The effect of matrix strength on the fracture resistance of an alpha-Beta titanium alloy, corona-5
- PDF / 1,253,733 Bytes
- 10 Pages / 594 x 774 pts Page_size
- 6 Downloads / 175 Views
I.
INTRODUCTION
IT has been recognized for some time that microstructure plays a highly significant role in the fracture toughness of titanium alloys, t -~21 In the fracture toughness testing of ductile materials the J-integral has been used to evaluate fracture resistance, and fracture resistance is expressed in terms of crack initiation resistance, J~c o r Jq, and crack growth toughness, Tn. Recently, it has been shown that these two quantities do not necessarily have the same relationship with microstmcture for A1-Li alloys, t13] and it has been proposed that microstructure would have a greater influence on crack growth than on crack initiation, t141 In this study the role of microstructure and matrix yield strength will be shown to have a marked influence on fracture behavior, with the Jq and the tearing resistance T revealing somewhat different influence of microstructure. II.
EXPERIMENTAL PROCEDURE
A. Material CORONA-5, an a-/3 titanium alloy, containing 4.73 pct Mo, 4.75 pct A1, 1.43 pct Cr, 0.071 pct Fe, 0.007 pct N, 0.133 pct O, and balance Ti (by weight), was the material used. The alloy was prepared as a 91-Kg, 20.3-cm diameter ingot. The ingot was forged in the beta field at 1038 ~ to ll.4-cm square, then forged to 7.6-cm round at 885 ~ in the a-/3 field. The beta transus was found to lie between 921 and 927 ~ Subsequent working was from 855 ~ The round material was then press forged from 7.6-cm to 5.7-cm round corner squares. Finally, it was hot rolled with a series of reheatings to 1.52- and 2.08-cm diameter rounds. Sizing and straightening of the bars was carried out during the processing, as needed, by hot swaging. K.R. NARENDRNATH is Analytical Materials Scientist with Vapor Technologies, Inc., Bradford Road, Mount Vernon, NY 10553. H. MARGOLIN is Professor, Department of Metallurgy and Materials Science, Polytechnic University, 333 Jay Street, Brooklyn, NY 11201. Manuscript submitted October 26, 1987.
METALLURGICALTRANSACTIONS A
B. Heat Treatment It was desired to obtain nominal yield strengths of 792 MPa (in the solutionized and quenched condition), 896- and 999-MPa (in the aged conditions) for two beta matrix grain sizes and for two Widmanst~itten o~particle sizes. The microstructures thus consisted of (1) coarse fl + coarse o~, (2) coarse/3 + fine a, (3) fine [3 + coarse a, and (4) fine /3 + fine a. For this purpose, initial heat treatments were carried out in the fl phase field, following which the material was either slow cooled in the furnace at a controlled rate to the solutionizing temperature or water-quenched. The quenched material was reheated into the or-/3 phase field and cooled at a controlled rate to the solutionizing temperature of 790 ~ held for 24 hours, and water quenched. The solutionizing temperature and duration were held constant for all microstructures so that the volume fraction of primary a was the same for the different microstructures. For all the Widmanst/itten o~ microstructures, except the coarse/3 + coarse o~, it was necessary to prestrain approximately 1 pct
Data Loading...
