The National Research Institute of Mechanical Engineering plans to organize the Institute-level doctoral thesis defense (LATS) for PhD candidate (NCS) Bui Van Khoan in January 2023. The Institute hereby publishes the information on the candidate's doctoral thesis as follows:

Full name of PhD candidate: Bui Van Khoan

Affiliation: Hung Yen University of Technology and Education 

Supervisory team: Assoc. Prof. Dr. Le Thu Quy, Dr. Phan Thach Ho

Field: Mechanical Engineering – Code: 9520103

Training institution: National Research Institute of Mechanical Engineering – Ministry of Industry and Trade

Thesis title: "Study on the influence of plasma spray coating technological parameters on the properties of Al₂O₃-TiO₂ ceramic coating on steel substrate"

Summary of new conclusions of the thesis

1. Based on experimental conditions at the training institution, the influence of three plasma spray parameters—spray current (I), spray distance (L), and powder feed rate (M)—on coating quality was selected and studied in depth. Microhardness, adhesive bond strength, porosity, and friction coefficient were evaluated and analyzed as important coating property indicators.

2. Using the Taguchi method combined with ANOVA analysis, the percentage influence of the three spray technological parameters on output quality indicators was determined. The thesis established single-objective optimal spray parameter sets to achieve the highest hardness (619.54 HV); lowest friction coefficient (0.49); highest shear bond strength (60.52 MPa); and lowest porosity (3.92%).

3. Using the least squares method, second-order empirical regression function equations were developed to express the relationship between hardness, bond strength, porosity, and friction coefficient of the coating with the three spray technological parameters I-L-M for predicting coating quality.

4. Through the Overall Evaluation Criterion (OEC), the optimal spray parameter set (I = 600 A; L = 110 mm; M = 1.9 kg/h) was identified, simultaneously ensuring three output mechanical property indicators of the coating (hardness 585.6 HV; shear adhesion 56.4 MPa; porosity 4.24%), with deviations from single-objective optimal results at a low level (< 10%).

5. Both single-objective and multi-objective optimization results show that among the three spray technological parameters I-L-M, spray current always has the greatest influence on coating quality indicators, significantly greater than the other two parameters. XRD analysis results determining the phase composition of coating samples compared to the initial spray powder phase composition show that, depending on the spray regime, under the effect of plasma energy, phase transformation occurred with the formation of some new phases when spray current increased, such as γ-Al₂O₃ (transformed from α-Al₂O₃), rutile-TiO₂ (transformed from anatase-TiO₂)_, Al₂TiO₅ (combination of Al₂O₃ and TiO₂).

Detailed information on the doctoral thesis of candidate Bui Van Khoan:
->For the full text of the thesis, please click here
->For the Vietnamese abstract of the doctoral thesis, click here
->For the Vietnamese summary of the doctoral thesis, click here
->For the English summary of the doctoral thesis, click here
->For the Vietnamese information file of the doctoral thesis, click here
->For the English information file of the doctoral thesis, click here