Creep behavior of near-peritectic Sn-5Sb solders containing small amount of Ag and Cu

Sn-5%Sb is one of the materials considered for replacing Pb-bearing alloys in electronic packaging. In the present study, the effects of minor additives of Ag and Cu on the as-cast microstructure and creep properties of the Sn-5Sb solder alloy are investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscope (EDS) and tensile tests. Results show that addition of Ag and Cu resulted not only in the formation of new Ag₃Sn and Cu₆Sn₅ intermetallic compounds (IMCs), but also in the refinement of the grain size of Sn-5Sb solder. Accordingly, the creep properties of the Ag or Cu-containing solder alloys are notably improved. Attention has been paid to the role of IMCs on creep behavior. The lead-free Sn-5Sb-0.7Cu solder shows superior creep performance over the other two solders in terms of much higher creep resistance and vastly elongated creep fracture lifetime. An analysis of the creep behavior at elevated temperatures suggested that the presence of hard Cu₆Sn₅ and fine SbSn IMCs in the Sn-5Sb-0.7Cu alloy increases the resistance to dislocation movement, which improves the creep properties.     

Power law indentation creep of Sn-5% Sb solder alloy

Creep behavior of the lead-free Sn-5%Sb solder alloy was studied by long time Vickers indentation testing at room temperature. Based on the steady-state power law creep relationship, the stress exponents were determined for the cast and wrought materials in the homogenized and unhomogenized conditions. The stress exponent values of 4.5 and 12, depending on the processing route of the material, are in good agreement with those reported for the same material in conventional creep testing at room temperature. The results are discussed on the basis of the microstructural features developed during different processing routes of the material.     

Joining of silicon nitride ceramics by hot pressing

The joining of hot-pressed silicon nitride ceramics, containing Al₂O₃ and Y₂O₃ as sintering aids, has been carried out in a nitrogen atmosphere. Uniaxial pressure was applied at high temperature during the joining process. Polyethylene was used as a joining agent. Joining strength was measured by four-point bending tests. The effects of joining conditions such as temperature (from 1400 to 1600°C), joining pressure (from 0.1 to 40 MPa), holding time (from 0.5 to 8 h) and surface roughness (R _max) of the joining couple (about 0.12, 0.22 and 1.2m) on the joining strength were examined. The joining strength was increased with increases in joining temperature, joining pressure and holding time. Larger surface roughness caused lower joining strength. The higher joining strength was attributed to a larger true contact area. The area was increased through plastic deformation of the joined couple at elevated temperatures. The highest joining strength attained was 567 MPa at room temperature, which was about half the value of the average flexural strength of the original body. The high temperature strength measured at 1200° C did not differ very much from the room-temperature value.     

Effect of hydrogen on the low-temperature mechanical properties of V-5 at % Ti alloys

The effects of grain size and hydrogen in solid solution or as hydrides on the strength and ductility of V-5 at % Ti was studied over the temperature range 15–448 K. Comparison of the strength and ductility characteristics of hydrogenated alloys where hydrides were not observed down to 78 K (1.8 and 1.9 at % H alloys) or where hydrides were observed to form near 230 K (3.8 and 3.9 at % H alloys) indicated that the presence of hydride precipitates had no apparent influence on the strength or ductility characteristics. It appears that the main consequence of hydride precipitation is that hydrogen is removed from solid solution making strengthening less effective than expected based on the total hydrogen content. Decreasing grain size from 31 m to 8 m had no apparent effect on ductility in the nonhydrogenated alloys (< 0.05 at % H) but it did increase the strength over most of the temperature range and especially at 15 K. In the hydrogenated alloys this decrease in grain size lowered the transition temperature about 10 K and it appreciably increased the degree of ductility return at 78 K and below. The ductility return below 78 K peaked near 50 K before decreasing below 30 K with the improvement in ductility being greatest in the alloys with the lower hydrogen contents.     

Superconductivity of heat-treated Nb-65 at.% Ti alloy

Brief reviews are given of the effect of heat-treatment on the microstructure of cold-worked bcc metals and the superconducting properties of niobium alloys. Particular attention is paid to the influence of interstitial impurities in these processes. The annealing effects in microstructure and superconducting properties of a cold-worked Nb-65 at.% Ti alloy, containing oxygen as a major impurity, have been studied. The precipitation process takes the form TiNb + O₂ various Ti oxides Ti + TiO. Differences in precipitation sequence are described for vacuum-annealing and annealing in impure argon. Flux-pinning is related to the microstructural observations. At least three pinning mechanisms appear to operate; dislocation pinning and two types of precipitate pinning. These observations are in accord with previously proposed pinning models.     

