The role of stress relaxation and creep during high temperature deformation in Ni-base single crystal superalloys - Implications to strain build-up during directional solidification

Research output: Contribution to journalArticlepeer-review


  • Neil D'Souza
  • Joe Kelleher
  • Shu Yan Zhang
  • Sam Gardner
  • Robert E. Jones
  • Duncan Putman

Colleges, School and Institutes

External organisations

  • Rolls Royce PLC
  • Rutherford Appleton Laboratory


The study of high temperature deformation of Ni-base superalloys finds a number of applications. In this study we consider how stress/strain resulting from directional solidification can be alleviated through phenomena such as relaxation and how this can be measured. Based on a modelling study, a range of stresses between 550 and 650 MPa were chosen for tensile testing at 900°C in the Ni-base superalloy, CMSX4. In-situ neutron diffractometry together with ex-situ transmission electron microscopy have been used to study relaxation occurring during high-temperature deformation. The behaviour of (100) and (200) lattice strains with macroscopic stress has been quantitatively analysed for single crystals with axial orientations within 5°from [100]. The (200) γ+γ/ fundamental peak has been used to relate the decay in applied macroscopic stress with lattice strain. At high stresses (above 600 MPa), relaxation was particularly pronounced with an immediate appreciable decay in lattice strain (and stress) within 20 min. At lower stresses, significant relaxation is only observed after prolonged hold. Relaxation occurs in both γ and γ/, as confirmed by presence of dislocations within both phases and it was also with minimal lattice rotation (


Original languageEnglish
Pages (from-to)322-332
Number of pages11
JournalActa Materialia
Early online date26 Jan 2016
Publication statusPublished - Mar 2016


  • CMSX4, In-situ neutron diffraction, Investment casting, Lattice strain, Stress relaxation, Thermal-mechanical modelling