co基和y基非晶合金成分设计及其性能研究-材料学专业毕业论文.docx

中南大学博士论文摘要
大大减少了氧对合金非晶形成能力的不利影响。同时提出了一个修正
理论计算参数s宰(s木=一AS胁/衄细),可以用来预测合金的GFA。
(5)用铜模吸铸法制备了直径分别为3mm和5mm的Y56A124C020 和Y41Scl5A124C020大块非晶合金。基于不同冷却速率条件下合金液体熔点偏移的计算方法得到Y4lScl5A124C020大块非晶合金的临界实际冷却速率为36刚s。在玻璃转变温度T2和晶化温度Tx之间的等温晶化过程中,该大块非晶合金的主要晶化过程Avrami指数n(x)>3,为三维形核长大过程。
(6)由VFT方程拟合得到Y4IScl5A124C020大块非晶合金的脆性参数m=24,小于典型非晶形成能力很强Zr基和Pd基合金的m值, 表明该合金具有很好的非晶形成能力。该大块非晶合金是目前最脆的金属玻璃,,是研究脆性问题的理想材料。
(7)以Y基非晶合金为研究对象,研究表明,随着冷却速率的
降低,非晶合金的硬度增大。同时在压痕周围伴有多重剪切带() 现象,这是由压痕形变区域内自由体积显著增加造成的。基于自由体积模型,高的冷却速率引起更高的缺陷浓度,导致原子的跃迁和扩散的可能性越大,从而增加了原子的通量和降低流变应力,最终导致非晶合金软化。
关键词非晶合金,非晶形成能力,晶化动力学,性能,自由体积
中南人学博十论文 ABSTRACT
ABSTRACT
Bulk metallic glasses(BMGs)have attracted increasing interests due to their outstanding major goal is to design new alloy systems with superior glass forming ability(GFA).Due to lack plete theory predicting GFA for new metallic glasses,Co-based and Y-based amorphous alloys were fabricated by the element substitution method in this conclusions are drawn as below:
(1)The effects of Zr on the microstructure,GFA and thermal stability of l oB20(x=0,2,4 and 6at.%)alloys have been l Zr4Nb 1 0820 alloy shows the most homogeneous microstructure,the best GFA and the highest thermal apparent activation energies of C045Fe21Zr4NbloB20 amorphous alloy from Kissinger equation are for Tg and for Txl,
respectively.
(2)The addition Of Y can improve greatly GFA and thermal stability
of C045Fe21Zr4NbloB20 main reason is that the reaction between yttrium and oxygen is thermodynamically pared to the reaction between oxygen and the other elements in the , the stability of the remaining liquid could be enhanced by the alleviation of the harmful effect of oxygen,and the GFA of Co—based alloys can be apparent activation energies of(C045Fe2iZr4NbloB20)96Y4 amorphous alloy are for Txl and for TDl respectively,which are the