Comparison of self-mated hardmetal coatings under dry sliding conditions up to 600 °C

Hardmetal coatings prepared by high velocity oxy-fuel (HVOF) spraying represent an advanced solution for surface protection against wear. In the current systematic study the high-temperature oxidation and unidirectional sliding wear in dry and lubricated conditions were studied. Results for a series of experiments on self-mated pairs in dry conditions as part of that work are described in this paper. Coatings with nominal compositions WC-10%Co4%Cr, WC-(W,Cr)₂C-7%Ni, Cr₃C₂-25%NiCr, (Ti,Mo)(C,N)-29%Ni and (Ti,Mo)(C,N)-29%Co were prepared with an ethylene-fuelled DJH 2700 HVOF spray gun. Electrolytic hard chromium (EHC) coatings and bulk (Ti,Mo)(C,N)-15%NiMo (TM10) hardmetal specimens were studied for comparison. The wear behaviour was investigated at room temperature, 400 and 600 °C. For the coatings sliding speeds were varied in the range 0.1–1 m/s for a wear distance of 5000 m and a normal force of 10 N. In some cases the WC- and (Ti,Mo)(C,N)-based coatings showed total wear rates (sum of wear rates of the rotating and stationary samples) of less than 10^?6 mm³/Nm, i.e., comparable to values typically measured under mixed/boundary conditions. Coefficients of friction above 0.4 were found for all test conditions. The P × V values as an engineering parameter for coating application are discussed. The microstructures and the sliding wear behaviour of the (Ti,Mo)(C,N)-based coatings and the (Ti,Mo)(C,N)-15%NiMo hardmetal are compared.     

Wear test of cemented tungsten carbide at high atmospheric temperature (400°C)

Cemented tungsten carbide–cobalt (WC–Co) alloy has good mechanical properties, so it is widely used for cutting tools, wear-resistant dies and rolls, and shock-resistant punching dies. In this study, a wear test between cemented WC–Co alloy and carbon steel is carried out using a pin-on-disc wear-testing machine. The characteristics as to wear rate, coefficient of friction and surface roughness are investigated. Pin specimen and disc specimen surfaces are analyzed by a fluorescent X-ray analyzer. In addition, the wear characteristics of WC–Co alloy are confirmed by SEM observation of the microstructure of the cemented WC–Co alloy specimen. This revised version was published online in August 2006 with corrections to the Cover Date.     

Erosion-oxidation of uncoated,aluminized and chromized-aluminized 9Cr–1Mo steels under fluidized-bed conditions at 550–700 °C

Protective coatings, deposited mainly by thermal spraying and diffusion techniques, are considered a solution to extend the lifetime of many components in the energy production sector, such as heat exchangers. In this paper, some results are presented for uncoated, aluminized and chromized-aluminized 9Cr–1Mo steel, subjected to air and to impacts by 200 μm silica particles at angles of 30° and 90° and speeds of 7.0–9.2 m s^?1 at 550 –700 °C, in a laboratory fluidized-bed rig, to determine whether or not aluminized and chromized-aluminized diffusion coatings could protect the steel under such conditions. Erosion-oxidation damage was characterized by measurement of the mean thickness changes using a micrometer and examination of worn surfaces by scanning electron microscopy.Under most conditions, the coatings provided some protection to the substrate: under 30° impacts, up to 650 °C, and under 90° impacts, at 700 °C, both coatings were effective, whereas under 90° impacts, up to 650 °C, only the chromized-aluminized coating gave significant protection. However, for 30° at 700 °C, the oxide scale on the substrate was protective and the coatings were not needed. Explanations for these observations are presented in this paper, in terms of interactions between the erosion and oxidation processes for the materials.     

