作者: Chang Liang Li, Hua Ding, Yong Qing Zhao, Lian Zhou
摘要: Superplastic forming provides a good way for Ti alloys which are usually difficult to
be deformed. Ti75 alloy with a nominal composition of Ti-3Al-2Mo-2Zr is a newly developed corrosion resistant alloy, with a middle strength and high toughness. In the present paper, superplastic behavior of the alloy was investigated, the microstructural evolution in superplastic deformation was observed and the superplastic deformation mechanisms were analyzed. The results showed that the strain rate sensitivity, m, of the Ti75 alloy was larger than 0.3 and the strain was over 2.0 without surface cracking at 800°C and 5×10-4s-1 in compressive testing.
During the first stage of superplastic deformation, a phase grains became equiaxed, fine and homogeneous due to the recrystallization in a phase and diffusion in b phase. Newly formed equiaxed a grains then could slide and rotate, exhibiting superplastic features. The stress concentration caused by grain sliding of a grains could be released by slip and diffusion in b phase between the a phase grains, which acted as accommodation mechanisms.
2969
作者: Jeong Min Kim, Bong Koo Park, Joong Hwan Jun, Ki Tae Kim, Woon Jae Jung
摘要: Small amounts of minor alloying elements such as RE and Sr were added to Mg-
8wt%Al-5wt%Zn (AZ91D+4%Zn), and their effects on the microstructure, mechanical properties and corrosion resistance were investigated. The microstucture of the investigated alloys could be characterized by dendritic Mg, Mg17Al12, a quasi-crystalline Zn-rich phase, and Al4RE (if RE is
added). Although the tensile strength of alloys was not improved, the creep strength was significantly enhanced by the additions of minor alloying elements. No apparent influence of the additions could be found on the corrosion resistance.
374
作者: T.S. Srivatsan, Mithun Kuruvilla, Lisa Park
摘要: In this technical manuscript the cyclic stress amplitude controlled fatigue properties and fracture
behavior of an emerging titanium alloy (referred to by its designation as ATI 425TM by the
manufacturer) is presented and discussed. The alloy was provided as rod stock in the fully
annealed condition. Test specimens of the as-received alloy were cyclically deformed under total
stress amplitude control at two different stress ratios (R = 0.1 and R = 0.3) with the purpose of
establishing the conjoint and mutually interactive influences of magnitude of cyclic stress, load ratio
and intrinsic microstructural effects on cyclic fatigue life, final fracture behavior and viable
mechanisms governing failure at the microscopic level. The high cycle fatigue resistance of this
titanium alloy is described in terms of maximum stress, load ratio, and maximum elastic strain. The
final fracture behavior of the alloy under cyclic loading conditions is discussed in light of the
mutually interactive influences of intrinsic microstructural features, magnitude of cyclic stress, load
ratio and resultant fatigue life.
271
作者: E.P. Masuku, Gonasagren Govender, L. Ivanchev, Heinrich Möller
摘要: Rheocasting of alloys A206 and A201 was investigated in this study. Conical bars with
different silver contents were produced using CSIR rheoprocess technology, together with high
pressure die casting. The results showed that addition of Ag to alloy A206 increased the mechanical
properties of the alloy. However, the addition of Ag also resulted in Cu-rich phases to precipitate at
the grain boundaries of the as-cast material. The solution treatment used in this study was unable to
dissolve all of this phase, especially in the 1.12%Ag-containing alloy. This resulted in slightly
decreased mechanical properties compared to the 0.63%Ag-containing alloy. The T6 mechanical
properties (strength and elongation) obtained in this study for rheocast A206 and A201 are better
than those reported for permanent mould castings of alloy A206 and A201.
151
作者: S.G. Shabestari, R. Gholizadeh
摘要: Dense precipitation of various intermetallic compounds is a common feature in the microstructure of Al-Si piston alloys. In this investigation, microstructure of LM13 alloy and three high Cu-containing Al-Si piston alloys with different amounts of Ni, Fe, and Mn were studied by means of optical microscopy (OM) and scanning electron microscopy (SEM). Chemical composition of the phases was determined by using energy dispersive X-ray analysis (EDX). The precipitation of the phases was studied through thermal analysis of the solidifying samples. Also, tensile properties and hardness of the samples were measured. The results showed that the various intermetallics such as Al12(FeMn)3Si2, Al3Ni, Al9FeNi, and Al3CuNi precipitated during the solidification. The high Cu-containing alloy with optimum levels of Ni (1.8 wt.%), Fe (0.75 wt.%), and Mn (0.3 wt.%) has the highest tensile strength (250 MPa) and hardness (110 BHN) among the other alloys.
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