Accession Number : ADA267042


Title :   Experimental Study of Oxygen-Assisted Crack Growth in Alloy 718 and Alloy TI-1100


Descriptive Note : Final rept. 30 Sep 90-29 Sep 91,


Corporate Author : ECOLE NATIONALE SUPERIEURE DES MINES DE PARIS EVRY (FRANCE) CENTRE DES MATERIAUX


Personal Author(s) : Andrieu, E ; Pineau, A ; Ghonem, H


Full Text : https://apps.dtic.mil/dtic/tr/fulltext/u2/a267042.pdf


Report Date : Feb 1993


Pagination or Media Count : 201


Abstract : The high Temperature fatigue crack growth behavior of alloy 718 is reviewed and investigated. FCGR have then been measured under constant K and various oxygen partial pressures. A transition pressure associated with an important increase of the FCGR is found. At this transition pressure (10-2mbar) the crack propagation path changes from transgranular to intergranular. From this study it is concluded, that intergranular crack growth requires the formation of Ni based oxide during the early stage of the oxidation as well as high intergranular internal stresses promoted by an inhomogeneous distribution of the deformation. The crack growth behavior of TI-1100 is investigated for loading frequencies ranging from 30 Hz to 0.005 Hz at temperature levels extending from 23 Cto 650 C in both air and vacuum environments. Two types of time-dependent damage mechanisms have been identified; oxidation and creep effects. It is concluded that effect of oxidation on the crack growth acceleration is rapid and constant in relation to the frequencies tested and is weekly dependent on cycle time. Creep effects, on the other hand, are dominant at low frequencies in both air and vacuum and are loading-rate dependent


Descriptors :   *CRACK PROPAGATION , *TITANIUM ALLOYS , MICROSTRUCTURE , OXIDATION , FATIGUE(MECHANICS) , HIGH TEMPERATURE


Subject Categories : Properties of Metals and Alloys
      Mechanics


Distribution Statement : APPROVED FOR PUBLIC RELEASE