Stress induced hydrogen redistribution in commercial titanium alloys

  • PDF / 1,373,218 Bytes
  • 7 Pages / 594 x 774 pts Page_size
  • 16 Downloads / 143 Views

DOWNLOAD

REPORT


Co

= VHOh,

[1]

where V~ = partial molal volume of hydrogen in an elastically isotropic lattice, R = gas constant, T -- absolute temperature, and where the hydrostatic tensile stress, a h, is considered positive. Eq. [1] is only an approximation since the constraints of a particular system and possible changes in activity coefficient with stress may also be of importance. Experimental observations are consistent with thermodynamic and kinetic considerations concerning the P. N. ADLER is Laboratory Head, Metals Science Laboratory, Research Department, and E. J. SCHNEID is Laboratory Head, R. L. SCHULTE, E. A. KAMYKOWSKI, and F. J. K U E H N E are Senior Research Scientists, Nuclear Detection and Analysis Laboratory, Grumman Aeorspace Corporation, Be thpage, NY 11714. Manuscript submitted November 30, 1979.

influence of stress. Wriedt and Oriani H showed that an elastically stressed 75 pct Pd-25 pct Ag alloy in a hydrogen atomosphere increased in hydrogen content under uniaxial tension and decreased in hydrogen under uniaxial compression. Bockris, et a112 studied Armco iron and 4340 steel and found that permeation of hydrogen was increased by tensile stress and decreased by compressive stress, with the diffusion coefficient being unaffected by the applied elastic stress. Waisman, Sines, and Robinson ~3measured the equilibrium pressure of hydrogen at elevated temperature in C.P. titanium and Ti-6A1-4V alloy as a function of applied stress and found the expected decrease in activity with tensile stress and an increase in activity with compressive stress. In addition, Schaumann, Volkl, and Alefeld~4used Gorsky effect measurements, i.e., relaxation strain accompanying point defect migration under a stress gradient, to determine the diffusion coefficient of hydrogen in V, Nb, and Ta. Previously, we have reported on the direct measurement of stress-induced hydrogen concentration changes in a fl-phase Ti-8Mo-8V-2Fe-3AI alloy, ~5and the effect of elastic and plastic loading on the extent and kinetics of hydrogen redistribution was identified. The present study provides a general characterization of the influence of stress on hydrogen redistribution in commercial titanium alloys by examining two additional fl-phase and two a-phase alloys as well as three morphologies of an a + fl alloy. Information concerning Ti-8Mo-8V-2Fe-3A1 has been included among the results throughout this paper for systematic comparison. EXPERIMENTAL Sample Description All samples examined in the course of this investigation were prepared from material obtained from commercial sources. The a-phase alloys, commercial purity titanium (C.P. Ti) and Ti-5A1-2.5Sn, were ex-

ISSN 0360-2133/80/0911-1617500.75/0 METALLURGICAL TRANSACTIONS A 9 1980 AMERICAN SOCIETY FOR METALS AND VOLUME 11A, SEPTEMBER 1980--1617 THE METALLURGICAL SOCIETY OF AIME

amined in the as-received condition. Heat treatment was utilized to obtain single phase fl in both Ti3A1-8V-6Cr-4Mo-4Zr and Ti-30Mo and also to obtain different a/B morphologies in Ti-6A1-4V. The compositions of the