【作者】 俞伟元；

【导师】 陈学定；

【作者基本信息】 兰州理工大学 ， 材料科学与工程， 2009， 博士

【摘要】 用X-射线衍射、差示扫描量热分析仪(DSC)、扫描电镜和电子探针等为主要研究手段,以Cu65.5Ni16.6P12.9Sn4.9非晶态钎料和AlSiCu快速凝固钎料为对象,通过对非晶态钎料钎焊升温过程中的组织演变、钎料与基材的相互作用、钎焊接头的形成过程、以及钎焊接头性能的详细研究,揭示了非晶态钎料润湿机理,钎料合金元素在钎焊过程中的扩散行为,非晶态钎料的晶化对钎焊过程的影响,从本质上解释了非晶态钎料性能优异的原因。通过以上研究发现：在钎焊升温过程中非晶态钎料在固态下虽然发生晶化并长大,但晶化后的晶粒细小,组织均匀,无宏观及显微偏析,这有利于钎焊时元素的扩散和液相的生成。普通晶态钎料在钎焊前已有粗大的初晶和化合物出现。粗大的Cu3P金属间化合物不仅使接头强度降低,而且对疲劳和冲击性能也有不良的影响。非晶钎料中的原子有很强的扩散能力,在固相加热过程中就与基材进行了相互作用,生成了接合良好的扩散溶解层,普通钎料这一过程较非晶钎料滞后,且不完全。通过数值计算获得了Sn元素在基体中的扩散系数和扩散激活能,计算结果表明非晶钎料的扩散系数大于普通钎料,扩散激活能更小,有利于原子扩散。Cu-P钎料的润湿由三个过程组成。首先是物理润湿过程,钎料在基材表面熔化后形成液体熔滴,在表面张力的作用下,液态钎料在基材表面润湿铺展,随时间的延长,熔滴与基材建立起物理平衡,在物理润湿阶段由于钎料与基材的界面张力较大,所以润湿角缓慢减小。其次是固溶润湿过程,在这个阶段润湿角迅速减小,这是由于钎料中的Sn原子通过表面扩散进入基材,固溶到基材后降低了钎料与基材的界面张力,增加了润湿驱动力,使润湿角迅速减小,当界面张力达到平衡后润湿角便不再减小,进入第三个过程。非晶态钎料与普通晶态钎料在润湿性上的差异主要是非晶态钎料固溶润湿过程提前,而且充分。非晶态钎料熔化前Sn原子已经扩散进入界面前沿的基材中形成固溶体,降低了界面张力。而普通钎料还需要一段时间完成这个过程,所以需要更长的时间或更高的温度才能润湿基材。另外,由于非晶态钎料中原子扩散能力强,基材中Sn原子的含量要高于普通钎料钎焊接头,这也有助于提高钎料的润湿性。非晶态钎料钎焊接头的形成由四个过程组成,它们分别是钎料的固相扩散过程,液态钎料的生成及润湿铺展过程,钎焊温度下元素向基材的扩散和基材向钎料的溶解过程,液态钎料凝固过程。在非晶态钎料接头形成的整个过程中,第一个过程和第三个过程起主导作用,而晶态钎料则以第二个过程为主。即非晶钎料在接头形成过程中更多地表现为以元素的扩散为主的“扩散钎焊”特征,而晶态钎料则更多地体现为以液态钎料的流动和铺展为主的“毛细钎焊”特征。钎料残余层由大量的Cu3P和少量的Ni2P以及Cu基固溶体组成,钎料残余层中的脆性化合物降低了钎焊接头强度。非晶态钎料残余层的厚度比晶态钎料小,是由于非晶态钎料钎焊间隙小,原子扩散距离短,溶质原子能快速固溶于界面前沿的基材中,并很快达到饱和,饱和的溶质原子在浓度梯度作用下向基体内部扩散,致使界面前沿溶质原子浓度降低,基材进一步溶解,如此反复进行,钎料残余层不断减薄。另外,非晶态钎料在钎焊升温过程中通过固相扩散使大量溶质原子进入基材,是非晶态钎料残余层厚度小于晶态钎料的另一个原因。与晶态钎料相比,非晶态钎料可以在更短的时间内完成钎焊,即钎焊温度和保温时间可低于晶态钎料,这是非晶态钎料物理润湿过程较短所致,有助于非晶态钎料钎焊薄小件,减少基材的溶蚀和晶粒长大。作为非晶态钎料大类中的一种,“快速凝固”钎料具有与非晶态钎料基本相同的钎焊特性。快速凝固钎料也具有钎焊接头强度高、润湿性好、元素均匀无偏析的特点。更多还原

