Delamination and Longitudinal Cracking in Multilayered Composite Nanostructured Coatings and Their Influence on Cutting Tool Wear Mechanism and Tool Life

The wear and failure mechanism for multilayered nanostructured coatings has a number of significant differences from the one typical for monolithic single-layered coatings. In particular, while the strength of adhesion bonds at the “substrate-coating” boundary is important for monolithic coatings, then for multilayered nanostructured coatings, the strength of adhesion and cohesion bonds at interlayer boundaries and boundaries of separate nano-sublayers becomes of significant significance. Meanwhile, the delamination arising in the structure of multilayered nanostructured coatings can have both negative (leading to loss of coating uniformity and subsequent failure of coating) and positive influences (due to decrease of internal stresses and inhibition of transverse cracking). Various mechanisms of formation of longitudinal cracks and delaminations in coatings on rake tool faces, which vary based on the compositions and architectures of the coatings, are studied. In addition, the influence of internal defects, including embedded microdrops and pores, on the formation of cracks and delaminations and the failure of coatings is discussed. The importance of ensuring a balance of the basic properties of coatings to achieve high wear resistance and maximum tool life of coated metal-cutting tools is shown. The properties of coatings and the natures of their failures, as investigated during scratch testing and dry turning of steel C45, are provided

Shock-induced melting and crystallization in titanium irradiated by ultrashort laser pulse

Modification of titanium microstructure after propagation of a melting shock wave (SW) generated by a femtosecond laser pulse is investigated experimentally and analyzed using hydrodynamic and atomistic simulations. Scanning and transmission electron microscopy with analysis of microdiffraction is used to determine the microstructure of subsurface layers of pure titanium sample before and after modification. We found that two layers of modified titanium are formed beneath the surface. A top surface polycrystalline layer of nanoscale grains is formed from a shock-molten layer via rapid crystallization. In a deeper subsurface layer, where the shock-induced melting becomes impossible due attenuation of SW, recrystallization of plastically deformed titanium leads to grain size changes in comparison with intact titanium. Molecular dynamics simulation of single-crystal titanium reveals that the SW front continues to melt/liquefy even after its temperature drops below the melting curve $T_m(P)$. The enormous shear stress generated in a narrow SW front leads to collapse/amorphization of the crystal lattice and formation of a supercooled metastable melt. Such melt crystallizes in an unloading tail of SW until its temperature becomes higher than $T_m(P)$ due to a rapid pressure drop. Later, crystallization of the subsurface molten layer will continue after the heat leaves it. After the shear stress drops below $\sim 12$GPa within the SW front, such the cold mechanical melting ceases giving place to the shock-induced plastic deformations. The depth of modification is limited by SW attenuation to the Hugoniot elastic limit, and can reach several micrometers. The obtained results reveal the basic physical mechanisms of surface hardening of metals by ultrashort laser pulses.Comment: 15 pages, 13 figures. The work was reported at the 38 International Conference ELBRUS-2023 on March 1, 2023, and submitted to Physical Review Applie

Nanostructured Multilayer Composite Coatings for Cutting Tools

The chapter deals with the specific features concerning the application of wear-resistant coatings to improve the performance properties of ceramic cutting tools. The paper discusses the theoretical background associated with the specific operation conditions and wear of ceramic cutting tools and influencing the choice of the compositions and structures of wear-resistant coatings. The studies were focused on the application of the Ti-(Ti,Al)N-(Zr,Nb,Ti,Al)N multilayer composite coating with a nanostructured wear-resistant layer, as well as the (Cr,Al,Si)N–(DLC–Si)–DLC–(DLC–Si) and (Cr,Al,Si)N–DLC composite coatings in order to improve the cutting properties of ceramic tools. The chapter presents the results of the comparative cutting tests for the tools with the coatings under study, uncoated tools, and tools with the Ti-(Ti,Al)N commercial coating. The wear mechanisms typical for ceramic cutting tools with coatings of various compositions have been investigated

Assessing the Effects of Cytoprotectants on Selective Neuronal Loss, Sensorimotor Deficit and Microglial Activation after Temporary Middle Cerebral Occlusion.

