Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Zdzisław Jasieński"

Low temperature deformation twinning in channel-die compressed aluminium single crystals evidenced by Acoustic Emission

Czytaj za darmo! »

It is commonly believed that twinning is the most efficient source of acoustic emission [1÷5] due to fast release of great amount of elastic energy. It is connected with the fact, that the velocity of twinning dislocations is higher from this of slip dislocations [4], which results in the increase of contribution of accelerating effects in the recorded AE impulses. Very often acoustic emission induced by twinning contains also an audible range. Hence, more or less loud characteristic knocks during deformation can be heard. One of the first AE investigations concerned the tensile test of titanium and its alloys [1], in which it was established, that the AE activity in Ti was bound with twinning from the beginning, while in Ti alloys the AE impulses from twinning appeared after a high degree of deformation. During compression of the γ-TiAl alloy, AE sources were identified as generally coming from slip, twinning and the appearance and development of microcracks. It was reported that “the detailed mechanisms by which moving dislocations create elastic waves are not fully understood" [3]. Moreover, the problem of twinning in Al has still remained controversial. In available literature authors did not find any data on this subject. It is believed quite commonly, that at least in simple uniaxial strain state - like in a tensile test - twins do not appear in Al. The aim of this work is to demonstrate, that there are numerous proofs that in a complex strain state, which occurs in the channel die compression of single Al crystals at temperature of liquid nitrogen the twinning processes do occur. MATERI ALS AND MET HODS The single crystals of Al and Ag (for comparison) were produced with the Bridgman method, of which samples of dimensions 10×10×10 mm of orientations {112}<111> and {531}<231> for Al and {112}<111> for Ag were cut out. The single crystals were subjected to tests of channel-die compression at temperature of liq[...]

 Strona 1