摘要
采用熔盐净化剂与循环过热相结合的方法,获得了过冷度高达180 K的DZ125高温合金深过冷熔体,研究了合金深过冷凝固的组织演化过程.结果表明,随着过冷度△T的增大,凝固组织经历3次转变过程:当△T<48 K时,合金的凝固组织为普通树枝晶;当48 K≤△T<85 K时,枝晶因再辉发生熟化和重熔,组织转化为第Ⅰ类粒状晶;当85 K≤△T<160 K时,再辉所产生的重熔效应大大降低,凝固组织为深过冷树枝晶;当△T≥160 K时,发生枝晶破碎及再结晶,凝固组织转变为第Ⅱ类粒状晶.
Investigations of microstructural evolution in undercooled metallic melts have been extensively conducted in different alloy systems, such as eutectic, peritectic and metallic compound, however, few reports about undercooled superalloys were found up to date. In this paper, DZ125 superalloy melt was undercooled by the method of molten salt purification combined with cycled superheating under Ar atmosphere, and a substantial undercooling up to 180 K was obtained. Based on the microstructural observation as well as the calculations of the dendritic tip radius, the dendrite growth velocity and undercooling with BCT （Boettinger, Coriell, Trivedi） dendrite growth model, the solidification behavior and structure transition results indicate that the microstructure undergoes mechanisms were systematically investigated. The three sequent transitions in the achieved range of undercooling range △T. When △T 〈 48 K, the dendrite growth is mainly controlled by solute diffusion, and the solidification structures are the common dendrites. When 48 K≤ △T 〈 85 K, the dendrites is remelted and the first kind of granular grains forms because of the serious remelting produced by recalescence. When 85≤ △T 〈 160 K, the effect of solute diffusion is weakened by solute trapping that results from high dendrite growth velocity, thermal diffusion plays the dominate role at the same time, the remelting effect decreases to a low level, and ripenings of dendrite are restrained, the granular grains turn into highly developed fine dendrites. When △T 〉 160 K, the second kind of granular grains is formed, the transition is caused by the stress originating from the rapid solidification contraction, which results in the recrystallization of the fine dendrite.
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第4期385-389,共5页
Acta Metallurgica Sinica
关键词
镍基高温合金
深过冷
过冷度
组织演化
Ni base superalloy, supercooling, supercooling degree, microstructure transition
