铜晶体的疲劳损伤微观机制

对Cu单晶体、双晶体和多晶体疲劳损伤微观机制的总结结果表明：在中、低应变范围Cu单晶体的疲劳裂纹主要沿驻留滑移带萌生,而在高应变范围则沿粗大形变带萌生;Cu双晶体中疲劳裂纹总是优先沿大角度晶界萌生和扩展,而小角度晶界则不萌生疲劳裂纹;对于Cu多晶体,疲劳裂纹主要沿大角度晶界萌生,有时也沿驻留滑移带萌生,而孪晶界面两侧由于滑移系具有相容的变形特征而未观察到疲劳裂纹萌生．     

垂直晶界和倾斜晶界Cu双晶的疲劳开裂行为及其机制

用扫描电镜（ＳＥＭ）研究了一种垂直晶界和两种倾斜晶界Ｃｕ双晶的疲劳开裂行为及其机制。这三种双晶组元晶体的取向均为「１３４」。结果表明,沿晶界的疲劳开裂是Ｃｕ双晶疲劳破坏的主要形式,但垂直晶界和倾斜晶界双晶疲劳裂纹萌生的机制有所不同。垂直晶界双晶沿晶疲劳裂纹主要由驻留滑移带撞击晶界面产生,而倾斜晶界双晶疲劳裂纹的萌生是由晶界两侧晶粒的滑移台阶而引起的应力集中所致。造成这种差别的原因同两种双晶的活动滑     

Ti-15-3板材中晶界特征及其对疲劳裂纹萌生与扩展的影响

研究Ti-15-3合金冷轧板晶界特征及其对疲劳滑移带萌生和短裂纹扩展的影响.结果表明:Ti-15-3合金冷轧板中晶界大多为大角度晶界,小角度晶界很少.在本文统计范围内,相邻晶粒取向差在40-～60-的范围内超过60%,小于15-的只占4%;大角度晶界有利于疲劳滑移带的萌生,对短裂纹穿越有阻碍作用,在小角晶界附近未发现有滑移带产生,但短裂纹很容易穿过小角度晶界.     

孪晶片层厚度对纳米孪晶Cu疲劳性能的影响

通过恒应力幅控制拉--拉疲劳实验, 比较了脉冲电解沉积制备的不同孪晶片层厚度纯Cu样品的疲劳寿命和疲劳耐久极限. 结果表明: 在应力疲劳下, 样品的疲劳寿命与疲劳耐久极限均随孪晶片层厚度的减小而提高. 疲劳样品的宏观表面变形形貌(SEM观察)和微观结构(TEM观察)表明:
当平均孪晶片层厚度为85 nm时, 材料的塑性形变由位错滑移和剪切带共同承担, 进而疲劳裂纹沿剪切带萌生; 而当平均孪晶片层厚度为32 nm时, 材料的塑性形变由位错--孪晶界交互作用主导, 从而导致疲劳裂纹沿孪晶界形成.     

定向凝固DZ38G合金热疲劳性能和组织结构的研究

本文研究了定向凝固DZ38G合金热疲劳性能及其组织结构的变化,并与其原型合金M38G对比.由于DZ38G合金消除了横向晶界和弹性模量低等原因,抗热疲劳性能有很大提高.热疲劳裂纹一般萌生在晶界或相界面,沿着枝晶间或晶界扩展,有时裂纹也沿着一定晶体学方向传播.合金经热疲劳后,晶界碳化物增多,γ′形态发生变化,并观察到裂纹两侧存在γ′相贫化和再结晶现象.     

TWIP钢退火织构与晶界特征

利用电子背散射衍射技术,研究了Fe-25Mn-2.5Si-2Al孪品诱发塑性钢(TWIP钢)冷轧变形后退火再结晶微观组织的晶界特征、晶粒取向差和织构,分析了不同退火温度对晶界特征和织构的影响.结果表明:随着退火温度的升高,TWIP钢中∑1CSL晶界含量减少,∑3CSL晶界含量增加;α-取向线密度呈下降的趋势,β-取向线密度总体上升;G{011}＜100＞取向强度呈下降趋势,而B{011}＜211＞、S{123}＜634＞、Cu{112}＜111＞等取向强度呈上升趋势.     

