The aging of a drawn eutectoid carbon steel with true strain 2.89 at different temperatures has been studied by means of TEM and electrical resistance measurement. The results indicated that the aging at 473K for 1hr improved the tensile strengths from 2245.65MPa of as-drawn to 2448.52MPa. Better mechanical property with combination of strength and ductility was observed after aging at 673K for 1h. Further increase of aging temperatures deteriorated the property possibly due to the recrystalization. The underlying mechanism of the better mechanical properties after aging at low temperature (673K) is considered to associate with the precipitation of fine carbide dissociated in the drawing.

There are reticular coarse Mg17Al12 and component segregation generated during solidification on grain boundary of AZ91 magnesium alloy as cast, which deteriorate the mechanical properties and the workability of ingots severely. In order to improve the workability, homogenizing treatment is researched. The homogenizing temperature is 350, 380, 420, 450℃ and the holding time is 5, 10, 15, 24h. After homogenizing treatment, the Mg17Al12 phase is scattered on the α-Mg matrix as fine grains, and dendritic segregation is eliminated almost. It is concluded from the mechanical properties test that the tensile strength of the AZ91 on the condition of as-cast, homogenized at 380℃15h and 420℃5h is about 163MPa, 243MPa and 246MPa, while the elongation is about 3.2%, 11.2% and 10%.

An analytical function for describing hardness distribution of round section in quenched steel, known as U-curve, has been established. The temperature field and cooling rate equation of Jominy at 700℃ were obtained by solving the heat conduction differential equation. The formula for expressing relations between sample radius, section position radius and section hardness was created by using the curve fitting according to the Jominy curves, cooling rate, measured section radius and cooling rate equivalent theory. This model includes hardenability coefficient, hardness maximum and hardness minimum that were obtained from Jominy test so that it displays advanced characteristic in theory and retains no correlation between hardenability and sample shape. The results show that the simulated curves are in good agreement with experimental values.

A transparent model alloy, succininitrile-1.48 wt%Salol, was directionally solidified on a temperature gradient stage at the constant velocity. The primary spacing, tip radius and tip temperatures have been measured as a function of growth rate. The critical velocity for planar interface instability Vc was obtained. It is shown that, with the increase of growth velocity, the primary spacing decreases first, go through a local minimum value, and then increases to a local maximum value, finally decrease again. The cell-dendrite transition happens when the primary spacing increases from the local minimum to maximum value. Experimental results were compared to BH-L and self-consistent model. It’s found that the tip temperature predicted by BH-L model shows a large difference with the experimental results, and there shows a good agreement between all experimental results and self-consistent model.

Microstructure and mechanical properties of a cast Ni-32Al-28Cr-3Mo-4Ti eutectic alloy have been investigated. The results show that the alloy consists of NiAl and Cr(Mo) eutectic zone, as well as a small amount of primary NiAl and Ni2AlTi. Its compressive yield strength surpasses Dy-doped NiAl-Cr(Mo) eutectic alloy, and is comparable to NiAl-28Cr-5Mo-1Hf eutectic alloy, indicating the addition of Ti is benefit to the strength of NiAl-Cr(Mo) eutectic alloy. Similar to the relationship between minimum creep rate and applied stress, the creep rupture life at 1000℃ vs. applied stress fits linear dual-logarithmic relationship. Modified Monkman-Grant equation can be used to describe the relationship between creep rupture life and minimum creep rate. The fracture mechanism at room temperature is cleaving of NiAl and Cr(Mo) eutectic phases as well as stripping of NiAl/Cr(Mo) interface, while the formation and aggregation of microvoids on eutectic boundaries leads to crept fracture.

In this paper, the hot compression test results of NiTi alloy have been analyzed. Errors caused by friction and thermal effect were corrected. The test temperature ranged from 725℃ to 975℃, and the strain rate ranged from 0.1 s-1 to 10 s-1. Constitutive equation at high temperature of NiTi alloy was established by curvilinear regression method. The simulation results agreed with the experiment. Research results provided the accurate material model for the numerical simulation of NiTi SMA plastic formation process.

