Student:	Oktay KUL
Supervisor:	Assoc. Prof. Dr. Gençağa PÜRÇEK
Department:	Makina Mühendisliği
Institution:	Graduate School of Natural and Applied Sciences
University:	Karadeniz Technical University, Turkey

Title of the Thesis:	Investigation of Microstructural Evolution, Tensile Properties and Wear Behavior of Pure Titanium and Al-Si12 Casting Alloy Processed by Severe Plastic Deformation
Level:	M.Sc.
Acceptance Date:	24/7/2009
Number of Pages:	96
Registration Number:	i2069

Summary:

In this study, two different materials were severely deformed by equal-channel

angular extrusion/pressing (ECAE/P). Commercially pure titanium (grade-2) and Al-Si12

casting alloy were selected as test materials in the present study. ECAE was applied to

titanium following route-E for 8 and 12 passes at 300 °C. Al-12Si casting alloy was

microstructural evolution, tensile properties and wear behavior of these materials were

examined in a systematical approach.

Multi-pass ECAE process led to a significant refinement in the microstructure of pure

titanium. After 8 and 12 ECAE passes, the grain size of as-received titanium with equiaxed

and coarse grained structure (average grain size of 110μm) decreased to 300 nm and 250

nm, respectively. Multi-passed ECAE process, the yield and tensile strength values of

titanium increased above %100 and %40, respectively. However, ECAE-processed

titanium exhibited a slight decrease in ductility. After 8 ECAE passes, elongation to failure

value decreased from 33% to 20%. ECAE process did not lead to the improvement of wear

resistance of titanium. This situation was mainly attributed to the oxide layer occurred on

the wear surface of titanium as a result of oxidative wear mechanism occurred by

tribochemical reactions.

Multi-pass ECAE applied using by route-A led to the fragmentation of the needleshaped

eutectic Si particles into smaller particles. The length and width of the Si particles

decreased from 35,5±31,8μm and 13,7±8,9μm without ECAE to 2,7±1,1μm and

during ECAE, the yield and tensile strength values of as-cast Al-Si12 alloy increased 98%

and %68, respectively. Also, the elongation to failure value of the as-cast alloy increased

for about 650%. ECAE process decreased slightly the wear resistance of Al-Si alloy.

Key Words: Severe Plastic Deformation, Equal-Channel Angular Extrusion, Titanium,

Al-Si Casting Alloys, Mechanical Properties, Wear