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Microstructures and properties of CoCrMo alloy by metal injection moulding process

Nur Aidah Nabihah, Dandang (2019) Microstructures and properties of CoCrMo alloy by metal injection moulding process. Masters thesis, Universiti Malaysia Pahang.

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Abstract

The CoCr-based alloy is used for surgical inserts due to their superior corrosion resistance, high strength and good in biocompatibility. Metal injection moulding (MIM) is one of the powder metallurgy process used for the fabrication of complex and near net shape assembly of high-performance materials. Currently, this method has also been used as an optional way to fabricate implants in surgery and dentistry befitting for economical mass production. MIM process involves mixing, injection moulding, debinding and sintering. Sintering and debinding is the main stage in the injection moulding process that could affect the properties of the sintered part. In some instances, no optimised parameters were apply to both process may cause defective for final products formed up to 25 %. Brittle, porous structure of brown compacts after debinding caused sintered compact after sintering process become easily cracks and not quality compacts were formed. This research interests in the persistence of optimum parameter for solvent debinding process, the effects of sintering parameters on microstructure of sintered compact and effect of sintering parameters on physical, mechanical properties and corrosion behaviours of sintered compacts. The CoCrMo alloy compacts were solvent debound in n-heptane solution at 50, 60 and 70˚C for 4 hours soaking time. The brown compacts produced was continued to a sintering process at temperature 1250, 1300 and 1350̊ C for 1 and 3 hours in an argon atmosphere respectively. The tensile and microhardness testing determined the mechanical properties of sintered CoCrMo alloy compacts. The corrosion properties were characterised from electrochemical method experiments. Metallographic studies of fractures surface and pore formation were observed by optical microscopy (OM) and scanning electron microscope (SEM). The results of the investigation indicate that solvent debinding at 60 ˚C for 4 hours was found to be optimum parameters for solvent debinding due to adequate mass loss of paraffin wax which reported at 76.9 %. While compacts sintered at 1350˚C-3h showed the highest density (92.5 %), hardness (308.1 Hv) and tensile strength (728.5 MPa) and desirable corrosion rate of 2.16E-06 mm/year compared to the sintered conditions at 1250˚C-1h, 1300˚C-1h, 1350˚C-1h, 1250˚C-3h and 1350˚C-3h. As the temperature increased, and holding time was prolonged to 3 hours, the tensile strength and the hardness increased gradually. While, from the morphology of sintered compacts, it shows that the morphological bonding between powder particles become denser with longer sintering time, 3 h highest sintering temperature of 1350 ˚C. Moreover, the decrease in porosity amount was shown to improve the mechanical properties of CoCrMo alloy sintered compacts. It can be concluded that the sintering temperature and time is a critical parameter for reducing the amount of porosity and improving mechanical properties of sintered compacts.

Item Type: Thesis (Masters)
Additional Information: Thesis (Master of Science) -- Universiti malaysia Pahang - 2019, SV: ASSOCIATE PROFESSOR DR. WAN SHARUZI WAN HARUN, NO. CD: 12264
Uncontrolled Keywords: Metal injection moulding (MIM); CoCrMo alloy
Subjects: T Technology > TJ Mechanical engineering and machinery
Faculty/Division: Institute of Postgraduate Studies
Faculty of Mechanical & Manufacturing Engineering
Depositing User: Mrs. Sufarini Mohd Sudin
Date Deposited: 24 Dec 2020 01:29
Last Modified: 24 Dec 2020 01:29
URI: http://umpir.ump.edu.my/id/eprint/30319
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