Query: cnt al powder metallurgy

title: Enhanced ductility by Mg addition in the CNT/Al Cu composites via flake powder metallurgy
abstract: The inevitable native oxide layer is a critical issue to achieve high mechanical performance of CNT/Al alloy composites, especially prepared by powder metallurgy. Here, an easy strategy was proposed to avoid and eliminate the negative effect of native oxide (Al2O3) layer by Mg addition, and significant improvement of ductility was achieved in the CNT/Al Cu composite. Native Al2O3 remained as continuous layers around CNTs or clusters of fragments in the CNT/Al Cu without Mg addition. Mg addition transformed the native Al2O3 layer into spinel MgAl2O4 nano phases dispersed both inside grains and on the interfaces. It is supposed that this transformation of oxide layer could improve the interfacial bonding due to Al Al and Al CNT direct interfacial contact. As a result, compared with CNT/Al Cu composites, the tensile strength only changed a little, however, almost two times of fracture ductility was achieved by Mg addition in the final composites.

title: Balanced strength and ductility in CNT/Al composites achieved by flake powder metallurgy via shift speed ball milling
abstract: Flake powder metallurgy via shift speed ball milling (SSBM) was proposed to combine the mechanisms of low speed and high speed ball milling (LSBM and HSBM) for carbon nanotube (CNT) reinforced, strong and ductile aluminum composites. LSBM featured mild ball to powder collision and slow flattening of spherical Al powders into flakes, leaving enough time for CNTs to be uniformly dispersed on the surface of Al flakes and causing little damage to CNTs; HSBM featured much stronger collision and cold welding of Al flakes, leading to clustered CNTs within the welded Al particles with serious damage but better inter flake bonding. Therefore, the coordination of CNT dispersion, integrity and interfacial bonding could be achieved by a smart powder processing of SSBM, namely a longer starting LSBM and a shorter following HSBM. As demonstrated, such SSBM resulted in comparable strength in 1.5 wt. CNT/Al composites but doubled and tripled ductility as those fabricated via LSBM and HSBM.

title: Enhanced interfacial bonding and mechanical properties in CNT/Al composites fabricated by flake powder metallurgy
abstract: A flake powder metallurgy route consists of a slurry based dispersion process and a short time ball milling process was proposed to fabricate strong and ductile CNT/Al composites reinforced with high content CNTs. To improve the interfacial bonding, the CNT/Al nanoflake powders prepared through slurry based dispersion process would go through a short time high energy ball milling process to break native Al2O3 skin and embed CNTs into Al matrix. With the dispersion homogeneity and well maintained structural integrity of CNTs achieved by the slurry based dispersion, and improvement of interfacial bonding from non bonding to physical bonding/diffusion assisted bonding and partial reaction bonding through the short time ball milling, an enhancement of tensile strength from 298 to 406 MPa and ductility from 1.9 to 8.8% was obtained for the 2 h ball milled 3 vol. CNT/Al composites, compared to the composites fabricated by sole slurry based dispersion process. It also outperformed that fabricated by direct high energy ball milling, indicating the flake powder metallurgy method could provide a good coordination between the CNT dispersion homogeneity, structural integrity and interfacial bonding.

title: Microstructure, microhardness and thermal expansion of CNT/Al composites prepared by flake powder metallurgy
abstract: Carbon nanotube/aluminum (CNT/Al) composites are prepared by a combination of flake powder metallurgy and hot isostatic pressing. The specimens are investigated by several techniques including Raman spectroscopy, optical microscopy, scanning and transmission electron microscopy. The composites show a layered microstructure with a stacking of CNT/Al flakes with a CNT rich layer between two flakes. The individual Al grains forming the flakes are about 500 nm in size. The CNTs are well dispersed within a flake and they bridge the micro cracks. The results reveal that the coefficient of thermal expansion (CTE) decreases markedly upon the increase in carbon content, reaching 15.4 x 10 6 K 1 for the specimen with a carbon content of 2.0 wt% (2.9 vol% i.e. a 30% decrease compared to the CTE of pure Al. This could arise from the layered microstructure resulting from the utilization of Al flakes as opposed to rounded particles.

title: High strength CNT/Al Zn Mg Cu composites with improved ductility achieved by flake powder metallurgy via elemental alloying
abstract: The uniform dispersion of carbon nanotubes (CNTs) is usually accompanied by severe grain refinement of Al matrix, which leads to the low ductility of CNT/Al alloy composites. To accommodate this dilemma, a flake powder metallurgy route via elemental alloying was proposed to fabricate CNT/Al Zn Mg Cu composites with improved ductility and high strength. CNT/Al flake powders were firstly obtained by ball milling at a low speed to achieve uniform dispersed of CNTs, and then milled with Zn, Mg and Cu elemental flake powders at a high speed to achieve lamellar CNT/Al Zn Mg Cu particles, which were consolidated and homogenized to obtain bulk CNT/Al Zn Mg Cu composites. Compared with the CNT/AA7075 counterparts fabricated by directly using CNTs and atomized AA7075 powders, the CNT/Al Zn Mg Cu composites exhibited improved ductility with high modulus and strength, due to the well protected and uniformly aligned CNTs, and good dislocation storage capability of the elongated ultrafine grains.

