Laser Surface Modified TI 6Al-4V

By Milan van Bree TU Delft 2008.

Objectives

The objectives are: • Understand the materials for implant design • Understand surface modification • Understand the role of microstructure • Research if microstructure changes corrosion

resistance • Research which microstructure is optimal

Outline

Introduction Purpose of the Research The Research Summary Conclusion

Introduction

The goal of orthopedic implants give people another chance at mobility.

What happens when these implants fail or corrode?

What can we as engineers do?

Engineering Implants

The main component for implant design has been material selection. • Stainless steel • Titanium • Cobalt

Titanium has become very popular due to its good: biocompatibility, high strength, and bone adhesion.

Titanium Implants

Titanium implants still have issues that are being addressed. • Poor wear resistance • Harmful wear and corrosion products

• Aluminum- Neurotoxin • Vanadium- Cytotoxin

How do we eliminate or reduce these problems with titanium?

Understanding Titanium

First, we must understand what makes titanium corrosion resistant. • The formation of a tenacious oxide layer • Close to the cathodic end of the galvanic series

Second, we must find a solution to improving the corrosion resistance. • Oxide thickening • Nitriding • Surface re-melting

Issues with Coatings

The oxide thickening and nirtiding method have promising results but not without consequence. • Hard and brittle • Crack and flake off easily when force is

applied

That leaves us with laser surface re-melting or modification.

Laser Surface Modification

Laser surface modification allows for the surface to retain most of the base materials properties.

The change that does occur comes from the morphing of the microstructure.

The change is made in two ways: • Surface melting • Surface heat treating

Titanium Microstructures

Titanium depending on its alloys comes in three forms. • Alpha phase (HCP) • Beta phase (BCC) • Alpha-beta phase (Mixed)

Titanium 6AL-4V is a alpha-beta phase alloy. This means that it is heat treatable.

Hexagonal Closed-Packed (HCP)

Body Centered Cubic (BCC)

Understanding the Microstructure

The microstructure of Ti-6Al-4V can still come in a variety of structures.

Understanding the Role of the Microstructure

We have shown that laser surface melting and heating has improved the corrosion resistance of TI-6Al-4V.

Credit has been given to oxide thickening. • Validity issue with microstructure

change

Open Circuit Potentials Vs. Time

What About Microstructure?

Other research has made the argument that the refinement and change in microstructure are to be given credit. • Validity with oxide layer formation

The question then becomes, regardless of the oxide layer which microstructure is the most corrosion resistant?

Current Plan of Research We are currently researching the effect of

microstructure of corrosion resistance. We have currently mapped out the boundary

line for melting and heat treating for laser processing.

Due to limited funds we are only looking at three microstructures. • As received condition • Laser melted condition • Laser heat treated condition

Current Plan of Research

After the treatment of each sample the samples will have the oxide layer removed and then subjected to corrosion tests.

If a certain microstructure performs better then a change in corrosion resistance can be linked to microstructure.

If this is the case then more research will be needed to determine the optimal microstructure for titanium implants.

Summary

Titanium implants have issues that need addressed.

Changing the microstructure of the titanium implant may help resolve these issues.

More research is needed to understand the role of the microstructure of titanium implants on corrosion resistance.

Conclusion

As more research is performed on the corrosion resistance of titanium microstructures, we as engineers will be able to better design and produce higher quality titanium implants.

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microscopical analysis of laser-treated titanium implant surfaces-a comparative study. Biomaterials 2000; 21:1067-1073.

Gyorgy E, Perez del Pino A, Serra P, Morenza JL. Surface nitridation of titanium by pulsed Nd:YAG laser irradiation. Applied Surface Science 2002; 186:130-134.

P, He XL, Li XX, Yu LG, Wang HM. Wear resistance of a laser surface alloyed Ti-6Al-4V alloy. Surface and Coatings Technology 2000; 130:24-28.

Mori JC, Serra P, Martinez E, Sardin G, Esteve J, Morenza JL. Surface treatment of titanium by Nd:YAG laser irradiation in the presence of nitrogen. Applied Physics A 1999; 69:S699-S702.