Vat Photopolymerization of Cemented Carbide Specimen

Numerous studies show that vat photopolymerization enables near-net-shape printing of ceramics and plastics with complex geometries. In this study, vat photopolymerization was investigated for cemented carbide specimens. Custom-developed photosensitive WC-12 Co (wt%) slurries were used for printing green bodies. The samples were examined for defects using quantitative microstructure analysis. A thermogravimetric analysis was performed to develop a debinding program for the green bodies. After sintering, the microstructure and surface roughness were evaluated. As mechanical parameters, Vickers hardness and Palmqvist fracture toughness were considered. A linear shrinkage of 26–27% was determined. The remaining porosity fraction was 9.0%. No free graphite formation, and almost no η-phase formation occurred. WC grain growth was observed. 76% of the WC grains measured were in the suitable size range for metal cutting tool applications. A hardness of 1157 HV10 and a Palmqvist fracture toughness of 12 MPam was achieved. The achieved microstructure exhibits a high porosity fraction and local cracks. As a result, vat photopolymerization can become an alternative forming method for cemented carbide components if the amount of residual porosity and defects can be reduced.

Instrumented Indentation of Super-Insulating Silica Compacts

Highly porous silica compacts for superinsulation were characterized by instrumented indentation. Samples showed a multi-scale stacking of silica particles with a total porous fraction of 90 vol %. The two main sources of silica available for the superinsulation market were considered: fumed silica and precipitated silica. The compacts processed with these two silica displayed different mechanical properties at a similar porosity fraction, thus leading to different usage properties, as the superinsulation market requires sufficient mechanical properties at the lowest density. The measurement of Young’s modulus and hardness was possible with spherical indentation, which is an efficient method for characterizing highly porous structures. Comparison of the mechanical parameters measured on silica compacts and silica aerogels available from the literature was made. Differences in mechanical properties between fumed and precipitated compacts were explained by structural organization.

Influence of porosity on the fatigue behaviour of additively fabricated TA6V alloys

This work is focused on the influence of porosity when dealing with the fatigue behaviour of the TA6V alloys fabricated by the selective laser melting (SLM) process. The presence of porosity is one of the major issue facing additive manufacturing (AM) of metallic components subjected to fatigue loading. In order to study the effect of porosity on the fatigue behaviour, a vast experimental campaign has been undertaken. These materials are fabricated by the SLM process with different building directions (horizontal, vertical and diagonal) thanks to which specimen batches with different pore sizes are obtained. It is observed that despite a low porosity fraction (around 0.01%), the influence of pores on the fatigue strength of the materials is pronounced. A mapping approach is presented, which links the applied stress, the pore size and the fatigue life. This approach makes it possible to accurately characterize the effect of the porosity size, and also to construct Kitagawa-Takahashi diagrams from S-N data.

Image Analysis Software for Porosity Measurements in Some Powder Metallurgy Alloys

The present research was aimed to study the porosity in some powder metallurgy (P/M) alloys using an image analysis software. The porosity in P/M parts is an important parameter because is affecting the mechanical properties. Also, porosity is in correlation with processing parameters such as green density, alloying elements, particle size. The conventional method for porosity measurements of powder metallurgy products is using the density technique. Another method for porosity measurements was using an image processing software and by applying filters and adjustments the detection of the pores (black areas) was done. Two types of powders obtained by water amotization were subjected to analyze. To obtain the green compacts, the powders were pressed at 600 MPa using a single die action. The green compacts were sintered in a laboratory furnace at 1150o C for 30 and 120 minutes. A metallographic analysis was performed for porosity measurements. The pore’s shape and porosity fraction were measured using both conventional and image analysis techniques. The porosity measurements for sitnered specimens obtained from image analysis was slightly higher than that from density technique.

Experimental analysis on metallic foams-a response surface methodology approach

This study aimed to fabricate metallic porous materials using powder metallurgy (PM) space-holder technique. In the PM route, Al powder was mixed with different ratios (7%, 10%, and 20%) and sizes (500 and 1000 μm) of sodium chloride granules as space-holder agent. The mixture was then compacted at different compacting pressures (150, 200, and 250 MPa) and then heated to 280 °C for sintering. Subsequently, sodium chloride granules were removed by dissolving in water to obtain the porous structure. Tests were performed on all porous Al specimens, and characteristics such as density and porosity were measured. A statistical approach was used to optimize processing parameters. ANOVA statistical tool was used to obtain the final evaluation of the most significant features, namely, relative density and porosity fraction.

Mechanical Properties of Al-Si-Mg Alloy Castings as a Function of Structure Refinement and Porosity Fraction

During design of the casting products technology, an important issue is a possibility of prediction of mechanical properties resulting from the course of the casting solidification process. Frequently there is a need for relations describing mechanical properties of silumin alloys as a function of phase refinement in a structure and a porosity fraction, and relations describing phase refinement in the structure and the porosity fraction as a function of solidification conditions. The study was conducted on castings of a 22 mm thick plate, made of EN AC-AlSi7Mg0,3 alloy in moulds: of quartz sand, of quartz sand with chill and in permanent moulds. On the basis of cooling curves, values of cooling rate in various casting parts were calculated. The paper also presents results of examination of distance between arms in dendrites of a solid solution α (DASL), precipitations length of silicon in an eutectic (DlSi) and gas-shrinkage porosity (Por) as a function of cooling rate. Statistical relations of DASL, DlSi, Por as a function of cooling rate and statistical multiparameter dependencies describing mechanical properties (tensile strength, yield strength, elongation) of alloy as a function of DASL, DlSi and Por are also presented in the paper.

X-Ray Microtomography Studies of Tannin-Derived Organic and Carbon Foams

Tannin-based rigid foams of different bulk densities and their carbonized counterparts were investigated for the first time by X-ray microtomography. This method allowed acquisition of three-dimensional pictures of such highly porous materials. Through mathematical treatment of the images, extremely useful physical characteristics such as porosity, fraction of open cells, connectivity, tortuosity, and pore-size distribution were determined as a function of the foam's density. The obtained information was compared with independent data derived from pycnometry measurements and scanning electron microscope image analysis. The agreement was shown to be acceptable in the limit of the accuracy of the laboratory microtomograph (4 μm). Moreover, recalculating properties like permeability were shown to be quite possible based on the results of standard microtomography data.

A Model for Comprehensive Studies of Porosity in Mesoporous Low-K Dielectrics

The successful integration of a porous low dielectric constant (k) material as an interlevel dielectric depends on the morphology of the embedded porosity. Simple site percolation models are utilized here to investigate porosity properties of low-kdielectrics with respect to the current technology trends. Significant differences between two generations of porous dielectrics,k< 2.4 andk< 2.1, are found. The porosity fraction in the latter is above the percolation threshold, which may have serious impact on the materials physical properties and its compatibility with production steps.