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Directionally solidified single crystal superalloy test bars were prepared by the spiral grain selection method. The microstructural evolution and orientation characteristics of the starter block and spiral part were studied, and the influence of the competitive growth of crystals on the microstructural characteristics was analyzed. The results show that the divergent grain groups, with small size and randomly oriented grains, appear at the bottom of the start block due to the chilling effect, which is an important area for competitive growth. As the height of the starter block increases, the primary dendrite spacing increases, and the grain density decreases; furthermore, the proportion of grains with an orientation deflection angle less than 10° gradually increases. The <001> texture gradually becomes stronger as the height of the starter block increases, which indicates that the competitive growth of crystals gradually weakens. At the initial stage of the crystal selection in the spiral part, the obstacle of adjacent grains and spiral passage is the main working mechanism. The grains located at the inner side of the front edge of the spiral passage have the growth advantage. The single crystal screening process is achieved at about two-thirds of the spiral height, and the single crystal with the orientation deviation angle of 6.7° from the casting axis is prepared. [ABSTRACT FROM AUTHOR]

• The nuclear and growth of stray grains lead to the defect of orientation deviation. • Direction of heat flow in the spiral part was inclined toward the spiral direction. • The inclined temperature gradient in spiral passage promoted stray grains' growth. Microstructure evolution and competitive grain growth in the spiral part of a single crystal sample whose crystal orientation deviating from the axial direction was analyzed. The results showed that the appearance of stray grains in the spiral part and the elimination of the originally preferred orientation grains by the competitive growth of stray grains are the reasons for the single-crystal orientation deviation defect. It was indicated that stray grains tend to nucleate at the initial stage of crystal selection in the spiral part. The inclined temperature gradient in the spiral part promoted the development of stray grains, whose growth direction was closer to the direction of the heat flow. Stray grains maintained the competitive growth in the spiral part, and a single crystal with the orientation deviated from the expected direction of 〈0 0 1〉 is formed. [ABSTRACT FROM AUTHOR]