Microstructures and hardness of as-cast {C, Ta or Ti or Hf of Zr}-containing Cr-rich Niobium-based alloys candidate for uses at elevated temperatures

Patrice Berthod ,Mélissa Léglise ,Ghouti Medjahdi

doi:10.24294/tse.v2i2.842

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Microstructures and hardness of as-cast {C, Ta or Ti or Hf of Zr}-containing Cr-rich Niobium-based alloys candidate for uses at elevated temperatures

Patrice Berthod

Mélissa Léglise

Ghouti Medjahdi

Thermal Science and Engineering 2019, 2(2); https://doi.org/10.24294/tse.v2i2.842

Submitted：20 May 2018

Accepted：29 May 2018

Published：15 Aug 2022

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Abstract

Four alloys based on niobium and containing about 33wt.%Cr, 0.4wt.C and, in atomic content equivalent to the carbon one, Ta, Ti, Hf or Zr, were elaborated by classical foundry under inert atmosphere. Their as-cast microstructures were characterized by X-ray diffraction, electron microscopy, energy dispersion spectrometry and while their room temperature hardness was specified by Vickers indentation. The microstructures are in the four cases composed of a dendritic Nb-based solid solution and of an interdendritic NbCr₂Laves phase. Despite the MC-former behavior of Ta, Ti, Hf and Zr usually observed in nickel or cobalt-based alloys, none of the four alloys contain MC carbides. Carbon is essentially visible as graphite flakes. These alloys are brittle at room temperature and hard to machine. Indentation shows that the Vickers hardness is very high, close to 1000HV_10kg. Indentation lead to crack propagation through the niobium phase and the Laves areas. Obviously no niobium-based alloys microstructurally similar to high performance MC-strengthened nickel-based and cobalt-based can be expected. However the high temperature mechanical and chemical properties of these alloys remain to be investigated.

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