Papers by Author: De Hai Ping

Abstract: Titanium (Ti) alloys are widely used in aerospace industries successfully up to 600°C. Increasing the operating temperature and performance of these alloys would be very useful for fuel economy. Numerous numbers of research works has been focused on the improvement of the high temperature performances of Ti alloys. It has been well known that Zirconium (Zr) is one of the important solid-solution strengthener in Ti-alloys. In the present study, the effect of Zr addition on the microstructure and mechanical properties of the near–α Ti-Al-Zr-Sn based alloys has been investigated.The compression test results showed that Zr addition significantly improves both room temperature and high temperature strength. The results obtained were explained based on the microstructural observation, room temperature and high temperature compressive tests.

Abstract: The microstructural evolution and elevated temperature tensile properties of Ti-6.6Al-5.2Sn-1.8Zr-(0~3.8)Sc (wt%) alloys have been investigated. The Sc-added alloys showed improved yield strength at 650°C and 750°C and with the elongation above 10%. Minor addition of Sc was found to significantly reduce the as-cast grain size. Higher amount of Sc additions resulted in the formation of high density of Sc-oxide, which causes the high strength at elevated temperatures and the reduction of ductility. High density of α2-Ti3Al fine precipitates with an average size of about 20 nm were observed inside equiaxed primary α (αp) grains in the Sc-free or minor Sc added alloys. However, precipitation free zone (PFZ) also formed in those alloys, where grain boundaries are free from any precipitates. Higher Sc addition was found to hinder the formation of PFZ and α2–precipitates.

Abstract: Tempering temperature dependence of the amount of the reversed austenite in the range of 570 oC to 680 oC was investigated by means of X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) in a low carbon Fe-13%Cr-4%Ni-Mo (wt.%) martensitic stainless steel. It was found that the reversed austenite began to form at the tempered temperature slightly above the As temperature. As the tempered temperature increased, the amount of the reversed austenite changed little in the temperature range of 580-595 oC. Then, the amount of the reversed austenite increased sharply with the increased tempered temperature. When the tempered temperature increased to about 620 oC, the amount of the reversed austenite exhibited a peak. Afterward, it decreased quickly at the elevated tempered temperature. The microstructural evolvement of the reversed austenite at different tempering temperature was also observed by TEM.

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.