Effect of Sn on microstructure and mechanical properties of Ti-base dendrite/ultrafine-structured multicomponent alloys

Ti_57−x Cu₁₅Ni₁₄Sn_4+x Nb₁₀ (x = 0, 5, or 10) alloys were prepared by copper mold casting. At Sn = 4 at. pct, a dendrite/ultrafine-structured multicomponent alloy was obtained, which exhibits 1271 MPa yield strength, 77 GPa Young’s modulus, and 2 pct plasticity at room temperature for 3-mm-diameter samples. The cooling rate significantly affects the as-cast microstructure and the mechanical properties. For 5-mm-diameter samples, the alloy exhibits 1226 MPa yield strength, 63 GPa Young’s modulus, and 2.5 pct plasticity. At Sn = 9 at. pct, Ti-, Sn-, and Nb-rich particles precipitate primarily. This near-hypereutectic alloy composition leads to the precipitation of intermetallics, which deteriorate the mechanical properties and result in the coexistence of ductile and brittle fracture mechanisms. At Sn = 14 at. pct, the alloy composition is completely in the intermetallic region, thus inducing the formation of Ti₂Cu, Ti₂Ni, and Ti₃Sn intermetallics. The alloy becomes very brittle because the intermetallic compounds dominate the fracture process.     

The transformation on annealing of the metastable electrodeposit,NiSnx, to its equilibrium phases

Under slow heating conditions hot-stage transmission electron microscopy has shown that the metastable single-phase intermetallic alloy electrodeposit NiSn₀.64 to 1.04, transforms to the equilibrium phases, Ni₃Sn₂ and Ni₃Sn₄, or Ni₃Sn₂ alone, depending upon its composition. The nature of the transformation depends upon whether the product is the two-phase mixture or the single phase, but is independent of the heating rate when only Ni₃Sn₂ is formed. However at fast heating rates direct transformation to Ni₃Sn₂/Ni₃Sn₄ does not occur. Instead a further metastable phase is formed first with structure and lattice parameters corresponding to a composition extension of the Ni₃Sn₂ phase. Calorimetry studies have enabled the activation energy of the transformation to be determined for slow heating conditions. Values of 0.76 and 0.96 ev have been measured for the formation of single-phase Ni₃Sn₂ and the Ni₃Sn₂/Ni₃Sn₄ phase mixture respectively. In addition a hitherto undetected composition-independent exothermic reaction at 200° has been interpreted in terms of local atomic rearrangements in grain boundaries.     

Isothermal section of the ternary Sn-Cu-Ni system and interfacial reactions in the Sn-Cu/Ni couples at 800 °C

The isothermal section of the Sn-Cu-Ni system at 800 °C has been experimentally determined. There is no ternary compound. A solid solution with a very wide compositional range, the γ phase is formed between the Ni₃Sn(H) phase and Cu₄Sn(H) phase; however, both of these two binary phases are not stable at 800 °C. The binary Ni₃Sn₂ phase also has extensive ternary solubility. The homogeneity ranges of both the γ and Ni₃Sn₂ phases are very large in parallel to the Cu-Ni side, but relatively narrow along the Sn direction. This phenomenon indicates that Cu and Ni are exchangeable in both phases. Three kinds of reaction couples, Sn-55 at. pct Cu/Ni, Sn-65 at. pct Cu/Ni, and Sn-75 at. pct Cu/Ni, were prepared and reacted at 800 °C for 5 to 20 minutes. The reaction paths are liquid/Ni₃Sn₂/γ/Ni₃Sn(L)/Ni for the Sn-55 at. pct Cu/Ni and Sn-65 at. pct Cu/Ni couples, and the reaction path is liquid/γ/Ni₃Sn(L)/Ni for the Sn-75 at. pct Ni couples.     

