Key Engineering Materials Vols. 353-358

Abstract: An unequal interval grey forecast model GM (1, 1) was proposed based on the grey system theory and the measurement data of the rate of high temperature abrasion of water-wall tubes in circulating fluidized bed (CFB) boilers. According to the former part of measurement data, the latter part of high temperature abrasion rate of water-wall tubes was forecasted by using the GM (1, 1) model. Through comparing the computation values with the measurement values, the accuracy and the feasibility of the model were verified. The result shows that under small statistics conditions, the unequal interval grey forecast model can offer precisely prediction results, which can provide scientific basis and guidance for the condition-based maintenance of the water-wall tubes in CFB boilers.

Abstract: The knowledge of tribological properties of silicon is important due to its potential application for micromechanical devices. Single crystal silicon wafers were implanted by carbon ion with an energy of 80 keV and different implantation doses of 2×1015 ions/cm2 and 2×1016 ions/cm2, respectively. The nanohardness and elastic modulus of silicon wafers before and after C+ implantation were studied on the nano-mechanical testing system. The micro sliding tests on silicon wafers before and after C+ implantation were performed on the UMT-2 Micro-tribometer to investigate the coefficient of friction and wear volume. The results demonstrate that the nanohardness and elastic modulus of silicon wafer at the implantation dose of 2×1015 ions/cm2 decrease and those of 2×1016 ions/cm2 have little change. C+ implantation improves friction-reducing effect of silicon wafers and the coefficient of friction decreases to a great extent. But when the load reaches a certain value, the coefficient of friction increases sharply and the worn trace occurs on the silicon surface. Adhesive and abrasive wear are the main mechanisms at light loads and micro fatigue is the main mechanism at heavy loads.

Abstract: By choosing appropriate annealing temperature and annealing time, diffusion couples made of aluminum bronze and tool materials were prepared to simulate the diffusion and phase formation during the actual machining. These results were compared to those obtained from turning experiments. In agreement with results obtained from diffusion couple experiments, all turning experiments showed that major elements in both tool materials and workpiece diffused into their counterparts. The diffusion of C away from the tool will reduce the tool strength. It is helpful to use diffusion couple results to comprehend the diffusion effect in the actual turning process.

Abstract: Numerical analysis by influence function method (IFM) is demonstrated in this study in order to investigate the fretting wear problems on the secondary side of the steam generator, caused by flow induced vibration. Two-dimensional numerical contact model is developed in terms of Cauchy integral equation. The distributions of normal pressures, shear stresses and displacement fields are derived between two contact bodies which have similar elastic properties. The work rate model is adopted to find the wear amounts between two materials. The results are compared with the solutions by finite element analyses, which validates the application of the present method to fretting wear problems.

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: Recent researches have found that surfaces with non-glazed or laser dimpling topography offer improved lubricating efficiency and wear resistance under lubrication conditions over their conventional glazed status. It was carried out in this paper to simulate a pin-on-disk experimental condition and perform hydrodynamic lubrication (HL) calculations for both non-glazed and glazed surfaces under conditions of different sliding velocities and loads with a view of understanding the tribological mechanism and characteristics of non-glazed surfaces. The results showed that the minimum film thickness of non-glazed surfaces, which closed to a typical elasto-hydrodynamic lubrication (EHL) film thickness, was thicker than that of glazed surfaces under the condition of low sliding velocities and small loads. At the same time, a decreased maximum pressure of full-film of non-glazed surfaces demonstrated an even pressure distribution on them.

Abstract: The number of peri-prosthetic femoral fractures in todays aging population is increasing. Fractures of the femur may occur intra-operatively or post-operatively, either at the tip of the femoral stem or in areas where cortical thinning has occurred. This is further enhanced if the patient is osteoporotic. These fractures can be difficult to treat due to the complexity of the mechanical status and further complicated biologically by the presence of ultra high molecular weight polyethylene (UHMWPE) wear debris that can migrate from the articulating surface of the prosthesis to the fracture site. In this study, the effect of PE wear debris on the healing of osteoporotic fractures was investigated using a rodent ovariectomised (OVX) model. One hundred female Sprague Dawley rats were subjected to either bilateral OVX or Sham surgery at 10 weeks of age. Three months later, a closed fracture was created in the right femur using a 3-point bending device and an intramedullary k-wire for fixation. Animals were divided into 4 groups (n=3-8). A 0.2ml suspension of Ceridust (PE wear debris), hyaluronic acid & saline was injected directly into the fracture site at the time of surgery into half the animals. Control animals received comparable injections excluding the Ceridust. Animals were sacrificed at 1, 3 and 6 weeks. The OVX animals had a greater body weight compared to the Sham animals (p<0.05). DEXA analysis revealed that the presence of PE wear debris had no effect on the BMD within the fracture callus at either time-point. Mechanical analysis revealed an increase in bone strength with time. The presence of PE had no statistical effect upon the ultimate peak load or stiffness, however there was a trend towards increased peak load in the PE groups at 3 and 6 weeks following 3-months oestrogen deficiency. Histological analysis showed that the control OVX fractures had more cartilage development than the Sham group at 3 weeks and delayed remodeling at 6 weeks. The PE treated OVX group showed more fibrous tissue at the fracture gap and inside the diaphysis tunnel showing further delayed healing compared to the Sham group with PE. In this study after 3-months of oestrogen deficiency, no differences in mechanical or BMD was found in the fractured limbs between the PE –treated and non-PE treated fractures. However, histologically, PE wear debris induced fibrous tissue at the fracture site which further delayed the healing process. More care should be taken with aged patients receiving revision surgery, as these patients become harder to manage when fractured due to the influence of both osteoporosis and PE wear debris.

Abstract: In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness and microstructure of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction-hardened SPS5 steel. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness. Also, we observe the wear type changes from the plowing wear to the adhesive wear as the hardness increases and the adhesive wear particles act as an obstacle to the transmission of the force of friction, reducing the coefficient of friction and the wear rate.

Abstract: This study aims at investigating the effect of the sliding speed and the applied load on the dry sliding wear behavior of thermally sprayed Ni-based self-flux alloy coating. Ni-based self-flux alloy powders were flame-sprayed onto a carbon steel substrate and then these coatings were heat-treated at temperature of 1000 oC. Dry sliding wear tests were performed using the sliding speeds of 0.2, 0.4, 0.6 and 0.8 m/s and the applied loads of 5, 10, 15 and 20 N. AISI 52100 ball (diameter 8 mm) was used as counterpart material. Wear behavior of Ni-based self-flux alloy coatings was studied using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that microstructure and wear behavior of the Ni-based self-flux alloy coatings were much influenced by the sliding speed and the applied load.

Abstract: SiC particulates reinforced Al matrix composites were fabricated by thermal spray process, and the dry sliding wear behavior against four different counterparts was investigated under a varying of the sliding speed and the applied load conditions. Al/SiC composites were fabricated by flame spraying, and the dry sliding wear tests were performed using the sliding speed of 0.4 m/s and 0.8 m/s at the applied load of 3 N. Sliding distance was kept at 1000 m for all the tests. Al2O3, ZrO2, Si3N4 and AISI 52100 balls were used as the counterparts. Wear tracks on the Al/SiC composites were investigated using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear behavior of Al/SiC composites was much influenced by counterpart materials.