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@MISC{Dippel:396848,
      author       = {Dippel, Ann-Christin and Zhang, Jian and Raabe, Dierk},
      title        = {{A}nalysis reveals new crystal structure in "gum metal"},
      reportid     = {PUBDB-2017-12928},
      year         = {2017},
      abstract     = {A phase transition observed for the first time in a
                      titanium alloy could pave the way for new structural
                      materialsScientists from the Max-Planck-Institut für
                      Eisenforschung (MPIE) in Düsseldorf have observed a new
                      phase transformation in a titanium alloy at DESY. The
                      mechanism they discovered could further our understanding of
                      some surprising properties of certain alloys and be used to
                      develop new materials. The team around main author Jian
                      Zhang of MPIE presents its findings in the journal Nature
                      Communications.The scientists used DESY’s X-ray source
                      PETRA III to examine the inner structure of a special alloy
                      consisting of the (transition) metals titanium, niobium,
                      tantalum and zirconium. This titanium alloy displays some
                      unusual mechanical properties which have earned it the name
                      “gum metal”. When mechanical stress is applied to the
                      alloy, it behaves in a very interesting way: “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
                      MPIE, who co-authored the paper.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.It is not yet quite clear why this alloy
                      can be deformed to such a high degree. Various experiments
                      have revealed peculiarities in its nanostructure, but have
                      not yet shown a direct connection with its properties.
                      Titanium alloys normally occur in two different phases,
                      whereby the term phase refers to the crystal structure in
                      which the atoms are arranged. 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.The researchers at MPIE have now 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. At DESY’s X-ray source PETRA III, the scientists
                      were able to examine the crystal structure of the alloy in
                      great detail 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 DESY
                      co-author Ann-Christin Dippel, who supervised the
                      experiments technically and scientifically at the measuring
                      station P02.1.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.Xi'an Jiaotong
                      University in China and the Massachusetts Institute of
                      Technology in the USA were also involved in the research.},
      cin          = {DOOR / FS-PE},
      cid          = {I:(DE-H253)HAS-User-20120731 / I:(DE-H253)FS-PE-20120731},
      pnm          = {6213 - Materials and Processes for Energy and Transport
                      Technologies (POF3-621) / 6G3 - PETRA III (POF3-622)},
      pid          = {G:(DE-HGF)POF3-6213 / G:(DE-HGF)POF3-6G3},
      experiment   = {EXP:(DE-H253)P-P02.1-20150101},
      typ          = {PUB:(DE-HGF)21},
      url          = {https://bib-pubdb1.desy.de/record/396848},
}