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

Corrosion and Tensile Behavior of 304L Rebars under the Influence of a Concrete Additive and Migrating Corrosion Inhibitors

This study examines the effect of a Ca-rich fly ash additive, a liquid migrating corrosion inhibitor (Inhibitor B), and a vapor phase inhibitor (Inhibitor C), individually and in combination, on the corrosion performance of 304L stainless steel rebars embedded in concrete cubes. This was assessed through open circuit potential (OCP) measurements over 1 m in an acid rain (AR) simulating electrolyte, salt spray testing for 4 m and tensile testing of 304L rebars following the corrosion tests. For 304L rebars embedded in concrete cubes containing fly ash (FA), Inhibitor B, Inhibitor C, and combinations of FA with Inhibitor B, immersed in AR for 1 m during OCP testing, there was more than a 90% probability that corrosion did not occur. Both Inhibitors B and C improved the corrosion resistance of the rebars in AR in the absence of FA, but when combined with FA, their inhibiting effects were neutralized. The 20 wt.% FA content improved the corrosion behavior of 304L rebars compared to 0 wt.% FA. After 1 m of OCP testing in AR, % elongation increased in all cases except without inhibitors. After 4 m of salt spraying, a slight decrease in strength was observed for the 304L reinforcement, both in the absence and presence of any inhibitors, though within standard deviation

Electrochemical Behavior of Al–Al9Co2 Alloys in Sulfuric Acid

Al–Co alloys of various Co contents (2–20 wt.% Co) were fabricated by vacuum arc melting (VAM) with the scope to investigate the influence of cobalt on the microstructure and corrosion resistance of Al in 1 M H2SO4. The obtained microstructures were directional, consisting of Al9Co2 platelets (grown to coarse acicular plates as the Co content increased) uniformly dispersed in an Al-matrix. Alloying Al with Co did not decrease the rate of uniform corrosion of Al but it considerably increased its passivation ability. Moreover, all Al–Co alloys displayed lower uniform corrosion rate and notably higher passivation ability than market leading Al-alloys. The underlying mechanisms during anodic polarization in 1 M H2SO4 were identified and correlated with the microstructure. High Co content alloys (7–20 wt.% Co) presented superior passivation ability in 1 M H2SO4 as compared to the low Co content alloys

Effect of fly ash on the corrosion performance and structural integrity of stainless steel concrete rebars in acid rain and saline environments

The corrosion behavior of 304L stainless steel rebars in an alkaline solution simulating new concrete subjected to acid rain attack and a mildly to slightly acidic solution simulating corroded cover concrete that ex­posed the reinforcement to direct acid rain attack, was investigated by reverse polarization. Both solutions contained Ca(OH)2 and fly ash (0-25 wt.% of the dry mixture). Concrete cubes containing 0-25 wt.% fly ash and reinforced with 304L rebars were subjected to salt spraying for 4 m. Although the polar­ization behaviors in the two electrolytes were different, the relative trends with respect to the fly ash contents were similar. The beneficial effect of fly ash (up to 20 wt.%) on the corrosion resistance of 304L rebars was de­mon­strated. How­ever, a deteriorating effect was realized at 25 wt.% addition. Partial re­placement of cement by fly ash did not significantly affect the tensile properties of the 304L rebar before or after 4 m of salt spraying. The elastic modulus and percent elongation presented a slight decrease after 4 m of salt spraying, ir­respectively of FA content. Corrosion-wise, 304L can replace 316L stainless steel provided that FA has been added to the concrete mixture, even at low contents (10 or 15 wt.%)

A Critical Review on Al-Co Alloys: Fabrication Routes, Microstructural Evolution and Properties

Al-Co alloys is an emerging category of metallic materials with promising properties and potential application in various demanding environments. Over the years, different manufacturing techniques have been employed to fabricate Al-Co alloys, spanning from conventional casting to rapid solidification techniques, such as melt spinning, thus leading to a variety of different microstructural features. The effect of the fabrication method on the microstructure is crucial, affecting the morphology and volume of the precipitates, the formation of supersaturated solid solutions and the development of amorphous phases. In addition, the alloy composition has an effect on the type and volume fraction of intermetallic phases formed. As a result, alloy properties are largely affected by the microstructural outcomes. This review focuses on highlighting the effect of the fabrication techniques and composition on the microstructure and properties of Al-Co alloys. Another goal is to highlight areas in the field that are not well understood. The advantages and limitations of this less common category of Al alloys are being discussed with the scope of future prospects and potential applications

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

Microstructure and wear behaviour of powder and suspension hybrid Al2O3–YSZ coatings

Suspension based plasma sprayed coatings can yield superior microstructural and tribological properties compared to conventional powder based plasma sprayed coatings. This study investigates a new hybrid method, using simultaneous spraying from powder and suspension, to produce composite coatings using alumina and yttria stabilised zirconia (YSZ), with potentially excellent wear and thermal properties. Dry sliding wear showed the alumina suspension-YSZ suspension coating yielded half the specific wear rate of the alumina powder-YSZ suspension, explained by preferential gamma alumina formation and increased porosity in the latter. Both YSZ-containing samples showed superior toughness and wear rate than simple alumina powder and suspension coatings