Thesis_Thaneshan_SAPANASHAN.pdf

2019-05-01T17:10:34Z (GMT) by Thaneshan Sapanathan
Innovative manufacturing processes are considered as the alternate solutions to produce materials for the growing demand. Hybrid materials become attractive alternatives in engineering applications; they can provide multiple attributes in a single solution. Cladded hybrid rods and tubes, a special type of hybrid metals are fabricated using various techniques, such as extrusion, drawing, hydrostatic extrusion processes.
From a literature survey, it was identified that new sophisticated processes are required to eliminate the existing issues in those hybrid metals manufacturing methods and to obtain the product with multiple attributes. Meanwhile, severe plastic deformation (SPD) processes are well known for delivering high strength processed materials because of their capability of producing materials with significant grain refinement. Therefore, two novel axi-symmetric SPD processes were investigated by utilizing the synergic effect of these processes in hybrid materials fabrications.
Firstly, the axi-symmetric forward spiral composite extrusion process (AFSCE) was investigated for a fabrication of Al/Cu clad rods which produces the hybrid rods with good quality bond with bonding shear strength of ~50.5MPa. A dedicated blanking test was designed to evaluate the bond strength of the processed samples. AFSCE is also a near-zero shape change process and has better dimensional control on the core and clad of the products. The extruded samples were investigated using FIB, SEM, EDX, XRD, EBSD and micro-hardness test to characterize the bonded interface and parent materials. A cup shape hardness behavior of hardness was identified in both materials and ultrafine grain formation was confirmed in the copper region at the interface.
Then a confined high pressure torsion process (CHPT), was used to fabricate Al/Cu cladded discs are presented in the 2nd part of the thesis. The CHPT process showed a significant improvement in the compacted aluminum powder samples and the powder regions of the Al/Cu clad components. The compacted Al powder samples have higher shear strength than Al alloy “AA5005-H34” and 5 times higher shear strength than pure bulk aluminum. The effective compaction of this process is promising for fabrication of high strength materials in an economical way which can eliminate the sintering process which is required for the traditional powder processing methods.