Dangsheng Xiong

Tribological Properties of Laser Surface Texturing and Molybdenizing Duplex-Treated Ni-Base Alloy

Laser surface texturing (LST) and surface molybdenizing duplex-treatment was performed on Ni-base alloy in order to improve its wear resistance at high temperature. Surface molybdenizing was performed on the laser surface textured Ni-base alloy by a double glow plasma surface alloying technology. The friction and wear properties of the duplex-treated, the single-treated, and the untreated alloys were tested on a ball-on-disk tribometer by rubbing against an alumina ceramic ball from room temperature to 600°C. The topography of the laser surface textured dimples was measured by a white light interferometer and optical microscope. The dimples are 150-200 μ m in diameter and 45-50 μ m in depth. The distance between the dimples is 500 μ m. The molybdenized layer is approximately 20 μ m in thickness. The elastic modulus of Ni-base alloy is improved by molybdenizing. After texturing and the molybdenizing duplex treatment, the friction coefficient of the Ni-base alloy decreases from 0.38 to 0.26 at room temperature and from 0.42 to 0.34 at 600°C. The wear rate of the duplex-treated alloy is much lower than that of the pristine alloy at 600°C due to the textured dimples storing lubricious oxides.

Swelling, mechanical and friction properties of PVA/PVP hydrogels after swelling in osmotic pressure solution

The potential of polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) hydrogels as articular cartilage replacements was in vitro evaluated by using a macromolecule-based solution to mimic the osmotic environment of cartilage tissue. The effects of osmotic pressure solution on the morphology, crystallinity, swelling, mechanical and friction properties of PVA/PVP hydrogels were investigated by swelling them in non-osmotic and osmotic pressure solutions. The results demonstrated that swelling ratio and equilibrium water content were greatly reduced by swelling in osmotic solution, and the swelling process was found to present pseudo-Fickian diffusion character. The crystallization degree of hydrogels after swelling in osmotic solution increased more significantly when it compared with that in non-osmotic solution. After swelling in osmotic solution for 28days, the compressive tangent modulus and storage modulus of hydrogels were significantly increased, and the low friction coefficient was reduced. However, after swelling in the non-osmotic solution, the compressive tangent modulus and friction coefficient of hydrogels were comparable with those of as-prepared hydrogels. The better material properties of hydrogels in vivo than in vitro evaluation demonstrated their potential application in cartilage replacement.

Compositions and tribological properties of PEO coatings on Ti6Al4V alloy

ABSTRACT Hard oxide coatings were deposited on Ti6Al4V alloy using plasma electrolytic oxidation process from mixed aluminate/phosphate electrolytes. The influence of aluminate/phosphate proportion on the phase compositions, mechanical and tribological properties was systematically investigated. The results showed that plasma electrolytic oxidation (PEO) coatings with high compactness and hardness were formed in high aluminate/phosphate ratio electrolyte and the wear resistance and load bearing capacity were greatly improved due to the presence of hard γ- and α-Al2O3 phases. Low aluminate/phosphate ratio electrolyte led to thin and loose coatings without α-Al2O3 phase. It was shown that a thicker coating could provide only a limited improvement in wear resistance unless it is hard and free of porosity.

Robust superhydrophobic coating and the anti-icing properties of its lubricants-infused-composite surface under condensing condition

Superhydrophobic surfaces (SHS) are accessible by means of incorporating a micro- or nano-structured low-energy surface that creates an air layer beneath water droplets. However, poor stability towards abrasion, low temperatures, and chemical corrosion have hindered their wide application. In our study, a SiO2–UHMWPE (ultra-high molecular weight polyethylene)-based SHS that could resist severe abrasion, multiple tape peelings, water dripping, and corrosion upon exposure to strong chemical agents was fabricated. However, the water droplets were pinned on the prepared SHS at low temperatures (below 0 °C) due to ice/water capillary bridges. To overcome this problem, slippery liquid-infused porous surfaces (SLIPSs) were prepared by infusing different lubricants into the SHSs, and the water droplets smoothly travelled under the conditions of low temperatures, suggesting superior anti-icing properties. Moreover, the travelling speed of water droplets on the prepared SLIPSs was restrained under the conditions that favored the condensation of atmospheric humidity.

The water-locking and cross-linking effects of graphene oxide on the load-bearing capacity of poly(vinyl alcohol) hydrogel

The poor load-bearing capacity of the poly(vinyl alcohol) (PVA) hydrogel has limited its application in biomedical and orthopedic fields. In the present study, PVA/GO composite hydrogels were fabricated by the freeze–thaw method, and their mechanical and tribological properties as a function of GO content were evaluated. The results demonstrated that the GO sheets exhibited excellent interfacial interactions with the PVA hydrogel matrix. The tensile and compressive strength were improved by about 116% and 161% for the PVA/GO hydrogels with the optimized GO contents of 0.10–0.15 wt% compared to neat PVA. The GO sheets worked as the cross-linking points between the PVA molecular chains, and the individually dispersed GO sheets in the PVA matrix could maximize the fillers effect on restricting the movement of polymer chains, which was positive to the enhancement in the mechanical properties. Moreover, the water block effect of GO was thought to impede the water infiltration between the PVA molecules, which could enlarge the instantaneous pressurization under compressive load and further improve the load-bearing capacity of PVA. This was also beneficial to improving the tribological properties of PVA hydrogels.

