Direct observation of ternary solid state transformation in Bi–Cd–In alloy system

Abstract

Cast or solution treated specimens of a Bi–9·0Cd–26·7In (wt-%) alloy were observed to form a fine, three phase microstructure on aging at room temperature, replacing a single phase formed at a higher temperature. The three phases resulting from this solid state reaction were found to grow with a lamellar morphology into the high temperature phase, with a growth rate of 0·5–1·0 μm h^-1 at room temperature. The equilibrium temperature for the transformation was found to be ～25°C. Using a Hitachi S-4500 field emission SEM, the phase transformation was followed in progress at magnifications of 3000 and 10 000 times. It was noted that a volume change was associated with the transformation. It was concluded that the transformation is of the ternary eutectoid type.     

Self-accommodated and pre-strained martensitic microstructure in single-crystalline,metamagnetic Ni–Mn–Sn Heusler alloy

Metamagnetic shape memory alloys are a unique class of materials capable of large magnetic field-induced strain due to reverse martensitic phase transformation. A precondition for large shape change is martensite deformation, which heavily depends on microstructure. Elucidation of microstructure is therefore indispensable for strain control and deformation mechanics in such systems. The current paper reports on a self-accommodated martensitic microstructure in metamagnetic Ni₅₀Mn_37.5Sn_12.5 single crystal. The microstructure here is hierarchically organised at three distinct levels. On a large scale, martensite plate colonies, distinguished by intercolony boundaries, group individual martensitic plates. Plates are separated by interplate boundaries and deviate by 2.2° from an ideal twin relation. On the lower scale, plates are composed of subplate twins. Conjugation boundaries separating two pairs of twins arise in relation to a subplate microstructure. Modulation boundaries separating two variants with perpendicular modulation directions and with parallel c-axes also appear. Mechanical training frees larger plates from fine subplate microtwins bringing macro-lamellae into twin relation, what then permits further detwinning until a single variant state.     

Phase transition and mechanical properties of constraint-aged Ni–Mn–Ga–Ti magnetic shape memory alloy

Ni–Mn–Ga Heusler-type ferromagnetic shape memory alloys are attractive materials for micro-actuator, but the relatively poor ductility and low strength of Ni–Mn–Ga alloys have triggered a great deal of interest. In this study, we attempt to introduce some ductile second phase in the alloy by partially substituting Ti for Ga and constraint aging treatment. The results show that the martensitic transformation temperature first decreases and then increases slightly with the increasing of constraint-aging temperature, which can be attributed to the decrease of Ni content in the matrix and strengthening effect of the second particles. It is found that the amount of the Ni-rich precipitates by constraint-aged samples is more and the size of the second phase particle is smaller than that of the free-aged samples. The compressive stress and ductility can be significantly improved by the constraint-aging treatment, and the maximum compressive stress for constraint-aging alloy is about 1400 MPa, which is the highest value up to date compared with the 400 MPa in solution-treated Ni–Mn–Ga–Ti alloy and about 900 MPa in Ni–Mn–Ga–Ti alloy free-aged at 1073 K for 3 h. Scanning electron microscopy observations of fracture surfaces confirm that the Ni-rich second phase play a key role in improving the compression stress and ductility of Ni–Mn–Ga–Ti alloy.     

Determination of interfacial energies of solid Sn solution in the In–Bi–Sn ternary alloy

The equilibrated grain boundary groove shapes of solid Sn solution (Sn-40.14 at.% In-16.11 at.% Bi) in equilibrium with the In–Bi–Sn liquid (In-21.23 at.% Bi-19.04 at.% Sn) were observed from the quenched sample at 59 °C. Gibbs–Thomson coefficient, solid–liquid interfacial energy and grain boundary energy of the solid Sn solution have been determined from the observed grain boundary groove shapes. The thermal conductivity of solid phase for In-21.23 at.% Bi-19.04 at.% Sn alloy and the thermal conductivity ratio of liquid phase to solid phase at the melting temperature have also been measured with radial heat flow apparatus and Bridgman type growth apparatus, respectively.     

Energetic ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy thin film

The ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin film is investigated. Thin films of Ni–Mn–Sn FSMA synthesized by DC magnetron sputtering on Si substrate at 200 °C are irradiated by a beam of 120 MeV Ag ions at different fluence varying from 1 × 10¹² to 6 × 10¹² ions/cm². X-ray diffraction pattern reveals that the pristine film grows in L2₁ cubic austenite phase with poor crystallinity and crystallinity of the film improves with increasing ion fluence, which is attributed to the strain relaxation by the energy deposited by incoming ions and promotes the grain growth. Grain growth is further confirmed by Atomic force microscopy. The temperature dependent magnetization measurements show improvement in the magnetic and shape memory properties of the films with increasing fluence, which is ascribed to the ordering of austenite phase. Nanoindentation measurements show that with increasing fluence of 120 MeV Ag ions, films exhibit a greater stiffness and smaller tendency towards plastic deformation.     

