Papers by Author: Satoshi Iwasaki

Abstract: The effect of α₂ precipitation on the creep and tensile properties was investigated for bimodal and lamellar microstructures in two Ga-added near-α Ti alloys with Al equivalences of 10.6 and 11.5. Fine α₂ phase formed in the α phase of both alloys. The volume fraction of the α₂ phase for the Al equivalences of 10.6 and 11.5 is equivalent to 57.6 % and 73.3 %, respectively, in the binary Ti-Al system at 600 °C. Creep tests were carried out under a constant stress of 310 MPa at 600 °C and tensile tests were performed at room temperature. Lamellar microstructure showed lower minimum creep strain rates than bimodal microstructure for both alloys. The increase in Al equivalence increased creep life by a factor of 1.6 and decreased the minimum creep strain rate from 6.51 × 10^-8 s^-1 to 3.99 × 10^-8 s^-1 in bimodal microstructure. In addition, the increase in Al equivalence decreased room temperature tensile elongation although both alloys contained a similar volume fraction of equiaxed α in a bimodal microstructure.

Abstract: The tensile and creep properties of near-α Ti alloys with added Al, Ga, Sn, Zr, Mo, Nb, Ta, W, Si, and Ge were analyzed by using a regression analysis technique. The tensile test was performed at room temperature for 27 alloys. The creep test was carried out under a constant stress of 137 MPa at 650 °C for 30 alloys and 310 MPa at 600 °C for 21 alloys. The squared multiple correlation coefficients for the tensile elongation and minimum creep strain rate were 0.97 and 0.84, respectively. In addition, the effect of α stabilizing elements on the tensile and creep properties of those alloys was examined. The tensile elongation and minimum creep strain rate decreased between Al equivalences of 8 and 10. However, those values can be scattered depending on the composition and microstructure even with an almost constant value regarding the Al equivalence. The effect of adding Ga on the tensile elongation and minimum creep strain rate was also examined by using regression equations.

Abstract: The Snoek relaxation, a specific point-defect induced anelastic relaxation phenomenon, is characteristic of an internal friction peak in bcc metals with interstitial solutes. Such internal friction mechanism has not been applied in the development of high damping alloy while grain boundary and twin boundary featured anelastic relaxations are applied in some high damping alloys. In this paper, the fundamental principles and experimental results concerning the Snoek relaxation are reviewed, and the feasibility to apply the Snoek relaxation mechanism into high damping alloys is discussed. Due to the peak-shape behavior in the Snoek relaxation type damping, composition design of a high damping alloys should takes temperature position, broadness and also peak height into account. Ti-Nb-O and Ti-V-Cr-O alloys are designed and fabricated by CCLM casting in our laboratory. It is conformed that the damping behaviors of the alloys are of Snoek relaxation type showing obvious frequency and temperature dependence. While the broadened damping peak caused by the substitutional solutes is advantage to improve the temperature stability of damping capacity, a large concentration of interstitial solute and texture control are required to improve the reduced damping capacity.

Abstract: M2052 alloy is a MnCu based high damping alloy that shows high damping capacity and the superior workability. In the present work, the microstructure and damping behavior of the alloy in different solidification cooling rates are investigated with directionally cast alloy plate. For the variation of solidification cooling rate in the range of 250~10K/s, the secondary dendrite arm spacing of the cast alloy changes from 4 to 18mm and grain size varies in the range of 100~200mm except the surface regions and center regions in the cast plate. As compared to the worked and heat treated alloy, the as-cast alloy shows a high temperature damping above the average phase transformation temperature of the alloy irrespective to the solidification cooling rate. On the other hand, a higher damping peak is observed in the cast alloy which is attributed much to the twin boundary damping, however, the magnitudes of the damping peak are found to be varied corresponding to the respective solidification conditions.