Strengthening bulk metallic glasses with minor alloying additions

Abstract Cu47Ti34Zr11Ni8, (Cu47Ti34Zr11Ni8) 99 Si and (Cu47Ti34Zr11Ni8) 99 Al bulk metallic glass were prepared by copper mold casting method, and the thermal stability, mechanical properties and microstructures of them were studied. With minor alloying of Si and Al additions, the glass transition temperature ( T g ), crystallization temperature ( T x1 ) and temperature interval of supercooled liquid region Δ T x (= T x1 - T g ) and reduced glass transition temperature ( T rg ) were proved to be changed from 672 K, 734 K, 62 K, 0.575 to 691 K, 752 K, 61 K, 0.592 and to 681 K, 729 K, 48 K, 0.590, respectively. The results indicate that the glass-forming ability (GFA) are improved with minor alloying additions. And the bulk glasses also exhibits high three point-bending flexural strength. Because of the additions of Si and Al, three point-bending flexural strength and flexural modulus of the bulk glass change from 2 350 MPa, 102 GPa to 3 260 MPa, 102 GPa and 2 970 MPa, 108GPa respectively. The obvious strengthening is due to the appearance of the medium-range ordered regions with a size of 2–5 nm under the high-resolution TEM image. The reason that the mixed amorphous and nanocrystalline phases caused by minor alloying of Si and Al additions, is that Si or Al is the third kind of elements, which are different from other constituting elements, and there are a strong bonding and atoms size effects between constituting elements, which cause the glass-forming ability (GFA) and the bulk metallic glasses strength improving.

In situ repair of graphene defects and enhancement of its reinforcement effect in polyvinyl alcohol hydrogels

Defects cause unexpected and unsatisfactory effects in graphene when it is used as a reinforcement in composites. Herein, γ-ray irradiation was introduced as a facile and efficient method to simultaneously repair the defects of reduced graphene oxide (rGO) and enhance the reinforcement effect of graphene in a polyvinyl alcohol (PVA) matrix. Under the action of γ-ray irradiation, the surfaces of rGO were activated and free radicals were produced on PVA chains. At higher irradiation doses, random chain scissions of the PVA main-chain were linked with the reactive groups around the edge of defects on the rGO, leading to the repair of the crystalline graphene, which was evidenced by the decrease of ID/IG and stronger 2D bands of the irradiated PVA/rGO hydrogel composites. Thus, the reinforcement effect of graphene is enhanced by γ-ray irradiation. The tensile and compressive strength of the PVA/rGO hydrogel composites achieved their maximum values at irradiation doses of 100 kGy and 150 kGy, respectively, which were 44% and 171% higher than the nonirradiated composites, and 113% and 336% higher than those of pure PVA hydrogel, respectively.

Improved biotribological properties of PEEK by photo-induced graft polymerization of acrylic acid

The keys of biomaterials application in artificial joints are good hydrophilicity and wear resistance. One kind of the potential bio-implant materials is polyetheretherketone (PEEK), which has some excellent properties such as non-toxic and good biocompatibility. However, its bioinert surface and inherent chemical inertness hinder its application. In this study, we reported an efficient method for improving the surface wettability and wear resistance for PEEK, a layer of acrylic acid (AA) polymer brushes on PEEK surface was prepared by UV-initiated graft polymerization. The effects of different grafting parameters (UV-irradiation time/AA monomer solution concentration) on surface characteristics were clearly investigated, and the AA-g-PEEK specimens were examined by ATR-FTIR, static water contact angle measurements and friction tests. Our results reveal that AA can be successfully grafted onto the PEEK surface after UV irradiation, the water wettability and tribological properties of AA-g-PEEK are much better than untreated PEEK because that AA is a hydrophilic monomer, the AA layer on PEEK surface can improve its bearing capacity and reduce abrasion. This detailed understanding of the grafting parameters allows us to accurately control the experimental products, and this method of surface modification broadens the use of PEEK in orthopedic implants.

Semi-degradable porous poly (vinyl alcohol) hydrogel scaffold for cartilage repair: Evaluation of the initial and cell-cultured tribological properties

Tissue engineering for articular cartilage repair has shown success in ensuring the integration of neocartilage with surrounding tissue, but the rapid restoration of biomechanical and biotribological functions remains a significant challenge. Poly (vinyl alcohol) (PVA) hydrogel is regarded as a potential articular cartilage replacement for its fair mechanical strength and low surface friction, while its lack of bioactivity limits its utility. Combining the advantages of tissue engineering materials and PVA hydrogel, we developed a semi-degradable porous PVA hydrogel through addition of ploy (lactic-co-glycolic acid) (PLGA) microspheres and salt-leaching technique. Friction coefficient, continuous friction tested by a ball-plate tribometer and worn surface observed by Environmental Scanning Electron Microscopy (ESEM) were characterized for scaffolds prepared with variable porogen and PLGA content. Scaffolds cultured with rabbit chondrocytes for 4 weeks were also studied. The results showed that friction coefficient increased with a rise in porogen content, while it firstly increased and then decreased with increasing PLGA content. Similar results were obtained from cell-cultured scaffolds. In continuous friction test and worn morphology characterization, samples were more prone to be damaged with an increase in porogen and PLGA content. However, wear resistance was obviously improved for all scaffolds after 4 weeks of culture, though friction coefficient went up to a certain extent.

Wide temperature lubrication of LST/PEO/Ag/MoS2 multilayer coating

ABSTRACT The Ag film and MoS2 film were successively deposited onto the LST/PEO duplex-treated titanium alloy substrate. The friction tests were conducted at 25°C, 350°C and 600°C, respectively. The worn morphologies were analysed by optical microscopy and Raman spectrum. The results showed that the LST/PEO/Ag/MoS2 coating exhibited more excellent friction behaviour in comparison to the LST/PEO coating at 25–600°C. The combined lubrication of Ag diffused from surface micro-pores and Ag2MoO4 formed on the surface is responsible for the decrease of friction coefficient at 600°C. It also revealed that the friction heat can promote the formation of Ag2MoO4 in comparison to the high test temperature.