Tribo-mechanical properties of thin boron coatings deposited on polished cobalt alloy surfaces for orthopedic applications

Abstract

This paper presents experimental evidence that thin (< approximately 200 nm) boron coatings, deposited with a (vacuum) cathodic arc technique on pre-polished Co-Cr-Mo surfaces, could potentially extend the life of metal-on-polymer orthopedic devices using cast Co-Cr-Mo alloy for the metal component. The primary tribological test used a linear, reciprocating pin-on-disc arrangement, with pins made of ultra-high molecular weight polyethylene. The disks were cast Co-Cr-Mo samples that were metallographically polished and then coated with boron at a substrate bias of 500 V and at about 100 degrees C. The wear tests were carried out in a saline solution to simulate the biological environment. The improvements were manifested by the absence of a detectable wear track scar on the coated metal component, while significant polymer transfer film was detected on the uncoated (control) samples tested under the same conditions. The polymer transfer track was characterized with both profilometry and Rutherford Backscattering Spectroscopy. Mechanical characterization of the thin films included nano-indentation, as well as additional pin-on-disk tests with a steel ball to demonstrate adhesion, using ultra-high frequency acoustic microscopy to probe for any void occurrence at the coating-substrate interface.

Boron films produced by high energy Pulsed Laser Deposition

“…For known substrate properties, and if the film mass density is known, the only independent parameters to be determined are thus C 11 and C 44 . The minimization has been performed for two different values of the film mass density: 2.51 g/cm 3 estimable from the quartz microbalance and the bulk β-boron value of 2.35 g/cm 3 . The two values allow to fit the experimental dispersion relation in almost indistinguishable ways, but obviously by different values of the elastic constants, as presented in Table 2.…”

“…Thanks to their extreme hardness, up to 30-60 GPa [1], B films can be exploited as protective coatings [2]. When exposed to ambient air, B surfaces get oxidized forming a hydroxide layer (boric acid), which acts as a solid lubricant that allows high wear properties as well as antibacterial properties [2,3]. Boron surfaces exhibit high reflectance in the extreme ultraviolet (40 nm -200 nm), and are therefore suitable for the production of extreme UV optics that find applications in plasma diagnostics, spectroscopy, synchrotron radiation, and free electron lasers [4].…”

The recent progress of tribological biomaterials

“…The second generation is Co-Cr-based alloys, which are widely used in artificial hip and knee joints because of their wear resistance ability; however, the development of nickel-free Co-Cr-based alloys is imperative for the allergy of nickel. Various routes such as ion implant [33], surface coating [34,35] and doping [36] are used to enhance the wear resistance, reduce the friction coefficient and increase the hard of Co-Cr based alloys. The third generation is titanium-based alloys, which are extensively studied [37][38][39][40][41][42] and used in implant of artificial bones because of its good biocompability, mechanical properties and wear resistance ability [31,43].…”

Optimization of wear loss in silicon nitride (Si3N4)–hexagonal boron nitride (hBN) composite using DoE–Taguchi method

“…Hexagonal boron nitride is well known solid situ lubricating material with biocompatibility (Gangopadhyay et al 1997 ; Saito et al 1999 ; Shah et al 2013 ). Anabtawi et al ( 2008 ) evaluated the biocompatibility of boron coatings and Klepper et al ( 2008 ) presented tribomechanical properties of thin boron coatings on cobalt alloy in an orthopedic application with no loss of coating during the test. The lubrication properties of h-boron nitride are comparable to those of phospholipids, which are the best lubricant in human (Pawlak et al 2008 ).…”