Introduction: Diffusion aluminide coatings are widely used in hot components of aero- and land-base gas turbines to protect from oxidation and hot corrosion. The effect of doping diffusion aluminide coating with reactive element (zirconium) was studied under different concentrations. Materials and methods: Nickel-based super alloy were coated with diffusion aluminide by means of the Vapour Phase Aluminizing (VPA). Firstly the effects of different activators salts during the coating process was studied: for this reason several concentrations of two different fluorides activator salts (NH4F and AlF3) were investigated and the process parameters of the conventional (undoped) aluminide were optimized. In a second step a Zr-doped coating was developed introducing ZrF4 in the activator salts mix with the process parameters obtained from the first step of experimental procedure. The oxidation kinetics was evaluated by measuring the mass gain at different exposure times. The microstructural evolution induced by the high temperature treatments was investigated by SEM, EDS and XRD analysis. The zirconium concentrations were assessed by means of GDOES. Results: The results of different activator salts in the VPA process are a thicker layer of β-NiAl and a consequent interdiffusion zone (IDZ) for AlF3 depositions. This increase can be explained by considering the different quantities of aluminum available on the super- alloy surface as diffusion occurs. The effect of the reactive element addition, in terms of oxidation and hot corrosion resistance and microstructural evolution, was assessed by comparing the performance of the modified coatings with the standard diffusion aluminide systems. Discussion: The results show that modified coatings exhibits an enhanced oxidation and hot corrosion resistance in comparison to standard diffusion aluminide coatings. The improvement of oxidation resistance for the doped samples can be explained by EDS mapping results. After 100h of oxidation tests, Zr prevents the path of oxygen that penetrate through the Al2O3 scale blocking the degradation phenomena typical fot the standard aluminide coating (spallation, depletion layer of aluminum with consequent change of concentration in β-NiAl). Furthermore the diffusivity of Zr can counteract against the porosity made by the different diffusivity of Al and Ni during oxidation (Kirkendall effect).
EFFECT OF ZIRCONIUM CONCENTRATION FOR MODIFIED DIFFUSION ALUMINIDE COATING IN HOT CORROSION AND OXIDATION TESTS / Marra, Francesco; Genova, Virgilio; Fedrizzi, Lorenzo; Lanzutti, A; Bartuli, Cecilia; Pulci, Giovanni; Valente, Teodoro. - In: JOURNAL OF APPLIED BIOMATERIALS & FUNCTIONAL MATERIALS. - ISSN 2280-8000. - ELETTRONICO. - 14(3):(2016), pp. 356-356. [DOI: 10.5301/jabfm.5000321]
EFFECT OF ZIRCONIUM CONCENTRATION FOR MODIFIED DIFFUSION ALUMINIDE COATING IN HOT CORROSION AND OXIDATION TESTS
MARRA, FRANCESCOMembro del Collaboration Group
;GENOVA, VIRGILIOMembro del Collaboration Group
;FEDRIZZI, LorenzoMembro del Collaboration Group
;BARTULI, CeciliaMembro del Collaboration Group
;PULCI, GiovanniMembro del Collaboration Group
;VALENTE, TeodoroMembro del Collaboration Group
2016
Abstract
Introduction: Diffusion aluminide coatings are widely used in hot components of aero- and land-base gas turbines to protect from oxidation and hot corrosion. The effect of doping diffusion aluminide coating with reactive element (zirconium) was studied under different concentrations. Materials and methods: Nickel-based super alloy were coated with diffusion aluminide by means of the Vapour Phase Aluminizing (VPA). Firstly the effects of different activators salts during the coating process was studied: for this reason several concentrations of two different fluorides activator salts (NH4F and AlF3) were investigated and the process parameters of the conventional (undoped) aluminide were optimized. In a second step a Zr-doped coating was developed introducing ZrF4 in the activator salts mix with the process parameters obtained from the first step of experimental procedure. The oxidation kinetics was evaluated by measuring the mass gain at different exposure times. The microstructural evolution induced by the high temperature treatments was investigated by SEM, EDS and XRD analysis. The zirconium concentrations were assessed by means of GDOES. Results: The results of different activator salts in the VPA process are a thicker layer of β-NiAl and a consequent interdiffusion zone (IDZ) for AlF3 depositions. This increase can be explained by considering the different quantities of aluminum available on the super- alloy surface as diffusion occurs. The effect of the reactive element addition, in terms of oxidation and hot corrosion resistance and microstructural evolution, was assessed by comparing the performance of the modified coatings with the standard diffusion aluminide systems. Discussion: The results show that modified coatings exhibits an enhanced oxidation and hot corrosion resistance in comparison to standard diffusion aluminide coatings. The improvement of oxidation resistance for the doped samples can be explained by EDS mapping results. After 100h of oxidation tests, Zr prevents the path of oxygen that penetrate through the Al2O3 scale blocking the degradation phenomena typical fot the standard aluminide coating (spallation, depletion layer of aluminum with consequent change of concentration in β-NiAl). Furthermore the diffusivity of Zr can counteract against the porosity made by the different diffusivity of Al and Ni during oxidation (Kirkendall effect).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
