Xudong Ren

Morphology selective preparation and formation mechanism of graphene nanoribbons from graphite by liquid-phase pulsed laser ablation

The paper studied preparation and formation mechanism of free-standing 3D graphene nanoribbons (GNRs) from graphite by pulsed laser ablation in liquid. The method to fabricate freestanding graphene nanoribbons directly was simple and controllable, which does not need other precursor materials and has no byproducts. Prepared graphene nanoribbons are shown composed of up to 14 layers of graphene, spaced about 0.30–0.35u2009nm and have a length of hundreds of nanometers. Formation mechanism of graphene nanoribbons was proposed based on the interaction between laser and material which can be demonstrated that the exfoliation of GNRs is a carbon plasma collision connecting-graphene segments-graphene sheets-multilayer graphene-graphene nanoribbons process. The high degree of repeatability and particularity found in the obtained GNRs might suggest their unique advantages and potential applications in nano-devices and spin electronics.

A conversion model of graphite to ultrananocrystalline diamond via laser processing at ambient temperature and normal pressure

The synthesis mechanism of ultrananocrystalline diamond via laser shock processing of graphite suspension was presented at room temperature and normal pressure, which yielded the ultrananocrystalline diamond in size of about 5u2009nm. X-ray diffraction, high-resolution transmission electron microscopy, and laser Raman spectroscopy were used to characterize the nano-crystals. The transformation model and growth restriction mechanism of high power density with short-pulsed laser shocking of graphite particles in liquid was put forward.

Graphite to ultrafine nanocrystalline diamond phase transition model and growth restriction mechanism induced by nanosecond laser processing

To have a clear insight into nanocrystal growth from graphite to diamond upon high energy pulsed laser irradiation of graphite suspension, synthesis of ultrafine nanocrystalline diamonds with laser energy set up from 0.3 J to 12 J, repetition rate of 10 Hz has been studied. The method allows synthesizing ultrafine nanocrystalline particles continuously at the ambient temperature and normal pressure. The particle size is shown independent of laser energy, which is ultrafine and ranges in 2–6 nm. The theoretical grown size of nano-diamonds is found in well agreement with the experiment results. Four kinds of production were found: nano-diamond, spherical carbon nano-particles, flocculent amorphous carbon, and graphene nano-ribbon rolls. A solid-vapor-plasma-liquid coexistence model describing phase transition from graphite to diamond induced by nanosecond laser processing was proposed. Graphene nano-ribbon rolls might be the intermediate phase in the conversion from graphite to diamond.

Micro-dent arrays fabricated by a novel net mask laser shock processing on the surface of LY2 aluminum alloy

A novel technology called net-mask laser shock processing (NMLSP) was introduced to fabricate micro-dent arrays on the surface of LY2 aluminum alloy. Experimental results showed that the as-fabricated micro-dents whose diameter and depth were about 230-250u2009μm and 9.3u2009μm, respectively, was closed to be circular although the original shape of the net mask was square. The height of upwarped area around micro-dent was about 4u2009μm. Moreover, the interference of neighboring surface shock waves would affect the topography of micro-dents. A dynamic analysis performed by ABAQUS/Explicit code exhibited that the dynamic formation process of micro-dents fabricated by NMLSP, and the simulation results were mostly consistent with experiment results.

High temperature wear performance of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy subjected to laser shock peening

ABSTRACT This paper investigates the influence of laser shock peening (LSP) parameters on surface integrities and high temperature wear performances of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy. Surface integrities include surface roughness, residual stress and micro-hardness are measured. High temperature wear performance of TC11 alloy with and without LSP are investigated. The results indicate that multiple LSP impacts can improve surface micro-hardness and induce compressive residual stress in the surface layer. Moreover, the friction coefficient and wear rate of TC11 alloy significantly decrease after LSP with optimised parameters. The improved wear performance is ascribed to the low surface roughness, higher surface micro-hardness and compressive residual stress induced by multiple LSP impacts in the surface layer.

Conversion Model of Graphite

This chapter gives a well-rounded presentation of the continuous synthesis of UNCD via laser shock processing (LSP) of graphite particles suspended in water by a Nd:YAG laser system with high power density (109 W/cm2) and short pulse width at room temperature and normal pressure, which yielded the ultra-nano-crystalline diamond in size of about 5 nm. X-ray diffraction, high-resolution transmission electron microscopy, and laser Raman spectroscopy were used to characterize the nano-crystals. The method studied is helpful in understanding the formation mechanism and enhancing the yield rate of nano-diamond.