Baixing Liu

The effect of the addition of aramid fibers on tribological properties of the polyimide after ultraviolet or atomic oxygen irradiation

The aramid fibers reinforced polyimide composites were fabricated by means of a hot-press molding technique. The mechanical and tribological behaviors of the reinforced composites were studied. The friction and wear properties of the composites, rotating against a GCr15 steel ball, were investigated on a ball-on-disc test rig. To contrast the effects of the ultraviolet radiation and atomic oxygen, experiments without radiation or after ultraviolet or atomic oxygen radiation were conducted. Experimental results revealed that 20% aramid fiber reinforced polyimide exhibited higher modulus. However, the coefficient of friction decreased with the increase of the aramid fiber content. The composites had a lower wear rate value after atomic oxygen radiation. Microstructure of worn surface of the tested composites was inspected by scanning electron microscopy, and X-ray photoelectron spectroscopy study of the composite surface showed that the chemical composition of the surface changed after ultraviolet or atomic oxygen radiation because of the oxidation.

Structural and Tribological Properties of Polyimide/Al2O3/SiO2 Composites in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polyimide/Al2O3/SiO2 composites were investigated in a ground-based simulation facility, in which the energy of AO was about 5 eV and the flux was 7.2 × 1015 cm−2.s−1. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (FTIR-ATR), while the tribological changes were evaluated by friction and wear tests as well as scanning electron microscopy (SEM) analysis of the worn surfaces. It was found that AO irradiation induced the oxidation and degradation of polyimide (PI) molecular chains. The destructive action of AO changed the surface chemical structure, which resulted in changes of the surface morphology and chemical composition of the samples. Friction and wear tests indicated that AO irradiation decreased the friction coefficient but increased the wear rate of both pure and Al2O3/SiO2 filled PIs.

One-step electrochemical fabrication of bilayered MgO/polymer coating on magnesium alloy

This research demonstrates a novel one-step electrochemical method to fabricate thick bilayer coatings on magnesium alloy in acid phosphate electrolyte containing aniline monomer and styrene-acrylic emulsion (SAE) with pulsed DC voltage. The morphologies, XRD and FTIR results show that the bilayer coating consists of an inner oxide layer and an outer polyaniline (PANI)/SAE composite layer. It is believed that the bilayered structure achieved results from a hybrid process combining electropolymerization (EPM) of aniline, electrophoretic deposition (EPD) of SAE and plasma electrolyte oxidation (PEO) of magnesium alloy substrate. Electrochemical corrosion tests indicate that the bilayer coating can provide superior corrosion protection to the magnesium alloy substrate in 3.5 wt.% NaCl solution.

A comparative study of characterisation of plasma electrolytic oxidation coatings on carbon steel prepared from aluminate and silicate electrolytes

ABSTRACT Two kinds of PEO coatings were prepared on low carbon steel from aluminate electrolyte and silicate electrolyte, respectively. The coating surface and cross-section morphologies were observed by scanning electron microscope. The elemental and phase compositions were investigated by energy-dispersive spectrometer and X-ray diffraction, correspondingly. The scratch test was employed to examine the adhesion of the PEO coating. The electrochemical tests were used to evaluate the anti-corrosion property of PEO coatings. It was found that more substrate was oxidised during PEO process under the same constant voltage for the same length of time in silicate electrolyte than that in aluminate electrolyte. Besides, the silicate PEO coating grew faster than aluminate PEO coating. Compared with the uniform distribution of elements in aluminate PEO coating, silicate PEO coating exhibited a two-layered structure. The two-layered structure of the silicate PEO coating led to a negative effect on the adhesion. The aluminate PEO coating showed a better anti-corrosion property because of its denser structure.

Proton irradiation effects on the structural and tribological properties of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was irradiated with protons in a ground-based simulation facility to study the effects of proton irradiation on the structural and tribological properties of PTFE. The structural changes were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total-reflection FTIR (ATR-FTIR), while the tribological properties were evaluated by friction and wear tests. It was found that proton irradiation induced the degradation of PTFE molecular chains, resulting in the increase of C concentration and the decrease in F concentration on the sample surfaces, and the surface chemical structure and morphology of the samples changed, which affected the friction coefficient and decreased the wear rate of the specimens as the friction and wear tests revealed.

Structural and Tribological Properties of Polytetrafluoroethylene Composites Filled with Glass Fiber and Al2O3 in Atomic Oxygen Environment

Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of polytetrafluoroethylene (PTFE) composites filled with both glass fibers and Al2O3 were investigated in a ground-based simulation facility, in which the average energy of AO was about 5 eV and the flux was 5.0 × 1015/cm2 s. It was found that AO irradiation first induced the degradation of PTFE molecular chains on the sample surface, and then resulted in a change of surface morphology. The addition of Al2O3 filler significantly increased the AO resistance property of PTFE composites. Friction and wear tests indicated that AO irradiation affected the wear rate and increased the friction coefficient of specimens. The PTFE composite containing 10% Al2O3 exhibit the best AO resistance and lower wear rate after long time AO irradiation.