Stable Eutectic Formation in Spray-Formed Cast Iron
- PDF / 2,939,373 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 61 Downloads / 198 Views
PRAY forming is an advanced casting process that allows the production of billets, sheets, and tubular preforms with refined microstructure directly from the liquid. There are several reports of numerous sprayformed alloys such as Al-based alloys,[1–7] high alloy tool steels,[8–13] Ni-based superalloys,[14–16] and high-chromium cast irons,[17–20] among others.[21–25] Spray-formed microstructures are typically composed of equiaxed grains with diameter ranging from 10 to 100 lm, complete absence of columnar/dendritic morphologies, high levels of microstructural homogeneity, and low macro-segregation levels.[26,27] Such microstructural features are obtained regardless the alloy system, making spray forming a good choice for manufacturing alloy compositions whose high metallurgical quality is difficult to be achieved by conventional casting processes. Although the advantageous microstructure of spray-formed materials is well known, how the microstructure evolves during
GUILHERME ZEPON, JULIA F.M. FERNANDES, and CLAUDEMIRO BOLFARINI are with the Department of Materials Engineering, Federal University of Sa˜o Carlos (UFSCar), Sa˜o Carlos, SP 13565-905, Brazil. Contact e-mail: [email protected] LUCAS B. OTANI is with the Graduate Program of Materials Science and Engineering, Federal University of Sa˜o Carlos (UFSCar), Sa˜o Carlos, SP 13565-905, Brazil. Manuscript submitted April 27, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
atomization and deposition to give rise to the final spray-formed structure is not yet completely clear in literature. The complexity of the microstructural evolution in spray forming comes from its sequential steps: (i) atomization and (ii) deposition. At atomization, the melt stream is gas atomized to produce a spray cone composed of alloy droplets with diameter ranging from 10 to 50 lm. At this stage, the liquid droplets are cooled at high rates (102 to 104 K s1) and accelerated up to 100 m s1[26,28] Therefore, during flight, some of the droplets solidify under high cooling rates. At the deposition stage, the atomized droplets, which may be fully liquid, partially solid, and completely solid, are deposited onto a substrate generating the bulk material. The cooling rates measured during deposition are considerably lower than those measured during atomization, between 0.1 and 10 K s1, depending on the alloy properties and process conditions. The final microstructure of a spray-formed alloy will strongly depend on what happens with the microstructure of the gas-atomized droplets. Many authors have reported spray forming as a rapid solidification technique because of the atomization step and the microstructural features of spray-formed alloys. In 2007, in a theoretical and experimental work, Grant[26] proposed that the atomized droplets, once arriving in the deposition zone, are rapidly thermo equilibrated in relation to each other. Because of this thermal equilibration, the completely solidified droplets
can be partially remelted and the remaining solid fraction in the deposition zone acts as inocul
Data Loading...