无磁性强立方织构Cu_(60)Ni_(40)合金基带的制备和性能

采用轧制辅助双轴织构技术(RABi TS)制备了无磁性强立方织构的Cu60Ni40合金基带。对Cu60Ni40合金基带冷轧及再结晶退火后的织构进行分析。结果表明:轧制总变形量及再结晶退火工艺是影响Cu60Ni40合金基带再结晶晶粒取向的主要因素。经过大变形量冷轧,Cu60Ni40合金基带表面可以得到典型的铜型轧制织构。通过优化的冷轧及两步再结晶退火工艺获得了立方织构含量高达99.7%(≤10°)、小角度晶界含量高达95.1%的Cu60Ni40合金基带,Σ3孪晶界含量为0.1%。     

原位拉伸法研究GH3625合金退火孪晶界稳定性及断裂行为

孪晶界作为低能稳定界面易在低层错能金属中被调控而成为近年来研究的热点。固溶态GH3625合金组织中含有大量退火孪晶组织。本实验采用室温原位拉伸结合扫描电子显微镜(SEM)观察和能谱(EDS)分析的方法研究了固溶态GH3625合金中孪晶组织演变及断裂行为。结果表明,GH3625合金在原位拉伸变形过程中,孪晶组织内部主要以单滑移为主;在拉伸直至断裂的过程中,随变形量的增加,孪晶界逐渐发生弯曲,但孪晶界始终存在于合金组织中,起阻碍位错的作用,具有良好的室温机械稳定性。GH3625合金断裂时既有韧性断裂又有脆性断裂,碳化物偏析是造成晶界裂纹以及晶内孔洞形成的主要原因。     

小角度晶界对单晶高温合金高周疲劳性能的影响

用双籽晶法制备了带有9°小角度晶界的DD6单晶高温合金试板,研究了小角度晶界对合金700℃高周疲劳性能的影响,并与[001]取向合金的疲劳性能进行了对比分析,用扫描电镜和透射电镜分析了其断口形貌和断裂机制。结果表明,带有9°小角度晶界合金的高周疲劳极限比[001]取向合金的稍有降低。疲劳裂纹萌生于试样表面或亚表面,而不在晶界上形成。小角度晶界试样的疲劳断裂机制有两种情况,大部分试样为类解理断裂,其它试样为类解理与沿晶混合断裂。     

纯铝双晶体交变形变损伤断裂过程中晶界的作用机制

从同一块纯名双晶体截取试样，分别垂直或平行于其晶界面进行对称拉压疲劳实验，结果表明，在这两种加载方式下，晶界在晶体交变形变损伤断裂过程中的作用及机制有明显区别，横向晶界在变形过程中形成明显的不均匀形变带及多层次的影响区，比较容易萌生裂纹，而纵向晶界变形极小，只发现沿主滑移带的变形及微裂纹形核。     

Fatigue cracking at twin boundaries: Effects of crystallographic orientation and stacking fault energy

The combined effects of crystallographic orientation and stacking fault energy (SFE) on the cracking behaviors of twin boundaries (TB) under low-cycle fatigue (LCF) tests were studied in pure Cu, Cu–Al and Cu–Zn alloys. A new approach, called the slipping morphology method, based on the crystallographic characteristics of Σ3 TB in face-centered cubic materials, was developed to determine the grain orientations by studying the twin-slip morphology characteristics on the sample surfaces after LCF tests. Through analyzing the dislocation–TB interaction and the damage this causes to TBs, a new parameter, defined as the difference of Schmid factors (DSF), was proposed to describe the effects of crystallographic orientation on the LCF cracking behaviors of TBs. A semi-quantitative relationship was established among DSF, SFE, dislocation slip mode and the critical conditions of TB cracking by systematically studying more than a hundred post-fatigue surface morphologies of pure Cu, Cu–Al and Cu–Zn alloys. It is interesting to find that the TB cracking relies strongly on the cooperation of both DSF and SFE. Furthermore, taking into account the interactions between slip dislocations and different boundaries, the fatigue cracking possibilities of several typical interfaces were compared and discussed. The results demonstrate that low-angle grain boundaries (GBs) are the strongest in resisting fatigue cracking, high-angle GBs are the weakest, and TBs are in between, which contributes the most to the final fatigue performance of materials. This new finding will help understanding of the interfacial properties under cyclic loading and may be beneficial to the design of high-performance materials with optimal fatigue properties in the future.     