Diffusion Parameters and Growth Mechanism of Phases in the Cu-Sn System

The tracer diffusion coefficients of the elements as well as the integrated interdiffusion coefficients are determined for the Cu₃Sn and Cu₆Sn₅ intermetallic compounds using incremental diffusion couples and Kirkendall marker shift measurements. The activation energies are determined for the former between 498 K and 623 K (225 °C and 350 °C) and for the latter between 423 K and 473 K (150 °C and 200 °C). Sn is found to be a slightly faster diffuser in Cu₆Sn₅, and Cu is found to be the faster diffuser in Cu₃Sn. The results from the incremental couples are used to predict the behavior of a Cu/Sn couple where simultaneous growth of both intermetallics occurs. The waviness at the Cu₃Sn/Cu₆Sn₅ interface and possible reasons for not finding Kirkendall markers in both intermetallics in the Cu/Sn couple are discussed.     

Diffusion of63Ni in the intermetallic B82-alloys in the systems Ni/Sn and Ni/In

The self-diffusion of⁶³Ni has been investigated in single crystals of the ordered intermetallic compounds Ni₆₁Sn₃₉, Ni₆₂Sn₃₈ and Ni₆₄In₃₆. The activation energies for diffusion perpendicular and parallel to the hexagonal c-axis are nearly the same and the values are between 2.14 and 2.34 eV. Moreover the D₀-values are direction dependent and range from 0.5 to 0.8 cm²/s for Ni/Sn and from 65 to 110 cm²/s for Ni/In. The experimental values of D_⊥/D_∥ are between 1.13 and 1.68 for Ni/Sn and between 0.87 and 0.79 for Ni/In, depending on temperature. These values are to be compared with theoretical values for the different diffusion mechanisms. The majority mechanism should be a site change of the tracer atom between the Ni-chains in c-direction and the double tetraeder interstices (DTI) with a further jump to another chain. Moreover two other mechanisms as minority mechanisms are possible. With rising temperature and filling the DTI's the part of minority mechanisms increases.     

Thermal stability of electroless-nickel/solder interface: Part A. interfacial chemistry and microstructure

The thermal stability of the interface between the Sn-Pb eutectic alloy and an electroless Ni-P coating was examined by cross-sectional transmission electron microscopy (TEM). The interface was formed by reflowing the eutectic Sn-Pb solder alloy between electroless Ni-P deposits. The microchemistry and microstructure of the interface were analyzed in the as-reflowed, mild-aged, and overaged conditions, by energy-dispersive spectroscopy (EDS), selected-area electron diffraction (SAD) convergentbeam electron diffraction (CBED), and bright- and dark-field imaging. In the as-reflowed condition, the interfacial microstructure consisted of a thin Ni₃Sn₄ intermetallic layer and a thin P-rich layer. The P-rich layer was composed of two phases, face-centered cubic (fcc) Ni and Ni₃P, and the excess P was primarily due to the ejection of P from the electroless Ni-P when it reacted with Sn in the reflow process. Following the mild aging, a trilayer interfacial microstructure was found, including a coarsened Ni₃Sn₄ layer, a P-rich layer with increased P concentration, and a P-deficient layer. With overaging, a multilayer interfacial microstructure was developed, which consisted of two Ni-Sn intermetallic layers, Ni₃Sn₄ and Ni₃Sn₂, and three distinct P-rich layers, Ni₁₂P₅, Ni₁₂P₅ + Ni₃P, and Ni₃P + Ni.     

Ni-Nb-Sn Bulk Metallic Glass Matrix Composites Fabricated by Microwave-Induced Sintering Process

Using a gas-atomized Ni_59.35Nb_34.45Sn_6.2 metallic glassy alloy powder blended with Sn powder of various contents, Ni-Nb-Sn bulk metallic glassy matrix composites were fabricated by a microwave (MW)–induced sintering process in a single-mode 2.45 GHz MW applicator in a separated magnetic field. The Ni_59.35Nb_34.45Sn_6.2 glassy alloy powder and its mixed powders containing Sn particles could be heated well in the magnetic field. The addition of Sn particles promoted densification of the sintered Ni_59.35Nb_34.45Sn_6.2 metallic glassy powder. Bulk samples without crystallization of the glassy matrix and with good bonding state among the particles were achieved at a sintering temperature of 833 K.     

