Cheng Xian-hua

Effect of rare earths on mechanical and tribological properties of carbon fibers reinforced PTFE composite

The effect of a rare earth (RE) surface treatment on the mechanical and tribological properties of carbon fiber (CF) reinforced polytetrafluoroethylene (PTFE) composites was experimentally investigated. The tensile properties of the CF reinforced PTFE (CF/PTFE) composites treated with air oxidation and RE modifier were superior to those of untreated CF/PTFE composites, while RE treatment was most effective in promoting the tensile strength and strain at break of the CF/PTFE composite. The bending strength of the RE treated CF/PTFE composite was improved by about 16% compared with that of untreated composites, while 2% improvement was achieved by air oxidation. Under oil-lubricated conditions, RE treatment was more effective than air oxidation to reduce the friction coefficient and wear of PTFE composite. RE treatment effectively improved the interfacial adhesion between CF and PTFE. The strong interfacial coupling of the composite made CF not easy to detach from the PTFE matrix, and prevented the rubbing-off of PTFE, accordingly improved the friction and wear properties of the composite.

Investigation of Tribological Behavior of Lanthanum-Based Thin Films Deposited on Sulfonated Self-Assembled Monolayer

Abstract 3-mercaptopropyl trimethoxysilane (MPTS) was prepared on glass substrate so as to form a two-dimensional self-assembled monolayer (SAM), and the terminal -SH group in the film was in situ oxidized to -SO 3 H group to confer good chemisorption ability to the film. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM, making use of the chemisorption ability of -SO 3 H group. Atomic force microscopy (AFM) and X-ray photoelectron spectrometry (XPS) and contact angle measurements were used to characterize the thin films. The tribological properties of the as-prepared thin films sliding against a steel ball were evaluated on a friction and wear tester. Tribological experiment shows that the friction coefficient of glass substrate decreases from 0.8 to 0.08 after the rare earth (RE) self-assembled films (SAMs) are formed on its surface. And the RE self-assembled films have longer wear life (500 sliding passes). It is demonstrated that RE self-assembled film exhibits good wear-resistant property. The marked decrease in friction and the longer wear life of RE films are attributed to the excellent adhesion of the film to the substrate and to the special characteristics of the RE elements. The frictional behaviors of RE thin-films-coated silicon surface were sensitive to the applied load and the sliding velocity of the steel ball.

Tensile property of surface-treated poly-p-phenylenebenzobisoxazole (PBO) fiber-reinforced thermoplastic polyimide composite:

The current study examined the effect of rare earth (RE) solution surface modification of poly-p-phenylenebenzobisoxazole (PBO) fibers on the tensile property of PBO fiber-reinforced thermoplastic polyimide (PBO/PI) composites. Experimental results revealed that RE surface treatment could effectively improve the interfacial adhesion between PBO fibers and PI matrix. Compared with the untreated and coupling agent-treated PBO/PI composite, the RE-treated composite had better interfacial adhesion. For RE-treated PBO/PI composites, the tensile strength and tensile modulus varied with RE concentrations, and the optimum value was obtained at 0.6 wt% of RE concentration. The fracture surface morphologies of the samples were investigated by scanning electron microscopy (SEM) to analyze the effect of various surface treatments. X-ray photoelectron spectroscopy (XPS) study of PBO fibers surface showed that the ratio of oxygen/carbon on the surface of PBO fibers was obviously increased after RE treatment, which indicated the content of polar groups on the surface of PBO fibers increased compared with the others. The increase in the amount of polar groups strengthened the interfacial adhesion between PBO fibers and PI matrix and accordingly enhanced the tensile properties.

Tribological Properties of Polytetrafluoroethylene Composites Filled with Rare Earths Modified Glass Fibers

Rare earths were used to modify the surface of glass fiber in order to enhance the interfacial adhesion and improve the tribological properties of GF/PTFE composites. Three surface modifiers, a coupling agent, rare earths, and a mixture of coupling agent and rare earths, were investigated. It is found that the tensile properties of rare earths modified GF/PTFE composites were improved considerably under the same experimental conditions. The PTFE composites, filled with rare earths modified glass fibers, exhibited the lowest friction coefficient and the highest wear resistance under both dry friction and oil-dropped lubrication conditions. In addition, rare earths modified GF/PTFE composites showed the highest wear resistance under reciprocating impact load. The worn surfaces observation shows that rare earth elements modifier are superior to coupling agent modifier and the mixture of coupling agent and rare earths in promoting interfacial adhesion between the glass fiber and PTFE, accordingly improve tribological properties of GF/TFE composites due to their outstanding chemical activity.

High temperature wear characteristics of a new hot work die steel CH95

High temperature wear characteristics of a new hot work die steel CH95 doped with a small amount of rare earth (Re) and boron (B) have been investigated and compared with those of conventional die steel H11 at a series of temperatures and loads. Worn surfaces of CH95 steel and H11 steel were analyzed with a scanning electron microscope. It is found that high temperature mechanical properties of CH95 steel are much better than those of H11 steel. The oxide layer formed on the worn surface plays an important role in wear resistance at high temperature. When the load is less than 63 N, the surface oxide layer keeps integrated and the effect of load on high temperature wear is small. When the load is higher than 63 N, the supporting ability of matrix to the oxide layer decreases with the increase of load, which results in an increase of wear rate. Compared with H11 steel, the wear resistance of CH95 steel is much better and the worn surface of CH95 steel is smoother. It is easier for CH95 steel to form a compact and integrated surface oxide layer at high temperature than for H11 steel, which protects the worn surface and reduces wear.

The cavitation erosion damage process of dynamically loaded journal bearings

The cavitation damage model was built using finite element analysis software MSC.Marc. This paper attempted to numerically analyze the action process based on damage mechanics when a jet created by bubble collapse acted on the bearing surface in the process of cavitation erosion. The numerical results show that the values of equivalent plastic strain and void volume fraction increase with time. The values of damage scalar are higher on the bearing surface and subsurface, and decrease when it approaches the interface of overlay and nickel layer. The strain history and damage evolvement of bearing material acted on by jet impact load can be calculated efficiently using the proposed method, which develops a new method of analyzing cavitation erosion failure of the bearing surface.