Casting Microstructures

In order to start the multiscale modeling, internal state variables were adopted to reflect void/crack nucleation, void growth, and void coalescence from the casting microstructural features (porosity and particles) under different temperatures, strain rates, and deformation paths [115, 116, 221, 283]. Furthermore, internal state variables were used to reflect the dislocation density evolution that affects the work hardening rate and, thus, stress state under different temperatures and strain rates [25, 283-285]. In order to determine the pertinent effects of the microstructural features to be admitted into the internal state variable theory, several different length scale analyses were performed. Once the pertinent microstructural features were determined and included in the macroscale internal state variable model, notch tests [216, 286] and control arm tests were performed to validate the model s precision. After the validation process, optimization studies were performed to reduce the weight of the control arm [287-289]. 

Microstructure evolution in solids formed from a melt is important in processes such as prilling or casting. For example, in aluminum alloy shape casting the final microstructure depends directly on the as-cast microstructure since the only post-casting process is the heat treatment. The micro-porosity formed owing to the combined effects of the volumetric shrinkage upon the solidification of the melt and the precipitation of the dissolved hydrogen affects the final properties of the aluminum alloy. 

The purpose of the present work is to provide a systematic compilation of solidification data, describing the formation of the as-cast microstructures in steels of technical importance. The compositions have been chosen to cover a large part of the spectrum of steels in current production. Where a specific steel is not included, it should be possible to gain an outline of its solidification characteristics from related compositions present. 

Fig. 10.6. As cast microstructure of Cu-O alloy with 0.78% oxygen content. The dendritic regions are CU2O. Micrograph 2257 from Metals Handbook (ASM 1972).

KEYWORDS functionally graded material, centrifugal cast, microstructure, mechanical property, TiC, Al alloy... 

One-step processing for superplasticity from cast sheet or hot-pressed powder metallurgy sheet A conventionally cast microstructure can be converted to a superplastic microstructure in many steps. The present process of microstructural refinement can be used directly on cast sheets. This leads to very economical manufacturing. Ma et al. (Ref 46)... 

The stress-relieved and refined FSP microstructures have shallower dealloyed layers than the coarse as-cast microstructures, because dealloying is confined to manganese-rich regions... 

Sn-5Sb solder has a near-peritectic composition and a relatively high-liquidus temperature, around 238°C, which is significantly higher than the melting point of eutectic Sn-Pb solder, 183°C. Unlike other alloying elements, the addition of Sb to Sn raises the melting point of Sn gradually as the solid solubility of Sb in Sn increases [49]. The peritectic reaction, which occurs near 246 ° C, produces Sn- Sb microstructures which are complex. A typical cast microstructure of Sn-5Sb alloy solidified rapidly is shown in Fig. 2. This microstructure exhibits coarse dendrites of Sn-rich solid solution with Sn Sb intermetallic compounds dispersed between the dendrites. 

Addition of Sn could eliminate the pesting oxidation damage at low temperatures and further decrease oxidation rate by working together with Ti addition [292,303,305]. It was found that Sn has a significant effect on the niobium solid solution, leading to the formation of Sn-rich and Sn-poor parts in the solid solution in the as-cast microstructure. In the presence of Sn, the Si solubility in Nbss increases considerably while... 

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