Thermal shock resistance of Zr2(4-17)wt% Y23 has been investigated by subjecting disk shaped specimens to a heat cycle of 1100/room temperature at a maximum cooling rate of about 500/min. Partially stabilized Zr2-4wt% Y23 consisting mainly of monoclinic Zr2 phase exhibits poor thermal shock resistance because of its large volume change associated with the martensitic transformation of monoclinic phasetetragonal phase. Furthermore, fully stabilized Zr2(12-17)wt% Y23 with 100wt% cubic phase , which undergoes no martensitic transformation, also shows inferior thermal shock resistance. This is assumed to result from its low fracture toughness. Relatively excellent thermal shock resistance is obtained in partially stabilized Zr2-7wt% Y23. This is probably due to its combined effect of small volume change through the martensitic transformation and higher fracture toughness. The effect of A23 or Si2 addition to Zr2-7wt% Y23 has been also investigated to enhance its thermal shock resistance. Zr2-7wt% Y23(5-4)wt% A23 indicated the improved thermal shock resistance. This improvement could be attributed to their higher fracture toughness , together with higher hardness in comparison with those of Zr2-7wt% Y23, and also to the morphological change of monoclinic Zr2 phase. In Zr2-7wt% Y23 the monoclinic Zr2 grains tended to coalesce into large clusters in the cubic Zr2 matrix. As a result, large cracks tend to initiate from the monoclinic phase during the martensitic transformation. On the other hand, the addition of A23 results in the isolated spherical grains of monoclinic Zr2 phase , eading to improved thermal shock resistance. The addition of (0.5-1)wt% Si2 to Zr2-7wt% Y23 causes no morphological change in the monoclinic Zr2 grains and consequently results in no improvement in thermal shock resistance. [Received August 29 , 1984]
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