Structural and electrical properties of Bi5Ti3FeO15 ceramics

Bi₅Ti₃FeO₁₅ (BTF) is a multiferroic material of Aurivillius structural family with (perovskite) layered structure. This material has special interest and position in the family because it is a combination of multiferroic BiFeO₃ and ferroelectric Bi₄Ti₃O₁₂, and can be used as new magneto-electric material for devices. The compound (Bi₅Ti₃FeO₁₅) was synthesized by a standard and widely used a high-temperature solid-state reaction method using high purity oxides. Preliminary structural analysis of the compound from the room temperature X-rays diffraction data confirmed the formation and good quality of the material. The nature of the microstructure (i.e., distribution, size and shape of grains, etc.) of sample recorded at room temperature using scanning electron microscopy exhibits formation of high-density sample. Studies of capacitive (permittivity and tangent loss) and resistive (impedance, electrical modulus and electrical conductivity) properties of the material as a function of frequency (1–1,000 kHz) at different temperatures (30–500 °C) using a complex impedance spectroscopy technique have provided many interesting and vital information on contribution of grains, grain boundary and interface in the material.     

Thermoelectric power of Nb - 48 at % Ti alloy in the temperature range 5 – 25 K

The thermoelectric power of the switched superonductor has been determined. Nb-48 at at % Ti was used since it was a high specific resistance in the normal state. The diffusion component, S, decreased smoothly and gradually with increasing temperature, but with a distinct discontinuity near the critical temperature.     

Microwave dielectric properties of Sr2Ce2Ti5O16 ceramics

Sr₂Ce₂Ti₅O₁₆ dielectric ceramics were prepared by conventional solid-state ceramic route. The structure and microstructure of the ceramics were investigated by X-ray diffraction and scanning electron microscopic methods. The Sr₂Ce₂Ti₅O₁₆ has a psuedocubic structure. It has ɛ_r of 113, unloaded quality factor (Q_u × f) of 8000 GHz and temperature coefficient of resonant frequency of 306 ppm/°C. The effects of various dopants on the structure, microstructure and microwave dielectric properties of the material have been investigated. It is found that addition of small amount of dopants such as PbO, Al₂O₃, Nd₂O₃, MoO₃, CeO₂, La₂O₃, Fe₂O₃ and NiO improve the microwave dielectric properties of Sr₂Ce₂Ti₅O₁₆.     

Tailoring the microwave dielectric properties of BaRE2Ti4O12 and BaRE2Ti5O14 ceramics by compositional variations

Ceramic dielectric resonators in the BaO-RE₂O₃-TiO₂ (RE=rare earth) system have been prepared by the conventional solid state ceramic route. The dielectric properties have been tailored by substitution of different rare earth oxides and by bismuth oxide addition. The dielectric constants increased with Bi addition whereas the Q decreased. The temperature coefficient of the resonant frequency improved with bismuth addition.     

Ultrasonic attenuation in the mixed state of V-42 at % Ti

The ultrasonic attenuation in the mixed state of V-42 at % Ti was measured at T = 4.14K, using shear and longitudinal waves with frequencies 10–130 MHz, in magnetic fields up to 100 kG. The results are compared to a phenomenological model in which the mixed-state resistivity is used as an effective resistivity in the Alpher-Rubin theory. For our V-42 at % Ti, pinning forces are weak, so that the mixed-state attenuation is particularly sensitive to the dc flux-flow resistivity. For magnetic fields 40–60 kG, the attenuation is in quantitative agreement with a model employing the dc flux-flow resistivity of Kim et al., % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaacqaHbpGCdaWgaa% WcbaacbaGaa8NzaaqabaGccqGH9aqpcqaHbpGCdaWgaaWcbaGaa8NB% aaqabaGccaWFibGaai4laiaa-HeadaqhaaWcbaGaam4yaiaaikdaae% aacaGGQaaaaOGaaiikaiaaicdacaGGPaaaaa!400D!\[\rho _f = \rho _n H/H_{c2}^* (0)\]. For high frequencies, where pinning may be neglected, the magnetic field dependence of the attenuation for HH_c2 is in better agreement with the use of the flux-flow resistivity calculated from the time-dependent Ginzburg-Landau equation.Research supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq).Supported by Comissão de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).     

