3D Analysis of Microstructure Changes Occurring during Creep Tests of Ultra-Fine Grained Materials

2013 ◽  
Vol 753 ◽  
pp. 46-49 ◽  
Author(s):  
Petr Král ◽  
Jiří Dluhoš ◽  
Pavel Peřina ◽  
Tomáš Barták
Keyword(s):  
Diffusion Processes ◽  
Ion Beam ◽  
Creep Behaviour ◽  
Synergetic Effect ◽  
Thermal Exposure ◽  
Grain Boundary Sliding ◽  
Electron Back Scatter Diffraction ◽  
3D Analysis ◽  
Creep Tests ◽  
Microstructure Changes

Experiments were conducted to determine microstructure changes occurring during thermal exposure in metals processed by equal-channel angular pressing (ECAP). The ECAP pressing was performed at room temperature by route Bc. Static annealing and constant load creep tests in tension were conducted at 0.3-0.5 Tm. The microstructure was examined by scanning electron microscope combined with focus ion beam - TESCAN LYRA 3 equipped with electron back scatter diffraction (EBSD). It was found that creep behaviour is influenced by synergetic effect of additional creep mechanisms like grain boundary sliding, more intensive diffusion processes or recrystallization.

Microstructural Evolution and Creep of an Al-0.2wt.%Sc Alloy after Equal-Channel Angular Pressing

2008 ◽  
Vol 584-586 ◽  
pp. 846-851 ◽  
Author(s):  
Petr Král ◽  
Jiří Dvořák ◽  
Vàclav Sklenička
Keyword(s):  
Electron Microscopy ◽  
Applied Stress ◽  
Creep Resistance ◽  
Creep Behaviour ◽  
Shear Bands ◽  
Synergetic Effect ◽  
Grain Boundary Sliding ◽  
Creep Testing ◽  
Creep Tests ◽  
Angular Pressing

Experiments were conducted on an Al-0.2wt.%Sc alloy to evaluate the effect of equalchannel angular pressing (ECAP) on its creep behaviour. ECAP was conducted at room temperature with a die that had an internal angle of 90° between the two parts of the channel. The subsequent extrusion passes were performed by route BC up to 8 ECAP passes. Creep tests in tension were performed on the as-pressed samples at 473 K under an applied stress range between 10 to 50 MPa. For comparison purposes, some creep tests were performed also on the unpressed alloy. Following ECAP and creep testing, samples were prepared for examination by means of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with an electron back scattering diffraction (EBSD) unit. The observation of the surface of the ECAPed samples after creep exposure showed the occurrence of mesoscopic shear bands. The EBSD data reveal that these bands are separated by high angle grain boundaries. The creep resistance of an alloy is a little decreased after one ECAP pass. However, successive ECAP pressing lead to a noticeable decrease of the creep properties. Thus, the Al-0.2wt.%Sc alloy processed by 8 ECAP passes exhibited faster creep rate by about two and/or three orders of magnitude than the unpressed alloy when creep testing at 473 K and at the same applied stress. The detrimental effect of ECAP on the creep resistance is probably a consequence of a synergetic effect of mesoscopic sliding of groups of grains along shear bands, more intensive grain boundary sliding and creep cavitation in creep of the ultrafine-grained material.

Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

2017 ◽  
Vol 270 ◽  
pp. 162-167
Author(s):  
Petr Král ◽  
Vaclav Sklenička ◽  
Květa Kuchařová ◽  
Marie Svobodová ◽  
Marie Kvapilová ◽  
...  
Keyword(s):  
Welded Joints ◽  
Creep Behaviour ◽  
Creep Damage ◽  
Electron Back Scatter Diffraction ◽  
Steel Pipe ◽  
Tensile Creep ◽  
Creep Tests ◽  
P92 Steel ◽  
Welding Technology ◽  
Fracture Ductility

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

Thermal Stability and Creep Behaviour of MgNiYCe-Rich Mischmetal Alloys Processed by a Powder Metallurgy Route

