Protection of cobalt-based refractory alloys by chromium deposition on surface

Michel, Grégory; Berthod, Patrice; Vilasi, Michel; Mathieu, Sandrine; Stein, Nicolas

doi:10.1016/j.surfcoat.2011.03.067

Cited by 5 publications

(3 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It is possible to benefit from both high temperature strength and high oxidation resistance by decoupling the properties required for the bulk and for the surface, this by choosing a Co content high enough for the bulk to stabilize the TaC carbides and by enriching the outer part of the alloy in chromium. Recent work precisely demonstrated that this is precisely possible for TaC‐containing Cr x C y ‐free Cr rich {cobalt, nickel}‐based alloys with significant improvement of the high temperature oxidation behavior when the Cr content obtained in subsurface is 30 wt% . The thermodynamic calculations carried out in the present work showed that such resulting enrichment did not induce any serious problem for the microstructure of the Cr‐enriched outer zone.…”

Section: Resultssupporting

confidence: 61%

Behavior in oxidation at elevated temperature of {25Cr, 0.4C‐6Ta}‐containing Ni and Co‐based cast alloys versus their proportion in nickel and cobalt

Berthod

Himeur

2018

Materials & Corrosion

Self Cite

View full text Add to dashboard Cite

A series of six alloys from Ni‐25Cr‐0.4C‐6Ta to Co‐25Cr‐0.4C‐6Ta with a progressive addition of Co in substitution to Ni were elaborated. They were tested for 24 h at 1237 °C in laboratory air. The corrosion products formed around the samples and the deterioration of the subsurface were analyzed to characterize the high temperature oxidation behavior of these alloys. Three of the studied alloys, the nickel‐richest ones, well behaved until 24 h at this temperature. Their external oxide scales were essentially composed of chromia. In contrast, locally, the three cobalt‐richest alloys were starting to oxidize catastrophically. The significant worsening of the oxidation behavior from the 27 wt% Co‐containing alloy to the 41 wt% Co‐containing one suggests that a critical Co content exists between these two values.

show abstract

Section: Resultssupporting

confidence: 61%

Behavior in oxidation at elevated temperature of {25Cr, 0.4C‐6Ta}‐containing Ni and Co‐based cast alloys versus their proportion in nickel and cobalt

Berthod

Himeur

2018

Materials & Corrosion

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is also due to the interdendritic TaC carbides, which may facilitate the outward diffusion of chromium during oxidation as they facilitated its inward diffusion during cementation. 14 On the other hand, a C free Co based alloy was submitted to thermal cycling under conditions that mimic thixoforming of steels. The eutectic carbides, typical of Stellite alloys, are replaced in this alloy with Mo rich coarse secondary phase particles dispersed predominantly at interdendritic sites.…”

Section: Introductionmentioning

confidence: 99%

Oxidation mechanism of cobalt based alloy at high temperatures (800–1100°C)

Buscail

Riffard

Issartel

et al. 2012

Corrosion Engineering, Science and Technology

View full text Add to dashboard Cite

A cobalt based Phynox alloy has been oxidised in the 800-1100uC temperature range. Kinetic results show that the parabolic behaviour is followed under isothermal conditions. The scale growth mechanism of cobalt based Phynox alloy in air is consistent with a growth mechanism limited by the diffusion process in a growing Cr 2 O 3 oxide scale. Thermal cycling tests show that the best scale adherence is found at 1000uC. This temperature permits a rapid chromium supply from the substrate to form a continuous chromia scale. A keying effect at the internal interface is promoted by the presence of silicon and molybdenum. At 900uC, CoCr 2 O 4 cobalt containing oxide formation is favoured and leads to a bad scale adherence. At 1100uC, thermal cycling conditions lead to scale spallation and chromium depletion. Then, important weight losses are registered corresponding to the oxidation of cobalt and molybdenum to induce CoCr 2 O 4 and CoMoO 4 formation. IntroductionCobalt based alloys are widely used as wear resistant and corrosion resistant materials for industrial application in molten glasses, 1-4 in the presence of a deposit of salt or ash 5 or for gas turbine applications. 6-10 In the present work, a Phynox Co based alloy [Co-20?45Cr-15?1Ni-14?1Fe-7?1Mo-1?85Mn-0?43Si-0?4Ti (wt-%)] is investigated under high temperature oxidation conditions. The Phynox substrate is an iron containing alloy. The effect of iron additions in the range 5-15 wt-% on the microstructure and properties of two Co-Mn-Cr-Si wear resistant alloys (Tribaloys T400 and T800) has been investigated. 11 Iron additions were found to stabilise the fcc form of the cobalt solid solution, to give a fully eutectic matrix and to decrease the volume fraction of the primary laves phase. These microstructural modifications have little effect on the strain fracture toughness but result in a significant increase in the modulus of rupture. The addition of iron induces only minor changes in the corrosion and oxidation resistance. Zhang et al. have studied the oxidation behaviour of a Co based Tribaloy T-800 [Co-17?5Cr-28?5Mo-3?4Si (wt-%)] exposed isothermally in air at 800 and 1000uC. 12 Results have indicated that the oxidation mechanism was dependent on the exposure temperature. The oxidation of the alloy followed subparabolic oxidation kinetics at 800uC. The oxide scale at this temperature exhibited a multilayered structure, including an outer layer of cobalt oxide, a layer composed of complex oxide and spinel, a non-uniform Mo rich oxide layer, an intermediate mixed oxide layer and an internal attacked layer with different protrusions into the laves phase. During 1000uC exposure, mass gain followed linear kinetics. The oxidation rendered a relatively uniform external Cr rich oxide layer coupled with a thin layer of spinel on the top surface and voids at the scale/alloy interface and intergranular region together with internal Si oxide at 1000uC.In the literature, no papers are available on the reaction mechanisms during the Co based Phynox oxidation at high tempera...

