Fracture behaviour of nc-TiAlN/a-Si₃N₄ nanocomposite coating during nanoimpact test

Abstract

Cyclic nanoimpact tests were carried on nc-TiAlN/a-Si 3 N 4 nanocomposite, TiN and multilayered TiN/nanocomposite (NC) coatings to evaluate their resistance to fracture under cyclic impact loads. Fracture behaviour of the coatings was ascertained from fracture probability obtained from time-depth curves and focus ion beam milling images of resulting indentation impressions. TiN coating mainly showed intercolumnar cracks while the other coatings showed other modes of cracking, that is, lateral, inclined, bending, edge cracks, during testing. The performance ranking of the coatings, TiN > TiN/NC > nc-TiAlN/a-Si 3 N 4 , is linked to their β 0 value, representing relative indentation depth of the coating-substrate composite hardness system at which the fractional hardness improvement equal to 50% of the maximum is retained and also their corresponding microstructure. Apart from enabling prediction of fracture resistance of the coatings, these studies provide useful insights into design and selection of coating materials for targeted machining applications.

Tribological and dry drilling performance of WS₂/Cr-AlCrN coatings

“…The most used tool coatings are transition metal carbides/nitrides with high hardness and excellent thermal stability, such as TiN, CrN, TiAlN, AlCrN, TiAlSiN, etc. They can increase tool wear resistance by several times (Ravi et al, 2017;Liu et al, 2018;Su et al, 2017). However, those hard coatings sometimes increase workpiece material adhesion on tool surface (Li, S. et al, 2018), leading to chip removal difficulties in dry drilling process.…”

Dynamic fracture of CrN coating by highly-resolved nano-impact

“…Nano-impact tests are proving effective in the study of localized dynamic failure of thin hard coatings. The nano-impact test is a dynamic instrumented impact indentation with nanoscale depth resolution, which can probe the dynamic deformation and failure of various bulk materials and coating systems [9][10][11][12][13]. Repetitive nano-impact can simulate different coating damage scenarios including nano-fatigue, erosion, and wear [14][15][16][17][18].…”

Fracture behaviour of nc-TiAlN/a-Si3N4 nanocomposite coatings under cyclic nano impact testing

“…However, the hard coatings used for cutting tool applications should invariably have sufficient toughness [11]. Apparent contradictions have been observed in literature regarding the influence of various attributes of the PVD coatings such as elastic strain to failure (H/E), resistance to plastic deformation (H 3 /E 2 ) as a measure for toughness of the coatings and their increasing or decreasing values influencing the tribological performance [12][13][14][15]. It is suggested by Beake et al [13] that cyclic nanoimpact test is a better technique to take a direct approach towards assessing simultaneously the coating toughness and damage tolerance under dynamic loading conditions, instead of a quasi-static loading during nanoindentation.…”

“…It is suggested by Beake et al [13] that cyclic nanoimpact test is a better technique to take a direct approach towards assessing simultaneously the coating toughness and damage tolerance under dynamic loading conditions, instead of a quasi-static loading during nanoindentation. Parameters such as fracture probability, time-to-failure and overall change in impact depth evaluated during the impact tests are found useful to determine the onset of coating's failure as a function of number of impacts [12,13].…”