Papers by Author: Dang Sheng Xiong

Abstract: As an active metal, chromium is easy to form oxides film on the surface, which acts as an obstacle to the nitrogen diffusion in plasma nitriding. Rare earth (RE) was introduced into the conventional plasma nitriding (CPN) to improve the nitriding behavior. Chromium coatings were treated by CPN and rare earth plasma nitriding (REPN) at 620°C for 5 and 10 hours respectively. Comparative study showed that the addition of RE prompted greatly the formation of higher nitrogen containing phase CrN, rather than Cr2N. It created a crack-free, much denser and thicker nitrides layer, which contributed to the increase of hardness. The dynamic ultra micro hardness of the samples treated by REPN was nearly 1600GPa, which was much higher than the original and the CPN treated samples. The conclusion could be drawn that compared to CPN, REPN are more efficient for chromium coating nitriding.

Abstract: Plasma arc, a kind of high energy density beam, is proposed as one kind of surface treatments in this paper to improve the adhesive properties of the chromium coatings to the steel substrate. Scratch tests are used to obtain the critical load (Lc) of the coatings. The wear behaviors are evaluated by a reciprocating ball-on-flat wear machine and the wear tracks of the coating were characterized by scanning electronic microscope (SEM). Results show that plasma arc treatment could promote the adhesive and the wear performances of the chromium coatings. Optimal value of Lc and the wear resistance of the treated coatings could be obtained when the average output energy density of the plasma arc (E) grow to 1.05×105J/m2. The comparative study indicates that the promotion of the adhesion could be attributed to the formation of the inter-diffused alloyed layer and the improved hardness distribution. This promotion then contributes to the improvement of the wear performance, which makes up, even exceeds the loss of it caused by the drop of the coatings hardness.

Abstract: The tribological properties of Zr-based and Cu-based bulk metallic glasses (BMGs) sliding against discs of SUS 304 and Si3N4 at room temperature under dry and lubrication of fresh plasma, distilled water, and physiological distilled water were investigated on a pin-on-disc testing machine. The results demonstrated the influences of counterface materials, lubrication conditions and the characteristics of BMGs on the frictional behaviors of the Cu- and Zr-based BMGs. It is found that the steady state friction coefficients and the wear rates sometimes are not consistent, and the wear resistance was been improved when the counterface change from SUS304 to Si3N4. Otherwise, wear rates of the BMGs under lubrication conditions are much lower than that of under dry sliding conditions, and the Cu-based BMGs exhibits higher wear resistance than Zr-based BMGs under same experimental conditions because it is a nanocrystalline amorphous alloy and has the higher glass transition and crystallization temperatures.

Abstract: Poly(vinyl alcohol) (PVA) hydrogel is a promising articular cartilage biomaterial. In this paper, the effects of different variable factors on the friction coefficient of Poly(vinyl alcohol) (PVA) hydrogel were investigated when sliding against stainless steel ball by ball-pan tribometer. Factors included lubrication condition, sliding speed, diameter of stainless steel ball, and load. It was shown that the free water in PVA hydrogel has an excellent lubrication on the counterparts. The friction coefficients have little difference between dry and lubricants lubrication condition at initial friction test. With the friction test time prolonged, friction coefficient of PVA hydrogel under dry condition increased rapidly. Friction coefficient decreased with the increase of sliding speed and the diameter of stainless steel ball, and increased with the increasing load. The rising rate of friction coefficient at low load region is obviously larger than that at high load region.

Abstract: Wear is the primary cause of failure of joint replacement prostheses. Poly(ether-ether-ketone)(PEEK) was reinforced with nano-Al2O3 particals of various mass fractions in this study. The effect of nanometer Al2O3 mass fractions on the contacted angle of the reinforced PEEK composites was investigated. Tribological properties of composites under distilled water and physiological saline lubrication condition was measured. And the morphologies of the worn surfaces were observed with optical microscope. The results shows that the wettability and wear resistance were all improved with appropriate nano-Al2O3.The wear resistance of composites filled with 7% nano-Al2O3 was the best under both distilled water and physiological saline lubrication. In addition, it can be found that there is serious plough on the surface of pure PEEK. This indicated that serious fatigue wear occurred on the worn surface of pure PEEK. Moreover, there are only light fatigue wear on the worn surfaces of PEEK composites filled with nano-Al2O3.

