Effect of silicide precipitation on tensile properties and fracture of alloy Ti-6Al-5Zr-0.5Mo-0.25Si
- PDF / 2,437,516 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 14 Downloads / 196 Views
I.
INTRODUCTION
I T is well established that the addition of a small amount of silicon up to about 0.5 wt pct in titanium alloys is made primarily to improve their creep resistance. ~-9 Although the mechanism by which creep resistance is improved is not clear, silicon in solid solution as well as in the form of silicide dispersions has been considered important in affecting creep behavior of titanium alloys, depending upon the test conditions. 6-9 Silicon is known to affect not only the creep resistance but also the microstructure and static strength of titanium alloys. 1~ The authors ~4have recently investigated the precipitation and characteristics of silicides in alloy 685. Hoeppner ~5 has reported that silicide precipitation in alloy 685 promotes crack initiation, and cleavage facets are observed in the structural components failed in service. A number of investigators have reported faceted fracture in near a titanium alloys, exclusively in the /3 annealed and slow cooled specimens with large colonies of the platelets, tested in monotonic as well as in cyclic loading. 16'~7'~8 Faceted fracture has recently been reported in alloy VT-9 in tension at RT due to long aging treatment at elevated temperature, following beta annealing and slow cooling. 19 The degree of faceting and the size of the facets have been found to increase with the size of the colonies of similarly oriented aligned a-platelets. ~8,20The tendency for multicolony faceted fracture has been observed in the material with larger prior/3 grains because of the Burgers relation between the colonies. 21 The examination of the orientation of the facets in alloys Ti-SAI-IMo-IV,22 IMI 6 8 5 , 23,24 and Ti-l124 has shown that the facets form primarily on the basal plane (0001), with marginal deviations from it depending upon the test conditions. Different mechanisms, like intense shear activity on certain crystallographically favored planes,17'25-28creep deformation and hydrogen interaction and hydride precipitation at the tip of C. RAMACHANDRA, Lecturer, and VAKIL SINGH, Reader, are with the Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi-221 005, India. Manuscript submitted September 29, 1983. METALLURGICALTRANSACTIONS A
intense shear band, 29 have been proposed for the formation of the facets in the microstructure with large colonies of the a platelets. The present investigation deals with the effects of silicide precipitates (in the WQ specimens) on the tensile properties and fracture behavior of the alloy 685. It shows that the tendency for faceted fracture is significantly enhanced due to silicides in the microstructure with fine martensitic a' platelets, and hence the faceted fracture is not limited only to microstructures with large colonies of coarse aligned a platelets, as reported by earlier investigators 17'2~'25,26in alloys where the silicides are not a factor. II.
EXPERIMENTAL
The alloy used in the present investigation was procured from Titanium International, U.K., in the form of 25 m
Data Loading...
