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@MISC{Raabe:396846,
      author       = {Raabe, Dierk and Zhang, Jian},
      title        = {{G}um metals pave the way for new applications},
      reportid     = {PUBDB-2017-12926},
      year         = {2017},
      abstract     = {Metals which can be bent as gum pave the way for new
                      industrial applications for example in the aerospace
                      industry. These so-called gum metals exist but the mechanism
                      behind this behaviour was still unsettled and thus difficult
                      to be used for applications. Scientists from the
                      Max-Planck-Institut für Eisenforschung (MPIE) in
                      Düsseldorf have observed a new phase transformation in a
                      titanium alloy that could further our understanding of
                      exactly this behaviour whereby the term “phase” refers
                      to the crystal structure in which the atoms are arranged.The
                      material scientists of the MPIE used X-rays to reveal the
                      inner structure of a special alloy consisting of titanium,
                      niobium, tantalum and zirconium. This titanium alloy
                      displays some unusual mechanical properties under mechanical
                      stress: “On being deformed, it does not become harder or
                      brittle, the way metals usually do, but instead it bends,
                      almost like honey. In scientific terms, it has a very low
                      elastic stiffness and very high ductility,” explains Dierk
                      Raabe, director at the MPIE.This makes the alloy extremely
                      attractive for various industrial applications. In the
                      aerospace industry, for example, it can be used as a kind of
                      crash absorber. “When an aircraft’s turbine is damaged
                      by hail or a bird strike, there is a risk that individual
                      parts may shatter and damage the fuselage too. If parts of
                      the protective casing around a turbine were made of this
                      type of gum metal, they could capture the flying debris
                      because the impact would not destroy but only deform
                      them,” says Raabe.The researchers have revealed
                      peculiarities in its nanostructure using various techniques
                      like X-rays, transmission electron microscopy and atom probe
                      tomography. Titanium alloys normally occur in two different
                      phases. At room temperature, the atoms are usually found in
                      the so-called alpha phase, at high temperatures they switch
                      to the beta phase. The metals display different properties,
                      depending on which phase they occur in. Gum metals primarily
                      consist of the beta phase, which is stable at room
                      temperature in the case of these alloys.With the help of
                      X-rays at the accelerator centre DESY the Max Planck
                      scientists were able to analyse the crystal structure of the
                      alloy during the transition. “When you shine X-rays onto a
                      sample, the radiation is reflected by the crystal lattice.
                      This produces a distinct pattern of reflections, a so-called
                      diffractogram, from which we are able to deduce the relative
                      positions of the atoms, in other words the crystal structure
                      that they adopt,” explains Ann-Christin Dippel, who was in
                      charge of the X-rays experiments at the DESY measuring
                      station.This way the researchers at the MPIE have discovered
                      a new mechanism during the phase transformation. The team of
                      Jian Zhang has observed a new structure, which forms when
                      the beta phase is transformed into the alpha phase: the
                      omega phase. If the beta phase is cooled down rapidly from a
                      high temperature, some of the atoms change position to adopt
                      the energetically more favourable arrangement of the alpha
                      phase. The movements of these atoms lead to mechanical
                      stress along the phase boundary, almost as if the different
                      phases were tugging on each other. When this stress exceeds
                      a critical value, a new arrangement is adopted, the
                      so-called omega phase. “This newly discovered structure
                      only arises when sheer stress is generated at the phase
                      boundary, and it facilitates the transformation of the alpha
                      into the beta phase. It can only exist between two other
                      phases because it is stabilised by them,” reports Raabe.
                      When the stress drops below the critical value because of
                      the new layer, a new alpha phase layer is formed bordering
                      on an omega phase. This results in a microstructure
                      consisting of lots of layers, some of them on an atomic
                      scale, each having a different structure. This transition
                      also occurs when static forces are applied and is completely
                      reversible. The scientists are now hoping that the newly
                      discovered structure will help them to better understand the
                      properties of this material and later to develop new,
                      improved varieties of titanium alloys.},
      cin          = {DOOR / FS-PE},
      cid          = {I:(DE-H253)HAS-User-20120731 / I:(DE-H253)FS-PE-20120731},
      pnm          = {6G3 - PETRA III (POF3-622)},
      pid          = {G:(DE-HGF)POF3-6G3},
      experiment   = {EXP:(DE-H253)P-P02.1-20150101},
      typ          = {PUB:(DE-HGF)21},
      doi          = {10.3204/PUBDB-2017-12926},
      url          = {https://bib-pubdb1.desy.de/record/396846},
}