Investigation into the characteristics of white layers produced in a nickel-based superalloy from drilling operations

Christopher Herbert, Dragos Axinte, Mark Hardy, Paul D. Brown

Research output: Journal PublicationArticlepeer-review

23 Citations (Scopus)


The nature of white layers generated during metal cutting operations have for some time been the object of scientific controversy in reference to their metallurgical nature/structure. This research aims to study the structure of the white layer from an abusive cutting operation (i.e., drilling) in a nickel-based superalloy at both macro and micro scale levels. This has been achieved by using (1) a Focus Ion Beam to mill a sample for Transmission Electron Microscopy to analyse the grain size within the white layer, (2) Scanning Electron Microscopy to see shape characteristics of the white layer generated, (3) X-ray diffraction to see any alterations to the crystallinity of the structure, and (4) nano-indentation within this layer to compare its hardness with that of the bulk material. The in-depth analysis of white layers generated from non-standard drilling parameters of alloy RR1000 has shown that the layer is of the same structure as the bulk material: face centre cubic (FCC). The analysis has also shown the layer possesses a greatly reduced grain size of approximately 50nm as opposed to the bulk material which has an average grain size of 22-63m (ASTM 8-5). Although nano-indentation has also shown that the analysed layer has a 45% higher hardness than that of the bulk material. This analysis indicates that the white layer created from machining is a combination of both mechanical and thermal effects and not only thermal as previously shown.

Original languageEnglish
Pages (from-to)40-52
Number of pages13
JournalMachining Science and Technology
Issue number1
Publication statusPublished - 1 Jan 2012
Externally publishedYes


  • drilling
  • nickel-based superalloy
  • white layer

ASJC Scopus subject areas

  • General Materials Science
  • Mechanical Engineering
  • Industrial and Manufacturing Engineering


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