Effect of crystallographic orientation and grain boundary character on fatigue cracking behaviors of coaxial copper bicrystals

Four coaxial copper bicrystals were employed to study the slip morphologies and fatigue cracking behaviors during cyclic deformation. Three of them had high-angle grain boundaries (GBs) with nearly the same misorientation and one bicrystal had a twin boundary (TB). Different slip bands (SBs) operated near the GBs and TB, generating different dislocation arrangements, which are mainly determined by the crystallographic orientations of the component grains. The GBs suffered impingement or shear damage caused by slip difference from both sides. It is suggested that there is an energy increase in the interfaces between matrix and persistent slip bands (PSBs), GBs and TBs per cycle during cyclic deformation due to the accumulation of lattice defects, which would make the interface unstable. After a certain number of cycles, fatigue cracks initiated firstly at GBs for some bicrystals while fatigue cracking occurred preferentially at PSBs for the others. It is confirmed that the energy growth rate is an increasing function of the shear stress, strain amplitude and strain incompatibility, which results from slip differences on both sides of the interfaces. Interfaces with different energies and strain incompatibilities have different fatigue cracking resistance. It is found that GBs with defective and complex structure, and hence high interfacial energy accompanied by high modulus of the residual GB dislocation (GBD), are preferential sites for fatigue cracking, while the fatigue cracking appeared predominantly at PSBs when the modulus of the residual GBD is lower than that of a perfect dislocation with simple GB structure and low interfacial energy. The present model for the energy can predict well which kind of interface would form cracks preferentially during cyclic deformation in one coaxial bicrystal and which GB would need more cycles to initiate fatigue cracking between coaxial bicrystals with different GB characters.     

Effect of rare earth metal Ce addition to Sn-Ag solder on interfacial reactions with Cu substrate

The effect of adding a small amount of rare earth cerium (Ce) element to low Ag containing Sn-1wt%Ag Pb-free solder on its interfacial reactions with Cu substrate was investigated. The growth of intermetallic compounds (IMCs) between three Sn-1Ag-xCe solders with different Ce contents and a Cu substrate was studied and the results were compared to those obtained for the Ce-free Sn-1Ag/Cu systems. In the solid-state reactions of the Sn-1Ag(-xCe)/Cu solder joints, the two IMC layers, Cu₆Sn₅ and Cu₃Sn, grew as aging time increased. Compared to the Sn-1Ag/Cu joint, the growth of the Cu₆Sn₅ and Cu₃Sn layers was depressed for the Ce-containing Sn-1Ag-xCe/Cu joint. The addition of Ce to the Sn-Ag solder reduced the growth of the interfacial Cu-Sn IMCs and prevented the IMCs from spalling from the interface. The evenly-distributed Ce elements in the solder region blocked the diffusion of Sn atoms to the interface and retarded the growth of the interfacial IMC layer.     

β-Sn晶粒取向及温度对Cu/SAC305/Cu微焊点时效界面反应的影响

为了探究不同等温时效温度下β-Sn晶粒取向及晶界特征对界面反应的影响,采用准原位观测手段对不同Sn取向的Cu/Sn3.0Ag0.5Cu/Cu(Cu/SAC305/Cu)微焊点进行研究. 结果表明,在不同温度下时效时,微焊点两侧界面IMC(Cu₆Sn₅ + Cu₃Sn两相)自始至终呈现对称性生长,表明时效过程中β-Sn晶粒取向及晶界的存在不会影响界面反应. 但是随着时效温度的升高,界面IMC的形貌和厚度发生明显变化. 在100 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的不连续的Cu₃Sn层;在125 ℃时效后,界面处生成扇贝状的Cu₆Sn₅和较薄的连续的Cu₃Sn层;而在150 ℃时效后,界面IMC由层状Cu₆Sn₅和层状Cu₃Sn双层结构组成. 时效温度的升高促使Cu和Sn原子扩散加快,促进了扇贝状Cu₆Sn₅向层状转变并造成Cu₃Sn的快速生长. 同时,基于界面IMC厚度随时效时间的演变规律,获得了不同时效温度下微焊点界面IMC生长曲线,可为Sn基微焊点的可靠性评价提供依据.     