Effect of structural transition in an amorphous Ni80P20 alloy on the wetting by a eutectic Sn–Bi solder

Annealing-induced structural transition from amorphous to nanocrystalline states is believed to have a significant effect on the wettability of metallic glass alloys. In this study, an amorphous Ni₈₀P₂₀ alloy was pre-annealed at various temperatures to yield different structures and then wetted by a eutectic Sn–Bi solder at 473 K in a high vacuum using a dispensed sessile drop method. The results show that the structural relaxation and primary crystallization in the amorphous substrates greatly deteriorate the wettability while large-scale eutectic crystallization and the growth of nanocrystallites after high-temperature annealing improve it primarily due to the formation of a precursor film ahead of triple line. Moreover, the amorphous Ni–P substrates are more reactive with the molten Sn–Bi solder than the crystallized ones. The interfacial reaction yields Ni₃Sn₄ and a P-rich crystalline layer consisting mainly of Ni₃P and Ni₂SnP intermetallics. The presence of this layer dramatically retards the subsequent growth of the Ni₃Sn₄ phase.     

Direct measurement of oxygen in lead-based ceramics using the ζ-factor method in an analytical electron microscope

X-ray absorption of oxygen is significant in thin specimens of Pb(Mg_1/3Nb_2/3)O₃-35 mol% PbTiO₃ [PMN-35PT] due to the presence of heavy elements such as Pb and Nb. Therefore, direct measurement of the oxygen concentration in these types of systems can be difficult. Furthermore, assumption of the composition from stoichiometric considerations may not be feasible, particularly if the valence state of one or more of the cation species is variable. Using only XEDS data, the -factor method provides absorption corrected compositional information. In the present study, it was shown that such data were in very good agreement with the nominal values for PMN-35 PT, whereas the uncorrected data underestimated the oxygen content by 300%. In previous work, it was theorized that the swelling of samples containing excess PbO was linked to changes in the composition of the intergranular liquid phase. The -factor technique was used to show that the oxygen to lead ratio of this second phase changes upon annealing.     

Newly observed prismatic Mg2Sn laths in a Mg–Sn–Zn–Mn alloy

Lath-shaped Mg₂Sn precipitates with their habit planes parallel to the prismatic planes of the Mg matrix are characterized in a Mg–Sn–Zn–Mn alloy. The orientation relationships (ORs) between these β-Mg₂Sn precipitates and α-Mg matrix are [0 1 1]_β//[0 1 ?1 0]_α and (0 1 ?1)_β deviating 0.36° to 1.20° from (0 0 0 1)_α, in which the deviation angle of 0.39° is most frequently observed. Although the ORs vary, the laths always exhibit four side facets bearing fixed relationships with g vectors in reciprocal space. Their major side facets incline to the basal plane of Mg matrix from 4.3° to 14.3°.     

Effect of cooling rates on the dendritic morphology transition of Mg–6Gd alloy by in situ X-ray radiography

The effect of cooling rate on the transition of dendrite morphology of a Mg-6 Gd(wt%) alloy was semiquantitatively analyzed under a constant temperature gradient by using synchrotron X-ray radiographic technique. Results show that equiaxed dendrites, including exotic 'butterfly-shaped' dendrite morphology, dominate at high cooling rate(1 K/s). When the cooling rate decreases in the range of 0.5–1 K/s, the equiaxed-to-columnar transition takes place, and solute segregates at the center of two long dendrite arms(LDA) of the 'butterfly-shaped' dendrite. When the cooling rate is lower than 0.3 K/s, directional solidification occurs and the columnar dendritic growth direction gradually rotates from the crystalline axis to the thermal gradient direction with an increase in cooling rate. Meanwhile, interface moves faster but the dendrite arm spacing decreases. Floating, collision and rotation of dendrites under convection were also studied in this work.     

Role of Ti in direct active bonding of SiC substrate using Sn–Ag–Ti alloy filler

Journal of Materials Science: Materials in Electronics - Low-temperature active bonding of silicon carbide substrate using Sn3.5Ag4Ti(Ce,Ga) active solder filler was carried out at...     

