Energy-efficient and environment-friendly elastocaloric refrigeration, which is a promising replacement of the conventional vapor-compression refrigeration, requires extraordinary elastocaloric properties. Hitherto the largest elastocaloric effect is obtained in small-size films and wires of the prototype NiTi system. Here, we report a colossal elastocaloric effect, well exceeding that of NiTi alloys, in a class of bulk polycrystalline NiMn-based materials designed with the criterion of simultaneously having large volume change across phase transition and good mechanical properties. The reversible adiabatic temperature change reaches a strikingly high value of 31.5 K and the isothermal entropy change is as large as 45 J kg −1 K −1 . The achievement of such a colossal elastocaloric effect in bulk polycrystalline materials should push a significant step forward towards large-scale elastocaloric refrigeration applications. Moreover, our design strategy may inspire the discovery of giant caloric effects in a broad range of ferroelastic materials.

Biocompatibility of HEAs in the TiZrHfNbTa system in which all the constituents are non-toxic and allergy-free was scrutinized systematically, and novel biomechanical materials with a unique combination of low modulus (57 GPa, almost half that of conventional biomedical titanium alloys), good mechanical biocompatibility and low magnetic susceptibility (1.71 × 10 −6 cm 3 g −1 , similar to that of pure Zr) were successfully developed. Moreover, the underlying mechanisms responsible for phase formation and promising properties were explored. This work not only offers a series of novel bio-metallic materials with prominent properties for practical applications, but also shed light on understanding of phase formation and strengthening of HEAs in general. IMPACT STATEMENT Several biocompatible TiZrHfNbTa HEAs with prominent properties for practical applications were developed and the relevant alloy design principles were revealed.

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In order to apply the concept of the dissipation function during the first-order phase transition (FOPT) in solids, we measured the internal friction Q ' and shear modulus p for a range of frequencies of polycrystalline ceramics VO2 as the sample passed through a FOPT across the temperature range of 300-420 K. The experiment was repeated for different temperature variation rate T. We have found that for each frequency, a maximum of Q ' and a minimum of p. occurred at the same temperature T" when T was kept constant. The numerical values of the dissipation function S 6& plus other FOPT parameters have been deduced using Q ' data. The general trend of b, gR Tand o-ther results are found to be consistent with known physical aspects.

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