Statistical study of the primary-dendrite spacings in single-crystal superalloys

Three generations of single-crystal superalloys (AM3, DD5 and DD90) were produced with directional solidification and seeding. The square-calculation method and direct-measurement method were used to study the primary-dendrite spacings of the three single-crystal superalloys at different solidification distances (50, 150 and 250) mm. Statistical results showed that, firstly, as the solidification heights increased, the average primary-dendrite spacings of the three alloys were gradually enlarged; secondly, the average primary-dendrite spacings calculated with the square-calculation method and the direct-measurement method were similar, which indicated the high precision of the two methods; thirdly, the primary-dendrite spacings of the three alloys were distributed randomly in a relatively large range, following a normal distribution. The maximum values of the primary-dendrite spacings were 4.7–8.5 times larger than the minimum ones at different solidification distances and were different from the values from previous studies.