Experimental investigation and optimization of EDM process parameters for machining of aluminum boron carbide (Al–B4C) composite

This study investigates the effect of electric discharge machining (EDM) process parameters [current, pulse-on time (T_on), pulse-off time (T_off) and electrode material] on material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) during machining of aluminum boron carbide (Al–B₄C) composite. This article also summarizes a brief literature review related to aluminum metal matrix composites (Al-MMCs) based on different process and response parameters, work and tool material along with their sizes, dielectric fluid and different optimization techniques used. The MMC used in the present work is stir casted using 5% (wt) B₄C particles of 50 micron size in Al 6061 metal matrix. Taguchi technique is used for the design of experiments (L₉-orthogonal array), while the experimental results are analyzed using analysis of variance (ANOVA). Response table for average value of MRR, EWR and SR shows that current is the most significant factor for MRR and SR, while electrode material is most important for EWR. ANOVA also confirms similar results. It is also observed that the optimum level of process parameters for maximum MRR is A₃B₁C₃D₃, for minimum EWR is A₁B₂C₃D₁, and for SR is A₁B₃C₃D₃.     

Development of 1232°C (2250°F) Erosion and Impact Tests for Thermal Barrier Coatings

High temperature erosion and impact texts were developed for evaluation of thermal barrier coating (TBC) systems that are being generated for the High-Speed Civil Transport supersonic aircraft under NASA's Enabling Propulsion Materials program. The TBC-coated test specimen is a 6.1-mm (0.24-inch) diameter cylindrical pin. Twelve pins are mounted on a carousel with a pitch diameter of 46 mm (1.813 inch). This carousel is rotated at 500 rpm, 50 mm (two inches) from the combustor exhaust of a burner rig, while the TBC temperature is controlled at 1232°C (2250°F) using a pyrometer. The particulate is injected radially into the combustor in two horizontally opposed positions.

Two separate types of particulate are used in the tests: 50-micron and 560-micron crushed alumina. The effects of the 50-micron erosion and 560-micron impact tests are quite different, but in each case excellent similarity is seen between damage to test specimens and that of commercial engine service hardware. The temperature of the impinging particulate is above 1450°C (2642°F), and the particulate velocities were determined to be. 174 and 9 meter/second (570 and 30 feel/second), respectively, for the 50-micron and 560-micron materials.

A mathematical expression was developed for erosion wear as a function of particle size, velocity, hardness and density. The ranges over which these parameters were varied are particle size 10 to 180 micron, velocity 107 to 332 meter per second, hardness 820 to 2100 kg/mm² Knoop, density 2.2 to 5.7 gram/cc. Erosion wear is linear with the accumulated mass of eroding particulate used. Impact wear caused by 560-micron alumina is distinctly nonlinear.     

Experimental studies on optimization of process parameters and finite element analysis of temperature and stress distribution on joining of Al�CAl and Al�CAl2O3 using ultrasonic welding

This study is carried out to optimize the process parameters like weld time, weld pressure, and amplitude of vibration to maximize the weld strength in Al?CAl welding using Taguchi??s design of experiments methodology. Experiments are conducted using 0.3-mm thick pieces of aluminum, and the temperature generated at the weld interface and the weld strength for all the specimens are measured. Also, a finite element model is developed that is capable of predicting the interface temperature and stress distribution during welding. Further, a preliminary study on the joining of alumina to aluminum is also carried out, and the finite element models of temperature and stress distribution during welding are simulated. Results of experimental work and FEM studies are compared and found to be in good agreement.     

Experimental investigations of mechanical properties and slurry erosion behaviour of high velocity oxy fuel and plasma sprayed Cr2O3–50%Al2O3 coatings on CA6NM turbine steel under hydro accelerated conditions

Slurry erosion behaviour of HVOF (High Velocity Oxy Fuel) and plasma sprayed coatings on CA6NM hydraulic turbine steel has been investigated at different levels of various parameters. The Cr₂O₃–50%Al₂O₃ composite powder was prepared and deposited on CA6NM steel samples to get the uniform thickness coatings. The surface roughness, porosity and microhardness of as-coated samples were measured. The as-coated samples were subjected to SEM/EDS analysis to evaluate the surface microstructure of the developed coatings. Erosion tests were performed on self made erosion test rig under hydro accelerated conditions. The study reveals that the velocity, impact angle and slurry concentration were the most significant parameters, influencing the erosion rate of these coatings. The average particle size had least affect on the erosion rate. HVOF-coated samples showed better corrosion resistance as compared to plasma-coated samples due to high hardness of HVOF-coated CA6NM samples.     

