Increasing Solidification Rate Research Articles

Apparent Viscosity of Al-10mass%Cu Semi-solid Alloys.

Cold model and stirring experiments for Al-10mass%Cu semi-solid alloys by continuous cooling investigated factors affecting viscosity and the relationship between apparent viscosities and stirring conditions of semi-solid alloys.In the cold model experiments, the suspension viscosity of spherical particles was lower than that of irregularly shaped particles, and decreased with the broadening of particle size. These behaviors were explained very well by the equation proposed by Mori-Ototake that defines viscosity as a function of particle shape, the critical fraction of solid for fluidity and the fraction of solid of suspension. The coefficients of this equation were determined by fitting the measured apparent viscosities of Al-10mass%Cu semi-solid alloys using regression method. The measured values were well fitted to the determined curves of this equation. And it has been shown that the determined coefficients varied with solidification rate and shear rate. The apparent viscosity increased with increasing solidification rate and increasing shear rate. The critical fraction of solid for fluidity increased with decreasing solidification rate and increasing shear rate. These results depended on the shapes of suspended particles in semi-solid alloys. In dendritic structures with many arms or network structures, the viscosity was increased and the critical fraction of solid was decreased. The apparent viscosity equation of Al-10mass%Cu semi-solid alloy proposed was:ηa=ηLa{1+(2.41×105C1/3γ−4/3)/[2(1/fs−1/(0.72−8.82C1/3γ−1/3))]} (Pa · s)

A numerical study of thermal interaction of solidification fronts with spherical particles during solidification of metal-matrix composite materials

The potential influence of the presence of copper, iron, mica, TiB 2, graphite and alumina particles dispersed in melts of several matrix metals including aluminum, copper and lead was studied. Specifically the influence of the particles on the solidification fronts during freezing of various matrix melts was numerically studied in order to understand the experimentally observed solidification microsctructures in metal-matrix composites. Irregular geometries of the composite material were mapped into simple rectangles through numerical conformal mapping techniques to analyse the influence of a single particle or a row of particles on a unidirectionally advancing planar solidification front. The particles were assumed to be spherical and located in the center of the cylindrical mold. The study showed that for particles with lower thermal conductivity than the melt, the interface first goes through acceleration as it approaches and encapsulates the front half of the particle, and then it decelerates as it encapsulates the remaining half of the particle. The acceleration and deceleration phenomenon of the interface increases as the thermal conductivity ratio of particle to melt decreases. With low thermal conductivity ratios ( K p K l ⪡ 1 ), the interface is orthogonal to the particle. When the conductivity of the particle is lower than that of the melt, the interface becomes convex facing the particle; this mode would lead to pushing of the particle ahead if it was free to move as has been experimentally observed during solidification of several metal-matrix composites when K p K l ⪢ 1 , the phenomenon is the opposite to that mentioned above and the interface would become concave facing the particle tending to entrap the particle. The temperature vs solidification time plots of two points, one in the particle and the other in melt, show that the particle with a conductivity lower than the matrix is at a temperature higher than the melt; the temperature difference between the two points decreases with increasing solidification rate for all the positions of the interface before it touches the particle. The influences of these temperature differences between the melt and the particles on solidification of composites are discussed.

Effect of magnesium, iron (impurity) and solidification rates on the fracture toughness of Al7Si0.3Mg casting alloy

A dynamic fracture toughness study on Al7Si0.3Mg casting alloy with cadmium trace addition and at varying magnesium and iron levels and solidification rates was carried out using an instrumented impact testing machine. With an increase in magnesium and iron contents, the load-time curves showed a change from sinusoidal to triangular shape. Even at a low iron level of 0.2%, with an increase in magnesium content from 0.32 to 0.65% the total energy absorbed to fracture E T dropped significantly by about 50%, demonstrating the enhancement of the embrittlement effect of magnesium on the alloy. At 0.32% Mg, an increase in iron content from 0.2 to 0.8% significantly decreased E T, the dynamic fracture toughness K d and the critical flaw size a cr. The embrittling effect on the alloy containing a higher level of iron (0.8%) is attributed to the presence of β phase (FeSiAl 5). A distinct brittle fracture seen on the fractured specimens and the ratio P max/ P gy of unity both further confirmed this embrittling effect. Generally, an increase in solidification rate produces higher E T, K d and a cr values, and teh effect was more pronounced at lower magnesium and iron levels than at higher levels.

