Thermo-mechanical Behavior of HEA Alloys Containing Interdendritic MC Carbides
Résumé
The casting route allows obtaining in situ composites which combine a HEA dendritic matrix and an interdendritic network of MC carbides. This association bring the simultaneous benefit of the intrinsic good creep resistance of the HEA matrix and of the delayed {steady state to tertiary} transition of creep regime given by the improved cohesion between neighbor dendrites resulting from script–like carbides. However, the difference in thermal expansion behavior between matrix and carbides may induce curious geometrical behavior of the whole alloy at high temperature, as earlier observed for cobaltbased [1] and {iron and/or nickel}-based alloys [2]. This work aims to investigate the dimensional behavior of MC–strengthened HEA alloys at high temperature during heating as well as during an isothermal stage at H.T., in order to observe the possible consequences of the internal interaction between matrix and carbides resulting from differential thermal expansion. Effectively, in contrast with the carbides–free quinary HEA alloys based on Co, Ni, Fe, Mn and Cr, the alloys based on these HEA and added with TaC or HfC carbides can be expected to behave similarly to the TaC–containing Co–based and Fe(Ni)–based alloys evocated above.
The presence of carbides obviously led to the high temperature visco-plastic deformation of the matrix under the compressive stresses applied by the carbides, until the total decrease of the tensile stresses which developed in the carbide network during the first part of heating. These MC–reinforced HEA alloys are thus affected by the phenomena of matrix/carbides interactions and internal stresses development previously observed for Co, Fe or Ni–based alloys containing carbides with similar characteristics. Such behavior can cause problems of dimensional precision as well as of internal deterioration of the alloys, especially in situation of thermal cycling.
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