Microstructure investigations of ball milled materials

Abstract

HREM and FEG TEM were emphasized and extensively used to follow the most subtle changes in the structure and composition of ball‐milled Cu, Fe‐Cu, and thermally decomposed Fe60Cu40. Some significant results are obtained and summarized as follows: HREM shows that the deformation of ball‐milled copper proceeds mainly by twinning and shear bands (SBs) formation. The nano‐grains formed during ball milling (BM) contain a high density of dislocations. The grain boundaries (GBs) of nanocrystalline (NC) Cu prepared by BM are ordered, curved, and strained, but disordering, lattice distortion, and nanovoids in local regions were frequently observed. Nanoscale composition analysis on mechanically alloyed Fe16Cu84 shows that the average Fe content in both the interior of grains and the GBs is close to the designed composition, which proves that a supersaturated solid solution has really formed. However, the Fe content is rather inhomogeneous between the larger and smaller grains, which infers the inhomogeneous mixing of Fe and Cu during mechanical alloying (MA). NC structure and the mechanical force‐enhanced fast diffusion are the reasons of the formation of supersaturated solid solutions in immiscible systems with positive enthalpy of mixing. HREM observations carried out with the thermally decomposed Fe60Cu40 solid solution show that the Nishiyama (N‐W) or Kurdyumov‐Sachs (K‐S) orientation relationships exist between α‐Fe and Cu. Energy dispersive X‐ray spectra (EDXS) results show that the Cu content in these α‐Fe grains reaches as high as 9.5 at.% even after heating to 1,400°C, which is even higher than the maximum solubility of Cu in γ‐Fe at 1,094°C. Microsc. Res. Tech. 40:101–121, 1998. © 1998 Wiley‐Liss, Inc.

Temperature induced phase transformations and microstructural changes in nanostructured FeCu solid solutions using in situ neutron powder thermo-diffraction

“…It must be pointed out that the intensity is normalized for all the patterns. The pattern obtained at 300 K for the as-milled powders show a broad peak, as mentioned above, corresponding to a fcc (bcc) phase in Fe 15 Cu 85 (Fe 85 Cu 15 ) sample. The width of the peaks decreases when the temperature reaches 770 K, indicating thermal relaxation of the microstructure.…”

Effect of gallium doping and ball milling process on the thermoelectric performance of n-type ZnO

“…1(a)]. HE ball milling is known to produce lattice disorders and high density of point defects, [17][18][19] which might act as carrier scatterers due to which the resistivity of HE sample is higher than LE sample. It appears that the differences in the properties of the samples prepared through three different ball milling conditions are not completely intrinsic but strongly depended on the sample preparation method.…”

“…This kind of void formation has been reported for other systems as well. 18 Field emission scanning electron microscopy (FESEM) images [Figs. 2(a) and 2(b)] of the surface and the cross section of the as-sintered Zn 0.995 Ga 0.005 O (HE wet milled) sample show a dense microstructure, which consists of voids, roughly ;900 nm in size.…”

Microstructural features and properties of high-hardness and heat-resistant dispersion strengthened copper by reaction milling

“…During milling, heavy deformation is introduced into the particles. This is manifested by the presence of a variety of crystal defects, such as dislocations, vacancies, stacking faults, and increased number of grain boundaries [22] . The presence of this defect structure decreases the diffusion distances and increases the diffusivity of oxygen absorbed on the particle surface into the copper matrix at low temperature.…”