The Effect of Laser Nitriding on Surface Characteristics and Wear Resistance of NiTi Alloy with Low Power Fiber Laser

Hao Wang,Evgeny L Gurevich,Andreas Ostendorf,Ralf Nett

doi:10.3390/app11020515

Hao Wang, Evgeny L Gurevich + Show 2 more

Open Access

https://doi.org/10.3390/app11020515

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Abstract

The laser nitriding was performed in nitrogen gas at room temperature (20 °C) and low temperature (−190 °C) by a low power fiber laser to modify the wear and abrasion resistance of NiTi alloy. The surface roughness and element composition were analyzed by roughness device and energy-dispersive X-ray spectroscopy respectively. The results of roughness show that laser treatment can change the surface roughness due to the laser remelting. The effect of laser nitriding on the microhardness, friction coefficient, and worn scars of NiTi alloy was also studied, which shows that the microhardness of the NiTi alloy increases after laser nitriding. The optical microscope and scanning electron microscope were used to characterize the surface of NiTi alloy after wear testing to observe the microstructure of worn scars. The results show that the laser nitriding with different parameters can induce a nitride layer with different thicknesses and the higher energy deposition is the key factor for the formation of the nitride layer, which can decrease the friction coefficient and reduce wear loss during the application of NiTi alloy. The improvement of wear resistance can be attributed to the hard nitriding layer.

Highlights

With the development of medical science and technology, there are increasing requirements for implanted materials that can replace or assist the natural organs of humans [1], like stents, heart valves, bones, skull, and knee implant metals
Hu et al used the surface mechanical attrition treatment (SMAT) to induce grain refinement on the top layer of NiTi alloy, which shows that the friction coefficient decreased and the wear resistance was improved after surface treatment with mechanical attrition [11]
Zhang et al studied the effect of laser shock peening on the corrosion resistance and surface mechanical property of NiTi alloy and they found that the laser shock peening can increase the surface microhardness and enhance the mechanical property of NiTi alloy [13]

Summary

Introduction

With the development of medical science and technology, there are increasing requirements for implanted materials that can replace or assist the natural organs of humans [1], like stents, heart valves, bones, skull, and knee implant metals. Due to the generation of wear and abrasion during the application as the bone of NiTi alloy in the human body, it is necessary to replace the implanted joints within 15–20 years [7]. Many surface modification treatments have been studied to improve the surface corrosion, wear, and abrasion resistance of NiTi alloy to extend its service life, including ion implantation, shot peening, and so on [9,10]. Hu et al used the surface mechanical attrition treatment (SMAT) to induce grain refinement on the top layer of NiTi alloy, which shows that the friction coefficient decreased and the wear resistance was improved after surface treatment with mechanical attrition [11]. The laser nitriding process with fiber laser was used to modify the surface mechanical property of NiTi alloy to enhance its wear and abrasion resistance. The NiTi alloy would be processed with low power fiber laser in nitrogen gas at different temperatures (room temperature (RT) about

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Results

Conclusion