Kinetics of spreading in initial stages in metallic systems with different types of interaction between components. IV. Effect of chemical reaction on the kinetics of spreading in tin—Iron group metal systems

A droplet flowing over onto a plate introduced from above has been used to study the kinetics of spreading and to describe the observable characteristics of spreading of tin on iron, cobalt, nickel, and the intermetallic compounds Ni₃Sn, Ni₃Sn₂ under a vacuum of (2–4)·10⁻³ Pa at 400–1000°C, droplet mass 0.01–0.06 g. We show by a formal kinetic analysis of experimental data that in the low-temperature range (400–500°C) the kinetic regime dominates, and in the high-temperature range (600–1000°C) the inertial—kinetic regime dominates. In spreading of tin on iron, cobalt, nickel, and the intermetallic compounds Ni₃Sn and Ni₃Sn₂, the nature of the interaction corresponds to the phase equilibrium in the studied systems. The results for the kinetics of spreading of tin on nickel and the intermetallic compound Ni₃Sn showed that spreading of the main bulk is preceded by spreading of a precursor film. Deceased. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(402), pp. 65–72, July–August, 1998.     

Solidification of Highly Undercooled Hypereutectic Ni-Ni3B Alloy Melt

The solidification of undercooled Ni-4.5 wt pct B alloy melt was investigated by using the glass fluxing technique. The alloy melt was undercooled up to ΔT _p ~ 245 K (245 °C), where a mixture of α-Ni dendrite, Ni₃B dendrite, rod eutectic, and precipitates was obtained. If ΔT _p < 175 K ± 10 K (175 °C ± 10 °C), the solidification pathway was found as primary transformation and eutectic transformation (L → Ni₃B and L → Ni/Ni₃B); if ΔT _p ≥ 175 K ± 10 K (175 °C ± 10 °C), the pathway was found as metastable eutectic transformation, metastable phase decomposition, and residual liquid solidification (L → Ni/Ni₂₃B₆, Ni₂₃B₆ → Ni/Ni₃B, and L_r → Ni/Ni₃B). A high-speed video system was adopted to observe the solidification front of each transformation. It showed that for residual liquid solidification, the solidification front velocity is the same magnitude as that for eutectic transformation, but is an order of magnitude larger than for metastable eutectic transformation, which confirms the reaction as L_r → Ni/Ni₃B; it also showed that this velocity decreases with increasing ΔT _r, which can be explained by reduction of the residual liquid fraction and decrease of Ni₂₃B₆ decomposition rate.     

Interface microstructures in the diffusion bonding of a titanium alloy Ti 6242 to an INCONEL 625

A Ti6242 alloy has been diffusion bonded to a superalloy INCONEL 625. The microstructures of the as-processed products have been analyzed using optical metallography, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM) techniques. The interdiffusion of the different elements through the interface has been determined using energy-dispersive spectroscopy (EDS) microanalysis in both a SEM and a STEM. Several regions around the original interface have been observed. Starting from the superalloy INCONEL 625, first a sigma phase (Cr₄Ni₃Mo₂), followed by several phases like NbNi₃, Ŋ/Ni₃Ti, Cr(20 pct Mo), β Cr₂Ti, NiTi, TiO, TiNi, and Ti₂Ni intermetallics, just before the Ti6242 have been identified. Because the diffusion of Ni in Ti is faster than the diffusion of Ti in the superalloy, a Kirkendall effect was produced. The sequence of formation of the different phases were in agreement with the ternary Ti-Cr-Ni diagram.     

Precipitation in a rapidly solidified and aged NiAlMo alloy

The early stages of decomposition of a highly supersaturated nickel-base alloy have been studied using transmission electron microscopy, scanning transmission electron microscopy and X-ray diffraction. The material was produced as a metastable solid solution by chill-block melt-spinning. On ageing the material exhibited a number of decomposition products appearing in series or concomitantly. Some of the decomposition products of this alloy, Ni₄Mo, Ni₃Mo (D0₂₂) and Ni₂Mo, are related to those found in NiMo binary alloys. α-Mo formed during solidification was distinguished from that formed by precipitation in the solid state by orientation relationships.     

