影响灰铸铁气缸盖表面硬度的因素分析

分析了灰铸铁表层铁素体层的形成原因,综述了影响灰铸铁缸盖表面硬度的影响因素,包括生铁加入量、时效处理温度、孕育剂加入量、熔炼过热温度.通过试验验证表明,型砂含水量的增加促进气缸盖表面形成一层铁素体层,降低硬度值;生铁加入量越高,气缸盖表面硬度降低越明显.     

Grain refining action of Ti existing in electrolytic low-titanium aluminum with Al-4B addition for superheated Al melt

The effects of superheating temperature on the grain refining efficiency of Ti existing in electrolytic low-titanium aluminum (ELTA) without and with the Al-4B addition and the Al-5Ti-1B master alloy in pure Al were comparatively investigated. The results show that the Ti existing in ELTA without Al-4B addition exhibits a certain grain refining efficiency when the melt superheating temperature is lower, but the efficiency decreases rapidly when the superheating temperature is higher. The grain refining efficiency of the Al-5Ti-1B master alloy is better than that of the Ti existing in ELTA without Al-4B addition at any superheating temperature, but it also decreases obviously with the increase of the superheating temperature. One important reason is that the TiB2 particles coming from the Al-5Ti-1B master alloy can settle down at the bottom of the Al melt easily when the superheating temperature is increased, thus decrease the number of the potent heterogeneous nuclei retained in the Al melt. If the Al-4B master alloy is added to the ELTA melt, the grain refining efficiency of the Ti existing in ELTA can be improved significantly, and does not decrease with the increase of the superheating temperature. This perhaps provides us a possible method to suppress the effect of the superheated melt on the microstructures of aluminum..     

Incipient Boiling of Sodium in Seven-Pin Bundle under Forced Convection Conditions

Experimental studies were carried out on incipient boiling of sodium flowing in an electrically heated seven-pin bundle under forced convection.

In the first series of experiments temperature distributions in the bundle were measured under non-boiling conditions. The measured temperature distributions agreed fairly well with the calculation by the NORMAL code.

In the second series of experiments incipient-boiling (IB) phenomena were investigated, with particular reference to the IB superheat and the voiding patterns. The IB wall superheat decreased with increase in flow velocity. The observed coolant voiding was limited in the central subchannel because of the steep radial temperature gradient in the bundle. In order to describe this voiding process a two-dimensional voiding model was required.     

Melting and Volume Vaporization Kinetics Effects in Tungsten Wires at the Heating Rates of 1012 to 1013 K/s

Experimental results on electrically exploded tungsten wires at the heating rates of 10¹²–10¹³K · s^–1 and their interpretation in the framework of a one-dimensional magneto-hydrodynamic model are presented. The effects of both melting and volume vaporization observed in these experiments are discussed. It is shown that superheating of solid tungsten does not take place at these heating rates (within a 10% experimental uncertainty). Some direct measurements performed in this study, and comparison of different quantities measured and calculated by the model, suggest that the volume vaporization starts close to a binodal line.     

Superheating of Liquid Alkali Metals

The maximum attainable temperature of superheating and the critical temperature of cesium, rubidium, and potassium are correlated using the generalized van der Waals equation of state. This study shows that the maximum attainable temperatures of superheating for liquid cesium, rubidium, and potassium are 1722, 1802, and 2039 K, respectively. The results of the determination of the maximum attainable temperatures of superheating of liquid cesium, rubidium, and potassium are in agreement with experimental data. The given study establishes that liquid cesium, rubidium, and potassium can be superheated up to temperatures of about 200 K below their critical temperatures of 1924, 2017, and 2280 K, respectively. Moreover, cesium, rubidium, and potassium have been found to obey the single-parameter law of corresponding states, with the maximum attainable reduced temperature of superheating as the thermodynamic similarity parameter.     

熔体温度处理的研究现状及展望

熔体温度处理主要研究的是材料熔体结构与温度的对应关系,及其在冷却和凝固过程中的演化规律,通过适当的熔体温度处理,可以改善合金的组织和提高综合力学性能.详细介绍了熔体温度处理的几种方法,如熔体超温处理、熔体混合处理、固液混合铸造等.分析了国内这些领域的研究进展和一些具体的应用情况,探讨了今后的发展方向.     

非自由表面大块晶体过热的初探

初步研究了非自由表面大块单晶A1及大块晶体Pb的过热.主要介绍通过有效的方法制得试样,用DSC-7准确测量出在包覆状态下大块单晶Al及大块晶体Pb的过热度,从而得出大块晶体过热的必要条件.     

非自由表面大块Pb晶体的动力学过热模型

主要对Pb-Al试样经差示扫描量热仪DSC-7以不同的加热速度进行加热后得到的测量结果进行分析,从而为进一步完善熔化及过热理论提供了可靠性。     

Superheating limits of liquid helium I

It is shown that the maximum superheat temperature ΔT_max in liquid helium I, determined under steady-state peak nucleate boiling conditions, cannot be realistically estimated from the thermodynamic limit of superheat (spinodal), as has been previously claimed. It is suggested that a more meaningful estimate of ΔT_max can be obtained from the kinetic limit of super-heat (homogeneous nucleation temperature). Experimental data on the homogeneous nucleation superheat temperature, ΔT_h, in liquid helium I over an extended temperature range are presented and compared with the ΔT_max measurements of several investigators. It is pointed out that in any quantitative predictions of ΔT_max, a knowledge of ΔT_h alone is not sufficient. In fact, the measured value of ΔT_max can lie either below or even above ΔT_h depending on the bath temperature, conditions of the surface, and the thermophysical properties of both heater and liquid.