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Mechanical and structural aspects of high temperature deformation in Ni alloy

Nowotnik A.

Journal of Achievements in Materials and Manufacturing Engineering

2008

Vol. 26, nr 2

143-146

Purpose: Experimental results on hot deformation and dynamic structural processes of nickel based alloy were reviewed. The attention was given to the analysis of dynamic structural processes which operate during hot deformation of the material. Design/methodology/approach: Hot compression tests were performed on solution treated precipitations hardenable nickel based superalloy of Inconel 718 within a temperature range of 720-1150*C at constant true strain rates of 10 -4, 4x10 -4 s -1. The flow stress curves and microstructure of deformed nickel based superalloy were presented. Findings: During hot compression of solution treated material, highly localized flow was observed at relatively low deformation temperatures 720-850*C. The particle distribution and their morphology were not found to be affected by localized flow within the investigated strain range. At low strain rate the shear banding and intergranular cracks and cavities growth were found to be responsible for the observed flow stress decrease at 720, 800 and 850oC and might result in a sample fracture at larger strains. Research limitations/implications: In spite of intense strain hardening due to deformation and phase transformation overlapping, light optical microstructure observation of deformed samples did not reveal significant effects of heterogeneous distribution of the phase components. Therefore, in order to complete and confirm obtained results it is recommended to perform further analysis of the alloy by using transmission electron microscopy technique (TEM). Practical implications: An interaction between dynamic precipitation and flow localization may become an important feature of high temperature performance and may also allow producing specific structures of materials. Originality/value: The contribution of flow localization to the strain hardening or flow softening and the flow stress-strain behavior during hot deformation of precipitation hardenable alloys is still a subject of extensive researches. The interaction between the flow localization and dynamic precipitation process was a subject of a very limited research works only.