【作者】 郭磊；

【导师】 陈枫；

【作者基本信息】 哈尔滨工程大学 ， 材料物理与化学， 2012， 硕士

【摘要】 本文以Ni₅₀Mn₄₁Sn₉合金为基础，添加第四元素Co分别替代部分Ni、Mn和Sn形成四元高温形状记忆合金Ni_50-xMn₄₁Co_xSn₉（x=5，7，9，10，12）、Ni₅₀Mn_41-xCo_xSn₉（x=1，2，3，4，5）和Ni₅₀Mn₄₁Sn_9-xCo_x（x=0.5，1，2，3，4），使用金相显微镜、XRD、DSC、压缩等测试方法，系统地研究了这些合金的马氏体相变、组织结构、力学性能和磁学性能。研究结果表明：Co取代Ni导致马氏体相变温度下降；Co取代Mn和Sn使马氏体相变温度先升高后降低。三种合金体系在冷却和加热时均发生一步热弹性马氏体相变和逆相变。显微组织分析结果表明，随着Co含量的增加，无论Co取代Ni、Mn还是Sn均导致合金中形成第二相，只是具体的形貌和分布方式不同：Co取代Ni，第二相主要分布在马氏体内部或是晶界上，第二相为面心立方结构，呈枝节状，并随着Co含量增加先增多后减少；Co取代Mn，第二相主要分布在晶界上，第二相为面心立方结构，呈黑色条纹状，并随着Co含量增加而增加；Co取代Sn，第二相形貌较为复杂，有颗粒状和长条状，其数量随Co含量增加而增加。力学测试结果表明，Co无论取代Ni、Mn还是Sn均能提高合金的塑性和强度，其中以Co取代Mn和Sn最为明显。但是对形状记忆效应的影响呈现不同规律，Co取代Ni使形状回复率上升，而Co取代Mn和Sn则使合金的形状记忆效应恶化。断口分析结果证实了力学性能的变化规律，Co取代Ni时，所有合金断口呈现典型的脆性断口特征。Co取代Mn和Sn时，随Co的加入断口由沿晶和穿晶混合断裂方式转变成穿晶解理和韧窝混合断裂形貌，合金表现出了部分韧性断裂的特征。磁学性能测试表明，Co取代不同合金元素对磁学性能的影响各不相同。对于Co取代Ni而言，随着Co含量的增加，合金由反铁磁性向铁磁性转变；Co取代Mn只是使合金反铁磁性增强；Co取代Sn使合金由顺磁性向反铁磁性转变。更多还原

【Abstract】 In the present paper, the fourth element, Co, is added into Ni50Mn41Sn9by substituting Ni, Mn and Sn, respectively, to form high temperature shape memory alloy. Martensitic transformation, microstructure, mechanical and magnetic properties of Ni50-xMn41CoxSn9(x=5,7,9,10,12), Ni50Mn41-xCoxSn9(x=1,2,3,4,5) and Ni50Mn41Sn9-xCox(x=0.5,1,2,3,4) are studied systematically by using optical microscope, SEM, XRD, DSC and compression test.The results show that, the substitution of Co for Ni lead to the decrease of martensitic transformation temperature;respectively; the substitution of Co for Mn and Sn increase martensitic transformation temperature initially and then decrease.all the alloys exhibit one step thermalelastic martensitic forward and reverse transformation upon cooling and heating, respectively.With the increase of Co content, the second phases with different morphology and amount precipitate in the case of the substitution of Co for Ni, Mn and Sn. When the Co substitutes for Ni, the second phase with FCC structure distributes along the grain boundary or inside the martensite. The second phases exhibit banded feature and initially increase then decrease with the increase of Co content. The characterization of second phase in the case of Co substituting for Mn is similar to the case of Co substituting for Ni. When Co substitutes Sn, the second phases exhibit complex morphology, some are granulated and others are like a straight line. In this case, the amount of second phases is increased with increasing Co content.Regardless of the substitution method, the addition of Co improves the ductility and strength of the alloys. While the effect of Co substitution on shape memory effect is different. The substitution of Co for Ni increases the shape recovery ratio, however, the substitution of Co for Mn and Sn deteriorates the shape memory effect.Fracture analysis confirms the results of mechanical properties caused by the addition of Co. All the alloys possess typical brittle fracture feature when Co substitutes Ni. In the case when Co replaces Mn and Sn, the fracture feature changes from the combination of intergranular crack and transgranular crack to the combination of transgranular crack and dimple fracture. Magnetic measurements show that, Co substitute Ni changes the magnetization of alloy from anti-ferromagnetic state to ferromagnetic state; Co substitute Mn just increases the magnetization of anti-ferromagnetic state; Co substitute Sn changes the magnetization of alloy from paramagnetic state to anit-ferromagnetic state.更多还原