Date of Award

Spring 2019

Document Type

Thesis

Degree Name

Master of Science in Materials Science and Engineering - (M.S.)

Department

Chemical and Materials Engineering

First Advisor

Petrova, Roumiana S.

Second Advisor

Levy, Roland A.

Third Advisor

Zhou, Tao

Fourth Advisor

Farinas, Edgardo Tabion

Abstract

Plasma Electrolytic Oxidation (PEO), a part of Plasma electrolytic Deposition (PED), has been developing for surface modification of metallic materials in the past 20 years. During PEO process, sample always connect with anode of DC power source, under high temperature, accelerating process of oxidation reaction to from an average and dense oxidation film. A general passage, Plasma electrolysis for surface engineering, written by A.L. Yerokhin, X. Nie gives us a trend of what happened during PEO process but did not determine specific material and value. Linxin Zhu’s Development of PEO invent a new boiling system and investigated relationship between surface roughness and coating and mentioned investigating on resistance of DC current at future work.

In this passage, focusing on the electrical model, PEO process is studied in both experimental and theoretic aspect. In practice, PEO industries could be distinguished by what terms it entered in according to different demand. And, the resistance in this term are quite different because of different structures at surface of sample. Theoretically, three types of electrical models have been built by MATLAB after analyzing the main influence factors of PEO process, which could help us explain how the structure and resistance change.

Experimentally, a Ti-6Al-4V piece was used as a sample to do all PEO experiments. Diversity results was obtained by change the conductivity of electrolyte and applied voltage. Others experimental parameters were controlled to be same as possible like surface roughness, contents of liquid solution and voltage increase speed. All the thing above purpose to make electrical model more reasonable and trustable.

All the experiments were recorded by a camera then select pictures in every second. Then input the statistics in the matrix in MATLAB as the original reference, which is used to compare to the simulation result. So that the simulation model could be adjusted until it meets the experiment results. Thus, the main factors which influence resistance could be inferred.

After analyzing, we found, at passive film stage, the majors resistance consists of resistance of electrolyte and passive oxidation film of anode (Ti-6Al-4V sample). Temperature would slightly influence resistance if electrolyte conductivity is big enough. The U-I in this stage is nearly a straight line. While, at the new oxidation film stage, current is significant increase because gradually dissolve of the passive oxidation film with time. So, the U-I curve is a trend of sharp increase. At the arcing stage, current decrease is because new oxidation film formed, and rest of the resistance is determined by temperature.

Besides, these PEO in three stage was simulated by MATLAB models according to the majority factors analyzed. The simulation results suitable for all kind of PEO in Ti-6Al-4V process with different conductivity but changeless surface roughness and increasing applied voltage. Prediction of optimizing applied voltage is possible with this model in PEO process in Ti-6Al-4V.

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