ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
A commercially pure niobium has been subjected to SPD at room temperature ( ~0.11TM) via ECAP (90º, route BC) up to 16 passes and via HPT up to shear strains γ =1000. ECAP-edsamples show an equiaxed structure after 8 and 16 passes with a decreasing average grain size. Theresults show that both the microstructure and mechanical properties of ECAP-ed samples do notreach a steady state up to at least 16 passes. HPT samples show at outer region a finer structural sizebut similar hardness values at similar equivalent strains. The nanoindentation results show anevident indentation size-effect even for the most deformed samples. The hardness values at the nanolevel converge for the recrystallized, the ECAP-ed and the HPT samples. This implies that, at thenano level, when the geometrically necessary dislocation density overcomes significantly the(initial) statistically stored dislocation density, hardness depends mainly on the physical intrinsicproperties of the material (Burgers modulus, bulk modulus...) and the contribution of bulkmechanical properties (i.e., bulk yield strength) to hardness is smoothed down. Strain-ratesensitivity (SRS) of plastic strength has been also measured by means of rate-jump nanoindentationtests. The SRS is proportional to the inverse of hardness
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.215.pdf
