脱氧胆酸钇络合物的EXAFS和FTIR表征

用ＥＸＡＦＳ，ＦＴＩＲ以及ＩＣＰ等实验方法，对脱氧胆酸钇的结构进行了初步探讨。实验结果证实，钇与脱氧胆酸配位，生成稀土络合物，其中钇周围有八个氧原子，配位数为八，Ｙ－Ｏ平均距离为０．２３４ｎｍ。脱氧胆酸中羧基氧原子，羟基氧原子均与钇发生配位作用。     

Effect of solution temperature and cooling rate on microstructure and mechanical properties of laser solid forming Ti-6A1-4V alloy

The effect of solution temperature and cooling rate on microstructure and mechanical properties of laser solid forming （LSF） Ti-6A1-4V alloy is investigated. The samples are solutions treated at 900, 950, and 1000 ℃, followed by water quenching, air cooling, and furnace cooling, respectively. It is found that the cooling rate of solution treatment hasα more important effect on the microstructure in comparison with the solution temperature. The martensite α formed during water quenching results in the higher hardness and tensile strength but lower ductility of samples. With decreasing the cooling rate and increasing the solution temperature, the width of primary α laths increases, and the aspect ratio and volume fraction decrease, which make the hardness and tensile strength decrease and the ductility increase.     

Chemical composition analysis for laser solid forming of titanium alloys from blended elemental powders

Laser solid forming （LSF） from blended elemental powders is an advanced technique to investigate new alloy systems and to create innovative materials. Accurate composition control is critical for the applications of this technique. In this letter, the composition analysis is performed on LSF titanium alloys from blended Ti, Al, and V powders. It is found that the composition of as-deposited sample can be controlled by keeping the identity of the divergence angle of each elemental powder stream. Based on the consistency condition for divergence angles of different elemental powder streams, the matching relation among the Ti, Al, and V powder characteristics （particle size and density） can be obtained, which ensures the consistency in composition between the laser deposits and the blended elemental powders under different laser processing parameters.     

用CA方法模拟界面能各向异性对胞晶生长形态的影响

用元胞自动机（CellularAutomaton,CA）模型研究了界面能各向异性对二维定向凝固胞晶的生长形态的影响,建立了判定胞晶生长达到稳态的判据．结果显示,当界面能各向异性强度非常小时,胞晶尖端很容易分岔,胞晶形态不容易稳定．而当界面能各向异性强度足够大时,容易形成稳定的胞晶形态,同时界面能各向异性强度会显著影响稳定胞晶的形态,界面能各向异性越强,稳态胞晶间距越小,胞晶尖端半径越小,尖端半径与胞晶间距的比值越小,固液界面前沿的浓度与过冷度越小．     

Microstructure characteristics of laser forming repaired Ti60 alloy

The microstructure characteristics of laser forming repaired (LFR) Ti60 (Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.3Nb) as-deposited and annealed samples are analyzed. The microstructure of as-deposited repaired zone (RZ) consists of epitaxial columnar prior β grains, in which fine woven α laths and β-phase between α laths exist. The heat-affected zone (HAZ) experiences a continuous microstructural transition from duplex microstructure of the base metal zone (BMZ) to the microstructure of RZ. The presence of silicide precipitates is observed in both RZ and BMZ in an annealed sample by transmission electron microscopy. They are identified as (Ti, Zr) 6 Si 3 distributed mainly at the α/β interface with the size of 100 300 nm. The fine αprecipitates are detected in BMZ by electron diffraction; there was no α detected in RZ.     

Absolute stability of the solidification interface in a laser resolidified Zn--2wt.%Cu hypoperitectic alloy

This paper reports on laser surface remelting experiments performed on a Zn--2wt.%}Cu hypoperitectic alloy by employing a 5kW CW CO₂ laser at scanning velocities between 6 and 1207mm/s. The growth velocities of the microstructures in the laser molten pool were accurately measured. The planar interface structure caused by the high velocity absolute stability was achieved at a growth velocity of 210~mm/s. An implicit expression of the critical solidification velocity for the cellular--planar transition was carried out by nonlinear stability analyses of the planar interface. The results showed a better agreement with the measured critical velocity than that predicted by M--S theory. Cell-free structures were observed throughout the whole molten pool at a scanning velocity of 652~mm/s and the calculated minimum temperature gradient in this molten pool was very close to the critical temperature gradient for high gradient absolute stability (HGAS) of the \eta phase. This indicates that HGAS was successfully achieved in the present experiments.