Although early reperfusion after stroke salvages the still-viable ischemic tissue, peri-infarct selective neuronal loss (SNL) can cause sensorimotor deficits (SMD). We designed a longitudinal protocol to assess the effects of cytoprotectants on SMD, microglial activation (MA) and SNL, and specifically tested whether the KCa3.1-blocker TRAM-34 would prevent SNL. Spontaneously hypertensive rats underwent 15 min middle-cerebral artery occlusion and were randomized into control or treatment group, which received TRAM-34 intraperitoneally for 4 weeks starting 12 h after reperfusion. SMD was assessed longitudinally using the sticky-label test. MA was quantified at day 14 using in vivo [11C]-PK111195 positron emission tomography (PET), and again across the same regions-of-interest template by immunofluorescence together with SNL at day 28. SMD recovered significantly faster in the treated group (p = 0.004). On PET, MA was present in 5/6 rats in each group, with no significant between-group difference. On immunofluorescence, both SNL and MA were present in 5/6 control rats and 4/6 TRAM-34 rats, with a non-significantly lower degree of MA but a significantly (p = 0.009) lower degree of SNL in the treated group. These findings document the utility of our longitudinal protocol and suggest that TRAM-34 reduces SNL and hastens behavioural recovery without marked MA blocking at the assessed time-points

Neuronal activity regulates remyelination via glutamate signalling to oligodendrocyte progenitors.

Myelin regeneration can occur spontaneously in demyelinating diseases such as multiple sclerosis (MS). However, the underlying mechanisms and causes of its frequent failure remain incompletely understood. Here we show, using an in-vivo remyelination model, that demyelinated axons are electrically active and generate de novo synapses with recruited oligodendrocyte progenitor cells (OPCs), which, early after lesion induction, sense neuronal activity by expressing AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)/kainate receptors. Blocking neuronal activity, axonal vesicular release or AMPA receptors in demyelinated lesions results in reduced remyelination. In the absence of neuronal activity there is a ∼6-fold increase in OPC number within the lesions and a reduced proportion of differentiated oligodendrocytes. These findings reveal that neuronal activity and release of glutamate instruct OPCs to differentiate into new myelinating oligodendrocytes that recover lost function. Co-localization of OPCs with the presynaptic protein VGluT2 in MS lesions implies that this mechanism may provide novel targets to therapeutically enhance remyelination.This work was supported by the Medical Research Council (R.T.K, R.J.M.F and H.O.B.G. G0701476; K.V. and R.T.K 1233560), Wellcome Trust (R.T.K. and K.A.E. 091543/Z/10/Z), Marie Curie training programme Axregen EC FP7 ITN (I.L. and R.T.K 214003), and core support grant from the Wellcome Trust and MRC to the Wellcome Trust – Medical Research Council Cambridge Stem Cell Institute.This is the author accepted manuscript. The final version is available from NPG via http://dx.doi.org/10.1038/ncomms951

The Effect of Elemental Composition and Nanostructure of Multilayer Composite Coatings on Their Tribological Properties at Elevated Temperatures

The chapter discusses the tribological properties of samples with multilayer composite nanostructured Ti-TiN-(Ti,Cr,Al,Si)N, Zr-ZrN-(Nb,Zr,Cr,Al)N, and Zr-ZrN-(Zr,Al,Si)N coatings, as well as Ti-TiN-(Ti,Al,Cr)N, with different values of the nanolayer period λ. The relationship between tribological parameters, a temperature varying within a range of 20–1000°C, and λ was investigated. The studies have found that the adhesion component of the coefficient of friction (COF) varies nonlinearly with a pronounced extremum depending on temperature. The value of λ has a noticeable influence on the tribological properties of the coatings, and the nature of the mentioned influence depends on temperature. The tests found that for the coatings with all studied values of λ, an increase in temperature first caused an increase and then a decrease in COF

Astrocyte response to motor neuron injury promotes structural synaptic plasticity via STAT3-regulated TSP-1 expression.

