Mechanical Properties of Ti-Cr-Sn-Zr Alloys with Low Young’s Modulus

This work investigates the mechanical properties of Ti-Cr-Sn-Zr alloys containing large amount of Zr. We focuses on the effect of the varying alloy composition on the microstructure, the Young’s modulus, the deformation mechanism and the deformation behavior. Ti-Cr-Sn-Zr alloys show much low Young’s modulus in the narrow composition range for Cr but wide for Zr. The Young’s modulus of Ti-2Cr-6Sn-xZr (x=5~60mass%) alloy decreases with increasing Zr and shows the minimum value of 41GPa in Ti-2Cr-6Sn-45Zr alloy. The alloys with low Young’s modulus consist in meta-stable β phase. The composition of the meta-stable β phase is close to the transition where the quenched microstructure transits from martensite to meta-stable β phase. Ti-2Cr-6Sn-45Zr alloy with lowest Young’s modulus show the super-elastic property.

Composition Range of Morphotropic Phase Boundary and Electrical Properties of NBT-BT System

(Na0.5Bi0.5)TiO3 (BNT) system ceramics are considered to be an excellent candidate for leadfree piezoelectric ceramics. In this paper, (1–x)Na0.5Bi0.5TiO3-xBaTiO3 (x = 0.03 ~ 0.10) was synthesized by conventional mixed-oxide technique. The powders were calcined at 950oC for 2 h and the pressed disks were sintered at 1145oC for 2 h in air atmosphere. The phase structure was investigated by X-ray diffraction technique (XRD). It is revealed that the morphotropic phase boundary (MPB) lies in a narrow composition range of x=0.05–0.08 but not a unique composition (x = 0.055 or 0.06) as shown before [1-4]. The microstructures of the ceramics were investigated by scanning electron microscopic. In addition, the piezoelectric and dielectric properties of this system were also investigated. It was indicated that both the piezoelectric and dielectric properties are better with the compositions lie near the tetragonal phase within the MPB than that whose compositions lie near the rhombohedral phase.

An isotropic glass phase in Al-Fe-Si formed by a first order transition

ABSTRACTWe present evidence of the nucleation and growth of a metallic glass phase from the melt, as if by a first-order transition. Microstructures of a number of rapidly solidified Al-Fe-Si alloys demonstrate that this glassy phase, which we term q-glass, is not a kinetically frozen liquid. It is the first phase to form from the melt as isolated nuclei that grow and deplete the melt of iron and silicon. From the nucleation behavior and the compositional partitioning, we infer an interface between the q-glass and the melt, and that, in a narrow composition range, the q-glass has a lower energy and entropy (is more ordered) than a conventional glass.

High-Ti magnetite in some fine-grained carbonatites and the magmatic implications

Magnetite is present in most carbonatites, and in the most abundant and best-known form of carbonatite, coarse-grained intrusions, it typically falls in a narrow composition range close to Fe3O4. A fine-grained carbonatite from Zambia contains magnetites with an extraordinary array of compositions (from 18–1% TiO2, 10–2% Al2O3, and 16–4% MgO) outranging previously-reported examples. Zoning trends are from high TiO2 to high Al2O3 and MgO. No signs of exsolution are seen. Checks on similar rocks from Germany, Uganda and Tanzania reveal magnetites with comparable compositions, ranges, and zoning. Magnetites from alkaline and alkaline ultramafic silicate volcanic rocks cover only parts of this array. Magnetite analyses from some other fine-grained carbonatites, reported in the literature, fall in the same composition field, suggesting that this form of carbonatite may be distinctive. The chemistry and zoning would be consonant with rapid high-temperature crystallization in the carbonatite melts, with the lack of exsolution pointing to fast quenching: this contrasts with coarse-grained intrusive carbonatites, in which the magnetite compositions are attributed to slow cooling, with final equilibration at low temperature. In some complexes, both forms of carbonatite, with their different magnetite compositions, are represented.

Mechanisms of Layer Structure Formation in Peritectic Alloys

ABSTRACTThe mechanisms of layer structure formation in the two phase region of peritectic systems are discussed. Under diffusive growth conditions, a banded structure is predicted within a narrow composition range in the hypoperitectic composition. Experimental studies show the formation of an oscillatory structure in the hyperperitectic region. It is shown that this structure is induced by convection in the melt, and it is a novel structure in which a large single tree-like structure of primary phase is surrounded by the peritectic phase. Basic ideas of convection that lead to this tree-like morphology are described.

Thermoelasticity and Stress Induced Crystallization of EPDM Elastomers

The thermoelastic behavior of various EPDM rubbers has been investigated by performing stress-temperature measurements at different stretching ratios in order to determine their thermodynamic properties and the occurrence of stress induced crystallization. A broad range of terpolymer compositions was investigated and the regularity of monomer sequence distribution was also taken into account. It has been found that statistical terpolymers, like the commercial ones, are generally amorphous and hardly crystallize under stretching for propylene contents higher than 40% by weight. Below this level it is possible to obtain, in a narrow composition range, amorphous polymers that can crystallize under stretching, provided that their monomer sequence distribution is regular enough. The influence of this microstructural parameter has been studied by testing a 3/1 ethylene/propylene model copolymer, obtained by hydrogenation of a sample of poly-3-methyloctenamer. Studying the influence of stretching ratio on crystallization temperature of standard EPDM rubbers, it has been noticed that crystallization occurs at low elongation, which might be related to the presence of “nuclei” in the undeformed state.

Binary and ternary interstitial alloys - II. The iron-carbon-nitrogen system

Chemical and X-ray investigation of the reaction of carbon monoxide with iron nitrides and of the reaction of ammonia with iron carbides discloses the existence of iron carbonitrides— a series of new ternary interstitial alloys containing iron, carbon and nitrogen. ζ-phase carbonitrides, with structures similar to those of ζ-iron nitrides, have a range of homogeneity extending approximately from Fe 8 N 4 to Fe 8 C 3 N. The latter is isomorphous with Fe 2 N. Є-phase carbonitrides, which are isomorphous with Є-iron nitrides, have a composition range of approximately 25 to 33 atomic % nitrogen plus carbon, i.e. from Fe 3 X to Fe 2 X , in which the higher carbon concentration limit is not less than 16 atomic %. Probable phase fields for part of the iron-carbon-nitrogen system are given on a ternary diagram. Prolonged reaction of carbon monoxide with iron nitrides results in complete elimination of nitrogen. Below 500° C the product is a carbide of iron, now called iron percarbide, the narrow composition range of which includes Fe 20 C 9 . Above 500° C the product of the same reaction is cementite.