Constitution of the Lead-Tin-Strontium System up to 36 Atomic Percent Sr

The constitution of the Pb-Sn-Sr system from the Pb-Sn binary up to 36 at. pct Sr was determined by differential thermal analysis, metallography, microprobe analysis, and X-ray diffraction. Pb₃Sr forms a continuous series of solid solutions with Sn₃Sr, and is referred to here as the8 phase. Sn₄Sr was the only other intermetallic phase found and is designated here as γ. A eutectic-like trough is formed between (Pb) and δ. It originates at 1.0 at. pct Sr and 324.5 °C (the (Pb)/Pb₃Sr eutectic) and falls monotonically to ~75 at. pct Pb, 24.5 at. pct Sn, and 0.45 at. pct Sr at 283 °C. At 283 °C, a Class II, four-phase reaction occurs: L + δ→ (Pb) + γ. A eutectic-like trough between (Pb) and γ falls from the four-phase plane at 283 °C to the ternary eutectic at ~26 at. pct Pb, ~74 at. pct Sn and <0.3 at. pct Sr at 182 °C. The ternary eutectic reaction is L → (Pb) + (Sn) + γ.     

The columnar to equiaxed transition in tin-lead alloys

Tin-lead alloys were solidified directionally and the position of the columnar to equiaxed transition determined on vertical sections of the ingots. The columnar length was found to increase with decreasing lead concentration and increasing heat transfer coefficient. A mathematical model of the heat flow in the system was used to determine local temperatures, temperature gradients, and velocities in the solidifying alloy. Comparing the position of the columnar to equiaxed transition and local thermal conditions, it was found that the transition occurred when the temperature gradient in the melt at the liquidus temperature was 0.11°C/mm for Sn 10 wt pct Pb, 0.10°C/mm for Sn 5 wt pct Pb, and 0.13°C/mm for Sn 15 wt pct Pb. The position of the transformation was found to be independent of melt superheat for the conditions considered.     

Tin-silver-copper eutectic temperature and composition

A careful investigation of the Sn-Ag-Cu phase diagram near the ternary eutectic composition was undertaken using annealed alloys and differential scanning calorimetry to settle some uncertainties in the eutectic composition. The eutectic composition was found to be 3.5 wt pct Ag, 0.9 wt pct Cu, and the balance Sn. The published eutectic temperature, 217 °C, was confirmed. A value of 217.2 °C was obtained in the present research.     

Thermal analysis of the compositional shift in a transient liquid phase during sintering of a ternary Cu-Sn-Bi powder mixture

In this work, differential scanning calorimetry (DSC) and microstructural analysis were used to study the transient-liquid-phase sintering (TLPS) of a Cu-Sn-Bi powder mixture. During sintering, the liquid phase shifts from a Sn-rich (i.e., ∼90 wt pct Sn) to a Bi-rich (i.e., >78 wt pct Bi) composition. In addition, the presence of Bi creates two melting events: a Sn:Bi eutectic reaction at 139 °C and a reaction involving the melting of (Bi) at 191 °C. The Sn:Bi eutectic melting event was fully transient. The melting event at 191 °C was consistent with the formation of a terminal Bi-rich liquid phase. The rate of compositional shift toward this terminal liquid phase at 260 °C was dependent on the rate of the reaction of the Sn with the Cu powder to form intermetallic phases. For mixtures made with medium and fine Cu powder, the terminal Bi-rich composition was reached after isothermal hold times of 20 and 15 minutes, respectively. This resulted in a new melting point for the mixture of 191 °C. For coarse Cu powders, the rate of the compositional shift toward a Bi-rich composition was much slower. The liquid phase remained at a hypoeutectic Sn-Bi composition estimated at 80 wt pct Sn, while the mixture maintained a melting point of 139 °C.     

