Qunfeng Zeng

Response of MC3T3-E1 osteoblast cells to the microenvironment produced on Co–Cr–Mo alloy using laser surface texturing

Osteoblast responses to Co–Cr–Mo alloy depend on not only the chemistry of alloy but also the physical properties of alloy surface, such as its microtopography and roughness. This study was undertaken to examine changes in cell adhesion, morphology, differentiation and gene expression during osteoblast interaction with different textured Co–Cr–Mo alloys. With laser surface texturing, three kinds of textured surfaces were fabricated. It showed that the microenvironment processed by laser surface texturing leads to an increase in surface roughness and DMEM contact angles of samples. Adhesion and differentiation tests demonstrated that osteoblast cells can discriminate surfaces with different roughness and surfaces with comparable roughness but different topographies such as triangle, circle and square textures. Morphological characteristics obtained by SEM imaging showed that osteoblast cells are elongated and are in polygonal shape on the textured surface. OPG/RANKL mRNA expression studies showed a significant and marked decrease in RANKL gene expression on the square-textured surface; by contrast, the ratio of OPG/RANKL showed a significant increase. These results indicate that Co–Cr–Mo surface textures affect osteoblast proliferation, morphology and gene expression; the microenvironment of implant should be considered in the future design.

Green superlubricity of Nitinol 60 alloy against steel in presence of castor oil

In the present work, first, we show that sliding Nitinol 60 alloy against steel under castor oil lubrication exhibits a new case of superlubricity (coefficient of friction CoF ≪ 0.01). So far, CoF below 0.01 have never been achieved under boundary lubrication at high contact pressure and in presence of vegetable oil as a green lubricant. Next, it is demonstrated that superlubricity is controlled by tribochemical reactions, involving chemical degradation of castor oil and the formation of metal oxy-hydroxides. Finally, to explain these findings, we propose a novel superlubricity mechanism consisting of hexanoic acid molecules intercalated between nickel and iron oxy-hydroxide lamellar layers, a structure very similar to the one found in Fe-Ni batteries. We propose that superlubricity is achieved due to repulsive electrostatic forces acting between the intercalated metal oxy-hydroxide lamellar compounds. This system would be suitable for practical engineering applications in many fields including biotechnologies.

Superlubricity behaviors of Nitinol 60 alloy under oil lubrication

Abstract The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol 60 alloy in the boundary lubrication regime. The experimental results were compared with a reference dry friction. It was found that Nitinol 60 alloy can be lubricated significantly and has shown remarkable lubrication performance. A superlubricity behavior of Nitinol 60 alloy was observed under castor oil lubrication. An ultra-low coefficient of friction of Nitinol 60 alloy about 0.008 between Nitinol 60 alloy and GCr15 steel was obtained under castor oil lubrication condition after a running-in period. Accordingly, the present study is focused on the lubrication behaviors of castor oil as potential lubrication oil for Nitinol 60 alloy. In the presence of castor oil, coefficient of friction is kept at 0.008 at steady state, corresponding to so-called superlubricity regime (when sliding is then approaching pure rolling). The mechanism of superlubricity is attributed to the triboformed OH-terminated surfaces from friction-induced dissociation of castor oil and the boundary lubrication films formed on the contact surface due to high polarity and long chain of castor oil allowing strong interactions with the lubricated surfaces.

Superlubricity of the DLC films-related friction system at elevated temperature

Superlubricity is defined as a sliding regime in which friction or resistance to sliding almost vanishes. While there are a number of superlubricity, providing a high temperature superlubricity remains a challenge. Here we present a high temperature superlubricity achieved from the diamond like carbon (DLC) films friction system. Superlubricity is found about 0.008 for more than 100 000 seconds at the steady state at the temperature of 600 °C due to the formation of the self-generated lubricious composite oxides of γ-Fe2O3 and SiO2 at the contact surfaces through tribochemistry reaction during the running-in process. We propose a superlubricity system based on the repulsive electrostatic forces between the self-generated composite oxides due to high temperature oxidation reaction and the shielding action of hydrogen at the contact surface, which is seem to be a reasonable explanation for super low friction at the elevated temperature.

