Thermal and mechanical properties of mechanically alloyed 304LSS-CNT metal matrix composites

Abstract

A methodology for the creation of 304LSS-CNT metal matrix composites using the mechanical alloying approach is presented. Planetary ball milled powders were both melted and hot pressed and achieved up to 96% theoretical density. High resolution scanning electron microscopy, Scanning Transmission Electron Microscopy, X-ray diffraction, energy dispersive spectroscopy, thermal diffusivity measurements, and Vickers microhardness measurements are used to characterize as processed and heat treated composites. Melted and solidified samples show highly anisotropic austenite/martensite microstructures with the presence of large dendritic carbon agglomerations, while hot-pressed samples show equiaxed austenite/martensite grains with a large number density of carbide precipitates. Grain size and thermal diffusivity decrease while microhardness increases up to 36% with up to 2% carbon nanotube addition for hot-pressed samples. Thus, mechanical alloying has been shown to be a potential option for the production of homogeneous 304LSS-CNT metal matrix composites for applications requiring increased strength.

Microstructures and high-temperature tensile properties of mechanically alloyed and spark plasma-sintered 304SS-CNT composites

“…The decomposition of CNTs and the formation of carbides were also observed in the fabrication of 304LSS-CNT composites by hot pressing at 1423 K for 30 min and by melting at 1873 K for 5 min. 8 In pure Fe-based CNT composites, it has been shown that the dispersion of CNTs in the composite could be achieved on a certain sintering condition. 26,27 By changing the condition, the CNTs decompose to be a Fe-C interstitial alloyed phase or to a Fe-Fe 3 C composite.…”

“…7 A recent research paper concerning the fabrication of 304 L SS-CNT composites using mechanical alloying combined with hot-pressing and melting has also been found. 8 The authors reported that the hot-pressed samples were composed of equiaxed austenitic and martensitic phases along with chromium carbides on the austenite grain boundaries. CNTs were not directly observed, but the scanning electron microscopy (SEM) and X-ray diffraction results showed possible retained CNTs in the matrix and along grain boundaries.…”

“…The purpose of this work is to investigate the microstructure and mechanical properties of the fabricated composites. Since the consolidation process used in this study is different from that used by Massey et al 8 and tensile tests were performed at high temperature, it is expected that more insight could be gained into the microstructural and mechanical characteristics of SS-CNT composites fabricated by powder metallurgy processing techniques.…”

Effects of CNTs addition on the microstructure and microhardness of stainless steel alloy/carbon-manganese non-alloyed steel welding

“…1 In this process, the metals were folding multiple times until forming cementite nanowires and CNTs, resulting in improvements on the mechanical properties. 2 In last years, the CNTs are used as reinforcement in metal matrix and they are added by several techniques, such as thermal spray, 3 chemical vapor infiltration process, 4 powder metallurgy, 5 and, more recently, by arc welding. 6,7 Many studies have shown that the one-dimensional structure of CNTs is helpful to improve the mechanical properties and change the microstructure of stainless steel (SS) metal matrix.…”

Stainless steel weld metal enhanced with carbon nanotubes

“…Due to its C–C bonds and an sp 2 hybridization, the CNTs have a higher tensile strength than Kevlar (100 GPa), a Young Modulus of 1.28 TPa, and also an elevated thermal conductivity of about 2000 , more than 500% higher than copper and 800% than aluminum 1 , 2 . Despite these outstanding properties, factors such as the Van der Waals forces, which operate at the walls of the nanotubes, manufacturing limitations that may result in CNTs with a poor crystallinity, and its insolubility in most solvents are still some of the shortcomings to be faced 3 , 4 .…”