Wetting transition of grain boundaries in the Sn-rich part of the Sn–Bi phase diagram

The microstructural evolution of tin-rich Sn–Bi alloys after the grain boundary wetting phase transition in the (liquid + β-Sn) two-phase region of the Sn–Bi phase diagram was investigated. Three Sn–Bi alloys with 30.6, 23, and 10 wt% Bi were annealed between 139 and 215 °C for 24 h. The micrographs of Sn–Bi alloys reveal that the small amount of liquid phase prevented the grain boundary wetting transition to occur during annealing close to the solidus line. The melted area of the grain boundary triple junctions and grain boundaries increased with increasing the annealing temperature. When the amount of liquid phase exceeded 34 wt% during annealing, increasing temperature has not affected the wetting behavior of grain boundaries noticeably and led only to the increase of the amount of liquid phase among solid grains in the microstructure. The XRD results show that the phase structure and crystallinity remained unchanged after quenching from various annealing temperatures.     

Deformation induced martensite characteristics in Fe–29Ni–2Mn alloy

Abstract

Deformation induced martensite characteristics in the austenite phase of Fe–29Ni–2Mn alloy were studied for different austenite grain sizes of alloy. Scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy and also differential scanning calorimetry techniques were applied to study in order to clarify the deformation induced martensite characteristics from morphological, crystallographical, magnetical and thermal points of view. Scanning electron microscope revealed that the increasing of deformation amount also increased the amount of existed martensite. Transmission electron microscope observations showed that the crystal structure of these deformation induced martensites morphology was lenticular plates with a bcc crystal structure. Also the magnetism of both austenite and martensite phases were determined with Mössbauer spectroscopy. Mössbauer spectrometer measurements showed paramagnetic character for austenite phases and ferromagnetic character for martensite phases in all samples. According to obtained differential scanning calorimetry cooling curves, deformation induced martensite start temperature M _d was found to be higher (?128°C) for larger grained samples than for smaller grained samples (?135°C).     

Investigation of microhardness and thermo-electrical properties in the Sn–Cu hypereutectic alloy

Sn–3 wt% Cu hypereutectic alloy was directionally solidified upward with different growth rates (2.24–133.33 μm/s) at a constant temperature gradient (4.24 K/mm) and with different temperature gradients (4.24–8.09 K/mm) at a constant growth rate (7.64 μm/s) in the Bridgman-type growth apparatus. The measurements of microhardness of directionally solidified samples were obtained by using a microhardness test device. The dependence of microhardness HV on the growth rate (V) and temperature gradient (G) were analyzed. According to these results, it has been found that with the increasing the values of V and G the value of HV increases. Variations of electrical resistivity (ρ) and electrical conductivity (σ) for casting samples with the temperature in the range of 300–500 K were also measured by using a standard dc four-point probe technique. The variation of Lorenz coefficient with the temperature for Sn–3 wt% Cu hypereutectic alloy was determined by using the measured values of electrical and thermal conductivities. The enthalpy of fusion for same alloy was determined by means of differential scanning calorimeter from heating trace during the transformation from eutectic liquid to eutectic solid.     

Statistical description of the effect of Zr addition on the behavior of microcracks in Cu–6Ni–2Mn–2Sn–2Al Alloy

As possible substitutes for high-strength Cu–Be alloys, Cu–6Ni–2Mn–2Sn–2Al alloys have been developed. To clarify the physical background of the effect of trace Zr on the fatigue strength of such alloys, the initiation and propagation behavior of a major crack that led to the fracture of the tested specimens was monitored. When the stress amplitude was less than σ _a = 350 MPa, the fatigue life of the alloys with Zr was about 2–2.5 times larger than that of the alloy without Zr. When σ _a > 350 MPa, the effect of Zr addition on the fatigue life dramatically decreases as the stress amplitude increases. The increased fatigue life due to Zr addition resulted from an enhancement of the crack initiation life and microcrack growth life. The enhanced crack initiation life was mainly attributed to the strengthening of grain boundaries due to the precipitation of SnZr compounds. A statistical analysis of the behavior of multiple cracks was made to quantitatively evaluate the scatter in fatigue behavior. The statistical analysis supported the conclusions obtained from the behavior of a major crack.     

