Mechanism of structure formation in a metastable melt and estimation of its spatial scale

An estimate of the dendritic parameter based on the assumption of the formation of the spatial structure of the solid phase in a metastable supercooled melt (MSM) is proposed. The solidification of MSM is considered in the quasichemical approximation, which assumes a transition state corresponding to the ideal solution system. It is shown, that the dimensions of the structural cell depend on the ratio of the diffusion rate within the cell and the rate of heat removal. The theoretical estimate of the structure parameter is consistent with the experimental dependence. Keywords: metastable melt, dendritic parameter, cooling rate, segregation zone, diffusion. [email protected]

Researching structire and properties of metal-powdered compositions made of corrosion-resistant steels obtained by gas atomization of alloy and intended for detail production by selective laser alloying

Investigations of the microstructure and technological properties (such as flow ability, bulk density, tapped density etc.) of novel Fe–Cr–Ni, Fe–Cr–Ni–Mo and Fe–Cr–Ni–Co–Mo stainless steel metal powders were carried on. These powders are intended for use in additive manufacturing processes. Morphology of the powders was researched and the dendritic parameter was estimated for powder particles with various sizes (diameters). Dependence of gas impurities contamination on particles size was determined. Complex of these investigations allows confirming high quality of metal powders for additive manufacturing processes. In particular, minimal value of flow ability was determined as 14 sec while standard requirements for additive technologies are within 20 sec.

Effect of Semisolid Metal Casting of Large Forging Ingots on Quality of Large-Sized Forgings Produced

The paper reports the findings on the effect of various casting methods on the quality and development of primary dendritic structure in large-sized forging ingots of steel 38ХН3МФА. One ingot was teemed as per a conventional teeming method while the other was teemed with an inoculated metal stream. It was established that the dendritic parameter value in the inoculated ingot is much smaller than that in the conventional ingot. Consequently, the solidification process occurs at a higher rate in the inoculated ingot compared with that in the conventional ingot, and this assumption is supported by a more homogeneous dendritic structure. It is demonstrated that disperse inoculants positively affect the structure, physical and chemical homogeneity as well as the mechanical properties of cast metal. This finding is clearly supported by the examination of the forgings made of the conventionally teemed ingot and the one teemed with an inoculated stream. When inoculants were introduced in the metal stream, total chemical heterogeneity increased on the average by 1.2-2 times. It is established that the best results for the inoculation casting method are achieved when 2.4-2.6% inoculants are introduced in the stream. Such quantity of inoculants forms at a distance of 5 meters between the guiding pipe and the hot top.

The Influence of Cooling Rate on Structure of EN AC 5083 Aluminum Alloy

In this paper it was studied the structure of EN AC 5083 aluminum alloy depending on cooling conditions. By cooling curves recorded for different casting conditions there were calculated the cooling rate (vr). The structural analyzes, performed by Image Pro-Plus 6.0 software, allowed both be highlighted structural particularities of various conditions for casting and establishing the correlation: lg d = lg v + n (where d is the dendritic parameter).