2009 ◽  
Vol 289-292 ◽  
pp. 127-136
Author(s):  
P. Pérez ◽  
K. Milicka ◽  
Jose Maria Badía ◽  
G. Garcés ◽  
J.M. Antoranz ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Powder Metallurgy ◽  
Diffusion Processes ◽  
Creep Behaviour ◽  
Cold Isostatic Pressing ◽  
Lattice Diffusion ◽  
Creep Tests ◽  
Long Term Stability ◽  
Powder Metallurgy Route

The thermal stability and creep behaviour of MgNi2Y1CeMM1 and MgNi3Y1.5CeMM1.5 alloys have been investigated at 523 and 623 K. Both alloys were processed by a powder metallurgy route involving rapid solidification of powders, cold isostatic pressing and extrusion at 673 K. The microstructure of both alloys was studied in the as-extrusion condition and after thermal treatments at 523 and 623 K up to 500 h. Mechanical characterization was carried out by hardness measurements in samples annealed at 523 and 623 K and stepwise stress compressive creep tests at these temperatures. Results have shown long-term stability of the microstructure after annealing at 523 K in both alloys and hardness values remained constant along all treatment. After treatment at 623 K, however, the microstructure of both alloys remained relatively stable and a decrease in hardness was noticed after 6 h. Creep behaviour of both alloys was very similar. The stress dependences of the creep rate can be well described by modified Garofalo sinh relationship. Activation energies for creep, practically twice of the activation enthalpy of lattice diffusion for pure magnesium (135 kJ mol-1), have been obtained. Therefore, no direct evidence of the controlling role of diffusion processes can be obtained from these experiments.

Creep Behaviour of Si3N4 Ceramics Sintered with RE2O3

2006 ◽  
Vol 514-516 ◽  
pp. 759-763
Author(s):  
Claudinei dos Santos ◽  
Kurt Strecker ◽  
Francisco Piorino Neto ◽  
Cosme Roberto Moreira Silva ◽  
Flávia A. Almeida ◽  
...  
Keyword(s):  
Solid Solution ◽  
Relative Density ◽  
Creep Behaviour ◽  
Rare Earth Oxide ◽  
Grain Boundary Sliding ◽  
Creep Tests ◽  
Sintering Additive ◽  
Compressive Stresses ◽  
Oxide Solid Solution ◽  
Boundary Sliding

The objective of this work was to evaluate the creep behaviour of Si3N4 based ceramics obtained by uniaxial hot-pressing. As sintering additive, an yttrium-rare earth oxide solid solution, designed RE2O3, that shows similar characteristics to pure Y2O3, was used. Samples were sintered using high-purity α-Si3N4 powder, with additive mixtures based on RE2O3/Al2O3 or RE2O3/AlN, at 5 and 20 vol.%, respectively. The sintered samples were characterized by X-ray diffractometry, scanning electron microscopy and density. Specimens of 3x3x6 mm3 were submitted to creep tests, under compressive stresses between 100 and 350 MPa at temperatures ranging from 1250 to 13750C in air. Samples with RE2O3/Al2O3 showed β-Si3N4 as crystalline phase, with grains of high aspect ratio, and a relative density around 99% of the theoretical density. The Si3N4/RE2O3/AlN samples presented α-Si3N4 solid solution, designed α-SiAlON, with a more equiaxed microstructure and slightly lower relative density (96-98%). The results of creep tests indicated that these ceramics containing α-SiAlON are the more creep resistant, with steady-state creep rates around 10-4 h-1, with stress exponents (n) in the range 0.67-2.53, indicating grain boundary sliding as the main creep mechanism.

