Wear processes and performance of blade pair in small-scale single-shaft plastic shredder machine

Shredder blades and fixed blades were used as a set of blade pair to perform the shredding action. Comparable research was performed on the blade pair to understand its wear mechanism and shredding performance. The loading distribution along the two-edge shredder blades in helix configuration was identified. Optical microscopy, scanning electron microscopy, energy dispersive x-ray, x-ray diffractometer analysis, and hardness tests were used to characterise the surface, elemental composition, microstructure, and hardness of the worn blade pair. The shredder blades’ wear mechanism was categorised as progressive wear which dominant by abrasive, following by adhesive and oxidation wear. The shredding efficiency of the two-edge shredder blades in helix configuration was 69.24 %, recycling efficiency at 96.83 % and retention of 3.17 % after the shredding process.     

Shark Skin Inspired Riblet Coatings for Aerodynamically Optimized High Temperature Applications in Aeroengines

The shark skin effect is the mechanism of wall friction reduction of a fluid due to a riblet structured surface. A new application for riblet surfaces may be jet engine blades. Riblet structured coatings on the blades would act as oxidation protection and additionally reduce the skin drag on the surface. In this study structuring surface areas of high temperature nickel‐based alloys is investigated. These alloys are used for compressor and turbine blades near the combustion chamber. Experiments are performed by depositing titanium on a nickel base alloy through particular metal grids using magnetron sputtering. For single‐digit micrometer structures, photolithography with subsequent electrodeposition of nickel as well as sputter deposition and thermal evaporation of several materials are investigated. Successfully fabricated structures are oxidized at 900–1 000 °C for up to 100 h and the resulting shape is characterized using scanning electron microscopy. The most accurate structures are obtained using photolithography and subsequent electrodeposition. The reduction of the wall shear stress was measured in an oil channel. The riblet structures prior to oxidation show a reduction of the wall shear stress of up to 4.9%.     

Refurbishing superalloy components for gas turbines

Abstract

Since 1968, FVV have developed specific maintenance techniques to ensure the safe operation of turbine blades. Among the new methods employed or shortly to be used is the non–destructive testing of blades by optical and scanning electron microscopy, and this is described in the paper. New possibilities for predicting remaining blade life under various conditions of stress and temperature are considered, and new types of coating obtained using plasma spraying and hot isostatic pressing are discussed.

MST/97     

Microscopic examination of a tool used in tire waste recycling

Tire recycling includes three steps: cutting strips, turning strips into small pieces, and shredding pieces into powder. The bases of the first stage machine’s cutting blades usually broke down provoking extensive down times. The paper is focused on the microscopic examination of the failed part. Historical data were collected, hardness measurements were carried out and chemical analysis was performed. The fracture surfaces and the cross section structure of the tool were in depth investigated by light and scanning electron microscopy. The fracture mechanism and the type of the fractures were discussed. The principal causes that led to the premature failure of the base are exposed. Considering the absence of similar failure analysis case studies in bibliography, the study may be useful for industries using similar cutting machinery.     

A Study on Wear Failure Analysis of Tungsten Carbide Hardfacing on Carbon Steel Blade in a Digester Tank

This paper addresses wear failure analysis of tungsten carbide (WC) hardfacing on a carbon steel blade known as the continuous digester blade (CD blade). The CD blade was placed in a digester tank to mix ilmenite ore with sulphuric acid as part of a production process. Tungsten carbide hardfacing was applied on the CD blade to improve its wear resistance while the CD blade was exposed to an abrasive and acidic environment. Failure analysis was carried out on the hardfaced CD blade in order to improve its wear resistance and lifetime. A thickness and hardness comparison study was conducted on worn and unworn specimens from the CD blades. The carbide distribution along with elemental composition analysis of the hardfaced CD blade specimens was examined using scanning electron microscopy and energy-dispersive spectroscopy. The investigation revealed that an inconsistent hardfacing thickness was welded around the CD blade. Minimum coating thickness was found at the edges of the blade surfaces causing failure to the blades as the bare carbon steel blades were exposed to the mixed environment. The wear resistance of the CD blade can be improved by distributing the carbide uniformly on the hardfaced coating. Applying extra coating coverage at the critical edge will prevent the exposure of bare carbon steel blade, thus increasing the CD blade lifetime.     

