title: Optimal conditions for alumina coating formation on the MA956 superalloy for prosthetic bearing applications.
abstract: An experimental study of the oxidation treatment at high temperature of the ODS MA956 superalloy was conducted in an attempt to achieve a protective alumina scale for biomedical applications. A quadratic response-surface model was developed in order to study the effects of treatment time and temperature (in the range of 1000 degrees C to 1250 degrees C) on scale thickness. The obtained model adequately represents the experimental response and shows that the thickness gradients of the layer increase with the temperature for each exposure time and decrease steadily to zero as the treatment time increases. The microstructural characterization reveals that the alumina scale formed at or above 1000 degrees C consists of an alpha-alumina phase. Treatments at temperatures above 1150 degrees C give rise to an alumina scale with some defect probability. An increase in the temperature up to 1200 degrees C gives rise to the appearance of some blistering of the superficial scale. An oxidation treatment of 100 h at 1100 degrees C was found to be the best for guaranteeing the formation of a defect-free, compact, adherent, and continuous alpha-alumina scale thick enough to support satisfactory wear and biological conditions.
authors.affiliation: Centro Nacional de Investigaciones Metalúrgicas, C.S.I.C., Madrid, Spain. jruiz@cenim.csic.es
authors.forename: J
authors.initials: J
authors.lastname: Ruiz
authors.forename: M L
authors.initials: ML
authors.lastname: Escudero
authors.forename: H
authors.initials: H
authors.lastname: Canahua
authors.forename: M C
authors.initials: MC
authors.lastname: García-Alonso
mesh_terms: D000497:Alloys; D000535:Aluminum; D000537:Aluminum Oxide; D002857:Chromium; D020099:Coated Materials, Biocompatible; D003343:Corrosion; D004577:Electron Probe Microanalysis; D007501:Iron; D008855:Microscopy, Electron, Scanning; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014025:Titanium; D014961:X-Ray Diffraction; D015019:Yttrium
chemical_list: D000497:Alloys; D020099:Coated Materials, Biocompatible; C092620:MA 956; D002857:Chromium; D015019:Yttrium; D000535:Aluminum; D014025:Titanium; D007501:Iron; D000537:Aluminum Oxide