Eutectic deformation

Eutectic deformation The composition within a system of two or more components, which on heating under specified conditions, develops sufficient liquid to cause deformation at the minimum temperature. 

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Table 13 is a representative Hst of nickel and cobalt-base eutectics for which mechanical properties data are available. In most eutectics the matrix phase is ductile and the reinforcement is britde or semibritde, but this is not invariably so. The strongest of the aHoys Hsted in Table 13 exhibit ultimate tensile strengths of 1300—1550 MPa. Appreciable ductiHty can be attained in many fibrous eutectics even when the fibers themselves are quite britde. However, some lamellar eutectics, notably y/y —5, reveal Htde plastic deformation prior to fracture. 

C M. Packer. R.H. Johnson, O.D Sherby, "Evidence for the importance of crystal- lo-graphic slip during superplastic deformation of eutectic Zinc - Aluminium". Trans.Met.Soc. AIME242, 2485, 1968... 

Phosphorus appears to have a beneficial effect on the growth rate. At sub-critical temperatures it helps to stabilise the carbide, while at temperatures up to about 900°C the presence of the hard phosphide eutectic network restricts the deformation to which the much more ductile matrix would otherwise be subject. Since the phosphide eutectic melts at about 950°C, irons containing appreciable amounts of this constituent should clearly not be exposed to this temperature. 

At metallographic research of structure melted of sites 2 mechanisms of education of spherical particles of free carbon are revealed. In one of them, sold directly at the deformed graphite the formed particles became covered by a film austenite, that testifies to development abnormal eutectic crystallization. In other sites containing less of carbons and cooled less intensively, eutectic crystallization the education numerous dispersed dendrites austenite preceded. Crystallization of thin layers smelt, placed between branches austenite, occured to complete division of phases, that on an example of other materials was analyzed in job [5], Thus eutectic austenite strated on dendrites superfluous austenite, and the spherical inclusions of free carbon grew in smelt in absence austenite of an environment. Because of high-density graphite-similar precipitates in interdendritic sites the pig-iron is characterized by low mechanical properties. 

It is important to select the components of the substrates with care and particularly to pay attention to the physical parameters they act upon, in particular the vitreous transition temperature (7g ) of the deep-frozen vaccine [20-25,30]. This temperature, also referred to as vitreous eutectic temperature, does indeed play a critical role in the deformation and collapsing of freeze-dried pellets [20,25], and possibly in the loss of infectivity titers. This temperature is dependent on the nature and concentration of the substrate molecules and may be determined in several ways [20,29,35,36]. In industrial practice, the most commonly utilized techniques are differential scanning calorimetry (DSC) as well as resistance and/or dielectric constant measurements. 

The composition of talc is situated close to the eutectic, so that the amount of liquid phase suddenly formed would deform the product. However, in a talc-day mixture, one may choose a proportion of components providing an amount of meJt just suitable for satisfactory sintering (about 30%) and for inhibition of the proto-enstatite-clinoenstatite inversion. This amount corresponds to approximately 10% clay. The composition of such a mix which roughly corresponds to commercial steatite compositions is indicated in Fig. 189 by point A. The diagram then allows equilibrium amounts of the melt to be evaluated for various temperatures, as shown in the diagram in Fig. 190. The shape of curve A indicates that about 30 % of melt is formed rapidly at 1345 °C. This is the temperature of the tridymite-enstatite-cordierite eutectic. The amount of melt increases with temperature, so that the sintering interval is comparatively narrow. 

Th( . fusion t( mp( raturc of the eutectic between AI2O3 and the next compound, Al iOa.SiOa, is 1,810 Xh The use of less refractory clay will lower this point still more and if t h( amount added is at all large, it will be the determining factor in the deformation tind(T th(i cfTect of Imat. Aluminous refractories should therefore contain but... 

The typical dependence of mechanical properties of Ti-Si binary alloys in as-cast and as-deformed states is shown in Fig. 3. It is seen that in as-cast state room temperature plasticity decreases with increase of silicon content, reducing practically to zero at silicon content of 2-3 wt. % then it raises a little at eutectic formation. Unfortunately, our attempts to increase room temperature plasticity in as-cast condition more or less substantially via employing various kinds of heat treatment procedures were not successful. At the same time, using thermo-mechanical treatment (forging at temperature 1050 °C), it was possible to increase plasticity of deformed alloys essentially. 

It was noted above, that the as-cast eutectic alloys of binary Ti-Si system have no appreciable plasticity at room temperature. Alloying with aluminum, zirconium and use of various modifiers has also not allowed appreciable RT plasticity to be obtained. Data on temperature dependence of mechanical properties of deformed alloys of system Ti-3A1 6Zr-(2-6) Si show that, in contrast to as-cast alloys, deformed state with about 2 % Si demonstrate high plasticity ( 4%) reducing to 1.8 % in alloy with 6-wt.% Si. At the same time high-temperature strength of these alloys are practically the same, at 540-560 MPa level (600 °C). In such a way there is no reason to increase silicon content higher 2-wt.% in deformed state. 

In the ternary A1 - Ti - Cr system a large compositional region has been established experimentally, in which the eutectic transformation of a melt into two solid phases is realized L <=> Ll2 + p. This transformation is univariant and occurs in a narrow temperature interval [29], The alloys formed by two cubic phases Ll2 and P possess a more attractive combination of strength and deformation before fracture (see Fig.5) than alloys, in which the decomposition of the P-phase produces the less symmetric intermetallic compounds AlCr2 or TiAlCr. 

The formation of a periodic microstructuie due to eutectic crystallization allows significant enhancement of the strength and deformation before fracture as compared to single-phase material. In this case, high values of the modulus of elasticity are obtained, micro-plastic deformation in bending tests appears, and the eutectic character of alloys ensures their high casting properties. 

Comprehensive structural study of Ti-3Al-5Zr-Si-alloys, as-cast and deformed, confirmed the features found with the binary Ti-Si-system described above. The transition from polygonal to dendritic structure takes place between 2- and 4-wt.% Si. Alloy with 2-wt.% Si fails with intergranular (but ductile) mode whereas alloys with 4- and 6-wt.% fail with mixed mode where dendritic structure may be recognized. In any case, eutectic areas, in contrast to dendrite or polygonal bodies, which are of a-phase failing with cleavage microcracking, fail with ductile mode - with voids coalescence (Fig. 8). Hot plastic deformation transforms the alloys studied into ductile or semi-ductile materials, which fail only with ductile void coalescence mode [1],... 

When the carbon content is greater than about 2 wt% and less than about 5 wt% carbon, the material cannot be heated to give a homogeneous solid solution. At all temperatures below the eutectic temperature of 1148 °C the solid is a mixture of austenite and cementite or ferrite and cementite (FeaC). The effect of this is that the materials are hard, brittle and resist deformation. The material can be cast into the desired shape, and is referred to as cast iron. Commercial cast irons rarely contain much more than about 4.5 wt% carbon. 

A simple BHJ solar cell was fabricated with C6PCH2 and PCBM by spin coating. For a 60 40 wt% blend of C6PCH2 and PCBM, power conversion efficiency (PCE) showed 3.1 % and >70 % of EQE was observed at Q-band region. Studies on the binary mixtures of C6PCH2 and PCBM indicate that the addition of PCBM into C6PCH2 leads to deformation of columnar lattice in the Col mesophase with decrease of isotropization temperature. At ca. 25 mol % of PCBM, one can see the eutectic point where the Col mesophase disappears. This molar ratio implies in the crystal blend that chain-like arrangement of PCBM is positioned... 

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