Zaki Ahmad

A study of the corrosion properties of TiN coated and nitrided Ti-6Al-4V

Abstract TiN PVD coating and plasma nitriding are two well-known techniques for improving tribological properties of treated samples. The study examines the corrosion resistance of plasma nitrided and TiN coated Ti-6A1–4V samples. The potentiodynamic polarization technique was used to measure the corrosion rate and corrosion resistance of the substrates. A micro PIXE technique was employed to determine the nitrided zone depth profile. SEM was carried out to investigate the pitting defects. To achieve a comparative study, TiN coated, nitrided and untreated samples were examined. It was found that TiN coating improves the corrosion properties, but nitriding worsens the corrosion resistance of the substrate.

The corrosion behavior of scandium alloyed Al 5052 in neutral sodium chloride solution

Alloying with scandium has a strong influence on the strengthening and weight saving characteristics of Al–2.5Mg alloys. Scandium addition (0.1–0.3 wt.%) to Al–2.5Mg alloys does not introduce any appreciable loss in their resistance to corrosion in 3.5 wt.% NaCl. The corrosion behavior of these alloys is not significantly affected by age hardening. Because of a unique combination of outstanding mechanical properties and a good resistance to corrosion Al–Mg alloys containing scandium represent a major improvement over the more familiar Al–Mg alloys.

Degradation of aluminum metal matrix composites in salt water and its control

Abstract Alloy Al 6013-20 Si in tempers O, F and T4 showed good resistance to corrosion in salt spray tests. The corrosion rate of the alloy decreased with increased exposure time due to the formation of boehmite (AlO·OH). Studies conducted in 3.5 wt.% NaCl solution containing suspended particles of polystyrene showed a linear increase in the erosion–corrosion rate with velocity. The localized attack was concentrated mainly on the Al 6013/SiC interface. A high dislocation density was observed at the Al 6013/SiC interface, which interfered with the formation of a homogeneous protective film of boehmite on the alloy surface. Addition of cerium chloride drastically suppressed the rate of corrosion. Sodium molybdate offered a lesser degree of protection compared to cerium chloride.

Effect of environmental factors on the atmospheric corrosion of mild steel in aggressive sea coastal environment

The eastern coast of Saudi Arabia has one of the most corrosive environments in the world. Dhahran is therefore an ideal location for the study of atmospheric corrosion. One out of every seven cars in the region is corroded. The atmosphere is contaminated by SO2 and a high concentration of suspended particulate matter (SPM) containing sand, salt and carbon particles, exceeding the World Health Organization (WHO) and Middle East Environmental Protection Agency (MEPA) limits most of the time. Corrosion proceeds in the Dhahran atmosphere at a R.H. as low as 40 per cent. At locations close to the sea (1.5 Km), β‐FeOOH is the major corrosion product and α‐ and γ‐FeOOH with some aluminates, silicates and hydrocarbons the minor products. At a location remote from the sea α‐ and γ‐FeOOH are found to be the major corrosion products as shown by XRD and FTIR spectroscopy. The concentration of hydrogen ions, chloride ions and SO2 appears to control the corrosion process during the initial exposure period up to one year and the adsorption of anions on the corrosion product films in the later period.

Mechanical Behavior and Fabrication Characteristics of Aluminum Metal Matrix Composite Alloys

THE DEVELOPMENT OF metal matrix composites has been a major breakthrough in materials in the last twenty years. The quantum leap in recent years has clearly established their potential for weight-critical applications in engineering components and structures in aerospace. Most of the attention, in the last decade, has been focused on aluminum as metal matrix because of its light weight, good mechanical properties and formability, economy and high resistance to environmental degradation. Aluminum alloys with tensile strengths as high as 687 MPa and with excellent resistance to corrosion are now available. Aluminum has capability of incorporating a wide variety of reinforcing agents, such as Al2O3, graphite fibers, whiskers, SiC and other particles. Aluminum alloys have an inherent compatibility with seawater and a good history in handling steam and high purity water in power plants and applications in process industry. Major alloying agents used are copper, manganese, silicon, magnesium, and minor elements, like nickel, titanium, chrome, lead, etc. Following is a summary of the effect of major alloying elements.

Effect of Temper on Seawater Corrosion of an Aluminum-Silicon Carbide Composite Alloy

Abstract The corrosion behavior of annealed (O), as-fabricated (F), and naturally age-hardened (T4) aluminum alloy Al 6013 (UNS A96013) with 20 vol% silicon carbide in particulate form (SiC[P]) was investigated in 3.5 wt% sodium chloride (NaCl) and in Arabian Gulf water. Of the three tempers, T4 showed the lowest corrosion rate (0.04 mpy and 2.61 mpy) in deaerated and aerated NaCl, respectively. The corrosion rate in seawater was slightly higher. Predominant forms of corrosion were pitting and intergranular corrosion. Formation of corrosion chimneys was observed. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and energy dispersive spectroscopy (EDS) showed intermetallic formation and the presence of a gelatinous film of aluminum hydroxide (Al[OH]3) of bayrite type. The higher corrosion resistance of the T4 temper resulted from finer and more homogeneously distributed precipitates compared to tempers F and O. In view of the the alloys good corrosion resistance and outstanding ult...

