Papers by Keyword: Intermetallic

Abstract: Various intermetallics can be synthetized by mechanical alloying depending on alloy composition, type of mill, and milling parameters. This work discusses on the phase transformations during ball milling and subsequent sintering of Ni-Sn and Ni-Mg powder mixtures. The structural evaluation of as-milled and sintered samples was conducted by X-ray diffraction and scanning electron microscopy. Metastable phases were formed during milling of the Ni-Sn and Ni-Mg powder mixtures. The Ni₃Sn and Ni₃Sn₂ compounds were produced after sintering from the as-milled Ni-25Sn and Ni-40Sn powders, respectively. Two-phase Ni₂Mg+NiMg₂ alloy was found after sintering of as-milled Ni-66Mg powders because the nominal Mg amount in starting powders was reduced due to its preferential cold welding during milling and/or evaporation during sintering.

Abstract: In this study, the effect of carbon addition the cast and rolled microstructures of Cantor alloy type FeCoCrNiMn high entropy alloys. Both as-cast FeCoCrNiMn and FeCoCrNiMnC_0.1 alloys have dendritic microstructure. Small particles, which may be associated carbon addition exist in the dendrite arms in FeCoCrNiMnC_0.1 alloy. After homogenization treatment at 1327K for 24 hrs., dendritic structure was completely eliminated after annealing. Dendritic structure was converted to the structure with elongated grains, especially for carbon added FeCoCrNiMnC_0.1. The development of elongated grains is associated with the direction of the primary arms in the dendritic structure. Carbides are segregated at the grain boundaries in FeCoCrNiMnC_0.1 alloy. It also appears that growth of grains is impeded by the segregation of carbides. It is apparent that the grain boundary precipitates are Cr-rich. Both the strength and ductility of FeCoCrNiMnC_0.1 increased over FeCoCrNiMn with the addition of 0.1 wt. % carbon. The increase of ductility in FeCoCrNiMnC_0.1 may be caused by the rapid hardening in FeCoCrNiMnC_0.1 due to dislocation-solute interaction.

Abstract: In this study, electro nickel coating was applied and its effect on the interfacial stability and cracking behaviors were investigated in the multi-layered Ni-plated-Cu/Al/Ni-plated-Cu clad composite. Ni plating with 5μm thickness on the Cu sheet before cladding does not form a continuous layer between Cu and Al because of its low ductility. Ni layer covers the part of the Cu/Al interface. In the interface region without Ni layer, CuAl₂, CuAl and Cu₉Al₄ were found to be formed after annealing whereas Al₃Ni₂ and Al₃Ni were found to be formed in the interface region with Ni layer. After bending, interface crack developed initially in the interface region with plated Ni layer. On the other hand, the interface region with no Ni layer, no interface cracks were found to formed, suggesting that the bonding between Al and Ni is not strong enough. After interface crack formation, cracks developed in the Al layer, which may lead to the fatal fracture.

Abstract: Tungsten carbide (WC) based composites are usually produced with cobalt, but this binder has the inconvenience of shortage, unstable price and potential carcinogenicity. The objective of this study was to develop WC composite with intermetallic Fe₃Al matrix. Powders of WC, iron and aluminum, with composition WC-10 wt% Fe₃Al, and 0.5 wt% zinc stearate were milled in a vibration mill for 6 h and sintered in a SPS (spark plasma sintering) furnace at 1150 °C for 8 min under pressure of 30 MPa. Measured density and microstructure analysis showed that the composite had significant densification during the (low-temperature, short time) sintering, and X-ray diffraction analysis showed the formation of intermetallic Fe₃Al. Analysis by Vickers indentation resulted in hardness of 11.2 GPa and fracture toughness of 24.6 MPa.m^1/2, showing the feasibility of producing dense WC-Fe₃Al composite with high mechanical properties using the SPS technique.

Abstract: The feasibility of using the ultrasonic melt treatment to prepare billets for thixocasting process of hypoeutectic Al-7%Si alloys was studied in this paper. The work covered the billet preparation, soaking treatments and thixocasting process, with focus on the microstructural features in each case. The results showed that the use of ultrasonic treatment in billet preparation resulted in highly uniform, fine and non-dendritic microstructures. Billets with globule sizes as small as 58 µm, and roundness of more than 0.7 were obtained by ultrasonic melt treatment. Different soaking conditions before thixocasting were done and the optimum from which was the soaking for 5 min at 580°C, which resulted in thixocast parts with excellent combination of fine globules of 80 µm and roundness of 0.7 - 0.81. The eutectic Si, as well, was greatly refined by the ultrasonic thixocasting process. Furthermore, high-Fe ultrasonic treated billets, which were thixocasted successfully, exhibited Fe-intermetallic particles in highly desirable fine compacted form. These results reveal the feasibility and competence of UST as a potential route for feedstock production.