show abstract

“…Clearly, such high Cr contents are to be avoided, even if high levels of chromium may be required in critical, hot corrosion problems in service (work in highly aggressive milieus). Surface and subsurface chromium enrichments, produced by the pack cementation process [18,19], for instance, can afford such high corrosion resistance without the loss of the necessary ductility and toughness at low and high temperatures.…”

Section: Discussionmentioning

confidence: 99%

Influence of the Chromium Content on the Characteristics of the Matrix, the Tantalum Carbides Population, and the Hardness of Cast Co(Cr)-0.4C-6Ta Alloys

Berthod

Bouaraba

Cai

2023

Micro

Self Cite

View full text Add to dashboard Cite

The mechanical and chemical behaviors of cast cobalt-base superalloys are governed by the carbides and by a reactive element, which is often chromium. The content of this later element, which is efficient in resisting hot oxidation and also hot corrosion, may have consequences on the melting temperature, microstructure, and mechanical properties at high temperatures and at room temperature. Seemingly, the effect of chromium content on the microstructure and properties of cast equi-axed Co-Cr-Ta-C superalloys containing TaC as single reinforcing carbide and in high-enough quantities to achieve a high level of creep resistance has not been the subject of previous investigations. The present work is devoted to the exploration of this influence of Cr content on the as-cast microstructure of a model alloy in this category, as well as on its microstructure transformations at high temperatures. The work aims to help rate the Cr content to achieve the best characteristics in machinability and high-temperature properties. This is of great importance for fabricability (production cost) and sustainability in service (long enough lifetime performance). A series of six alloys derived from a rather well-known alloy and presenting various Cr contents were thus elaborated by casting. Their microstructures were investigated in their as-cast state as well as in an aged state resulting from a 4-day stage at 1400 K. Vickers indentation was also carried out to study how hardness may evolve with Cr content. It was seen that the higher the Cr content, the lower the solidus temperature, the coarser the TaC population, the harder the alloy, and the higher the risk of brittleness. In order to reach the best compromise, the preferred Cr weight content range, as identified by this work, is 20–30%; indeed, for such Cr contents: (1) the matrix is austenitic, then dense, and then hard and not brittle, and thus is mechanically resistant and tough; (2) the TaC carbides are script-shaped and resistant against morphology changes at high temperatures, and thus efficiently preserve interdendritic cohesion for a long time, and, consequently, (3) the alloys are machinable, have expected good toughness, and can be resistant against creep deformation as well as oxidation and corrosion at high temperatures thanks to the Cr content, allowing for chromium-forming behavior.

show abstract

Protection of cobalt-based refractory alloys by chromium deposition on surface

Cited by 5 publications

References 16 publications

Behavior in oxidation at elevated temperature of {25Cr, 0.4C‐6Ta}‐containing Ni and Co‐based cast alloys versus their proportion in nickel and cobalt

Behavior in oxidation at elevated temperature of {25Cr, 0.4C‐6Ta}‐containing Ni and Co‐based cast alloys versus their proportion in nickel and cobalt

Oxidation mechanism of cobalt based alloy at high temperatures (800–1100°C)

Influence of the Chromium Content on the Characteristics of the Matrix, the Tantalum Carbides Population, and the Hardness of Cast Co(Cr)-0.4C-6Ta Alloys

Contact Info

Product

Resources

About