Boundary mechanics in lath martensite, studied by uni-axial micro-tensile tests

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Abstract

Lath martensite is the key constituent in advance steels that provides the overall strength. Martensite is known as hard and brittle, but recent evidence shows significant plasticity before fracture. The exactly reason is undisclosed but should relate to the underlying lath microstructure. Therefore, we studied the influence of sub-block and block boundaries on martensite plasticity through uni-axial tensile testing of individual micro-constituents, i.e. single block specimens and specimens with a single through-thickness block boundary parallel, perpendicular and at 45° to loading. A unique micro-tensile methodology was developed included micro-specimen fabrication with minimal FIB damage, EBSD at top and bottom surfaces, a home-built highly-sensitive uni-axial tensile tester, and in situ microscopic slip trace analysis. Interestingly, all specimens showed extensive plasticity before fracture and no cleavage, however, strong differences are observed. Detailed analysis of the rich experimental data shows that not only the block but also the sub-block boundaries show boundary strengthening following a Hall-Petch relation, in the case that the easiest slip systems are crossed by these boundaries. However, for boundaries oriented under 45°, often easy glide is observed along the boundary reducing the strength, possibly caused by retained austenite films at the boundaries. TEM analysis of the boundary structure is ongoing.

Original languageEnglish
Title of host publicationMicro and Nanomechanics, Volume 5
Subtitle of host publicationProceedings of the 2016 Annual Conference on Experimental and Applied Mechanics 
EditorsL.V. Starman, J. Hay, N. Karanjgaokar
Place of PublicationDordrecht
PublisherSpringer
Pages21-25
Number of pages5
ISBN (Electronic)978-3-319-42228-2
ISBN (Print)978-3-319-42227-5
DOIs
Publication statusPublished - 2017
Event2016 SEM International Congress and Exposition on Experimental and Applied Mechanics - Hilton Orlando Lake Buena Vista, Orlando, United States
Duration: 6 Jun 20169 Jun 2016

Publication series

NameConference Proceedings of the Society for Experimental Mechanics Series
Volume2017

Conference

Conference2016 SEM International Congress and Exposition on Experimental and Applied Mechanics
CountryUnited States
CityOrlando
Period6/06/169/06/16
OtherDynamic Behavior: Integrating Experimental Mechanics

Keywords

  • Damage characterization
  • Ductile damage
  • In situ mechanical testing
  • Lath martensite
  • Micromechanics

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    Hoefnagels, J. P. M., Du, C., & Geers, M. G. D. (2017). Boundary mechanics in lath martensite, studied by uni-axial micro-tensile tests. In L. V. Starman, J. Hay, & N. Karanjgaokar (Eds.), Micro and Nanomechanics, Volume 5: Proceedings of the 2016 Annual Conference on Experimental and Applied Mechanics  (pp. 21-25). (Conference Proceedings of the Society for Experimental Mechanics Series ; Vol. 2017). Springer. https://doi.org/10.1007/978-3-319-42228-2_4