Corrosion studies on the plasma‐sprayed nanostructured titanium dioxide coatings

Purpose: The purpose of this paper is to report the resistance of plasma-sprayed titanium dioxide (TiO2) nanostructured coatings in a corrosive environment.----- Design/methodology/approach: Weight loss studies are performed according to ASTM G31 specifications in 3.5?wt% NaCl. Electrochemical polarization resistance measurements are made according to ASTM G59-91 specifications. Corrosion resistance in a humid and corrosive environment is determined by exposing the samples in a salt spray chamber for 100?h. Microstructural studies are carried out using an atomic force microscope and scanning electron microscope.----- Findings: The nanostructured TiO2 coatings offer good resistance to corrosion, as shown by the results of immersion, electrochemical and salt spray studies. The corrosion resistance of the coating is dictated primarily by the geometry of splat lamellae, density of unmelted nanoparticles, magnitude of porosity and surface homogeneity.----- Practical implications: The TiO2 nanostructured coatings show promising potential for use as abrasion, wear-resistant and thermal barrier coatings for service in harsh environments.----- Originality/value: The paper relates the corrosion resistance of nanostructured TiO2 coatings to their structure and surface morphology.

Corrosion behavior of a discontinuously reinforced composite in salt water environment

In this study, the corrosion behavior of Al 6092/17.5 SiC(p) alloy is investigated. The alloy offers a good resistance to corrosion in 3.5 wt% NaCl as shown by weight loss and electrochemical studies conducted in a smoothly stirred condition up to 70 C. The alloy also offered a strong resistance to corrosion in a salt spray chamber. The corrosion behavior of the alloy, however, declined with an increase in velocity, temperature, and addition of polystyrene particles in the electrolyte. The declining corrosion resistance is attributed to the cracking and breakdown of the protective boehmite layer at elevated temperatures, higher velocities, and impact of polystyrene particles. Microanalytical studies reveal the intermetallic precipitates to be the preferred sites for initiation of pits. The alloy offers good service prospects in a marine environment at controlled flow velocities and temperatures.

Fog Collection by Mimicking Nature

Research on fog harvesting for drinking water is uncommon because it is not a continuous climatic phenomenon and concerns only arid and semi-arid regions abundant with fog. This paper proposes a new biomimetic-inspired method of harvesting fog by mimicking the skin of the Namib desert beetle. Stainless steel mesh panels are subjected to ultra shortening and annealing to create a hierarchical nano/micro hybrid surface, and an emulsion of PTFE, polyvinyl acetate and sodium benzene sulfonate is sprayed over the steel mesh. This produces hydrophilic nano/micro mounts and hydrophobic troughs. This method, although initially costly, offers a sustainable fog collecting system which can be adopted for arid and semi-arid regions of Pakistan and other similar regions.

Corrosion Resistance of a New AL 6013-20 SiC(P) in Salt Spray Chamber

Aluminum 6013 alloy (0.82Si, 0.95Mg, and 0.35Mn) is finding increasing usage in new aircraft designs, automotives, and structural applications due to its good stretch forming character in T4 temper (solution heat treated and naturally aged to a substantially stable conditions) compared to alloy 2024 (4.4Cu, 0.6Mn, 1.5Mg, and balance Al) and Al6061 (Si0.51 to 0.71, Fe0.35, Cu0.15, Mn0.85, Mg0.15, 0.25Cr, 0.15Zn, and balanced Al).The newly developed A1 6013 reinforced with 20 vol.% SiC(P) has a higher strength than its unreinforced counterpart. Whereas the corrosion behavior of A1 6013 has been reported in literature, there is no previous data on A1 6013 reinforced with SiC(P). A knowledge of the corrosion behavior of this alloy is crucial to its applications in aerospace, structural, and automotive industry. The first results of corrosion study of this alloy in 3.5 wt.% Na Cl in a salt spray chamber are presented.Three tempers F (as fabricated), O (annealed), and T4 (age hardened and stabilized at room temperature) of the alloy A1 6013-30 SiC(P) were exposed to environmental chamber in accordance with ASTM recommended practice. The corrosion rate of the alloy showed a decrease with increased exposure period and after 800 h of exposure no appreciable change in the rate of corrosion was observed. The lowest rate of corrosion (4.83 mdd) was shown by temper T4 followed by tempers F and O after 1200 h of exposure in the increasing order of corrosion rate. Fluctuations in the corrosion rate with time are related to the kinetics of growth and dissolution of Al(OH)3 film, which was detected by fourier transformation infrared (FTIR) spectroscopy (FTIS). The film was composed of an inner compact layer and outer bulk layer dependent on the refreshment rate from the bulk solution. Micrograph examination by scanning electron microscopy (SEM) showed the presence of pits covered by aluminum hydroxide gel, which isolates the pit from the bulk solution. The acidic conditions of pits also cause intergranular attack. Pitting was observed to be less pronounced in temper T4 compared to F and O tempers, the former also showing the highest resistance to corrosion.The data generated predict promising application potential of this alloy in environment where resistance to corrosion is also a major consideration.