Coffin-Manson Plot Research Articles

Effect of temperature on fatigue behavior and deformation mechanisms of nickel-based superalloy SU-263

The LCF behavior of SU-263 was investigated at various temperatures (1073, 1123, and 1173 K) and strain amplitudes of ± 0.4 to 0.8% at a constant strain rate of 3 × 10-3 s−1. The alloy displayed initial hardening followed by extensive cyclic softening until failure. It is observed that the presence of dislocation networks absorbs mobile dislocation, and the shearing of γ′ precipitates were responsible for cyclic softening at 1073 and 1123 K, whereas dissolution of γ′ precipitate and dislocation annihilation were responsible for cyclic softening at 1173 K. At elevated temperatures, the LCF behavior is significantly influenced by time-dependent processes such as dynamic strain aging (DSA), and oxidation. The occurrence of DSA manifests in the form of serrated plastic flow in stress–strain hysteresis loops, reduced half-life plastic strain amplitude, and increased cyclic work hardening. The alloy exhibits linear behavior in the Coffin-Manson (C-M) plot at 1073 and 1173 K. However, the C-M plot shows bi-linear behavior at 1123 K with the corresponding shift in the deformation mechanism at ± 0.5% strain amplitude. This study focuses on understanding the effects of temperature on fatigue behavior and the associated deformation mechanisms by using characterization techniques, such as scanning and transmission electron microscopy.

Effect of strain amplitude on the low cycle fatigue behavior and deformation mechanisms in alloy SU-263 at elevated temperature

The past studies in the low cycle fatigue (LCF) behavior of a γ′ strengthened nickel-based superalloy SU-263 were restricted to a maximum temperature of 923 K, though their service conditions far exceed this limit. In the present work, the LCF behavior of SU-263 is investigated at 1023 K with strain amplitude varying from ± 0.3% to ± 0.8% at 1023 K. During fatigue, the alloy displayed initial cyclic hardening followed by softening. The fatigue life decreased drastically with increasing strain amplitude. The alloy depicted gradual initial hardening at low strain amplitudes and sharp initial hardening at higher strain amplitudes, along with extensive softening until fracture. Significant increases in slip band density, stacking faults, dislocation network formation, and dislocation-dislocation and dislocation-precipitate interactions were identified as the deformation mechanisms responsible for cyclic hardening. In contrast, dislocation annihilation and shearing of γ′ precipitates were found to control cyclic softening. Dislocation-precipitate interactions were associated with looping at low strain amplitudes, while precipitate shearing occurred at high strain amplitudes. The alloy exhibited a tendency bilinear strain-life behavior in the Coffin-Manson plot with the corresponding shift in the fracture mode at ± 0.5% strain amplitude. At strain amplitudes below ± 0.5%, the alloy showed a mixed mode of failure, predominantly transgranular in nature, while at high strain amplitudes, the failure becomes predominantly intergranular.

Low Cycle Fatigue of an Ultrafine Grained AA5083 Aluminum Alloy Composite Produced by Cryomilling

Low cycle fatigue (LCF) properties were investigated for a novel cryomilled AA5083 aluminum composite with duplex coarse and ultrafine grain sizes and reinforced with boron carbide particulates, referred to as trimodal material. Fully reversed cyclic tests were conducted under plastic strain control at plastic strain amplitudes from 0.15 to 0.6 pct using a constant plastic strain rate in a servo-hydraulic testing system. A nonlinear elastic modulus was used to calculate the elastic contribution to the measured total strain. The LCF performance of this trimodal material is compared to previous results for unreinforced AA5083 aluminum alloy with bimodal grain size (85/15 pct CM/UM) and its coarse-grained wrought counterpart, AA5083-H131. Stress response curves for the trimodal material revealed slow hardening until failure associated with the presence of particulate reinforcements. The very small asymmetry between tension and compression stresses reflects a lack of strain localization beyond the initial cycles. The trimodal and 85/15 pct CM/UM alloys have similar and superior low cycle fatigue strength compared to AA5083-H131. From the Coffin-Manson plot, the trimodal material has a shorter fatigue life than 85/15 pct CM/UM alloy and AA5083-H131 for high plastic strain amplitudes, but nearly identical life at low amplitudes. Microcracks were observed near the dominant crack on trimodal specimen surfaces at failure. Back-scattered images revealed that particulates altered the crack propagation direction; cracks nearly always propagated around particulates.

