The influence of temperature at constant strain rate has been evaluated with respect to superplastic behavior of dispersion strengthened Al-Al4C3 composite with 4 vol.% of Al4C3 phase. The dispersion strengthened Al-Al4C3 was prepared by powder metallurgy. Material can be characterized by grain size around 1 mu m and dispersed particle Al4C3 size around 50 nm. This material showed superplastic behavior for strain rate 10(-3) s(-1) by test temperature 573 K. The mechanism of superplastic deformation was also investigated. For the presented material with low content of disperse particle slip on grain boundaries is typical. The final fracture is transcrystalline with dimples with their mean size 1.25 mu m. The dimples are initialized by Al4C3 particles in size from 40 to 50 nm.

Changes in the strain and fracture mechanism during tensile testing were investigated in dispersion strengthened Al-Al4C3 system. Al materials with volume fraction of 4 and 12 vol.% of Al4C3 were tested at temperatures from 293 to 673 K at different strain rates ranging from (epsilon) over dot = 2.5 x 10(-5) to 10(-1) s(-1). At room temperature, the strain was controlled by dislocation movement and interactions. Work hardening characterized the first part of the strain curve and the second part was characterized by the local strain in the neck. At higher temperatures and strain rates, the number of strain mechanisms was increased by a mechanism attributed to a dynamic recovery process. Fracture mechanism changes depend on temperature and strain rate. At lower temperatures the dispersion strengthened Al-Al4C3 system was characterized by transcrystalline fractures. Increase of the test temperature to 523 K and over that, led to intercrystalline fractures for low strain rates (epsilon) over dot = 2.5 x 10(-5) s(-1).

The development of the nanostructure in commercial pure copper and the strength and ductility after severe plastic deformation (SPD) with the technology of equal channel angular pressing (ECAP) are analysed. Experimental results and analyses show that both strength and ductility can be increased simultaneously by SPD. The final grain size decreased from the initial 50 mu m by SPD to 100-300 run after 10 passes. An increase of the ductility together with an increase of strength caused by SPD is explained by a strong grain refinement and by a dynamic equilibrium of weakening and strengthening, and it is visible on the final static tensile test stress-strain charts.

A review starting from material science trough production technology to testing properties of the Cu-Al2O3 system, based on several years of research and development in materials research, is presented. Microstructural design, microstructure evaluation by different methods, first the importance of correct secondary phase particle spatial distribution evaluation, influence of microstructure on properties, and modifications of production technology, are described. Evaluations are compared to microstructural parameters of a real material: volume fraction, distribution calculations, as well as interparticle distance. Strength and plastic properties at room and higher temperatures are presented and the failure mechanism described. A simplified model of the failure mechanism is proposed. Influence of dispersed Al2O3 particles on recrystallisation is characterised, too.

Deformation of the Al-Al4C3 composites with different volume fraction of Al4C3 phase was investigated at different temperatures (293-723 K) and different strain rates (2.5. 10(-5) s(-1) to 1.10(-1)s(-1)). At temperatures 673-723 K and at the highest strain rate 10(-1) s(-1), a significant ductility increase was observed. TEM analysis suggests that it is the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, which is known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the studied composite resulted in a shift in the deformation mechanism from more slip on grain boundaries to more grain rotation.

Deformation of the Al-Al4C3 composites with different volume fraction of Al4C3 phase was investigated at different temperatures (293-723 K) and different strain rates (2.5·10 -5 s -1 to 1·10 -1 s -1 ). At temperatures 673-723 K and at the highest strain rate 10 -1 s -1 , a significant ductility increase was observed. TEM analysis suggests that it is the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, which is known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the studied composite resulted in a shift in the deformation mechanism, from more slip on grain boundaries to more grain rotation.

The deformation of Al–Al4C3 composites with different volume fraction of Al4C3 phase was tested at different temperatures and different strain rates. It is shown that at temperatures between 400 and 450 °C and the highest strain rate applied 10−1 s−1, a significant ductility growth was observed. According to the results of TEM analysis, this behaviour is supposed to be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, known as strain induced dynamic recovery. The increase of the volume fraction of secondary phase in the investigated composite changed the deformation mechanism from more slip on grain boundaries to more grain rotation.

The influence of Al2O3 particles on fracture of the Cu–Al2O3 system is analyzed by ‘in situ tensile test in SEM’. It has been shown, that tensile strain in the extrusion direction produced first micro cavities on matrix–particle interfaces due to decohesion of particles from the matrix. The cavities grow and coalesce first in the direction of rows of particles with growing strain, and then in direction perpendicular to the rows, leading to final fracture. The strain at fracture is dependent on Al2O3 particle volume fraction. The fracture mechanism is not dependent on Al2O3 particle volume fraction in the tested range. Model explaining the fracture mechanism was introduced.

