|
|
Comparison of Creep Behaviour and Microstructural Changes in Electrodeposited Ultrafine-grained Nickel and its Particle-reinforced Nanocomposite
Kvapilová, Marie ; Sklenička, Václav ; Kuchařová, Květa ; Vidrich, G.
On the basic of the creep experimental results the paper reports comparison creep behaviour of electrodeposited ultrafine-grained nickel and its particle-reinforced nanocomposite. The objective of this research was to further improve the knowledge of the creep behaviour of monolithic nickel and to explore the role of nano-sized SiO2 particles in the potential creep strengthening of electrodeposited Ni nanocomposite. The creep behaviour and microstructure of the pure ultrafine-grained nickel and its nanocomposite reinforced by 2 vol.% nano-sized SiO2 particles were studied at temperatures in the range from 293 to 573 K and at the tensile stresses between 100 to 800 MPa. It was found that the creep resistance of the nanocomposite might be noticeably improved compared to the monolithic nickel. Possible creep mechanisms controlling the creep rate during the creep loading were discussed. The Coble creep as creep rate controlling mechanism was founded improbable.
|
|
|
Creep Behaviour and Microstructure of Ultrafine Grained Iron Processed by ECAP
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
Pure iron (99.99%) was subjected to equal-channel angular pressing (ECAP) with a die having an internal channel of 90°. The subsequent extrusion passes were performed by route A up to 4 passes. The microstructures of UFG iron were investigated using EBSD (electron back scatter diffraction) and transmission el. microscopy (TEM). Tension creep tests were performed on the as-pressed samples at temperature of 773 K and under applied load 60 MPa. For comparison purposes the same creep test was performed also on the unpressed state. The effect of number ECAP passes on creep behavior of pure Fe was investigated. Results showed that the creep resistance of pure Fe after ECAP is improved in comparison with the unpressed state.
|
|
|
Effect of different number of ECAP passes on creep in Cu-Zr alloy
Král, Petr ; Dvořák, Jiří ; Svoboda, Milan ; Kvapilová, Marie ; Sklenička, Václav
A coarse-grained binary Cu-0.2wt%Zr alloy was processed by equal-channel angular pressing (ECAP) in order to evaluate the effect of severe plastic deformation on the thermal stability of resulting ultrafine-grained microstructure after ECAP and on creep behaviour of the pressed alloy. Constant stress creep tests in tension were conducted at temperature 673 K and at the different applied stresses. It was found that the Cu-0.2Zr alloy after the first four ECAP passes exhibited higher creep resistance by comparison with unpressed state. However, the alloy processed by 8 ECAP passes showed faster creep rate than unpressed material under the same loading conditions. The measured value of stress exponent of the creep rate n~6 indicates possibility of an intragranular deformation mechanism as the rate-controlling process in creep of an alloy after 8 ECAP passes. Furthermore, creep behaviour of ECAPed material may be influenced by mesoscopic boundary sliding along shear bands.
|
|
|
Mechanical and creep properties of aluminium alloys processed by Equal-Channel Angular Pressing (ECAP)
Dvořák, Jiří ; Král, Petr ; Kvapilová, Marie ; Sklenička, Václav ; Svoboda, Milan
This work examines mechanical and creep behavior in UFG aluminium alloys. UFG microstructure was achieved after application 8 ECAP passes. The coarse-grained materials were subjected to ECAP at room temperature in a die, which had a 90° angle between the channels. The microstructural investigations were performed using TEM and EBSD. The experiments show that ECAP reduced the average grain size to approximately 300 nm and led to the higher occurrence of high-angle boundaries in comparison with the coarse-grained material. The mechanical properties of these alloys were investigated using hardness measurements and tensile testing at room temperature. In addition, constant stress creep tests in compression were conducted at the applied stresses from 10 to 80 MPa and at temperature of 473 K. The aim of this investigation was to determine the effect of ECAP on the mechanical behavior and creep resistance of aluminium alloys containing Mg and/or Sc.
|
|
|
Creep failure of Al-0.2%Sc alloy after severe plastic deformation (ECAP)
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
Experiments were conducted on a coarse grain Al-0.2%Sc alloy which was processed using ECAP method (equal-channel angular pressing). ECAP deformation was conducted at room temperature using a die with two channels inclined an angle 90°. Tensile creep tests were performed at 473 K and 20 MPa. The microstructure and the fracture surfaces were observed by light microscopy, SEM and using EBSD technique. Creep fracture elongation of Al-0.2%Sc alloy was increasing with the number of ECAP passes. The fracture behaviour of samples after ECAP deformation and subsequent creep exposure was controlled by the formation of the mesoscopic slip bands on the specimen surface. The analyzes of microstructures of samples after 2 and 4 ECAP passes showed that the failure probably occurred at the places with the maximum heterogeneity of the microstructure.
