Conor F. Dunne

Co-blasting of titanium surfaces with an abrasive and hydroxyapatite to produce bioactive coatings: Substrate and coating characterisation

The aim of this work is to assess the influence of two blast media on the deposition of hydroxyapatite onto a titanium substrate using a novel ambient temperature coating technique named CoBlast. CoBlast was developed to address the problems with high temperature coating techniques. The blasting media used in this study were Al2O3 and a sintered apatite powder. The prepared and coated surfaces were compared to plasma sprayed hydroxyapatite on the same substrates using the same hydroxyapatite feedstock powder. X-ray diffraction analysis revealed the coating crystallinity was the same as the original hydroxyapatite feedstock powder for the CoBlast samples while evidence of amorphous hydroxyapatite phases and β-TCP was observed in the plasma sprayed samples. The blast media type significantly influences the adhesive strength of the coating, surface roughness of both the substrate and coating and the microstructure of the substrate. The coating adhesion increased for the CoBlasted samples from 50 MPa to 60 MPa for sintered apatite powder and alumina, respectively, while plasma spray samples were significantly lower (5 MPa) when tested using a modified pull-test. In conclusion, the choice of blast medium is shown to be a key parameter in the CoBlast process. This study indicates that sintered apatite powder is the most suitable candidate for use as a blast medium in the coating of medical devices.

Blast Coating of Superelastic NiTi Wire with PTFE to Enhance Wear Properties

This work investigates the deposition of polytetrafluoroethylene (PTFE) onto a superelastic NiTi wire using an ambient temperature-coating technique known as CoBlast. The process utilises a stream of abrasive (Al2O3) and a coating medium (PTFE) sprayed simultaneously at the surface of the substrate. Superelastic NiTi wire is used in guidewire applications, and PTFE coatings are commonly applied to reduce damage to vessel walls during insertion and removal, and to aid in accurate positioning by minimising the force required to advance, retract or rotate the wire. The CoBlast coated wires were compared to wire treated with PTFE only. The coated samples were examined using variety of techniques: X-ray diffraction (XRD), microscopy, surface roughness, wear testing and flexural tests. The CoBlast coated samples had an adherent coating with a significant resistance to wear compared to the samples coated with PTFE only. The XRD revealed that the process gave rise to a stress-induced martensite phase in the NiTi which may enhance mechanical properties. The study indicates that the CoBlast process can be used to deposit thin adherent coatings of PTFE onto the surface of superelastic NiTi.

Deposition of Hydroxyapatite Onto Superelastic Nitinol Using an Ambient Temperature Blast Coating Process

This work investigates the deposition of hydroxyapatite (HA) onto superelastic nickel-titanium (NiTi) using an ambient temperature coating process known as CoBlast. The process utilises a stream of abrasive alumina (Al2O3) and a coating medium (HA) sprayed simultaneously at the surface of the substrate. The use of traditional coatings methods, such as plasma spray, is unsuitable due to the high temperatures of the process. This can result in changes to both the crystallinity of the HA and properties of the thermally sensitive NiTi. HA is a biocompatible, biodegradable and osteoconductive ceramic, which when used as a coating can promote bone growth and prevent the release of nickel from NiTi in vivo. Samples were coated using different blast pressures and abrasive particle sizes and were examined using a variety of techniques. The coated samples had a thin adherent coating, which increased in surface roughness and coating thickness with increasing abrasive particle size. X-ray diffraction analysis revealed that the process gave rise to a stress-induced martensite phase in the NiTi which may enhance mechanical properties. The study indicates that the CoBlast process can be used to deposit thin adherent coatings of HA onto the surface of superelastic NiTi.

Use of a blast coating process to promote adhesion between aluminium surfaces for the automotive industry

ABSTRACT The influence of surface roughness on adhesive bond strength for aluminium to aluminium bonding is investigated. firstly, the effect of varying surface roughness is investigated using grit-blast surface preparation. this is then compared to a novel ambient temperature blast coating technique known as coblast which, using a co-incident blast stream of abrasive and coating media, simultaneously removes a surface’s native passivation layer while depositing an active epoxy primer coating on the newly-exposed reactive metal surface. a range of al2o3 abrasive media with particle sizes from < 13 m to < 1200 m were used to prepare the varying surface roughness profiles. characterisation techniques such as surface profilometry, sem, edx, x-ray diffraction and light microscopy were used to investigate the level of coating coverage along with the degree of plastic deformation induced in the substrate as a result of the coating procedure. in addition, a modified lap shear test was conducted along with salt fog corrosion testing. results indicate that replacement of the grit-blast treatment with the epoxy coblast coating gives cohesive failure and an increase in lap shear strength of up to 15% before corrosion testing and up to 36% after 240 hours in a salt fog chamber.