Solid Particle Erosion of Nanocrystalline Nickel Coatings: Influence of Grain Size and Adiabatic Shear Bands

The primary objective of the present study is to investigate the influence of nanocrystalline grain size on the solid particle erosion behavior of nickel. For the above purpose, 450-μm-thick nanocrystalline Ni coatings having the average grain sizes of 21, 42, 70, and 195 nm were obtained using pulsed electrodeposition (PED). All these samples along with bulk annealed Ni samples (43 μm grain size) were subjected to solid particle erosion using SiO₂ particles as an erodent at a constant impact velocity of 45 m/s and two impact angles (30 and 90 deg). Erosion results indicate that bulk Ni and PED Ni coatings of grain sizes 195 and 70 nm exhibit the same erosion rate, while PED Ni coatings of 42 and 21 nm grain size exhibit marginally higher erosion rates with a clear trend of increasing erosion rate with decreasing grain size. It was also observed that the higher erosion rates exhibited by 21- and 42-nm-grain size PED Ni samples were associated with the formation of adiabatic shear bands (ASBs) originating from the eroded surface and propagating into the eroded sample. The experimental observations have been understood on the basis of a transition from a localization model for erosion for coarse-grained Ni (> 70 nm) to an ASB-induced erosion model for grain sizes less than 70 nm.     

Totalized input–output assessment of research productivity of nations using multi-dimensional input and output

Research evaluation is a multi-dimensional problem as there are multiple input dimensions, multiple output dimensions and a country space of many dimensions. The data making the connections are usually available in matrix form. In this paper, we use matrix normalization and multiplication so that totalized input and output measures can be obtained. This facilitates comparative research evaluation. The US and Japan lead as the major players when patents and papers are jointly considered. Most of the countries considered register totalized output that is commensurate with totalized input. Three countries are seen to be falling short of this ideal: China, Russia and Mexico.