熔体过热处理对M963合金组织和高温持久性能的影响

对M963合金熔体进行了过热处理并在1248K／225 MPa条件下测试了其持久性。结果表明，随熔体过热温度的升高，铸态组织中的初生MC碳化物不断细化和均匀分布，合金的持久断裂寿命和塑性明显提高，但温度高达2023K的熔体过热处理，使合金中的气体含量升高，导致显微疏松增加，持久性能降低。在1923K温度下进行熔体过热处理，可使M963合金在1248K／225MPa条件下的持久寿命和持久塑性同时提高一倍以上。     

On the Critical Point of Tungsten

Experimental results of exploding tungsten wire experiments with heating rates of 10¹⁰ to 10¹¹ Ks^–1 are interpreted using a one-dimensional hydrodynamic model. The vaporization dynamics under these conditions are discussed. It is shown that for the wires used the superheating of the liquid phase is small and vaporization starts close to the binodal line of the phase diagram. Due to inertia, a volume vaporization takes place in a thin surface layer, while in the bulk of the column formed by the exploding wire a pressure of the order of 10 kbar is maintained. Sufficiently uniform density and temperature distributions are formed in the liquid core surrounded by the two-phase layer. This behavior of vaporizing wires was used to obtain the thermal expansion coefficient of liquid tungsten along with its critical point parameters.     

Superheating and melting behaviors of Ag clusters with Ni coating studied by molecular dynamics and experiments

Using molecular dynamics with embedded-atom-type interatomic potentials, we simulated the melting behavior of a spherical Ag3055 cluster coated with Ni. The semi-coherent Ag/Ni interface formed at low temperatures acts as an effective barrier against the surface melting and leads to a substantial superheating of the Ag cluster. The melting point was found to be about 100 K above the equilibrium melting point of the bulk Ag crystal (1230 K?15 K) and about 290 K above that (1040 K) of the free Ag3055 cluster. A superheating of 70 K was observed in the high-temperature differential scanning calorimetry measurement for Ag particles with a mean size of 30 nm embedded in Ni matrix prepared by means of melt-spinning. Melting is initiated locally at the defective interfacial area and then propagates inwards, suggesting a heterogeneously nucleated melting event at the Ag/Ni interface.     

W型火焰锅炉动态特性的数值计算与研究

对Ｗ型火焰锅炉的蒸发系统、过热器系统的动态特性进行了数值计算与研究。详细分析了上安电厂Ｗ型火焰锅炉在不同负荷、不同运行方式、不同卫燃带面积等条件下的蒸发特性及汽温特性的动态变化过程,论述了其变负荷性能差的主要原因。计算数据反映的规律符合实际运行情况。     

Incipient Boiling of Sodium in Presence of Magnetic Field

A three-dimensional nuclear and thermo-hydrodynamic kinetics calculation code IBIS has been developed, envisaging the treatment of asymmetrical reactivity changes in a large fast breeder reactor. An example of calculation with this code is described, which reveals a difference of void propagation behavior, following a local disturbance, between homogeneous and heterogeneous cores, ascribable to the presence, in the latter case, of inner blanket layers, which act as barrier against void propagation. Of the two parameters of power-to-flow ratio and space-time variation in thermal power, the latter is the more influential on void propagation, and this makes it essential to perform three-dimensional space-dependent kinetic analysis for adequately simulating local perturbations in a heterogeneous core.     

Transient Boiling of Sodium in Seven-Pin Bundle under Transient Overpower Conditions

Transient sodium boiling experiments were conducted in an electrically heated 7-pin bundle under transient overpower conditions. In each run the heater power was gradually raised at almost constant rate under forced convection.

The observed coolant voiding was initially limited to the central subchannel on account of an appreciable time lag in temperature rise occurring between the central and peripheral subchannels. This would appear to call for calculations with two-dimensional voiding model.

The bulk pressure rises registered upon initial vaporization were markedly lower than the vapor pressure corresponding to the incipient-boiling (IB) wall superheat. The pressure pulse generated upon vapor bubble collapse correlated reasonably well with the re-entrant liquid velocity, but the measured value was very much smaller than predicted theoretically from sodium hammer analysis.     

DZ125镍基高温合金高温持久断裂后的位错组态

研究了熔体超温处理工艺对DZ125镍基高温合金铸态及热处理态高温持久试样位错组态的影响.结果表明:铸态试样的高温持久寿命随熔体超温处理温度的升高而增加.热处理态试样的高温持久寿命随超温处理温度的升高表现为先增加后减少,当超温处理温度为1650℃时,持久寿命达到最大值.随熔体超温处理温度的升高,铸态试样位错密度增大且位错...