Titanium alloy is widely used in different industrial applications. For the surface modification to improve the tribological properties, laser irradiation is a promising technology, which offers high efficiency, and high automation potential and geometrical flexibility. In this study, a novel method of surface modification for titanium alloys by carbonization using low fluence of laser irradiation in the atmosphere of PAO oil is proposed. Results show that the carbon content on the surfaces significantly increases with the laser shot number, with the laser irradiated spot showing little change of Ra. XPS analysis confirms that the carbon from the oil has bonded to the Titanium inside the alloy. By comparison with that irradiated without oil, the hardness of that irradiated in oil is much higher, demonstrating the feasibility of the surface modification of titanium carbide layer generation. To investigate the tribological properties, laser scanning irradiation in oil with different laser pulses were carried out to create laser modified areas and reciprocating ball-on-disk friction tests under oil lubrication were conducted. The laser modified areas show friction of 0.13, much lower than that of the unirradiated which is approximate 0.55, and the sliding lifetime of low friction is also increased with the laser pulse number. Moreover, by introducing patterning laser irradiation onto the uniformly irradiated area, the wear resistance can be further greatly improved, and the sliding lifetime can extend to 13 times of the optimal result of uniform irradiation.
With the pursuit of high-precision and high-efficiency machining, laser-assisted machining technology has attracted more and more attention. Especially, ultra-short pulse laser irradiation can facilitate a quite high cooling rate and produce a local active space, which can make the surface modification realized without any removal. In this study, a novel tribo-characteristic improvement technology using ultra-short pulse laser irradiation in oil, with the hydrocarbon composition in oil as a carbon source, was proposed, to realize the surface modification of the workpiece in the same process with machining. Herein, a Ti-6Al-4V disk was irradiated using a pico-second laser in PAO oil under 4 different conditions with changed effective irradiated laser pulses and scanning modes. Besides the uniform laser irradiation, patterning irradiation was also conducted. From the results of the reciprocating friction tests, compared to those uniformed irradiated specimens, patterning irradiation processed surfaces show obviously more stable friction than the as-received metal surface. More importantly, much longer lifetime has been obtained, indicating the enhanced wear resistance. According to the investigation of hardness distribution, laser-induced thermal strain in the patterning irradiation method is considered to be an important factor of wear resistance improvement.
Molybdenum carbides (MoC and Mo2C) are being reported for various applications, for example, catalysts for sustainable energies, nonlinear materials for laser applications, protective coatings for improving tribological performance, and so on. A one-step method for simultaneously fabricating molybdenum monocarbide (MoC) nanoparticles (NPs) and MoC surfaces with a laser-induced periodic surface structure (LIPSS) was developed by using pulsed laser ablation of a molybdenum (Mo) substrate in hexane. Spherical NPs with an average diameter of 61 nm were observed by scanning electron microscopy. The X-ray diffraction pattern and electron diffraction (ED) pattern results indicate that a face-centered cubic MoC was successfully synthesized for the NPs and on the laser-irradiated area. Notably, the ED pattern suggests that the observed NPs are nanosized single crystals, and a carbon shell was observed on the surface of MoC NPs. The X-ray diffraction pattern of both MoC NPs and LIPSS surface indicates the formation of FCC MoC, agreeing with the results of ED. The results of X-ray photoelectron spectroscopy also showed the bonding energy attributed to Mo–C, and the sp2–sp3 transition was confirmed on the LIPSS surface. The results of Raman spectroscopy have also supported the formation of MoC and amorphous carbon structures. This simple synthesis method for MoC may provide new possibilities for preparing Mo x C-based devices and nanomaterials, which may contribute to the development of catalytic, photonic, and tribological fields.
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