In the present study, AA6082 aluminium is deposited onto AISI 4140 steel substrates via friction surfacing (FS). Aiming to understand the influence of substrate surface for the bonding mechanism ...during the plasticising as well as the deposition phase, three different surface topographies have been manufactured via grinding and machining. Subsequently, FS process parameter dependencies on the deposits have been investigated. The resulting optical appearance, geometry and microstructure of the deposits have been studied. A deeper surface topography was found to facilitate plasticising and therefore FS layer deposition. Defect-free layer-to-substrate (LTS) joints have been generated for all topographies showing a fine-grained recrystallized microstructure as well as flow lines in the AA6082 deposits following closely the substrate surface topography, whereas no metallurgical changes in the AISI4140 substrates have been detected. At the LTS interfaces, a correlation of flow lines to an increased occurrence of high angle grain boundaries is identified. Appearance, geometries and grain size ratios of the AA6082 deposits show a dependency on substrate surface topography. Although complete bonding was achieved in the LTS joints, no distinct diffusion zone or interfacial mixing was observed. Mechanical interlocking on the micro scale was detected only for the samples with ground substrate surfaces.
•Deeper surface topography helps plasticising and homogeneous layer deposition.•No material mixing or distinct diffusion occurred at dissimilar material interface.•Deposit's microstructural flow lines closely follow substrate surface topography.•Deposit's average grain size tends to decrease with increasing surface topography.
The evaluation of wear progress of gear tooth flanks made of 16MnCr5 was performed using non-destructive micro-magnetic testing, specifically Barkhausen noise (BN) and incremental permeability (IP). ...Based on the physical interaction of the microstructure with the magnetic field, the micro-magnetic characterization allowed the analysis of changes of microstructure caused by wear, including phase transformation and development of residual stresses. Due to wide parameter variation and application of bandpass filter frequencies of micro-magnetic signals, it was possible to indicate and separate the main damage mechanisms considering the wear development. It could be shown that the maximum amplitude of BN correlates directly with the profile form deviation and increases with the progress of wear. Surface investigations via optical and scanning electron microscopy indicated strong surface fatigue wear with micro-pitting and micro-cracks, evident in cross-section after 3 × 10⁵ cycles. The result of fatigue on the surface layer was the decrease of residual compression stresses, which was indicated by means of coercivity by BN-analysis. The different topographies of the surfaces, characterized via confocal white light microscopy, were also reflected in maximum BN-amplitude. Using complementary microscopic characterization in the cross-section, a strong correlation between micro-magnetic parameters and microstructure was confirmed and wear progress was characterized in dependence of depth under the wear surface. The phase transformation of retained austenite into martensite according to wear development, measured by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) was also detected by micro-magnetic testing by IP-analysis.
The residual stress state in the subsurface is a key element of surface integrity. It is well known to have a significant impact on a component's properties in terms of fatigue behavior and ...resistance to wear and corrosion. For this reason, adjusting residual stresses during manufacturing is a major challenge in modern production engineering, to improve and ensure a component's fatigue strength. In this context, hydrostatic deep rolling of the workpiece surface using adapted parameters enables the targeted induction of compressive residual stresses into subsurface layers. Due to specific properties regarding subsurface and topography for functional components in tribological applications, a further machining operation by microfinishing following deep rolling seems to be purposeful. In particular with regard to the production of components exposed to periodic load changes when used, the process combination can enable a substitution of the typically required conventional subsurface zone hardening. With the aim of economical process design, the corresponding parts can be manufactured with significantly reduced time and costs. Efficient and well-founded methods for monitoring the resulting influence on the subsurface zone properties are essential for a reproducible and target-oriented process design. The prevailing method for the non-destructive assessment of residual stresses in both academia and industry is X-ray diffractometry using the sin2 ψ-method. However, this method is time-intensive and requires complex instrumentation. Thus, efforts have been undertaken in past decades to develop alternative methods for the efficient and reliable characterization of residual stresses. In this research, the applicability of the cos α-method in X-ray diffractometry and a micromagnetic approach for residual stress assessment was investigated, analyzing deep rolled and microfinished AISI 4140 specimen conditions. In addition to the diffractometric and micromagnetic measurements, metallographic and topographic analyses of machined surfaces were carried out. Deep rolling was found to induce significant compressive residual stresses of up to −1000 MPa. After microfinishing of the deep rolled surfaces, favorable compressive residual stresses remain in the subsurface, reaching approximately −600 MPa. Based on this, the production of tailored surfaces with respect to a suitable combination of topography and subsurface is possible. For all surface states investigated, a good agreement between the two approaches in X-ray diffraction was found. Magnetic Barkhausen noise (MBN) measurements prove to be well applicable for an efficient and holistic assessment of surface integrity in the subsurface of deep rolled and microfinished AISI 4140 specimens.
