Fracture toughness testing and toughening mechanisms of some commercial cobalt-free hardfacing alloys

[摘要] Hardfacing alloys are weld deposited to provide a wear-resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels. Since hardfacing alloys typically must be resistant to cracking to assure adequate in-service performance, fracture toughness is a critical material property. Fracture toughness (K-IC) measurements of Fe-base, Ni-base, and Co-base hardfacings were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K-IC data was observed for the Fe-base hardfacings, and lower bound 95% K-IC values were generally higher than the Ni-base hardfacing alloys. preliminary crack growth data obtained during pre-cracking indicate that the Ni-base hardfacings possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacings have K-IC values that are comparable to the reference Go-base hardfacing. The test specimens were machined from thick (0.5 ) weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinner deposits. Microstructural and fractographic examinations are used to characterize the fracture mechanisms and delineate the operative toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacings. (C) 1998 Elsevier Science S.A. All rights reserved.

[发布日期] 1998-10-10

[效力级别]  Proceedings Paper

[关键词] fracture toughness;hardfacing alloys;toughening mechanisms