Effects of cooling rate on the fracture properties of TA15 ELI alloy plates

The effects of cooling rate on the mechanical properties and the fatigue crack growth behavior of TA15 ELI alloy plates with different microstructures were investigated at room temperature. The results indicate that the cooling rate （water quench, air cooling, and furnace cooling） has a pronounced influence on the mechanical properties and on the fatigue crack growth, especially for air cooling and furnace cooling. Optical microstructure observation and scanning electron microscopy of tensile fracture surfaces were performed to gain an insight into the mechanism of properties. The dependence of mechanical properties and fatigue crack growth behavior on the cooling rate can be attributed to the oc lamellae width and the colony size, which induce the change in slip length. The microstmcture produced by air cooling shows the best damage tolerance behavior when compared with water quench and furnace cooling.     

Precipitation behavior of γ′ phase in superalloy FGH96 under interrupted cooling test

The precipitation behavior of γ′ phase,under various interrupt cooling tests after 1170℃,solution treatment was examined.The results indicate that the size of secondary γ′ precipitates increases with the decrease of interrupt temperature,and the shape changes from spherical to butterfly like.The fine tertiary γ′ can form either during the post cool air quenching at high interrupt-temperatures,or during the specified 5℃ min-1cooling.Air quenching at high temperatures cannot suppress further nucleation of tertiary γ′ phase.     

Performance of digital patternless freeze-casting sand mould

Digital patternless freeze-casting technology is a new approach for obtaining frozen sand moulds using digital milling technology.The change law of tensile strength and air permeability of frozen sand moulds (100-mesh and 200-mesh silica sand,and zircon sand moulds) under different freezing temperatures and water contents was studied.Results show that with the decrease of freezing temperature and the increase of water contents,the tensile strength and air permeability of the sand moulds are gradually improved.Meanwhile,computed tomography technology was used to characterize the shape and size of the water film between the sand particles mixed with 4wt.% water.The results show that in silica sand moulds,the form of water film is lumpy,and 200-mesh silica sand moulds have more water films and higher proportion of small-sized water films than 100-mesh silica sand moulds,while in zircon sand moulds,the form of water film is membranous.At the same freezing temperature and water content,the tensile strength of zircon sand mould is the highest,and 100-mesh silica sand mould is the lowest.A comparative solidification experiment of A356 aluminum alloy was carried out in frozen sand mould and resin sand mould.The results show that the primary α-Al phase appears in the form of equiaxed and eutectic silicon phase is needle-like in freezing sand mould casting,but the primary α-Al phase grows in the form of dendrites,and the eutectic silicon phase is coarse needle-like in the resin sand mould casting.The difference of microstructure is caused by the different cooling rate.The cooling rate of A356 aluminum alloy in frozen sand mould is higher than that in resin sand mould.     

Effects of rapid solidification on the microstructure and microhardness of a lead-free Sn-3.5Ag solder

A lead-free Sn-3.5Ag solder was prepared by rapid solidification technology. The high solidification rate, obtained by rapid cooling, promotes nucleation, and suppresses the growth of Ag3Sn intermetallic compounds （IMCs） in Ag-rich zone, yielding fine Ag3Sn nanoparticulates with spherical morphology in the matrix of the solder. The large amount of tough homogeneously-dispersed IMCs helps to improve the surface area per unit volume and obstructs the dislocation lines passing through the solder, which fits with the dispersion-strengthening theory. Hence, the rapidly-solidified Sn-3.5Ag solder exhibits a higher rnicrohardness when compared with a slowly-solidified Sn-3.5Ag solder.     

Effect of Ga on microstructure and properties of Sn-Zn-Bi solder for photovoltaic ribbon

In this study, SEM, EDS, XRD and other test methods were used to study the effects of different Ga contents(0～2 wt.%) on microstructure, electrical conductivity, spreading area and mechanical properties of Sn-9 Zn-3 Bi solder. The results revealed that the microstructure of Sn-Zn-Bi-Ga solder alloy was mainly composed of β-Sn, Zn-rich, Bi-rich phase and Sn-Zn eutectic structure. The Ga can significantly improve the wettability of Sn-Zn-Bi on the pure copper, the maximum wetting area was 105.3 mm2. With the increase of the Ga content the melting point of the solders decreased from 195 ℃ to 177 ℃. In addition, the Ga element can increase the oxidation resistance of solder. Its conductivity showed a decreasing trend with the gradual increase of the Ga content. With the increased of the Ga content the IMC(Intermetallic Compound) of Sn-Zn-Bi-x Ga/Cu is only Cu5 Zn8 and its thickness decreased remarkably.     

