EFFECT OF WETTING AGENT AND CARBIDE VOLUME FRACTION ON THE WEAR RESPONSE OF ALUMINUM MATRIX COMPOSITES REINFORCED BY WC NANOPARTICLES AND ALUMINIDE PARTICLES

Aluminum matrix composites were prepared by adding submicron sized WC particles into a melt of Al 1050 under mechanical stirring, with the scope to determine: (a) the most appropriate salt flux amongst KBF4 , K2 TiF6 , K3 AlF6 and Na3 AlF6 for optimum particle wetting and distribution and (b) the maximum carbide volume fraction (CVF) for optimum response to sliding wear. The nature of the wetting agent notably affected particle incorporation, with K2 TiF6 providing the greatest particle insertion. A uniform aluminide (in-situ) and WC (ex-situ) particle distribution was attained. Two different sliding wear mechanisms were identified for low CVFs (≤1.5%), and high CVFs (2.0%), depending on the extent of particle agglomeration

Pulsed plasma deposition of Fe-C-Cr-W coating on high-Cr-cast iron: Effect of layered morphology and heat treatment on the microstructure and hardness

Pulsed plasma treatment was applied for surface modification and laminated coating deposition on 14.5 wt%-Cr cast iron. The scopes of the research were: (a) to obtain a microstructure gradient, (b) to study the relationship between cathode material and coating layer microstructure/hardness, and (c) to improve coating quality by applying post-deposition heat treatment. An electrothermal axial plasma accelerator with a gas-dynamic working regime was used as plasma source (4.0 kV, 10 kA). The layered structure was obtained by alternation of the cathode material (T1 - 18 wt% W high speed steel and 28 wt% Cr-cast iron). It was found that pulsed plasma treatment led to substrate sub-surface modification by the formation of an 11–18 μm thick remelted layer with very fine carbide particles that provided a smooth transition from the substrate into the coating (80–120 μm thick). The as-deposited coating of 500–655 HV0.05 hardness consisted of “martensite/austenite” layers which alternated with heat-affected layers (layers the microstructure of which was affected by the subsequent plasma pulses). Post-deposition heat treatment (isothermal holding at 950 °C for 2 h followed by oil quenching) resulted in precipitation of carbides M7C3, M3C2, M3C (in Cr-rich layers) and M6C, M2C (in W-rich layers). These carbides were found to be Cr/W depleted in favor of Fe. The carbide precipitation led to a substantial increase in the coating hardness to 1240–1445 HV0.05. The volume fraction of carbides in the coating notably increased relatively to the electrode materials

Microstructure And Mechanical Properties Of Al-WC Composites

The scope of the research work is the production and characterization of Al matrix composites reinforced with WC ceramic nanoparticles. The synthesis process was powder metallurgy. The produced composites were examined as far as their microstructure and mechanical properties (resistance to wear, micro/macrohardness). Intermetallic phases (Al12W and Al2Cu) were identified in the microstrucutre. Al4C3 was not detected in the composites. Adding more than 5 wt% WC to the aluminum, microhardness and wear resistance exceed the values of Al alloy. Composites having weak interface bond performed the highest wear rate

Effect of SiO2 addition on solid state reduction of chromite concentrate

The effect of SiO2 addition on the solid state reduction of a Greek chromite concentrate, at 1300 and 1400 degrees C, has been studied. Addition of SiO2 in the chromite concentrate-graphite mixture generally promoted reduction at 1400 degrees C. However, there was a critical content of SiO2 after which lower final reduction degrees at higher silica contents were attained. This was due to the diluent effect of SiO2 on the contact between graphite and chromite. Increase in the carbon content of the charge resulted in higher critical silica contents. Two mechanisms of reduction took place: (i) solid state reduction by graphite and (ii) smelting reduction by dissolution of chromite into the molten siliceous slag and subsequent reduction of chromium and iron oxides at the slag/graphite and/or slag/metallic carbide interface. The addition of SiO2 did not have any significant effect at 1300 degrees C due to the non-formation of eutectic siliceous phases for the occurrence of the smelting reduction mechanism. (C) 1997 The Institute of Materials.Ironmaking & Steelmakin

Effect of Destabilization Heat Treatments on the Microstructure of High-Chromium Cast Iron: A Microscopy Examination Approach

A 18.22 wt.% Cr white iron has been subjected to various destabilization heat treatments. Destabilization at 800 A degrees C caused gradual precipitation of M(23)C(6) secondary carbide particles with time leading to a gradual increase in the bulk hardness. At 900, 1000, and 1100 A degrees C, an initial sharp increase in bulk hardness with time occurred, reaching a plateau that was followed by a slightly decreasing trend. The combination of martensite formed, stoichiometry, and morphology of the secondary carbides present (mostly M(7)C(3)) are responsible for the obtained values of hardness. At 1100 A degrees C, severe dissolution of the secondary carbides and consequent stabilization of the austenitic phase took place. Maximum hardness values were obtained for destabilization at 1000 A degrees C. The correlation between bulk hardness and microstructural features was elaborated.Journal of Materials Engineering and Performanc

Corrosion properties of HVOF cermet coatings with bond coats in an aqueous chloride environment

WC-17Co coatings with Ni-5Al bonding layers were deposited on Al-7075 by HVOF spraying. The top-coat consisted of layers comprising tungsten carbide particles embedded in a Co(W,C) matrix of varied composition. The coated specimens were subjected to potentiodynamic polarization in 3.5% aqueous NaCl at 25, 35 and 45 degrees C. The coatings exhibited pseudopassivity caused by the oxidation of tungsten, carbon and possibly cobalt. Chronoamperometric measurements indicated that the inhomogeneous binder composition induced active corrosion processes taking place simultaneously with pseudopassivity. Cyclic polarization suggested that the coatings were not susceptible to pit corrosion in the temperature range of 25-45 degrees C. The likely "critical pitting" temperature of the coatings was 60 degrees C. Higher testing temperatures led to lower corrosion potentials and faster corrosion kinetics. (C) 2007 Elsevier B.V. All rights reserved.Thin Solid Film