Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures
Surface enrichment in Al, Si, and Cr can greatly improve high temperature oxidation resistance of many alloys. Al, Si, and Cr coatings are commonly applied via simple slurries or more complex pack cementation processes. Due to the high melting point of Cr, the deposition of Cr-based diffusion coatin...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-12-01
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| Series: | Materials |
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| Online Access: | https://www.mdpi.com/1996-1944/16/23/7480 |
| _version_ | 1797399893519630336 |
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| author | Michael Kerbstadt Emma Marie Hamilton White Mathias Christian Galetz |
| author_facet | Michael Kerbstadt Emma Marie Hamilton White Mathias Christian Galetz |
| author_sort | Michael Kerbstadt |
| collection | DOAJ |
| description | Surface enrichment in Al, Si, and Cr can greatly improve high temperature oxidation resistance of many alloys. Al, Si, and Cr coatings are commonly applied via simple slurries or more complex pack cementation processes. Due to the high melting point of Cr, the deposition of Cr-based diffusion coatings by the slurry technique has proved challenging, and to date, Cr has mostly been applied by pack cementation. Here, a novel Cr-Si coating process via the slurry technique is described which has been developed and then demonstrated on two Ni-based superalloys, Rene 80 and Inconel 740H. The addition of Si to the slurry lowers the melting point via a Cr-Si eutectic and enables the formation of a liquid phase during heat treatment. Through this Cr-Si slurry coating process diffusion layers enriched by Cr and Si of about 150 µm were achieved. Oxidation behavior was studied through isothermal exposures at 900 °C for 1000 h in lab air. Uncoated Rene 80 and IN740H both showed formation of a Ti-containing Cr<sub>2</sub>O<sub>3</sub> scale below a thin TiO<sub>2</sub> top layer. Underneath the external scale a zone of internally oxidized Al grew over the exposure time and reduced the load-bearing cross-section progressively. In comparison, the Cr/Si-coated samples did not show internal Al oxidation, but a slow-growing Si-rich oxide film underneath the external Cr<sub>2</sub>O<sub>3</sub> scale. This subscale represents an additional oxygen diffusion barrier. Thus, the weight gain during exposure for the coated samples was significantly lower than for the uncoated materials. |
| first_indexed | 2024-03-09T01:46:42Z |
| format | Article |
| id | doaj.art-2c6c8c2df08d450288e1f9d2f10943e8 |
| institution | Directory Open Access Journal |
| issn | 1996-1944 |
| language | English |
| last_indexed | 2024-03-09T01:46:42Z |
| publishDate | 2023-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Materials |
| spelling | doaj.art-2c6c8c2df08d450288e1f9d2f10943e82023-12-08T15:21:24ZengMDPI AGMaterials1996-19442023-12-011623748010.3390/ma16237480Novel Cr/Si-Slurry Diffusion Coatings for High TemperaturesMichael Kerbstadt0Emma Marie Hamilton White1Mathias Christian Galetz2Dechema-Forschungsinstitut, 60486 Frankfurt am Main, GermanyDechema-Forschungsinstitut, 60486 Frankfurt am Main, GermanyDechema-Forschungsinstitut, 60486 Frankfurt am Main, GermanySurface enrichment in Al, Si, and Cr can greatly improve high temperature oxidation resistance of many alloys. Al, Si, and Cr coatings are commonly applied via simple slurries or more complex pack cementation processes. Due to the high melting point of Cr, the deposition of Cr-based diffusion coatings by the slurry technique has proved challenging, and to date, Cr has mostly been applied by pack cementation. Here, a novel Cr-Si coating process via the slurry technique is described which has been developed and then demonstrated on two Ni-based superalloys, Rene 80 and Inconel 740H. The addition of Si to the slurry lowers the melting point via a Cr-Si eutectic and enables the formation of a liquid phase during heat treatment. Through this Cr-Si slurry coating process diffusion layers enriched by Cr and Si of about 150 µm were achieved. Oxidation behavior was studied through isothermal exposures at 900 °C for 1000 h in lab air. Uncoated Rene 80 and IN740H both showed formation of a Ti-containing Cr<sub>2</sub>O<sub>3</sub> scale below a thin TiO<sub>2</sub> top layer. Underneath the external scale a zone of internally oxidized Al grew over the exposure time and reduced the load-bearing cross-section progressively. In comparison, the Cr/Si-coated samples did not show internal Al oxidation, but a slow-growing Si-rich oxide film underneath the external Cr<sub>2</sub>O<sub>3</sub> scale. This subscale represents an additional oxygen diffusion barrier. Thus, the weight gain during exposure for the coated samples was significantly lower than for the uncoated materials.https://www.mdpi.com/1996-1944/16/23/7480diffusion coatingschromium slurry coatingchromium-silicon coatinghigh-temperature oxidation |
| spellingShingle | Michael Kerbstadt Emma Marie Hamilton White Mathias Christian Galetz Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures Materials diffusion coatings chromium slurry coating chromium-silicon coating high-temperature oxidation |
| title | Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures |
| title_full | Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures |
| title_fullStr | Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures |
| title_full_unstemmed | Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures |
| title_short | Novel Cr/Si-Slurry Diffusion Coatings for High Temperatures |
| title_sort | novel cr si slurry diffusion coatings for high temperatures |
| topic | diffusion coatings chromium slurry coating chromium-silicon coating high-temperature oxidation |
| url | https://www.mdpi.com/1996-1944/16/23/7480 |
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