Date of Award

2010

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Engineering, Materials Science.

Supervisor

Nie, Xueyuan (Mechanical, Automotive and Materials Engineering)

Rights

info:eu-repo/semantics/openAccess

Abstract

In this dissertation, wear and corrosion properties of hard coatings were characterized under simulated dry machining, fuel cell and biomedical application conditions. The test results were analyzed, and potentials of the coatings for the targeted applications were discussed. To evaluate the effect of high temperature during the dry machining on the wear performance of various tool coatings, including TiN, TiAlN, CrN, CrAlN and DLC, the phase structurures as well as mechanical and tribological properties of un-annealed and annealed coatings were characterized. An industrial trial of CrAlN- and TiN-coated punches in an auto stamping plant was also conducted. The test results indicated that the CrN-based coating had a better thermal stability than the TiN-based and DLC coatings. The CrAlN coating exhibited the superior thermal stability and wear performance under both laboratorial pin-on-disc tests against ceramic Al2O3 and steel counterface materials and the industrial trial against high strength steel. DLC had a superior anti-sticking property when sliding against aluminum materials. A Cr(CrN)/C(DLC) coating system was also developed as a potential composite coating for dry machining of aluminum materials. The contact resistance and electrochemical properties of uncoated, TiN-, CrN- and TiAlN-coated SS316L substrates were investigated in a simulated proton exchange membrane (PEM) fuel cell environment. Both TiN- and CrN-coated SS316L could potentially be used as bipolar plate materials in the PEM fuel cell environment. However, since the corrosion is likely initiated at pinholes in physical vapor deposition (PVD) coatings, more efforts are needed to eliminate the pinholes. To exam the feasibility of those coatings for load-bearing medical devices and implants, the corrosion property of coatings was investigated in a simulated body fluid (SBF) environment, and the tribological property against polyethylene biomaterial was characterized. The results indicated that the CrN and DLC coatings had a high corrosion potential. TiAlN and CrAlN coatings had the least corrosion protection. TiN and DLC coatings presented a good wear resistance and chemical stability during the sliding tests with SBF. The uncoated and CrN-coated stainless steel samples were not compatible with polyethylene materials in the tested SBF condition.

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