Inhibition of cold-welding and adhesive wear occurring on surface of the 6061 aluminum alloy by graphene oxide/polyethylene glycol composite water-based lubricant

In this paper, graphene oxide/polyethylene glycol (GO/PEG) composite water-based lubricant was prepared by an ultrasonic dispersion method, and characterized and analyzed by Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The suspension performance of GO/PEG composite water-based lubricant in water was verified by static sedimentation and centrifugation, and then, the prepared GO/PEG composite water-based lubricant was added into 304 stainless steel and 6061 aluminum alloy, and the coefficient of friction (COF) curve, average COF value, average wear rate, corresponding photomicrographs of balls and disks after wear, and energy-dispersive spectrometer (EDS) elemental analysis were used to illustrate the lubrication effect and lubrication mechanism. The results show that the GO/PEG composite water-based lubricant possesses excellent suspension ability in water, and the average COF value and wear rate of GO/PEG composite water-based lubricant are reduced by 78.8% and 88.8%, respectively, compared with water lubrication. The excellent lubrication effect of GO/PEG composite water-based lubricant can effectively reduce the cold-welding and adhesive wear phenomenon, mainly because GO/PEG composite water-based lubricant first fills the uneven surface of friction mating to form a high-quality lubricating film and then because of the special space structure of GO and the low shear between GO layers and the synergistic lubrication effect of GO/PEG.     

Fabrication and analysis of thin-film GaAs solar cell on flexible thermoplastic substrate using a low-pressure cold-welding

We present flexible thin-film GaAs solar cells fabricated on thermoplastic substrates by a low-pressure cold-welding and epitaxial lift-off process. The use of polyethylene terephthalate (PET) film as a flexible substrate enables cold welding (130 °C) of gold layers between a thin-film GaAs solar cell and PET film with very low mechanical pressure (0.4 MPa), due to their thermoplastic properties. The feasibility of the proposed technique was demonstrated by fabricating GaAs single junction solar cells (without antireflection coating) on PET film, having an efficiency of 13.2%. The fabricated solar cell also showed a stable performance after 2000 cycles of bending.