2 research outputs found
Properties and influence of microstructure and crystal defects in FeVAl modified by laser surface remelting
Laser surface remelting can be used to manipulate the microstructure of cast
material. Here, we present a detailed analysis of the microstructure of
FeVAl following laser surface remelting. Within the melt pool, elongated
grains grow nearly epitaxially from the heat-affected zone. These grains are
separated by low-angle grain boundaries with 1{\deg}-5{\deg} misorientations.
Segregation of vanadium, carbon, and nitrogen at grain boundaries and
dislocations is observed using atom probe tomography. The local electrical
resistivity was measured by an in-situ four-point-probe technique. A smaller
increase in electrical resistivity is observed at these low-angle grain
boundaries compared to high-angle grain boundaries in a cast sample. This
indicates that grain boundary engineering could potentially be used to
manipulate thermoelectric properties
Microstructure of a spark-plasma-sintered Fe2VAl-type Heusler alloy for thermoelectric application
The influence of microstructure on thermoelectricity is increasingly
recognized. Approaches for microstructural engineering can hence be exploited
to enhance thermoelectric performance, particularly through manipulating
crystalline defects, their structure, and composition. Here, we focus on a
full-Heusler Fe2VAl-based compound that is one of the most promising
thermoelectric materials containing only Earth-abundant, non-toxic elements. A
Fe2VTa0.05Al0.95 cast alloy was atomized under a nitrogen-rich atmosphere to
induce nitride precipitation. Nanometer- to micrometer-scale microstructural
investigations by advanced scanning electron microscopy and atom probe
tomography (APT) are performed on the powder first and then on the material
consolidated by spark-plasma sintering for an increasing time. APT reveals an
unexpected pick-up of additional impurities from atomization, namely W and Mo.
The microstructure is then correlated with local and global measurements of the
thermoelectric properties. At grain boundaries, segregation and precipitation
locally reduce the electrical resistivity, as evidenced by in-situ four-point
probe measurements. The final microstructure contains a hierarchy of structural
defects, including individual point defects, dislocations, grain boundaries,
and precipitates, that allow for a strong decrease in thermal conductivity. In
combination, these effects provide an appreciable increase in thermoelectric
performance