Papers by Keyword: Intermetallic

Abstract: This work investigates the evolution of the microstructure of an Nb-23Ti-20Si (at.%) based alloy, from the primary plasma-melted material that is gas-atomized towards the consolidated material (here using SPS). The nature, morphology and size of the solid solution and the various silicides are followed by SEM, EDS and EBSD. Homogenous and fine microstructures are obtained after the SPS step and are improved by a subsequent heat treatment (1500°C, 100 h). However blocky silicides, already present in the powder particles, cannot be eliminated. A better control of the primary material’s microstructure would improve the microstructure of the final material.

Abstract: Thin layers of intermetallic (IMC) were prepared using Solid-Liquid Inter-Diffusion (SLID) process. 3μm of Tin was deposited on SiC dice, then soldered on a copper substrate at different temperature: 250-300-330-370°C and different soldering times: 5sec-300 sec - 15 min - 1h. The composition of the IMC was identified using energy dispersive X-Ray spectroscopy (EDX). Two types of intermetallic layers were identified: Cu₃Sn and Cu₆Sn₅. The samples were tested using die shear test. Then the internal stress was measured by X-Ray Diffraction (XRD). XRD spectrum obtained spotted only pure copper present underneath the intermetallic layer. The results showed that the level of residual stress is related to the amount of voids in the solder.

Abstract: The In Situ composites with microstructurally different types of intermetallic matrix such as nearly γ (TiAl) (composite A), multiphase with high amount of lamellar α₂(Ti₃Al) + γ (TiAl) regions (composite B) and fully lamellar α₂ + γ (composite C) were prepared by centrifugal casting and consecutive heat treatments of Ti-44.5Al-8Nb-0.8Mo-3.6C-0.1B, Ti-37Al-7Nb-0.8Mo-5.9C-0.1B and Ti-46.4Al-5Nb-1C-0.2B (at.%) alloys, respectively. The centrifugal casting results in a uniform distribution of coarse primary carbide particles in the as-cast samples. Hot isostatic pressing (HIP) and heat treatments have no effect on the Vickers hardness of the in-situ composite B but lead to a significant softening of the in-situ composites A and C. The in-situ composite C with a coarse-grained fully lamellar matrix shows a higher flow stress at 1000 °C and improved creep resistance at 800 °C compared to those of the in-situ composites A and B.

Abstract: Intermetallic TiAl alloys based on the γ-TiAl phase are already used as engineering light-weight high-temperature materials in aircraft and automotive engines. Thereby, they partly substitute the twice as heavy Ni-base superalloys. Present applications are, for example, blades in the low-pressure turbine of advanced aero-engines, turbine wheels for turbocharger systems of car diesel engines as well as engine parts used in racing cars. All these applications require balanced mechanical properties, i.e. certain ductility at room temperature as well as defined creep strength at elevated temperatures. The first part of this paper reviews the alloy design strategy, which was used for the development of a β-solidifying γ-TiAl-based alloy, the so-called “TNM alloy”, which exhibits an excellent hot-deformability. In the meantime, the TNM alloy with the nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in atomic percent, at.%) is introduced in a particular eco-friendly and fuel-saving aero-engine, which is powering a medium-range aircraft since the beginning of 2016. In the second part of this work the microstructural parameters are highlighted, which influence the failure strain at room temperature and creep strength at elevated temperatures. It will be shown how the creep resistance can be improved by tailoring phase fractions as well as the spatial arrangement of the microstructural constituents.

Abstract: This work is devoted to investigation of the structure of Ti-TiAl₃ composites reinforced by TiB₂ or TiC hard particles and obtained by spark plasma sintering of elemental foils and ceramic powders. Sintering was carried out at the temperature of 830 oC under the pressure of 40 MPa during 10 minutes. Microstructure of the composites obtained was represented by alternated layers of titanium and intermetallic compound TiAl₃. Also, it was found that at the Ti-TiAl₃ interfaces thin intermediate layers were formed. Quantitative elemental analysis of these layers showed that Ti₃Al, TiAl, and TiAl₂ compounds, as well as Ti (Al) solid solution could be formed in these zones. Diffraction analysis did not reveal any transformations of initial reinforcing phases after sintering. Interlayers with titanium diboride had the average microhardness level of 3988 HV, and the average microhardness level of interlayers with TiC was 1610 HV.

