[en] The microstructural and microchemical changes produced in a Ti endash 25Al endash 10Nb endash 3V endash 1Mo alloy (at.%) by charging at high temperatures in high pressures of hydrogen gas have been studied using TEM and x-ray methods. Hydrides incorporating all of the substitutional solutes which formed during charging have a face-centered cubic (fcc) structure and exhibit either a plate or fine-grained morphology. With increasing hydrogen content, the size of the hydrides decreases and their microchemistry changes as they approach the stable binary hydride, TiH₂. Rejection of substitutional solute elements from the hydride produces changes in the microchemistry, and consequently in the crystal structure, of the surrounding matrix. In alloys containing 50 at.% H, this solute redistribution results in the formation of an orthorhombic substitutional solid solution phase containing increased levels of Nb. The driving force for this redistribution of solutes is the reduction in the chemical potential of the system as the amount of the most stable hydride, TiH₂, forms. The hydrides reverted to a solid solution on annealing in vacuum at 1073 K, and the original microchemistry of the alloy was restored. Reversion from the hydride structure to the original α₂ ordered DO₁₉ structure proceeds via a disordered HCP phase. copyright 1996 Materials Research Society

[en] The growth of Ge(001) by molecular-beam epitaxy at temperatures T_s between 20 and 100 degree C, and deposition rates of 0.5 and 1 A s^-1, was investigated using a combination of in situ reflection high-energy electron diffraction and post-deposition cross-sectional transmission electron microscopy. All films consisted of three zones beginning with a defect-free epitaxial layer of thickness t₁ in which ln(t₁)∝(1/T_s). The second zone was a narrower intermediate layer containing {111} stacking faults and microtwins, while the third zone was amorphous. An atomistic growth model is proposed to explain the observed morphological breakdown during low-temperature growth

[en] The evolution of microstructure in Mo-Cu thin films during annealing has been investigated by in situ sheet resistance measurements, ex situ x-ray diffraction, and in situ hot-stage as well as conventional transmission electron microscopy. Mo-Cu thin films, deposited on various glass substrates by magnetron sputtering at ∼30 degree C, were supersaturated solid solutions of Cu in Mo with a nanocrystalline microstructure. The as-deposited films had large compressive residual stresses owing to the low homologous deposition temperature and low Ar pressure during deposition. Annealing results showed two distinct sets of microstructural changes occurring in the temperature ranges between ∼300 and 500 degree C, and ∼525 and 810 degree C. In the lower-temperature range, anisotropic growth of nanocrystallites was accompanied by stress relaxation without any observable phase separation. At temperatures greater than ∼525 degree C, the metastable solid solution collapsed and Cu precipitated at the grain boundaries. Increasing temperature resulted in the coarsening of Cu precipitates and simultaneous growth of Mo grains. At temperatures greater than ∼700 degree C, phase separation and grain growth approached completion. copyright 1995 American Institute of Physics