E. Poggio

Bio: E. Poggio is an academic researcher. The author has contributed to research in topics: Diffusion (business) & Surface-area-to-volume ratio. The author has an hindex of 2, co-authored 3 publications receiving 25 citations.

Microstructural and mechanical characterisation of some sinter hardening alloys and comparisons with heat treated PM steels

Abstract: Four grades of sinter hardening materials have been compared, using industrial equipment. Three powder types were completely prealloyed; the last one was a hybrid, combining prealloying and diffusion bonding. Different amounts of Cu have been added by mixing. The lubricated mixes, containing 0.6% graphite, have been compacted at different pressures, to form gears at green densities ≥7.0 g cm−3 ; the compacts have been sintered at 1120°C, under endogas from methane and fast cooled (at least 7 K s−1 within the range 850–400°C). The final step has been stress relieving, at 180°C, for 1 h. Material properties have been investigated, focusing on porosity, pore shape, hardness, microhardness, microstructure, local chemical composition and mechanical properties. For comparison, other gears, compacted in the same tool and at the same density level, but manufactured according to a more conventional cycle, i.e. starting from less alloyed powders and adding carbonitriding, quenching and stress relieving, ha...

Influence of density and surface/volume ratio on the cooling rate of sinter-hardening materials

Abstract: A numerical approach has been adopted to investigate the influence of porosity and surface/volume ratio on the cooling rate of sinter-hardening steels. Parallelepipeds (rectangular prisms) of constant cross section and different heights were compacted at two different densities (6.8 and 7.0 g/cm 3 ) from a hybrid traditional diffusion-bonded powder and sintered at 1120°C, for 25 minutes, in industrial sinter-hardening equipment. During sintering and fast cooling periods, the temperature at the core of 25 mm height rectangular prism has been recorded. Through a mathematical approach, the heat transfer coefficients at the boundaries of the prism have been calculated from the experimental temperature values. Due to asymmetric flow during fast cooling in the sintering furnace, the boundary condition on the upper surface was considered to be different from the lateral and the lower surfaces. After specifying the boundary conditions, the direct problem has been formulated in order to calculate the temperature distribution as a function of time inside parallelepipeds characterized by different surface/volume ratios. These equations were solved using a commercial finite volumes numerical code. The results obtained show that the cooling rate depends on density: the higher the density, the lower the cooling rate, i.e. the influence of porosity on material hardenability is positive.

Effect of Sinter Hardening on Microstructure and Mechanical Properties of Astaloy 85Mo

Abstract: Effect of sinter hardening on the microstructure, density, hardness and tensile properties of Astaloy 85Mo+ 0.7% graphite was investigated. For this purpose, Astaloy 85Mo, a pre-alloyed powder, was mixed with 0.7% UF4 graphite and then pressed in single action die and sintered at 1120 °C for 30 min in N 2 -10%H 2 atmosphere. Then samples were cooled from 0. 5 to 3 °C/s sintering temperature in accordance with different cooling rates. The difference in microstructure, hardness, density and tensile properties of the samples associated with different cooling rates from sintering temperature has been investigated. The results show that the microstructure remains bainitic by changing cooling rate, but it becomes finer and then the hardness and tensile strength of the samples will increase by increasing the cooling rate from sintering temperature.

Powder metallurgy steels for highly loaded precision parts

Abstract: Ferrous powder metallurgy precision components are increasingly being used for highly loaded applications. This requires consistent improvement in materials properties without sacrificing geometrical precision. Here, the various approaches for obtaining this goal are discussed. The relationships between density/porosity and properties, especially fatigue, are described, as is the effect of higher sintering temperatures. The resulting requirements towards equipment are discussed, and the consequences of sintering Cr and Mn containing steels for the sintering atmosphere are shown. Secondary operations performed in PM parts production are described and typical examples for high performance PM parts are shown, and the dominating trends are identified.

Microstructure of Laser-MAG Hybrid Welds of Sintered P/M Steel

Abstract: The microstructure and mechanical properties of iron-based powder metallurgical steels jointed by CO2 laser-metal active gas (MAG) hybrid welding were investigated. The cross-sectional morphology of hybrid weld bead consisted of arc zone and laser zone. The microstructure of arc zone consisted of columnar dendrite and fine acicular dendrite between the columnar dendrites, but that of laser zone was composed of fine equiaxed dendrite. The MAG weld had obvious heat-affected zone (HAZ) zone, while hybrid weld had very narrow HAZ zone because of the rapid cooling rate. The phase constitutions of the joint determined by x-ray diffraction were α-Fe (ferrite) and Cu. The 2θ value of α-Fe (200) peaks of hybrid weld was smaller than that of sintering compact. Compared to MAG weld, hybrid weld had finer grain size, higher micro-hardness, and higher micro-strain, which was caused by the difference of cooling rate and crystallizing.