Microstructure Evolution of a Single Crystal Nickel-Base Superalloy During Heat Treatment and Creep

Microstructure evolution of a single crystal nickel-base superalloy during heat treatment and tensile creep at 1010℃ and 248 MPa for 30h was observed and analyzed. Internal stresses because of lattice mismatch between γ and γ‘ phase provided the driving force for γ‘ shape evolution during heat treatment. More than 65 vol. % distorted cubic γ‘ phase keeping coherency with the γ matrix precipitated after solution at 1295℃ for 32h. The shape of γ‘ phase was perfectly cubic with increasing precipitate size during the two-step aging treatment. Due to the applied stress and intemal stress field the continuous γ-γ‘ lamellar structure perpendicutar to the apptied stress was fonmed after 30h tensile creep.     

Corrosion and wear behavior of an Mg–2Zn–0.2Mn alloy in simulated body fluid

In this work, the corrosion behavior of the ascast and extrusion and aging treatment Mg–2Zn–0.2Mn alloy in simulated body fluid(SBF) were studied. The wear behavior of Mg–2Zn–0.2Mn alloy was investigated using pin-on-disk technique and stainless steel as counterbody under a constant sliding velocity at different loads ranging from 2 to 5 N with deionized water and SBF as lubrication.The results showed that the extrusion and aging treatment Mg–2Zn–0.2Mn alloy exhibited better corrosion resistance compared with the as-cast alloy due to finer average grain size, more homogeneous phase distribution, and decrease in porosity. The friction coefficient of fractional pair under SBF and deionized water lubrication were obviously lower than that of dry sliding condition. However, the wear rate of Mg–2Zn–0.2Mn alloy under SBF lubrication was higher than that of dry sliding and deionized water lubrication due to the corrosiveness of SBF accelerated the wear of the magnesium alloy. The magnesium alloy exhibited different wear mechanisms with the variety of loads and lubrication conditions.     

Effects of combinatorial water atomization on microstructures and properties of Cu-Sn powder

A couple of additional cooling nozzles were assembled under traditional atomization nozzles in order to improve the process and produce the powder with fine microstructure and low oxygen. The influence of the process parameters on the properties of the powder was investigated. The results show that fmer powders with lower oxygen content and more irregular shape can be achieved by combinatorial atomizing process comparing with normal one under the same atomizing pressure.     

Effect of spray forming on evolution of microstructure and mechanical behavior of Mg-9Al-1Zn alloy

The cylindrical billet of Mg-9Al-1Zn alloy was produced by spray forming and hot extruded at 698-723 K with an extrusion ratio of 22：1, The microstructural evolution was investigated systematically. The mechanisms of grain refinement, solubility extension of Al and Zn elements in Mg matrix, and the precipitation of the second phase β-Mg17Al12 as well as their effect on the mechanical properties of the Mg-9Al-1Zn alloy were analyzed and discussed. The results show that the spray formed Mg-9Al-1Zn alloy has homogeneous equiaxed fine grains with the average grain size of 17 μm, of which the average grain size is refined further to 5 μm due to dynamic recrystallization during hot extrusion process. The evolution of size, proportion and distribution offl-Mg17Al12 phase was also observed and analyzed. The mechanical properties for the extruded rods are improved remarkably at ambient temperature.     

Comparative Study on Solid-State and Metastable Liquid-State Aging for SAC305/Cu Joints

In order to study the in?uence of the physical state of solder on the interfacial reaction of dip-soldered Sn-3.0 Ag-0.5 Cu/Cu system, two kinds of experiments were designed, including:(1) solid-state aging between the solder and Cu substrate;(2)liquid-state aging between the metastable supercooled liquid-state solder and Cu substrate. The aging times were 30, 60,120 and 180 min, respectively, and the aging temperature was 8 ℃ lower than the melting point of the Sn-3.0 Ag-0.5 Cu(SAC305) alloy(217 ℃). The experimental data revealed that the physical state of the solder obviously affected the formation of the intermetallic compound(IMC), and resulted in the difference in the diffusion of atoms on the interface between the SAC305 solder and Cu substrate. The IMC interface after aging for 30 min presents unique characteristics compared with that of the sample after dip soldering. The IMC interface of solid-state aged SAC305/Cu couple is relatively planar, while the IMC interface under metastable supercooled liquid-state aging conditions presents scallop-like shape.     

