Abstract: Ti-Ni based functionally graded alloy is a kind of the promising material, which has
potential to be used in aero engines. Using laser rapid forming, a Ti-Ni graded alloy with a continuous
compositional gradient from pure Ti to Ti-50wt.%Ni were fabricated. On comparison with the graded
alloy, a series of homogenous deposits with the typical composition between pure Ti to Ti-50wt.%Ni
were also laser rapid formed. The phase evolution along the compositional gradient direction in the
graded alloy is: α+β→β+Ti2Ni →(TiNi +Ti2Ni)+ TiNi; and the phase evolution in the corresponding
compositional homogeneous deposit is: α+β→ β+(β+Ti2Ni)→ β+Ti2Ni+(β+Ti2Ni)→
(TiNi+Ti2Ni)+TiNi. The phase transformation and microstructural evolution along the compositional
gradient were analyzed by using the microstructure selection map.
Abstract: Microstructures and Vickers hardness have been investigated in hot-rolled Mg-3mass%Y based
solid solution alloys containing microalloying elements (Ca, Ag, and Ni). Transmission electron micorscope
(TEM) observations have revealed that the stacking faults on the (0001) magnesium matrix planes have been
observed in Mg-Y-Zn based alloys and the stacking fault (SF) density depends on other additional
microalloying elements. In single addition of Zn to the Mg-Y alloy, SF density increases with increasing Zn
content and was saturated over 0.5 mass% addition. On the other hand, in simultaneous addition of Zn and Ca,
SF density increases with increasing Ca content significantly. Many precipitates were observed in Ni and Ag
added Mg-3Y-0.5Zn alloys and their SF densities were lower than Mg-3Y-0.5Zn. Vickers hardness increased
by the simultaneous microalloying of Zn and Ca, while Ag showed a negative effect for hardness in
Mg-3Y-0.5Zn (in mass%) ternary alloy. The dense SF density could act as obstacles to the dislocation motion
so that SF density has positive relationship in the Vickers hardness.
Abstract: The effectiveness of microalloying addition and two-step aging on the mechanical
properties of the Al-Zn-Mg alloy has been investigated using TEM, tensile test and nanoindentation.
By decreasing width of PFZ and size of grain boundary precipitates through the addition of (Ag+Sn)
or two-step aging process, tensile properties of Al-Zn-Mg alloys are markedly improved. The
elongation was quantitatively related to the three microstructural factors; i.e. the width of PFZ, size of
grain boundary precipitates and the level of proof stress, to predict ductility of the alloys with known
microstructural factors. The fracture mode change is reasonably in terms of the hardness difference
between grain interiors and PFZ region by a noindentation technique.
Abstract: It is well known that Ag additional Al-1.0mass%Mg2Si-excess0.4mass%Si alloy (ex.
Si-Ag alloy) has higher hardness and elongation than those of Al-1.0mass%Mg2Si-excess
0.4mass%Si alloy (ex. Si alloy). However, precipitation sequence of ex. Si-Ag alloy is not clear yet.
In this work, precipitation sequence of ex. Si-Ag alloy has been investigated using high resolution
transmission electron microscopy and X-ray energy dispersive spectroscopy. Precipitates were
classified into several kinds by HRTEM images and SAED patterns, and relative frequencies of
precipitates were also investigated. Its precipitation sequence was compared with that of ex. Si alloy.
Type-A, Type-B and Type-C precipitates as special metastable phase in excess Si type Al-Mg-Si
alloy, has been observed in ex. Si-Ag alloy, but β’ phase increased and Type-A and Type-B
precipitate decreased in this study. Type-A precipitate was found at only grain boundary.
Abstract: The purpose of this study is to identify the crystal structure of metastable phase in Ag
added Al-Mg-Si alloy to compare the formation of β’-phases in Al-Mg-Si alloys without Ag, using
images of high resolution transmission electron microscope (HRTEM), selected area electron
diffraction (SAED) patterns and an energy dispersive X-ray spectroscopy (EDS). The result of
SAED patterns and HRTEM images have been simulated and compared with images then SAED
patterns obtained from actual precipitates. SAED patterns and HRTEM images obtained from
metastable phase in the Ag added Al-Mg-Si alloy showed similar to those of β’-phase in Al-Mg-Si
alloy without Ag and the lattice spacings changed because of the effect of Ag.
