Study of improved casting methods for the manufacture of medical grade cobalt alloy

Kavanagh, Alan (2017). Study of improved casting methods for the manufacture of medical grade cobalt alloy. University of Birmingham. Ph.D.

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Abstract

Within many foundries, poor mould design and casting methods result in high levels of process variability, poor metal yield, scrap and inefficiencies leading to overall sub-optimal performance. The aim of this project was to try to try to address main problem areas through an alternate casting method (1-tree casting) used for the manufacture of ASTM F-75 cobalt chrome (Co-Cr) biomedical castings.
The mould filling of various runner systems was assessed using real-time X-ray imaging and computational modelling. Mechanical testing, CT-scanning and metallurgical inspection of as-cast and heat-treated test bars produced in industrial trials at the DePuy foundry were performed. Direct thermocouple measurements, thermal imaging and microstructure measurements examined the effect of casting method on solidification time and cooling rates. Numerical modelling using ProCAST casting simulation software was performed.
A statistical improvement in the as-cast tensile strength was observed with the 1-tree casting method compared to the established casting method. CT analysis indicated the presence of discrete gas porosity in some specimens which was attributed to high levels of air entrainment during pouring. The occurrence rate and morphology of the observed pores is described. Post heat-treatment the differences in the as-cast mechanical properties were eliminated with no evidence of casting method observed. However elongation to fracture results in both the as-cast and heat-treated conditions were lower than expected, and pose a challenge regardless of casting method. The 1-tree casting method reduced variation in alloy cooling rates and solidification times versus the established process.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):