Gaseous Porosity Research Articles

Laser‐Based Directed Energy Deposition Remanufacturing of Gray Cast Iron using Stainless Steel 316L and Inconel 625 Filler Materials

Directed energy deposition (DED) is identified as an ideal candidate for restoring damaged or worn cast iron components such as agricultural engine blocks, housings, and manifolds. While this laser‐based process offers superior control of the heat input compared to traditional arc‐based repair, gaseous porosity and brittle intermetallic structures reduce the strength and ductility of the fusion zone. Varying combinations of Fe–Ni–Cr alloys have found success in remanufacturing cast iron using laser‐based DED, but little attention has been given to the consequence of filler material composition and form, that is, wire versus powder. This study quantifies structural characteristics in cast iron repairs and offers microstructural and process‐specific insights to support these observations. With appropriate thermal conditions, up to 98.7% of the original tensile strength of gray cast iron may be achieved. These results point toward superior gray cast iron restoration using tunable laser‐based DED.

Tensile Fracture in Laser Welding Joints of Al-Cu-Li-Mg-X Alloy Bearing Gaseous Porosity

This article measures the impact of gaseous porosity on the mechanical performance of the laser welded thin sheet of an aerospace-grade Al-Cu-Li-Mg-X material. The laser fabricated joints were characterized by optical microscopy and scanning electron microscopy to reveal the metallurgical features. A uniaxial tensile test was carried out to measure the mechanical strength of the porosity free welds, and porosity bearing welds. The results showed that the welds bearing gaseous porosity performed nearly 24% lower mechanically than the porosity free welds. Fractography exposed the presence of fine spherical holes in porosity bearing welds, which acted as crack nucleation sites, and their further growth lead to a sudden failure at higher strain rates. Microstructural observations revealed that the laser processing has transformed the superior age-hardened microstructure of the base metal into a new as-cast microstructure. The freshly evolved microstructure was held responsible for the low mechanical properties of the joints with respect to the base metal.

The Influence of the Mould Filling Conditions on the Quality of Castings Made of EN AC-44000 Alloy

Abstract The work deals with the influence of change in the filling conditions of the ceramic moulds with plaster binder on the presence of gaseous porosity and the microstructure of the achieved test castings with graded wall thickness. Castings made of EN AC-44000 alloy, produced either by gravity casting, or by gravity casting with negative pressure generated around the mould (according to the Vacumetal technology), or by counter-gravity casting were compared. The results of examinations concerning the density of the produced castings indicate that no significant change in porosity was found. The increased size of silicon crystals was found for the increased wall thicknesses due to the slower cooling and solidification of castings.

Behavior of helium in steel 16Cr12W2VTaB under various implantation temperatures

Gaseous porosity formation and helium behavior have been investigated in the reduced activation ferritic–martensitic steel 16Cr12W2VTaB irradiated with 40 keV He + ions up to a fluence of 5 × 10 20 m −2 at temperatures from 290 to 900 K in two initial conditions: normalized + tempered (HT-1), and cold rolled + annealed (HT-2). After HT-1, cavitation was observed above 770 K, where bubbles with a maximum diameter 1 nm were formed. Large bubbles with a mean diameter 8 nm formed when irradiated at 900 K. On the other hand, a high density of small bubbles formed at the lower irradiation temperature of 570 K after HT-2. At 900 K, bubbles had an extremely nonuniform distribution in size, depending on their locations. The helium thermodesorption spectra had two intensive peaks owing to polymorphic transformation during heating. The peaks widened and gas release began at higher temperatures with formation of large bubbles.

Pressure and temperature changes in heat-cured acrylic resin during processing

Objectives: The aims of this study were to measure the pressure and temperature changes of acrylic resin during processing, to record the highest temperature reached when fast cured in boiling water and to determine the elevated boiling point of monomer under high pressure. Methods: A subminiature pressure transducer (temperature compensated to 94 °C) and a thermocouple were placed on the palate of a standardized maxillary complete denture base. A heat-cured resin (Trevalon C) was polymerized by a long heating cycle (72 °C for 6.5 h and 92 °C for 1.5 h). Recordings of pressure and temperature ( n=6) were made at initial clamping of denture flasks and throughout the processing cycles of resin. The temperature of the resin was also monitored during a fast cycle, which was accomplished by placing the flask directly into boiling water for 40 min. Results: The pressure of acrylic dough inside the clamped flask was initially 11.5 atm (SD=3.2) and reached a peak of 22.0 atm (SD=3.5) during the long heating cycle. The elevated boiling point of monomer at increased pressure was calculated to be about 193 °C (at 11.5 atm) and 228 °C (at 22.0 atm). These elevated boiling points are higher than the maximum temperature 131 °C (SD=6.6) reached during the fast curing cycle. No porosity was observed even in the denture bases heat-cured by the fast cycle. Significance: The highest temperature reached by heating of resin during processing is well below the elevated boiling point of monomer. Monomer therefore does not boil in clamped denture flasks under sufficient pressure. Thus adequate clamp pressure prevents gaseous porosity irrespective of curing cycle used.

The use of microwave energy to cure denture acrylic resins

Experiments have been carried out on the curing of poly(methyl methacrylate) denture base material in a microwave oven, using conventional dental flasks and flask clamps. It has been shown that it is important (a) to maintain sufficient pressure on the materials, (b) to avoid gaseous porosity by not heating too rapidly initially, and (c) to ensure that all metal is protected from exposure to microwaves. When the appropriate conditions of polymerisation were used, microwave-cured samples had satisfactory physical and mechanical properties according to American Dental Association specification number 12.

Rapid curing of acrylic denture-base materials

A rapid-cure polymerization of cure, including a terminal boil, with respect to transparency, residual monomer, mechanical properties, and generation of gaseous porosity. It was found that in order for porosity-free resin to be produced during rapid curing, a low concentration (∼0.26%) of benzoyl peroxide initiator in the powder component is vital, and a very small concentration (∼0.025%) of the chemical activator dimethyl-p-toluidine in the monomer component is an advantage. Mechanical properties were only influenced where substantial porosity existed, but it was recognized that a material “tailor-made” for rapid curing would be most welcome.

New technique for better titanium castings

Castings free of gaseous porosity are now being obtained by a double melting process. In the second melting a consumable arc furnace is used to vacuum cast titanium into expendable graphite molds.