Inhibition of metal dusting of alloy 800H by laser surface melting

Metal dusting is a catastrophic carburisation phenomenon that occurs at temperatures of 450-850°C in atmospheres of high carbon activity. The resistance of alloys to corrosion, including metal dusting, relies on the formation of a dense, adherent oxide layer that separates the alloy from the corrosive environment. For such an oxide layer to be protective, it must achieve full surface coverage, be crack-free and be established before significant material degradation has occurred. Formation of a protective oxide scale can be enhanced by increasing the population of rapid diffusion paths for the protective elements (e.g. Cr and Al) to reach the alloy surface. In this work, laser surface melting has been used to improve the metal dusting resistance of Alloy 800H by creating a rapid solidification microstructure and, thereby, increasing the density of rapid diffusion paths. Oxidation during laser processing has been found to be detrimental to metal dusting resistance. However, it has been demonstrated that the resulting oxide can be removed without compromising metal dusting resistance. Results of exposure to a metal dusting atmosphere (20% H2 80% CO at 650°C) are presented. Samples have been examined in plan and cross-section using optical and scanning electron microscopy. Selected samples were also examined by electron probe microanalysis and X-ray diffraction

Inhibition of metal dusting using thermal spray coatings and laser treatment

Alloy 600 and Alloy 800H are susceptible to metal dusting. Both alloys were thermally sprayed with two different corrosion resistant coatings: Ni50Cr and Ni31Cr11Al0.6Y. Laser remelting was used to enhance further the effectiveness of these coatings to resist metal dusting by eliminating interconnected porosity and improving coating adhesion. Uncoated, coated and laser-treated coated samples of Alloy 600 and Alloy 800H were exposed to a mixed gas atmosphere (20% H2, 80% CO at 650°C). Samples were examined in plan and cross-section using optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The extent of carbon deposition was tracked by mass difference measurements at intervals during exposure. The thermally sprayed coatings enhanced metal dusting resistance by acting as physical barriers to carbon ingress. The NiCrAlY coating performed well on both substrates. The NiCr coating itself underwent metal dusting and spalled from Alloy 800H due partly to CTE mis-match stresses. Laser treatment of both coatings successfully eliminated interconnected porosity and hence enhanced metal dusting resistance

A tight-binding potential for atomistic simulations of carbon interacting with transition metals: Application to the Ni-C system

We present a tight-binding potential for transition metals, carbon, and transition metal carbides, which has been optimized through a systematic fitting procedure. A minimal basis, including the s, p electrons of carbon and the d electrons of the transition metal, is used to obtain a transferable tight-binding model of the carbon-carbon, metal-metal and metal-carbon interactions applicable to binary systems. The Ni-C system is more specifically discussed. The successful validation of the potential for different atomic configurations indicates a good transferability of the model and makes it a good choice for atomistic simulations sampling a large configuration space. This approach appears to be very efficient to describe interactions in systems containing carbon and transition metal elements

Fungicide Resistance in Botrytis cinerea from Strawberry - Molecular Mechanisms and Management

The United States is the largest producer of strawberries worldwide, generating approximately $2.4 billion worth of fruit each year. Strawberry production, however, is often threatened by pathogens. One of the most destructive fungal pathogens is Botrytis cinerea, the causal agent of gray mold disease. The control of gray mold in commercial fields is largely dependent on the application of fungicides, including the dicarboximide iprodione and the hydroxyanilide fenhexamid. Because both fungicides are prone to resistance development, a survey was conducted to determine the occurrence and prevalence of fungicide resistance. Single-spore isolates were collected from strawberry fields in Florida (for the dicarboximide study), North Carolina, and South Carolina and subjected to a spore-germination assay that distinguishes sensitive from resistant isolates. Of the isolates collected, 16.8% were resistant to fenhexamid, 2% were moderately resistant to iprodione, and 17.6% had low levels of resistance to iprodione. Resistance to the two fungicides was found in almost every location, indicating that resistance was widespread but only accounted for a low percentage of the population. Resistance to fenhexamid was associated with nucleotide mutations in the target gene erg27, resulting in aa changes T63I, F412S, F412C, or F412I. A rapid method was developed based on polymerase chain reaction to specifically detect these mutations. Low and moderate resistance to iprodione was associated with mutations in target gene bos1 resulting in I365N, I365S or a combination of Q369P and N373S, respectively. The I365N/S mutations were also present in five highly resistant isolates that were included to investigate the molecular mechanism of iprodione resistance, but no mutation or mutation combinations in bos1 were uniquely associated with the highly resistant phenotype. Detached strawberry fruit assays indicated that field rates of Elevate 50 WDG (fenhexamid) did not control fenhexamid-resistant isolates, and field rates of Rovral 4 Flowable (iprodione) did not control isolates moderately and highly resistant to iprodione. Fitness studies revealed that iprodione-resistant isolates did not differ from sensitive isolates in regard to radial growth rate on artificial medium, sporulation, and pathogenicity on strawberry fruit. The results obtained in this study contribute to our understanding of fungicide resistance development in the gray mold fungus and are useful for improving current resistance management practices