Low-cycle fatigue properties of CoCrFeMnNi high-entropy alloy compared with its conventional counterparts

The behavior of CrCoFeMnNi high-entropy alloy (Cantor) during cyclic deformation at room temperature was compared with those of a twinning-induced plasticity (TWIP) steel and 304 stainless steel (SS304). The three materials with similar grain sizes (~65 μm) were made by controlled heat treatment and tested to evaluate tensile and low-cycle fatigue (LCF) properties. The tensile strength and ductility of Cantor were much lower than those of TWIP steel and SS304. Cantor and TWIP steel revealed cyclic hardening and then softening; SS304 showed secondary hardening at the latest stage of cyclic deformation due to formation of α′-martensite, which led to a significant decrease in its LCF life. At high total strain amplitudes >0.4% LCF life was longer in Cantor than in SS304, but shorter than in TWIP steel. However, at total strain amplitudes ≤0.4%, Cantor showed the shortest LCF life. It was found that the Coffin-Manson plot of Cantor followed the trend of TWIP steel rather than that of SS304. Microstructural analysis of the Cantor with increasing cycles revealed the formation of twins and well-defined cell structures, the latter of which is the evidence of wavy slip.

Fatigue behavior and bilinear Coffin-Manson plots of Ni-based GH4169 alloy with different volume fractions of δ phase

The effect of volume fraction of δ phase, which was changed through changing the heat treatment conditions, on the strain-controlled fatigue behavior of Nickel-based GH4169 alloys at room temperature was investigated. The δ phase had almost no effect on fatigue life at strain amplitude higher than 0.5%. However, the fatigue life increased with increasing volume fraction of δ phase at the strain amplitude of 0.4%. The alloys with three different volume fractions of δ phase exhibited dual-slope Coffin-Manson relationships, which could be attributed to the changes in the deformation mode from twinning to slip bands as well as the crack initiation mode from transgranular to intergranular with increasing strain amplitude.

Micromechanism of cyclic plastic deformation of alloy IN 718 at 600 °C

AbstractIn the present investigation, an attempt was made to understand the cyclic deformation micromechanism of gas turbine alloy Inconel 718 at 600 °C (i) by conducting low cycle fatigue and creep–fatigue interaction tests and (ii) by studying the microstructure evolution in the material during fatigue tests through extensive electron microscopy. Bilinear slope was obtained in the Coffin–Manson plot for all low cycle fatigue tests, and it was confirmed through transmission electron microscopic examination that microtwinning was the predominant mode of deformation at low plastic strain values, whereas slip and shearing of γ″ precipitates were the predominant mode of deformation at higher plastic strain values. Fatigue life was adversely affected when hold time was introduced at peak tensile strain during creep–fatigue interaction tests. Formation of stepped interface at microtwin boundaries and coarsening of niobium carbide precipitates were observed to be the major microsturctural changes during creep–fatigue interaction tests.

Cyclic deformation behaviors of a high strength carbide-free bainitic steel

The cyclic deformation behaviors of low-temperature bainite, lower bainite and upper bainite obtained on a high-strength carbide-free bainitic steel were examined through low-cycle fatigue testing. The relationship between the bainitic microstructure and fatigue behavior was systematically studied using scanning electron microscopy, transmission electron microscopy, atom probe technology, and electron back-scattered diffraction analyses. The results show that low-cycle fatigue undergoes three stages, namely, cyclic hardening, saturation or cyclic softening, and fracturing. The low-temperature bainite exhibits a long fatigue life under the total strain amplitudes, because of its high strength and larger high-angle misorientation distribution of the packets of bainitic ferrite plates. The low-temperature bainite also presents bilinearity in the Coffin–Manson plots. Coordinate deformation and high-uniform elongation lead to prolonged fatigue life at low plastic strain amplitude, whereas phase component primarily affects the fatigue life at high plastic strain amplitude. Highly stable film-like retained austenite is beneficial to arresting fatigue crack propagation. Blocky type retained austenite easily transforms to martensite, resulting in high compatible deformation capability. The hardening ability of the low-temperature bainite is higher than that of the upper bainite, which is attributed to its high pre-existent density of dislocations transformed from movable to immovable during initial hardening stage.