Abstract: Metallic biomaterials are used as bone plate, dental implant, wire, electrode, and so on. For the purpose of providing the medical services with higher quality, the frictional and wear behavior of Cu47Ti34Zr11Ni8, (Cu47Ti34Zr11Ni8)99Si, Zr41Ti14Cu12.5Ni10Be22.5 and Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glasses (BMG) against ceramic ( Si3N4) at room temperature under dry sliding and lubrication of fresh plasma, distilled water, and physiological saline conditions were investigated on a pin-on-disc testing machine. Under identical sliding condition, the steady state friction coefficients of BMGs were observed with values ranging from 0.6 to 0.9 under dry sliding, 0.5 to 0.8 under lubrication with distilled water, 0.5 to 0.7 under lubrication with physiological saline, and 0.3 to 0.7 under lubrication with fresh plasma, respectively. Wear rates of BMGs indicated significant difference that the Cu-based metallic glasses exhibited higher wear resistance than that of Zr-based glasses. The surface tracks indicated the existence of viscous flow and the material transfer occurred from BMG rod to the ceramic disc. Since tribological properties are not intrinsic properties, those results demonstrated the influences of the environment and the characteristics of BMGs on the frictional behaviors, and furthermore indicated that BMGs may be one of the promising biomaterials in the future.

Abstract: Wear is the primary cause of failure of joint replacement prostheses. In this paper, the Ultra High Molecular Weight Polyethylene (UHMWPE) as an artificial joint acetabular material was reinforce by nano-ZrO2 particles. The friction and wear properties of ZrO2 - UHMWPE composites sliding against the Co-Cr-Mo alloy were studied under lubrication of distilled water, saline and calf serum. The worn surface is observed by the optics microscope to examine the wear mechanism of the composite. The hardness and wetting angle of the composites were also measured. The result shows that the hardness, wettability, friction and wear resistance were all improved by filing with nano-ZrO2 particles. The 2%ZrO2 - UHMWPE composite had the lowest wear rate.

Abstract: As the aseptic loosening induced by polyethylene wear debris is the main cause of long-term failure of total joint replacements, increasing the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE) will be very important to obtain long-life artificial joint. In this paper the UHMWPE was implanted with 450 keV N+ ions to three doses of 5×1014/cm2, 2.5×1015/cm2 and 1.25×1016/cm2. The friction and wear behaviors of UHMWPE were studied under lubrication of distilled water and blood plasma using a ball-on-disk tribometer with a ZrO2 ceramic ball as a counterface. Experimental results showed that the friction coefficient of ions implanted UHMWPE are higher than un-implanted UHMWPE. Under blood plasma lubrication condition, the wear rate of implanted UHMWPE was lower than un-implanted UHMWPE, and the wear rate decreased with increasing implantation dose. The plow, plastic deformation and fatigue were wearing mechanism for un-implanted UHMWPE and the abrasive wear for implanted UHMWPE.

Abstract: Wear is the primary cause of the failure of joint replacement prostheses. In this paper, the ultra-high molecular weight polyethylene (UHMWPE) as an artificial joint acetabular material was filled with nano-powder of SiO2 of various mass fractions. The effect of SiO2 mass fraction on the tensile strength, tensile modulus, wetting property and tribological properties of the SiO2-UHMWPE composites were investigated when sliding against Ti-6Al-4V under lubrication of physiological saline water. The morphologies of the worn surfaces of composites were observed with optical microscope. As a result, the tensile strength, tensile modulus, wettability and wear resistance of the composites were all improved by filling with SiO2, and the composites had largely decreased friction coefficients under lubrication of physiological saline water compared with the unfilled UHMWPE. This was attributed to the reinforcing function of the nano-powder of SiO2 in the composites and the lubricating action of the water boundary film. The wear of pure UHMWPE was dominated by plowing, plastic deformation, while the SiO2-UHMWPE was characterized the mild fatigue wear.