ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Alloy 718 is known to be sensitive to oxidation assisted intergranular cracking. It is alsodemonstrated that the occurrence of jerky flow (also called Portevin-Le Châtelier effect) stops theintergranular damaging mechanism. As dynamic strain ageing is known to be linked with the alloycontent of interstitial species, the aim of the present work is to study the effect of carbon, nitrogenand oxygen concentrations on the mechanical behaviour of thin tensile specimens tested underoxidation conditions close to those encountered industrially for turbo machine disks. Thanks to heattreatments performed under reducing atmosphere, the content of interstitial species in tested alloy718 samples is gradually curbed. Tensile specimens were then tested between 550 and 700°C forthe strain rate range [10-5, 10-1] s-1. The key point of this work is that, for a given testingtemperature, the tensile tests clearly demonstrated that the transition from an intergranular fragilefracture mode to a transgranular ductile one was always linked with the occurrence of Portevin-LeChâtelier phenomenon but for slower strain rates in comparison with what was observed on the asreceived aged material tested in the same conditions. This shift of the transition of fracture modethrough the lower strain rates remained true until a threshold value of the heat treatment time underreducing atmosphere. Specimens heat treated over this value systematically exhibited a fullytransgranular ductile fracture mode, whatever the plastic flow regime was. Implication of such afinding on the intergranular embrittlement of alloy 718 by high temperature oxidation is thendiscussed
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/20/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.595-598.951.pdf
