Irradiation induced clustering in F/M alloys

Ferritic/martensitic (F/M) alloys are leading candidates for advanced nuclear fission and fusion reactor structural materials, owing to their high temperature strength and dimensional stability (i.e. resistance to void swelling).  However, irradiation has been shown to induce nanoscale clustering and phase separation in F/M alloys.  These nanofeatures subsequently alter the mechanical properties – including hardness, yield strength, and toughness – and irradiation tolerance of the materials.  Researchers commonly use charged particles to emulate neutron irradiation damage in faster experimental time frames and for lower cost.  However, neutrons and charged particles do not always produce comparable nanocluster evolution.  Our work aims to understand conditions which produce consistent nanocluster evolution using different irradiating particles.

We have studied commercial F/M alloys HT9 and HCM12A, and investigate the nucleation and growth of Cu-rich clusters, G-phase nanoclusters (Si-Mn-Ni-P phases), and α’ nanophases (Cr-rich clusters).  We utilize atom probe tomography (APT) to identify the morphologies and chemistries of the nanoclusters, which are below transmission electron microscopic (TEM) resolution.  We observe finer nanoclusters in the neutron irradiated specimens as compared to the charged particle (proton, Fe ion) irradiation specimens.  We also observe α-α’ phase separation only in neutron irradiated specimens.


  • DOE Nuclear Science User Facilities projects 13-419, 14-485, 16-625 and 16-710
  • US Nuclear Regulatory Commission award NRC-HQ-84-14-G-0056


  1. M.J. Swenson and J.P. Wharry. A predictive model for irradiation-induced nanocluster evolution in b.c.c. Fe-based alloys. The Minerals, Metals & Materials Society Annual Meeting, San Diego CA, March 2017.
  2. M.J. Swenson and J.P. Wharry. Comparison of Ion and Neutron Irradiations to 3 dpa at 500°C in Ferritic-Martensitic Alloys. Transactions of the American Nuclear Society – 2016 Annual Meeting and Embedded Topical Meeting: Nuclear Fuels and Structural Materials, 114 (2016) 1112-1115.
  3. M.J. Swenson. Irradiation evolution of nanoclusters in b.c.c. Fe-Cr alloys: NSUF support of Ph.D. student training. Nuclear Science User Facilities (NSUF) DOE Annual Review Meeting, Washington DC, November 2016.
  4. M.J. Swenson and J.P. Wharry. Cluster evolution in F/M alloys upon neutron, proton, and self-ion irradiation. Materials Science & Technology (MS&T) 2016, Salt Lake City UT, October 2016.
  5. M.J. Swenson and J.P. Wharry. The strengthening mechanism transition in nanofeatured ferritic-martensitic alloys. The Minerals, Metals & Materials Society Annual Meeting, Orlando FL, March 2015.
  6. J.P. Wharry, M.J. Swenson, and C.K. Dolph. Microstructure-mechanical property relationship in self-ion irradiated ODS and F/M alloys. European Materials Research Society, Warsaw, Poland, September 2014.

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