Room Temperature Low Cycle Fatigue Research Articles

Room-temperature low-cycle fatigue behaviour of a Ni-base superalloy

A nickel-base superalloy, Nimonic 90, was subjected to room-temperature low-cycle fatigue under constant total strain control. Cyclic stress response was investigated as a function of the total strain range. Hardening was attributed to slip band formation and softening to the shearing of γ′ precipitates Slip band spacing decreased with increasing strain range. Two-slope behaviour or bilinearity seen in Coffin-Manson and cyclic stress-strain plots has been attributed to a change in the deformation mode with increasing strain range.

Effect of surface roughness on the room temperature low cycle fatigue life of alloy Nimonic 90

Effect of surface roughness on the room temperature low cycle fatigue life of alloy Nimonic 90

Determination of the room-temperature cyclic stress—strain curve of AISI 304LN austenitic stainless steel by two different methods

A comparison is made between the companion specimen test (CST) and the incremental step test (IST) methods for determining the cyclic stress—strain curve of AISI 304LN stainless steel at room temperature. Only seven blocks were needed for obtaining a stable pattern in the IST. Also, Masing behaviour was seen only when this testing procedure was used. In both types of test, during room-temperature low-cycle fatigue deformation the metastable AISI 304LN stainless steel underwent a martensitic transformation. In the CST secondary hardening was observed in specimens tested at and above a strain amplitude of ±0.85% and this could be attributed to martensite formation. Two martensite phases formed: an ε-martensite (h.c.p) and an α′-martensite (b.c.c). The dislocation arrangement in the IST resembled that present in the specimens tested at higher strain amplitudes in the CST.

Room temperature deformation mechanisms in Nimonic 80A

The deformation mechanisms occurring during room temperature tensile and low cycle fatigue testing were investigated. During fatigue the ordered γ′ precipitates restricted the dislocation movement to isolated {111} slip planes. The dislocations often moved in pairs as a result of γ′ shearing. Surface grains deformed more homogeneously as indicated by the dislocation cells. A band structure was also observed which resembled persistent slip bands in other age hardened alloys. These bands produced lamellar extrusions on the gauge surface. At higher strain ranges (Δε, > 2%), the strain was also accommodated through micro-twinning and grain rotation. The rotation of the grains produced an asterism in the TEM diffraction patterns which was also observed at higher strains in the tensile specimens.

The prediction of LCF properties of HAZ obtained during the welding process of SA 508 Class 2 and DIN 22NiMoCr37 structural materials

The main objective of this investigation has been to study the influence of the heat affected zone (HAZ) on room temperature low cycle fatigue (LCF) properties of two structural steels, type SA 508 Class 2 and DIN 22NiMoCr37. The predicted LCF properties of the HAZ have been related to the corresponding material microstructure obtained under quenched and tempered conditions. The HAZ microstructure has been reproduced by a weld cladding simulation heat treatment and any subsequent heat treatment on the simulated HAZ microstructure has been omitted. Although the thermal cycle introduced by the simulated welding process modifies the structure of the affected region and, as a result, diminishes the monotonic and cyclic ductile properties, it has been found that the cyclic strength properties of the simulated HAZ microstructure have been increased. The Feltner and Landgraf prediction criterion has been applied in order to obtain a reliable estimation of the LCF resistance of the materials tested in this investigation.