High resolution microstructural investigations of interfaces between light weight alloy substrates and cold gas sprayed coatings.
Investigations on interfaces between light weight alloys (aluminum AA7022 and magnesium AZ91) and optimized cold gas sprayed (CGS) zinc-based coatings are carried out. The analyses include standard optical and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). By using TEM resolution within nanometric dimensions is realized.
Investigations by SEM show areas of an intensive mixing between substrate and coating material with a number of different grey values due to element contrast. By EDXS analyses in a 1 µm broad transition zone increased zinc concentration compared to the substrate material is detected. TEM investigations prove that in this transition zone no homogeneous solid solution exists, but additionally submicron and nanosized intermetallic phases with different concentration of aluminum, zinc and magnesium are found. Due to these results an intensive mechanical interaction must take place at the substrate-coating interface during CGS. Thus bond strength does not only depend on physical and chemical adhesion or thin metallurgically affected zones, but also highly on effects of mechanical alloying.
Wielage, B., H. Podlesak, T. Grund, A. Wank
Proceedings of the International Thermal Spray Conference, Basel, Switzerland, May 2nd - 4th 2005, pp. 154-157, ISBN 3-87155-793-5
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HVOF sprayed high chromium and high vanadium containing iron based hard coatings for combined abrasive wear and corrosion protection
HVOF sprayed WC/Co(Cr) and Cr3C2/Ni20Cr composite coatings have gained high acceptance in many industrial applications for protection of components against wear. The achieved coatings have quite good corrosion resistance for use of chromium containing matrices. Present research in the field of PTA-Surfacing resulted in the development of high chromium and high vanadium containing iron based hard alloys with simultaneous improvement of abrasive wear and corrosion resistance.
These properties of the PTA-Surfaced coatings were studied and it was found that the newly developed alloys have nearly same wear resistance and improved corrosion resistance compared to Co-based alloys reinforced with Fused Tungsten Carbides (FTC). One major advantage of high chromium and high vanadium containing iron based coatings is machinability by turning and milling processes. These features make it attractive to be used in thermal spraying. The absence of substrate melting in HVOF-spraying is advantageous, as the coatings preserve the properties of the alloy due to prevention of dilution with substrate material in contrast to PTA-Surfacing. High chromium and high vanadium containing iron based atomized powder was used for HVOF spraying and deposition efficiency was measured. The sprayed coatings were studied metallographically by optical microscopy, SEM, XRD and micro-hardness measurements. Later, abrasive wear and corrosion properties of the coatings are investigated.
Wielage, B., A. Wank, H. Pokmurska, U. Dilthey, B. Balashov, J. Gollnick, L. Stein, S. Kondapalli, E. Deppe, T. Schnick
Proceedings of the International Thermal Spray Conference, Basel, Switzerland, May 2nd - 4th 2005, pp. 887-891, ISBN 3-87155-793-5