温度对Ag颗粒增强SnCu基复合钎料蠕变性能的影响

采用1 mm2微型单搭接钎焊接头, 研究了恒定应力下温度对Ag颗粒增强SnCu基复合钎料钎焊接头蠕变寿命的影响, 研究结果表明： 增强颗粒Ag与基体会发生冶金反应, 在Ag颗粒周围形成了一薄层Ag-Sn金属间化合物, 使增强颗粒Ag与基体紧密结合, 从而使复合钎料钎焊接头蠕变寿命优于基体SnCu钎料;温度对复合钎料钎焊接头蠕变寿命影响较SnCu钎料明显.     

Ti—Cu—Nb合金钎料的制备及其在SiC表面润湿性的研究

采用真空电弧熔炼法制备Ti-50Cu-SNb（质量分数）合金钎料。根据DSC曲线确定出合金钎料的熔化温度为980～1050℃;通过能谱（EDS）和x射线衍射（XRD）分析得出钎料化学组成主要为Cu3Ti2和CuTi2,Nb元素以固溶体的形式存在于钛铜合金中;通过改良后的座滴法研究了钎料在1000、1050和1100℃下润湿角度的变化情况。实验表明在高温下钎料对基体均有很好的润湿作用;在钎料与SiC基体反应界面,主要生成物TiSi促进了润湿过程的进行。     

含锑软钎料钎焊黄铜组织与性能的研究

为判断含锑钎料钎焊黄铜是否可行 ,研究了锡铅锑钎料钎焊H6 2黄铜时锑与锌的作用 ,并对其接头的组织与性能进行了深入分析。研究结果表明锡铅锑钎料钎焊黄铜的接头组织中未发现锌锑化合物相 ,含锑量0 2 2 %～ 0 .8% (质量分数 )的锡铅锑钎料钎焊黄铜未引起接头性能下降 ,认为可以钎焊黄铜。     

典型添加元素对Sn-Zn系钎料性能的影响

Sn-Zn钎料被认为是传统Sn-Pb共晶钎料的最佳替代合金之一,它以低廉的成本、较好的力学性能以及其共晶成分与Sn-37Pb钎料熔点相近等优点引起了人们的广泛关注,但其润湿性、抗氧化性、抗腐蚀性不够理想.阐述了Bi、A1、In、Ag、Cu及稀土元素(RE)等典型添加元素对Sn-Zn钎料各种性能的影响,以期为Sn-Zn钎料的研究开发和应用提供参考.     

纳米压痕试验确定80Au/20Sn焊料蠕变参数

80Au/20Sn焊料合金被广泛用于微电子及光电子封装中,其焊料的蠕变性能对于器件的长期运行至关重要.描述蠕变行为的蠕变参数.对于求解蠕变本构模型及分析蠕变机制具有重要意义.在不同加载速率及不同温度下对80Au/20Sn焊料进行了恒加载速率/载荷纳米压痕试验,用半椭圆模型对出现"挤出"压痕的接触面积修正后由Oliver-Pharr法求得了不同温度下的弹性模量及硬度,基于压痕做功概念获得了蠕变参数.结果表明,基于压痕做功概念得到的蠕变应力指数和蠕变激活能与传统单轴拉伸蠕变测试结果相差在13%以内,说明该测试和分析方法能在一定程度上预测焊料的蠕变参数.     

Solidification Condition Effects on Microstructures and Creep Resistance of Sn-3.8Ag-0.7Cu Lead-Free Solder

Metallurgical, mechanical, and environmental factors all affect service reliability of lead-free solder joints and are under extensive study for preparation of the transition from Sn-Pb eutectic soldering to lead-free soldering in the electronic industry. However, there is a general lack of understanding about the effects of solidification conditions on the microstructures and mechanical behavior of lead-free solder alloys, particularly on the long-term reliability. This study attempts to examine the creep resistance of the Sn-Ag-Cu eutectic alloy (Sn-3.8Ag-0.7Cu, SAC387) with a variety of solidification conditions with cooling rates ranging from 0.3 °C/s to 17 °C/s. Results indicate that solidification conditions have a major influence on the creep resistance of SAC387 alloy; up to two orders of magnitude change in the steady-state creep rates were observed at low stress levels. An understanding of the mechanical property change with microstructures, which are determined by the solidification conditions, should shed some light on the fundamental deformation and fracture mechanisms of lead-free solder alloys and can provide valuable information for long-term reliability assessment of lead-free solder interconnections. This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation: in Honor of Prof. John Hunt,” which occurred March 13–15, 2006 during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

