טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZlotnikov Igor
SubjectCombustion Synthesis of Functionally Graded Composites
Reinforced by Hard Particles
DepartmentDepartment of Materials Science and Engineering
Supervisors Professor Elazar Gutmanas
Dr. Irena Gotman


Abstract

Functionally graded materials (FGMs) represent a second generation of composite materials designed to achieve superior levels of performance. An FGM is a two-component composite characterized by a compositional gradient from one component to the other.

Dense FGMs with gradually changing fraction of very hard and light-weight particles were fabricated employing an original Reactive Forging (RF) combustion synthesis method. The reported FGMs were prepared by stacking layers of highly exothermic Ti-C-Ni powder blend diluted with varying fractions of non-reacting B4C and TiC particles.

Temperature evolution in (Ti-Ni-C)-B4C powder compacts corresponding to different FGM layers was measured separately and in the stacked form. The better understanding of combustion process in B4C-diluted blends coupled with well-devised geometrical design allowed us to fabricate FGMs with high volume fractions of B4C in the surface layer.

The effect of non-reacting diluents on Reactive Forging (thermal explosion under pressure) of (Ti-Ni-C)-TiC FGMs has also been studied. Temperature evolution was measured in stacked layers, as well as in separate specimens with compositions corresponding to each FGM layer. It has been found that fine TiC particles (< 2 mm) are stronger combustion inhibitors than the coarser ones (~ 40 mm), so that a larger fraction of the coarse TiC (> 70 wt.%) was required to suppress thermal explosion compared to the fine TiC (~ 60 wt.%). This is explained by the more uniform heating of fine particles during the short combustion cycle, as well as by their geometrical effect on reactant distribution.