Influence of Load and Sliding Speed on Super-Low Friction of Nitinol 60 Alloy under Castor Oil Lubrication

In the present paper, the influence of load and sliding speed on super-low friction of Nitinol 60 alloy was investigated experimentally using Nitinol 60 alloy pin sliding over GCr15 steel disk under castor oil lubrication. Super-low coefficient of friction (COF) of Nitinol 60 alloy was achieved at the stable state, corresponding to so-called superlubricity regime in the presence of castor oil. The experimental results indicate that sliding speed employed in the friction tests plays great roles in the lubrication behaviors of Nitinol 60 alloy. When the friction tests are executed from low sliding speed to high sliding speed, COF decreases at the initial stage and on the contrary, COF increases at the stable stage. However, with the increase in load, COF firstly increases and then decreases at the initial stage. COF is unstable but still super low and remains almost the same value at the stable stage. These phenomena are explained and discussed in viewpoint of the characteristics of castor oil during the friction tests. It is found that the influence of sliding speed on the lubrication behaviors of Nitinol 60 alloy under castor oil lubrication is more obvious than that of load due to the characteristics structure of castor oil, therefore maintaining appropriate level of sliding speed to achieve super-low friction of Nitinol 60 alloy.

Lubrication properties of Nitinol 60 alloy used as high-speed rolling bearing and numerical simulation of flow pattern of oil-air lubrication

The friction and wear tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disk in a pin-on-disk tribometer system under PAO oil lubrication conditions. It was found that Nitinol 60 alloy can be lubricated well and has shown remarkable tribological performance. Average coefficient of friction (COF) of Nitinol 60 is 0.6 under dry friction; however, average COF decreases to 0.1 under PAO oil lubrication. SEM image of the worn surface shows that Nitinol 60 exhibits excellent wear resistance and the wear mechanism is mainly adhesive wear. Flow pattern of oil-air flow in oil pipe was simulated by FLUENT software with VOF model for acquiring working performance of oil-air lubrication. The optimum velocity of oil and air at the inlet was achieved, which provides the great proposal for the design of experiment of oil-air lubrication of Nitinol 60 alloy. The simulation results showed that the optimum annular flow of flow pattern was obtained when air velocity is 10 m/s and oil velocity is 0.05 m/s. The formation mechanism of annular flow was also discussed in the present study.

A comparative study on simulation and experiment of oil-air lubrication unit for high speed bearing

Purpose The purpose of this paper is to design an oil-air lubrication system with low temperature rise, vibration and noise simplifies the spindle configuration. The oil-air lubrication unit is a key component for high-speed grinding machine tools. The development of oil-air lubrication unit suitable for high/ultrahigh rotational speed is a daunting task owing to the lubrication challenges. Design/methodology/approach This paper emphasizes three main issues: the analysis of oil-air two-phase flow for tradition oil-air lubrication unit with the simulation method; the design of new oil-air lubrication unit for the high/ultrahigh-speed grinding machine tools and the comparative experiment research of tradition and new oil-air lubrication unit. The optimum structure parameters that create the optimum flow pattern and operating conditions resulting in low temperature increase, vibration and noise of oil-air lubricated spindle can be achieved by the simulation method and experiments. Findings The simulation and experimental results show that new oil-air lubrication unit lubricating a high speed electric spindle has a better performance with a small temperature increase and vibration, which means that our proposed method is an effective design method for oil-air lubrication system. Originality/value A design method suitable for high-speed oil-air lubrication unit is proposed. New oil-air lubrication unit is expected to apply for high/ultrahigh rotational speed grinding machine tools.