Role of shrinkage pores, carbides on cyclic deformation behaviour of conventionally cast nickel base superalloy CM247LC® at 870 °C

Cyclic deformation behaviour of conventionally cast and equiaxed grained nickel base superalloy CM247LC® has been studied at various strain amplitudes ranging from 0.3% to 0.9% at 870°C. Two features typical of cast materials viz., shrinkage pores and carbide particles were seen to influence the crack initiation and propagation process during strain controlled LCF testing in the alloy. While low overall dislocation density marked the deformation substructures of specimens cycled at low strain amplitudes, dislocation density levels were higher at higher strain amplitudes and were also seen to increase with cycling especially in gamma channels and around carbide particles. Cyclic stress response and dual slope behaviour in Coffin–Manson plots exhibited by the alloy have been analysed in light of deformation substructures and fractographic observations to gain insight into the fatigue deformation process and fracture mechanisms operating in the alloy.

On the Anomalous Coffin-Manson Behavior Observed under Elevated Temperature Ratcheting in Type 316LN SS

Ratcheting is the progressive directional accumulation of deformation due to asymmetric loading in structures. Coffin-Manson plots derived from ratcheting experiments conducted at temperatures over the range, 823-923 K showed anomalous behavior at 873 K and 923 K in the form of dual slope and positive slope respectively, which was attributed to a change in the deformation mechanism during ratcheting in the above temperature domain. This was also reflected in the transition in the fracture mode from fatigue to creep at 873 and 923 K.

Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part II: Fatigue Life and Fracture Behavior

Influence of nitrogen content on low cycle fatigue life and fracture behavior of 316LN stainless steel (SS) alloyed with 0.07 to 0.22 wt pct nitrogen is presented in this paper over a range of total strain amplitudes (±0.25 to 1.0 pct) in the temperature range from 773 K to 873 K (500 °C to 600 °C). The combined effect of nitrogen and strain amplitude on fatigue life is observed to be complex i.e., fatigue life either decreases/increases with increase in nitrogen content or saturates/peaks at 0.14 wt pct N depending on strain amplitude and temperature. Coffin–Manson plots (CMPs) revealed both single-slope and dual-slope strain-life curves depending on the test temperature and nitrogen content. 316LN SS containing 0.07 and 0.22 wt pct N showed nearly single-slope CMP at all test temperatures, while 316LN SS with 0.11 and 0.14 wt pct N exhibited marked dual-slope behavior at 773 K (500 °C) that changes to single-slope behavior at 873 K (600 °C). The changes in slope of CMP are found to be in good correlation with deformation substructural changes.

Effect of post-solutionizing cooling rate on microstructure and low cycle fatigue behavior of a cast nickel based superalloy

The influence of post-solutionizing cooling rate on low cycle fatigue (LCF) and cyclic stress–strain behavior at 650°C has been investigated for a double solution-treated and aged nickel-based superalloy (Ni–8.09Cr–9.35Co–9.41W–0.52Mo–3.24Ta–0.82Ti–5.51Al–1.53Hf–0.075C). The LCF behavior of this alloy has been characterized by dual-slope Coffin–Manson relationship. The bilinear Coffin–Manson plot for the samples subjected to the slowest post-solutionizing cooling rate has shown relatively lower transition plastic strain for the slope change, and this observation is attributed to their higher cyclic work hardening exponent and more uniform plastic deformation. The increase in amount of cyclic hardening with increasing total strain range and decreasing cooling rate is considered to be due to the increase in dislocation density. The presence of higher volume fraction of fine spherical secondary γ′ between the cuboidal primary γ′ precipitates, absence of γ′-depleted region near the grain boundaries, and uniform distribution of discrete secondary carbides (such as Cr23C6 and HfC) along the grain boundaries contribute to higher fatigue life and stable cyclic stress–strain behavior for the samples subjected to the slowest cooling rate.

High temperature low cycle fatigue behaviour of hot isostatically pressed superalloy Udimet 720 LI

Nickel base superalloy Udimet 720 LI was processed through a powder metallurgy (P/M) hot isostatic pressing (HIP) route. The effects of this consolidation technique (HIPing) on low cycle fatigue (LCF) properties were evaluated and are reported in this paper. Total strain controlled LCF tests have been conducted in air at 550°C at a nominal strain rate of 6.67 × 10−3 s−1. The as-HIPed Udimet 720 Li exhibits stable behaviour followed by very mild cyclic hardening at total strain amplitudes ± 0.4–0.5%. However, cyclic hardening has been observed at total strain amplitudes ± 0.6–1.2%. The cyclic hardening is attributed to dynamic strain aging (DSA). The dual slope behaviour in a Coffin-Manson plot is attributed to a change in fracture mechanism.

