【作者】 罗刚；

【导师】 高建荣；

【作者基本信息】 东北大学 ， 材料学， 2008， 硕士

【摘要】 深过冷状态下包晶合金的相选择具有非常重要的意义,因为它不但有助于人们认识非平衡凝固过程,而且还有很重要的工业应用价值。深过冷状态下,许多重要材料都会涉及到相选择,比如坡莫合金、不锈钢、稀土永磁材料和稀土氧化物高温超导材料等。然而,人们对包晶合金中相选择的规律和机理还没有清晰和统一的认识,因此需要深入研究。本文以铜锗包晶合金(Cu-14.8%Ge)和过包晶合金(Cu-18%Ge)为模型合金,采用电磁悬浮技术进行了深过冷快速凝固和相选择研究,并与玻璃基底悬淬、铜基底悬淬和落管实验结果进行对比,考察了过冷度与冷速对深过冷熔体中相选择规律的影响。在电磁悬浮实验中,‘包晶成分合金获得了157K-244K的过冷度,过包晶成分合金获得了124K-241K的过冷度,、初生相均为α-Cu。在玻璃基底悬淬实验中,包晶成分合金获得了32K-174K的过冷度,初生相为α-Cu；过包晶成分合金获得了179K～294K的过冷度,当过冷度超过280K后初生相为包晶相ζ-Cu5Ge。在铜基底悬淬实验中,两种成分合金中的包晶相ζ-Cu5Ge均可以初生相的形式析出。在落管实验中,所有包晶成分合金和大多数过包晶成分合金中的初生相为α-Cu,只有在少数的过包晶成分合金中,包晶相ζ-Cu5Ge以初生相的形式析出。上述结果表明,铜锗包晶合金熔体中的包晶相以初生相形式析出很困难。但是,只要过冷度足够大(>280K),即使是低冷速下包晶相ξ-Cu5Ge也能成为初生相。深过冷状态铜锗包晶合金熔体中发生相选择时,过冷度是决定性因素,冷速是诱导性因素。更多还原

【Abstract】 Phase selection in undercooled melts of peritectic alloys is of much interest because it is helpful to an understanding of non-equilibrium solidification, and of great value in industries. It occurs in undercooled melts of many engineering materials such as permalloy, stainless steel, rare earth permanent magnet materials, and rare earth high-temperature superconducting materials. However, a clear and general understanding of it is missing in literature, and therefore, much work should be done in this respect.In the present thesis work, peritectic Cu-14.8%Ge composition and hyperperitectic Cu-18%Ge composition were chosen as model alloys for the purpose of investigating phase selection in undercooled melts. They were undercooled and rapidly solidified using the electromagnetic levitation technique. Parallelly, glass and metal substrate-quenching experiments and drop tube experiments were carried out on the same compositions, aiming at a comparative investigation of influences of undercooling and cooling rate on phase selection.In the EML experiments, Cu-14.8%Ge and Cu-18%Ge compositions were undercooled below liquidus by an amount of 157K to 244K and by an amount of 124K to 241K, respectively. Theαphase was crystallized primarily in both compositions. In the glass substrate-quenching experiments, the peritectic Cu-14.8%Ge composition was undercooled by an amount of 32K to 174K, and crystallized into primaryαphase; the hyperperitectic Cu-18%Ge composition was undercooled by an amount of 179 to 294 K, and crystallized into primaryζphase for undercoolings above 280 K. In the metal substrate-quenching experiments, both compositions were solidified via primary crystallization of the peritecticζphase. In the drop tube experiments, all samples of the peritectic Cu-14.8%Ge composition and most of the samples of the hyperperitectic Cu-18%Ge composition were crystallized into primary a phase, whereas few samples of the composition Cu-18%Ge were crystallized into primaryζphase, at least at the initial stage ofthe solidification process.The above results showed that primary crystallization of the peritecticζphase in peritectic Cu-Ge alloys is fairly difficult. However, it is able to become a primary phase even under slow cooling conditions, provided that a liquid undercooling of greater than 280 K is achieved. It. is thus concluded that with respec to the phase selection in undercooled Cu-Ge alloys, undercooling is a decisive factor, whereas cooling rate is a beneficial factor.更多还原