Effect of Low Chloride and Sulfate Concentrations on Corrosion Behavior of Aluminum and Zinc Arc Thermal Sprayed Coatings

The aim of this study was to determine the suitability of arc sprayed zinc and aluminum coatings as materials for protective coatings of different heating systems. The most aggressive chemical agents occurring in heating water are chloride and sulfate anions. Both ions are responsible for the corrosion of metals due to their high electronegativity and standard electrochemical potential. Water in heating systems should not contain more than 150 mg/L anions, including no more than 50 mg/L of chlorides and 100 mg/L of sulfates. To determine the corrosion resistance of three types of zinc and aluminum coatings, open circuit potential and linear polarization resistance (LPR) tests were conducted in eight alkaline solutions with different sulfate and chloride contents. The SEM/EDS structural properties of sprayed coatings at specific arc process parameters were investigated. Zinc coatings exhibit the most stable corrosion potentials in varying environments but have higher corrosion current density. Aluminum coatings exhibit much higher potential values in a chloride environment than in any other. A chloride environment also causes the lowest corrosion rates for aluminum-coated samples. A small addition of aluminum to the zinc coating (15 wt.%) does not appear to affect the stability of the corrosion potential but does result in a reduction in corrosion rates in chloride solutions

Synthesis, Properties and Applications of Intermetallics, Ceramic and Cermet Coatings

The production of intermetallic and ceramic protective coatings can be relatively simple, beneficial, and highly predictable [...

Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating

The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones

Wear analysis of a gun barrel drill blade in 1.0503 steel drilling process in Milpro HG12 oil environment with addition of ultra-dispersive copper particles and copper oxides

This paper presents structural solutions for guiding a single-sharp barrel drill blade during deep hole drilling, and it analyzes the structural and technological problems associated with two modes of inserting the drill into the processed material in the first stage of drilling – with the use of a pilot hole or a guide sleeve. The kinematics of the object-tool system (P-N) and other technological parameters affecting the execution of pilot holes under strictly defined conditions were analyzed during deep drilling with barrel drills in the FNE 40NC AVIA vertical numerical milling machine. Performance tests involving two types of cooling-lubricating agents, Milpro HG12 oil with and without the addition of ultra-dispersive copper particles and copper oxides (0.05 ÷ 0.6 µm) and Panther GP-1 additive (PWPH PantherOil Poland), applied in a 1:100 ratio, were described. The wear of the barrel drill blade along the entire drilling path (Lw = 8,000 mm) for 112 holes, and the geometric wear coefficient Kw of the drill bit were determined in 1.0503 steel with the use of EB80 drills made of K15 cemented carbide (WC 94%, Co 6%) with a diameter Dc = 8 mm. The results of wear tests were compared with the results of tribological tests involving cooling lubricants and 1.0503 steel with the chemical composition of K15 tungsten carbide. The abrasive wear of friction pair and the performance of the barrel drill blade during deep hole drilling were analyzed under identical conditions

Corrosion Behavior of Detonation Gun Sprayed Fe-Al Type Intermetallic Coating

The detonation gun sprayed Fe-Al type coatings as an alternative for austenitic valve steel, were investigated using two different methods of testing corrosion resistance. High temperature, 10-hour isothermal oxidation experiments at 550, 750, 950 and 1100 °C show differences in the oxidation behavior of Fe-Al type coatings under air atmosphere. The oxide layer ensures satisfying oxidation resistance, even at 950 and 1100 °C. Hematite, α-Al2O3 and metastable alumina phases were noticed on the coatings top surface, which preserves its initial thickness providing protection to the underlying substrate. In general, only negligible changes of the phase composition of the coatings were noticed with simultaneous strengthening controlled in the micro-hardness measurements, even after 10-hours of heating at 1100 °C. On the other hand, the electrochemical corrosion tests, which were carried out in 200 ppm Cl− (NaCl) and pH ~4 (H2SO4) solution to simulate the acid-rain environment, reveal higher values of the breakdown potential for D-gun sprayed Fe-Al type coatings than the ones for the bulk Fe-Al type alloy and Cr21Mn9Ni4 austenitic valve steel. This enables these materials to be used in structural and multifunctional applications in aggressive environments, including acidic ones

Nondestructive Methodology for Identification of Local Discontinuities in Aluminide Layer-Coated MAR 247 during Its Fatigue Performance

In this paper, the fatigue performance of the aluminide layer-coated and as-received MAR 247 nickel superalloy with three different initial microstructures (fine grain, coarse grain and column-structured grain) was monitored using nondestructive, eddy current methods. The aluminide layers of 20 and 40 µm were obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 and 12 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of MAR 247 nickel superalloy and the coating were characterized using light optical microscopy (LOM), scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). It was found that fatigue performance was mainly driven by the initial microstructure of MAR 247 nickel superalloy and the thickness of the aluminide layer. Furthermore, the elaborated methodology allowed in situ eddy current measurements that enabled us to localize the area with potential crack initiation and its propagation during 60,000 loading cycles

Influence of gas detonation spraying parameters on the geometrical structure of Fe-Al intermetallic protective coatings

The paper presents the results of an analysis of the geometrical structure of Fe-Al intermetallic protective coatings sprayed under specified gun detonation spraying (GDS) conditions. Two barrel lengths, two powder injection positions (PIP) at the moment of spark detonation, and two numbers of GDS shots with 6.66 Hz frequency were applied as variable parameters in the GDS process. Surface profile measurements were conducted by contact profilometry with the use of the TOPO-01 system and the Mitutoyo SJ 210 profilometer. The measured parameters were used to analyze surface topography in two-dimensional (2D) and three-dimensional (3D) systems. It was assumed that roughness can be regarded as a non-stationary parameter of variance in surface amplitude which is highly dependent on the sampling rate and spraying distance. Therefore, changes in surface amplitude parameters and functional properties were analyzed across segments with a length (ln) of 1.25, 4 and 12.5 mm. The development of the geometric structure of the surface was analyzed with the RMS (Root Mean Square) fractal method, and the geometric structure of the surface stretched by several orders of magnitude was evaluated based on the correlation between roughness (Rq), segment length (ln) and fractal dimension (D). The RMS method and the calculated fractal dimension (D) supported the characterization of the geometric structure of intermetallic Fe-Al protective coatings subjected to GDS under the specified process conditions based on the roughness profiles of surface segments with a different length (ln)

Aluminide Thermal Barrier Coating for High Temperature Performance of MAR 247 Nickel Based Superalloy

In this paper, mechanical properties of the as-received and aluminide layer coated MAR 247 nickel based superalloy were examined through creep and fatigue tests. The aluminide layer of 20 µm was obtained through the chemical vapor deposition (CVD) process in the hydrogen protective atmosphere for 8 h at the temperature of 1040 °C and internal pressure of 150 mbar. A microstructure of the layer was characterized using the scanning electron microscopy (SEM) and X-ray Energy Dispersive Spectroscopy (EDS). It was found that aluminide coating improve the high temperature fatigue performance of MAR247 nickel based superalloy at 900 °C significantly. The coated MAR 247 nickel based superalloy was characterized by the stress amplitude response ranging from 350 MPa to 520 MPa, which is twice as large as that for the uncoated alloy