Ferritic steels with and without hafnium (Hf) addition were irradiated by 250 keV nickel-ions at 300 oC in a ion accelerator attached to the Multi-beam High Voltage Electron Microscope (JEOL ARM1300) to study the influence of Hf additions on radiation-induced segregation in a ferritic/martenitic steel. Grain boundary segregation of phosphorus, silicon, chromium and molybdenum were measured by field emission gun transmission electron microscopy with an energy dispersive analyser. The results show that radiation induces the enrichment of undersized atoms (P) and the depletion of oversized atoms (Cr) in the materials without Hf addition. The addition of Hf suppresses radiation-induced undersized atom enrichment and oversized atom depletion. A radiation-induced non-equilibrium segregation (RIS) model is developed to predict undersized and oversized atom segregation behaviour at the grain boundary. The effect of hafnium on freely migrating defect population is discussed and estimated to indicate the effect of the element on segregation behaviour of the elements like P and Cr in the ferritic steel. The predicted results are compared with experimental data.

Thermal-gradient chemical vapor infiltration (TCVI) is a novel and effective process for fabricating C/C composites. However, the changing of the temperature field during infiltration is rather complex, which is difficult to obtain the results by the resolution method. In this paper, the finite element model concerning unstable temperature field for TCVI process was set up, and, temperature field and temperature distribution during the whole infiltration process were given out by numerical simulation. The relationship between deposition temperature and infiltration efficiency was also investigated. The experimental results of the temperature distribution were accordant to the simulation results.

Based on the meso-mechanical model established for T6-treated SiCP/6061Al alloy composites, the monotonic tensile and uniaxial cyclic deformation behaviors of the composites were simulated numerically by using elastic-plastic finite element code ABAQUS; and then the simulated results were compared with the corresponding experiments in order to discuss the reasonability of the finite element simulation. It is shown that: since a newly developed cyclic constitutive model describing the ratcheting behavior reasonably is employed for T6-6061Al alloy matrix, the finite element model established in this work simulate the uniaxial cyclic deformation of the composites well, especially for the ratcheting behavior. It is also shown that the cyclic deformation of the composites is heterogeneous and complicated in meso-scale.

A study of thermal fatigue (TF) behavior of cast nickel-base superalloy K445 was conducted between the temperatures ranging from 800℃ to 900℃ and RT, using plate specimens notched to induce crack initiation. Conventional optical microscopy (OM) and scanning electron microscopy (SEM) examinations were conducted to investigate the damage mechanisms of thermal fatigue. Almost all the primary fatigue cracks at elevated temperatures propagate intergranularly and the secondary crack is transgranular. At 800℃, coarse MC carbides either at grain boundaries or within the grain interior, as well as decohesion of MC/matrix interface, are the preferential sites of crack initiation and propagation. At 900℃, crack propagation is an oxidation-dominant and carbide-assisted process. Stress assisted grain boundary oxygen (SAGBO) embrittlement is the principle mechanism of the environmental degradation to the alloy at the crack-tip region.

Nb/ Nb5Si3 in-situ composites were prepared by arc melting in vacuum. Effects of Ta content on the microstructure and mechanical properties of the alloys were investigated. The results show that Ta mainly distributes in Nb solid solution phase. With increasing Ta content the amount of Nb5Si3 phase decreases, while that of Nb solid solution phase increases. Ta promotes the transformation ofβ-Nb5Si3 to α-Nb5Si3. The addition of Ta is beneficial to the compressive strength at room temperature and high temperature. In addition, the compressive strength of 5at.% Ta-containing alloy is superior to that of other alloys at high temperature.

The nano-crystallization behavior of amorphous pure Ni under compression deformation has been investigated by using a molecular dynamics simulation. The effect of adiabatic procedure on the nano-crystallization was studied. The nucleation and growth of nano crystal was observed by through the evolution of micro structure. It was shown that the transition from the metastable structure to crystal structure was driven by the compression deformation. The shorted ordered clusters combined and grew into the nano-crystal with the strain increasing.

By use of the Gasar process (unidirectional solidification of metal-gas eutectic), porous magnesium samples with radial pore distribution have been fabricated successfully through altering the heat transferring from the axial to radial direction. In addition, this paper also studied the structural features and the effect of gas pressure on porosity, pore size and distribution.

