Journal of Materials Research and Technology Journal of Materials Research and Technology
J Mater Res Technol 2017;6:361-8 DOI: 10.1016/j.jmrt.2017.05.009
Original Article
Influence of Mo alloying on the thermal stability and hardness of ultrafine-grained Ni processed by high-pressure torsion
Garima Kapoora, Yi Huangb, V. Subramanya Sarmac, Terence G. Langdonb, Jenő Gubiczaa,,
a Department of Materials Physics, Eötvös Loránd University, Budapest, Hungary
b Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK
c Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, India
Received 11 April 2017, Accepted 25 May 2017
Abstract

The influence of Mo alloying on the thermal stability of grain size, dislocation density and hardness of ultrafine-grained (UFG) Ni alloys was studied. The UFG microstructure in alloys with low (∼0.3at.%) and high (∼5at.%) Mo contents was achieved by high-pressure torsion (HPT) performed for 20 turns at room temperature. The thermal stability of the two alloys was studied by calorimetry. A Curie-transition from ferromagnetic to paramagnetic state was not found for the Ni–5% Mo alloy due to the high Mo content. It was found that heating at a rate of 40K/min up to ∼850K resulted in a complete recovery and recrystallization of the UFG microstructure in the alloy with 0.3% Mo. The same annealing for Ni–5% Mo led only to a moderate reduction of the dislocation density and the grain size remained in the UFG regime. Therefore, the higher Mo content yielded a much better thermal stability of the Ni alloy. The influence of the change of the microstructure during annealing on the hardness is discussed.

Keywords
High-pressure torsion, Ni–Mo alloys, Dislocations, Grain size, Hardness, Thermal stability
J Mater Res Technol 2017;6:361-8 DOI: 10.1016/j.jmrt.2017.05.009