Comparative cavitation erosion test on steels produced by ESR and AOD refining

Cavitation erosion studies of steels produced by Electroslag Refining (ESR) and Argon Oxygen Decarburization (AOD refining) have been carried out. The experiments were conducted using the modified ultrasonically induced cavitation test method. Erosion rates were measured and the morphology of damages under cavitation action was studied by scanning electron microscopy and optical microscopy techniques. The present work is aimed at understanding the cavitation erosion behaviour of electroslag refined steel (ESR) compared with the steel produced by Argon Oxygen Decarburization (AOD refining), commonly used in the production of hydraulic machinery parts (Pelton blades). The results exhibited lower cavitation rate of ESR steel compared with AOD steel, as a consequence of its better mechanical properties and homogeneous and fine-grained microstructure.     

Deposition of a nanocomposite (Ti,Al, Si)N coating with high thickness by high-speed physical vapor deposition

Nanocomposite coatings such as (Ti, Al, Si)N have been demonstrated as promising candidates for the use as protection against solid particle erosion for compressor blades. Typically, nanocomposite (Ti, Al, Si)N coatings are deposited by different physical vapor deposition (PVD) techniques. However, the relatively low coating thickness up to a few micrometers due to low deposition rates leads to a limited lifetime of the coatings under erosive particle bombardment. In this study, the deposition of a nanocomposite (Ti, Al, Si)N coating was performed by a hollow cathode gas flow sputtering method, the high-speed physical vapor deposition, which enables the high-rate deposition of thick coatings. Morphology and microstructure of the coating were investigated via scanning electron microscopy and transmission electron microscopy, respectively. Tribological characterization by impact tests and erosion tests demonstrates that the nanocomposite (Ti, Al, Si)N coated sample reveals a promising resistance against impact loads and the solid particle erosion. Summarily, nanocomposite (Ti, Al, Si)N coatings deposited by the high-speed physical vapor deposition provide a high potential for the erosion protection of compressor blades.     

GCr15钢旋片式助力泵泵体磨损失效分析

某GCr15钢旋片式助力泵泵体内环面在安装使用后短期内出现较多的断续磨痕,发生磨损失效;采用化学成分分析、金相检验和扫描电镜及能谱分析等方法,对泵体的磨损失效原因进行了分析。结果表明:由于该助力泵叶片在装配工序中装配精度不足,直接影响到叶片与泵体的配合精度,使叶片在高速旋转过程中,与泵体表面发生严重的塑性变形,产生粘着磨损。     

Failure analysis of a hydraulic Kaplan turbine shaft

This paper shows the results of the failure analysis of a 105 MW Kaplan turbine auxiliary shaft from a hydropower plant. As a part of the failure analysis, the turbine operation history was revised and the metallographic study was done. A sample of the cracked turbine shaft was examined using optical microscopy and scanning electron microscopy. Failed auxiliary shaft was coupled to the main turbine shaft and its principal function was turning the runner blades according to flow direction. In order to complement the cause of failure, a finite element analysis (FEA) was done to calculate the stress level under the maximum and minimum turbine blade inclination position. The results of present investigation showed that failure was caused by high cycle and low stress fatigue. The presence of a stress concentrator on the turbine shaft was a crucial factor to the fatigue crack-initiation phase. The FEA revealed also that the frequently load variations, showed in the operation history, could have contributed to the crack propagation.     

Analysis of the local current in GdBCO coated conductors using low-temperature scanning laser and Hall probe microscopy

The distribution of the local current in GdBCO coated conductors was investigated using low-temperature scanning laser and Hall probe microscopy (LTSLHPM). We prepared GdBCO coated conductors to study the spatial distribution of the current density in a single bridge. Inhomogeneity in the bridge was analyzed using the experimental results of scanning laser microscopy near the superconducting transition. The local transport and screening currents in the bridge were also obtained by scanning Hall probe microscopy. From the experimental results of scanning laser and Hall probe microscopy, we have observed redistribution of the current caused by defects of the coated conductors.     

