Ti-Mo System Research Articles

Crystallographic Features of α"-Martensite in Titanium Alloys

Equilibrium volume fractions of twins (α 0 ) and habit plane orientation (n 0 ) of the orthorhombic α-manensite in titanium alloys with β-stabilizing elements were determined by minimization of the elastic strain energy. Calculations were made in the basis of one of the twinned domains. It was shown that these parameters are varying considerably depending on the solute element content. For Ti-Ta and Ti-Mo systems habit plane rotated from {434} β to {433} β pole and α 0 grew with Ta (Mo) content increase. For Ti-20at%Ta α 0 reached the value of 1, i.e. martensite plate became monodomain. For Ti-Mo system monodomain state was not achieved. For Ti-Nb system converse concentrational dependence of martensite parameters was obtained : α 0 decreased with Nb content increase, and n showed a rotation from {434} β pole in a direction opposite to that for Ti-Ta and Ti-Mo systems.

Application of first-principles methods to binary and ternary alloy phase diagram predictions

First-principles energy calculations, using the LMTO ASA method, have been performed for seven binary alloys (Ti-Al, Ti-Mo, Ti-Nb, Ti-W, Al-Mo, Al-Nb and Al-W). For the Ti-Mo system, our results lead to stability of the B32 ordered compounds, in contradiction with the experimental phase diagrams, which display a miscibility gap for the BCC lattice. Meanwhile, recent unpublished neutron diffraction measurements have been performed at a high temperature; they indicate the presence of a short-range order by a ( 1/2 1/2 1/2 ) q-vector, in perfect agreement with the stability of B32 at low temperatures. Secondly, we proceed to a cluster expansion, using the Connolly-Williams inversion scheme and the formation energies of a finite set of ordered configurations. We obtain, for each alloy, a set of cluster interactions and we test the transferability of this set to the formation energies of other ordered compounds. Finally, in order to calculate a ternary phase diagram (isotherm), the Connolly-Williams inversion scheme has been applied to a ternary formation energy. Then, we have calculated an isotherm of the Ti-Al-Nb system and found perfect agreement with the isotherm already calculated in an earlier publications, using a different approach.

メカニカルアロイングによるTi-Mo系合金化過程と不純物Feの混入

メカニカルアロイングによるTi-Mo系合金化過程と不純物Feの混入

The stable and metastable Ti-Nb phase diagrams

The phase transformations which occur in the Ti-Nb binary alloy system have been discussed in two recent papers. The phase relationships were investigated by varying alloy composition and thermal history. In this paper, these results are summarized in complete and thermodynamically consistent calculations of the stable and metastable phase diagrams. The calculations of the metastable equilibria are relevant to the Ti-V and Ti-Mo systems, as well as to several other titanium and zirconium-based transition metal alloy systems.

The decomposition of Ti-Mo alloy martensites by nucleation and growth and spinodal mechanisms

A detailed study has been made of the precipitation reactions which occur when martensites of the Ti-Mo system are aged. In hexagonal α′martensite, produced in alloys containing up to 4 wt% Mo, both heterogeneous and homogeneous precipitation can occur by a nucleation and growth mechanism. The homogeneous precipitation produces significant age hardening. Although six precipitate variants are formed in the hexagonal α′plates, domains containing only two mutually accommodating variants occur in homogeneously nucleated dispersions: these exhibit a highly regular interparticle spacing. In alloys containing more than 4 wt% Mo a spinodal decomposition reaction takes place which is conditional upon the formation of the orthorhombic α′ form of martensite. Rapid age hardening results from this reaction which produces only two variants of precipitate. The habit planes of the two variants rotate during ageing. This is believed to be due to the change in the lattice parameters of the two coherent orthorhombic phases and associated changes in directions of minimum elastic modulus. Ageing above a critical temperature results in reversion of the α′ phase to β which subsequently decomposes to the equilibrium α and β phases.

