Formation of ZrO<Subscript>2</Subscript>–SiC Composite Coating on Zirconium by Plasma Electrolytic Oxidation in Different Electrolyte Systems Comprising of SiC Nanoparticles

Plasma electrolytic oxidation (PEO) coupled with electrophoretic deposition (EPD) was used to fabricate ZrO₂/SiC composite coating on the zirconium metal. The PEO–EPD process was carried out in three different electrolyte systems consisting of 5 g/l sodium aluminate or trisodium orthophosphate or sodium metasilicate with 4 g/l SiC nanoparticles. The X-ray diffraction results indicate monoclinic zirconia is the major phase in phosphate and silicate electrolyte while the coating produced in aluminate electrolyte is composed of tetragonal zirconia. The potentiodynamic polarization studies (PDP) indicate that composite coating produced in phosphate?+?SiC nanoparticle containing electrolyte exhibit superior resistance to corrosion, which can be attributed to the pore-free morphology of the coating. All the PEO–EPD coatings show exceptionally good adhesion strength (L_c ?> 40 N). The coating fabricated in phosphate?+?SiC nanoparticles is found to be the best coating because of its superior resistance to corrosion and reasonably good adhesion strength.     

Oxidation Behavior of Ta–W–Ti–Al Multialloys Prepared by Spark Plasma Sintering

Powder Metallurgy and Metal Ceramics - In this study, Ta–W–Ti–Al multialloys were prepared by spark plasma sintering (SPS) as a new powder metallurgy technology based on discharge...     

Mechanical and Tribological Behavior of Powder Metallurgy Processed Aluminum–Graphite Composite

Russian Journal of Non-Ferrous Metals - In this research, the mechanical and tribological behavior of aluminum–graphite (Al–Gr) composite has been investigated in order to determine the...     

Ni–ZrO2 Composite Coating by Electro-Co-Deposition

In the present investigation Ni–ZrO₂ metal matrix composite coatings were prepared on steel substrate using watt’s type solution through electro-co-deposition process with different weight percentages of zirconia powder dispersed in the bath. In the coating, nickel is present with faceted appearance along with ZrO₂. The microhardness and wear resistance of the coatings increase with increasing weight percentage of particles content in the coating. The hardness of the resultant coatings was found to be 325 VHN for pure Ni coating whereas 401VHN for Ni–ZrO₂ (15 g/l ZrO₂) coating depending on the particle volume in the Ni matrix. The results also showed that the wear resistance of the composite coatings was improved as compared to unreinforced Ni deposited material. Strengthening of the coating was attributed to the ZrO₂ dispersion and partially favorable texture.     

Effect of Speed on the Tribological Behavior of Fe–Cu–C Based Self Lubricating Composite

In this work, the effect of different speeds on the tribological properties of sintered iron–copper–graphite (Fe–Cu–C) based self lubricating composites have been studied. Fe–Cu–C based self-lubricating composites were prepared by powder metallurgical compaction and sintering method. CaF₂, a solid lubricant in weight percentages of 0, 3, 6, 9 and 12 was added to the base matrix consisting of Fe-2Cu-0.8C. The fabricated samples were tested for friction and wear at a constant load of 10 N and three different speeds of 0.5, 5 and 10 m/s. The surface properties of unworn and worn surfaces were analyzed using optical and scanning electron microscope. The friction and wear test of the composites exhibited decrease in coefficient of friction and increase in wear loss with the increase in speed. The results also revealed different trends in the friction behavior of the developed composites at low (0.5 m/s) and high speeds(5 and 10 m/s). However, at all test speeds, COF of samples with 3, 6 and 9 wt.% was less than the base matrix, and wear loss of 3 wt.% CaF₂ sample was the lowest at all speeds. Ploughing, adhesive and delamination wear were the dominant wear mechanism as revealed by SEM. Based upon the findings, the developed material could be used for low and high speed antifriction applications.     