Effect of carbon addition on the strength and creep resistance of FeAl alloys

We investigated the effect of carbon content (0.05, 0.12, and 0.2 wt pct C) and heat-treatment temperature (1100°C and 1300°C for 2 hours and air cooled) on the tensile and the creep properties of Fe-24 wt pct Al alloy. The increase of carbon content increased the yield strength without affecting the tensile ductility of the alloys. Carbon content appears to be beneficial in suppressing the hydrogen embrittlement at the grain boundary, because the fracture mode changes from predominantly intergranular failure in a low carbon (0.05 wt pct C) alloy to a predominantly transgranular cleavage failure in a high carbon (0.2 wt pct C) alloy. With the increase of carbon content, the anomalous yield strength peak shifted to a higher temperature possibly due to the interaction between carbon and vacanies. Significant improvements were noted in the tensile and the creep properties of medium (0.12 wt pct C) and high carbon (0.2 wt pct C) alloys after heat treating at 1300°C. The improvements in the tensile and the creep properties were attributed to the synergetic effect of retained vacancies and fine carbide precipitates present in the alloys after 1300°C heat treatment. However, the improved strength and creep properties associated with 1300 °C heat treatment were lost when the heat-treated alloys were further subjected to a vacancy removal annealing. Our results suggest that the retained vacancies present in the FeAl alloys after high-temperature heat treatment and air cooling are effective in improving the creep resistance at 700°C, and yield strength up to 800°C. The creep resistance of the present high carbon FeAl alloy is comparable to or better than several grades commercial heat-resistant Fe-based and Ni-based alloys. The work was carried out when the authors were with Chrysalis Technologies Inc., Richmond, VA. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

Unidirectionally solidified Ti−TiB and Ti−Ti5Si3 eutectic composites

Induction melting and electron beam melting techniques were employed in the production of unidirectionally solidified eutectic composites of Ti-1.7 wt pct B and Ti-8.5 wt pct Si. The grown eutectics were reinforced by 7.7 volume pct of TiB fibers and 31 volume pct of Ti₅Si₃ fibers respectively. Controlled dendritic solidification of a hypereutectic composition of Ti-12 wt pct Si was also accomplished. Tensile, compressive, creep, and stress rupture specimens were cut from the eutectic composites and tested with reinforcing fibers parallel to the load axis. Ti?TiB eutectic was found to have less than the critical volume fraction of fibers necessary for reinforcement, while Ti?Ti₅Si₃ composite attained a compressive yield strength of 275,000 psi and a compressive Young's modulus of 30×10⁸ psi after heat treatment. The 500 and 4000 hr stress rupture properties of Ti?Si eutectic were superior to commercial titanium alloys at 1000° and 1200°F. The minimum creep rate of Ti?Ti₅Si₃ eutectic composite was lower than all other titanium alloys at 1000°F. Tensile, compressive, and creep properties of the Ti-8.5 wt pct Si eutectic are discussed in terms of the current theories of composite behavior.     

Dynamic recrystallization during creep in a 45 Pct Ni-35 pct Fe-20 pct Cr alloy system

A combined 3.5 wt pct Mo + 1.2 wt pct Ti imparted dynamic recrystallization in a 35 wt pct Fe-45 wt pct Ni-20 wt pct Cr alloy system during creep at 700 °C, whereas 3.5 wt pct Mo addition alone did not initiate recrystallization. Dynamic recrystallization substantially increased the creep elongation and produced a high ductile fracture topography in the present alloy system. A subgrain coalescence nucleation mechanism for dynamic recrystallization mechanism was operative during creep. The critical initiation strain requirements are also discussed.     

The solubility and solution behavior of antimony and tin in α-lron and the effects of nickel and chromium additions

The solid solubilities of Sn and Sb in α-Fe have been determined by means of lattice parameter measurements. The Sb solubility ranges from a maximum of 11 wt pct (5.4 at. pct) at 1000°C down to 5.3 wt pct (2.5 at. pet) at 600°C; the Sn solubility ranges from a maximum of 17.7 wt pct (9.2 at. pet) at 900°C to 6.5 wt pct (3.2 at. pet) at 600°C. These solubilities are remarkably large in view of the large sizes of the Sb and Sn atoms in relation to the Fe atom. It was not possible to rationalize the variation of the α-phase lattice parameter with Sb or Sn content from the point of view of atomic diameter or atomic volume. The addition of 1 wt pct Ni lowers the Sb solubility at 600°C from 5.3 to 3.5 wt pct (2.5 to 1.6 at. pet); the effect of Cr on the Sb solubility appears to be small. The addition of 1 wt pct Ni or 1 wt pct Cr lowers the Sn solubility from 6.5 to 5.2 wt pct (3.2 to 2.5 at. pet). It was found that a substantial amount of Ni substitutes for Fe in both the FeSb phase and the Fe₅Sn₃ phase. Formerly Research Fellow, Department of Metallurgy and Materials Science and LRSM, University of Pennsylvania     