Metallurgical investigation into the failure of a chopper blade used for cutting of hot-rolled steel coils

In the present work, failure investigation of a chopper blade received from an integrated steel plant has been presented. Chopper blades are used in chopping machines for cutting trimmed edges of hot-rolled coils into pieces to convert them into scrap. These blades are manufactured from hot forged or rolled billets or flats of high carbon high chromium cold work tool steel. The investigation consists of visual examination, chemical analysis, microstructural analysis through optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and hardness measurement. The chemical analysis confirmed the steel as equivalent to D2 grade in AISI notation. Carbide volume fraction of the broken blade was in the normal range of 10–15% as commonly observed in D2 tool steel. Microstructural examination under light and scanning electron microscopy showed non-uniform distribution of large eutectic primary carbides of irregular morphology forming strings or bands in tempered martensite matrix preferentially aligned in a specific direction. The uneven carbide arrangement in the matrix made the structure highly anisotropic and susceptible to localized stress concentration. The carbides were identified mainly as M₂₃C₆ type. Cracks were observed to initiate at the edges of the blade and propagate to the interior through clustered zones of carbides. SEM study suggests that the crack initiation was associated with decohesion of carbide particles in the cluster which culminated into final fracture by the mechanism of void coalescence and subsequent crack growth.     

Characterization of Damage Induced by Impacting Objects in Udimet-500 Alloy

Foreign object damage (FOD) is one of the common mechanisms in turbine blade failures which reduces high cycle fatigue life and contributes significantly to premature failure. Therefore, this study experimentally simulated FOD on the first stage blade of a gas turbine. Foreign objects with two parameters of object nose shape (spherical, conical, and flat) and impact angle (90° and 45° relative to the blade surface) were impacted on the surface of flat specimens of Udimet-500 at a temperature of 733°C with velocity of 300 m/s (same as working condition of blades). In order to evaluate the impact site morphologies, induced craters were first studied by scanning electron microscopy (SEM). Then samples were sectioned symmetrically, and by using image analysis tool software, the depth of each crater was measured. Finally, based on the results, it was found that maximum and minimum stress concentration factors and induced microcracks, respectively, are regarding to flat projectiles with impact angel of 45° and spherical at impact angle of 90°.     

Field Experience of Platinum Aluminide Coated Turbine Blades

This paper describes the results obtained from an evaluation of several platinum aluminide coated first stage turbine blades returned from the field. The IN-738LC blades had accumulated from 3,900 to 27,500 service hours in Centaur (1) 50 industrial gas turbine engines, operating in a high temperature oxidizing environment. The coating performance and condition were assessed using optical and electron microscopy. The condition of the coating was correlated to blade operating temperatures, which were estimated using the gamma prime coarsening technique. The degradation mechanism of the coating, remaining coating life, and blade repairability were also addressed.     

Evolution of ordering in iron oxide nanoparticle monolayers using electrophoretic deposition

Iron-oxide nanoparticle monolayers and multilayers were assembled using dc electrophoretic deposition. The rate of deposition and the total particle deposition were controlled by varying the concentration of nanoparticles and the deposition time, respectively. Using scanning electron microscopy, we performed a time-resolved study that demonstrated the growth of the monolayer from a single isolated nanoparticle to a nearly complete layer. We observed tight, hexagonal packing of the nanoparticles indicating strong particle-particle interaction. Multilayer growth was assessed using scanning electron microscopy and atomic force microscopy, revealing a monolayer-by-monolayer growth process.     

