Ling, Jester Lih Jie (2017) Effect of electro-carburisation process on the tribological behavior of mild steel. Doctoral thesis, Universiti Malaysia Sabah.
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Abstract
The effect of carburisation process utilizing Na2e03-NaCI as electrolyte on the microstructure and sliding wear behavior of mild steel had been investigated. The carburisation process was conducted at a constant voltage supply of 4.5 V at 860 ° e for 1 and 3 hours. Sliding tests of the carburised steels were conducted at different loads and speeds under dry, vacuum and oil lubrication conditions. The wear morphology of the sliding tests were analysed. Increasing duration of the carburisation process led to a significant increase in the peak hardness and case depth. The steel specimen carburised for 1 hour had a peak hardness of 910 HV and a case depth of 450 μm. Three hours of carburisation produced higher peak hardness and case depth of 1014 HV and 690 μm, respectively. The hardness were significantly higher than the non-carburised specimen with the hardness of 520 HV. The surface of the carburised specimen was dominated by retained austenite with grain boundaries along with some martensite. Towards the peak hardness, the grain boundaries gradually diminished, and the amount of retained austenite decreased while the amount of martensite increased. In the initial stage of sliding wear test at 10 m/min speed, patches of nascent cavities on the worn surfaces produced by adhesion were formed. These acted as preferential sites for fracture to take place, resulting in a marked increase in the frictional force. Longer carburisation duration also resulted in higher tendency of the carburised layer to form a better anti-wear oxide during sliding. The oxide formed on the worn surface of the specimen carburized for 1 hours was hematite. Both hematite and magnetite known for its better lubricity, were detected on the worn surface of the specimen carburised for 3 hours. The increase in peak hardness and formation of the magnetite enhanced the adhesive wear resistance which in turn reduced the tendency of the specimen to fracture. Longer carburisation duration also resulted in the formation of expanded martensite and shallower grain boundaries with lesser cementite which further enhance the fracture resistance of the carburised specimen. The wear of the counterpart we ball reflected the severity of fractured worn surface on sliding specimen. At 10 m/min speed, severe fracture caused the formation of severe grooving, cavities, undermined and cracked we grains. Whereas, micro-fracture resulted in wear characterised by fine grooves and fewer cavities and undermined we grains. Sliding at 70 m/min speed induced formation of magnetite and hematite on the worn surface of specimen carburised for 1 hour. Surface fracturing was hindered when sliding on carburised specimen. The effect of matrix softening was greatly reduced as compared with non-carburised specimens sliding at the same speed. Protrusion was formed on the we ball sliding on the carburised specimen which replicated from the narrow and deep groove formed on the worn carburised specimen. Under lubricated condition, carburised specimen showed formation of magnetite and hematite on the worn surface at very high load. Cavities was formed owing to the fracture of the oxide on the sliding surface. The oxide debris would either rolled between the gap of the sliding surface, causing reduction in the coefficient of friction or adhered on the mating we ball that induced groove marks on the worn sliding surface. The results obtained, either in dry or lubrication condition, concluded that carburised 3 hours specimen showed better wear and fatigue resistance during sliding.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Keyword: | Electro-carburisation, Tribological, Mild steel |
| Subjects: | T Technology > TJ Mechanical engineering and machinery > TJ1-1570 Mechanical engineering and machinery > TJ1040-1119 Machinery exclusive of prime movers |
| Department: | FACULTY > Faculty of Engineering |
| Depositing User: | DG MASNIAH AHMAD - |
| Date Deposited: | 15 Dec 2023 16:08 |
| Last Modified: | 15 Dec 2023 16:08 |
| URI: | https://eprints.ums.edu.my/id/eprint/37860 |
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