Structure and Tribological Properties of B83 Babbit–Based Composite Rods and the Coatings Produced from Them by Arc Surfacing

Surfacing composite rods based on a B83 babbit alloy reinforced by silicon carbide and boron carbide particles are fabricated by extrusion. The structure and the tribological properties of the rods are studied. Extrusion allowed us to introduce and to uniformly distribute reinforcing fillers and to change the size and the morphology of the intermetallic phases in the matrix alloy. The wear resistance of the rods made of the B83 babbit + 5 wt % SiC composite material is shown to be higher than that of commercial B83 alloy samples by a factor of 1.2. Arc surfacing is used to deposit antifriction coatings, which are made of the surfacing composite rods based on B83 babbit reinforced by boron carbide or silicon carbide particles, onto steel substrates. The deposited layers exhibit good adhesion to the substrates: the melting line is continuous and does not contain discontinuities. The structure and the tribological properties of the deposited coatings are studied. The wear resistance of the composite coatings is higher than that of the B83 alloy–based coating by 30%.     

Synthesis of the ZrN–ZrB2 Composite by Spark Plasma Sintering

Powder Metallurgy and Metal Ceramics - Reactive spark plasma sintering of ZrH2, BN, and B powder mixtures in the temperature range 1500–1900°C was used to produce a ZrN–ZrB2...     

Effect of Y2O3 Content on Microstructure of Gradient Bioceramic Composite Coating Produced by Wide-Band Laser Cladding

Hydroxyapatite (HA) ,a kind of bioactive materi-al , has wide application prospect in hard tissue re-placemen and repairment due to its si milar chemicalcomposition and crystallographic structure to that ofbone mineral[1 ,2]. Since HA has lowstrength (50 …     

Investigation of Tribological Behavior of Lanthanum-Based Thin Films Deposited on Sulfonated Self-Assembled Monolayer

3-mercaptopropyl trimethoxysilane （MPTS） was prepared on glass substrate so as to form a two-dimensional self-assembled monolayer （SAM）, and the terminal - SH group in the film was in situ oxidized to - SO3H group to confer good chemisorption ability to the film. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM, making use of the chemisorption ability of -SOaH group. Atomic force microscopy （AFM） and X-ray photoelectron spectrometry （XPS） and contact angle measurements were used to characterize the thin films. The tribological properties of the as-prepared thin films sliding against a steel ball were evaluated on a friction and wear tester. Tribological experiment shows that the friction coefficient of glass substrate decreases from 0.8 to 0.08 after the rare earth （RE） self-assembled films （SAMs） are formed on its surface. And the RE self-assembled films have longer wear life （500 sliding passes）. It is demonstrated that RE self-assembled film exhibits good wear-resistant property. The marked decrease in friction and the longer wear life of RE films are attributed to the excellent adhesion of the film to the substrate and to the special characteristics of the RE elements. The frictional behaviors of RE thin-films-coated silicon surface were sensitive to the applied load and the sliding velocity of the steel ball.     

Influence of Nanometric Ceria Coating on Oxidation Behavior of Chromium at 900 ℃

Isothermal and cyclic oxidation behaviors of chromium samples with and without nanometric CeO2 coating were studied at 900℃ in air. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and high-resolution electron microscopy （HREM） were used to examine the morphology and microstructure of the oxide film. It was found that ceria coating greatly improved the oxidation resistance of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission （AE） technique was used in situ to monitor the cracking and spalling of oxide film, and AE signals were analyzed in time-domain and number-domain according to related oxide fracture model. Laser Raman spectrometer was also used to study the stress of oxide film formed on Cr with and without ceria. The improvement in oxidation resistance of chromium is believed mainly due to that ceria greatly reduced the growth speed and grain size of Cr2O3. This fine grained Cr2O3 oxide film might have better high temperature plasticity and could relieve parts of the compressive stress by means of creeping and maintained ridge character and relatively lower level of internal stress. Meanwhile, ceria application reduced the size and number of interfacial defects, remarkably enhanced the adhesive property of Cr2O3 oxide scale formed on Cr substrate.     

Influence of Nanometric Ceria Sol-gel Coating on Oxidation Behavior of Chromium at 1000℃

 Isothermal oxidation behavior of chromium with and without nanometric sol-gel CeO2 coating is studied at 1000℃ in air. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to examine the surface morphology and microstructure of their oxide films. It is found that ceria coating greatly improves the anti-oxidation property of chromium. Laser Raman spectrometer and X-ray diffraction spectrometer (XRD) are also used to study the stress level in oxide films formed on ceria-coated and ceria-free Cr. Secondary ion massive spectrum (SIMS) is used to examine Cr, O and Ce element distribution in depth in oxide films. Results show that nano-ceria application greatly reduces the growing speed and grain size of Cr2O3 film, and his fine grain-sized Cr2O3 film probably has better high temperature plasticity, i.e. oxide film relieves part of the compressive stress by means of creeping. Meanwhile, CeO2 changes the oxide film growing mechanism from predominant cation outward diffusion to anion inward diffusion. XRD and Raman testing results both show the stress declination effect due to nano-CeO2 application, and their discrepancy is analyzed concerning to the rare earth effect.     

