High-temperature strengthening mechanisms of Laves and B2 precipitates in a novel ferritic alloy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:720

Article

Chen, Tianyi¹  Parish, Chad M.¹  Yang, Ying¹  Tan, Lizhen¹ 

[1] Oak Ridge Natl Lab, Oak Ridge, TN 37831 USA

关键词: Creep;    Fracture;    Microstructure;    Dislocation;    Orowan strengthening;    Precipitation strengthening;   

DOI  :  10.1016/j.msea.2018.02.013

来源: Elsevier

【 摘 要 】

Precipitates of the Laves and B2 phases were engineered in a newly-designed advanced ferritic alloy. Under creep test at 650 degrees C with 120 MPa, the material showed a steady-state minimum creep rate of 1 x 10(-4) h(-1) about one order of magnitude lower than T91. Microstructural characterization of the ferritic alloy revealed primarily ductile and partially brittle fractures after the creep test. Coarse Laves phase (similar to 1 mu m) was observed associating with the brittle fracture, resulting in reduced creep ductility. However, fine Laves phase precipitates (similar to 100 nm) helped the dimple-ductile fracture and strengthened the material through impeding the motion of dislocations and boundaries. Unlike the B2 precipitates remained coherent exerting the classic Orowan bypassing mechanism at the brittle location, some of the B2 precipitates at the ductile location became incoherent and can develop an attractive interaction with dislocations. This coherency change of 82 precipitates, together with the nucleation of ultrafine (similar to 40 nm) Laves phase precipitates during the creep test, would compensate for the coarsening-induced loss of Orowan strengthening of coherent B2 precipitates.

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