Nucleation and Growth Dynamics of Equiaxed Dendrites in Thin Metallic Al–Cu and Al–Ge Samples in Microgravity and on Earth

Abstract In this study, the nucleation and growth characteristics of equiaxed dendrites in near-isothermal solidification experiments, performed during two sounding rocket missions, MAPHEUS-6 7, are investigated. Two samples composition Al–15 wt pct Cu one sample Al–46 Ge were processed microgravity several on ground. situ X-radiography was to observe dynamics microstructure evolution 200 µ m thin, disc-shaped samples. The measured dendritic rates observed concentration distributions liquid indicate no difference between on-ground horizontal line with previous observations. On contrary, a behavior found. all experiments bursts observed, which is different from comparable where occurs continuously. combined analyses suggest that small variations fields probably originate convective flow buoyancy grains lead spatially variable undercooling distribution hence continuous nucleation. contrast, absence results more uniform distribution. therefore nucleate at surface walls, when necessary reached.