Spectrometry analysis of fumes of (U<Subscript>0.80</Subscript>Pu<Subscript>0.20</Subscript>)O<Subscript>2</Subscript> hybrid nuclear fuel samples heated to a temperature of 2000°C

The results of the spectrometry analysis of a gaseous cloud that forms over (U_0.80Pu_0.20)O₂ hybrid uranium-plutonium fuel samples for reactors, which were heated to a temperature of >2000°C, are described. Samples were heated using a laser facility designed for conducting out-of-pile experiments with the nuclear fuel. The obtained results will make it possible to empirically forecast the isotopic composition of volley emissions from the reactor core during accidents on the 1000-MW power reactor with the (U_0.80Pu_0.20)O₂ hybrid fuel.     

Effect of Mo and Ag on the friction and wear behavior of ZrO2 (Y2O3)–Ag–CaF2–Mo composites from 20 °C to 1000 °C

In this paper, a series of ZrO₂ matrix high-temperature self-lubricating composites were prepared by hot-press technique. The effect of Mo and Ag on the friction and wear behavior of the ZrO₂(Y₂O₃)–Ag–CaF₂–Mo composites in a wide temperature range was investigated. The XRD results showed that CaMoO₄ formed on the worn surface above 400 °C. The excellent lubrication performance of CaMoO₄ endowed the low coefficient of friction of the ZrO₂(Y₂O₃)–Ag–CaF₂–Mo composites at high temperatures. The ZrO₂(Y₂O₃)–10Ag–10CaF₂–10Mo composites showed favorable wear resistance at all the tested temperatures which was attributed to the combined action of hardness and phase transformation.     

Experimental Study of Leakage and Friction of Rectangular,Elastomeric Hydraulic Seals for Reciprocating Motion from −54 to +135°C and Pressures from 3.4 to 34.5 MPa

Hydraulic seals for reciprocating motion are used in mechanisms, machines, and devices most commonly in automotive, aerospace, marine, and general industrial sectors. Applications vary from those of a cheap medical injector and tire pump to mechanisms controlling ultra-expensive equipment in power stations, ships, and space vehicles. Unfortunately, elastomeric seals are flexible solids with nonlinear response to changes in their environment involving stress or strain, heat transfer, interaction with fluids, and aging. Unsurprisingly, research into their performance is ongoing for more than 80 years. The present experimental study is a step toward a better understanding of sealing performance in a broad range of temperatures and sealed pressures. Hundreds of experiments were conducted in conformance to international standards and in controlled conditions within tight tolerances of all parameters, including mechanical properties, solid dimensions, and operating conditions. Rectangular elastomeric seals for aerospace applications were studied under sealed pressures of 3.4 to 34.5 MPa (500 to 5,000 lb/in²) and in ambient temperatures of ?54 to +135°C. The combined range of pressures and temperatures exceeds what is available in the literature, particularly on the low temperature side. Other parameters varied in the experiments include the seal dimensions and radial interference, the surface roughness of the cooperating shafts, and the support of seals by one or two back-up rings. The results of the parametric study, summarized in eight tables and two figures, have been sorted for ascending leakage and friction force at each of the studied ambient temperatures for quick selection of optimal values.     

Investigation into the wear behaviour of Stellite 6 during rotation as an unlubricated bearing at 600 °C

The wear behaviour of Stellite 6 was studied during rotational sliding in a bespoke bearing rig at 600 °C for times between 2 min and 12 h. Six stages of wear were identified: (i) formation of a mixed oxide ‘glaze’, (ii) cobalt and chromium elemental diffusion to the ‘glaze’ surface forming chromium- and cobalt-dominated oxide layers, (iii) oxygen diffusion into the ‘glaze’ leading to a chromium-dominated oxide layer at the ‘glaze’/substrate interface, (iv) spallation of the ‘glaze’ through chemical failure, (v) re-formation of the ‘glaze’ and (vi) elemental diffusion within the ‘glaze’, again resulting in discrete oxide layer formation.     

