title: Wear and surface degradation of commercial ZTA femoral heads under boundary lubrication conditions.
abstract: The effect of frictional sliding on the surface degradation of commercially available zirconia-toughened alumina (ZTA) femoral heads was studied using a pin-on-ball wear tester under three different lubricating conditions: dry, water, and squalene. Water and squalene were employed under boundary lubrication regimes. Despite the unique (non-standard) character of this apparatus, standard loading conditions could be applied, which effectively determined dynamic friction coefficients as basic material properties. Two types of surface degradation were observed: (i) the polymorphic tetragonal-to-monoclinic (t→m) transformation of the zirconia (ZrO2) dispersoids, and (ii) the off-stoichiometry drift caused by oxygen vacancy formation within the alumina matrix. Scanning laser microscopy (SLM), Raman spectroscopy (RS), scanning electron microscopy (SEM), cathodoluminescence (CL), and X-ray photoelectron spectroscopy (XPS) were utilized to evaluate the fractions of transformed zirconia phase and the stoichiometric evolution of the oxygen sub-lattice at the surface of wear-tested ZTA components. Wear tracks on the surface of the femoral heads were only detected under dry conditions. Dry wear also showed the highest frictional forces and the most pronounced formation of oxygen vacancies among the tested conditions. Conversely, equivalent or greater amounts of the t→m transformation were observed with water and squalene lubrication when compared to the dry wear condition.
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Kyoto, Japan. Electronic address: n14i0002@kit.ac.jp.
authors.forename: Elia
authors.initials: E
authors.lastname: Marin
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Kyoto, Japan.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Rondinella
authors.affiliation: Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, Osaka, Japan.
authors.forename: Wenliang
authors.initials: W
authors.lastname: Zhu
authors.affiliation: AMEDICA Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States.
authors.forename: Bryan J
authors.initials: BJ
authors.lastname: McEntire
authors.affiliation: AMEDICA Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States.
authors.forename: B Sonny
authors.initials: BS
authors.lastname: Bal
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Kyoto, Japan. Electronic address: pezzotti@kit.ac.jp.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
mesh_terms: D000537:Aluminum Oxide / Q000032:analysis*; D005270:Femur Head; D006622:Hip Prosthesis; D008153:Lubrication; D008422:Materials Testing; D013499:Surface Properties; D015040:Zirconium / Q000032:analysis*
chemical_list: D015040:Zirconium; D000537:Aluminum Oxide
keywords: Biolox delta; Monoclinic transformation; Oxygen vacancies; Raman spectroscopy; ZTA; lubrication