スラリー状半凝固金属の粘度におよぼす合金成分の影響

Stirring experiments of Al, Cu and Fe semi-solid alloys on continuous cooling were carried out to investigate the effect of chemical composition and stirring conditions on the apparent viscosity of semi-solid metals.The apparent viscosity of every alloy increased with increasing solidification rate and decreasing shear rate and the critical fraction solid for fluidity increased with decreasing solidification rate and increasing shear rate. The equation for apparent viscosity ηa of semi-solid alloy is proposed as follows, ηa=ηLa{1+αρmC1/3γ-4/3/2[1/ƒS-1/(0.72-βC1/3γ-1/3)] }(Pa·s)α=2.03×102(X/100)1/3β=19.0(X/100)1/3where ηLa is the apparent viscosity of liquid, ρm is the density of alloy, C is solidification rate, γ is shear rate and ƒS is fraction solid. The α, β values depended on chemical composition of alloys and became larger with increasing solute content X. These results were explained by the shape parameter value of suspended particles and the trapped liquid volume in suspended particles in semi-solid metals.

Numerical simulation of a solidifying Pb-Sn alloy: The effects of cooling rate on thermosolutal convection and macrosegregation

Numerical simulations of a binary metal alloy (Pb-Sn) undergoing solidification phase change are performed using a continuum model for conservation of total mass, momentum, energy, and species. The system is contained in an axisymmetric, annular mold which is cooled along its outer vertical wall. Results show that thermosolutal convection in the melt and mushy zones is strongly coupled and that macrosegregation is reduced with increased cooling rate. For low cooling rates, solutally induced convection in the mushy zone favors the development of channels, which subsequently spawn macrosegregation in the form of A-segregates. With increasing solidification rate, however, thermosolutal interactions in the melt contribute to reducing the formation of channels and A-segregates.

The potential of rapid solidification in oxide-dispersion-strengthened copper alloy development

The feasibility of producing yttria (Y 2O 3)-dispersion-strengthened copper by internal oxidation of rapidly solidified CuY alloys was investigated. Alloys containing about 1 at.% Y were prepared via conventional solidification, supersonic gas atomization and splat-quenching techniques. The spacing of the CuY intermetallic phase was found to depend on the solidification velocity as λV″ = constant, where n increased from about 0.4 to about 0.6 as the solidification rate increases. Y 2O 3 particles were produced by the oxidation of the yttrium present in the intermetallic phase, which was tentatively identified as Cu 7Y. Specimens internally oxidized at 873 or 1123 K revealed that a relatively uniform distribution of fine Y 2O 3 dispersoids was produced in the splat-quenched material. On the contrary, the Y 2O 3 particles in the conventionally cast and gas-atomized powders were largely confined to the prior interdendritic segregate, presumably because of insufficient refinement in the scale of the cast microstructure. Selected-area diffraction pattern analysis of Y 2O 3 particles in the splats indicated an {100} Y 2O 3 |{100} Cu and 〈100〉 Y 2O 3 |〈100〉 Cu orientation relationship with the copper matrix.

Directionally solidified Bi2O3-6Bi2O3 � SiO2 eutectic

The phase diagrams of the systems Bi2O3-6Bi2O3 · SiO2 and (Bi2O3)0.85 (Nb2O5)0.15-6Bi2O3 · SiO2 were determined by a quenching method. Melts of the eutectic and neighbouring compositions in these systems were unidirectionally solidified at various rates of 0.5 to 10 mm h−1 under a temperature gradient of 100° C cm−1. At any solidification rate examined, the ingot was of irregular structure in the former system and was of well-aligned regular structure in the latter system at the eutectic composition and those deviated from that by 10 mol%. In the latter ingots, fibrousδ-(Bi2O3)0.85 (Nb2O5)0.15 crystals were embedded in parallel and with a uniform spacing in a matrix ofγ-6Bi2O3 · SiO2 crystal. The diameter,d, of the fibrous crystals and the interfibre spacingλ decreased from 3.8 to 0.7 μm and 10 to 1.9 μm, respectively, with increasing solidification rate,R, in the range 0.5 to 10 mm h−1, following the relationsd= 2.5R−1/2 andλ=6.9R−1/2. The volume fraction of the fibrous crystals increased from 0.14 to 0.23 with an increase in the (Bi2O3)0.85 (Nb2O5)0.15 content of the melt from 46 to 66 mol%. The elongation direction 〈110〉 of the fibrous crystal was parallel to the 〈111〉 direction of the matrix crystal. The difference in the microstructure of the ingots between the systems is discussed in terms of the solidification process.

