There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Revisiting fundamental welding concepts to improve additive manufacturing: From theory to practice

Ti-6Al-4V (TA6V) titanium alloy is widely used in industrial applications such as aeronautic and aerospace due to its good mechanical properties at high temperatures Experiments on two different resistive pulse heating devices (CEA Valduc and TU-Graz) have been carried out in order to study thermophysical properties (such as electrical resistivity, volume expansion, heat of fusion, heat capacity, normal spectral emissivity, thermal diffusivity, and thermal conductivity) of both solid and liquid Ti-6Al-4V Fast time-resolved measurements of current, voltage, and surface radiation and shadowgraphs of the volume have been undertaken At TU-Graz, a fast laser polarimeter has been used for determining the emissivity of liquid Ti-6Al-4V at 6845 nm and a differential scanning calorimeter (DSC) for measuring the heat capacity of solid Ti-6Al-4V This study deals with the specific behavior of the different solid phase transitions (effect of heating rate) and the melting region, and emphasizes the liquid state (T > 2000 K)

Thermophysical Properties of Solid and Liquid Ti-6Al-4V (TA6V) Alloy

The microscopic mechanisms of femtosecond laser ablation of an Al target are investigated in large-scale massively parallel atomistic simulations performed with a computational model combining classical molecular dynamics technique with a continuum description of the laser excitation and subsequent relaxation of conduction band electrons. The relatively large lateral size of the computational systems used in the simulations enables a detailed analysis of the evolution of multiple voids generated in a sub-surface region of the irradiated target in the spallation regime, when the material ejection is driven by the relaxation of laser-induced stresses. The nucleation, growth, and coalescence of voids take place within a broad (\(\sim \)100 nm) region of the target, leading to the formation of a transient foamy structure of interconnected liquid regions and eventual separation (or spallation) of a thin liquid layer from the bulk of the target. The thickness of the spalled layer is decreasing from the maximum of \(\sim \)50 nm while the temperature and ejection velocity are increasing with increasing fluence. At a fluence of \(\sim \)2.5 times the spallation threshold, the top part of the target reaches the conditions for an explosive decomposition into vapor and small clusters/droplets, marking the transition to the phase explosion regime of laser ablation. This transition is signified by a change in the composition of the ablation plume from large liquid droplets to a mixture of vapor-phase atoms and clusters/droplets of different sizes. The clusters of different sizes are spatially segregated in the expanding ablation plume, where small/medium size clusters present in the middle of the plume are followed by slower (velocities of less than 3 km/s) large droplets consisting of more than 10,000 atoms. The similarity of some of the characteristics of laser ablation of Al targets (e.g., evolution of voids in the spallation regime and cluster size distributions in the phase explosion regime) to the ones observed in earlier simulations performed for different target materials points to the common mechanical and thermodynamic origins of the underlying processes.

Microscopic mechanisms of laser spallation and ablation of metal targets from large-scale molecular dynamics simulations

http://www-geodyn.mit.edu/zubersite/pdfs/Elkins-Tanton_305EPSL2011.pdf

Chondrites as samples of differentiated planetesimals

Thermal conductivity data for molten metals, published since the review of Touloukian et al. in 1970, are collated and evaluated. Where possible recommended values are given. Where availability of data permits, the Wiedemann-Franz-Lorenz equation relating electrical and thermal conductivities has been assessed. It has been found to be valid for most pure metals at their melting point.

Thermal conductivities of molten metals: Part 1 Pure metals

The aim of this study is to optimise the stainless steel oxidation behaviours during hot rolling. The high temperature oxidation behaviours of ferritic stainless steels B443NT and B445J1M were studied over the temperature range from 1000 to 1150 °C in a humid atmosphere containing 18% water vapour, as measured by a thermogravimetric analyser (TGA). The results indicate that breakaway oxidation occurs at 1090 °C for the B443NT steel, which is 60 °C lower than that for the B445J1M steel. The occurrence of iron oxide nodules on the steels marks the onset of breakaway oxidation; however, the breakaway oxidation phenomenon of B445J1M is different from that of B443NT due to a compact and continuous Mn–Cr spinel which is formed on the surface of B445J1M. The oxide nodules with regenerated Cr2O3 scale underneath the Fe–Cr spinel display better adhesion without showing pores at the metal–scale interface.

/pdf/characteristics-of-oxide-scale-formed-on-ferritic-stainless-23nzbm4w9n.pdf

Characteristics of oxide scale formed on ferritic stainless steels in simulated reheating atmosphere

In this study, the mineral matter layer that forms between coke, and liquid iron during carbon dissolution has been characterised. Rectangular prisms of coke were immersed in an iron‐2 mass% carbon melt at representative ironmaking temperatures for 20 min then drop quenched. The quench sample was then sectioned and the coke‐iron interface was examined in the SEM. A mineral matter layer was observed at the experimental temperatures 1 400°C, 1 450°C and 1 500°C, but not at 1 550°C. Though no layer was found at 1 550°C a slag was observed on the metal surface. This slag was not evident at other temperatures. The formation of the mineral matter layer and its temperature dependence is described in terms of a temperature activated fusion process. Further the mineral matter layer and adjacent coke were found to be significantly depleted in SiO2. This has been explained in terms of SiO2 reduction.

/pdf/observations-of-the-mineral-matter-material-present-at-the-i4tde1n9t7.pdf

Observations of the Mineral Matter Material Present at the Coke/Iron Interface During Coke Dissolution into Iron

The rate of dissolution of alumina micro-particles in liquid CaO–SiO 2 –Al 2 O 3 based oxides has been investigated using laser scanning confocal microscopy. Over the temperature range investigated (1477–1577 °C) it was found that the rate controlling mechanism was mass transfer control in the liquid oxide phase. Alumina diffusion coefficients measured during this study are of the order 10 −11 to 10 −10  m 2  s −1 and are in reasonable agreement with previously reported data.

Dissolution behavior of alumina micro-particles in CaO–SiO2–Al2O3 liquid oxide

The kinetics of dephosphorization of carbon-saturated iron by oxidizing slags were studied at 1330 °C. Nine slag compositions were investigated in the systems CaO-Fe2O3-SiO2-CaF2 and CaO-Fe2O3-SiO2-CaCl2. Increasing Fe2O3 up to 50 pct was found to increase the rate and extent of dephosphorization, whereas further increases were found to decrease the rate and extent of dephosphorization. This was explained in terms of two competing effects on the driving force, where increased levels of iron oxide increase the oxygen potential for dephosphorization, hence the driving force, but simultaneously dilute the basic components in the slag, lowering the driving force for dephosphorization. CaF2 and CaCl2 were found to decrease the rate and extent of dephosphorization at levels higher than 12 pct. The rate of dephosphorization was found to be first order with respect to phosphorous in the metal and was controlled by mass transport in the slag. The oxygen potential at the slag/metal interface was controlled by the FeO activity in the slag. When the kinetic results were analyzed to take account of different driving forces, Fe2O3, CaF2 and CaCl2 were all found to increase the mass transfer coefficient of phosphorous in the slag, and a quantitative relationship has been demonstrated between these mass transfer coefficients and the slag viscosity for each system studied.

Brian J Monaghan

Papers

Thermal conductivities of molten metals: Part 1 Pure metals

Characteristics of oxide scale formed on ferritic stainless steels in simulated reheating atmosphere

Observations of the Mineral Matter Material Present at the Coke/Iron Interface During Coke Dissolution into Iron

Dissolution behavior of alumina micro-particles in CaO–SiO2–Al2O3 liquid oxide

The Kinetics of Dephosphorization of Carbon-Saturated Iron Using an Oxidizing Slag