SUNConferences, 17th Annual Conference of the Rapid Product Development Association of South Africa

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Direct laser melting of hydroxyapatite for surface modification of high nitrogen stainless steel for orthopaedic implant applications
MUKUL SHUKLA

Last modified: 2016-10-17

Abstract


Abstract

In this research, the Laser rapid manufacturing (LRM) additive manufacturing process was used to deposit hydroxyapatite (HAP) for surface modification of high nitrogen stainless steel. This process, unlike the conventional coating processes, is able to achieve coatings with good metallurgical bonding and little dilution. The microstructure and antibacterial properties of the deposited coatings were studied using optical microscopy, scanning electron microscopy and Fluorescence Activated Cell Sorting (FACS). Micro-structural studies showed that the laser modified surface consisted of austenite dendrities while the FACS test confirms significantly superior antibacterial properties of laser modified samples compared to pristine samples.

 

Keywords: Laser rapid manufacturing, Laser surface modification, Implant, Stainless steel, Hydroxyapatite

 

Introduction

In spite of the lower corrosion resistance (in comparison to titanium), internal fixation devices are still being made of austenitic stainless steels (largely SS316L). This is owing to their excellent mechanical properties and low cost in comparison to titanium.1-2 Absence of toxic effect as confirmed by cytotoxicity results and high nitrogen content of 254SS have made it a candidate for scientific investigation, towards developing a futuristic orthopaedic implant material.3-4

Experimental work

An additive manufacturing system (LRM type) equipped with a 2.0 kW continuous wave, ytterbium-doped, fiber laser with a beam size of 2.5 mm, was used to carry out direct laser melting of already prepared, preplaced HAP powder beds for the surface modification of high nitrogen stainless steel (SS254) substrates (100 × 50 × 3 mm3 sheets). Several coating samples, over 100 mm2 area, were prepared at 1000 W laser power and 1m/min scan speed.

Results and discussion

The cross-sectional microstructure of the laser surface-modified sample is shown in Fig. 1. As can be seen, the modified surfaces are free from any gross defects such as porosity or cracks. The modified surfaces exhibited an as-cast microstructure with austenite dendrites.

Conclusions

In the current study, a successful attempt is made to modify the surface of high nitrogen stainless steel (SS254) with HAP using an LRM system. The modified surfaces showed microstructure with austenite dendrites. FACS test confirms the laser surface-modified samples have significantly superior antibacterial property compared to the unmodified samples. The present work demonstrates that it is feasible to modify 254 stainless steel (used as a biomedical orthopaedic material)  with HAP using a laser additive manufacturing system.

References

[1]  Disegi, JA. et al., Injury. 2000; 4: 2-6.[2] Walczac, J. et al., Biomaterials. 1998; 19: 229-237.

[3]  Afonso, MLCA. et al., Colloids Surf A: Physicochem Eng  Asp. 2008; 317: 760-763.

[4]  Afonso, MLCA. et al., Mater Lett. 2015; 148: 71-75.

 


Keywords


Keywords: Laser rapid manufacturing, Laser surface modification, Implant, Stainless steel, Hydroxyapatite