Effect of solidification conditions on the solidification sequence of austenitic chromium‐nickel stainless steels

Unlike the well‐known effect of alloy elements in promoting the ferritic or austenitic solidification of stainless and acid‐resisting chromium‐nickel steels, kinetic effects have as yet not been so widely looked into.For this reason, the impact of the solidification rate on the ratio of the amounts of ferritic and austenitic liquid solidification was investigated for the steels of grades X8CrNiTi18.10 and X8CrNiMoTi18.11. A microanalysis for the determination of the primary ferrite content of samples taken from ingots of different size and at different distances from the ingot surface for a total of 161 heats revealed the following: – Increasing solidification rate causes the primary ferrite content produced during solidification to rise for steels with peritectic solidification sequence due to the resultant approach of the distribution coefficient to unity. – Increasing solidification rate causes the austenite content to rise for steels with a primary simultaneous crystallization of austenite and ferrite due to a low total segregation in case of austenite crystallization as compared with ferrite crystallization. – The effect of an elevated solidification rate is qualitatively equivalent to a shift of the saturation lines of the three‐phase space l+δ+γ in the Fe—Ni—Cr ternary system for liquid and γ‐crystals in the direction S with the two saturation lines approaching each other. Hence, contrary to what is expected according to the equilibrium diagram of Schürmann and Brauckmann, austenitic Cr—Ni steels solidify primarily in peritectic mode and, in the area of the line of the double‐saturated liquid, through a primary simultaneous crystallization of austenite and ferrite. – The boundary composition between primary ferritic and primary austenitic crystallization changes with an increase in cooling rate by seven orders of magnitude from 1.25 to 1.70 as expressed in the ratio of the Cr—Ni equivalents according to Hammar and Svensson.

Boron segregation at grain boundaries in rapidly solidified Ni 3Al

The work reported here was performed to test the suggestion that the suppression of beneficial boron segregation to grain boundaries as a result of the increasing quench rate was responsible for the ductile-to-brittle transition on increasing solidification rate. Auger analysis and scanning electron microscopy of the fractured surfaces were the primary methods used. Auger spectroscopy results show along with previous work on bulk materials, that the critical concentration for strengthening grain boundaries is between 7 to 11 at. % B.

Submicron eutectic thin-film structure

Pb-Sn, Cd-Pb, and Al-Al2Cu eutectic thin films were directionally solidified at rates between 0.0015 and 0.15 cm/sec with both a lamp and a laser heat source to fabricate fault-free submicron periodic structures. A transition from lamellar to cellular structures with increasing solidification rate was observed with a thermal gradient of 200 °C/cm applied with the lamp heat source. Cells did not form with the increased thermal gradient produced by the laser heat source, 8000 °C/cm. Spacings as fine as 0.1 μ were observed in the Cd-Pb eutectic. A maximum theoretical growth rate was estimated which corresponds to a spacing of 80 Å.

The solidification and mechanical properties of chill-cast AI-AI3IMi and AI-AI2Cu eutectic alloys

This paper describes the effect of chill-casting on the solidification behaviour and mechanical properties of the AI-AI3Ni and AI-AI2Cu eutectic alloys. Cellular microstructures were obtained by casting the eutectic alloys into preheated split-steel moulds mounted on either a water-cooled or plain copper chill, to promote growth along the length of the ingot and not radially from the mould wall. This produced the required cellular microstructure with good alignment of AI3Ni fibres or AI2Cu lamellae within the cells, with an interfibre/interlamellar spacing of ∼ 1 μm. The experimental solidification results showed an increase in solidification rate with increasing distance from the chill associated with a decrease in interfibre/interlamellar spacing along the length of the solidifying ingot. There were no significant variations in the room-temperature tensile properties of the two chill-cast aluminium based eutectic alloys for the various casting conditions. Variations in solidification rate along the ingots for the different chill-casting conditions were not sufficient to affect the stress-strain behaviour of the chill-cast alloys. The room-temperature tensile behaviour of the chill-cast AI-AI3Ni eutectic alloy was very similar to, and that of the AI-AI2Cu eutectic alloy significantly different from, those obtained by Lawson and Kerr. The ultimate tensile strengths of the chill-cast eutectic alloys were not as high as those of the corresponding unidirectionally-solidified eutectic alloys prepared at a slow and constant solidification rate although the reasons for this were different for the two alloys. The ultimate tensile strength of the chill-cast AI-AI3Ni eutectic alloy was found to be in reasonable agreement with that expected from the rule of mixtures for discontinuous fibre reinforcement.

