Study on Thermal Shock of Sintered Tungsten Alloys for a First Partition of Nuclear Fusion Furnace by the Method of Fracture Mechanics

研究了不同体积分数钨颗粒对W-Ni-Fe烧结合金高温力学性能的影响。烧结钨合金的0.2%屈服强度和抗拉强度均高于其它耐热合金如18 Cr-8 Ni钢，但随着温度的升高而降低。烧结钨合金的断裂韧性随钨颗粒体积分数的增加而降低。当钨颗粒的体积分数较低时，稳定的裂纹主要在Ni-Fe基体相中生长，导致高的韧性。为了研究烧结钨合金的缺口强度，进行了三点弯曲试验。弯曲载荷与裂纹长度之间存在线性关系。裂纹萌生载荷表明，钨颗粒体积分数高的钨合金的值较低。烧结钨合金的热震试验中观察到钨颗粒或钨-钨晶界出现裂纹。尽管重复了热冲击试验，但裂纹从未扩展到其他钨晶粒或基体相中。采用有限元法分析了钨颗粒周围的应力分布，并分析了钨颗粒体积分数的变化对应力分布的影响。通过计算得到的应力分布，研究了钨颗粒中裂纹的萌生机制。

Mechanical Properties of W-Ni-Fe sintered alloys with the various volume fractions of tungsten particles were investigated at elevated temperature. 0.2% proof stress and tensile strength of sintered tungste alloys by tension tests, which were higher than those of the other heat-resistance alloy such as 18Cr-8Ni steel, decreased with increasing temperature. Fracture toughness of the sintered tungsten alloys decreased with increasing volume fraction of tungsten particles. When the volume fraction of tungsten particle is low, a stable crack dominantly grows in the Ni-Fe matrix phase, resulting in high toughness. Three point bending tests were carried out in order to study the notch strenght of sintered tungsten alloys. There existed the linear elation between the bending load and the crack lenght. The crack initiation load indicated the low values for the tungsten alloys with high volume fraction of tungsten particle. A crack in the tungsten particle or the tungsten-tungsten grain boundary was observed by the the thermal shock tests for the sintered tungsten alloys. This crack never propagated into the otether tungsten grain or the matrix phase although the thermal shock tests were repeated. The stress distributions around the tungsten particles were analyzed by using a finite element method, and they varied by the change of the volume fraction of tungsten particles. Mechanism of crack initiation in the tungsten particle was investigated by the calculated stress distributions.