In the present work the deformation of the Al-Al4C3 composite is analysed at different temperatures and strain rates. As shown at 400 degreesC and highest strain rate applied 10(-1) s(-1), a significant elongation growth was observed with a corresponding reduction of the fractured area. On the base of TEM analysis and according to our previous papers, it is supposed to be the result of dynamic grain polygonisation, rotation and partial recrystallisation in the tested system, known as strain-induced dynamic recovery.

Dispersion strengthened Al-Al4C3 materials prepared by mechanical alloying posses good high-temperature properties at low specific weight. Their structure is heterogeneous and consists of fine grained matrix and Al4C3 particles created by chemical reaction between Al and C. The particles are incoherent, different in size.The failure mechanism was analyzed by "in situ tensile test in SEM" for Al-Al4C3 composites with 8 vol.% of Al4C3 Strain rate 6.6 10(-4) s-(1) was applied by direct loading of the thinned test piece in the scanning electron microscope in vacuum at 20 degrees C. The crack creation, coalescence, and propagation ill the test piece was analyzed.The first cracks were shown to create by failure of large Al4C3 particles in the process of loading. Further load increase caused further crack propagation by particle cracking, and matrix-particle interphase boundary decohesion. Cracks propagated also in the direction of load trough the concentration of smaller particles grouped in bands. The fracture ended by tearing the ligaments between the bands. Failure mechanism model has been introduced.

The influence of Al2O3 particles volume fraction on the fracture mechanism in the Cu–Al2O3 system is analyzed by “in situ tensile test in SEM”. It is shown that tensile strain first produces microcavities on matrix–particle interfaces due to decohesion of particles from the matrix. The cavities grow and coalesce first in the direction of rows of particles with growing strain. Cracks develop in both directions: in the rows, and in the direction perpendicular to the rows, leading to final fracture. The deformation value at fracture is dependent on Al2O3 particle volume fraction. A model explaining the fracture mechanism is introduced.

Strain and fracture mechanisms of Cu–TiC system with 5.3 vol % TiC was studied by an `in situ tensile test in SEM'. It was shown that during tensile strain the first cracks appear in the places with the largest strain after decohesion of larger particles or clusters of small particles from the matrix. A further stress increase causes the formation of `saw-like fracture' in an angle of 45° by interconnecting the rows of particles in the direction of tension. The fracture morphology is transcrystalline ductile. A model of fracture mechanism of the investigated system was suggested.

In the paper a study of fracture mechanism of Cu-TiC system by an "in situ tensile test in SEM" was done, It is shown that during tensile strain the first cracks appear in the places with the largest critical strain epsilon = 0.16 after decohesion of larger particles or clusters of small particles. The further stress increase causes formation of a saw-like fracture in an angle alpha = 45 degrees following rows of particles declined from the direction of tension. The fracture morphology is transcrystalline ductile. A model of fracture mechanism in the investigated system was suggested.

I , 2 2 , • J. ZRNIK, M. BESTERCI, L. KOVAC 1Technical University of Kosice Department of Materials Science Park Komenskeho 11, 040 OJ Kosice, Slovakia 2 Institute of Materials Research, Slovak Academy of Science, Watsonova 47, 043 53 Kosice, Slovakia The mutual relationship between mechanical properties and microstructure changes in Al-A14C3 composite system is characterised by tensile test in wide range of testing temperatures. The dominant mechanism of plastic deformation at the deformation temperatures up to 300°C regardless of used strain rate was dislocation glide. In temperature region from 300 to 450°C and for lower strain rates the grain boundary glide participates in deformation process. The phenomenon of superplasticlike behaviour was observed at deformation temperature of 450°C and the

In the presented work the change in fracture for the Al-Al4C3 system was investigated and analyzed at temperatures from 20 to 450°C and strain rates from 2.5 10−5 to 10−1 s−1. At room temperatures during tensile testing the strain is controlled by dislocation movement and reactions. The first part of the strain is characterized by work hardening expressed by the exponent “n”, the second part by the local strain in the neck. For high temperatures in the investigated region the principal mechanism keying the strain is the presence of dynamic recovery processes. Strain rate influences on fracture are analyzed.

In this work the change in the nature of the strain for the Al-Al 4 C 3 system was investigated and analyzed at temperatures from 20 to 450°C and strain rates from 2.5.10 -5 to 10 -1 s -1 . At room temperature during tensile testing the strain is controlled by dislocation movement and reactions. The first part of the strain is characterized by work hardening expressed by the exponent n, the second part by the local strain in the neck. For high temperatures in the investigated region the principal mechanism keying the strain is the presence of dynamic recovery processes. Strain rate influences on fracture are analyzed. The values measured at the temperature 450°C and strain rate 10 -1 s -1 are, we suppose, the onset of the superplastic behavior.

Dispersion strengthened Al-Al4C3 composite with 8 vol.% of Al4C3, has been tested at 400 degrees C by creep, and by fatigue superimposed on creep. The strain and life to fracture were tested at different loading schedules defined by the stress ratio Q. The criteria used to analyze the resistance to creep, or creep - fatigue, have been the life to fracture, the strain to fracture, and fractography.