Huang Bai-yun

Erosion wear behaviour and model of abradable seal coating

The abradable seal coating for an aircraft turbine engine is mostly composed of metal phase, self-lubricating non-metal phase and many pores. The erosion wear resistance is one of the most important properties of the coating. The erosion wear behaviour and mechanism of several kinds of middle temperature seal coatings were investigated by a CMS-100 self-made vacuum sand erosion machine. The results show that the relationship between the erosion mass loss and the erosion time is linear, the coatings hold a maximum erosion rate at 60° impact angle, and the relation between the erosion rate and the impact speed is an exponential function. The speed exponent increases with the increase of the impact angle. At 90° impact, the abrasive particles impinging on the coating surface produce indentations and extruded lips, and then the lips are work-hardened and fall off; and flattened metal phase grains are impacted repeatedly, loosed and debonded. At 30° impact, the micro-cutting, plowing and tunneling via pores and non-metal phase are involved. The model of the erosion mechanism is advanced on the basis of the above-mentioned erosion wear behaviour.

Particle size characterization of ultrafine tungsten powder

Abstract The aim of this research was to investigate the particle size measurement of as-supplied and lab-milled ultrafine tungsten powders. The ultrafine tungsten powder derived from X-ray diffraction pure WO3 by hydrogen reduction process under “dry” reduction conditions was milled for 1, 2 and 4 h, respectively. Then the as-supplied and lab-milled tungsten powders were used to perform particle size measurement by laser diffraction method and Fisher sub-sieve sizer (FSSS) method and BET method through adsorption isotherms. Results show that the mean particle size values of as-supplied and lab-milled powders measured by laser diffraction method and FSSS method were misleading because of the defects of the measurement system or unsuitability of measurement theory. And the calculated particle size of dBET values from the formula 6/(S BET density ) were smaller than that of by SEM method, which was resulted from the neglect of the effect of surface roughness and pore area on dBET calculation. The fractal dimension D of surface roughness and external surface area St of pores were obtained from adsorption isotherms, which were used to modify dBET calculation formula. The modified formula was d BET ( M ) =k (D/2)×6/(S BET density ), where coefficient k was a constant, it was a function of pores area, D was fractal dimension value of surface roughness. As to the ultrafine tungsten powders in this investigation, k was defined as SBET/St, so modified dBET(M) may be expressed as 3D/( S t density ). By the modified formula, the calculated dBET(M) values of four powders in this study were in good agreement with the SEM sizes.

Rheological behavior of fumed silica suspension in polyethylene glycol

The rheological behavior of fumed silica suspensions in polyethylene glycol(PEG) was studied at steady and oscillatory shear stress using AR 2000 stress controlled rheometer. The systems show reversible shear thickening behavior and the shear-thickening behavior can be explained by the clustering mechanism. The viscosity and the degree of shear-thickening of the systems strongly depend on the mass fraction of the silica, the molecular weigh of PEG and the frequency used in the rheological measurement. The silica volume fraction of the systems is 1.16%–3.62%, corresponding to the mass fraction of 4%–9%. The shear-thickening taking place in the low volume fraction may contribute to the fractal nature of the silica. At oscillatory shear stress, when the shear stress is less than the critical stress, the storage modulus decreases significantly, meanwhile the loss modulus and the complex viscosity almost remain unchanged; when the shear stress is larger than the critical stress, the storage modulus, the loss modulus and the complex viscosity increase with the increase of shear stress. The loss modulus is larger than the storage modulus in the range of stress studied and both moduli depend on frequency.

Influence of porosity and total surface area on the oxidation resistance of C/C composites

Abstract The oxidation tests of five different porosity C/C composites for non-isothermal oxidation and three different porosity samples for isothermal oxidation in O 2 and two samples which had approximate porosity and different total surface area values for static air oxidation were performed. Results show that the oxidation was controlled by the total surface area other than by the open porosity or the densification degree of samples or amount of pore entrance. The oxidation occurred preferentially at the fiber–matrix interface and pyrocarbon–pyrocarbon interface, and then progressed along the micro-cracks between the interfaces.

Influence of tungsten oxides' characteristics on fineness, homogeneity and looseness of reduced ultrafine tungsten powder

This paper deals with the influence of the characteristics of tungsten oxides on fineness, homogeneity and looseness of tungsten powder by conventional hydrogen reduction techniques.