The role of remote astrocyte (AC) reaction to central or peripheral axonal insult is not clearly understood. Here we use a transgenic approach to compare the direct influence of normal with diminished AC reactivity on neuronal integrity and synapse recovery following extracranial facial nerve transection in mice. Our model allows straightforward interpretations of AC-neuron signalling by reducing confounding effects imposed by inflammatory cells. We show direct evidence that perineuronal reactive ACs play a major role in maintaining neuronal circuitry following distant axotomy. We reveal a novel function of astrocytic signal transducer and activator of transcription-3 (STAT3). STAT3 regulates perineuronal astrocytic process formation and re-expression of a synaptogenic molecule, thrombospondin-1 (TSP-1), apart from supporting neuronal integrity. We demonstrate that, through this new pathway, TSP-1 is responsible for the remote AC-mediated recovery of excitatory synapses onto axotomized motor neurons in adult mice. These data provide new targets for neuroprotective therapies via optimizing AC-driven plasticity.This is the final version. It was first published in Nature Communications here: http://www.nature.com/ncomms/2014/140711/ncomms5294/abs/ncomms5294.html

Oligodendrocyte progenitor cells become regionally diverse and heterogeneous with age

Oligodendrocyte progenitor cells (OPCs), which differentiate into myelinating oligodendrocytes during central nervous system (CNS) development, are the main proliferative cells in the adult brain. OPCs are conventionally considered a homogeneous population, particularly with respect to their electrophysiological properties, but this has been debated. We show, by using single-cell electrophysiological recordings, that OPCs start out as a homogeneous population, but become functionally heterogeneous, varying both within and between brain regions and with age. These electrophysiological changes in OPCs correlate with the differentiation potential of OPCs; thus, they may underlie the differentiational differences in OPCs between regions and likewise differentiation failure with age.We acknowledge the support of the Wellcome - MRC Cambridge Stem Cell Institute core facility managers, in particular for this work Dr Maike Paramor and Miss Victoria Murray with RNA sequencing, and all staff members of the University Biomedical Services (UBS). This project has received funding from: the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 771411; R.T.K, K.A.E); the Wellcome Trust, a Research Career Development Fellowship (R.T.K. and K.A.E. 091543/Z/10/Z) and a Studentship (102160/Z/13/Z; Y.K); The Paul G Allen Frontiers Group, Allen Distinguished Investigator Award (12076, R.T.K., D.K.V.); The Medical Research Council, a studentship (S.O.S.); The Gates Foundation, a Gates Scholarship (S.S.), The Biotechnology and Biological Sciences Research Council, a studentship (S.A.); Homerton College Cambridge, a Junior Research Fellowship (D.K.V); The UK MS Society, a Cambridge Myelin Repair Centre grant (50; R.T.K, O.D.F.); The Fonds de recherche du Québec-Santé, a scholarship (Y.K.); The Cambridge Commonwealth European & International Trust, a scholarship (Y.K.); and the Lister Institute, a Research Prize (R.T.K., K.A.E, SOS)

Oligodendrocyte Progenitor Cells Become Regionally Diverse and Heterogeneous with Age

We thank J. Trotter (Johannes Gutenberg University, Mainz, Germany) for the NG2-EYFP mice, Dr. Moritz Matthey for help with minipump transplantation, Miss Mariann Kovacs with embryonic dissection, and Dr. Katrin Volbracht for critical comments on the work. We acknowledge the support of the Wellcome – MRC Cambridge Stem Cell Institute core facility managers, in particular for this work Dr. Maike Paramor and Miss Victoria Murray with RNA-seq, and all staff members of the University Biomedical Services (UBS). This project has received the following funding: funding from the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (grant agreement 771411 to R.T.K. and K.A.E.), a Wellcome Trust research career development fellowship (091543/Z/10/Z to R.T.K. and K.A.E.) and studentship (102160/Z/13/Z to Y.K.), Paul G. Allen Frontiers Group Allen Distinguished Investigator Award 12076 (to R.T.K., D.K.-V., and K.A.E.), a Medical Research Council studentship (to S.O.S.), a Gates Cambridge Trust Gates scholarship (to S.S.), a Biotechnology and Biological Sciences Research Council studentship (to S.A.), a Homerton College Cambridge junior research fellowship (to D.K.-V.), UK MS Society Cambridge Myelin Repair Centre grant 50 (to R.T.K. and O.d.F.), a Fonds de Recherche du Québec - Santé scholarship (to Y.K.), a Cambridge Commonwealth, European and International Trust scholarship (to Y.K.), and a Lister Institute research prize (to R.T.K., K.A.E., and S.O.S.). Publisher Copyright: © 2018 The Author(s)Spitzer et al. show that oligodendrocyte progenitor cells (OPCs) acquire ion channels and sensitivity to neuronal activity that differ between region and age. The onset and decline of ion channels follow developmental milestones. This heterogeneity indicates different functional states of OPCs.Peer reviewe