Electron beam hardening of PVD-coated steels: Improved load-supporting capacity for Ti1-xAlxN layers

This paper deals with the results of combining Ti1 − xAlxN coatings with a subsequent electron beam surface-hardening process. The coatings – differing in their chemical composition (Al = 17…30 at.%; Ti = 18…30 at.%) and thickness (1–6 μm) – were deposited by reactive magnetron sputtering onto the heat-treatable steel 51CrV4. During electron beam hardening (EBH), a special energy transfer field causes an isothermal surface temperature distribution. By varying energy input and interaction time, the resulting hardening depth could be adjusted in the range of 0.1 to 0.4 mm. The results are characterised by means of optical and scanning electron microscopy, hardness measurements and the evaluation of the chemical composition of the coatings by glow discharge optical spectroscopy. The load supporting capacity and the adhesion of the hard coatings was determined using scratch tests with increasing load. The chemical composition and thickness of the coatings applied by physical vapour deposition (PVD) significantly affected the results of subsequent EBH. Hardening depth increased with the increasing thickness and increasing Al content of the PVD layer. Furthermore, the coatings exhibited increasing resistance against thermal stress during EBH for decreasing layer thickness and increasing Ti content. Load support of the base material was improved by a factor of 2 to 3. Therefore, the duplex treatment PVD + EBH has a high potential for industrial application with respect to locally highly loaded components

Duplex surface treatment - physical vapor deposition (PVD) and subsequent electron beam hardening (EBH)

Subsequent EBH improves the load-supporting capacity of PVD-coated steels. The influence of the chemical composition and layer thickness of Ti1−xAlxN coatings on the results of EBH was investigated. Increasing Al contents, along with increasing layer thicknesses improve the heat input during EBH. It is possible to harden the steel through the PVD layer without negative influences on the metastable coatings

Investigations of electron beam hardening on TiAlN coated heat-treatable steel

In this investigation, an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti₍₁₋x₎AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputtering. For electron beam surface hardening following hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition, and mechanical properties of the coatings remained mostly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of the near-interface coating elements into the substrate occurred, and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths, a plausible description of the observed effects was derived. The EBH caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties

Surface hardening after hard coating deposition - combining TiAlN tribological coatings with subsequent electron beam treatment

In this investigation an electron beam hardening (EBH) procedure was applied to heat-treatable steel 51CrV4 coated with Ti(1-x)AlxN hard coatings, where x ranged from 0.3 to 0.6. The coatings with variable composition and mechanical properties were deposited by reactive magnetron sputter deposition. For electron beam surface hardening followed by hard coating deposition, the energy distribution within the energy transfer field caused a nearly constant hardening temperature on the treated material surface. Morphology, composition and mechanical properties of the coatings remained nearly unchanged, whereas the coating-substrate interface and the steel surface region were highly modified. Diffusion of interface-near coating elements into the substrate occurred and the corresponding region of the substrate showed clear changes in morphology and composition. These changes can be correlated with substantial improvements of the coating adhesion properties. Based on temperature measurements and calculations of electron penetration depths a plausible description of the observed effects was derived. The electron beam hardening caused a significant improvement of delamination resistance, especially for coatings with insufficient adhesion properties

The zinc-binding protein Hot13 promotes oxidation of the mitochondrial import receptor Mia40

A disulphide relay system mediates the import of cysteine-containing proteins into the intermembrane space of mitochondria. This system consists of two essential proteins, Mia40 and Erv1, which bind to newly imported proteins by disulphide transfer. A third component, Hot13, was proposed to be important in the biogenesis of cysteine-rich proteins of the intermembrane space, but the molecular function of Hot13 remained unclear. Here, we show that Hot13, a conserved zinc-binding protein, interacts functionally and physically with the import receptor Mia40. It improves the Erv1-dependent oxidation of Mia40 both in vivo and in vitro. As a consequence, in mutants lacking Hot13, the import of substrates of Mia40 is impaired, particularly in the presence of zinc ions. In mitochondria as well as in vitro, Hot13 can be functionally replaced by zinc-binding chelators. We propose that Hot13 maintains Mia40 in a zinc-free state, thereby facilitating its efficient oxidation by Erv1

Factors Supporting Cysteine Tolerance and Sulfite Production in Candida albicans.

The amino acid cysteine has long been known to be toxic at elevated levels for bacteria, fungi, and humans. However, mechanisms of cysteine tolerance in microbes remain largely obscure. Here we show that the human pathogenic yeast Candida albicans excretes sulfite when confronted with increasing cysteine concentrations. Mutant construction and phenotypic analysis revealed that sulfite formation from cysteine in C. albicans relies on cysteine dioxygenase Cdg1, an enzyme with similar functions in humans. Environmental cysteine induced not only the expression of the CDG1 gene in C. albicans, but also the expression of SSU1, encoding a putative sulfite efflux pump. Accordingly, the deletion of SSU1 resulted in enhanced sensitivity of the fungal cells to both cysteine and sulfite. To study the regulation of sulfite/cysteine tolerance in more detail, we screened a C. albicans library of transcription factor mutants in the presence of sulfite. This approach and subsequent independent mutant analysis identified the zinc cluster transcription factor Zcf2 to govern sulfite/cysteine tolerance, as well as cysteine-inducible SSU1 and CDG1 gene expression. cdg1Δ and ssu1Δ mutants displayed reduced hypha formation in the presence of cysteine, indicating a possible role of the newly proposed mechanisms of cysteine tolerance and sulfite secretion in the pathogenicity of C. albicans. Moreover, cdg1Δ mutants induced delayed mortality in a mouse model of disseminated infection. Since sulfite is toxic and a potent reducing agent, its production by C. albicans suggests diverse roles during host adaptation and pathogenicity