Abstract: Directional solidification technique permits materials to grow along specific
orientation, in order to obtain mechanical and/or physical anisotropy. The present research
attempts to introduce the research work in the field of processing of some advanced materials
by innovative directional solidification techniques performed at State Key Laboratory of
Solidification Processing and with author’s intended research work.
The paper deals with the specific topics on state of the art of directional solidification:
single crystal superalloy and Nd-Fe-B alloys under high thermal gradient, Cu-Ni alloys under
deep supercooling of the melt.
The relevant solidification phenomena, such as morphological evolution, crystal growth
for multi-phases in the processing of directional solidification, are discussed briefly. The trends
of developments of directional solidification techniques are also prospected.
Abstract: Degradation mechanism and life prediction method of high chromium ferritic creep
resistant steels have been investigated. In the high stress condition, easy and rapid extension of
recovered soft region results in significant decrease in creep strength, however, ductility is high. In
the low stress condition, extension of recovered soft region is mainly controlled by diffusion and it
is slow, therefore, deformation is concentrated in the recovered soft region along grain boundaries
and ductility is extremely low. Delta-ferrite produces concentration gap due to difference in
equilibrium composition of austenite and ferrite phases at the normalizing temperature. It increases
driving force of diffusion and promotes recovery of tempered martensite adjacent to delta-ferrite.
Concentration gap may be produced also in heat affected zone (HAZ), especially in fine grain HAZ
similar to dual phase steel, and it has possibilities to promote recovery and, therefore, to decrease
creep strength. It has been confirmed the advantage of region splitting analysis of creep rupture
strength for high chromium ferritic creep resistant steels, through a residual error analysis. It is
important to avoid a generation of concentration gap in order to improve stability of microstructure
and to maintain high creep strength.
Abstract: Alloy 718 ingot with a diameter of 400mm was made by the vacuum melting process ;
VIM followed by VAR. Compression tests were conducted on samples collected from columnar
zone of the VIM/VAR-processed Alloy 718 ingot in wide temperature and strain rate ranges, i.e.
750~1,200OC and 10~0.001s-1 in order to understand the deformation behavior and evolution of
microstructure. Tensile tests at high temperature were also conducted on samples in temperature
ranges, i.e. 750~1,100OC. Effects of process parameters on the flow behavior as well as on the
microstructure evolution during compression tests at high temperatures are considered.
As a result of the deformation simulation, The VIM/VAR ingot was heat-treated for
homogenization, and casting structure of the ingot was broken down for uniform microstructures
and mechanical properties by controlled cogging process using a hydraulic press.
The observation of the microstructure and grain size distribution was carried out to evaluate the
effects of optimum process parameters during cogging and mechanical property tests were
performed in this study.
Abstract: The deformation features are analyzed for titanium alloy and superalloy during
isothermal/hot die forging process, and proper finite element models with appropriate parameter
values are determined. On the platform of DEFORM software, the formation processes of
vane-integrated disk and compressor disk, made of titanium alloy and superalloy respectively, are
simulated and analyzed. Based on the simulation results, some important suggestions to the process
design and parameter determination are brought forward, which have been taken into consideration or
adoption in practice. As a result, the production yield is promoted, and a large amount of expenses of
testing and die trial-manufacture are saved.
Abstract: Boron-fiber-reinforced Al-matrix composite was fabricated by a pulsed current hot
pressing (PCHP) process at a pressure of 32MPa for 600s. It was found that the boron fiber and
the Al-matrix were well bonded when the PCHP process was performed at a holding temperature of
773K. No interfacial reaction layer was observed along the interface between the boron fiber and
the matrix when PCHP was done at 773K for 600s. Tensile deformation carried out at room
temperature for the composite showed that the tensile yield stress increased with increasing volume
fraction of the boron fiber in the composite. The composite with 17.2 vol.% of boron fiber
presented a tensile yield stress of 600MPa. This value was about 90% the yield stress estimated by
a force equilibrium equation of a composite taking into account the direction of fiber axis.
Abstract: The growth of TiNi thin films by ion beam sputter deposition using a Kaufmann type ion
source is described. Argon ions are used to sputter separate Ti and Ni targets to deposit nearequiatomic
TiNi thin films. Typically, ion energies and current densities of 1500 eV and 1 mA cm-2
respectively are used, with an argon overpressure of around 0.05 mtorr, to achieve deposition rates
of order 1 μm hr-1. The thermophysical properties of the deposited films were investigated by
thermal imaging. Patterning of TiNi films and foils with micrometre resolution using KrF excimer
laser ablation at 248 nm wavelength, with beam fluence up to 2.5 J cm-2, 15 ns pulse duration and
pulse rates up to 100 Hz has also been investigated.
Abstract: Effect of chemical composition was investigated on martensitic transformation
temperatures, Curie temperature, magnetization and microstructures for Ni-(Mn, Fe, Co)-Ga and
Cu-Mn-Ga systems. In the Ni-(Mn, Fe, Co)-Ga alloys, which is a modification of Ni-Mn-Ga systems,
the Af and TC over 400 K were achieved. Cu-Mn-Ga alloy exhibited shape memory effect at
temperatures above 373 K and had TC over 400 K. Furthermore, Cu-Mn-Ga exhibits good ductility
even in polycrystalline condition unlike the case of Ni-Mn-Ga. Effect of addition of the fourth
element to improve the magnetic property is under investigation.
Abstract: Effect of isothermal aging on martensitic transformation temperatures, mechanical
properties and microstructure was investigated for a Ni-rich Ti-Zr-Ni shape memory alloy at
temperatures ranging from 673 K to 773 K. The aging behaviour was two stage process: the first stage
associated with an increase in the Vickers hardness and a decrease in martensitic transformation
temperatures and the second stage with a decrease in the hardness and increase in the transformation
temperatures. Second stage was also characterized by the appearance of nano-scale precipitates,
which has never been reported.