SEMINAR: Anisotropic mechanical behaviour in some titanium and magnesium alloys
Friday, January 15, 2010
When
Friday 15 January 2010 – 3pm to 4pm
Where
Faculty of Engineering & Industrial Sciences - Swinburne University of Technology
EN Building, Hawthorn Campus – Lecture Room EN101 (Melway Map 45 E10)
Anisotropic mechanical behaviour in some titanium and magnesium alloys
Prof. Bevis Hutchinson*
- Swerea-KIMAB (formerly Swedish Institute for Metals Research)
- Stockholm, Sweden
- Visiting Fellow at ITRI, Deakin University
Abstract
Plastic behaviour of hexagonal metals usually differs significantly from that in the common structural metals that have cubic crystal structures. Several different types of slip system may be activated, having individual critical resolved shear stresses (CRSS), while mechanical twinning is also a prominent deformation mechanism in most cases. In combination with the strong crystallographic textures that often exist in hexagonal metals, these mechanisms can lead to plastic behaviour that varies markedly depending on the applied stress state and temperature. Plasticity is characterised by significant deviations from the von Mises and Lévy-Mises rules. For example, in some cases the strength in tension is much greater than in compression while in other cases the opposite is true. Values of the plastic strain ratio in uniaxial tests (r-value) may vary strongly with temperature and, in some situations, may even be negative.
This presentation will include observations on titanium 6/4 alloy having different textures and compare this with the behaviour with some magnesium alloys including AZ31, ZM61 and binary Mg-RE alloys.
It is shown that mechanical testing to evaluate the yield locus under biaxial loading conditions can be helpful in analysing the role of different deformation mechanisms. Twinning together with slip of <a> dislocations on different planes are the usual deformation modes. However, glide of <c+a> dislocations can also be activated and this as associated with an unusual asymmetry in the CRSS. Furthermore, in the AZ31 alloy there is clear evidence that grain boundary sliding or local deformation in the vicinity of grain boundaries plays an important role at temperatures as low as 150ºC, at least in fine grained material.
*Bevis Hutchinson (bevis@kimab.com) obtained his Bachelor degree in metallurgy at the University of Manchester in 1965 and studied for his doctorate in the University of Birmingham under the guidance of Prof. Ian Dillamore, receiving the Ph.D. degree in 1969. He continued in the academic sphere, as lecturer and senior lecturer in Birmingham, until 1982, teaching and supervising research, later receiving from the university the degree of Doctor of Science. Since 1982, Prof. Hutchinson has been a research leader and manager at the Swedish Institute for Metals Research in Stockholm. The title of Professor was conferred by the Swedish State in 1991. From 1992 until 1997 he was Chairman for the Swedish Society for Materials Technology. Prof. Hutchinson is a Member of the Royal Swedish Academy of Engineering Sciences and a Fellow of the Royal Academy of Engineering in the UK.