Research Papers

Continuous Mode Laser Coating of Hydroxyapatite/Titanium Nanoparticles on Metallic Implants: Multiphysics Simulation and Experimental Verification

[+] Author and Article Information
Martin Yi Zhang, Gary J. Cheng

School of Industrial Engineering, Purdue University, West Lafayette, IN 47906

J. Manuf. Sci. Eng 133(2), 021010 (Mar 15, 2011) (12 pages) doi:10.1115/1.4003692 History: Received August 26, 2010; Revised February 15, 2011; Published March 15, 2011; Online March 15, 2011

A novel methodology of laser coating of mixture of bioceramic and titanium nanoparticles onto metal implants is developed in this work. Feasibility of this approach is demonstrated via both multiphysics simulation and experiments. Treating incident laser as an electromagnetic wave, an electromagnetic (EM) module is coupled with a heat transfer (HT) module. The EM-HT model analyzes the interaction between laser and nanoparticles and ends up with a temperature rise in the system. Hydroxyapatite (HAp) and titanium nanoparticles are coated on the Ti–6Al–4V substrate. Processing parameters such as laser power, beam radius, scan speed, and layer thickness are studied, and correlation between these parameters and the final temperature is presented. The effect of the HAp/Ti mixing ratio to the generated temperature is also examined. Experiments are carried out to verify the model. Good agreements have been found between the EM-HT model and experiments.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic of simulation EM-HT modeling. Electromagnetic module was solved first and ended up with resistive heating. The coupled heat transfer model with resistive heating input as heat source. Finally, the combined model resulted in temperature elevation on the sample.

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Figure 2

Setup of the FEM using FEMLAB . The insertion displays the precoated HAp/Ti layer. The coated layer thickness in this case is 15 μm. Laser scans from left to right. The mixing ratio of HAp and Ti is 50%.

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Figure 3

A typical resistive heating distribution carried out by EM module using COMSOL . The mixing ratio of HAp and Ti is 50%. Colored spheres denote titanium particles due to interaction with laser beam, while white spheres denote HAp particles since they absorb very limited laser energy.

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Figure 4

A typical temperature distribution calculated by coupled EM-HT model. HT model heat source to HT model is the resistive heating, as shown in Fig. 3.

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Figure 5

Temperature distribution during laser coating in five different time frames. Original point “0” of horizontal axis denotes the interface of the implant, negative horizontal axis stands for the titanium substrate, and positive horizontal axis represents sintered coating composed of HAp/Ti particles (mixing ratio of 50%).

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Figure 6

Experimental schematic for laser coating of HAp nanoparticles on Ti substrates

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Figure 7

Temperature elevation in laser coating as a result of different processing parameters. Calculated temperature obtained by simulation was compared with real temperature spectra collected by IR camera during laser coating process. (a) Laser power (p) effects. (b) Laser beam radius (r) effects. (c) Laser scanning speed (v) effects. (d) Layer thickness (L). Mixing ratio (m) is fixed at 50% in these cases.

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Figure 8

Resistive heating distribution as a result of laser irradiation to a precoated layer of (a) pure HAp nanoparticles, (b) 50% mixture of HAp and titanium nanoparticles, and (c) pure titanium nanoparticles. The laser parameters, layer thickness, and size of nanoparticles were kept the same in all cases.

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Figure 9

Resulting temperatures as a result of different mixing ratios (m). Lines (solid, dashed, and dotted) stand for simulation data, while discrete symbols (square, triangle, and circle) stand for experimental data. Mixing ratios, with respect to HAp concentration, were set to be 100%, 50%, and 0%; laser power used ranges from 12 W to 30 W. Other parameters are kept constant: Laser scan speed is 1 mm/s, and laser beam size is 0.5 mm.

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Figure 10

HAp/Ti nanoparticle mixing ratio (m) effects on final temperature distribution after laser coating. Temperatures were collected using calibrated IR camera during laser irradiation.

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Figure 11

Infrared camera examined temperature field during laser coating process. The above shown spatial temperature distribution corresponds to the dashed line drew in the insert image in left-upper corner. Processing parameters were as follows: laser power of 30.5 W, laser beam diameter of 1 mm, and scan speed of 1 mm/s.

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Figure 12

SEM micrograph of laser treated titanium substrate coated with single layer of 50% mixed HAp and Ti nanoparticles. (a) and (b) show the same region of the sample but with different magnifications. Processing parameters were as follows: laser power of 30.5 W, laser beam radius of 0.5 mm, and scan speed of 1 mm/s.



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