铋和磷元素对Sn-Zn-RE电子微连接钎料组织与性能的影响

制备了含不同Bi,P元素的（Sn-9Zn0.05Ce）xBi和（Sn-9Zn0.05Ce）xP钎料合金,观察并分析了钎料的显微组织形貌,测试了钎料的抗拉强度、断后伸长率以及维氏硬度.结果表明,添加Bi元素能显著提高Sn-9Zn0.05Ce钎料合金的抗拉强度和硬度,但同时会明显降低其断后伸长率,而添加微量P元素对钎料的抗...     

凝固条件和应变速率对Sn-58Bi钎料拉伸性能和断裂行为的影响

研究了熔炼制备的Sn-58Bi无铅钎料于水冷、空冷、炉冷三种方式冷却后在应变速率0.001,0.002,0.004 s−1下的拉伸性能和断裂行为. 结果表明,水冷和空冷钎料共晶组织细小,尤其是空冷钎料共晶组织更为均匀,而炉冷钎料共晶组织粗大且偏析严重. 随着应变速率增大,三种钎料抗拉强度均提高而断后伸长率均变小. 炉冷钎料组织偏析导致硬脆富Bi相聚集,抗拉强度最大,但断后伸长率极低,为典型的脆性断裂;水冷和空冷钎料的均细共晶组织显著提高了钎料断后伸长率,具有更均匀共晶组织的空冷钎料断后伸长率最大,呈现韧性或韧脆性混合断裂.     

Sn-9Zn/Cu无铅焊点ZnO须自发生长

研究了Sn-9Zn/Cu无铅焊点ZnO须自发生长行为.结果表明,在室温条件下Sn-9Zn/Cu无铅焊点因为富锌相的氧化,在富锌相表面自发生长出大量的ZnO须,ZnO须呈现针状、块状、花朵状等不同形态;对ZnO须进行FIB测试,发现在富锌相中出现明显的空洞,主要是因为Zn元素扩散导致的.另外,证实在Zn元素扩散与氧发生反应的过程中,富锌相发生体积收缩,诱使结构中出现明显的拉应力,拉应力为ZnO须生长提供驱动力.     

Sn-9Zn-xPr钎料钎焊性能及显微组织

研究了稀土元素Pr的添加量对Sn-9Zn无铅钎料的润湿性能、显微组织和焊点力学性能的影响.结果表明,镨的加入不仅改善了钎料的润湿性能和抗氧化性能,而且细化了钎料基体中的富锌相,使得界面组织更为稳定,有利于焊点可靠性的改善;Sn-9Zn无铅钎料中镨的添加量为质量分数0.08%时,钎料的润湿性能最佳,综合性能最好;当镨的添...     

The effects of cooling rate on microstructure and mechanical behavior of Sn-3.5Ag solder

The microstructure, tensile, and creep behavior of bulk Sn-3.5Ag solder were studied as a function of cooling rate. Controlled cooling rates were obtained by cooling specimens in different media: water, air, or furnace. The cooling rate significantly affected secondary dendrite arm size and spacing of the tin-rich phase, as well as the morphology of Ag₃Sn. Ag₃Sn was relatively spherical at the fastest cooling rate and had a needle-like morphology at the slowest cooling rate. Both the yield strength in tension and creep resistance of Sn-3.5Ag solder increased with increasing cooling rate while the strain-to-failure decreased. In this study, the mechanical behavior was correlated with the observed microstructure, creep-stress exponents, and fracture behavior, in order to understand the underlying damage mechanisms. For more information, contact N. Chawla, Arizona State University, Department of Chemical and Materials Engineering, P.O. Box 876006, Tempe, AZ, 85287-6006; (480) 965-2402; fax (480) 965-0037; e-mail nchawla@asu.edu.     