title: Fabrication of CNT/Al composites with low damage to CNTs by a novel solution assisted wet mixing combined with powder metallurgy processing
abstract: A novel solution assisted wet mixing processing was developed to efficiently produce CNT/Al composite powders. CNTs were firstly dispersed in zwitterionic surfactant aqueous solution, and then the flaky Al powders, produced from spherical Al powders by ball milling, were mixed with the CNT solution to adsorb the dispersed CNTs in the solution. It was indicated that CNTs could be uniformly adsorbed onto the flaky Al powders and CNT/Al powders with a maximum CNT concentration of 7.5 vol% could be obtained after filtering and drying. 1.5 and 3 vol% CNT/Al composites were then fabricated using the resultant composite powders through a powder metallurgy route. CNTs with average lengths of 0.9 mm and well retained wall structure were uniformly dispersed in the Al matrix and aligned arrangement of CNTs was achieved after hot forging. Furthermore, it was found that most of CNTs were distributed at the grain boundaries and the CNT Al interfaces were well bonded. The strengths of the CNT/Al composites were significantly increased, which could be attributed to the efficient load transfer of CNTs.

title: Hot deformation and processing maps of as sintered CNT/Al Cu composites fabricated by flake powder metallurgy
abstract: The deformation behaviors of as sintered CNT/Al Cu composites were investigated by isothermal compression tests performed in the temperature range of 300 550 degC and strain rate range of 0.001 10 s 1 with Gleeble 3500 thermal simulator system. Processing maps based on dynamic material model (DMM) were established at strains of 0.1 0.6, and microstructures before and after hot deformation were characterized by scanning electron microscopy (SEM) electron backscatter diffraction (EBSD) and high resolution transmission electron microscopy (HRTEM) The results show that the strain has a significant influence on the processing maps, and the optimum processing domains are at temperatures of 375 425 degC with strain rates of 0.4 10 s 1 and at 525 550 degC with 0.02 10 s 1 when the strain is 0.6. An inhomogeneous distribution of large particles, as well as a high density of tangled dislocations, dislocation walls, and some sub grains appears at low deformation temperatures and strain rates, which correspond to the instability domain. A homogeneous distribution of fine particles and dynamic recrystallization generates when the composites are deformed at 400 and 550 degC under a strain rate of 10 s 1, which correspond to the stability domains.

title: Crack Formation in Powder Metallurgy Carbon Nanotube (CNT)/Al Composites During Post Heat Treatment
abstract: After the post heat treatment (PHT) process of powder metallurgy carbon nanotubes (CNT)/Al composites, micro cracks were observed in the composites, leading to greatly degraded mechanical properties. To understand and suppress the crack formation, an in situ observation of CNT/Al composites was performed at elevated temperatures. PHT was also applied to various bulk pure Al and CNT/Al composites fabricated under different processes. It was observed that the composites consolidated by hot extrusion might form micro cracks, but those consolidated by spark plasma sintering (SPS) showed no crack after PHT. A high temperature SPS process before hot extrusion was effective to prevent crack formation. The release of residual stress in severe plastic deformed (SPD) materials was responsible for the cracking phenomena during the PHT process. Furthermore, a good particle bonding was essential and effective to suppress cracks for SPD materials in the PHT process.

title: Enhanced tensile properties and electrical conductivity of Cu CNT nanocomposites processed via the combination of flake powder metallurgy and high pressure torsion methods
abstract: Using flake powder metallurgy (FPM) technique, combined with high pressure torsion, super high strength ductile Cu CNT nanocomposite with high electrical conductivity is developed. The nanocomposite with 4 vol% CNT showed high tensile strength of ~474 MPa, high electrical conductivity of ~82.5% IACS as well as appreciable ductility of ~11% According to microstructural studies, the excellent properties of the nanocomposite are attributed to the formation of trimodal grains, high density of twin and low angle grain boundaries, improvement in CNT and Cu interfacial bonding, and appropriate distribution and maintaining the microstructure of the nanotubes in the production process. The results of this work provide a new pathway to produce strong, conductive, and ductile metal matrix nanocomposites.

title: NACRE INSPIRED STRONG AND DUCTILE CNT AL COMPOSITES FABRICATED BY FLAKE POWDER METALLURGY
abstract: In order to combine high tensile strength and ductile behavior, a nacre inspired CNT/Al nanolaminated composite stacked alternatively with parallel aligned CNTs and Al lamellae was fabricated by a bottom up flake powder metallurgy route, using Al nanoflakes and carboxyl functionalized carbon nanotube (CNT) as starting materials. Compared to conventional homogeneous nanocomposites composed of the same constituents, the final bulk product with nacre like architecture exhibits a simultaneous enhancement in tensile strength and uniform elongation.