【摘要】 采用真空非自耗电弧炉熔炼得到纽扣锭,利用优化的真空吸铸工艺吸铸制备定向凝固用送料棒。在光学浮区炉中先制备出由单一垂直片层组织构成的Ti-43Al-3Si合金定向试棒,切取合适取向后采用机械镶嵌法与多晶TiAl试棒连接固定后作为初始籽晶。制备圆台形试棒作为送料棒,在5 mm/h的生长速率下,利用初始籽晶引晶圆台试棒制备终极籽晶。终极Ti-43Al-3Si籽晶的片层方向平行于生长方向。用终极籽晶来引晶控制Ti-47Al合金PST晶体的片层取向,结合显微分析研究了晶体生长过程。结果表明,制得的送料棒达到光学浮区炉的入炉生长要求;圆台试棒的使用可有效避免因尺寸突变引起的杂晶形核;在5和180 mm/h的生长速率下,Ti-43Al-3Si合金的初生相均为α相。制得的终极籽晶片层一致性好,由单一晶粒组成,在引晶过程中可以保持片层组织稳定,无杂晶形核。使用该终极籽晶可有效控制整个Ti-47Al合金PST晶体的片层取向。更多还原

【Abstract】 Button ingots were prepared by arc melting and feed bars for directional solidification were prepared by optimized drop casting technique. The Ti-43 Al-3 Si directionally solidified bars with lamellar boundaries perpendicular to the growth direction were prepared at the growth rate of 180 mm/h in an optical floating zone furnace. Cylindrical sections were cut from these perpendicular lamellae with appropriate direction and then fixed on polycrystalline TiAl bars by mechanical setting method to serve as the initial seeds. The ultimate Ti-43 Al-3 Si seeds with parallel lamellar microstructure were successfully prepared from these initial seeds at the growth rate of 5 mm/h. To avoid the nucleation of stray grains,drop-cast bars with the shape of frustum of a cone were used for the preparation of ultimate seeds. At the growth rates of 5 and 180 mm/h, the primary phase of Ti-43 Al-3 Si alloy was always the α phase. Polysynthetically twinned(PST) crystals of Ti-47 Al alloy were obtained from the Ti-43 Al-3 Si ultimate seeds and the seeding process was studied by microscopic analysis. Lamellar microstructure of the seed kept stableand recrystallization of the seed was not found. Lamellar orientation of Ti-47 Al PST crystals was successfully controlled by the ultimate Ti-43 Al-3 Si seed.更多还原