Surface Modification of Laser Metal Deposited Ti-6Al-4V+10%Mo for Biomedical Applications

Arianna Rachel Ziemer

Abstract


The main goal of the project is to observe characteristic changes in laser metal deposited Ti-6Al-4V + 10% Mo at varying scan speeds.  Laser metal deposition is an additive manufacturing technique that begins with two hoppers that hold the powdered metals. In the first hopper there is Ti-6Al-4V and the second hopper contains molybdenum.  Ti-6Al-4V is a titanium alloy that contains 6 wt% aluminum and 4 wt% vanadium. When the molybdenum is added to the Titanium alloy the hardness, biocompatibility and corrosion resistance of the material are affected. The hoppers release the powder such that there is 90 wt% Ti-64 and 10 wt% Mo. The powders are deposited through a nozzle and a focused laser creates a melt pool of the two metal powders onto a substrate. A three dimensional design program is used to create the path that the laser follows, depositing layers of the metal, until the desired part is achieved. Five samples of the laser deposited Ti-6Al-4V + 10% Mo were completed at the CSIR National Laser Center in Pretoria, South Africa. The five samples consist of scan speeds varied from 0.50 meters per minute up to 1.50 meters per minute, while the laser power remains at a constant 1700 Watts. The microstructure, micro hardness and corrosion resistance of the samples are the main focus in this project. Currently, Ti-64 is used in biomedical implants such as hip replacements. The results showed that the samples with the lower scan speeds have longer grain sizes, as the samples with the faster scan speeds have smaller grain sizes. The longer grain sizes create a stronger bond so the slower scan speeds of 0.50 and 0.75 m/min are ideal for biomedical applications. Additionally, the scan speeds of 0.75, 1.00 and 1.25 m/min have Vickers hardness values between 353 and 357. These high hardness values are not ideal because they could possibly cut into the surrounding bone of a hip replacement. On the other hand, the scan speeds of 0.50 and 1.50 m/min had average Vickers Hardness values of 322 and 324. The lower hardness value is ideal for biocompatible applications so that the implant does not cut into the surrounding bone. The corrosion resistance test first revealed that the surface of the samples are rough. This is important for osseointegration to occur. When the samples were removed from the 7-day corrosion test the grooves on the surface became deeper. All samples corroded to the same extent. Therefore, the scan speed of 0.50 m/min is considered ideal for biomedical applications. In the future, a higher laser power should be used in order to successfully integrate the powdered metals by melting the molybdenum particles. Additionally scanning speeds lower than 0.50 m/min should be further researched.

Keywords


Biomedical Implants; Laser Metal Deposition; Titanium Alloy;

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