טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHorvitz Dror
SubjectReactive Forging - a Novel Method of Pressure Assisted
Combusrtion Synthesis of Dense Ceramics and
in Situ Composites: Ti-O-Al-Mg, B-C-Ti,
and Mg-Si Systems
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Elazar Gutmanas
Dr. Irena Gotman
Mr. Leonid Klinger


Abstract

In the course of the research, a novel Reactive Forging method has been developed - a process where thermal explosion (TE) is ignited by heat transfer from the preheated press rams and the application of a moderate uni-axial pressure shortly after TE effectively consolidates the sample to near full density. During Reactive Forging, temperature in different parts of the specimen is measured by W-Re or chromel-alumel thermocouples and is accurately recorded by a special computer card with very high time resolution.

The developed RF process was used to fabricate 98 % dense Al2O3-titanium aluminide and MgAl2O4-titanium aluminide composites from TiO2-Al and TiO2-Al-Mg powder blends, respectively. In 2Mg-Si powder blend no consolidation was achieved due to the relatively low maximal combustion temperature, Tcomb.

A novel approach to measuring the activation energy of thermal explosion using the RF experimental set up has been proposed; the activation energy for 2Mg+Si®Mg2Si reaction was in a good agreement with the literature data.

A mathematical model describing the effect of powder size and dispersity on the ignition (i.e. initial stage) of thermal explosion has been developed indicating the possibility of early ignition of coarse powder blends by adding a small amount of a very fine powder.

Another model developed describes temperature evolution in the course of thermal explosion in the 2Mg-Si blend. Comparison between the predicted curves and the experimental results for 2Mg-Si blend suggested that the formation of Mg2Si in the course of thermal explosion was controlled by reaction, probably due to the presence of fast diffusion paths (e.g. cracks) in the Mg2Si product.