Contents lists available at ScienceDirect Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea High temperature stabilization of a nanostructured Cu-Y 2 O 3 composite through microalloying with Ti Dengshan Zhou a,b, ⁎ , Hongwei Geng a,b , Wei Zeng c , Dengqi Zheng c , Hucheng Pan a , Charlie Kong d , Paul Munroe e , Gang Sha f , Challapalli Suryanarayana g , Deliang Zhang a,b a Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China b Institute of Ceramics and Powder Metallurgy, School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China c State Key Laboratory for Metal Matrix Materials, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China d Electron Microscopy Unit, The University of New South Wales, Sydney 2052, Australia e School of Materials Science and Engineering, The University of New South Wales, Sydney 2052, Australia f Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, China g Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816-2450, USA ARTICLE INFO Keywords: Oxide dispersion-strengthened Cu Nanocrystalline metal matrix composite Thermal stability Ti addition Microalloying Hall-Petch relation ABSTRACT The effects of minor additions (0.2, 0.4 and 0.8 wt%) of Ti on the thermal stability of both Cu nanograins and Y 2 O 3 particles in nanostructured Cu-5 vol%Y 2 O 3 composite powder particles were investigated via 1 h iso- chronal annealing at temperatures ranging from 300 to 1000 °C. It was found that a small amount addition of 0.4 wt%Ti effectively inhibits the coarsening of the Y 2 O 3 particles during annealing at a very high homologous temperature of 0.87T m , where T m is the melting point of Cu, which, in turn, stabilizes Cu nanograins and retains the hardness value of the as-milled powder sample. However, this is in clear contrast with the significant de- crease in hardness of the Ti-free and 0.2 wt%Ti doped milled powder samples annealed at the same condition, resulting from the coarsening of the Y 2 O 3 particles and growth of Cu nanograins. The energy dispersive X-ray spectrometry elemental analysis shows that the stabilizing mechanisms responsible for the improved thermal stability of the Y 2 O 3 particles are associated with the chemical reactions between Ti, O and Y 2 O 3 . 1. Introduction Oxide dispersion-strengthened (ODS) Cu-based materials have at- tracted extensive attention because they exhibit important engineering applications in the fields of nuclear, electronic and spot welding elec- trode materials [1–6]. Nanoscale Al 2 O 3 [7,8] and Y 2 O 3 particles [9,10] are frequently chosen as dispersion hardeners to strengthen Cu, or other metallic materials such as Ni [11] and ferritic alloys [12], at room and elevated temperatures via interacting with both dislocations and grain boundaries. This interaction requires an effective oxide dispersoid to have merits in terms of both fine distribution and small sizes. An oxide that has a high enthalpy of formation is beneficial in resisting their coarsening and thus keeping them small as well as generating a homogeneous particle distribution. The formation enthalpy of Y 2 O 3 is 1905 kJ/mol and higher than the equivalent value for Al 2 O 3 (1667 kJ/ mol) [1]. Therefore, it is more favorable for Y 2 O 3 to be used as an oxide dispersoid in a Cu matrix to produce ODS Cu-based materials. The coarsening of insoluble oxides is also affected by two other factors, i.e., the oxide/matrix interfacial energy and diffusivity of the species in the oxides [13]. These two factors can be tuned by doping oxides with an alloying element. Generally, an appropriate alloying element that acts as a dopant should either exhibit low diffusivity to retard the coarsening of the alloyed oxide or modify the oxide/matrix interfacial structure to lower its energy. For example, in ODS ferritic alloys, Ti is used as an ideal stabilizing agent for Y 2 O 3 by forming small and coherent Y-Ti-O nanoclusters [11,14], which have smaller sizes and higher thermal stability in comparison with pure Y 2 O 3 particles. Fur- thermore, titanium can react with excess oxygen in the systems to form stable TiO 2 , which is also beneficial in inhibiting the coarsening of the oxides [15]. As such, Ti plays an important role in stabilizing the oxides and optimizing their distribution in ODS metallic materials. In this work, we report a highly thermally stable Ti-doped nanos- tructured Cu-Y 2 O 3 composite. With only 0.4 wt%Ti addition, the sta- bility of Y 2 O 3 particles is significantly increased, which, in turn, results in the average Cu grain size that is still well within the nanometer range and hardness value that remains unchanged after annealing for 1 h at a very high homologous temperature of up to 0.87T m (900 °C). The scanning transmission electron microscopy (STEM)-energy dispersive https://doi.org/10.1016/j.msea.2017.11.105 Received 9 October 2017; Received in revised form 25 November 2017; Accepted 25 November 2017 ⁎ Corresponding author at: Institute of Ceramics and Powder Metallurgy, School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China. E-mail address: zhoudengshan@mail.neu.edu.cn (D. Zhou). Materials Science & Engineering A 712 (2018) 80–87 0921-5093/ © 2017 Elsevier B.V. All rights reserved. T