The Growth of Submicron Eutectic Thin Film Structures

AbstractAs the minimum dimension of electronic circuits is reduced below one micron, there has been increased interest in developing techniques for fabricating submicron structures. Pb-Sn, Cd-Pb and Al-Al 2Cu eutectic thin films were directionally solidified at rates between .0015 cm/sec and .15 cm/sec with both a lamp and a laser heat source to fabricate fault free submicron periodic structures. A transition from lamellar to cellular structures with increasing solidification rate was observed with a thermal gradient of 200°C/cm applied with the lamp heat source. Cells did not form with the increased thermal gradient produced by the laser heat source, 8000° C/cm. Spacings as fine as .1 micron were observed in the Cd-Pb eutectic. A maximum theoretical growth rate was estimated which corresponds to a spacing of 80A.

Directional solidification of SiC-B 4C eutectic: Growth and some properties

Directionally solidified SiC-B 4C eutectic formed lamellar microstructures with no colonies if the solidification rate (R) was below 2cm/hr. It was determined that 〈001〉 of B 4C and 〈111〉 of SiC were parallel to the eutectic growth direction, and that the interlamellar spacing was proportional to the inverse square root of solidification rate. The Knoop hardness increased with the increasing solidification rate. The minimum wear was found with compositions close to eutectic. At R ≈ 9cm/hr the most wear resistant specimens were obtained. SiC-B 4C eutectic ingot solidified at approximately 9cm/hr had considerably better wear resistance than solidified B 4C or hot pressed SiC.

On the mechanism of lamellar spacing adjustment in eutectic alloys

Well controlled undirectional solidification experiments with continous increased rate were performed for eutectic alloys in the systems Ag-Cu, Al-Zn, Al-Cu and Al-Ni. In the Ag-Cu and Al-Zn alloys it was observed that discontinous changes in the lamellar spacing occured at low solidification rates. At high solidification rates such discontinuities could not be observed. Anyway the lamellar spacing always larger than observed at constant rate experiments. In Al-Cu alloys discontinous changes in the lamellar spacing with increasing solidification rate were also observed. However, after each change the lamellar spacing increased gradually up to a lamellar distance of 20% lower than before the abrupt decrease. All-Ni eutectic alloys gives a rod like eutectic structure. In this alloy no discontinous changes could be observed. A theoretical analyses of the observation based on well known theoretical models are discussed.

Effect of superheating on structure of some aluminum alloys

The effect of increasing pouring temperatures was investigated on several aluminum alloys, which were frozen at various rates ranging from less than 0.01°C/s (furnace cooled) to more than 20°C/s (thin metal mold). It was found that the higher the superheat, the faster the solidification rate. Interdendritic spacing, size of primary and eutectic constituents and grain size decrease with the increasing solidification rate that results from increased superheating, in spite of the fact that the actual freezing time increases. Indications are that aluminum alloys contain a nucleant that acts at zero undercooking and that superheating up to 500°C above the freezing point reduced the size and possibly the number of nucleating particles, but does not eliminate them completely.

急冷凝固したAl-1∼5%Mn合金の機械的性質と組織分布

By rapid quenching of Al-1∼5%Mn alloys from the liquid state, an equilibrium structure, a structure formed by movement of the eutectic point, an incompletely super-saturated solid solution and a completely solid solution were obtained successively with increase in solidification rate. Micro-Vickers hardness measurement, tensile test and thermal analysis were used to examine the relations between the mechanical properties and these structures. The result obtained were as follows:(1) With increase in solidification rate (V) (or change of solidified structures), Micro-Vickers hardness (Hv), ultimate tensile strength (σB) and elongation (δ) rose according to the relation of Y=AV+B or Y=C (Y: σB, Hv, δ, V: solidification rate, A, B, C: constant).(2) The ranges of solidification rate at which each structure was formed, were shown by a diagram for Al-1∼5%Mn alloys.(3) The constitution diagrams to show the relations of average solidification rate—thickness distance and Mn content—thickness distance were obtained.