Low cycle fatigue properties and cyclic deformation behavior of as-extruded AZ31 magnesium alloy

The low cycle fatigue(LCF) properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4%–1.2% with strain rate of 1×10 −2 s −1. Due to the twinning effect in compression during loading and the detwinning effect during unloading, the alloy showed an asymmetric hysteresis loop. The cyclic stress response exhibited cyclic hardening at high total strain amplitudes. The cyclic deformation behaviors were discussed using the Coffin-Manson plot, which divided the plastic strain amplitudes into the tension side and the compression side. Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%, the interaction between the twinning effect and dislocation was analyzed. The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy, respectively.

High temperature low cycle fatigue properties of a HF30-type cast austenitic stainless steel

This work investigated the high temperature low cycle fatigue behavior of HF30-type, cast austenitic stainless steel. In addition to the preliminary results from tensile and thermal expansion tests, isothermal strain controlled fatigue tests at 600°C and 800°C were carried out with a total strain amplitude from ±0.20 % to ±0.65% and with a strain rate of 10−3/s. The plastic strain amplitudes during cyclic strain loading were measured and correlated with the fatigue lifetime using Coffin–Manson plots at each test temperature. These plots were re-constructed into a general superposition curve containing the results from both temperatures using a constitutive equation of the energy criterion for fatigue failure in terms of thermally activated dislocation motion. The cast and wrought stainless steels showed similar fatigue properties.

Influence of hold time on low cycle fatigue behaviour of near alpha titanium alloy IMI 834 at 873K

In the present work, IMI 834, a near α titanium alloy was evaluated for tensile and low cycle fatigue (LCF, with and without hold time) behavior at 873K. Tensile tests were performed at the initial strain rate of 4 × 10−3 s−1 at 873K. Fully reversed, total strain control LCF tests were conducted at total strain amplitude of ± 1.0% at constant strain rate of 4 × 10−3 s−1 at 873K. For LCF tests with dwell, hold time were imposed in tension, compression and tension — compression mode with varied hold times of 60 sec, 120 sec, 180 secs. In LCF tests without dwell, the Coffin-Manson plot showed dual slope behavior at 873K. In LCF tests with dwell, at 873K, tensile, compressive and tensile — compressive hold time tests have shown lower LCF resistance than that of the tests without hold time. Among the three modes of hold times employed, the tensile hold has exhibited the highest LCF resistance followed by tensile — compressive and compressive hold time tests. In the present study, tensile hold introduces compressive mean stresses while the compressive hold introduces tensile mean stresses. Further, the creep effect of stress relaxation was examined at 873K in order to explain the hold time effects.

Correlation between residual stress and plastic strain amplitude during low cycle fatigue of mechanically surface treated austenitic stainless steel AISI 304 and ferritic–pearlitic steel SAE 1045

Mechanical surface treatments such as deep rolling are known to affect the near-surface microstructure and induce, e.g. residual stresses and/or increase the surface hardness. It is well known that, e.g. compressive residual stress states usually increase the lifetime under fatigue loading. The stress relaxation behaviour and the stability of the residual stress during fatigue loading depend on the mechanical surface treatment method. In this paper three different surface treatments are used and their effects on the low cycle fatigue behaviour of austenitic stainless steel (AISI 304) and ferritic–pearlitic steel (SAE 1045) are investigated. X-ray diffraction is applied for the non-destructive evaluation of the stress state and the microstructure. It is found that consecutive deep rolling & annealing as well as high temperature deep rolling produce more stable near-surface stress states than conventional deep rolling at room temperature. The plastic strain amplitudes during fatigue loading are measured and it is shown that they correlate well with the induced residual stress and its relaxation, respectively. Furthermore, Coffin–Manson plots are presented which clearly show the correlation between the plastic strain amplitude and the fatigue lifetime.

