Update links_ref.rst

doc/links_ref.rst

@@ -162,6 +162,7 @@ Dislocation nucleation during (nano)indentation
 * `Wang Y. et al., "Dependence of pop-in behavior of a high-entropy alloy FeCoCrMnNi on tip radius" (2019). <https://doi.org/10.1007/s00339-019-2409-z>`_
 * `Pöhl F., "Orientation-Dependent Deformation Behavior of316L Steel Manufactured by Laser Metal Depositionand Casting under Local Scratch and Indentation Load" (2020). <https://doi.org/10.3390/ma13071765>`_
 * `Ohmura T. and Wakeda M., "Pop-In Phenomenon as a Fundamental Plasticity Probed by Nanoindentation Technique" (2021). <https://doi.org/10.3390/ma14081879>`_
+* `Wang D. et al., "Understanding the hydrogen effect on pop-in behavior of an equiatomic high-entropy alloy during in-situ nanoindentation", Journal of Materials Science & Technology (2021). <https://doi.org/10.1016/j.jmst.2021.04.060>`_
 
 Dislocation nucleation during compression of pillar
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