A Simple Method to Assess Surface Roughness by Photothermal Investigation (PTR) Using an Effective Semitransparent Layer

Samples of a titanium?Caluminum?Cvanadium alloy (Ti6Al4V) having different values of roughness are studied by photothermal radiometry. Among the numerous studies carried out on the influence of surface roughness on the photothermal signal, those that relate the air/substrate interfacial volume to an apparent homogeneous layer with effective thermal properties are considered. For such a system, a one-dimensional heat transfer model can successfully be used to describe the response to harmonic excitation up to high frequencies where the thermal diffusion length is of the order of magnitude as the roughness. The breakdown of the effective layer model at high frequencies has prompted some authors to develop more sophisticated methods to describe the complex phenomena encountered. In this study, it is proposed to keep the simple, effective layer model, but also to modify it by including an effective optical absorption coefficient and a reflection coefficient closely related to the surface characteristics. The effective layer becomes semitransparent to the excitation as it turns thermally thick (thickness/thermal diffusion length >1). The apparent thickness of the layer is shown to be directly related to the average difference between the maximum peak and the minimum trough of the surface profile and linearly correlated with the average roughness. This model can be used over a wide range of roughnesses.     

Surface Tension Measurements on Industrial Alloys by the Drop-Weight Method

The drop-weight method has been successfully applied to a representative set of industrial alloys (W–Re₂₆, Mo–Re₅₀, Pt–Rh₁₀, Pt–Rh₃₀, Ti–Al₆–V₄, AISI 316 L stainless steel, INCONEL 182 and 600 alloys), with the result that very reproducible surface tension measurements ( /<0.5%) have been established for these materials at the liquidus temperature. This work supports the idea that the simplicity of the drop-weight method should attract much more attention for production control or to provide reference values at the liquidus temperature, although it cannot be used for temperature coefficient measurements of the surface tension.     

Martensitic Transformations and Mechanical and Corrosion Properties of Fe-Mn-Si Alloys for Biodegradable Medical Implants

Metallurgical and Materials Transactions A - The Fe-Mn-Si alloys are promising materials for biodegradable metallic implants for temporary healing process in the human body. In this study, three...     

Thermal Treatment Optimization of Electrodeposited Hydroxyapatite Coatings on Ti6Al4V Substrate

Thermal behavior of electrodeposited hydroxyapatite (HAP) coating on a titanium alloy (Ti6Al4V) is investigated in order to optimize the heat treatment conditions for this prosthetic material. The synthesized coatings are annealed in air atmosphere at 400, 600, 800, and 1000 °C, and then characterized by X‐ray diffraction (XRD) and selected area electron diffraction (SAED) for structure and phases analysis. Scanning and transmission electron microscopy associated to energy dispersive X‐ray microanalysis (SEM‐EDXS and STEM) are used for morphology and composition analysis. The results show that when the electrodeposited coating is annealed at temperatures greater than 600 °C, a well‐crystallized HAP is obtained with a notable change of its morphology. However, at these temperatures the surface of Ti6Al4V alloy (uncoated zones of the implant) is deteriorated by the formation of a thick surface oxide layer. Therefore, we limit the heat treatment temperature for the electrodeposited coatings on a Ti6Al4V alloy at 550 °C. At this optimized temperature it is demonstrated that the link between the coating and the substrate is improved and the crystallinity of the coating is controlled which make it well bioactive.     

Wetting of ceramics by molten silicon and silicon alloys: a review

The surface of silicon is very sensitive to interactions with oxygen present as impurity in furnace atmosphere. It is shown that three types of Si surfaces can be obtained depending on the oxygen’s partial pressure in the furnace and on temperature: oxidized, oxide-free but containing adsorbed oxygen and adsorption free. The influence of oxygen on the surface tension of molten Si is also discussed. Wetting by Si and Si alloys is then described and analysed for three types of ceramics: (i) ionocovalent oxides (Al₂O₃, SiO₂, MgO, etc.), with a particular emphasis on the Si/silica couple, (ii) the different types of carbons where wetting is assisted by the reaction between Si and carbon, and (iii) the predominantly covalent ceramics (SiC, Si₃N₄, AlN, BN, etc). The role of wetting in the processing of silicon or silicon-based multimaterials is also illustrated.     

Spontaneous rupture of the rectum. Contribution of CT scan. Apropos of a case

We report a case of spontaneous rupture of the rectosigmoid junction demonstrated by surgical and histological examination. This rare complication of chronic constipation is difficult to confirm except in the case of the typical clinical presentation with lower abdominal pain after defaecation and evisceration of small intestine loops through the anus. No radiological procedure is usually performed except for plain abdominal radiograph, to demonstrate inconstant (retro)peritoneal emphysema. CT scan could detect free air outside of the rectosigmoid lumen, suggesting parietal rupture and allowing appropriate surgical treatment on the lower digestive tract.     

Resistance to oxidation of graphite silicided by reactive infiltration

In order to improve the oxidation resistance of graphite at high temperatures, graphite surfaces are modified by two silicidation processes involving reactive infiltration of molten silicon or, alternatively, of gaseous silicon monoxide.The resistance to oxidation of silicided graphite is studied by cyclic oxidation tests performed under a dry air flux at temperatures in the range 1550-1600 °C.During oxidation three successive regimes are evidenced: (i) initial growth of a passive silica layer on the continuous SiC superficial layer responsible for the remarkable oxidation resistance at 1550 °C; (ii) then, slow mass consumption in the intermediate composite SiC-C region; (iii) and finally, rapid local consumption of the underlying non-infiltrated porous graphite.The temporal stability of the silicided layer in air is analyzed and the reactions affecting this stability are identified. The analysis interprets the experimental findings in a satisfactory manner, especially the dramatical variation with temperature of silicided graphite lifetime observed in this temperature range.     

Reactive infiltration by Si: Infiltration versus wetting

This paper focuses on spontaneous infiltration by liquid metals in reactive metal/ceramic systems. Two cases of reactive infiltration, where a molten silicon drop is in contact with two different porous bodies, graphite and (oxidized) silicon nitride, are briefly described and discussed. For each solid, the dynamics of wetting on the solid surface is compared to the dynamics of infiltration into the porous medium in order to determine the common points and the main differences between these two processes.     

Wetting and adhesion of Si on Si3N4 and BN substrates

Wetting, adhesion and reactivity are the principal factors determining the capability of a solid to be used as mould material. In this work wetting of silicon and boron nitrides by molten silicon is studied in neutral gas atmosphere by the sessile drop technique at temperatures close to the silicon melting point. Adhesion is qualified by the behaviour of solidified droplets under the effect of thermo-mechanical stresses generated during cooling at room temperature. The reactivity at silicon/nitride interfaces is studied by scanning electron microscopy and EDX-microanalysis.