Effect of Equal-Channel Angular Pressing (ECAP) on Creep in Aluminium Alloys

2007 ◽  
Vol 539-543 ◽  
pp. 2904-2909 ◽  
Author(s):  
Vàclav Sklenička ◽  
Jiří Dvořák ◽  
Marie Kvapilová ◽  
Milan Svoboda ◽  
Petr Král ◽  
...  
Keyword(s):  
Equal Channel Angular Pressing ◽  
Aluminium Alloys ◽  
Creep Resistance ◽  
Room Temperature ◽  
Creep Behaviour ◽  
Coarse Grained ◽  
Pure Aluminium ◽  
Creep Tests ◽  
Angular Pressing ◽  
Compression Creep

This paper examines the effect of equal-channel angular pressing (ECAP) on creep behaviour of pure aluminium, binary Al-0.2wt.%Sc alloy and ternary Al-3wt.%Mg-0.2wt.%Sc alloy. The ECAP was conducted at room temperature with a die that had a 90° angle between the channels and 8 repetitive ECAP passes followed route BC. Constant stress compression creep tests were performed at 473 K and stresses ranging between 16 to 80 MPa on ECAP materials and, for comparison purposes, on the initial coarse-grained materials. The results showed that the creep resistance of the ECAP processed Al-Sc and Al-Mg-Sc alloys was markedly deteriorated with respect to unpressed coarse-grained materials.

scholarly journals Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 877 ◽  
Author(s):  
Vagner Gobbi ◽  
Silvio Gobbi ◽  
Danieli Reis ◽  
Jorge Ferreira ◽  
José Araújo ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Creep Resistance ◽  
High Performance ◽  
Creep Behaviour ◽  
Ductile Failure ◽  
Microstructural Characterization ◽  
Dislocation Slip ◽  
Creep Tests ◽  
Experimental Conditions ◽  
Wide Range

Superalloys are used primarily for the aerospace, automotive, and petrochemical industries. These applications require materials with high creep resistance. In this work, evaluation of creep resistance and microstructural characterization were carried out at two new nickel intermediate content alloys for application in aerospace industry and in high performance valves for automotive applications (alloys VAT 32 and VAT 36). The alloys are based on a high nickel chromium austenitic matrix with dispersion of intermetallic L12 and phases containing different (Nb,Ti)C carbides. Creep tests were performed at constant load, in the temperature range of 675–750 °C and stress range of 500–600 MPa. Microstructural characterization and failure analysis of fractured surfaces of crept samples were carried out with optical and scanning electron microscopy with EDS. Phases were identified by Rietveld refinement. The results showed that the superalloy VAT 32 has higher creep resistance than the VAT 36. The superior creep resistance of the alloy VAT 32 is related to its higher fraction of carbides (Nb,Ti)C and intermetallic L12 provided by the amount of carbon, titanium, and niobium in its chemical composition and subsequent heat treatment. During creep deformation these precipitates produce anchoring effect of grain boundaries, hindering relative slide between grains and therefore inhibiting crack formation. These volume defects act also as obstacles to dislocation slip and climb, decreasing the creep rate. Failure analysis of surface fractures of crept samples showed intergranular failure mechanism at crack origin for both alloys VAT 36 and VAT 32. Intergranular fracture involves nucleation, growth, and subsequent binding of voids. The final fractured portion showed transgranular ductile failure, with dimples of different shapes, generated by the formation and coalescence of microcavities with dissimilar shape and sizes. The occurrence of a given creep mechanism depends on the test conditions. At creep tests of VAT 32 and VAT 36, for lower stresses and higher temperature, possible dislocation climb over carbides and precipitates would prevail. For higher stresses and intermediate temperatures shear mechanisms involving stacking faults presumably occur over a wide range of experimental conditions.

scholarly journals In vivo 3D analysis of systemic effects after local heavy-ion beam irradiation in an animal model

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Kento Nagata ◽  
Chika Hashimoto ◽  
Tomomi Watanabe-Asaka ◽  
Kazusa Itoh ◽  
Takako Yasuda ◽  
...  
Keyword(s):  
Animal Model ◽  
Ion Beam ◽  
Heavy Ion ◽  
Systemic Effects ◽  
3D Analysis ◽  
Beam Irradiation ◽  
Ion Beam Irradiation ◽  
Heavy Ion Beam

scholarly journals Ion Beam Analysis for the Investigation of Diffusion Processes

2020 ◽  
Vol 13 ◽  
pp. 51
Author(s):  
H.-W. Becker
Keyword(s):  
Diffusion Processes ◽  
Ion Beam ◽  
Depth Profiling ◽  
Depth Resolution ◽  
Ion Beam Analysis ◽  
Beam Analysis ◽  
Diffusion Studies ◽  
New Applications ◽  
Diffusion Of Hydrogen ◽  
High Depth