Time Dependent Surface Corrosion Analysis and Modelling of Automotive Steel Under a Simplistic Model of Variations in Environmental Parameters

This research presents time-dependent corrosion analysis of automotive steel utilised in a large military vehicle in real operating environment, followed by simulated environmental tests and simplistic surface corrosion modelling. Time-dependent surface corrosion accumulated on this specific component was observed to be approximately 250 µm thick, with the identification of surface contaminants such as chlorine and sulphur. Simulated environmental tests considering temperature and relative humidity variations were performed to evaluate quantitative corrosion damage to the structure of the vehicle. The relationship of various temperatures and relative humidity with respect to time, within the context of corrosion initiation and propagation, has been presented. A mathematical model to incorporate corrosion accumulation on the surfaces derived from the simulated environmental tests is presented

An Evaluation of the Fe-N Phase Diagram Considering Long-Range Order of N Atoms in γ'-Fe4N1-x and ε-Fe2N1-z

The chemical potential of nitrogen was described as a function of nitrogen content for the Fe-N phases α-Fe[N], γ'-Fe4N1-x, and ε-Fe2N1-z. For α-Fe[N], an ideal, random distribution of the nitrogen atoms over the octahedral interstices of the bcc iron lattice was assumed; for γ'-Fe4N1-x and ε-Fe2N1-z, the occurrence of a long-range ordered distribution of the nitrogen atoms over the octahedral interstices of the close packed iron sublattices (fcc and hcp, respectively) was taken into account. The theoretical expressions were fitted to nitrogen-absorption isotherm data for the three Fe-N phases. The α/α + γ', α + γ'/γ', γ'/γ' + ε, and γ' + ε/ε phase boundaries in the Fe-N phase diagram were calculated from combining the quantitative descriptions for the absorption isotherms with the known composition of NH3/H2 gas mixtures in equilibrium with coexisting α and γ' phases and in equilibrium with coexisting γ' and ε phases. Comparison of the present phase boundaries with experimental data and previously calculated phase boundaries showed a major improvement as compared to the previously calculated Fe-N phase diagrams, where long-range order for the nitrogen atoms in the γ' and ε phases was not accounted for

Resistance to multiple fungicides in Botrytis cinerea isolates from commercial strawberry fields in the eastern USA

Chemical control of gray mold of strawberry caused by Botrytis cinerea Pers. is essential to prevent pre- and postharvest fruit decay; however, resistance to multiple chemical classes of fungicides including APs (cyprodinil), DCs (iprodione), MBCs (thiophanate-methyl), PPs (fludioxonil), QoIs (pyraclostrobin), SBIs (fenhexamid), or SDHIs (boscalid) is a well-known and well-described phenomenon in B. cinerea from strawberry fields in Florida, Germany, North Carolina, and South Carolina. As part of a resistance-monitoring program conducted during 2012 and 2013, a total of 1,890 B. cinerea isolates where collected from 10 states in the eastern USA. The isolates were analyzed for fungicide resistance using a mycelial growth assay. The overall resistance frequencies in 2012 for thiophanate-methyl, pyraclostrobin, boscalid, cyprodinil, fenhexamid, iprodione, and fludioxonil were 76, 42, 29, 27, 25, 3, and 1%, respectively. Frequencies in 2013 were 85, 59, 5, 17, 26, 2, and 1%, respectively. Isolates were resistant to either one (23%), two (18%), three (19%), four (14%), five (3%) or six (0.1%) chemical classes of fungicides in 2012. In 2013 this distribution was 24%, 29%, 26%, 8%, 2%, 0.3%, respectively, and also 0.3% (6 isolates) were resistant to all classes of fungicides. Resistance to thiophanate-methyl, iprodione, boscalid, pyraclostrobin and fenhexamid was based on target gene mutations in β-tubulin, bos1, sdhB, cytb, and erg27, respectively. Isolates were MDR1 or MDR1h dependent on sensitivity to fludioxonil and variations in transcription factor mrr1. Expression of ABC transporter atrB was highest in MDR1h isolates. The discovery of B. cinerea isolates resistant to all registered site-specific fungicides for gray mold control represents an unprecedented milestone of resistance development in B. cinerea that signals a failure of current anti-resistance management strategies.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech