Corrosion Behavior Of As-cast Research Articles

Mechanical properties and corrosion behavior of electron beam cold hearth melting high strength and high corrosion resistant Ti-0.3Mo-0.8Ni alloy with different states

In this study, a large size Ti-0.3Mo-0.8Ni (TA10) alloy ingot melted by electron beam cold hearth melting (EBCHM) technology was investigated. The microstructure, mechanical properties, and corrosion behavior of as-cast, hot-rolled, and annealed TA10 alloys were investigated. The results show that different states of TA10 alloys have different microstructure and properties. The microstructure of the as-cast TA10 alloy exhibits the Widmanstätten α phase, and the hot-rolled TA10 sheet shows a fibrous structure with an obvious rolling streamline. After 650 °C annealing, the intergranular β phase decreases, and most of the strip α phase changes to the equiaxed α phase. With the annealing temperature increasing to 840 °C, the microstructure gradually changed from an equiaxed structure to a duplex structure. The mechanical properties of the TA10 alloy were enhanced after hot-rolling with an increase in ultimate tensile strength from 386.5 MPa to 610 MPa. Additionally, the elongation increased from 15.6 % to 23.3 %. Upon annealing at varying temperatures, it was observed that the strength decreased, reaching to 423.5 MPa at 650 °C and 478.2 MPa at 840 °C, while the plasticity increased significantly, reaching to 26.5 % at 650 °C and 28.6 % at 840 °C. The improved strength was attributed to the better grain boundary slip of the equiaxed structure. The corrosion resistance of titanium alloys is closely connected with their microstructure. The results of the immersion corrosion test indicate that the samples in various states exhibit similar corrosion behavior. Additionally, the hot-rolled TA10 alloy shows the highest corrosion resistance, with a lower corrosion rate of 0.34459 mm/year. The as-cast TA10 alloy shows the lowest corrosion resistance, with a lower corrosion rate of 1.37559 mm/year.

Corrosion Behavior of As-Cast and Heat-Treated Al-Co Alloys in 3.5 wt% NaCl.

The present work evaluates the effect of Co content on the microstructure and corrosion performance of Al-Co alloys of various compositions (2-32 wt% Co), fabricated by flux-assisted stir casting. A preliminary investigation on the effect of heat treatment (600 °C, up to 72 h) on the microstructure and corrosion behavior of Al-20 wt% Co and Al-32 wt% Co was also conducted. The Al- (2-10) wt% Co alloys were composed of acicular Al9Co2 particles uniformly dispersed in an Al matrix. The Al-20 wt% Co and Al-32 wt% Co alloys additionally contained Al13Co4 blades enveloped in Al9Co2 wedges. Heat treatment of Al-20 wt% Co and Al-32 wt% Co led to a significant reduction in the volume fraction of Al13Co4 and a decrease in hardness. Al-Co alloys with high Co content (10-32 wt% Co) exhibited greater resistance to localized corrosion in 3.5 wt% NaCl, but lower resistance to general corrosion compared to the (0-5 wt% Co) alloys. Heat treatment led to a slight increase in the corrosion resistance of the Al-Co alloys. The microstructure of the produced alloys was analyzed and correlated with the corrosion performance. Finally, corrosion mechanisms were formulated.

Enhancing mechanical properties and corrosion resistance of nickel-aluminum bronze via hot rolling process

The mechanical properties and corrosion behavior of as-cast, as-annealed and hot-rolled nickel-aluminum bronze (NAB) alloy (Cu-9Al-10Ni-4Fe-1.2 Mn, all in wt.%) in 3.5 wt.% NaCl solution were investigated. The results show that annealing introduces a large number of κ phases to precipitate in the α phase. However, after further hot rolling, the original continuous κ phases are spheroidized and dispersed, increasing the strength, hardness, and elongation of the alloy. In addition to the enhanced mechanical properties, the corrosion resistance of the NAB samples is also improved significantly by hot rolling, as revealed by the mass loss measurements, electrochemical impedance spectroscopy (EIS), and cross-sectional corrosion morphology. Selective phase corrosion occurs by the preferential corrosion of the α phase, which acts as an anode to the κ phases, and the uncorroded κ phases are retained in the corrosion product film. The interfaces between the κ phases and the surrounding corrosion products become discontinuous caused by the spheroidization of κ phases, reducing the corrosion of the substrate by the corrosive medium via the channels. As a result, the corrosion rate and the maximum local corrosion depth of the hot-rolled NAB sample are greatly reduced.