Abstract: This paper investigates the effect of 1 wt% TiO₂ on the formation of primary and interfacial Cu₆Sn₅ in Sn-0.7wt%Cu and Sn-0.7wt%Cu-0.05wt%Ni solder pastes soldered on a Cu substrate using a real-time synchrotron imaging technique. It was found that TiO₂ had altered the nucleation time of the primary Cu₆Sn₅ intermetallics and increased the number of particles observed. In addition, a more planar Cu₆Sn₅ interfacial layer had formed in joints made with TiO₂ reinforced solders. This indicated that TiO₂ promotes nucleation of primary Cu₆Sn₅ intermetallics in the early stages of soldering while being a barrier for further growth of interfacial Cu₆Sn₅ intermetallics. The synchrotron imaging technique provides direct evidence of the sequence of events in the soldering reaction and how these are influenced by TiO₂ reinforcement.

Abstract: The wettability and mechanical properties of solder the joint of Sn-Cu-Ni-xSi₃N₄ had been investigated. In this study, five different silicon nitride (Si₃N₄) percentage addition were chosen (0 wt. %, 0.25 wt. %, 0.5 wt. %, 0.75 wt. %, and 1.0 wt. %). Contact angle measurement demonstrated that with Si₃N₄ addition, the wetting perfomances had been improved with the decrease of wettability contact angle. It is believed that the Si₃N₄ particles suppresses the interfacial IMC growth and thus improves the shear strength. Interfacial IMC thickness measurement and shear strength results showed that with thinner IMC layer (by increasing amount of wt.% of Si₃N₄), the higher the shear strength of the joint. Fracture surface of sheared samples shows a combination of both brittle and ductile fracture.

Abstract: Sn-3Ag-3Bi-3In solder has been investigated to improve the understanding of microstructure formation in this solder during solidification and soldering to Cu and Ni substrates. The as-solidified microstructures of Sn-3Ag-3Bi-3In samples were found to consist of a significant fraction of βSn dendrites with a complex eutectic between the dendrites. In total five phases were observed to form during solidification: βSn, Ag₃Sn, Bi, ζAg and a “Sn-In-Bi” ternary compound. Soldering of Sn-3Ag-3Bi-3In to substrates changed the phase equilibria in the system and caused the formation of additional phases: Cu₆Sn₅ during soldering to Cu and Ni₃Sn₄ and metastable NiSn₄ during soldering to Ni. It is shown that metastable NiSn₄ forms as a primary phase in a complex 5-component Sn-3Ag-3Bi-3In-Ni system. In and Bi were detected in solid solution in the βSn matrix in amounts of ~1.5-2at% and ~1.2at% respectively. Bi also existed as fine particles of two distinct types. (i): sub-micron (<500nm) coral-like particles and (ii) facetted particles measuring up to 7-8 μm.

Abstract: Phosphorus (P) is often added to wave-solder baths as an anti-oxidation agent for older generation eutectic Sn-37wt%Pb solders. For Pb-free solder alloys trace amounts of germanium (Ge) have been added successfully in Sn-0.7wt%Cu-0.05wt%Ni for anti-oxidation purposes during the wave soldering process. Despite this practice, there is little information on how P and Ge distribute in solder alloys and dross in this alloy system. In this paper, the effects of combinations of trace levels of Ge (< 100ppm) and P (< 100ppm) in Sn-Cu-Ni solder alloys and their dross has been investigated by XRD and SEM/EDS. It was found that the weight fraction of tin oxides in the dross is increased with an addition of less than 100ppm P. The dross consists on SnO oxide with Sn in samples containing Ge and no P, while SnO and SnO₂ oxide are both present when P and Ge additions are made. In samples containing P, (Cu,Ni)₆Sn₅ and Ni-P and/or Ni-Sn-P intermetallics particles were found.

Abstract: The solidification of Sn-3Ag-0.5Cu and Sn-0.7Cu-0.05Ni are overviewed and compared. In joints on Cu substrates, both solders begin solidification with primary Cu₆Sn₅ growing in the bulk liquid prior to tin nucleation. In freestanding balls and joints, SAC305 generally solidifies with a single tin nucleation event and exhibits a mutually-twinned tin grain structure. In contrast, SN100C BGA balls and joints exhibit multiple independent tin grains that grow as a columnar array in joints.