•Combining deep rolling with microfinishing enables the production of functional components with an adapted plateau topography and surface integrity.•Evidence is provided that compressive residual stresses in the subsurface, induced by deep rolling, were maintained during microfinishing. After microfinishing residual stresses of up to σ < −300 MPa were found up to a depth of h = 300 μm in axial and tangential directions.•X-ray diffractometry according to the innovative cos α-method was found to be a very time-efficient and reliable alternative for sin2 ψ measurements.•Magnetic Barkhausen noise analysis is well applicable for a holistic characterization of surface integrity resulting from deep rolling and microfinishing.
Cutting tool materials are the backbone of machining and play a vital role in the manufacturing industry. Innovation in cutting tools is important for customized and demanding applications. This ...state-of-the-art review is focused on innovations and future research directions for cutting tools covering i) tool materials/microstructure/property relationships, ii) coatings and their effect on tool performance, iii) cutting edge and functional surface preparation and effect on tool performance, iv) tool geometry for high performance and stable machining considering rapid machining, sustainability, and circularity aspects. The vision is to identify tool material/coating/geometry/functional surface relationships for significant improvement in machining performance. This paper includes perspectives from several research groups with a detailed discussion on current advances, capabilities, and challenges in engineered design of cutting tools, materials, coatings, structures and sets a new agenda for future tooling and research directions.
Diamond impregnated tools are commonly used for the machining of concrete and rocks, e.g. sawblades or core drills. These tools consist of a metal bond and randomly distributed diamonds. The grinding ...of inhomogeneous materials like concrete is a complex system which is interfered by a large number of influencing factors. Although simple models exist describing the material removal processes, there is still a lack of knowledge concerning the fundamental mechanisms during grinding. Thus, the optimisation and development of diamond tools are mainly based on experience and empirical methods. Concrete is described as a compound material which exhibits different phases of minerals like cement and aggregate phases. In reinforced concrete, steel is a further phase which has got highly different properties in comparison to the mineral phases. The detailed analysis of the material removal mechanisms is difficult because of the random phase composition of concrete and the random diamond distribution within the tools as well. But, the knowledge of the material removal mechanisms are of vital interest for the development of efficient tools. A fundamental understanding of material removal processes and wear mechanisms can be drawn from single grain scratch tests. Recent developments in diamond tool manufacturing provide the defined positioning of diamond grains in the tool body. This offers new possibilities based on scratch tests regarding tool development. Thus, scratch tests on concrete and reinforced concrete were conducted using single grain diamond tools. First basic understanding was achieved by scratch tests with diamond indenters by varying feed speed and analysing the resulting forces. Detailed investigations were accomplished by installing a tribometer within a scanning electron microscope (SEM). This setup allowed the analysis of the development of the resulting scratch groove.