Sn-Bi/Cu焊接接头的剪切性能及界面微观组织分析

通过对断口形貌和界面微观组织的观察分析,研究了3种Sn-Bi/Cu焊接接头的剪切断裂机理.结果表明:3种Sn-Bi/Cu焊接接头均在弹性变形阶段断裂,并且均沿Sn-Bi焊料/Cu基板界面处断裂.孔洞降低了3种Sn-Bi/Cu焊接接头的有效连接面积,从而降低了其剪切强度.根据3种Sn-Bi/Cu焊接接头断口形貌,Sn59.9Bi40Cu 0.1/Cu和Sn57.9Bi40Zn2Cu 0.1/Cu焊接接头剪切断裂机制属于准解理、沿晶脆性断裂和韧窝的混合型断裂,而Sn42Bi58/Cu焊接接头剪切断裂机制属于准解理断裂.微观组织分析显示,3种焊料合金焊接接头界面处的金属间化合物层均为连续的Cu6Sn5相.     

添加微量稀土元素对Sn-Ag-Cu系无铅焊料性能的影响

以Sn-3．0Ag-0．5Cu（质量分数，％）焊料为母合金，探讨了微量稀土元素Ce、Er、Y和Sc对Sn—Ag—Cu合金物理性能、润湿性能以及力学性能的影响。试验结果表明：稀土元素对焊料的性能有不同的影响，添加微量Ce元素可以更好地改善焊料综合性能。     

Type IV Creep Damage Behavior in Gr.91 Steel Welded Joints

Modified 9Cr-1Mo steel (ASME Grade 91 steel) is used as a key structural material for boiler components in ultra-supercritical (USC) thermal power plants at approximately 873 K (600 °C). The creep strength of welded joints of this steel decreases as a result of Type IV creep cracking that forms in the heat-affected zone (HAZ) under long-term use at high temperatures. The current article aims to elucidate the damage processes and microstructural degradations that take place in the HAZ of these welded joints. Long-term creep tests for base metal, simulated HAZ, and welded joints were conducted at 823 K, 873 K, and 923 K (550 °C, 600 °C, and 650 °C). Furthermore, creep tests of thick welded joint specimens were interrupted at several time steps at 873 K (600 °C) and 90 MPa, after which the distribution and evolution of creep damage inside the plates were measured quantitatively. It was found that creep voids are initiated in the early stages (0.2 of life) of creep rupture life, which coalesce to form a crack at a later stage (0.8 of life). In a fine-grained HAZ, creep damage is concentrated chiefly in an area approximately 20 pct below the surface of the plate. The experimental creep damage distributions coincide closely with the computed results obtained by damage mechanics analysis using the creep properties of a simulated fine-grained HAZ. Both the concentration of creep strain and the high multiaxial stress conditions in the fine-grained HAZ influence the distribution of Type IV creep damage.     

焊粉对锡膏稳定性的影响

研究了焊粉粒度分布和氧含量对锡膏稳定性的影响。试验采用Malcom粘度计测试不同保存时间锡膏的粘度变化;采用锡膏搅拌机模拟锡膏使用过程,观察锡膏状态随搅拌时间的变化。实验结果表明焊粉D50越小,所制备锡膏的使用稳定性越好,但锡膏的储存稳定性变差,锡膏呈现沙化状态;焊粉氧含量越低,所制备锡膏的储存和使用稳定性均较好。试验对搅拌沙化后的锡膏进行了金属含量测定,结果表明焊粉与助焊剂之间的化学反应是锡膏沙化的主要原因。     

微电子封装中助焊剂残留物对无铅焊点电化学迁移的影响研究

采用96.5Sn3.0Ag0.5Cu无铅焊料以及一种免清洗助焊剂NCF(焊后不清洗)和一种水溶性助焊剂WSF(焊后清洗和焊后不清洗)分别焊接了3组PCB试件,进行了电化学迁移测试,评价助焊剂焊后残留物的绝缘可靠性。试验结果表明:使用NCF焊接后的第一组试件和使用WSF焊接(焊接后清洗)的第三组试件可以满足标准要求;使用WSF焊接(焊接后未清洗)的第二组试件最终绝缘电阻值下降幅度最大,不符合标准要求,并且在高倍显微镜下观察试件发现有树枝晶生成,说明助焊剂残留物的存在使得试件在试验条件下发生了电化学迁移现象。分析探讨了电化学迁移发生的原因,认为电化学迁移与清洗工艺、助焊剂的成分、固体含量和酸度有关。     