Effect of heat treatment on wear and corrosion behavior of high chromium white cast iron

AbstractThe abrasive wear and corrosion behavior of as-cast, heat-treated and tempered high chromium white cast iron was studied, and the results were evaluated by means of microstructure, hardness, surface roughness and corrosion resistance. The samples were subjected to wear on the ball-on-flat tribometer test machine under different loads. Corrosion tests were carried out using the potentiodynamic scanning (PDS) technique in both alkaline (3.5 % NaCl) and acidic (0.5 M H2SO4) media. According to the results obtained, the wear rate and hardness of the as-cast alloy were relatively low. After heat treatment higher wear resistance and hardness were achieved thanks to the thinned and elongated primary carbides, excessive amount of secondary carbides and the martensitic matrix. After the tempering process, the primary carbides were rounded and shortened, and all the carbides were homogeneously dispersed. This resulted in lower material hardness. Although the hardness of the tempered sample was lower than that of the heat-treated sample, the wear resistance was higher in virtue of the microstructure. The corrosion results showed that the differences between the corrosion resistance of as-cast, heat-treated and tempered samples are only due to microstructural transformation. The differences are related to the Cr/C ratio, primary carbide content and its form in the matrix, and residual stress. In addition, the study showed that secondary carbides play an influential role at the initialization of corrosion but that the primary carbide content in the alloy are dominant in the progression and orientation of the corrosion in the structure.

Effect of Mg on the Corrosion Behaviour of As-Cast and Heat Treated Al–4.5Cu–3.4Fe In-Situ Composites

The influence of Mg addition on the corrosion behaviour of as-cast and heat treated Al–4.5Cu–3.4Fe in-situ composite was investigated. The composite was produced by solidification processing whereby Al3Fe intermetallic formed in-situ in Al–Cu matrix. Magnesium additions were made to the composite to modify the microstructure of the in-situ composite. Specimens were then heat treated at 580 °C for homogenization. The as-cast and heat treated in-situ composites were subjected to corrosive media comprising of NaCl + H2O2 solution and the corrosion rate was evaluated by gravimetric weight loss method. Both the as-cast and heat treated in-situ composite were found to be susceptible to intergranular corrosion (IGC), the heat treated specimens being less prone to attack. Optical and scanning electron micrographic observation of the corroded surface revealed highly corroded network in the as-cast in-situ composite. On the contrary, the heat treated composite revealed minimal corrosion network. The rate of corrosion and the IGC network for both the as-cast and heat treated in-situ composite decreases as Mg additions are increased.

Corrosion Behaviour of Heat-Treated Aluminum-Magnesium Alloy in Chloride and EXCO Environments

Machines designed to operate in marine environment are generally vulnerable to failure by corrosion. It is therefore imperative that the corrosion susceptibility of such facilities is evaluated with a view to establishing mechanism for its mitigation. In this study, the corrosion behaviour of as-cast and retrogression-reagion (RRA) specimens of aluminum alloy containing 0.4–2.0 percent magnesium additions in NaCl, FeCl3, and EXCO solutions was investigated. The corrosion simulation processes involved gravimetric and electrochemical techniques. Results show substantial inducement of Mg2Si precipitates at a relatively higher magnesium addition, 1.2–2.0 percent, giving rise to increased attack. This phenomenon is predicated on the nature of the Mg2Si crystals being anodic relative to the alloy matrix which easily dissolved under attack by chemical constituents. Formation of Mg2Si intermetallic without corresponding appropriate oxides like SiO2and MgO, which protect the precipitates from galvanic coupling with the matrix, accentuates susceptibility to corrosion.