|
|
|
Creepové chování hliníkových slitin zpracovaných metodou ECAP
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
This work examines creep behaviour in ultrafine-grained aluminum alloys (with Mg and Sc). The coarse-grained materials were subjected to ECAP (equal-channel angular pressing) at room temperature. The microstructural investigations were performed using transmission electron microscopy (TEM). The experiments show that ECAP reduced the average grain size to ~300 - 400 nm and led to the higher occurrence of high-angle boundaries in comparison with the coarse-grained material. The movement of boundaries and the growth of grains, created by ECAP, was restricted by nano Al3Sc coherent precipitates (up to 10 nm).Constant stress creep tests in compression were conducted at the applied stresses from 10 to 80 MPa and temperature of 473 K . In this work the values of the stress exponent for UFG materials and the unpressed material were determined. creep rates recorded for the as-pressed samples were significantly faster, by about two orders of magnitude, than the unpressed alloys.
|
|
|
Effect of Number of ECAP Passes on Creep Behaviour and Microstructure of Pure Aluminium and Al-Sc Alloy
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
Experiments were conducted to determine an effect of equal-channel angular pressing (ECAP) on the creep behaviour and the microstructure of pure aluminium and an Al-Sc alloy. The coarse-grained materials in their as-received states were subjected to ECAP at room temperature using a die, which had a 90° angle between the channels. Experiments show that ECAP reduced the average grain sizes of ~1µm and ~0.3µm for pure Al and Al-Sc. The grain sizes after 8 ECAP passes and subsequent creep exposure are ~12µm and ~2µm for Al and Al-Sc alloy, respectively. The fracture analysis and morphology of creep fracture surfaces of an Al-Sc alloy revealed the formation of shear bands which were orientated along the direction of the last ECAP pass. The application of ECAP method causes a substantial continuous decrease in the creep resistance of Al and Al-Sc alloy with increasing numbers of ECAP passes which can be explained by increasing contribution of grain boundary sliding to the total creep strain.
|
|
|
Creep behaviour of Al-0.2%Sc alloy processed by ECAP Method
Dvořák, Jiří ; Král, Petr ; Kvapilová, Marie ; Sklenička, Václav
An Al-0.2wt.%Sc aluminium alloy was subjected to equal-channel angular pressing (ECAP) at room temperature to refine its coarse – grain size corresponding to its as-received state. For this purpose the ECAP die was used which had a 90° angle between the die channels. By application of this method at room temperature an ultrafine-grained microstructure was achieved with the grain size of ~ 0.3mm after 8 ECAP passes by route BC. Following creep tests in tension were performed at 473 K and at applied stresses ranging from 10 to 50 MPa on ECAP material and, for comparison purposes, on unpressed one. The results indicate, that the creep resistance of ECAP material is markedly lower after 8 passes in comparison with creep behaviour of coarse – grained one. The detrimental effect of ECAP on the creep resistance is probably caused by increasing contribution of grain boundary sliding to the overall creep deformation.
|
|
|
Vliv metody ECAP na mikrostrukturu a creepové chování slitiny AL-3Mg-0,2Sc
Dvořák, Jiří ; Král, Petr ; Kvapilová, Marie ; Sklenička, Václav
The coarse-grained material (Al-3Mg-0.2Sc alloy) was subjected to ECAP at room temperature. Compression creep tests were conducted on both states of material at the applied stresses from 16 to 80 MPa and temperature of 473 K. The results demonstrate that the minimum creep rate of the ultrafine-grained (UFG) material is up to two order at magnitude higher than that of the unpressed coarse-grained material. A microstructural investigation of this alloy was performed using electron microscopy (TEM and EBSD). The experiments show that ECAP reduced the average grain size to ~ 300 nm and led to the higher occurrence of high-angle boundaries. It should be stressed that the application of eight ECAP passes causes a substantial decrease in the creep resistance of the alloy. Based upon the results it may be possible to suggest, that the creep behaviour of UFG alloy is influenced by grain boundary sliding accommodated by diffusion-controlled movement of intragranular mobile dislocations.
|
guest ::
RSS feed.