Martensitic transformations in Ti-Mo alloys

A detailed investigation has been made of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from theβ-phase region. With increase in molybdenum content, the martensite structure changes from hexagonal (α′) to orthorhombic (α″) at ∼4 wt% Mo, and at 10 wt% Mo, the structure is completely retained β. For alloy compositions <4 wt% Mo, there is a diffusional component in the transformation of the β-phase at the quench rates employed. There is a transition, with increase in molybdenum content, in morphology (from massive to acicular) and in substructure (from dislocations to twins). However, the transitions in crystallography, morphology and sub-structure are not directly related to one another except for an abrupt loss of dislocation substructure at theα′/α″ transition. The α toα″ crystallographic transition has the characteristics of a second order transformation, and evidence has been obtained of the existence of a spinodal within the metastable orthorhombic system. The orthorhombic martensites of Ti-6 and 8 wt% Mo decompose during quenching producing a fine modulated structure within the martensite plates, consistent with a proposed spinodal mode of decomposition.

Manufacture and properties of sintered titanium alloyed with Mo, Zr, and Nb

1. Increasing the degree of alloying raises the pressure necessary for the extrusion of sintered Ti blanks. 2. Alloying with Mo, Zr, and Nb markedly strengthens sintered titanium parts, the addition of 9% Mo more than doubling their strength (and slightly decreasing their ductility). 3. The microstructure of sintered alloys of the Ti-Zr system (1–9%Zr) is typical of single-phase castα alloys and that of alloys of the Ti-Mo (1–9% Mo) and Ti-Nb (1–9% Nb) systems, of two-phaseα +β alloys. 4. To obtain a homogeneous structure, high-temperature annealing should be performed after hot extrusion.

Superconducting Transition Temperature, Lattice Instability, and Electron-to-Atom Ratio in Transition-Metal Binary Solid Solutions

In a series of transition-metal binary alloys, as the average electron-to-atom ratio $\mathfrak{z}$ decreases from 6.0 to 4.0, the measured electronic-specific-heat coefficient $\ensuremath{\gamma}$, and with it the average Fermi density of states $n({E}_{F})$ rises to a maximum near $\mathfrak{z}=4.4$. From an analysis of the coupled results of low-temperature calorimetric and magnetic susceptibility measurements it has been shown in a previous paper that, at least for the Ti-Mo system, the maximum in average $n({E}_{F})$ was induced through the influence of submicroscopic metallurgical inhomogeneities (clustering and second-phase precipitation) present in the as-quenched $\mathfrak{z}\ensuremath{\lesssim}4.3$ material, and was not a property of the (hypothetical) single-phase bcc alloy. In addition, it was demonstrated that were it not for this precipitation, the effects of which became increasingly noticeable as $\mathfrak{z}$ decreased below about 4.3, $n({E}_{F})$ would otherwise increase monotonically as $\mathfrak{z}$ decreased from 6.0 to 4.0. In this paper, which is an extension of that work, the superconducting behavior of Ti-Mo is explored. The results of calorimetric measurements yield both a superconducting transition temperature ${T}_{c}$ and a Debye temperature ${\ensuremath{\Theta}}_{D}$ which (through the elastic constants ${c}_{\mathrm{ij}}$) may be related to lattice stability. Again, if we postulate the existence of single-phase bcc Ti-Mo alloys, in which precipitation for $\mathfrak{z}\ensuremath{\lesssim}4.3$ has been inhibited, a semiquantitative argument shows that ${T}_{c}$ should also increase monotonically with decreasing $\mathfrak{z}$. As a generalization of this result, it is suggested that in the well-known double-humped curve of ${T}_{c}$ vs $\mathfrak{z}$ for transition-metal binary alloys the local maximum near $\mathfrak{z}=4.4$ is induced (or at least strongly contributed to) by microstructural effects, rather than being a property of single-phase bcc alloys. Finally, a connection is made between the superconducting behaviors of transition-metal binary alloys, which might be regarded as low-perturbation systems, and the tightly bound transition-metal-nontransition-metal intermetallic compounds, for which the very opposite is true. The coupling parameter is "lattice stability" which decreases with decreasing $\mathfrak{z}$, in the range under consideration, for both the alloys as well as the compounds. The increase of ${T}_{c}$ with decreasing $\mathfrak{z}$ generally terminates at the edge of the regime of phase stability (e.g., at the low-concentration limit of the equilibrium single-phase bcc field, in the case of Ti-Mo alloys).

Superconducting Properties of bcc Alloys in the Nb–Ti–Mo System

Superconducting Properties of bcc Alloys in the Nb–Ti–Mo System