Selenium (Se) is an essential micronutrient for human health. Se deficiency affects hundreds of millions of people worldwide, particularly in developing countries, and there is increasing awareness ...that suboptimal supply of Se can also negatively affect human health. Selenium enters the diet primarily through the ingestion of plant and animal products. Although, plants are not dependent on Se they take it up from the soil through the sulphur (S) uptake and assimilation pathways. Therefore, geographic differences in the availability of soil Se and agricultural practices have a profound influence on the Se content of many foods, and there are increasing efforts to biofortify crop plants with Se. Plants from the Brassicales are of particular interest as they accumulate and synthesize Se into forms with additional health benefits, such as methylselenocysteine (MeSeCys). The Brassicaceae are also well-known to produce the glucosinolates; S-containing compounds with demonstrated human health value. Furthermore, the recent discovery of the selenoglucosinolates in the Brassicaceae raises questions regarding their potential bioefficacy. In this review we focus on Se uptake and metabolism in the Brassicaceae in the context of human health, particularly cancer prevention and immunity. We investigate the close relationship between Se and S metabolism in this plant family, with particular emphasis on the selenoglucosinolates, and consider the methodologies available for identifying and quantifying further novel Se-containing compounds in plants. Finally, we summarize the research of multiple groups investigating biofortification of the Brassicaceae and discuss which approaches might be most successful for supplying Se deficient populations in the future.
High consumption of Brassica vegetables is considered to prevent especially colon carcinogenesis. The content and pattern of glucosinolates (GSLs) can highly vary among different Brassica vegetables ...and may, thus, affect the outcome of Brassica intervention studies. Therefore, we aimed to feed mice with diets containing plant materials of the Brassica vegetables broccoli and pak choi. Further enrichment of the diets by adding GSL extracts allowed us to analyze the impact of different amounts (GSL-poor versus GSL-rich) and different patterns (broccoli versus pak choi) of GSLs on inflammation and tumor development in a model of inflammation-triggered colon carcinogenesis (AOM/DSS model). Serum albumin adducts were analyzed to confirm the up-take and bioactivation of GSLs after feeding the Brassica diets for four weeks. In agreement with their high glucoraphanin content, broccoli diets induced the formation of sulforaphane-lysine adducts. Levels of 1-methoxyindolyl-3-methyl-histidine adducts derived from neoglucobrassicin were the highest in the GSL-rich pak choi group. In the colon, the GSL-rich broccoli and the GSL-rich pak choi diet up-regulated the expression of different sets of typical Nrf2 target genes like Nqo1, Gstm1, Srxn1, and GPx2. GSL-rich pak choi induced the AhR target gene Cyp1a1 but did not affect Ugt1a1 expression. Both colitis and tumor number were drastically reduced after feeding the GSL-rich pak choi diet while the other three diets had no effect. GSLs can act anti-inflammatory and anti-carcinogenic but both effects depend on the specific amount and pattern of GSLs within a vegetable. Thus, a high Brassica consumption cannot be generally considered to be cancer-preventive.
MALDI-TOF mass spectrometry (MS) may be used as a rapid typing method for nosocomial pathogens. Here, we evaluated MALDI-TOF MS for discrimination of hospital outbreak-related clusters of
Serratia ...marcescens
and carbapenemase-producing
Citrobacter freundii
. Thirty-three
S. marcescens
isolates collected from neonatal intensive care unit (NICU) patients, and 23
C. freundii
isolates including VIM-positive isolates from a hospital colonization outbreak were measured by Vitek MS. Consensus spectra of each isolate were clustered using SARAMIS software. Genotyping was performed by whole-genome sequencing (WGS). First, a set of 21
S. marcescens
isolates from 2014 with seven genotypes including three monoclonal clusters was used for the evaluation of MALDI-TOF typing. MS clustering was largely in agreement with genotyping results when the similarity cut-off for clonal identity was set on 90%. MALDI-TOF cluster analysis was then investigated for the surveillance of
S. marcescens
in the NICU in 2017 and demonstrated the introduction of new strains into the hospital and nosocomial transmissions. MS analysis of the
C. freundii
outbreak in 2016 revealed a monoclonal cluster of VIM-positive isolates and the separation of epidemiologically non-related VIM-positive and negative isolates. Two additional VIM-positive
Citrobacter
isolates from food samples were closely related to the large monoclonal cluster. WGS confirmed the MS results. MALDI-TOF MS may be used as a first-line typing tool for
S. marcescens
and
C. freundii
to detect transmission events in the hospital because isolates of an identical WGS type were grouped into the same MS cluster.
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