Investigation on the Behavior of Austenite and Ferrite Phases at Stagnation Region in the Turning of Duplex Stainless Steel Alloys

This paper investigates the deformation mechanisms and plastic behavior of austenite and ferrite phases in duplex stainless steel alloys 2205 and 2507 under chip formation from a machine turning operation. SEM images and EBSD phase mapping of frozen chip root samples detected a build-up of ferrite bands in the stagnation region, and between 65 and 85 pct, more ferrite was identified in the stagnation region compared to austenite. SEM images detected micro-cracks developing in the ferrite phase, indicating ferritic build-up in the stagnation region as a potential triggering mechanism to the formation of built-up edge, as transgranular micro-cracks found in the stagnation region are similar to micro-cracks initiating built-up edge formation. Higher plasticity of austenite due to softening under high strain is seen responsible for the ferrite build-up. Flow lines indicate that austenite is plastically deforming at a greater rate into the chip, while ferrite shows to partition most of the strain during deformation. The loss of annealing twins and activation of multiple slip planes triggered at high strain may explain the highly plastic behavior shown by austenite

Reduced Bone Mass and Muscle Strength in Male 5α-Reductase Type 1 Inactivated Mice

Androgens are important regulators of bone mass but the relative importance of testosterone (T) versus dihydrotestosterone (DHT) for the activation of the androgen receptor (AR) in bone is unknown. 5α-reductase is responsible for the irreversible conversion of T to the more potent AR activator DHT. There are two well established isoenzymes of 5α-reductase (type 1 and type 2), encoded by separate genes (Srd5a1 and Srd5a2). 5α-reductase type 2 is predominantly expressed in male reproductive tissues whereas 5α-reductase type 1 is highly expressed in liver and moderately expressed in several other tissues including bone. The aim of the present study was to investigate the role of 5α-reductase type 1 for bone mass using Srd5a1−/− mice. Four-month-old male Srd5a1−/− mice had reduced trabecular bone mineral density (−36%, p<0.05) and cortical bone mineral content (−15%, p<0.05) but unchanged serum androgen levels compared with wild type (WT) mice. The cortical bone dimensions were reduced in the male Srd5a1−/− mice as a result of a reduced cortical periosteal circumference compared with WT mice. T treatment increased the cortical periosteal circumference (p<0.05) in orchidectomized WT mice but not in orchidectomized Srd5a1−/− mice. Male Srd5a1−/− mice demonstrated a reduced forelimb muscle grip strength compared with WT mice (p<0.05). Female Srd5a1−/− mice had slightly increased cortical bone mass associated with elevated circulating levels of androgens. In conclusion, 5α-reductase type 1 inactivated male mice have reduced bone mass and forelimb muscle grip strength and we propose that these effects are due to lack of 5α-reductase type 1 expression in bone and muscle. In contrast, the increased cortical bone mass in female Srd5a1−/− mice, is an indirect effect mediated by elevated circulating androgen levels

Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy Crystallographic Orientation Influence on the Serrated Yielding Behavior of a Single-Crystal Superalloy

Abstract: Since Ni-based single-crystal superalloys are anisotropic materials, their behavior in different crystal orientations is of great interest. In this study, the yielding behavior in both tension and compression for 〈001〉, 〈011〉 and 〈111〉 oriented materials at 500 °C has been investigated. The 〈011〉 direction showed a serrated yielding behavior, a great tension/compression asymmetry in yield strength and visible deformation bands. However, the 〈001〉 and 〈111〉 directions showed a more homogeneous yielding, less tension/compression asymmetry in yield strength and no deformation bands. Microstructure investigations showed that the serrated yielding behavior of the 〈011〉 direction can be attributed to the appearance of dynamic strain aging (DSA) and that only one slip system is active in this direction during plastic deformation

Immigrants' life satisfaction in Europe: between assimilation and discrimination

Using data from the three rounds of the European Social Survey, this article investigates the disparities in life satisfaction measures between the first- and second-generation immigrants, on the one hand, and the natives, on the other hand, in 13 European countries. Two major theoretical hypotheses explaining the lower level of immigrants’ subjective well-being are tested: the straight line assimilation and the effect of discrimination. The main finding is that immigrants’ relative dissatisfaction does not diminish with time and across generations, which refutes the predictions of the assimilation paradigm. However, when ethnic groups are compared, the discrimination some of them perceive in the host society seems to be a more consistent explanation for their lower life satisfaction level. The effect of discrimination is measured with an attempt to correct for the endogeneity bias that it may lead to by using simultaneous regressions with instrumental variables

Thermomechanical fatigue in single crystal superalloys

Thermomechanical fatigue (TMF) is a mechanism of deformation which is growing in importance due to the efficiency of modern cooling systems and the manner in which turbines and associated turbomachinery are now being operated. Unfortunately, at the present time, relatively little research has been carried out particularly on TMF of single crystal (SX) superalloys, probably because the testing is significantly more challenging than the more standard creep and low cycle fatigue (LCF) cases; the scarcity and relative expense of the material are additional factors. In this paper, the authors summarise their experiences on the TMF testing of SX superalloys, built up over several years. Emphasis is placed upon describing: (i) the nature of the testing method, the challenges involved in ensuring that an given testing methodology is representative of engine conditions (ii) the behaviour of a typical Re-containing second generation alloy such as CMSX-4, and its differing performance in out-of-phase/in-phase loading and crystallographic orientation and (iii) the differences in behaviour displayed by the Re-containing alloys and new Re-free variants such as STAL15. It is demonstrated that the Re-containing superalloys are prone to different degradation mechanisms involving for example microtwinning, TCP precipitation and recrystallisation. The performance of STAL15 is not too inferior to alloys such as CMSX-4, suggesting that creep resistance itself does not correlate strongly with resistance to TMF. The implications for alloy design efforts are discussed

Creep and Stress Relaxation Anisotropy of a Single-Crystal Superalloy

In this study, the TMF stress relaxation and creep behavior at 1023 K and 1223 K (750 °C and 950 °C) have been investigated for a Ni-based single-crystal superalloy. Specimens with three different crystal orientations along their axes were tested; 〈001〉, 〈011〉, and 〈111〉, respectively. A highly anisotropic behavior during TMF stress relaxation was found where the 〈111〉 direction significantly shows the worst properties of all directions. The TMF stress relaxation tests were performed in both tension and compression and the results indicate a clear tension/compression asymmetry for all directions where the greatest asymmetry was observed for the 〈001〉 direction at 1023 K (750 °C); here the creep rate was ten times higher in compression than tension. This study also shows that TMF cycling seems to influence the creep rate during stress relaxation temporarily, but after some time it decreases again and adapts to the pre-unloading creep rate. Creep rates from the TMF stress relaxation tests are also compared to conventional constant load creep rates and a good agreement is found.On the day of the defense data of the Licentiate Thesis the status of this article was Manuscript.</p

Residual Stresses in Uniaxial Cyclic Loaded Pearlitic Lamellar Graphite Iron

Abstract. The mechanisms behind residual stress generation have been a topic of interest for quite some time since it is well-known that residual stresses can benefit the fatigue life of components. We have studied the residual stresses in lamellar graphite iron generated by fatigue damage. Cylindrical test specimens, with close to zero residual stresses of fully pearlitic lamellar graphite iron, manufactured and subjected to uniaxial load controlled cyclic loading, have been investigated. The load conditions used were: pure tension, pure compression, and alternating tension/compression over one thousand cycles. Measurements were performed using a four-circle goniometer Seifert X-ray machine equipped with a linear sensitive detector and a Cr-tube. Evaluation of the residual stresses were conducted using the sin²-method on the -Fe {211} diffraction peak together with material removal technique to obtain depth profiles. Introduction It is well known that compressive residual stresses (RS) at the surface of a specimen prolongs the fatigue life. The associated increase in strain hardening of the surface, can be equally important for the specimen fatigue life since the combination of strain and compressive RS at the surface of the sample inhibits crack nucleation and propagation. Steels, aluminium, titanium, and nickel alloys are some of the metallic materials in which work hardening at the surface can result in compressive RS and increased fatigue strength of the material Relaxation of near surface RS due to cyclic loading are a well-known phenomenon. Local plastic deformations (microcracks) as well as pinning and un-pinning of dislocations are believed to be a source of stress relaxation In multiphase materials, such as duplex steels, the different phases are known to have different amounts of RS and often also different signs on the stresse

Thermomechanical fatigue crack growth in a cast polycrystalline superalloy

Thermomechanical fatigue (TMF) crack growth testing has been performed on the polycrystalline superalloy IN792. All tests were conducted in mechanical strain control in the temperature range between 100 and 750 °C. The influence of in-phase (IP) and out-of-phase (OP) TMF cycles was investigated as well as the influence of applying extended dwell times (up to 6 hours) at the maximum temperature. The crack growth rates were also evaluated based on linear elastic fracture mechanics and described as a function of the stress intensity factor KI. Without dwell time at the maximum temperature, the crack growth rates are generally higher for the OP-TMF cycle compared to the IP-TMF cycle, when equivalent nominal strain ranges are compared. However, due to the fact that the tests were conducted in mechanical strain control, the stress response is very different for the IP and OP cycles. Also the crack closure level differs significantly between the cycle types. By taking the stress response into account and comparing the crack growth rates for equivalent effective stress intensity factor rages ΔKeff defined as Kmax − Kclosure, very similar crack growth rates were actually noticed independent of whether an IP or OP cycle were used. While the introduction of a 6 hour dwell time significantly increased the crack growth rates for the IP-TMF cycle, a decrease in crack growth rates versus ΔKeff were actually seen for the OP-TMF cycle. The fracture behaviour during the different test conditions has been investigated using scanning electron microscopy