Distinctive characteristics of solid-state reactions in mechanically alloyed Ti-Al-Si-C powder mixtures
- PDF / 2,935,642 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 31 Downloads / 202 Views
l–Si–C powder mixtures of two different compositions, namely, 58Ti–30Al–6Si–6C (at.%) and 50Ti–15Al–20Si–15C (at.%), were mechanically alloyed to investigate the solid-state reactions during such a process. The mechanically alloyed powders were characterized as a function of milling time by x-ray diffraction (XRD), scanning electron microscopy, energy-dispersive spectrometry, and transmission electron microscopy (TEM). XRD results showed that solid solutions of Ti were formed for a powder mixture of 58Ti–30Al–6Si–6C in about 20 h of milling, whereas Ti5(Al,Si)3 and Ti(Al,Si)C compounds started to form in the powder mixture of 50Ti–15Al–20Si–15C within just 5 h of milling. TEM observations demonstrated that the particle sizes were of nano and submicron scale in both cases. This investigation indicated that in mechanically alloyed Ti–Al–Si–C powder mixtures, the main solid-state reactions are due to interdiffusion and mechanically induced self-propagating reaction.
I. INTRODUCTION
TiAl-based alloys and composites have become a subject of intensive research during the last decade with the aim of developing new materials, which can be used in a wide range of high-temperature applications.1 Recently, composites have been studied with ceramic particle reinforcements like Ti5Si32,3 and TiC or Ti2AlC4–7 as these particles can improve the strength, both at ambient and elevated temperatures. Si additions often result in precipitation of the titanium silicide phase such as Ti5Si3 during heat treatment or creep deformation due to limited solubility of Si in the TiAl phase.8 Studies have shown that carbon is not only an efficient solid solution strengthener in TiAl, but also an effective precipitation strengthener by providing fine dispersion of carbides.9,10 With respect to titanium carbides, TiC has a higher melting point and specific strength at elevated temperature than TiAl does. Such characteristics are beneficial for improving engineering properties of TiAl-based composites. It has been demonstrated that ceramic and intermetallic materials can exhibit a fair degree of ductility at room temperature if they have a nanocrystalline structure.11 The mechanical alloying (MA) process has been known
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0042 J. Mater. Res., Vol. 20, No. 2, Feb 2005
http://journals.cambridge.org
Downloaded: 04 Apr 2015
as a technique to produce nanostructured materials and synthesizing a variety of compounds by milling elemental powders. The heavy working of powder particles during such process results in intimate alloying by repeated deformation, fracturing, and welding; thus nanocrystalline (grain size 艋 100nm) or sub-microcrystalline (grain size 艋 1m) structures can be formed. The purpose of the present attempts on mechanical alloying of Ti–Al–Si–C powder mixtures was to prepare the precursors necessary for further synthesizing of TiAlbased alloys containing silicides and carbides. Such precursors are rich in Ti and in metastable state, for examp
Data Loading...
