铸型涂层对熔体过冷度和凝固组织的影响

EFFECT OF STRUCTURE OF SiO_2 COATING ON THE UNDERCOOLABILITY AND MICROSTRUCTURE OF Cu_(70)Ni_(30) MELTS

利用溶胶－凝胶方法，在铸型内表面玻璃涂层上制备 ＳｉＯ２晶态和非晶态薄膜涂层，将深过冷 的Ｃｕ７０Ｎｉ３０。合金熔体浇入两种涂层铸型中．分别获得９０Ｋ和１９８Ｋ的过冷度．提出了用重合密度和重 合原子中心偏离度分析涂层结构对合金熔体形核惰性影响的模型．用ＢＣＴ模型分析过冷熔体凝固过程中 枝晶生长与过冷度的关系，结果表明， ８０Ｋ为临界过冷度，△Ｔ＜８０Ｋ时，枝晶生长受成分过冷控制； △Ｔ＞８０Ｋ时，受热过冷控制．在深过冷范围内．凝固组织为细密挺直枝晶．

Cristobilite and amorphous film coatings were successfully prepared by using sol-gel principle on the surface of basic glassy coating of investment casting mold. When pouring undercooled Cu70Ni30 melts into the two kinds of coated molds, 90K and 198K undercoolings can be obtained, respectively. The model of atomic coincidence density and deviation degree of the coincidence atoms at low index plane of crystal lattice was used to investigate the effects of coating structure on melts undercoolingability. The calculated results based on BCT model demonstrated that solidification behavior of undercooled Cu70Ni30 alloy is controlled by a critical undercooling (80K). When the undercooling is less than the critical one, the solute undercooling controls the solidification behavior. On the other hand, the thermal undercooling controls the behavior. The microstructure obtained during experiment can be explained by the calculated results.