Enhanced Scratch Performance of Plasma Sprayed Hydroxyapatite Composite Coatings Reinforced with BN Nanoplatelets

Yao Chen,Jia Ren,Dong Zhao,Weiwei Liu

doi:10.3390/coatings10070652

Abstract

In recent years, research on hydroxyapatite (HA) coatings has been driven by the demands of clinical applications. However, the intrinsic brittleness of HA limits its potential in the use for the load-bearing implant. To improve mechanical properties of the HA coating itself, a HA composite coating reinforced with hexagonal boron nitride nanoplatelets (BNNP) was fabricated using plasma spray, and its scratch behavior was investigated in this research. Typical brittle fractures such as microcracks both in and beyond the residual groove and material chipping were observed in the HA coating, while stronger and tougher BNNP/HA coatings exhibited a dominant role in protecting them from scratch damage through resisting plastic deformation and brittle microfracturing. Moreover, easier grain sliding within a splat and splat sliding at the splat boundaries due to the presence of BNNPs, and the nature porosity at different length scales of the as-sprayed HA composite coatings would provide significant self-lubricating effects to reduce the lateral force during scratching and alleviate the contact damage. Therefore, the addition of BNNPs renders HA coating with low scratch friction and enhanced tolerance to surface damage, which is naturally beneficial for the long-term durability and reliability of the implants.

Highlights

Titanium alloys with a combination of high toughness and specific strength have been widely used for orthopedic implants [1]
The addition of boron nitride nanoplatelets (BNNP) renders HA coating with low scratch friction and enhanced tolerance to surface damage, which is naturally beneficial for the long-term durability and reliability of the implants
To achieve improved mechanical properties of HA coating, HA composite coatings reinforced with a second phase, such as alumina (Al2 O3 ) [7,8], yttria-stabilized zirconia (YSZ) [9,10], and titania [11,12] have been considerably developed in the past two decades

Summary

Introduction

Titanium alloys with a combination of high toughness and specific strength have been widely used for orthopedic implants [1]. The low wear resistance and the nature of the bioinert-induced inferior adhesion bonding with the bone tissues are well known to impair their long-term clinical performance. These metallic materials usually release harmful metallic ions and lead to adverse effects on the surrounding tissues when they get in contact with body fluids [2]. Despite significant improvement achieved in fracture toughness of these HA composite coatings, it should be noted that the addition contents of these ceramic particles, basically biologically inert, are usually as high as 30–50% in weight fraction (wt.%), inevitably leading to degradation of the excellent bioactivity and osteointegration associated with HA

Methods

Results

Conclusion