Influence of Laser Treatment on the Creep of the Ti-6Al-4V Alloy

Titanium and its alloys are excellent materials for structural applications in components submitted to high temperatures because of their high strength, weight ratio, good corrosion resistance, and microstructural stability. However, the affinity to oxygen is one of the main factors that limit their application as structural materials at high temperatures. The objective of this work was to estimate the influence of laser treatment on the creep of a Ti-6Al-4V alloy. Constant load creep tests were conducted at 873 K (600 °C) in a standard creep machine at a stress of 125 to 319 MPa. Samples with a gage length of 18.5 mm and a diameter of 3.0 mm were used for all tests. It was observed that the effect of the oxidation was smaller and the behavior of the creep curves showed that the life time in laser treated samples was better than in the received samples. An increase of ductility of final strain and in the lifetime for the laser-treated material was observed. The decrease of the steady-state creep occurred in conjunction with the oxidation process reduction, showing that for the Ti-6Al-4V alloy, the lifetime is affected strongly by the laser treatment with an increase in this superficial protection.     

Influence of Grain Boundary Character on Creep Void Formation in Alloy 617

Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP), which will operate at temperatures exceeding 760 °C and a helium pressure of approximately 7 MPa. Observations of the crept microstructure using optical microscopy indicate creep stress does not significantly influence the creep void fraction at a given creep strain over the relatively narrow set of creep conditions studied. Void formation was found to occur only after significant creep in the tertiary regime (>5 pct total creep strain) had occurred. Also, orientation imaging microscopy (OIM) was used to characterize the grain boundaries in the vicinity of creep voids that develop during high-temperature creep tests (900 °C to 1000 °C at creep stresses ranging from 20 to 40 MPa) terminated at creep strains ranging from 5 to 40 pct. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular, or 45 deg to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids, while coincident site lattice (CSL)–related grain boundaries did not appear to be consistently associated with void development. Similar results were found in oxygen-free, high-conductivity (OFHC) copper, severely deformed using equal channel angular extrusion, and creep tested at 450 °C and 14 MPa.     

Creep Strength of Dissimilar Welded Joints Using High B-9Cr Steel for Advanced USC Boiler

The commercialization of a 973 K (700 °C) class pulverized coal power system, advanced ultra-supercritical (A-USC) pressure power generation, is the target of an ongoing research project initiated in Japan in 2008. In the A-USC boiler, Ni or Ni-Fe base alloys are used for high-temperature parts at 923 K to 973 K (650 °C to 700 °C), and advanced high-Cr ferritic steels are planned to be used at temperatures lower than 923 K (650 °C). In the dissimilar welds between Ni base alloys and high-Cr ferritic steels, Type IV failure in the heat-affected zone (HAZ) is a concern. Thus, the high B-9Cr steel developed at the National Institute for Materials Science, which has improved creep strength in weldments, is a candidate material for the Japanese A-USC boiler. In the present study, creep tests were conducted on the dissimilar welded joints between Ni base alloys and high B-9Cr steels. Microstructures and creep damage in the dissimilar welded joints were investigated. In the HAZ of the high B-9Cr steels, fine-grained microstructures were not formed and the grain size of the base metal was retained. Consequently, the creep rupture life of the dissimilar welded joints using high B-9Cr steel was 5 to 10 times longer than that of the conventional 9Cr steel welded joints at 923 K (650 °C).     

Forces on Plunge Pool Slabs: Influence of Joints Location and Width

The hydrodynamic pressures due to jets impinging on plunge pools must be taken into account in the stability design of pool floor concrete slabs. The contraction joints between slabs are normally sealed with waterstops, which prevent the transmission to the foundation of the pressures applied on the upper faces of the slabs. However, a waterstop failure will allow pressure transmission to the foundation, inducing uplift forces on the slabs. The use of open joints might also become a feasible solution for the lining of plunge pool floors if the pressure field that develops around each slab could be adequately evaluated. This paper presents an analytical model and experimental research developed to assess the forces on plunge pool slabs, considering either open or closed. The influence of the relative width of the contraction joints and the joint between the slabs and the foundation is analyzed. The mean value and standard deviation of the hydrodynamic vertical force are determined based on point pressure measurements, and their relative importance is discussed.