance can be obtained at ZA27-0.5% B4C（in weight） nanocomposite with values of tensile strength（247 MPa） and hardness（141,18 BH） and low partial porosity（0.5%）. After a pick point, increasing B4C ratio may cause the formation of agglomeration in grain boundaries, that＇s why density, tensile strength, and hardness values are declined.