Devitrification of Fe-Based Amorphous Metal SAM 1651: A Structural and Compositional Study

Abstract

The effect of heat treatment on the chemistry and structure of an Fe-based bulk metallic glass (BMG) Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 (SAM 1651) was examined experimentally. Chemical segregation was found in the as-received material, with islands 10 to 200 nm in diameter enriched in Y, Mo, and C and depleted in Fe and Cr, with respect to the surrounding matrix. Heat treatment in the range of 600°C to 800°C caused partial devitrification of the BMG with the formation of nanocrystalline (Fe, Cr) 23 C 6 and (Fe, Cr) 7 C 3 carbides in a matrix of the remaining amorphous phase. The devitrification process followed a primary crystallization route. Amorphous particlefree zones (PFZs) in the devitrified material were found, corresponding to the Y-Mo-rich islands in the fully amorphous SAM 1651. The formation of Cr-rich carbide during devitrification caused the formation of nanometer-sized Cr-depleted zones surrounding the carbide particles, which is detrimental to the corrosion performance of the alloy after thermal exposure.

Crystallization Mechanism in Spark Plasma Sintered Bulk Metallic Glass Analyzed using Small Angle Neutron Scattering

“…1 is about 9 nm for samples annealed at both 700 °C and 725 °C for 100 min. This result is consistent with previous observations where the size of (Fe,Cr) 23 C 6 crystals evolved during annealing at 700 °C for 180 min estimated by the Scherrer equation was reported to be about 16 nm 46 . However, a number of limitations in employing the Scherrer equation must be noted.…”

“…www.nature.com/scientificreports www.nature.com/scientificreports/ First, over the low Q-range below 0.02 Å −1 , scattering indicates the presence of structural inhomogeneities larger than 30 nm that could possibly be Y and Mo-rich precipitate free zones (PFZs) embedded within the metallic glass matrix 49 . These PFZs have been observed during annealing of as-cast iron based metallic glass with diameter up to 200 nm 46 . They develop from the metallic glass matrix and upon further enrichment by Y possess an increased glass forming ability (GFA) 50 .…”

“…The peaks corresponding to the crystals, identified to be complex carbides of (Fe,Cr) 23 C 6 41,46 , are observed to exhibit significant broadening which are suggestive of their small sizes. The size of crystals evolved from an amorphous matrix of iron based metallic glass upon thermal processing can be approximately estimated according to the Scherrer equation expressed as 47 :…”

Corrosion behavior of ZrTiCuNiBe bulk metallic glass subjected to friction stir processing

“…With different chemical potentials, the nano-crystallites form galvanic cells with the amorphous matrix resulting in increased dissolution from the surface. Increase in corrosion rate due to the presence of secondary phases has been demonstrated for metallic glasses in earlier studies as well [23,24]. From potentiodynamic polarization curves ( Fig.…”

Characterisation of three-dimensional porosity in an Fe-based amorphous coating and its correlation with corrosion behaviour

“…The residual stress in the coating could reduce the corrosion resistance and increase the crack formation due to high internal pressure within the structure [57]. In addition, crystalline phases in the amorphous coating could also reduce the corrosion resistance to a certain extent [47,58]. In our work, the amorphous coating might undergo early stages of crystallization, although there are no remarkable crystalline peaks in the XRD patterns.…”