【Abstract】 By employing the X-ray diffraction, differential scanning calorimetry(DSC), scanning electron microcopy and electron microproble analysis, the structure evaluation of amorphous Cu65.5Ni16.6P12.9Sn4.9 filler metal and rapidly solidification AlSiCu filler metal, the interaction between filler metal and matrix metal,the forming process and capability of joint have been systematically investigated. The wetting mechanism, element diffusion behavior of amorphous filler metal has also been investigated.At last, the root reason that amorphous filler metal is better than Ordinary crystalline filler metal has been found. Based on above-mentioned investigations, the following results can be obtiained:During the ramp-up period, amorphous filler metal began crystallization and grow up into a fine grain of homogeneous, non-segregation, which is benefit to the element diffusion and the generation of liquid.The Ordinary crystalline filler metal is composed of large crystal and the compound appeared.The thick CU3P intermetallic compounds not only reduce the joint strength, but also for fatigue and impact properties has also adversely affected.The element in amorphous filler metal is stongth diffusion ability, filler metal interactive with matrix metal when it was warming up. The process is behand and incomplety for Ordinary crystalline filler metal in the period. The diffusion coefficient of Sn is caculated, the resulte indcated that the amorphous filler metal have larger diffusion coefficient and little diffusion activation energy which is benefit to the element diffusion.The wetting process of Cu-P is composed of three stages. The first stage is physical wetting, in which a liquid filler metal on a solid surface will spread to some extent on the surface and then comes to rest reaching a first metastable equilibrium contact angle. After the short transient stage a thin continuous solid solution layer is then formed along the solid/liquid interface. Thereafter, since the solid solution layer is better wetted than the original substrate, the drop starts spreading again as the layer expands outward of the tripleline, parallel to the interface.In this second spreading process, the drop spreading rate is controlled, not by the metal viscosity, but rather by the rate at which the reaction product layer can grow at the triple line, parallel to the solid surface. Spreading continues in this manner until the contact angle becomes equal to the equilibrium contact angle of the alloy on the reaction product. Following this, the drop remains stable even though the reaction layer may continue to grow, both in thickness and further out-wards of the triple line, along the substrate free surface. The obviously difference of wettability between amorphous filler metal and crystalline filler metal is the amorphous has a shorter transient stage and a thicker continuous solid solution layer is then formed along the solid/liquid interface. When it was warming up,atoms in amorphous filler metal has diffused into original substrate then a thin continuous solid solution layer is then formed along the solid/liquid interface, however crystalline filler metal need more time to do this,in addition to solid solution layer is thicker than the original filler metal.The amorphous bonding process is characterized as a four-step process, which is the solid diffusion of the filler metal, the wetting and spread of the liquid filler metal, the liquid diffusion of the filler metal and the solidification of the liquid filler metal. The fist and third stage is more important to amorphous filler metal, however the second stage is major process to crystalline filler metal. So the amorphous bonding process is characterized as "diffusion brazing",and the crystalline filler metal bonding process is characterized as "capillary brazing".A remain layer of filler metal was composed of a mount of(Cu,Ni)3P compound and a few Cu base solid solution. Since the remain layer of amorphous filler metal is thinner than that of crystalline filler metal,the joint strngth of brazing with amorphous is better. Due to the clearance between substrate is thinner, after the element diffusion stage, the thickness of remain layer of amorpouse is thinner and thinner. In the solid diffusion stage of the filler metal, a mount of atoms in amorphous filler metal had diffused into matrix,so remain layer of amorpouse is thinner than crystalline filler metal.Comparing with crystalline filler metal, a good joint could been brazed with amorphous filler metal in shorter brazing time. It was attributed to short physical wetting time when brazing with amorphos filler metal.The brazing capabilty of rapidly solidificatio filler metal is almost same as amorphous filler metal, that is a stonger joint stength, a good wettability, a homogeneous micrstrcture.更多还原