Joining of Si3N4 using Ag57Cu38Ti5 brazing filler metal

Hot-pressed Si₃N₄ was joined using Ag₅₇Cu₃₈Ti₅ brazing filler metal at 1103 to 1253 K for 5 min in a vacuum. The interface reactions between Si₃N₄ and the brazing filler metal during brazing are reported. An important event is sufficient interface reaction, characterized by the formation of a layer of TiN with an appropriate thickness at the ceramic-filler interface. The joining strength of the butt joint depends on the interface reaction, and a maximum joining strength of 490 MPa measured by the four-point-bend method is achieved for the Si₃N₄-Si₃N₄ joint brazed at 1153 K for 5 min. It is also discussed how to design the best brazing filler metal for joining ceramic to ceramic or ceramic to metal.     

AEM characterization of interfacial reactions between Ti-coating and 95% Al2O3-5% silicate ceramics

Characterization of the interface reaction region of Ti-95% Al₂O₃ upon exposure to heat treatment at 980 °C has been carried out to investigate changes in microstructure and chemistry of interfacial phases by using energy dispersive X-ray spectroscopy and convergent beam electron diffraction methods. Reactions of titanium-coating with an amorphous grain boundary phase and Al₂O₃ substrate form suicide layers and columnar Ti₃Al grains at the interface respectively.     

Ti4+取代Zn2+、Nb5+对Bi2O3-ZnO-Nb2O5系介质材料结构和性能的影响

研究了Ti4 取代Zn2 ,Nb5 对Bi2O3-ZnO-Nb2O5系介质材料结构和性能的影响,研究表明,少量替代对于材料的结构和性能没有太大的影响;随着替代量的增加,相结构中出现正交Bi4Ti3O12相;微观形貌中出现棒晶,介电常数逐渐增大,温度系数逐渐向负温度系数方向移动,适量Ti4 替代可以获得性能很好的NP0介质材料。     

Effect of Sb5+ substitution on the dielectric properties of Ba3LiTa3Ti5O21 ceramics

The effects of substitution Sb for Ta on the sintering behavior and the microwave dielectric properties of Ba₃LiTa₃Ti₅O₂₁ ceramic were studied. Single-phase polycrystalline microwave dielectric ceramics Ba₃LiTa_3?x Sb _x Ti₅O₂₁(x = 0–3) were prepared by the solid-state reaction method. The sintering behavior and microwave dielectric properties of Ba₃LiTa_3?x Sb _x Ti₅O₂₁ ceramics were found to be affected by Sb substitution for Ta. With the increasing Sb content, the densified (>95 % of their theoretical X-ray density) temperatures of Ba₃LiTa_3?x Sb _x Ti₅O₂₁ ceramics increased from 1,160 to 1,220 °C, the dielectric constant (ε _r ) decreased from 55.5 to 27, and the Q × f value enhanced significantly from 18,480 to 29,400 GHz, with τ _f improving from 70 to ?25 ppm/°C. A near zero τ _f value could be obtained by carefully adjusting the Sb content.     

Structural and Phase Transformations in Alloys during Spark Plasma Sintering of Ti + 23.5 at % Al + 21 at % Nb Powder Mixtures

We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α₂ and Nb₂Al phases and small precipitates of the O-phase (intermetallic compound Ti₂AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.     

Processing of porous Ti and Ti5Mn foams by spark plasma sintering

Titanium and its alloys are one of the best metallic biomaterials to be used for implant application. In this study, porous Ti and Ti5Mn alloy with different porosities were successfully synthesized by powder metallurgy process with the addition of NH₄HCO₃ as space holder and TiH₂ as foaming agent. The consolidation of powder was achieved by spark plasma sintering process (SPS) at 16 MPa and pressureless conditions. The morphology of porous structure was investigated by using scanning electron microscopy (SEM) and X-ray micro-tomography (μ-CT). Nano-indentation tester was used to evaluate Young’s modulus of the porous Ti and Ti5Mn alloy. Experimental results showed that pure Ti sample, which sintered under pressure of 16 MPa, full relative density was achieved even at a relative low sintering temperature 750 °C; however, in the case of pressureless condition at sintering temperature 1000 °C the porosity was 53% and Young’s modulus was 40 GPa. The Ti5Mn alloy indicated a good pore distribution, and the porosity decreased from 56% to 21% by increasing the sintering temperature from 950 °C to 1100 °C. Young’s modulus was increased from 35 GPa to 51.83 GPa with increasing of the sintering temperatures from 950 °C to 1100 °C.