Sn-0.7Cu-xNb复合钎料微观组织和力学性能

文中主要研究了纳米Nb颗粒对Sn-0.7Cu基复合钎料显微组织和力学性能的影响。结果表明,添加纳米Nb颗粒细化了Sn-0.7Cu复合钎料微观组织,提高了Sn-0.7Cu复合钎料的抗拉强度。当Nb含量为0.12%时抗拉强度达最大值25.36 MPa,但此时钎料的断后伸长率有所降低。Sn-0.7Cu-x Nb复合钎料的断裂模式均为塑性断裂,随Nb含量的增加,Sn-0.7Cu基复合钎料断口表面的韧窝尺寸逐渐变小,表明微量的纳米Nb可以抑制合金内Cu 6 Sn 5金属间化合物的长大。     

Ag的添加量对Sn-9Zn无铅钎料性能的影响

研究Ag的添加量对Sn-9Zn无铅钎料性能的影响规律。结果表明,Ag不仅对Sn-9Zn无铅钎料的润湿性能和显微组织有明显作用,而且对钎料接头的力学性能也有较大的影响。添加0.3%Ag (质量分数, 下同)后,钎料的抗氧化性能得到提高,因此钎料的润湿性能得到改善。Sn-9Zn-0.3Ag具有比Sn-9Zn钎料更均匀的组织。研究结果还表明,添加0.3%Ag后,钎料接头的力学性能最佳,接头断口显示有大量的细小均匀的韧窝组织。当Ag的添加量添加到1%时,在韧窝底部出现Cu-Zn、Ag-Zn金属间化合物,此时,接头力学性能下降     

添加铜对Sn-9Zn无铅钎料性能的影响

采用向钎料合金熔体中添加铜粉的方法得到了原位生长金属间化合物颗粒增强的Sn-Zn基复合无铅钎料,并对其熔化行为、组织、力学性能和在铜基体上的润湿性进行了研究.差示扫描量热计(DSC)测量结果表明,少量铜粉对Sn-9Zn的熔点影响较小,但铜粉添加量达3%时将使其熔点急剧升高.铜粉的添加使Sn-9Zn钎料中形成了较均匀分布的Cu5Zn8化合物颗粒相,同时棒状富Zn相相应减少.力学性能测试结果显示,复合钎料的抗拉强度和塑性都得到了改善,抗蠕变性能显著提高;润湿性测量表明,复合钎料对铜的润湿性也有所改善.     

固溶后冷却方式对Inconel X-750合金组织和性能的影响

采用SEM、TEM、EDAX和相分析等分析手段,研究Inconel X-750合金固溶后不同冷却方式下组织和性能的变化。结果显示:水冷和油冷抑制合金中γ′相的析出,时效后均析出球形的γ′相。炉冷后合金中析出一次立方体形γ′相和二次球形γ′相,时效后再次析出球形γ′相;水冷和油冷后晶界上无碳化物析出,时效后晶界上均析出细小针状M₂₃C₆。炉冷后合金晶界上析出块状M₂₃C₆,时效后碳化物尺寸略微长大,形状基本不变;炉冷+时效后合金的强度最高,水冷+时效后合金的冲击性能最好。     

热处理冷却方式对TC10钛合金组织与性能的影响

对不同温度加热后的TC10钛合金棒材进行水冷、空冷、炉冷3种不同冷却方式的处理,通过光学显微镜、扫描电镜以及拉伸性能和冲击性能试验,研究了合金在不同冷却方式下的组织和力学性能。结果表明,TC10钛合金锻棒原始组织中α相有两种形态,一种为初生等轴α相,另一种为次生α相。当加热温度低于相变点时,形成的组织以双态组织和等轴组织为主,当加热温度高于相变点时,合金组织以全片层β转变组织和粗片层β转变组织为主。3种冷却方式下,水冷后合金的强度最大,炉冷后合金塑性最好。合金在炉冷后的冲击性能最高,其次为空冷、水冷。当加热温度在两相区时,3种冷却方式下合金的拉伸和冲击断口形貌包含韧窝和解理面,高低起伏明显;当加热温度在单相区时,合金的拉伸断口形貌为结晶状,撕裂棱明显,冲击断口具有晶间断裂特征。