Early deformation mechanisms in the shear affected region underneath a copper sliding contact

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. This work explores the initiation of a tribologically induced microstructure in the vicinity of a copper twin boundary. Two distinct horizontal dislocation traces lines (DTL) are observed in their interaction with the twin boundary beneath the sliding interface. DTL formation seems unaffected by the presence of the twin boundary but the twin boundary acts as an indicator of the occurring deformation mechanisms. Three concurrent elementary processes can be identified: simple shear of the subsurface area in sliding direction, localized shear at the primary DTL and crystal rotation in the layers above and between the DTLs around axes parallel to the transverse direction. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes. Quantitatively separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts

The Effect of Surface Preparation on the Precipitation of Sigma During High Temperature Exposure of S32205 Duplex Stainless Steel

This is an Open Access Article. It is published by Springer under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/Although the formation of sigma phase in duplex stainless steels is reasonably well documented, the effect of surface finish on its formation rate in surface regions has not been previously noted. The growth of the sigma phase precipitated in the subsurface region (to a maximum depth of 120 μm) has been quantified after heat treatment of S32205 duplex stainless steel at 1073 K (800˚C) and 1173 K (900˚C) after preparation to two surface finishes. Here, results are presented that show that there is a change in the rate of sigma phase formation in the surface region of the material, with a coarser surface finish leading to a greater depth of precipitation at a given time and temperature of heat treatment. The growth rate and morphology of the precipitated sigma has been examined and explored in conjunction with thermodynamic equilibrium phase calculations

Combination of in situ straining and ACOM TEM: A novel method for analysis of plastic deformation of nanocrystalline metals

Nanocrystalline metals are expected to exhibit different deformation mechanisms when compared to their coarse grained counterparts because the dislocation storage capacity decreases and the grain boundary mediated processes become more pronounced with decreasing grain size. As a new approach to directly image and quantify the plastic deformation processes in nanocrystalline thin films, a combination of automated crystal orientation mapping in microprobe STEM mode with in situ straining inside a TEM was developed. ACOM-TEM closes the gap between EBSD and BF/DFTEM by providing full orientation maps with nanometer resolution. The novel combination with in situ straining provided for the first time the possibility to directly image and quantify the structural changes of all crystallites in the ensemble of a thin film at the nanometer scale during mechanical deformation. It was used to characterize the metallographic changes during tensile deformation of a nanocrystalline Au thin film prepared by magnetron sputtering. The investigation of the grain size, grain orientation and twinning on a global (grain average over a micron sized area) and local (assembly of selected grains) scale allowed for the development of an in depth picture of the deformation processes. Grain boundary motion and local grain rotation were two of the processes acting to dissipate the applied stress. Additionally, twinning/detwinning occurred simultaneously during straining. These processes, which occurred locally already in the micro-plastic regime, led to global grain growth starting at the transition to the macro-plastic deformation regime

Carbon segregation and cementite precipitation at grain boundaries in quenched and tempered lath martensite

Tempering is widely applied to make carbon atoms beneficially rearrange in high strength steel microstructures after quenching; though the nano-scale interaction of carbon atoms with crystallographic defects is hard to experimentally observe. To improve, we investigate the redistribution of carbon atoms along martensite grain boundaries in a quenched and tempered low carbon steel. We observe the tempering-induced microstructural evolution by in-situ heating in a transmission electron microscope (TEM) and by compositional analysis through atom probe tomography (APT). Probe volumes for APT originate from a single martensite packet but in different tempering conditions, which is achieved via a sequential lift-out with in-between tempering treatments. The complementary use of TEM and APT provides crystallographic as well as chemical information on carbon segregation and subsequent carbide precipitation at martensite grain boundaries. The results show that the amount of carbon segregation to martensite grain boundaries is influenced by the boundary type, e.g. low-angle lath or high-angle block boundaries. Also, the growth behavior of cementite precipitates from grain boundary nucleation sites into neighboring martensite grains differs at low- and high-angle grain boundaries. This is due to the crystallographic constraints arising from the semi-coherent orientation relationship between cementite and adjacent martensite. We also show that slower quenching stabilizes thin retained austenite films between martensite grains because of enhanced carbon segregation during cooling. Finally, we demonstrate the effect of carbon redistribution along martensite grain boundaries on the mechanical properties. Here, we compare microscale Vickers hardness results from boundary-containing probe volumes to nanoindentation results from pure bulk martensite (boundary-free) probe volumes

Study the Growth Attributes of Cotton as Influenced by Various Levels of Nitrogen under Rainfed Condition

The field investigation was carried out at Department of Agronomy farm, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola during 2019-20. The experiment was laid out in randomized block design with three replications and seven different nitrogen levels treatment with an objective to study the growth and yield of cotton as influenced by various levels of nitrogen under rainfed condition. Treatments consisted of different nutrient management practices including FYM and nitrogen doses viz., Absolute Control (N1), FYM @ 5 t ha-1 (N2), N2 + 30 kg N ha-1 (N3), N2 + 60 kg N ha-1 (N4), N2 + 90 kg N ha-1 (N5), N2 +120 kg N ha-1 (N6) and N2 + 150 kg N ha-1 (N7). Cotton crop was sawn on 29th June 2019 while it was harvested in four pickings. The result revealed that a significant differences in plant height, leaf area, number of sympodial branches and dry matter accumulation and until harvest. Growth attributes viz., plant height and numbers of sympodial branches were maximum in treatment of FYM @ 5 t ha-1+150 kg N ha-1. However, leaf area and dry matter accumulation were maximum with treatment of FYM @ 5 t ha-1+120 kg N ha-1

Feasibility of Multispectral Observations for Detecting Nitrogen Stress and Yield Potential in Cotton (Gossypium hirsutum L.) through Remote Sensing

The present investigation was conducted during kharif 2019-20 at Department of Agronomy farm, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola. The experiment was laid out in randomized block design with seven treatments and three replications. Treatments consisted of different nutrient management practices including FYM and nitrogen doses viz., Absolute Control (N1), FYM @ 5 t ha-1 (N2), N2 + 30 kg N ha-1 (N3), N2 + 60 kg N ha-1 (N4), N2 + 90 kg N ha-1 (N5), N2 +120 kg N (N6) and N2 + 150 kg N ha-1 (N7). Cotton crop was sown on 29th June 2019 and was harvested in four pickings. Among various spectral bands, significantly higher positive and negative correlation coefficient values (at 0.05 % level of significance) for plant chlorophyll content were noted with the simple ratio of NIR/G (r2=0.829) and G/NIR(r2=-0.826), respectively, being most efficient in detecting the nitrogen stress in cotton crop. Yield potential of cotton was established (at 0.05 % level of significance) with negative and positive (both) correlation coefficient of simple ratio of R/NIR (r2=-0.815 and r2=-0.869) and NIR/R (r2=0.811and r2=0.865) respectively at 180 DAS

Early deformation mechanisms in the shear affected region underneath a copper sliding contact

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. This work explores the initiation of a tribologically induced microstructure in the vicinity of a copper twin boundary. Two distinct horizontal dislocation traces lines (DTL) are observed in their interaction with the twin boundary beneath the sliding interface. DTL formation seems unaffected by the presence of the twin boundary but the twin boundary acts as an indicator of the occurring deformation mechanisms. Three concurrent elementary processes can be identified: simple shear of the subsurface area in sliding direction, localized shear at the primary DTL and crystal rotation in the layers above and between the DTLs around axes parallel to the transverse direction. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes. Quantitatively separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts