Loss of strength in Ni3Al at elevated temperatures

Stress decrease above the stress peak temperature (750 K) is studied in h123i single crystals of Ni3(Al, 3 at.% Hf ). Two thermally activated deformation mechanisms are evidenced on the basis of stress relaxation and strain rate change experiments. From 500 to 1070 K, the continuity of the activation volume/temperature curves reveals a single mechanism of activation enthalpy 3.8 eV/atom and volume 90 b3 at 810K with an athermal stress of 330 MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores is evidenced through serrated yielding, peculiar shapes of stress–strain curves while changing the rate of straining and stress relaxation experiments. This complicates the identification of the deformation mechanism, which is likely connected with cube glide. From 1070 to 1270 K, the high-temperature mechanism has an activation enthalpy and volume of 4.8 eV/atom and 20 b3, respectively, at 1250 K

MECHANICAL PROPERTIES OF AL THIN FILM MEASURED BY TWO DIFFERENT METHODS

Abstract Mechanical properties of an aluminium thin film were measured by microcompression and indentation tests. The microcompression technique combines preparation of specimens using focused ion beam (FIB) and compression test by a nanoindeter device. Cylindrical specimens were prepared by focused ion beam milling. The height of cylindrical specimens was about 2 µm and their diameter about 1,3 µm. The load and displacement were continuously measured during tests. The stress-strain curves were obtained in two representations. Stresses of the first plastic bursts were determined in both representations. Hardness and Young modulus were measured by indentation test using continuous stiffness method. Representative values of thin film were calculated

Multiaxial elastoplastic cyclic loading of austenitic 316L steel

Cyclic stress-strain response and fatigue damage character has been investigated in austenitic stainless steel 316L. Hollow cylindrical specimens have been cyclically deformed in combined tension-compression and torsion under constant strain rate condition and different constant strain and shear strain amplitudes. In-phase and 90° out-of-phase cyclic straining was applied and the stress response has been monitored. Cyclic hardening/softening curves were assessed in both channels. Cyclic softening followed for higher strain amplitudes by long-term cyclic hardening was observed. Cyclic stress-strain curves were determined. Study of the surface damage in fractured specimens revealed the types and directions of principal cracks and the sources of fatigue crack initiation in slip bands

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

Can empathy lead to emotional exhaustion in teachers? The mediating role of emotional labor

Objectives: The present study was designed to examine the links between empathy, emotional labor (both surface and deep acting), and emotional exhaustion as well as determine if emotional labor mediates the relationship between empathy and emotional exhaustion in teachers. It was assumed that emotional labor can take two opposite directions (positive mood induction and negative mood induction). Thus, the additional aim of the study was to analyze the mediating role of mood regulation strategies in the relationship between empathy and emotional exhaustion. Materials and Methods: A sample of 168 teachers from Łódź and its surroundings completed a set of questionnaires: Emotional Labor Scale; Mood Regulation Scales, Maslach Burnout Inventory, and Empathic Sensitivity Scale. Results: The results provided mixed support for the hypotheses indicating that both types of emotional labor, negative mood induction and emotional exhaustion were positively intercorrelated. Moreover, deep acting was a significant mediator in the relationship between empathy and emotional exhaustion. The analyzed link was also mediated by negative mood induction, whereas positive mood induction did not emerge as a significant mediator. Conclusions: The study provided insight into the role of empathy and emotional labor in the development of teacher burnout. It also confirmed that deep acting and negative mood induction mediate the relationship between empathy and emotional exhaustion in teachers

About the determination of the thermal and athermal stress components from stress-relaxation experiments

The determination of the thermal and athermal stress components using relaxation experiments along a stress-strain curve is critically evaluated. Short-term stress-relaxations are performed along the stress-strain curve of single crystals of Ge at 850 K, Cu, and Ni3Al at 300 K. They are analyzed by three different equations with two or three parameters including the athermal stress. The stress components obtained are compared to the values determined by stress-reduction experiments considered as the reference method. The relaxation rate is considered successively to be a power function or a hyperbolic sine function of the effective stress or a hyperbolic decrease of stress with time is assumed. It is shown that the three methods overestimate or underestimate the stress components depending on the material and deformation conditions. The error can be as large as about 100%. Reasons for the inadequacy of short-term relaxation experiments for the determination of the stress components are discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Microstructural stability of ODS steels in cyclic loading

The remarkable microstructural stability of high chromium steels prepared by powder metallurgy and strengthened by dispersion of nanometric yttrium oxides in cyclic loading at high temperatures is reported. Contrary to the continuous cyclic softening and profound changes in the microstructure during fatigue of common high chromium steels, the addition of 0.3wt% Y2O3 stabilizes the microstructure and significantly reduces cyclic softening of investigated steels. The evolution of microstructure as a result of fatigue loading at room temperature, 650 and 750 degrees C, was examined by means of transmission electron microscopy. Only minor changes in the microstructure were detected. The stability of oxide particles after high-temperature exposure was confirmed by energy dispersion spectroscopy chemical analysis. The microstructural features are discussed in relation to the cyclic behaviour of the oxide dispersion strengthened steels. The analysis of the hysteresis loop indicates that oxide nanoclusters are intersected and dissolved in slip bands of ODS Eurofer steel. This process contributes to cyclic softening