Application of MIVM for Pb-Sn System in Vacuum Distillation

The activity coefficients of components of the Pb-Sn binary alloy system were calculated based on the molecular interaction volume model (MIVM). A significant advantage of this model lies in its ability to predict the thermodynamic properties of liquid alloys using only two binary infinite activity coefficients. Based on the MIVM, the vapor-liquid phase equilibrium of the Pb-Sn alloy system in vacuum distillation has been predicted using the activity coefficients of Pb and Sn. The results showed that the content of tin in the vapor phase was 0.008?wt?pct, while in the liquid phase, it was 83?wt?pct at 1173?K (900?°C); it reached 0.022?wt?pct in the vapor phase, while in the liquid phase, it was 92?wt?pct at 1223?K (950?°C); and it was 0.052?wt?pct in the vapor phase, while in the liquid phase, it was 97.88?wt?pct at 1273?K (1000?°C). The content of tin in the vapor phase increased with the distillation temperature increasing. Experimental investigations into the separation of Pb and Sn from the Pb-Sn alloy by vacuum distillation were carried out for the proper interpretation of the results of the model. The influence of the distillation time (20 to 80?minutes) and the distillation temperatures of 1173?K, 1223?K, and 1273?K (900?°C, 950?°C, and 1000?°C) on the separating effect was also studied. The experimental results showed that the content of tin in the vapor phase was 0.085?wt?pct, while in liquid phase, it was 83?wt?pct under the operational conditions of distillation temperature of 1173?K (900?°C), evaporation time of 20?minutes, and chamber pressure of 20?Pa; it reached 0.18?wt?pct in the vapor phase, while in the liquid phase, it was 92?wt?pct at 1223?K (950?°C), 20?minutes, and 20?Pa; and it was 0.35?wt?pct in the vapor phase, while in the liquid phase, it was 97.88?wt?pct at 1273?K (1000?°C), 20?minutes, and 20?Pa. In all these experiments, it was observed that the content of tin in the vapor phase increased as the distillation time and temperatures were increased. The experimental results are in good agreement with the predicted values of the MIVM for the Pb-Sn binary system.     

The Au-In-Pb system:The AuIn2-In-Pb portion

The Au-In-Pb system was investigated in the AuIn-In-Pb portion of the system. Pb-AuIn and Pb-AuIn₂ quasibinary systems were found:the first, consisting of a eutectic and a monotectic reaction and the second, a eutectic with an inflection in the liquidus. The chief source of information was differential thermal analyses and verification by metallography, X-ray diffraction and microprobe analyses. Four isothermal reactions were found as follows: 1) L₁ ? L₂ + AuIn₂ + AuIn at 433°Celsius 2) L₁ ? Pb + AuIn₂ + AuIn at 316°Celsius 3) Pb + L ? α + AuIn₂ at 172°Celsius 4) α₁ + L ? AuIn₂ + In at 159°Celsius. Verification of these events and the isopleth from 50-50 wt pct Pb-In, a typical solder, to ≈ 47 wt pct Au are given.     