High Temperature Low-Cycle Fatigue, Deformation Microstructure and Final Fracture Behavior of a Nickel-Base Superalloy

The low-cycle fatigue (LCF) properties of a nickel-base precipitation-strengthened superalloy (GH4145/SQ), obtained at a temperature of 538 o C, were reported and discussed in this paper. The properties investigated include cyclic stress response, fatigue life, deformation microstructure and final fracture features as a function of applied strain amplitude. It was shown that the alloy exhibited a pronounced initial hardening followed by continuous softening to failure at high plastic strain amplitudes ( > 0.2% ap ε ), while at low plastic strain amplitudes ( < 0.2% ap ε ) the initial hardening was followed by a well-defined saturation stage. Bilinear behavior with a change of slope at a plastic strain amplitude of about 0.2% was observed in the cyclic stress-strain (CSS) and Coffin-Manson (C-M) plots. TEM observations revealed that slip band density increased with increasing total strain amplitude and precipitate degradation resulting from dislocation-precipitate interactions took place with continuous cyclic straining. The change in the microstructure during cycling is thus responsible for the fatigue hardening / softening behavior of the alloy. SEM examinations indicated that at low plastic strain amplitudes ( < 0.2% ap ε ) crack propagation was basically transgranular, while at high plastic strain amplitudes ( > 0.2% ap ε ) crack propagation exhibited intergranular features, as a whole. The variation in both the number of operating slip systems and the fracture modes with the strain amplitude employed was used to explain the observed two-stage LCF behavior of the present investigated superalloy.

Effect of corrosion on the low cycle fatigue behavior of Sn–4.0Ag–0.5Cu lead-free solder joints

Isothermal low cycle fatigue tests using Sn–4.0Ag–0.5Cu solder joints were performed according to a full factorial design of experiments in different corrosive environments. Temperature, humidity and salt solution were varied according to literature. The application of salt solution resulted in extensive corrosion of the solder joints and a decrease in fatigue life. The factor with the highest effect on the fatigue life was salt solution followed by temperature. The factor humidity was not significant for the present fatigue tests performed. The experiments performed at room temperature at different strain ranges also revealed that the application of salt decreases the fatigue life (90% confidence). The fatigue exponent α increases and C decreases when salt solution (concentration of 1 M) is applied to the solder joints. The two Coffin–Manson plots diverged from each other when decreasing the plastic strain range.

Fatigue behavior and damage characteristic of ultra-fine grain low-purity copper processed by equal-channel angular pressing (ECAP)

The S–N and Coffin–Manson plot, cyclic stress–strain response, changes of microstructure, and the surface morphology of ultra-fine grain (UFG) low-purity copper processed by ECAP were tested and observed in present study. And the formation mechanism of shear bands was discussed in detail. The results show that the UFG Cu represents longer lifetime under stress-controlled fatigue, but lower fatigue resistance under strain-controlled fatigue when compared with the coarse grain counterpart. Cyclic stress–strain responses of UFG Cu under stress-controlled fatigue alter from cyclic softening to cyclic hardening as stress amplitude decreases. But the responses always show cyclic softening under strain-controlled fatigue in present testing. By electron back scattering diffraction and transmission electron microscope technique, the shear bands were discovered on the surface of all cycled samples and no grain coarsening was discovered near the shear bands, which indicated that there was no inevitable relationship between formation of SBs and cyclic softening/grain coarsening. The discovery should be related to impurities in copper. The oriented distribution of defects along the shear plane in the last ECAP processing is one of the major mechanisms of SBs formation.

Cyclic deformation behavior of steels and light-metal alloys

The detailed knowledge of the cyclic deformation behavior of metallic materials is an essential condition for the comprehensive understanding of fatigue mechanisms and a reliable lifetime calculation of cyclically loaded specimens and components. Various steels and light-metal alloys were investigated under stress and strain control on servohydraulic testing systems. In addition to mechanical stress–strain hysteresis measurements, the changes of the specimen temperature and the electrical resistance due to plastic deformation processes were measured. The plasticity-induced martensite formation in metastable austenitic steels was detected in situ with a ferritescope sensor. As advanced magnetic measuring technique giant-magneto-resistance sensors in combination with an universal eddy-current equipment were used for the on-line monitoring of fatigue processes. Due to their direct dependence on microstructural changes, all physical values show a clear interaction with the actual fatigue state. The results of the plastic strain, thermometric, electric and magnetic measuring techniques were presented versus the number of cycles as well as in Morrow and Coffin-Manson plots. The microstructures were characterized by scanning electron microscopy.