Abstract: Effect of solution and aging treatment on the microstructure of Mg-7Zn-3Al alloy is
studied by using optical microscopy, scanning electron microscopy, X-ray diffraction, transmission
electron microscopy and quantitative image analysis. The results show that the as-aged microstructure
is composed of α-Mg matrix, grain boundary τ (Mg32(Al,Zn)49 ) phase, and fine dispersed τ particles
inside the grain. The solution degree has significant effects on the formation, morphology, and size of
the grain boundary τ phase. The volume fraction and the size of the undissolved eutectic τ phase
decrease with the increase of solution time treated at 325°C. Through sufficient solution treatment,
discontinuous eutectic τ phase retains fine strip morphology after aging, in contrast to the
microstructure in sample undergone insufficient solution which manifests as-cast feature, while at the
same time nano-sized particles precipitate out from the matrix. The precipitates display paralleled
short bar, having certain orientation relationship with the matrix.
Abstract: Microstructure and texture evolution during equal channel angular pressing (ECAP) of
Al-5 mass%Ti alloy are investigated for up to 8 passes via routes A and BC. Platelet-shaped Al3Ti
particles in the Al-5mass%Ti alloy are cracked severely with repetitive ECAP passes, and the mean
size of the Al3Ti particles is decreased with increasing the number of ECAP passes.
Microstructural observation showed that an Al–Ti supersaturated solid solution is formed during the
ECAP process. It is also found that the Al-Ti alloy after ECAP by route A and route Bc methods
have very different microstructures. Namely, after ECAP by route Bc, the fine Al3Ti particles are
homogeneously dispersed in Al matrix, while the microstructure has highly anisotropic distribution
after ECAP by route A.
Abstract: The mechanical properties of the AZ31B alloy sheets processed by differential speed
rolling (DSR) from the cast ingots homogenized at two different conditions were investigated. There
still existed the uneven distribution of Al and Zn in the ingot homogenized at 673 K for 6 h, while it
was homogeneous for the ingot homogenized at 723 K for 24 h. Compare with the sheet rolled from
the ingot homogenized at 673 K for 6 h, the sheet rolled from the ingot homogenized at 723 K for 24
h exhibited a lower proof stress, a larger elongation, and a lager strain hardening exponent. The
improvement in the ductility can be attributed to the elimination of the microsegregation of Al and Zn
in the matrix.
Abstract: The importance of determining and understanding the very high cycle fatigue behaviors of
materials has gained strength in recent years. Ti-alloys, in view of their high strength-to-weight ratio,
have a range of structural applications. Of these, Ti-6Al-4V, belonging to the alpha-beta type is the
most widely used. The present paper deals with investigations on the fatigue behavior of TC4, the
Chinese equivalent to Ti-6Al-4V, up to very high cycles. Fatigue testing was carried out on a
piezoelectric ultrasonic fatigue machine operating at 20 kHz frequency. Hourglass shaped resonant
specimens were tested in ambient air at room temperature under completely reversed loading
conditions (R = -1). Failure in the alloy was seen to occur right up to the gigacycle regime, with the
fractures being found to initiate from the surface unlike in steels. The fracture surfaces exhibit brittle
characteristics containing river patterns and cleavage facets, as well as striations.
Abstract: Traditional computational models always assume idealized crack geometry. However,
actual crack geometry is very complex in real materials and thus, those simulations do not
realistically represent the actual loading conditions of a real crack. In this paper, three-dimensional
(3D) image-based simulation was performed to investigate the fracture behavior of an aluminum
alloy, and the model takes into account the real crack geometry based on the 3D images of the crack.
Accordingly, many essential features of fracture can be identified and interpreted, and some new
insight into fracture behavior in real materials can be offered.