Effects of Alloying Elements on Creep Properties of Mg-Gd-Zr Alloys

The minimum creep rate and microstructures of aged samples of Mg-Gd-Zr alloys, with and without alloying additions of Zn and/or Y, have been investigated in the present work. The creep tests were performed at 523 K (250 °C) and under 80 to 120 MPa, and the microstructures before and after creep tests were characterized using scanning electron microscopy, transmission electron microscopy, and the high-angle annular dark-field imaging technique. It is found that dislocation creep predominates in the steady-state creep stage for all alloys. The Mg-2.5Gd-0.1Zr (at. pct) alloy, strengthened by the β′ precipitates, has minimum creep rates in the range 1.0 × 10^?8 to 3.8 × 10^?8 s^?1 under 80 to 120 MPa. The addition of 1.0 at. pct Zn to the Mg-2.5Gd-0.1Zr alloy reduces the 0.2 pct proof strength and increases the minimum creep rate, resulting from the formation of γ′ basal plates at the expense of β′ precipitates. The replacement of 1.0 at. pct Gd by Y in the Mg-2.5Gd-1.0Zn-0.1Zr alloy leads to a substantial reduction in the minimum creep rate, even though it does not cause much change to the 0.2 pct proof strength. The reduced minimum creep rate is attributed to a much lower diffusivity of Y atoms than Gd in the solid magnesium matrix. An increase in the Gd content from Mg-1.5Gd-1.0Y-1.0Zn-0.1Zr to Mg-2.5Gd-1.0Y-1.0Zn-0.1Zr leads to a denser distribution of precipitates, a higher 0.2 pct proof strength, and a further reduction in the minimum creep rate.     

Combined effects of pb and sn additions on the corrosion of Zn-12 Pct Al-1 Pct Cu-0.02 Pct Mg sand cast alloy in wet steam

The effects of varying the Sn content from 0 to 0.01 pct at 0.005 and 0.015 pct Pb on the corrosion of sand-cast Zn-12 pct Al-1 pct Cu-0.02 pct Mg alloy in saturated water vapour at 95°C were investigated. Within the relevant specification limits there was no interaction between Pb and Sn, the combined effect being equivalent to that of Sn alone. The tolerance of the alloy for Sn was so low that the maximum for this impurity was considered to be 0.001 pct. For Pb, 0.01 pct produced substantially the same corrosive attack as 0.001 pct and would be considered as the upper limit for this alloy.     

Combined effects of Pb and Sn additions on the corrosion of Zn-12 pct am pct Cu-0.02 pct Mg sand cast alloy in wet steam

The effects of varying the Sn content from 0 to 0.01 pct at 0.005 and 0.015 pct Pb on the corrosion of sand-cast Zn-12 pct Al-1 pct Cu-0.02 pct Mg alloy in saturated water vapour at 95°C were investigated. Within the relevant specification limits there was no interaction between Pb and Sn, the combined effect being equivalent to that of Sn alone. The tolerance of the alloy for Sn was so low that the maximum for this impurity was considered to be 0.001 pct. For Pb, 0.01 pct produced substantially the same corrosive attack as 0.001 pct and would be considered as the upper limit for this alloy.     

Characterization of room-temperature

Damping of aluminum-indium alloys with up to 16 wt pct indium was studied at fixed frequencies between 0.1 and 5.0 Hz. In the strain amplitude-independent regime, the damping initially decreased with the addition of indium and reached a minimum at 10 wt pct. The frequency-dependent damping was modeled for these alloys using a diffusion-controlled dis- location relaxation model for the high-temperature background, and an expression for multi- phase materials was given. At indium concentrations greater than 10 wt pct, a relaxation peak at 25 °C and 1.0 Hz was observed. This peak was associated with the indium inclusions, and an activation energy of 0.6 ± 0.2 eV was experimentally determined. It was suggested that a critical indium inclusion size is necessary before the relaxation peak becomes appreciable and that this damping mechanism is analogous to that observed for graphite in gray cast irons.     

The Au-In-Pb system:The AuIn2-In-Pb portion

The Au-In-Pb system was investigated in the AuIn-In-Pb portion of the system. Pb-AuIn and Pb-AuIn₂ quasibinary systems were found:the first, consisting of a eutectic and a monotectic reaction and the second, a eutectic with an inflection in the liquidus. The chief source of information was differential thermal analyses and verification by metallography, X-ray diffraction and microprobe analyses. Four isothermal reactions were found as follows: 1) L₁ ⇌ L₂ + AuIn₂ + AuIn at 433°Celsius 2) L₁ ⇌ Pb + AuIn₂ + AuIn at 316°Celsius 3) Pb + L ⇌ α + AuIn₂ at 172°Celsius 4) α₁ + L ⇌ AuIn₂ + In at 159°Celsius. Verification of these events and the isopleth from 50-50 wt pct Pb-In, a typical solder, to ≈ 47 wt pct Au are given. This work was supported by the United States Energy Research and Development Administration.     