The unique advantages of ion beam analysis, such as the depth resolved unam- biguous stoichometric information of RBS or the possibility to detect hydrogen with high depth resolution still opens new applications in fundamental as well as applied science. Two examples are presented here.The diffusion of hydrogen in cement during the formation of cement has been studied with the 15N hydrogen depth profiling. It could be shown, that the known stages of the hydration process are correlated with the diffusion of hydrogen on a nanometer scale.Diffusion processes play also an important role in geology. The investigation of such processes with RBS will be presented. Prospects of diffusion studies using isotopie tracing with low lying resonances will be discussed.

Rheological modelling of masonry creepThis article is one of a selection of papers published in this Special Issue on Masonry.

2007 ◽  
Vol 34 (11) ◽  
pp. 1506-1517 ◽  
Author(s):  
Kyoung-Kyu Choi ◽  
Shelley L. Lissel ◽  
Mahmoud M. Reda Taha
Keyword(s):  
Stress Level ◽  
Rheological Model ◽  
Creep Behaviour ◽  
Model Development ◽  
Sustained Load ◽  
Creep Tests ◽  
Standard Type ◽  
Rheological Models ◽  
Proposed Model ◽  
Rheological Modelling

In the present study, masonry creep was experimentally investigated. Creep tests were performed on masonry prisms, which were produced using standard fired clay brick and standard Type S mortar. A total of 11 sets of loaded and unloaded masonry specimens were tested under sustained load with three main parameters: stress level, masonry age at loading, and relative humidity. The unloaded prisms compensated for the effects of shrinkage. In this article, the ability of a number of rheological models reported in the literature are examined for their ability to predict masonry creep. Moreover, a new rheological model, one that considers the effect of stress level and masonry age at loading, is proposed. The system parameters of the proposed model were identified using the experimental data. The proposed model was then validated using masonry creep data that was reported by other researchers, but not used in model development. It is shown that the creep behaviour of masonry can be modelled with good accuracy using the proposed rheological model.

Creep Behavior of a Solder Paste With Bi Addition

2017 ◽  
Author(s):  
Pedro E. Ribeiro ◽  
Delfim F. Soares ◽  
Maria F. Cerqueira ◽  
Senhorinha F. Teixeira ◽  
Daniel A. Barros ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Solder Joint ◽  
Mechanical Performance ◽  
Creep Behaviour ◽  
Real Life ◽  
Production Costs ◽  
Solder Paste ◽  
Creep Tests ◽  
Pcb Assembly ◽  
Solder Joint Fatigue

A common failure mode of electronic PCB’s is the appearance of cold solder joints between the component and PCB, during product life. This phenomenon is related to solder joint fatigue and is attributed mainly to the mismatch of the coefficients of thermal expansion (CTE) of component-solder-PCB assembly. Although some experiments show that newer lead-free tin-silver-copper (Sn-Ag-Cu, or SAC) solders perform better than the older SnPb ones, with today’s solder joint thickness decreasing and increasing working temperatures, among others, the stresses and strains due to temperature changes are growing, leading to limited fatigue life of the products. As fatigue life decreases with increasing plastic strain, creep occurrence should have significant impact, especially during thermal cycles. In order to improve mechanical properties, but also as an attempt to reduce maximum reflow cycle temperatures due to component damage and production costs, various SAC solder alloying additives are being considered to use in industrial production facilities. Solder paste producers are proposing new products based on new solder paste formulations, but the real life effects on thermo-mechanical performance aren’t well known at the moment. In this paper a dynamic mechanical analyser (DMA) is used to study the influence of Bismuth (Bi) addition, up to 5 wt %, on SAC405 solder paste, in terms of creep behaviour. Creep tests were made on three-point-bending configuration, isothermally at 30 °C, 50 °C and 75 °C, and three different stresses of 3, 5 and 9 MPa. The results shown not only a significant Bi concentration influence on creep behaviour but also a noticeable temperature dependence.

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