Phase composition, transition and structure stability of functionally graded cemented carbide with dual phase structure

The phase composition, phase transition and phase structure transformation of the wire-cut section of functionally graded WC-Co cemented carbide with dual phase structure were investigated by XRD phase analysis. It is shown that the composition of η phase in the core zone is Co3W3C (M6C type). The structure of cobalt based solid solution binder phase is fcc type. At the cooling stage of the sintering process, the phase transition of η phase, i.e. M6C→M12C and the martensitic phase transition of the cobalt based solid solution binder phase, i.e. fcc→hcp are suppressed, which facilitates the strengthening of the alloy. Because the instantaneous temperature of the discharge channel is as high as 10 000 °C during the wire cutting process, the processed surface is oxidized. Nevertheless, the oxide layer thickness is in micro grade. In the oxide film, η phase is decomposed into W2C and CoO, and cobalt based solid solution binder is selectively oxidized, while WC remains stable due to the existence of carbon containing liquid organic cutting medium.

Determination of physical characterization of tungsten oxides

The physical characterization of surface area, micropore volume, micropore size distribution, mesopore volume, average pore diameter and fractal dimensions of four tungsten oxides of ammonium tungsten bronze, (NH4)0.5WO3 (ATB), hydrogen tungsten bronze, H0.33WO3 (HTB), violet tungsten oxide, W18O49 (TVO), and tungsten blue oxide, WO3+WO2.9 (TBO) were evaluated from the analysis of nitrogen adsorption–desorption isotherm data. Analysis of the adsorption–desorption isotherm data suggested that in this study TVO with the largest mesopore volume, the smallest micropore volume, the narrowest micropore size distribution, the lowest fractal dimension value and the biggest average pore diameter was advantageous for hydrogen reduction during fine tungsten powder production process and disadvantageous for doping process; HTB with the largest micropore volume, the widest micropore size distribution, the highest fractal dimension value and the smallest average pore diameter was favorable for doping process, and characterization properties of ATB and TBO in this investigation were just between TVOs and HTBs. Results showed that it was a preferable method to investigate the physical characterization of oxides by using adsorption–desorption isotherms in this study and the physical characterization of tungsten oxides should be taken into account before they are used in reduction process or in doping process.

Preparation and characterization of poly(D,L-lactide) and its porous biomaterials

Poly(D,L-lactide) was synthesized by indirect method from D,L-lactic acid and characterized by infrared spectrum and proton nuclear magnetic resonance. The influences of monomer purity, initiator concentration, polymerization temperature and polymerization time on the relative molecular mass of poly(D, L-lactide) were investigated. The polylactide was made into porous materials by using solvent-casting particulate-leaching method. Under the optimized conditions, polylactides with a viscosity average molecular mass up to 1.82 × 105 are obtained and the results are fairly reproducible. Scanning electron microscope observation indicates that the sample is highly porous and well-distributed with good interconnections between pores and the pore size of porous materials is in the range from 200 µm to 500 µm and it can be used as scaffold for bone tissue engineering.

Recycling of heavy metal alloy turnings to powder by oxidation-reduction process

Abstract The processes of direct recycling heavy metal turnings by oxidation–reduction technique have been investigated in details. The average particle size of recycled alloy powders was about 1.5 μm, and the shape of powder particle was regular when the final reduction temperature was 850 °C. The average size of the particle increased to 5 and 8 μm when increasing the reduction temperature to 900 and 950 °C, respectively. However, if the reduction temperature was above 900 °C, the surface of powder was complicated. Increasing reduction temperature from 900 to 950 °C, the particle of recycled powder grew slightly, and the content of oxygen decreased from 0.2314% to 0.1700%. It has been also found that the chemical composition of the recycled alloy powder is the same as the primary heavy metal turnings.

Biocompatibility of MIM 316L stainless steel

To evaluate the biocompatibility of MIM 316L stainless steel, the percentage of S-period cells were detected by flow cytometry after L929 incubated with extraction of MIM 316L stainless steel, using titanium implant materials of clinical application as the contrast. Both materials were implanted in animal and the histopathological evaluations were carried out. The statistical analyses show that there are no significant differences between two groups (P>0.05), which demonstrates that MIM 316L stainless steel has a good biocompatibility.