The creep behavior of W-5 re

Polycrystalline W-5 wt pct Re was creep-tested in tension from 1500° to 1900°C at stresses from 2500 to 10,000 psi in a vacuum of 10^?8 torr. The steady-state strain rate was directly proportional to stress to the 5.5 power, and the apparent activation energy for creep was 104 kcal per mole. Dislocation substructure that developed during high-temperature deformation was studied by transmission electron microscopy. The total dislocation density was dependent on stress to the 2.1 power and was insensitive to temperature and strain. No subgrains were found in creep tested specimens. The rate-controlling deformation mechanism was ascribed to dislocation climb where the governing diffusion process was dislocation core diffusion. Comparison of creep data for tungsten, W-5 wt pct Re, and W-25 wt pct Re showed that W-5 wt pct Re alloy has significantly better creep properties than the other two materials.     

The influence of cobalt,tantalum, and tungsten on the elevated temperature mechanical properties of single crystal nickel-base superalloys

The influence of composition on the tensile and creep strength of [001] oriented nickel-base superalloy single crystals at temperatures near 1000 °C was investigated. Cobalt, tantalum, and tungsten concentrations were varied according to a matrix of compositions based on the single crystal version of MAR-M247.* For alloys with the baseline refractory metal level of 3 wt pct Ta and 10 wt pct W, decreases in Co level from 10 to 0 wt pct resulted in increased tensile and creep strength. Substitution of 2 wt pct W for 3 wt pct Ta resulted in decreased creep life at high stresses, but improved life at low stresses. Substitution of Ni for Ta caused large reductions in tensile strength and creep resistance, and corresponding increases in ductility. For these alloys with low Ta plus W totals, strength was independent of Co level. The effects of composition on properties were related to the microstructural features of the alloys. In general, high creep strength was associated with high levels ofγ′ volume fraction,γ-γ′ lattice mismatch, and solid solution hardening.     

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.     

Experimental Determination of the Austenite + Liquid Phase Boundaries of the Fe-C System

Differential thermal analysis has been employed to achieve an accurate determination of the solidliquid equilibria for γ-Fe at temperatures between 1147 °C and 1430 °C and compositions in the range 1.5 to 4.42 wt pct C. Several small but significant changes to the established phase diagram have been proposed. In particular, the liquidus in the vicinity of the eutectic has been raised by approximately 15 °C and the temperature of the graphite eutectic lowered to 1150.5 °C. Consequently, the eutectic compositions have been increased to 4.39 and 4.42 wt pct C for the graphite and cementite eutectics, respectively. The possibility of some modification to the γ-solidus has also been suggested, and a revised phase diagram is presented.     

Creep deformation and fracture of a Cr/Mo/V bolting steel containing selected trace-element additions

The article reports the creep behavior, at 565 °C, of 1Cr1Mo0.75V (Ti, B) (Durehete D1055) steel, in each of two grain sizes and doped with individual trace elements such as P, As, and Sn, in comparison to a reference cast of the base material containing 0.08 wt pct Ti. The addition of the trace elements P, As, or Sn (each <0.045 wt pct) appears to produce no significant effect on creep strength or creep crack-growth resistance at 565 °C. The fine-grained material shows low creep strength but notch strengthening, while the coarse-grained material shows higher creep strength and exhibits notch weakening for test times up to 2750 hours. From creep crack-growth tests, it appears that the C* parameter is not appropriate for correlating the creep crack-growth rate under the present test conditions. The parameters K _I or σ _net are found to correlate better, but, from the present data, it is not possible to judge which of these parameters is more appropriate for general use. It is suggested that the presence of Ti in CrMoV steels has an inhibiting effect on trace-element embrittlement.