Papers by Keyword: Isothermal Ageing

Abstract: Vickers hardness and electric conductivity measurements as well as micro-structure analysis were used to investigate the effects of trace element Hf atoms on the precipitation and recrystallization resistance in Al-Er-Zr alloys. The results of the present study indicated that the behaviors of precipitation process in Al-0.04Er-0.08Zr and Al-0.04Er-0.08Zr-0.05Hf (at. %) alloys are similar. When alloys were annealed at 350 °C for 96h, the nanoscale and coherent Al₃(Er, Zr) and Al₃(Er, Zr, Hf) precipitates form, corresponding to the peak hardness values of 56.2 ± 0.9 (ternary alloy), 58.9 ± 1.5 HV (quaternary alloy), respectively. The higher peak hardness in Al-0.04Er-0.08Zr-0.05Hf alloys mainly benefit from the decomposition of Hf. It was shown that the existence of precipitates could improve the recrystallization resistance obviously. Due to the similar retarding force, recrystallization temperatures of both alloys are almost the same, approximate 450 °C.

Abstract: In this paper we will try to further clarify the creep-strength degradation of selected advanced creep resistant steels. In order to accelerate some microstructural changes and thus to simulate degradation processes in long-term service, isothermal ageing at 650°C for 10000 h was applied to P91, P92 and P23 steels in their as-received states. The accelerated tensile creep tests were performed at temperature 600°C in argon atmosphere on all steels in the as-received state and after long-term isothermal ageing, in an effort to obtain a more complete description of the role of microstructural stability in high temperature creep of these steels. Creep tests were followed by microstructural investigations by means of both transmission and scanning electron microscopy and by the thermodynamic calculations. It is suggested that microstructural instability is the main detrimental process in the long-term degradation of the creep rupture strength of these steels.

Abstract: The interfacial reactions and shear properties of Sn-37Pb (wt.%) solder bumps with two different under bump metallizations (UBMs), Cu and Ni, were investigated after high temperature storage (HTS) tests at 150
C for up to 65 days. Two different intermetallic compounds (IMCs), Cu6Sn5 and Cu3Sn, were formed at the bump/Cu interface, whereas only a Ni3Sn4 IMC layer was formed at the bump/Ni interface. The thicknesses of these IMCs increased linearly with the square root of duration time. The IMC growth rate at the bump/Cu UBM interface was much greater than that at the bump/Ni UBM interface. The shear properties of the bumps with the Cu UBM were greatly decreased with increasing duration time, compared with those with the Ni UBM.

Abstract: The evolution of microstructure, precipitate size, volume fraction and integrated intensity of Al-8.0Zn-2.05Mg-1.76Cu (7055) and 7055-1.0Li alloys during isothermal ageing has been studied by transmission electron microscopy (TEM) and synchrotron-radiation small angle X-ray scattering (SAXS). According to the TEM results, referring to the thermodynamic phase diagram, it was found that the addition of Li changed the types of the precipitates. T1 phase was observed in the 7055-1.0Li alloy besides the GP zones, η' and η with variant orientations with matrix, η1、η2 and η4. The super-lattice spots of L12 (Cu3Au) structure were probably due to the existence of Al3Li (δ') or Al3(Zr,Li). Furthermore, the precipitation sequence has been modified in Li-containing Al-Zn-Mg-Cu alloys. The precipitate volume fraction derived from the integrated intensity for 7055 alloy reached an plateau except ageing at 120°C and the maximum was about 0.052-0.054 in the temperature range 140-160°C.

Abstract: To develop new shape memory and super-elastic alloys for medical applications, titanium alloys using non-toxic metallic elements, such as Ta and Nb, are being actively investigated. In this study, aimed at developing new shape memory Ti alloys, we investigate the effect of oxygen, a powerful alpha stabilizing interstitial element, on the heat treatment behavior of Ti-50mass%Ta-5mass%Zr through electrical resistivity and Vickers hardness measurements and shape-recovery tests. Ti-50Ta-5Zr-0.14Ox and 0.33Ox alloys, and the β and α” bi-phase was confirmed by XRD. Only the β phase was identified in the Ti-50Ta-5Zr-0.62Ox alloy. Upon isochronal heat treatment, the resistivity at LN and resistivity ratio of Zr-0.33 and 0.62Ox alloys decreased up to around 523 K. In the 5Zr-0.62Ox alloy, orthorhombic martensite and the α” and β phases were identified in the specimens heat-treated at 473 and 523 K. The decreases in resistivity at liquid nitrogen temperature and resistivity ratio are due to the formation of α” during isochronal heat treatment. The formation of α” was confirmed by X-ray diffraction in the 5Zr-0.62Ox alloy. The shape memory effect was observed in 5Zr-0.14 and 0.33Ox alloys and the shape recovery ratio of both alloys was about 40% at 673 K.