Structural,Micromechanical and Tribological Characterization of Zn–Ni Coatings: Effect of Sulfate Bath Composition

Zn and Zn–Ni alloy coatings were electrodeposited on mild steel from sulfate-based bath containing Sn as additive. The effect of Ni content on the microstructure, morphology, microhardness and the tribological behavior of these coatings were studied and discussed. Adding Sn in the sulfate bath had a significant effect on the surface morphology, particularly on the Zn–8 wt% Ni coatings. By increasing the Ni concentration from 8 to 14 wt%, the X-ray patterns showed that the phase structure of Zn–Ni alloy coatings was changed from η-phase Ni₃Zn₂₂ to γ-phase Ni₅Zn₂₁. The plastic deformation and delamination were found to be wear mechanisms for the investigated coatings. While the Zn–14 wt% Ni alloys had the best wear resistance, Zn films had the most severe wear volume loss and the highest friction coefficient.     

Influence of the Substrate on the Creep of SN Solder Joints

The creep rate of Sn solder joints is noticeably affected by joint metallization. Cu|Sn|Cu joints have significantly higher creep rates than Ni|Sn|Cu joints, which, in turn, have higher creep rates than Ni|Sn|Ni joints. Replacing Ni by Cu on both substrates increases the creep rate at 333 K (60 °C) by roughly an order of magnitude. The increased creep rate appears with no apparent change in the dominant creep mechanism; the change in the constitutive equation for creep (the Dorn equation) is in the pre-exponential factor. The decreased creep rate on substituting Ni is accompanied by an increase in the hardness of the polygranular solder but a decrease in the nanohardness of the grain interiors. The source of the strong influence of the Ni substrate appears to be the introduction of an array of Ni₃Sn₄ intermetallic precipitates along the grain boundaries. These precipitates inhibit grain boundary sliding, boundary reconfiguration, and grain growth during creep. The intermediate creep rate of the asymmetric Ni|Sn|Cu joint has two causes: a decrease in grain boundary mobility due to precipitate decoration and a restriction in the free volume of the joint due to rapid intermetallic growth from the substrate on the Ni side. The sources of this anomalous intermetallic growth are discussed.     

A Comparative Study on the Microstructure and Mechanical Properties of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> and Cu<Subscript>3</Subscript>Sn Joints Formed by TLP Soldering With/Without the Assistance of Ultrasonic Waves

In this study, the microstructure and mechanical properties of Cu₆Sn₅ and Cu₃Sn intermetallic joints, formed by the transient liquid phase (TLP) soldering process with and without the assistance of ultrasonic waves (USWs), were compared. After the application of USWs in the TLP soldering process, Cu-Sn intermetallic compounds (IMCs) exhibited a novel noninterfacial growth pattern in the molten solder interlayer. The resulting Cu₆Sn₅ and Cu₃Sn joints consisted of refined equiaxed IMC grains with average sizes of 3 and 2.3 µm, respectively. The Cu₆Sn₅ grains in the ultrasonically soldered intermetallic joints demonstrated uniform mechanical properties with elastic modulus and hardness values of 123.0 and 5.98 GPa, respectively, while those of Cu₃Sn grains were 133.9 and 5.08 GPa, respectively. The shear strengths of ultrasonically soldered Cu₆Sn₅ and Cu₃Sn joints were measured to be 60 and 65 MPa, respectively, higher than that for reflow-soldered intermetallic joints. Ultrasonically soldered Cu₆Sn₅ and Cu₃Sn joints both exhibited a combination of transgranular and intergranular fractures during shear testing.     

