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Engineering

Research project: Tribological behaviour of ultrafine-grained alloys formed by severe plastic deformation

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Materials with submicron- or nano-scaled grains produced by severe plastic deformation (SPD) offer new structural and functional properties for innovative products in a wide range of applications. The aims of this study are to understand the effect of SPD processing on wear behaviour of materials, to seek a way to use SPD processing to improve the mechanical properties of materials and their wear resistance.

Al-1050 was processed using equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) respectively. Microhardness evolution showed clear evidence of strength improvement by SPD. However, dry sliding testing showed that both ECAP and HPT led to a decrease to the wear resistance to Al-1050. The decrease of wear resistance of Al-1050 after SPD processing is attributed to a lack of work hardening capacity during the severe wear stage and a higher oxidation rate during the oxidation wear stage.

In addition, commercial purity Ti was processed via HPT and heat treatment. The micro-tribological behaviour of UFG Ti was studied for the first time via microscratch testing. The results showed that HPT-processing of Ti inhibited operation of adhesion and ploughing during wear tests and led to better wear resistance.

To enhance the wear resistance of UFG Ti as bio-implant materials, TiN coatings were deposited on to Ti substrates via physical vapour deposition methods. Wear tests indicated a significant improvement of wear resistance after coating deposition. Adhesion tests showed that the thin coatings had much enhanced load bearing capacity with UFG Ti as the substrate compared to coarse-grained Ti, which is explained by a modified composite hardness model.

An improved bio-implant design was proposed for total joint replacement applications. This design involves fabricating the main body of the bio-implant from UFG pure Ti processed by SPD and subsequently applying a hard thin coating to protect the head of the implant. It is anticipated this design will provide the implant with high strength, good fatigue life, good corrosion resistance, together with good wear and tribo-corrosion resistance from the coating and a non-toxic ion release. Therefore, this design has a very strong application prospect.

Related research groups

national Centre for Advanced Tribology at Southampton (nCATS)
Engineering Materials
of Ti substrates.
Microstructure and tensile curves
on (a) CG Ti and (b) UFG Ti after 1400 repeats of micro-wear test.
Wear surfaces of TiN coating

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