scholarly journals Metallographic examination of commercial galvanized coatings - part II

1961 ◽  
Author(s):  
J J Sebisty ◽  
R H Palmer
Keyword(s):  
Metallographic Examination ◽  
Galvanized Coatings

The Influence of Coating Thickness and Composition on the Corrosion Propagation Rates of Galvanized Rebar in Cracked Concrete

CORROSION ◽  
10.5006/2370 ◽  
2017 ◽  
Vol 74 (1) ◽  
pp. 134-143 ◽  
Author(s):  
I.G. Ogunsanya ◽  
C.M. Hansson
Keyword(s):  
Coating Thickness ◽  
Exposure Period ◽  
Alloy Coating ◽  
Threshold Concentration ◽  
Galvanized Steel ◽  
Al Alloy ◽  
Metallographic Examination ◽  
Cracked Concrete ◽  
Galvanized Coatings ◽  
Active Corrosion

A study has been conducted of the chloride-induced corrosion behavior of four different batches of galvanized steel reinforcement embedded in sound and in cracked concrete. One batch of bars was of conventionally produced hot-dipped galvanized (HDG) steel, two were prototypes of continuously galvanized rebar, and the fourth was a hot-dipped bar with an experimental Zn-Al alloy coating. Carbon (black) steel bars were also tested for comparison purposes. The continuously galvanized process is aimed at producing a thinner, but more ductile coating than that formed by conventionally hot-dipped galvanizing process. Metallographic examination of the as-received galvanized bars showed a wide variation of the coating thickness around and along the bars, and the continuously galvanized coatings were consistently thinner than specified. All bars were cast in concrete which was subsequently cracked either parallel to or perpendicular to the embedded bars. Additional specimens were tested in the sound (non-cracked) concrete. All specimens were constantly exposed to a chloride brine for 64 weeks, and were electrochemically assessed bi-weekly during the exposure period. The electrochemical results and visual examination after autopsy showed that no active corrosion was initiated in either the galvanized or black rebar reinforced non-cracked concrete specimens. Therefore, the data in this project give no indication of initiation time or chloride threshold concentration for corrosion of these bars. On the other hand, in all cracked concrete specimens, corrosion initiated at the base of the crack and extended along or around the bars. In the cracked specimens, all galvanized bars exhibited lower current densities than the black bars, with the HDG being the lowest. Recommendations are given for appropriate interpretation of half-cell potentials of the galvanized bars investigated in terms of high or low probability of active corrosion.

Microstructure of Electro-Eroded Cemented Carbide Surfaces

1968 ◽  
Vol 26 ◽  
pp. 284-285
Author(s):  
V. N. Filimonenko ◽  
M. H. Richman ◽  
J. Gurland
Keyword(s):  
Surface Layer ◽  
Cobalt Content ◽  
Cemented Carbides ◽  
Face Centered Cubic ◽  
X Ray Diffraction ◽  
Metallographic Examination ◽  
Standard Procedures ◽  
Face Centered ◽  
Diamond Paste ◽  
Plastic Carbon

The high temperatures and pressures that are found in a spark gap during electrical discharging lead to a sharp phase transition and structural transformation in the surface layer of cemented carbides containing WC and cobalt. By means of X-ray diffraction both W2C and a high-temperature monocarbide of tungsten (face-centered cubic) were detected after electro-erosion. The W2C forms as a result of the peritectic reaction, WC → W2C+C. The existence and amount of the phases depend on both the energy of the electro-spark discharge and the cobalt content. In the case of a low-energy discharge (i.e. C=0.01μF, V = 300v), WC(f.c.c.) is generally formed in the surface layer. However, at high energies, (e.g. C=30μF, V = 300v), W2C is formed at the surface in preference to the monocarbide. The phase transformations in the surface layer are retarded by the presence of larger percentages of cobalt.Metallographic examination of the electro-eroded surfaces of cemented carbides was carried out on samples with 5-30% cobalt content. The specimens were first metallographically polished using diamond paste and standard procedures and then subjected to various electrical discharges on a Servomet spark machining device. The samples were then repolished and etched in a 3% NH4OH electrolyte at -0.5 amp/cm2. Two stage plastic-carbon replicas were then made and shadowed with chromium at 27°.

scholarly journals Investigation of Failure in Gas Turbines: Part 2 — Engineering and Metallographic Aspects of Failure Investigation

1993 ◽  
Author(s):  
Robert E. Dundas
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Heavy Duty ◽  
Metallographic Examination ◽  
Fracture Surfaces ◽  
Failure Investigation ◽  
Materials Used ◽  
Component Failures

This paper opens with a discussion of the various mechanisms of cracking and fracture encountered in gas turbine failures, and discusses the use of metallographic examination of crack and fracture surfaces. The various types of materials used in the major components of heavy-duty industrial and aeroderivative gas turbines are tabulated. A collection of macroscopic and microscopic fractographs of the various mechanisms of failure in gas turbine components is then presented for reference in failure investigation. A discussion of compressor damage due to surge, as well as some overall observations on component failures, follows. Finally, a listing of the most likely types of failure of the various major components is given.

Characterization of high temperature hot dip galvanized coatings

1991 ◽  
Vol 46 (3) ◽  
pp. 245-253 ◽  
Author(s):  
P.R. Chidambaram ◽  
V. Rangarajan ◽  
W.J. van Ooij
Keyword(s):  
High Temperature ◽  
Galvanized Coatings
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