טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRan Gur
SubjectProcessing and Properties of Nano and Sub-Micron Iron Based
Composites
DepartmentDepartment of Materials Science and Engineering
Supervisors Full Professor Gutmanas Elazar
Dr. Gotman Irena
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Composites of metallic, or inter-metallic, alloy matrix reinforced with particulate ceramics (or fibers) are candidate materials for structural applications, when high temperature, oxidation and wear resistance and mechanical strength are in demand.

One particular approach, where both, matrix and reinforcement are simultaneously formed by a chemical reaction of powder reagents, is the self-propagating high-temperature synthesis (SHS).

SHS is a technique in which initial reagents, when ignited, due to the exothermic heat of reaction, spontaneously transform into products. The rapid energy release, that creates very high heating rates, is called thermal explosion (TE). In the current research, SHS/TE approach was combined with Short Distance Infiltration (SDI) processing route. During SDI processing, a non-dense compact, containing 5 to 20 volume percent of a lower melting phase, is heated rapidly, to a temperature that exceeds the melting point of the lower melting phase. Then, pressure is applied. Thus, forcing the so formed liquid phase into filling the compact’s pores, consequently, yielding a full densification.

This research deals with the in-situ formation of Fe based ceramic/metallic (or intermetallic) composites. The reagents: Fe2O3, Fe4N Fe, Ag72Cu28 and Al powders react via thermal explosion (TE) and/or SDI, under uniaxial pressure, in a press ram (reactive forging, RF).

In the present research, dense Fe/Al2O3, Fe/AlN and Fe/Ag72Cu28 (eutectic) composites containing up to 60 volume percent of hard particles diluents: B4C, CBN, Diamond and SiC, were synthesized from fine powder blends. Green compacts were fed into a preheated press ram. Thermal explosion (SHS) was initiated at ram temperatures as low as 8000C. The temperature, of the combustion synthesis specimens, was accurately monitored. Upon thermal explosion, the application of a relatively low pressure resulted in full densification of the so synthesized composites. Another applied processing route was the Reactive Hot Pressing (RHP) of dense, cold sintered compacts.

The microstructure of the composite specimens was characterized by x-ray diffraction (XRD) and scanning electron microscopy with chemical analysis (SEM/EDS).

Results of the present research suggest that submicron Fe based dense composites, with and without the addition of hard particles, could be synthesized through the following routes:

1.      Short Distance Infiltration (SDI) of low melting phase in Fe2O3-2Al, Fe4N-Al and Fe- Ag-Cu eutectic systems via pressure assisted Thermal Explosion (TE) mode of Self-Propagating High-Temperature Synthesis.

2.      Cold Sintering - high pressure consolidation to a full density compact, followed by solid state and solid-liquid phase reactions (reactive hot pressing).