From defect to design feature: optimising LB-PBF-induced porosity for altering tribological behaviours of cocrmo surfaces for orthopaedic applications
File(s)
Author(s)
Shi, Qingyue
Type
Thesis
Abstract
Additive manufacturing has expanded the design possibilities for orthopaedic implants, enabling complex geometries and patient-specific customisation that are difficult to achieve with conventional manufacturing. Among these techniques, Laser Beam Powder Bed Fusion (LB-PBF) has been widely adopted for processing metals. Cobalt-chromium-molybdenum (CoCrMo) alloys have been the standard bearing material in many designs of artificial hip joints for their high mechanical strength and wear resistance. Despite extensive work on LB-PBF mechanical properties and on the tribology of conventionally manufactured CoCrMo, the tribology of LB-PBF CoCrMo remains not well understood. Porosity is an intrinsic feature of LB-PBF, arising from the interaction of process parameters and thermal histories. In the context of articulating surfaces, LB-PBF process-induced pores represent a microstructural feature whose effects on tribological performances have yet to be fully defined. Understanding whether such features behave as defects to be eliminated or as functional surface textures with potential performance benefits requires a combined additive manufacturing-tribology approach. This thesis addresses this gap by progressing from elucidating fundamental process-structure relationships, through assessing tribological behaviours of LB-PBF CoCrMo, to demonstrating the feasibility of manufacturing bearing surfaces with spatially tailored porosity. The results demonstrate that LB-PBF process-induced porosity in CoCrMo can be systematically controlled through the combined effects of process parameters, enabling porosity levels ranging from near-dense to highly porous. Tribological evaluation showed that the effects of porosity are strongly affected by lubrication conditions: under protein-rich lubrication, friction and wear performance depend on the porosity level, whereas under water lubrication, higher porosity led to increased friction and apparent wear volume loss. The fabrication and testing of hybrid bearing surfaces with locally engineered porosity revealed that spatial porosity contrasts introduced additional complexity and increased frictional variability and wear. The outcomes provide a foundation for optimising LB-PBF processing strategies and exploring new design approaches for orthopaedic implants.
Version
Open Access
Date Issued
2025-08-29
Date Awarded
2026-02-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Myant, Connor
Publisher Department
Dyson School of Design Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)