一方向凝固させたＡｌ‐４％Ｃｕ合金中に生成される気孔について

Conditions for the pore formation in an Al-4%Cu alloy were examined by the unidirectional solidification technique. Gas pressure in pores and negative pressure due to solidification contraction were calculated from the gas content, and the quantity of pores with the metallographic method. Main results obtained were as follows:(1) Gas pressure in pores was 2 to 5 atms at the pore formation temperature.(2) Initial gas content required for gas pore formation increased with an increase in solidification rate. When there was not enough gas for pore formation, a shrinkage pore was formed.(3) When the solidification rates were 3, 6, 12, and 60cm/hr, the negative pressures were 1, 1.5, 2 and 5 atms respectively.(4) The critical gas content for pore formation was approximately 0.15cc/100g.

The structure and mechanical behavior of the Mg-Mg2Ni eutectic composite

The structure and mechanical behavior of the unidirectionally-solidified Mg-Mg2Ni eutectic have been studied over a range of solidification rates frorm 3 to 250 cm per hr. The yield and ultimate strengths of the composite tend to increase with increasing solidification rate and microstructural fineness. The mechanical behavior, however, is also strongly influenced by changes in eutectic crystallography and matrix deformation mode which occur with increasing solidification rate. When yielding of the matrix is controlled by slip, the effect of solidifica tion rate on composite yield strength can be quantitatively accounted for by an analysis based on a simple dislocation model. Under some conditions, however, yielding of the ma trix occurs by\(\left\{ {11\bar 24} \right\}\) twinning, resulting in markedly different mechanical properties. When solidified at 250 cm per hr the Mg-Mg2Ni eutectic has higher yield and ultimate strengths than the strongest commercial magnesium alloys, but its poor ductility and corrosion resistance will severely limit its use as a high performance engineering material.

Mechanical behavior of rapidly solidified Al-Al2Cu and Al-Al3Ni composites

The eutectic alloys Al-Al2Cu and Al-Al3Ni have been unidirectionally solidified at rates from 1.05 to 6.80 in, per min by a semicontinuous casting technique, and then tested in tension at room temperature. In both alloys the flow stress and ultimate tensile strength increased with increasing solidification rate, except for the highest solidification rate. The increases in matrix work-hardening rate with solidification rate were too great to be accounted for by dislocation pileup mechanisms, but were found to correlate with elastic constraint effects of the matrix aluminum phase by the reinforcing phases. In the Al-Al2Cu eutectic the strength of the Al2Cu platelets increased as the platelet width decreased with increasing growth rate. Misalignment of the composite caused by either a cellular or a macroscopically concave solid-liquid interface resulted in a decrease in the ultimate strength, especially in the rod-like Al-Al3Ni alloy. This has been related to the fracture behavior of the composites. The very low fracture toughness of the lamellar Al-Al2Cu eutectic is consistent with models of composite materials, and seriously limits the alloy’s usefulness for engineering applications.

The effect of solidification rate on structure and high-temperature strength of the eutectic NiAl-Cr

The eutectic NiAl-Cr, consisting of chromium rods in a NiAl matrix, was directionally solidified at rates varying from 1/4 to 30 in. per hr. The inter-rod spacing and elevated temperature tensile properties were measured and the structure determined for each solidification rate. The spacing, λ, obeyed the relation λ2V= Constant, whereV is the solidification rate. AtV greater than 1 in. per hr, a cell or colony structure formed and the cell size decreased with increasing solidification rate. At 600°C, the tensile strength increased substantially with decreasing inter-rod spacing, reaching 100,000 psi at the highestV. At 800° and 1000°C, the strength first increased then decreased at the highest solidification rates reaching maximum strengths of 63,000 psi and 47,000 psi, respectively. At 1200°C, the strength decreased slightly with increasing solidification rate. Fracture occurred by shear along grain boundaries and cell walls. The decreased strength at the highest solidification rates may be related to the increased cell boundary area.