Electrochemical Corrosion Investigation of 49-Cell Combinatorial Library of Titanium-Based Alloys Fabricated by DMD

Abstract

This combinatorial materials science study investigated the corrosion resistance of titanium alloys. A combinatorial library of 49 alloys of titanium was fabricated by the direct metal deposition ͑DMD͒ technique. This library consisted of a single cube of metal with discrete 4 ϫ 4 ϫ 20 mm regions, each region containing discrete, selected percentages of aluminum and iron. In situ characterization of these regions allowed a rapid evaluation of the 49 alloys for potential use in biomedical implants. The resistance to electrochemical corrosion in Hanks' solution of each titanium-based alloy was tested using the cotton tape electrochemical polarization method. High concentrations of Al ͑corrosion rate of the Ti-9Al = 0.06 mm/yr in the 49-cell sample͒ or Fe ͑corrosion rate of the Ti-17Fe = 8.32 ϫ 10 −3 mm/yr͒ caused an uneven distribution of alloying elements in the phases, which resulted in poor corrosion resistance in biofluids compared to pure titanium ͑corrosion rate 2.93 ϫ 10 −6 mm/yr͒. The best corrosion resistance in Hanks' solution was demonstrated by the Ti-5Al-4Fe ͑corrosion rate 9 ϫ 10 −5 mm/yr͒. The discovery of materials with enhanced properties can be a time-consuming and unpredictable trial-and-error process, and is becoming more difficult with the increasing complexity of modern materials. [1][2][3][4] Compared to the conventional one-alloy-at-a-time approach, the combinatorial materials science method increases the efficiency of research by coupling the parallel synthesis of large libraries of compositions with efficient screening for desired properties. 5,6 The success of the combinatorial method often depends on the ability to rapidly screen the combinatorial library. The sample size and geometry must therefore be designed to match the requirement of the appropriate screening method. 7-10 A previous study 11 demonstrated electrochemical corrosion screening of a 7-cell library of titanium alloys fabricated using direct metal deposition ͑DMD͒. This article extends that work and reports the fabrication and efficient screening for 49-cell libraries.The titanium alloy Ti-6Al-4V is often used in biomedical implants. The vanadium in this alloy has raised concerns about the long-term toxicity. 12 While the substitution of iron for vanadium would eliminate these concerns, in vivo corrosion resistance must be maintained.The work is aimed at demonstrating the combinatorial method for selection among a large number of DMD-built alloys with different composition. The corrosion resistance of each elemental cell without library separation in Hanks' solution can be studied by applying the cotton tape technique. ExperimentalFabrication of combinatorial library.-The DMD process consists of three powder feeders which deliver metal powders to the focus of a CO 2 laser, melting and depositing the resulting alloy onto a substrate. The DMD 3000 machine ͑The POM Group, Auburn Hills͒ at the University of Louisville fabricated solid blocks of alloy by layer-by-layer deposition utilizing a 3000 W CO 2 laser to melt metal powd...

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