Three-dimensional finite-element heat-transfer model was established to predict temperature in a continuous casting mold for steel during operation. The effects of copper plate thickness, water slot depth and nickel layer thickness on copper plate temperature are analyzed in detail. The results show that decreasing copper plate thickness and nickel layer thickness, and increasing water slot depth are available in decreasing the copper plate temperature, and therefore improving the mold life.

ABSTRACT A physical model was established to study the mechanism of molten slag behavior in slab continuous casting mould with high casting speed and argon blowing, and the effects of operation parameters on the liquid surface level oscillation and the slag entrapment were investigated. The results showed that slag entrapment was mainly caused by the turbulent large bubbles at the interface of slag and molten steel in mould with high casting speed and gas bubbling, and the vortex at the surface also was the way to cause slag entrapment, but there is no phenomenon of entrapment occurring due to high shear stress that was mentioned the main reason previously. In addition, the behavior and mechanism of typical slag entrapment were discussed, and the measures to eliminate slag entrapment were also presented.

The physical metallurgical characteristics of the titanium microalloyed strip produced by thin slab casting and rolling (TSCR) process, which include the precipitation of titanium containing compounds, matrix microstructure and strengthening mechanism, is briefly reviewed in this paper. It is shown that the precipitation of titanium occurs at various stages from thin slab casting to coiling. The ferrite grain size is gradually refined by the addition of titanium, but it will reach a limiting value when the titanium content is over 0.045%. Both the ferrite grain refinement and the nano-sized TiC precipitates can contribute to the increase in yield strength of the steel strip, and the latter is dominant when the titanium content is over 0.045%.

The deformation behaviour of Mg-Y-Nd-Zr alloy at temperatures of 300-500℃ and strain rates of 0.001-1s-1 has been studied by compressive tests. Processing map of this alloy was established on the basis of Dynamic Material Model; it is suggested that, with microstructural observation, the processing map of this alloy could be characterized as the following four domains: First, dynamic recrystallization (DRX) domain at 450-500℃ and about 0.01s-1. Second, boundary cracking domain at temperatures higher than 450℃ and strain rates of about 0.005s-1. Third, flow instability domain probably due to mechanical twinning at temperature lower than 350℃ and strain rate of about 0.01s-1. Last, shearing fracture at about 450℃ and strain rates higher than 0.5s-1.

Fine grained dual phase steel obtained by deformation enhanced transformation (DEFT) was investigated by using hot compressing simulation experiments. The evolution of ferrite grains and M/A islands distribution during deformation were analyzed. The effects of initial austenite grain size、deformation temperature and strain rate on ferrite transformation kinetics were taken into consideration. The experimental results showed that the microstructure of fine grained ferrite(2～3μm)with fine granular M/A islands dispersing in the matrix can be achieved by controlling the initial austenite grain size and DEFT. Fine dual phase structure can be achieved by austenite recrystallization and the subsequent controlled DEFT.

Molten steel flow field in tundish nozzle and influence of some factors on deposition rate were researched by method of numerical simulation. The deposition near slide gate and bottom of submerged entry nozzle(SEN) is seriously. Flowrate of argon has influence markedly upon pressure in the nozzle, and the pressure drops suddenly down the slide gate. To avoid inspiration of air, flowrate of argon is more than 10L/min when casting speed is 1.2m/min. Deposition rate of alumina is linear with mass concentration of alumina, and is also increasing with casting speed. Blowing argon decreases deposition rate at appropriate range of argon flowrate. The flowrate of 5L/min and 30L/min have the same effect for decreasing deposition rate at the same casting speed.

Local plastic shearing band is initialized near blanking clearance during fine-blanking, and forming failures such as ductile fracture and large roll-over usually occur. By using MSC/MARC software, an axisymmetric FE model is created, and mixed u-p updated Lagrange FEM is used to simulate the severe plastic deformation, which could overcome shear locking and volume locking. Together with adaptive remeshing technique based on strain gradient and surface curvature, the strain localization phenomenon could be captured. Schiffmann damage work density model is used to predict the developments of damage and fracture in sheet metal. The height of roll-over, height of burnish band and fine-blanking force are predicted, and qualified part was obtained using optimized process parameters from simulation.