Erratum to “Prediction of fracture parameters of circumferential throughwall cracks in the interface between an elbow and a pipe under internal pressure”

Journal of Mechanical Science and Technology - There are two corrections to make to the original article. Firstly, Table 2 in the original article, was erroneously given. The Table 2 should read as...     

Spectrometry and Performance Characteristics of a BGO–ФЭУ-165 Scintiblock in a Temperatire Range of +25 to –140°C

The possibility of the joint operation of a -165 photomultiplier based on microchannel plates and a BGO crystal, which are cooled to a temperature required for the operation of a semiconductor Ge detector, is investigated taking into account the temperature dependence of proper PMT characteristics. The system was cooled from room temperature to –140°C for 8 h. The limiting temperature at which the PMT holds its serviceability was determined, and the temperature changes in the spectroscopic characteristics of the system (the energy resolution and signal-to-noise ratio) were studied.     

Multi-variable measurements and optimization of GMAW parameters for API-X42 steel alloy using a hybrid BPNN–PSO approach

This research addresses multi criteria modeling and optimization procedure for Gas Metal Arc Welding (GMAW) process of API-X42 alloy. Experimental data needed for modeling are gathered as per L₃₆ Taguchi matrix. Model inputs include work piece groove angle as well as the five main GMAW process parameters. The proposed back propagation neural network (BPNN) simultaneously predicts weld bead geometry (WBG) and heat affected zone (HAZ). Image processing technique along with Bridge Cam and AWS gauges are used to take accurate measurements of WBGs and HAZs. The adequacy of the developed BPNN is established through comparisons against measured process outputs. Measurements indicate that the BPNN model simulates GMAW process with average errors of 0.33 to 0.82%. Next, the BPNN model is implanted into a particle swarm optimization (PSO) algorithm to simultaneously optimize HAZ and WBG characteristics. The hybrid BPNN–PSO determines process parameters values and groove angle so as a desired WBG is achieved while HAZ is minimized. Verification tests demonstrate that the proposed BPNN–PSO is quite efficient for in multi-criteria modeling and optimization of GMAW.     

An Experimental Setup for Studying the Solubility and Phase Transitions in a Hydrocarbon–Supercritical CO2 System in a Wide Range of Pressures and Temperatures

Instruments and Experimental Techniques - A system for saturating a porous medium with hydrocarbon and supercritical CO2 has been designed. A procedure for carrying out an experiment on the...     

Development of a new theory of thermal cutting processes 3. Influence of cutter’s front angle on the cutting temperature and influence of preheating of the blank on the cutting force

Within the framework already established, attention turns to the influence of the cutter’s front angle on the cutting temperature and to the influence of preheating of the blank on the cutting force.     

Phase discrimination and a high accuracy algorithm for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump

PIV technology is an efficient and powerful measurement method to investigate the characteristics of fluid flow field. But for PIV particle image post-processing, some problems still exit in two-phase particles discrimination and velocity field algorithm, especially for high-speed rotating centrifugal slurry pump. In this study, through summarization and comparison of the various phase discrimination methods, we proposed a two-phase identification method based on statistics of gray-scale level and particle size. The assessment of performance through experimental PIV images shows that a satisfying effect for particle identification. For high speed rotation of the impeller, a combination of adaptive cross-correlation window deformation algorithm and multistage grid subdivision is presented. The algorithm is applied to experimental PIV images of solid–liquid two-phase flow in a centrifugal slurry pump, the results show that the algorithm in the present study has less pseudo vector number and more matching particle pairs than those of fixed window and window translation methods, having the ability to remove pseudo vector efficiently. It confirmed that the algorithm proposed in the present study has good performance and reliability for PIV image processing of particle–fluid two-phase flow inside high-speed rotating centrifugal slurry pump.