Microstructure, Properties and Atomic Level Strain in Severely Deformed Rare Metal Niobium

Abstract

The mechanical and physical properties relationship from atomic level strain/stress causes dislocation density and electrical conductivity relationship, as well as crystallites deformation and hkl-parameter change in the severely deformed pure refractory rare metal Nb at ambient temperature and during short processing times. The above mentioned issues are discussed in this study.

For ultrafine-grained and nanocrystalline microstructure forming in metal the equal-channel angular pressing and hard cyclic viscoplastic deformation were used. The flat deformation and heat treatment at different parameters were conducted as follows. The focused ion beam method was used for micrometric measures samples manufacturied under nanocrystalline microstructure study by transmission electron microscope. The microstructure features of metal were studied under different orientations by X-ray diffraction scattering method, and according to the atomic level strains, dislocation density, hkl-parameters and crystallite sizes were calculated by different computation methods.

According to results the evolutions of atomic level strains/stresses, induced by processing features have great influence on the microstructure and advanced properties forming in pure Nb. Due to cumulative strain increase the tensile stress and hardness were increased significantly. In this case the dislocation density of Nb varies from 5.0E+10 cm^–2 to 2.0E+11 cm^–2. The samples from Nb at maximal atomic level strain in the (110) and (211) directions have the maximal values of hkl-parameters, highest tensile strength and hardness but minimal electrical conductivity. The crystallite size was minimal and relative atomic level strain maximal in (211) orientation of crystal. Next, flat deformation and heat treatment increase the atomic level parameters of severely deformed metal.

DOI: http://dx.doi.org/10.5755/j01.ms.18.4.3091