Determination of the Phase Equilibria in the Mn-Sn-Zn System at 500 °C

The isothermal section of the Mn-Sn-Zn system at 500 °C was determined with 20 alloys. The alloys were prepared by melting the pure elements in evacuated quartz capsules. The alloy samples were examined by means of X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. A new ternary phase Mn₄Zn₈Sn (λ) was found to have a bcc structure with a lattice parameter a = 0.92508 (5) nm. Its composition range spans 25 to 35 at. pct Mn, 4 to 8 at. pct Sn, and 55 to 70 at. pct Zn. The Zn is substituted for Mn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂. The solubility of Zn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂ was measured to be about 17, 12, and 4 at. pct, respectively. The phase boundaries of the liquid and β-Mn phases were well established. The following 3 three-phase equilibria were well determined: (1) β-Mn + ε-MnZn₃ + Mn₃Sn, (2) λ + Mn₃Sn + Mn₂Sn, and (3) L + λ + Mn₂Sn. The additional 5 three-phase equilibria, which are ε-MnZn₃ + λ + Mn₃Sn, ε ₁-MnZn₃ + ε-MnZn₃ + λ, ε ₁-MnZn₃ + λ + L, Mn₂Sn + L + MnSn₂, and Mn₃Sn₂ + MnSn₂ + Mn₂Sn, were deduced and shown with dashed lines in the present isothermal section.     

Synthesis of nanodispersed phases during rapid solidification and crystallization of glasses in Ti75Ni25 alloys

The formation of the metallic glass and crystalline phases and related microstructures and the decomposition behavior of rapidly solidified Ti₇₅Ni₂₅ alloys obtained under different processing conditions have been investigated in detail. The competition between glass transition and nucleation of β-Ti during rapid solidification leads to the possibility of synthesizing the nanocomposites of β-Ti and glass. Additionally, it is shown that the presence of a small amount of Si also promotes simultaneous nucleation of fine Ti₂Ni intermetallic compound. Thermodynamic calculation of the metastable phase diagram indicates the presence of a metastable eutectic reaction between α-Ti and Ti₂Ni. Evidence of this reaction at lower cooling rates has been presented. On heating, the glass decomposes through this reaction. Finally, on the basis of understanding of the microstructural evolution during decomposition, a new approach has been adopted to synthesize a nanodispersed composite of α-Ti in the crystalline Ti₂Ni matrix with a narrow size distribution by controlling the devitrification heat treatment of the metallic glass.     

Interfacial IMC Layer and Tensile Properties of Ni-Reinforced Cu/Sn–0.7Cu–0.05Ni/Cu Solder Joint: Effect of Aging Temperature

Thermal aging behavior on the intermetallic compounds (IMCs) layer and mechanical properties of Cu/Sn–0.7Cu/Cu and Cu/Sn–0.7Cu–0.05Ni/Cu joints has been investigated from aging temperature of 60–180 °C for 100 h. Layer thickness increases as aging temperature rose for both the joints. Mechanical properties deteriorates with increase in aging temperature. After aging at 180 °C, any signs of ductile fracture surface with a large amount of dimples are absent. Instead, an intergranular fracture surface is obtained for both the joints, indicating that the process transformes from ductile to brittle behavior. However, brittle Cu₃Sn layer is observed between Cu₆Sn₅ layer and Cu substrate for Cu/Sn–0.7Cu/Cu joint after aging at 60 °C, while (Cu, Ni)₃Sn IMC layer is detected until aged at 140 °C for Cu/Sn–0.7Cu–0.05Ni/Cu. Compared with Cu/Sn–0.7Cu/Cu joint, the interfacial morphology directly changes from scallop-shaped into layer-shaped structure with lower Gibbs free energy, and the layer thickness is obviously suppressed after addition of Ni particle. Excellent mechanical properties, including UTS, elongation, and hardness, are obtained for Cu/Sn–0.7Cu–0.05Ni/Cu because of the slight increase in layer thickness and dense layer-shaped interfacial morphology. Thermal aging reliability is enhanced for the Cu/Sn–0.7Cu–0.05Ni/Cu solder joint after doping with 0.05 wt% Ni particle.