Correlation between energy transfers and solid state reactions induced by mechanical alloying on the Mo 33 Si 66 system
- PDF / 443,107 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 28 Downloads / 156 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Correlation between energy transfers and solid state reactions induced by mechanical alloying on the Mo33 Si66 system L. Liu and M. Maginia) ENEA-INN-NUMA, CRE-CASACCIA, Via Anguillarese 301, Rome, Italy (Received 1 July 1995; accepted 28 March 1997)
Phase transformations of the Mo33 Si66 powder mixture under different milling conditions have been systematically investigated by x-ray diffraction, and scanning and transmission electron microscopy. The effect of the milling conditions on the MoySi solid state reactions (SSR) has been examined in detail. The energy transfer from the milling tools to the powder under processing has been quantified by an already assessed collision model. It has been found that the higher energetic input favors the formation of the room temperature stable phase aMoSi2 , while the lower energetic input promotes the formation of the metastable phase bMoSi2 . In addition, if the energy transfer is high enough, the MoySi reaction proceeds in a form of self-propagating high temperature synthesis (SHS). Thermodynamics and kinetics aspects related to the different SSR’s are discussed.
I. INTRODUCTION
Mechanical alloying (MA), a process first developed for production of oxide dispersion strengthened superalloys,1 has been found to be a versatile technique for the production of other unique structures and alloys. A variety of phases have been produced in the last decade by this technique including amorphous alloys,2–4 extended solid solutions,5,6 quasicrystalline phases,7 and, recently, nanocrystalline intermetallic compounds with high melting point.8–10 Phase transformations induced by mechanical alloying largely depend on the process parameters. What we realize in a milling process is an energy transfer from the milling tools to the powder. Therefore, it is expected that the milling conditions should strongly affect the final product. The specific mechanism of a given mill, the ball diameter, the mill rotation speed, and the ball-to-powder mass ratio are the main process parameters that can control the feasibility or rate of a given transformation. Our previous work on mechanical alloying of Fe– Zr11 and Pd–Si systems12,13 has clearly shown the relationships between mechanical energy transfer and phase transformation. In general, highly energetic milling conditions always led to formation of intermetallic compounds, while lower energy transfers promoted the formation of an amorphous phase. According to a theoretical model and based on the assumption that collision is the main energy transfer event, a large number of experiments on the Pd–Si system were fairly well rationalized into an “energy map” correlating the input energy and the final products.13
a)
Author to whom correspondence should be addressed. J. Mater. Res., Vol. 12, No. 9, Sep 1997
http://journals.cambridge.org
Downloaded: 13 Mar 2015
In this paper, attention was focused on the Mo –Si system since MoSi2 intermetallic compound is considered to be one of the most promising material
Data Loading...
