2 research outputs found
Nanocrystalline High-Entropy Alloys: A New Paradigm in High-Temperature Strength and Stability
Metals
with nanometer-scale grains or nanocrystalline metals exhibit
high strengths at ambient conditions, yet their strengths substantially
decrease with increasing temperature, rendering them unsuitable for
usage at high temperatures. Here, we show that a nanocrystalline high-entropy
alloy (HEA) retains an extraordinarily high yield strength over 5
GPa up to 600 °C, 1 order of magnitude higher than that of its
coarse-grained form and 5 times higher than that of its single-crystalline
equivalent. As a result, such nanostructured HEAs reveal strengthening
figures of merit–normalized strength by the shear modulus above
1/50 and strength-to-density ratios above 0.4 MJ/kg, which are substantially
higher than any previously reported values for nanocrystalline metals
in the same homologous temperature range, as well as low strain-rate
sensitivity of ∼0.005. Nanocrystalline HEAs with these properties
represent a new class of nanomaterials for high-stress and high-temperature
applications in aerospace, civilian infrastructure, and energy sectors
Microscale Fracture Behavior of Single Crystal Silicon Beams at Elevated Temperatures
The micromechanical
fracture behavior of Si [100] was investigated as a function of temperature
in the scanning electron microscope with a nanoindenter. A gradual
increase in <i>K</i><sub>C</sub> was observed with temperature,
in contrast to sharp transitions reported earlier for macro-Si. A
transition in cracking mechanism via crack branching occurs at ∼300
°C accompanied by multiple load drops. This reveals that onset
of small-scale plasticity plays an important role in the brittle-to-ductile
transition of miniaturized Si