Structural and chemical characterization of the hardening phase in biodegradable Fe-Mn-Pd maraging steels

Fe-Mn-Pd alloys are promising candidates as biodegradable material for use in temporary implant applications. In this study, the hardening phase of Fe-rich martensitic alloys containing 1, 3, and 6 wt.% Pd and a fixed Mn content of 10 wt.% was investigated. All of these alloys show considerable age-hardening upon isothermal aging at 500 °C, exhibiting a behavior characteristic of maraging steels. Atom probe tomography (APT) and x-ray diffraction (XRD) measurements were performed to characterize the composition and crystallography of nanometer-sized precipitates forming in the overaged region of the Fe-Mn-Pd alloys. The precipitates consist mainly of Mn and Pd and the peaks of the intermetallic particles observed in the XRD spectra can be ascribed to the face-centered tetragonal β1-MnPd phase. The precipitation sequence for Fe-Mn-Pd is revealed to be similar to that reported for Fe-Mn-Ni and Fe-Mn-Pt maraging steel

Calculated phase diagrams and the corrosion of die-cast Mg-Al alloys

The corrosion of commercial die-cast Mg-Al alloys was elucidated by a study, of the corrosion in 3% NaCl, of(i) high-pressure die-cast (HPDC) model Mg-Al alloys, (ii) low-purity Mg, (iii) high-purity (HP) Mg and (iv) HP Mg heat treated at 550 degrees C. HPDC is the most important route for the production of Mg components. The corrosion of the model alloys was dominated by the Fe impurity element. The present research identified the appearance of the Fe-rich particles in the microstructure. In high magnification (similar to 1000x to 5000x) secondary electron images, they appear as small white features, typically less than 1 pm in diameter. In order to understand the impurity tolerance limits, (i) the appropriate corrosion literature was summarised and reviewed and (ii) Mg phase diagrams were calculated using the Pandat software package. Calculated phase diagrams can explain (i) the tolerance levels for Fe and Cu and (ii) the production of high-purity castings by means of control of melt conditions; this has high significance for the production of quality castings from recycled Mg. A full analysis requires that the Mg database be extended to include Ni, Co and some RE. The Fe tolerance limit is similar to 5-10 ppm for cast HP Mg heat treated at 550 degrees C. Analysis of the Mg corrosion literature indicates that several studies have been dominated by the Fe impurity content and have not dealt with the stated aims: it means that the full chemical composition should be reported in all studies of the corrosion of Mg alloys. (C) 2008 Elsevier Ltd. All rights reserved