Structure optimization for improving the strength and ductility of heterogeneous carbon nanotube/Al–Cu–Mg composites

Bimodal carbon nanotube reinforced 2009Al (CNT/2009Al) composites were fabricated by powder metallurgy followed with extrusion. It indicated that the width, length and grain size in the coarse grain (CG) bands increased with the increase of the extrusion temperature, while no obvious grain size change was observed in the ultra-fine grain zones. The bimodal composite showed a double yield phenomenon. The first yield strength which resulted from the yielding of the CG, was similar for all composites extruded with different temperatures. The second yield strength decreased, but the ultimate tensile strength retained stable and the elongation increased with increasing the extrusion temperature. The composite extruded at 470 °C exhibited a 76% ductility increase with nearly no ultimate tensile strength loss as compared to one extruded at 370 °C. The better stress relaxation ability of large-sized grains in the CG bands was believed to be the reason for the good strength-ductility.

Improving ductility of bimodal carbon nanotube/2009Al composites by optimizing coarse grain microstructure via hot extrusion

The limited ductility of carbon nanotubes reinforced Al matrix (CNT/Al) composites hinders their engineering applications, which is an urgent problem to be solved. Herein, texture optimization through hot-rolling was employed to improve the strength-ductility of the CNT/7055Al composites. Microstructural examinations indicate that the composite subjected to extrusion (CNT/7055Al-E) had a bimodal structure with the coarse and ultrafine grains. The composite subjected to extrusion followed by hot-rolling (CNT/7055Al-ER) exhibited a uniform ultrafine grain structure. No further structure damage or aggregation was detected for the CNTs after hot-rolling. The texture analysis demonstrates that the CNT/7055Al-E had a fiber texture, while the CNT/7055Al-ER had a plate texture including {011} , {113} and {215} components with higher texture intensity. Compared with the CNT/7055Al-E, the CNT/7055Al-ER increased twofold in elongation with a slight decrease in strength, which was attributed to the favorable grain orientations, the increased proportion of low angle grain boundaries, as well as the fine and densely distributed precipitates. Further, the mechanical property anisotropy of the composite was weakened after hot-rolling due to the elimination of coarse grain bands.

Enhancing strength-ductility synergy of carbon nanotube/7055Al composite via a texture design by hot-rolling

Achieving prominent strengthening efficiency of graphene nanosheets in Al matrix composites by hybrid deformation

In this study, the effect and characteristics of the laser clad interstitial CoCrFeNi high entropy alloy coating reinforced with carbon nanotubes (CNTs) was investigated. 1.0 wt% of CNTs were added as the reinforcement. To prepare composite powders before cladding, the CNTs and pre-alloyed CoCrFeNi powders were mechanically mixed without ball milling treatment. As a result, the microstructure of the CNTs on powder surface was well protected from serious damage. The effects of the CNTs upon the microstructure and wear behavior of the produced interstitial CoCrFeNi-CNTs coating were evaluated. The results showed that the intergranular (Fe, Cr) 7 C 3 /α eutectics were found to fully precipitate in the clad CoCrFeNi-CNTs coating. The hardness of the CoCrFeNi-CNTs coating was enhanced by 42.2% compared with that of the CoCrFeNi coating. The wear property was positively correlated with the hardness. The wear rate of the CoCrFeNi-CNTs coating (2.18 × 10 −5 mm 3 ·N −1 ·m −1 ) was significantly lower than that of the CoCrFeNi coating (10.54 × 10 −5 mm 3 ·N −1 ·m −1 ). The enhancements of the wear property originated from the solution strengthening of carbon on grains and the precipitation strengthening of (Fe, Cr) 7 C 3 carbides on grain boundaries. In wear process, the lamellar (Fe, Cr) 7 C 3 /α eutectics deposited on worn surface and eventually formed a carbide hardening layer structure and prevent severe wear on the CoCrFeNi-CNTs coating. • Mechanical mixing can avoid agglomeration of carbon nanotubes on powder surface. • Intergranular carbide eutectic precipitates with the addition of carbon nanotubes. • The carbide hardening layer is formed by carbide eutectic deposition in wear test. • Wear resistance of CoCrFeNi coating is enhanced by the carbide hardening layer. 

Microstructure and wear behavior of laser clad interstitial CoCrFeNi high entropy alloy coating reinforced by carbon nanotubes

Microstructure evolution and hot deformation behavior of carbon nanotube reinforced 2009Al composite with bimodal grain structure

High-energy ball milling (HEBM) combined with powder metallurgy route was used to fabricate carbon nanotube (CNT) reinforced 7055Al composites. Two powder morphology evolution processes (HEBM-1 and HEBM-2) were designed to investigate the dispersion and damage of CNTs during HEBM process. HEBM-1 evolution process involved powder flattening, cold-welding and fracture, while HEBM-2 evolution process consisted of powder flattening and fracture. For HEBM-1, the repetitive fracture and cold-welding process was effective for dispersing CNTs. However, the powder flattening process in HEBM-2 was unsuccessful in dispersing CNTs due to two reasons: (1) the thickness of flaky Al powders exceeded the critical value, and (2) the clustered CNTs embedded in flaky Al powders could not be unravelled. Because of the broadening of D band and the appearance of a new defect-related D’ band, product of ID/IG and full width half maximum of D band, rather than ID/IG, was used to evaluate the actual damage of CNTs. It indicates that the damage of CNTs was severe in powder flattening and fracture stages, while the damage of CNTs was small in powder cold-welding stage.

S. Bi

Papers

Microstructure evolution and hot deformation behavior of carbon nanotube reinforced 2009Al composite with bimodal grain structure

Enhancing strength-ductility synergy of carbon nanotube/7055Al composite via a texture design by hot-rolling

Dispersion and Damage of Carbon Nanotubes in Carbon Nanotube/7055Al Composites During High-Energy Ball Milling Process

Different fatigue behavior between tension-tension and tension-compression of carbon nanotubes reinforced 7055 Al composite with bimodal structure