Interfacial Reactions and Bonding Strength of Sn-xAg-0.5Cu/Ni BGA Solder Joints

The present study details the microstructure evolution of the interfacial intermetallic compounds (IMCs) layer formed between the Sn-xAg-0.5Cu (x = 1, 3, and 4 wt.%) solder balls and electroless Ni-P layer, and their bond strength variation during aging. The interfacial IMCs layer in the as-reflowed specimens was only (Cu,Ni)₆Sn₅ for Sn-xAg-0.5Cu solders. The (Ni,Cu)₃Sn₄ IMCs layer formed when Sn-4Ag-0.5Cu and Sn-3Ag-0.5Cu solders were used as aging time increased. However, only (Cu,Ni)₆Sn₅ IMCs formed in Sn-1Ag-0.5Cu solders, when the aging time was extended beyond 1500 h. Two factors are expected to influence bond strength and fracture modes. One of the factors is that the interfacial (Ni,Cu)₃Sn₄ IMCs formed at the interface and the fact that fracture occurs along the interface. The other factor is Ag₃Sn IMCs coarsening in the solder matrix, and fracture reveals the ductility of the solder balls. The above analysis indicates that during aging, the formation of interfacial (Ni,Cu)₃Sn₄ IMCs layers strongly influences the pull strength and the fracture behavior of a solder joint. This fact demonstrates that interfacial layers are key to understanding the changes in bonding strength. Additionally, comparison of the bond strength with various Sn-Ag-Cu lead-free solders for various Ag contents show that the Sn-1Ag-0.5Cu solder joint is not sensitive to extended aging time.     

EVOLUTION OF MICROSTRUCTURE OF Sn-Ag-Cu LEAD-FREE FLIP CHIP SOLDER JOINTS DURING AGING PROCESS

Flip chip bonding has become a primary technology that has found application in the chip interconnection process in the electronic manufacturing industry in recent years. The solder joints of the flip chip bonding are small and consist of complicated microstructures such as Sn solution, eutectic mixture, and intermetallic compounds （IMCs）, whose mechanical performance is quite different from the original solder bulk. The evolution of microstructure of the flip chip solder joints under thermal aging was analyzed. The results show that with an increase in aging time, coarsening of solder bulk matrix and AuSn4 IMCs occurred within the solder. The IMCs that are formed at the bottom side of the flip chip bond were different from those on the top side during the aging process. （Cu, Ni, Au）0Sn5 were formed at the interfaces of both sides, and large complicated （Au,Ni, Cu）Sn4 IMCs appeared for some time near the bottom interface after aging, but they disappeared again and thus （Cu,Ni, Au ）0Sn5 IMC thickness increased considerably. The influence of reflow times during the flip chip bonding （as-bonded condition） on the characteristics of interfacial IMCs was weakened when subjected to the aging process.     

电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响

研究了温度为150℃,电流密度为5.0×10³A/cm²的条件下电迁移对Ni/Sn3.0Ag0.5Cu/Cu焊点界面反应的影响.回流焊后在Sn3.0Ag0.5Cu/Ni和Sn3.0Ag0.5Cu/Cu的界面上均形成了（Cu,Ni）₆Sn₅型化合物.时效过程中界面化合物随时效时间增加而增厚,时效800 h后两端的化合物并没有发生转变,仍为（Cu,Ni）₆Sn₅型.电流方向对Cu基板的消耗起着决定作用.当电子从基板端流向芯片端时,电流导致基板端Cu焊盘发生局部快速溶解,并导致裂纹在Sn3.0Ag0.5Cu/（Cu,Ni）₆Sn₅界面产生,溶解到钎料中的Cu原子在钎料中沿着电子运动的方向向阳极扩散,并与钎料中的Sn原子发生反应生成大量的Cu₆Sn₅化合物颗粒.当电子从芯片端流向基板端时,芯片端Ni UBM层没有发生明显的溶解,在靠近阳极界面处的钎料中有少量的Cu₆Sn₅化合物颗粒生成,电迁移800 h后焊点仍保持完好.电迁移过程中无论电子的运动方向如何,均促进了阳极界面处（Cu,Ni）₆Sn₅的生长,阳极界面IMC厚度明显大于阴极界面IMC的厚度.与Ni相比,当Cu作为阴极时焊点更容易在电迁移作用下失效.     

热冲击条件下倒装组装微焊点的可靠性——裂纹生长机理

研究热冲击条件下细间距倒装微焊点的裂纹萌生及扩展,通过观察裂纹生长路径,并结合累积塑性应变能密度及应变在焊点上的分布,分析裂纹的生长机理. 结果表明,裂纹形成在微焊点外侧,位于镍焊盘界面IMC与焊料基体之间的界面上;随着循环次数的增加,裂纹进入镍焊盘附近的焊料基体中,沿着焊盘平行的方向扩展,累积塑性应变能密度及应变在微焊点上的分布与裂纹扩展方向一致. 对裂纹生长机理探讨可知,IMC与微焊点之间的界面处于双重应力集中状态,因此裂纹易在微焊点及IMC之间的界面上萌生;随着循环次数的增加,焊料基体的塑性变形增加,高塑性的焊料区域为裂纹扩展提供了条件.