Estimation of useful life in turbines blades with cracks in corrosive environment

Geothermal turbines of 110 MW were installed in the Federal Electricity Commission in Cerro Prieto Mexico, which operating time exceeds 150,000 h. Therefore, the critical components which determine the useful life of the turbine should be evaluated to determine the rehabilitation or replacement of them. The critical components are the blades of the last stage in the steam turbine. It has been observed that different blades of the turbine of 110 MW with cracks presented corrosion products, which resulted in a failure for corrosion fatigue mechanisms. In this paper, it was studied the effect of crack propagation produced in a geothermal turbine blade of the last stage, L-0, which is made of stainless steel AISI 410 exposed to corrosion under a sea water solution. The corrosion phenomena including localized corrosion suffered by the cracking sample were studied through the electrochemical noise technique in current and potential and polarization curves. The tests were conducted on pieces of blades subjected to fatigue. The results indicated that the exposure to the corrosion solution modified the width and the length of the cracks. Using a scanning electron microscopy (SEM), the surface of the crack was observed, showing that the corrosion mechanism produced a significant increment of the velocity of crack propagation and therefore, a decrement of the useful life of the material. This research will allow us to understand the corrosion process in addition to estimate the useful life of the blades when they are subjected to load cycles.     

Analysis of surface quality of multi-film cooling holes in nickel-based single crystal superalloy

The effect of the surface quality of multi-film cooling holes processed by laser drilling (LD) and electrical discharge machining (EDM) on the mechanical properties of blades have been studied. The physical features of the cooling holes, including the diameter, conicity and shape of the holes, are measured by optical microscopy, demonstrating that the EDM process is not as accurate as the LD process. Meanwhile, metallurgical characteristics, including the recast layer, heat affected zone and micro-cracking within the surface layer, are analysed by scanning electron microscopy, demonstrating that the radial crack generated in the LD process is more dangerous than the circumferential cracks generated in the EDM process. Using finite element analysis (FEA), the single crystal superalloy specimens with multi-film holes are simulated based on the crystal plasticity theory, showing that a significant increase of the stress gradient is observed in a real hole model than in an ideal circular hole model, which means that a shape simplification in the blade design will reduce the reliability of the blade. Based on the findings above, the influence of the surface quality of holes is investigated to obtain the possible damages to nickel single crystal turbine blades.     

Isoconversional kinetic analysis of the crystallization phases of amorphous selenium thin films

The crystallization kinetics of Se thin films were determined under nonisothermal conditions using a differential scanning calorimetry (DSC) technique. The development of crystal phases by thermal treatment of the film at various temperatures was analyzed by X-ray diffraction. Microstructures were identified by studying the morphology of the films using scanning electron microscopy and atomic force microscopy. This study reveals the simultaneous presence of distinct hexagonal and monoclinic phases; the DSC crystallization curve is formed by overlapping the exothermic crystallization curves of both phases. Two isoconversional methods, the Kissinger-Akahira-Sunose and Vyazovkin methods, were used to determine the variation of the activation energy for crystallization with temperature. The results show that the crystallization activation energy decreases with the extent of crystallization or temperature, which suggests that the examined phases follow multi-step kinetics.     

Production of carbon black acrylic composite as an electrophotographic toner using emulsion aggregation method: Investigation the effect of agitation rate

Toner as a composite of colorant, polymer and additives is a primary component of electrophotographic printing and copying processes. It can be produced by conventional mechanical milling or by more recently developed chemical polymerization methods. The emulsion aggregation is a popular chemical method that allows tight control on the size, size distribution and shape of the synthesized toner particles. These characteristics are important for producing high quality, high-resolution printed images. This research investigated the effect of agitation speed on toner synthesis using emulsion aggregation method. Particle size analysis, scanning electron microscopy, and field emission scanning electron microscopy were used to study the size, shape, and morphology of toner particles. It was found that toner particles synthesized using emulsion aggregation method is spherical in shape and decrease in size as agitation speed increases. Differential scanning calorimetry and spectrophotometric analyses results showed that the toner synthesized by this method had appropriate thermal and colorimetric characteristics as compared to an industrial toner.     

Synthesis and electrochemical properties of polyaniline nanofibers by interfacial polymerization

Polyaniline nanofibers were prepared by interfacial polymerization with different organic solvents such as chloroform and carbon tetrachloride. Field emission scanning electron microscopy and transmission electron microscopy were used to study the morphological properties of polyaniline nanofibers. Chemical characterization was carried out using Fourier transform infrared spectroscopy, UV-Vis spectroscopy, and X-ray diffraction spectroscopy and surface area was measured using BET isotherm. Polyaniline nanofibers doped with lithium hexafluorophosphate were prepared and their electrochemical properties were evaluated.