Microstructural and Tribological Characteristics of Al–10Cu–Fe alloy Produced by Vertical Centrifugal Casting process

In this study, an attempt has been made to produce Al–10Cu–Fe alloy by vertical centrifugal casting at speeds ranging from 800 to 2850 rpm. The microstructural features, mechanical and wear properties have been investigated. The microstructure of Al–10Cu–Fe alloy consists of equiaxed grain morphology of the primary α-phase with eutectic phases in the interdendritic regions. It has been observed that there is a variation in the grain size from the inner surface of the casting to its outer surface. The speed also has a strong influence on the grain size and subsequent mechanical properties of the alloy. The wear properties of the alloy have been evaluated at a constant sliding velocity of 1 m/s for a range of applied load and sliding distance. The variations in the wear behavior are attributed to the size and solidification morphology of the castings.     

Influence of Nano-Ceria Sol-Gel Coating on Oxidation Behavior of Chromium at 1 000℃

Isothermal oxidation behavior of chromium with and without nanon sol-gel CeO_2 coating is studied at 1 000 ℃ in air. Scanning electron microscopy (SEM)and transmission electron microscopy (TEM)are used to examine the sur-face morphology and mierostructure of the oxide films. It is found that ceria coating greatly improves the anti-oxida-tion property of chromium. Laser Raman spectrometer and X-ray diffraction spectrometer (XRD)are also used to study the stress level in oxide films formed on ceria-coated and ceria-free Cr. Secondary ion mass spectrometer (SIMS)is used to examine Cr, O and Ce element distribution in depth in oxide films. Results show that nano-ceria application greatly reduces the growth speed and grain size of Cr_2O_3 film, and this fine grained Cr_2O_3 film probably has better high temperature plasticity, i.e. , oxide film relieves part of the compressive stress by means of creeping. Meanwhile, CeO_2 changes the oxide film growth mechanism from predominant cation outward diffusion to anion in-ward diffusion. XRD and Raman testing results both show the stress declination effect due to nano-CeO_2 application, and their discrepancy in the rare earth effect is analyzed.     

Tribological Properties of ZrN–Si3N4–TiN Composites Consolidated by Spark Plasma Sintering

Powder Metallurgy and Metal Ceramics - The production of ZrN–Si3N4 and ZrN–Si3N4–TiN composites by spark plasma sintering and the mechanical and tribological properties of the...     

High-Temperature Oxidation of ZrB2–MoSi2–AlN Composite Ceramics

Powder Metallurgy and Metal Ceramics - The oxidation mechanism of ZrB2–MoSi2–AlN composite ceramics has been studied in the range 1550–1680°C. The oxidation stages and scale...     

Production of Co–Cr–Ti Composite and Investigation of Mechanical Properties

Intermetallic materials such as Co₂Ti, Cr₂Ti are among advanced technology materials that have outstanding mechanical and physical properties for high temperature applications. Especially creep resistance, low density and high hardness properties stand out in such intermetallics. The microstructure, mechanical properties of %64Co–%32Cr and %4Ti powders were investigated using specimens produced by tube furnace sintering at 800–1200 °C temperature. A composite consisting of ternary additions, a metallic phase, Ti, Cr and Co have been prepared under Ar shroud and then sintered in tube furnace. XRD, scanning electron microscope, were used to characterize the properties of the specimens. Experimental results carried out for composition %64Co–%32Cr–%4Ti at 1200 °C suggest that the best properties as 182.09 HV and 5,584 g/cm³ density were obtained at 1200 °C.     

Oxidation Behavior of La_2O_3 Oxide Dispersion Strengthened Aluminum－Diffusional Coating

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Toughening Mechanisms of Alumina Matrix Ceramic Composite Toughened by Rare Earth Additive

Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites with nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It is indicates that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550℃ and 28 MPa for 30 min are improved evidently. Based on mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistant, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All the above are beneficial to the improvement of mechanical properties of alumina matrix ceramic composites.