Solidification processing

: A framework based on the relationship between variations in cooling rates and volume fraction of reinforcements during solidification processing to enhance the deformation behavior of aluminum alloy AA6061 matrix composite produced with a hybrid system of reinforcements is investigated in this study. The aluminum matrix composite with 5 %, 10 % and 20 % volume fraction of reinforcements (Al 2 O 3-SiC) was synthesized by infiltrating molten aluminum AA 6061 at a pouring temperature of 740 0 C into prefabricated preforms of reinforcements at a pressure of 80 MPa, die preheat temperature of 300 0 C and pressure holding time of 15 s using the squeeze casting method. By employing water jet spraying at the rate of 0.1, 0.2 and 0.3 kg/s and taking measurements using a K-type thermocouple, cooling rates were obtained in correspondence with varying volume fractions of reinforcements. The developed composites were sectioned and microstructural features were examined by optical microscopy. Tensile testing was conducted according to ASTM B557 standard using an MTS testing machine. It was observed that cooling rates decreased as the volume fraction of reinforcements was increased and the cooling time also increased accordingly during this process. With respect to deformation behavior, higher cooling rates are associated with an improvement in mechanical properties at 5 % and 10 % additions of hybrid reinforcement particles but this effect diminishes as the volume fraction of reinforcements was increased to 20 %. Also, the strain rate sensitivity (SRS) exponent increased considerably with strain rates and volume fraction of reinforcements, but the tensile elongation values decreased with increasing volume fraction of reinforcements; and the variations in these properties were most significant for samples containing 20% volume fraction of hybrid reinforcements. From the foregoing, it follows that an experimentally-determined optimal solidification range is critical to the enhancement of deformation parameters as the volume fraction of reinforcements is varied in a squeeze casting process.

The transport of solid crystals in the liquid pool during solidification of large ingots is known to have a significant effect on their final grain structure and macrosegregation. Numerical modeling of the associated physics is challenging since complex and strong interactions between heat and mass transfer at the microscopic and macroscopic scales must be taken into account. The paper presents a finite element multi-scale solidification model coupling nucleation, growth, and solute diffusion at the microscopic scale, represented by a single unique grain, while also including transport of the liquid and solid phases at the macroscopic scale of the ingots. The numerical resolution is based on a splitting method which sequentially describes the evolution and interaction of quantities into a transport and a growth stage. This splitting method reduces the non-linear complexity of the set of equations and is, for the first time, implemented using the finite element method. This is possible due to the introduction of an artificial diffusion in all conservation equations solved by the finite element method. Simulations with and without grain transport are compared to demonstrate the impact of solid phase transport on the solidification process as well as the formation of macrosegregation in a binary alloy (Sn-5 wt pct Pb). The model is also applied to the solidification of the binary alloy Fe-0.36 wt pct C in a domain representative of a 3.3-ton steel ingot.

Hydrogen embrittlement in 304L austenitic stainless steel fabricated by laser powder-bed-fusion (LPBF) was investigated and compared to conventionally produced 304L samples with two different processing histories; casting plus annealing (CA) and CA plus thermomechanical treatment (CA-TMT). Interestingly, no significant difference in the amount of deformation-induced α ′ martensite between the LPBF and CA-TMT samples was observed, suggesting that the solidification substructure in the LPBF sample enhanced the strength without promoting the harmful hydrogen embrittlement effect. These results are discussed in terms of the chemical inhomogeneity, hydrogen-assisted cracking behavior, and hydrogen diffusion and trapping in the present 304L samples.

A wide variety of technologies is available for the treatment of contaminated soil in both the vadose zone (originating above the water table) and saturated zone (originating below the water table). Several processes involve immobilizing soil contaminants by physically, chemically or biologically. Among them, a wide range of wastes, both solids and liquids, are being treated by "solidification / stabilization" (S/S). In solidification, by adding binding reagents, physical state of the waste being changed by encapsulating a waste to form a solid material from liquid as well as to restrict contaminant migration to leaching by decreasing the exposed surface area. Whereas stabilization through chemical reactions immobilizes the hazardous materials by reducing them to less soluble or toxic form. Characteristics of different types of reagents/additives of S/S technology both from inorganic and organic origin are presented in this paper. In-situ and ex-situ application of S/S technology and their advantages-disadvantages are discussed with basic approaches. Finally, introducing with internal and external factors influencing the long-term durability of S/S treated materials as well as monitoring & treatment management of it after processing are briefly presented.