Tribological Properties of Self-Lubricating Polymer–Steel Laminated Composites

Self-lubricating polymer–steel laminated composites (SLC) consisting of matrix zones and filled zones were fabricated by a laminating–bonding process. The matrix zones were silicon steel sheets and the filled zones were polymer matrix filled with MoS2 and graphite, respectively. The control specimen was prepared by spraying a polymer composite coating on a GCr15 disc. The tribological properties of SLC were investigated using a ball-on-disc tribometer under different loads and frequencies. Compared to the control specimen, the friction coefficient and wear rate of SLC was reduced by 57% and threefold at 4 N and 6 Hz, respectively. In addition, the friction coefficient of SLC was low and stable under low reciprocating frequency, and it was high and fluctuating under high reciprocating frequency. In addition, the wear rate increased with increasing applied load and reciprocating frequency. Scanning electron microscopy (SEM) images show that the lubricating mechanism of SLC was that solid lubricants embedded in filled zones expanded and smeared a layer of transfer film on the sliding path to lubricate the surface. The thermal expansion of solid lubricants was simulated using ANSYS software with thermal-stress coupling. The simulation results showed the maximum temperature of the filled zones was 130°C, and the maximum normal displacement of solid lubricants was approximately 10 μm. This confirmed that the solid lubricants expanded effectively by the aid of frictional heat.

Fabricating hierarchical micro and nano structures on implantable Co–Cr–Mo alloy for tissue engineering by one-step laser ablation

Surface texturing is one of the effective strategies to improve bioactivity of implantable materials. In this study, hierarchical micro and nano structure (HMN) were fabricated on Co-Cr-Mo alloy substrate by a movable picosecond laser irradiation. Respectively, microgrooves with nano ripples and islands were produced on Co-Cr-Mo alloy by low and high laser power density. X-ray diffraction apparatus (XRD) phase analysis illustrated that substrate was in the phase of γ- face-centered cubic structure (FCC) before laser treatment, while it was in ε-hexagonal closest packing structure (HCP) phase dominant after laser treatment. Cell adhesion and proliferation studies showed that the HMN surface exhibits enhanced adhesion of MC3TC-E1 osteoblast and promoted cell activity. Analyzing of the morphology of osteoblast cells indicated cells were in high ratio of elongation on the HMN surface, while they mainly kept in round shape on the polished surface. Results indicated the formation of hierarchical structure on Co-Cr-Mo alloy was able to improve biological performances, suggesting the potential application in cobalt based orthopedic implants.

Superlow friction of high mileage used oil with CuDTC in presence of MoDTC

Purpose The purpose of this paper is to improve the antifriction and antiabrasive behavior of the used oil through the addition of a lubricant. Design/methodology/approach The author selected 85W-90 used oil with three kinds of 4,758, 10,507 and 16,223 km mileages, which may represent run-in wear period, steady-state wear period and rapid wear for used oil, respectively. Nano copper, molybdenum dithiocarbamate (MoDTC) and copper dioctyl dithiocarbamate (CuDTC) of lubricant additive are added to the used oil to improve its antifriction performances and service life. The influence of lubricant additive on the tribological properties of used oil is investigated by the friction tests. Findings An abnormal phenomenon has been observed by the friction test under high mileage used oil with CuDTC in presence of MoDTC lubrication, and superlow friction coefficient of 0.04 has been achieved after a running-in period for the first time. It is found that CuDTC additive is beneficial to improve greatly the antifriction behavior of used oil, especially when MoDTC is present. The results indicate that the dissoluble of CuDTC and the tribochemical reaction of MoDTC play an important role in superlow friction of high mileage used oil. Moreover, the superlow friction is also closely related to the viscosity of used oil. Originality/value The possible mechanism of superlow friction is attributed to the additive thinning effect and the synergistic effect of the dissoluble of CuDTC and the tribochemical reaction of MoDTC binary lubricant additives in high mileage used oil. This work will extend the application of CuDTC additive widely and explore a new method to the reutilization and the life extension of used lubricating oil.