A new approach for the reinforcement of SS 304L via arc welding: Using nanostructured flux cored electrode

Abstract

Carbon nanotubes (CNT) are revolutionary materials and, since its discovery, the scientific community seeks ways to use the unique electrical and mechanical properties of CNT as in nanocomposites, incorporated in metal matrices via processes such as welding and thermal spraying. Despite an increasing number of researches involving the success in incorporating CNTs in metals, such as copper and aluminum, the knowledge concerning the use of stainless steel (SS) as metal matrix is yet underdeveloped. This paper uses the Mechanical Alloying (MA) process to incorporate Multi Walled Carbon Nanotubes in a Stainless Steel (SS) 304L powder. The mixture of SS 304L and 5 wt% MWCNTs was placed in a planetary ball mill along with a ball-to-powder ratio of 30:1, and rotated at 200 rpm. Samples with 0 min, 30 min, 60 min and 90 min of MA process were collected to be characterized using X-ray Diffraction (XRD), Raman spectroscopy and Scanning Electron Microscope (SEM). The results indicated that the 60 min sample achieved homogeneous dispersion and aggregation in the metal matrix, which qualifies such parameters as more suitable to produce the nanostructured powder of 304LSS-CNT. Thus, for the nanostructured cored flux electrode conception, a tubular electrode was filled with 304LSS-CNT powder from 0 min and 60 min of MA for welding via Pulsed Gas Tungsten Arc Welding (P-GTAW). Vickers hardness tests analyzed the mechanical properties, with 25% and 30% improvement of lateral hardness for the 60 min of MA, if compared to 0 min and SS powder only, respectively.