Characterisation of severely deformed Tribolayer by using high-resolution TEM coupled with Precession Electron Diffraction

Session

Poster Session Two

Authors

Dr jiahui Qi (2), Dr Dikai Guan (2), Dr John Nutter (2), Dr Bo Wang (1), Prof Mark Rainforth (2)

Affiliations

1. Surry University
2. the University of Sheffield

Keywords

Carbon nano onion (CNO); EELS; Geometrically necessary dislocations (GND); Precession electron diffraction (PED); Tribocorrosion

Abstract text

Tribological contact often leads to surface deformation, which will cause a substantial increase in dislocation density and often a considerable refinement in the microstructural scale. This frequently changes the material's behaviour in the local environment. Therefore, knowing the structure change is vital to its effect on the remaining service life and capacity. It has been a challenge to characterise the severely deformed structure underneath the worn surface due to 1) it being often site-specific (especially in the case of fretting) and 2) the size of the nanocrystalline layer being too small for conventional TEM and EBSD.  

Conventional TEM allows some information to be acquired, but diffraction information is usually averaged over a significant length scale. Precession electron diffraction (PED) is a recent technique in the TEM to fully quantify fine-scale deformation structure in terms of phase constitution, nanoscale misorientation and dislocation density. PED offers a spatial resolution of 0.5-5 nm, with an outstanding angular resolution of ~0.1°. Here we use the NanoMegas STAR™ PET and ASTAR™ ACOM-TEM systems integrated into the JEOL F200 TEM to characterise nanocrystalline deformation structures generated by tribological contact. The deformed structure was characterised by measuring the grain size distribution and GND density using PED, which gives a quantitative measure of the damage accumulation. This information is very difficult, if not possible, to be provided by other conventional methods on such a scale. This helps us understand the correlation between work environment, tribofilm formation and surface strain at the nanoscale. 

References

Qi J, Guan D, Nutter J, Wang B, Rainforth WM. Insights into tribofilm formation on Ti-6V-4Al in a bioactive environment: Correlation between surface modification and micro-mechanical properties. Acta Biomater. 2022;141:466-480. doi:10.1016/j.actbio.2022.01.027