Tribological Properties Of Laser Cladded Wollastonite Bioceramic Coatings

Wollastonite coatings had relatively high adhesive strength and excellent bioactivity biocompatibility as well,for which wollastonite coating was regarded as potential substitute material for bone graft in human body.Bone substitute material was generally required to meet certain mechanical and biological performance requirements.After being implanted into bodies,wollastonite coating would guide the generation of bone tissue after dissolution and degradation.But it was rapidly dissolution.And at present,tribological properties of wollastonite coating was insufficient discussed.Wollastonite composite ceramic coatings?named with W10,W8Z2 and W6Z4?were prepared on titanium alloy matrix with different mass fraction of ZrO₂?0wt.%,20 wt.% and 40 wt.%?through laser cladding technology.The microstructure,bioactivity and tribological properties of coating were investigated.?1?The coating structure had compactness with no observation of micro-cracks.Coating were metallurgical bonded to the substrate.The micro-structure of the ceramic coatings was mainly cellular and cellular-dendrite structure.The roughness of the dendrites was increased with added ZrO₂,and the micro-hardness and bonding strength of coating increased with the add ZrO₂ content.W10 coating is composed of ?-CaSi O₃?CaTiO₃,?-Ca₂?SiO₄?,SiO₂,TiO₂ and CaO.W8Z2 and W6Z4 coating in the ZrO₂ was still partly in the form of tetragonal phase,ZrO₂ and CaO reacted to generate ZrO₂.?2?Tris-HCl solution immersion test showed that adding zirconia phase in coatings could increase coatings' degradation rate which might decrease by more than 30% after 7 days later.Some calcium phosphate was deposited on the coating by SBF solution immersion test.It indicated that coating had some biological activity.The nucleation and growth process of apatite deposition on the coating surface were also analyzed.However,added zirconia phase in the coatings might decrease the bioactivity of the coatings.?3?Fiction and wear properties of coatings were tested with wear-test machine,and stress distribution and changes during sliding contact process were analyzed by numerical stimulation.In the case of dry friction,the friction coefficient of the wollastonite coatings increased with the increase of zirconium oxide content in the stable friction stage.However,the wear loss of the coating was smaller in the case.Typical fatigue spalling characteristics appeared on the wear surfaces of W10 coating and W8Z2 coating,while the main wear mechanism of W6Z4 coating was mainly in the form of plowing effect,abrasive wear and adherence.Under the environment of bovine serum lubrication,friction coefficient and wear loss decreased of the coating with increase of zirconium oxide content.furrow traces appeared on the coating surface.the addition of zirconium oxide increased the fracture toughness and the hardness of the coatings,so that the friction coefficient could be reduced and the wear resistance of the coatings.Load had a significant impact on the amount of wear and coefficient of friction coating.Under heavy load conditions,the lubricating effect of bovine serum decreased resulting in thinner lubricant film and worse lubrication performance,for which bigger abrasion loss and higher friction coefficient would appear.?4?The results of ANSYS analysis showed that: the contact interface pressure,friction force and equivalent stress at the contact interface pressure were increased suddenly.SEM showed that more serious wear phenomenon appeared in the end part of coatings' wear trace,which was related to the sudden increase of the stress,and the results of simulation corresponded to the experimental results.During the process of using coatings practically,more attention should be paid to the unsteady wear condition.