Production and Corrosion Resistance of Thermally Sprayed Fe-Based Amorphous Coatings from Mechanically Milled Feedstock
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TRODUCTION
SURFACE corrosion, wear, and fracture are major problems in engineering environments that contribute to the deterioration of structural materials. Fe-based amorphous alloys have been attracting great attention due to their excellent corrosion and wear properties combined with the relatively low cost of iron.[1–6] However, brittleness greatly restricts their application as structural materials.[7,8] Coating technology is an GUILHERME Y. KOGA and ALBERTO M. JORGE JUNIOR are with the Departamento de Engenharia de Materiais, Universidade Federal de Sa˜o Carlos, Rod. Washington Luis, km 235, Sa˜o Carlos, CEP 13565-905, Brazil and also with the Grenoble Alpes University, CNRS, LEPMI, 38000 Grenoble, France. Contact e-mail: guilherme.koga@dema.ufscar.br VIRGINIE ROCHE and CAROLE LOABLE are with the Grenoble Alpes University, CNRS, LEPMI. RICARDO P. NOGUEIRA is with the Grenoble Alpes University, CNRS, LEPMI and also with the Gas Research Center, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates. ROBERT SCHULZ and SYLVIO SAVOIE are with the Hydro-Quebec Research Institute, 1800 Boul. Lionel Boulet, Varennes, QC J3X 1S1, Canada. ANA K. MELLE, CLAUDEMIRO BOLFARINI, CLAUDIO S. KIMINAMI, and WALTER J. BOTTA are with the Departamento de Engenharia de Materiais, Universidade Federal de Sa˜o Carlos. Manuscript submitted December 14, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
interesting and cost-effective route to overcome the limited plasticity of bulk metallic glasses (BMGs) at room temperature.[9,10] In addition, the volume restrictions imposed by the critical cooling rates of BMGs are reduced, and therefore, large and complex crystalline substrates can be coated with wear- and corrosion-resistant amorphous alloys.[10–12] Fe-based amorphous coatings are an attractive surface technology to protect inexpensive steel components which withstand aggressive environments.[13–17] However, to obtain thick coatings, amorphous alloys must have a high glass-forming ability (GFA), which is commonly achieved by the addition of an optimal number of noble elements and high purity of raw materials in complex multicomponent systems, hindering their extensive industrial applications. A low-cost and simpler alternative to produce protective amorphous coatings is the Fe-Cr-Nb-B system because (i) it is a system with relatively few components, (ii) it can be obtained from commercial precursors such as trading stainless steel modified with minor low-cost additions (e.g., Fe-B and Fe-Nb),[18,19] and (iii) it can be designed to present excellent corrosion resistance even with low Cr content (up to 10 at. pct) which does not decrease the GFA.[20]
With respect to the processing route, thermal-spraying techniques have been used to produce amorphous Fe-based coatings thanks to their high deposition rates and the sufficiently rapid cooling rates of molten droplets (104–107 K/s) that inhibit long-range diffusion and crystallization.[21–23] For instance, Fe-based coatings have been obtained by air plasma spraying (A