Tensile creep behavior of Sn–Ag–Cu–Ni multicomponent lead-free solder alloy

In the process of electronic packaging, the dissolution of under bump metallizations, such as Cu and Ni, into liquid solder occurs during soldering, which can change the original solder to a multicomponent one. Under the trend of miniaturization, it is quite necessary to evaluate the properties of multicomponent solder with excessive Cu and Ni compositions. In this study, the tensile creep behavior of Sn–3.5Ag–2.0Cu–0.5Ni multicomponent lead-free solder alloy is investigated at three temperatures, i.e., 303, 348 and 393 K. The steady-rate creep rates are obtained in the range of 10^?4–10^?8 s^?1, when the normalized stress, σ/E, is in the range of 10^?4–10^?3. Based on the Dorn equation, the apparent stress exponent (n _a), threshold stress (σ _th), and activation energy of creep (Q _C) are calculated at the three temperatures. It is found that the Sn–3.5Ag–2.0Cu–0.5Ni solder alloy shows a better creep performance than pure tin and eutectic Sn–3.5Ag solder due to the strengthening effect of Ag₃Sn and (Cu,Ni)₆Sn₅ IMC precipitations. The true stress exponent for creep is identified to be 7, indicating that the creep behave is controlled by the dislocation-pipe diffusion in the tin matrix.     

Effect of Al on the microstructure and mechanical properties of Mg–6Zn–2Sn–0.5Mn alloy

The microstructure and mechanical properties of Mg–6Zn–2Sn–0.5Mn–xAl (x?=?0, 1, 2, 3) alloy are investigated. The addition of Al leads to the refinement of grain size and the formation of Al₆Mn, Mg₃₂(Al,Zn)₄₉ also forms when the amount of Al is higher than 2?wt-%. Because of the addition of Al, the precipitates in the alloy after ageing treatment are refined. The alloy containing 1?wt-% Al shows good mechanical properties in the as-cast state which is attributed to the refined grains and low volume fraction of large second phases, it also shows high strength after ageing treatment resulted mainly from the homogeneously distributed fine precipitates, the yield strength, ultimate tensile strength and elongation are 183, 310?MPa and 11%, respectively.     

Influence of cold rolling on the precipitation in an Al–Mn–Zr alloy

The aim of the experiments was to study the influence of the rolling reduction (39, 87, and 96%) on the size and distribution of secondary particles and recrystallization behaviour of Al–Mn sheets with Zr addition prepared by twin-roll casting (TRC) in the industrial conditions. Samples, cold rolled on a laboratory mill, were subjected to a two-step precipitation annealing. Their microstructure (grain structure, substructure, particle analysis) as well as mechanical and physical properties (microhardness, electrical conductivity, resisitivity) were then characterized. The material cold worked with 39% reduction shows a moderate decrease of microhardness due to recovery, while sheets cold worked with 87 and 96% reduction soften more due to recrystallization. Regardless of the cold rolling reduction, the highest density of precipitates of α-Al(Mn,Fe)Si phase form during heating to 450 °C in the temperature range from 350 °C to 450 °C. Quantitative particle analysis of the sheets after the whole annealing cycle indicate that the alloy deformed 96% shows the highest density of particles in the size range from 50 to 140 nm. In addition, many spherical particles up to 15 nm were observed by transmission electron microscopy, some of them were identified by electron diffraction as Al₃Zr phase with L1₂ crystal structure.     

Evolution behavior of δ phase in Cu12Sn2Ni alloy and the corresponding effects on alloy property

With the increase of tin content in tin bronze, the rise of δ phase made the strength, hardness of tin bronze increase and the ductility decrease sharply, that difficult to process. In this paper, the Cu12Sn2Ni alloy was prepared by centrifugal casting, the microstructure and phase formation before and after heat treatment were observed by x-ray diffraction, scanning electron microscope, and transmission electron microscope. The results showed that the as-cast sample microstructure was composed of equiaxed grains rather than coarse dendrites. centrifugal casting inhibits tin diffusion to form metastable phase β′-Cu_13.7Sn. The as-cast sample had good deformability and its tensile strength and elongation were 381.9 MPa and 12.4 %, respectively, which are higher than the mechanical properties of gravity casting. The tensile strength and elongation of the sample after furnace cooling at 620 °C/8 min are 439.5 MPa and 24.4 %, respectively, the increase was 16.6 % and 85.07 %, compared with the as-cast samples, due to the solid solution strengthening, the second phase strengthening and the homogenization of the microstructure.     

Study on low temperature brazing of magnesium alloy to aluminum alloy using Sn–xZn solders

In this article, a series of Sn–xZn solders are designed for joining Mg/Al dissimilar metals by low temperature brazing. The effect of Zn content in Sn–Zn solders on microstructure evolution and mechanical properties of the different brazed joints are investigated. The experimental results indicate that Sn–30Zn alloy is identified as the optimized solder. Al–Sn–Zn solid solutions form and disperse in the brazing zone of the Mg/Sn–30Zn/Al brazed joint, decreasing the risk of embrittlement of the brazed joint. The average shear strength of Mg/Sn–30Zn/Al brazed joint can reach 70.73 MPa. The joint fractures in the coarse blocky Mg₂Sn intermetallic phases in the center of the brazing zone.