November_December_2021_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 1 2 4 Longitudinal veins parallel to the main axis of the piece were revealed, too (Fig. 4), and could be either cracks or low-density products. However, the internal porous area located at the head of the nail remains to be understood. CHEMISTRY AND MICROSTRUCTURE The general structure at the sur- face and in the core was observed and analyzed (Figs. 6 and 7). Chemical analy- sis by energy dispersive x-ray spectros- copy (EDS) of the cross section revealed the presence, in descending order, of the following elements: oxygen, iron, silicon, aluminum, calcium, carbon, and magnesium (Fig. 7a). Attempts to reveal the nail microstructure through the small, allowed amount of sampling showed that the nail is made with an iron-base low-carbon material. Etching with a solution of 5% nitric acid in etha- nol (5%Nital), which is normally used in metallography to reveal the microstruc- ture of steels, has not yielded any signif- icant result. The steel was not sensitive to the etching reagent (Fig. 6) as low carbon iron alloys of ferritic microstruc- ture (or wrought iron) would be. The presence of Ca, Mg, Al, and Si is consistent with the chemistry of slags resulting from the smelting of iron ore [1] and would give information about the site from which the ore comes but the study did not go this far. A low-magnification optical mi- crograph of the general microstructure (Fig. 6a) shows the contrast between the Fig. 3 — Basic shape of the nail deduced from visual and cross-section examinations. (a) (b) Fig. 4 — X-ray radiography images showing longitudinal veins (darker areas are those that let x-rays pass through and are then less dense). Fig. 5 — Areas revealed by x-ray radiography. Fig. 6 — Optical micrographs showing (a) the general microstructure and (b) surface as observed by SEM. (a) (b)