CYCLIC PLASTIC BEHAVIOUR OF UFG COPPER UNDER CONTROLLED STRESS AND STRAIN LOADING

<em>The influence of stress- and strain-controlled loading on microstructure and cyclic plastic behaviour of ultrafine-grained copper prepared by equal channel angular pressing was examined. The stability of microstructure is a characteristic feature for stress-controlled test whereas grain coarsening and development of bimodal structure was observed after plastic strain-controlled tests. An attempt to explain the observed behaviour was made.</em

Effect of Al-Si diffusion coating on the fatigue behavior of cast Inconel 713LC at 800°C

AbstractCylindrical specimens of Inconel 713LC in as-received condition and with surface treatment by Al-Si diffusion coating were cyclically strained under strain control at 800 °C in air. Changes in the shape and size of the superalloy precipitates during the surface treatment are documented. The structural and hardness characteristics of the hardened surface layer are presented. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The sections parallel to the specimen axis and fracture surfaces have been examined to study fatigue damage mechanisms. The coating results in fatigue life improvement while the stress response of the treated material is lower in comparison with the untreated one

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

Low cycle fatigue testing of materials at elevated temperatures

Low cycle fatigue testing metod of materials at elevated temperature is presented. Low cycle fatigue tests were performed in the material Inconel 713LC at 500 °C. The test results are used to evaluate the fatigue life

High Temperature Fatigue Behaviour of Third Generation of TiAl Alloys

Low cycle fatigue properties of lamellar TiAl with 7.8 at.% Nb were studied at four temperatures: room temperature, 700, 750 and 800 °C. Up to 750 °C, stable cyclic behaviour is observed while cyclic softening is characteristic for 800°C. The strength of the alloy is still high even at 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling at RT. At 750 °C, the lamellar structure was in some places destroyed by cyclic plasticity and pure g-phase islands with high density of dislocation debris were formed. At 800 °C, the domains without lamellar structure cover about 10% of inspected volume and are almost dislocation free. The results show that the diffusion processes leading to vanishing of small prizmatic dislocation loops start to operate between 750 and 800 °C. The destruction of lamellar microstructure and annealing of dislocation debris is the reason for cyclic softening at 800 °C

Low cycle fatigue characteristics of austenitic stainless steel AISI 321 at 23 and 325 °C

Cylindrical specimens of austenitic stainless steel AISI 321 were cyclically strained under total strain control to fracture at room temperature and at 325 °C. Hardening/softening curves, cyclic stress-strain curves and fatigue life curves in the representation of total strain amplitude, plastic strain amplitude and stress amplitude versus number of cycles to fracture were evaluated

Low cycle fatigue of notched specimens of austenitic steel AISI 321 at 23 and 325 °C

Low cycle fatigue tests of notched specimens of AISI 321 steel were performed at 23 a 325 °C. Fatigue hardening/softening curves, fatigue life curves and cyclic stress-strain curves were evaluated

Effect of plasma sprayed AlSi coating on low cycle fatigue properties of cast superalloy Inconel 738LC

Air plasma spraying was applied to obtain AlSi protective surface coating on cylindrical specimens of cast polycrystalline superalloy Inconel 738LC. Chemical composition of the surface treated layer was studied and the hardness depth profile was measured. Surface treated and untreated specimens were cyclically strained under total strain control at 800 °C in air. Cyclic stress-strain response and fatigue life of both materials were obtained. The coating results in a slight decrease of cyclic stress-strain curve. A detrimental effect of the surface treatment on derived Wöhler curve is documented while Manson-Coffin curves of both materials are almost identical. Specimen section observations and fracture surface examinations help to discuss fatigue behaviour of both materials

Fatigue life and short crack growth in plasma nitrided 316L stainless steel

Cylindrical specimens with shallow notch of 316L austenitic stainless steel both with plasma nitrided and untreated surface were cyclically strained with constant plastic strain amplitude. Fatigue life, crack initiation, short crack growth and stress response were studied in both materials

Vývoj únavového poškození v kovových materiálech

Import 05/12/2006PrezenčníNeuveden