title: Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions.
abstract: Ti6Al7Nb alloy foams having 53-73% porosity were manufactured via evaporation of magnesium space holders. A bioactive 1µm thick sodium hydrogel titanate layer, NaxH2-xTiyO2y+1, formed after 5M NaOH treatment, was converted to crystalline sodium titanate, Na2TiyO2y+1, as a result of post-heat treatment. On the other hand, subsequent CaCl2 treatment of NaOH treated specimens induced calcium titanate formation. However, heat treatment of NaOH-CaCl2 treated specimens led to the loss of calcium and disappearance of the titanate phase. All of the aforementioned surface treatments reduced yield strengths due to the oxidation of the cell walls of the foams, while elastic moduli remained mostly unchanged. Accordingly, equiaxed dimples seen on the fracture surfaces of as-manufactured foams turned into relatively flat and featureless fracture surfaces after surface treatments. On the other hand, Ca- and Na-rich coating preserved their mechanical stabilities and did not spall during fracture. The relation between mechanical properties of foams and macro-porosity fraction were found to obey a power law. The foams with 63 and 73% porosity met the desired biocompatibility requirements with fully open pore structures and elastic moduli similar to that of bone. In vitro tests conducted in simulated body fluid (SBF) showed that NaOH-heat treated surfaces exhibit the highest bioactivity and allow the formation of Ca-P rich phases having Ca/P ratio of 1.3 to form within 5 days. Although Ca-P rich phases formed only after 15 days on NaOH-CaCl2 treated specimens, the Ca/P ratio was closer to that of apatite found in bone.
authors.affiliation: Çankaya University, Materials Science and Engineering Department, 06810 Ankara, Turkey; Middle East Technical University, Metallurgical and Materials Engineering Department, 06800 Ankara, Turkey. Electronic address: ebutev@cankaya.edu.tr.
authors.forename: Ezgi
authors.initials: E
authors.lastname: Bütev
authors.affiliation: Çankaya University, Materials Science and Engineering Department, 06810 Ankara, Turkey. Electronic address: ziyaesen@cankaya.edu.tr.
authors.forename: Ziya
authors.initials: Z
authors.lastname: Esen
authors.affiliation: Middle East Technical University, Metallurgical and Materials Engineering Department, 06800 Ankara, Turkey. Electronic address: bor@metu.edu.tr.
authors.forename: Şakir
authors.initials: Ş
authors.lastname: Bor
mesh_terms: D000497:Alloys; D001031:Apatites; D001672:Biocompatible Materials; D001826:Body Fluids; D002122:Calcium Chloride; D055119:Elastic Modulus; D006358:Hot Temperature; D020100:Hydrogels; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D012972:Sodium Hydroxide; D013499:Surface Properties; D014025:Titanium
chemical_list: D000497:Alloys; D001031:Apatites; D001672:Biocompatible Materials; D020100:Hydrogels; C070282:Ti-6Al-7Nb alloy; D012972:Sodium Hydroxide; D014025:Titanium; D002122:Calcium Chloride
keywords: Hydrothermal treatment; Mechanical properties; Simulated body fluid; Ti6Al7Nb alloy foam