Abstract: Ga and Ga-based alloys appear to be promising materials for low temperature soldering in microelectronics. This research involved an analysis of the joint interfaces that resulted from reactions between a eutectic Ga-Sn alloy and Au coated Cu substrates at both room temperature and 100°C. At both temperatures the intermetallic CuGa₂ accounted for the majority of the interfacial microstructure. This study has shown the possibility of using eutectic Ga-Sn alloys in low temperature soldering applications, as well as the advantages of Synchrotron XFM techniques in characterising trace element distributions in solder joints.

Abstract: The effect of bismuth (Bi) micro-alloying additions on wettability and mechanical properties of Sn-0.7Cu lead-free solder were explored. This paper also investigates the influences of various Bi percentages on the suppression of intermetallic compound formation. Scanning electron microscope (SEM) was used to observe the microstructure evolution of solder joint including the thickness of interfacial intermetallic layers. Overall, with the addition of Bi to Sn-0.7Cu solder, the size of primary Cu₆Sn₅ become smaller and suppresses the thickness of interfacial intermetallic compound between solder and the Cu substrate. Microhardness value and wetting properties also increased with Bi addition which resulted in smaller size of β-Sn and Cu₆Sn₅.

Abstract: In this study, electro nickel coating was applied and its effect on the electrical conductivity and mechanical properties was investigated in Cu/Ni/Al/Ni/Cu clad composite after annealing at various temperature. After annealing at 300^OC for 3hrs, the interface reaction layer at the Cu/Al interface was observed to be 3μm and no reaction layer was observed at the Ni/Al interface. After annealing above 400^OC for 3hrs, the interface reaction layer at the Cu/Al interface in the absence of Ni layer was observed to grow more rapidly with increase of annealing temperature compared to that at the Ni/Al interface. The electrical conductivity increased after annealing up to 300^OC for 3 hrs. possibly because of enhanced interface bonding and the recovery in the matrix. However, it was deteriorated after annealing above 400^OC for 3 hrs. because of the formation of interface intermetallic. The more localized bending in the as-roll-bonded clad composite and that annealed at 200°C can be attributed to the near-zero and negative hardening rate in bending over the whole displacement. In this case, once bending occurs, bending continue to occur in the localized region because the work hardening due to the localized bending is negligible, leading to the localized fracture.

Abstract: Cobalt is widely used to produce WC-Co hard metals, but this binder has problems of shortage and unstable price. In this work, cobalt was replaced by an iron aluminide intermetallic binder. WC-10%(Fe₃Al-3%B) composite was prepared by vibration milling of WC, Fe, Fe-B, and Al powders and sintered by spark plasma sintering (SPS) at 1150 °C for 8 min under 30 MPa. The milling time was 0.17, 12, 25 and 50 h. The SPS was efficient to consolidate the composite resulting in relative density of ~98% or higher. With increasing milling time, Vickers hardness (HV₃₀) of composite increased from 12 to 14 GPa due to the enhanced homogeneity of microstructure, while the fracture toughness, K_Ic, determined by an indention fracture method using Shetty equation, remained constant at around 9.1 MPa.m^1/2.

Abstract: The present work reports on the microstructure and oxidation resistance of Ni-25Nb, Ni-20Nb-5Ta and Ni-15Nb-10Ta alloys produced by high-energy ball milling and subsequent sintering. The sintered samples were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive spectrometry, and static oxidation tests. Homogeneous microstructures of the binary and ternary alloys indicated the major presence of the β-Ni₃Nb compound as matrix, which dissolved large amounts of tantalum. Consequently, the β-Ni₃Nb peaks moved toward the direction of smaller diffraction angles. Iron contamination lower than 6.7 at.-% was detected by EDS analysis, which were picked-up during the previous ball milling process. After the static oxidation tests (1100°C for 4 h) the sintered Ni-25Nb, Ni-20Nb-5Ta and Ni-15Nb-10Ta alloys presented mass gains of 31.5%, 30.5% and 28.8%, respectively. Despite the higher densification of the Ni-15Nb-10Ta alloy, the results suggested that the tantalum addition contributed to improve the oxidation resistance of the β-Ni₃Nb compound.