Abstract : Viewgraphs from presentation on phase relationships and properties of multicomponent Titanium-Silicon based alloys as a fundamental background for the elaboration of high-temperature Titanium materials.

By the methods of DTA, X-ray diffraction, metallography and microprobe analysis, phase equilibria in the Ti-corner (more than 50 at.% Ti) of the Ti–Si–Sn system were studied. The solidus projection and the melting diagram (solidus+liquidus) were constructed. A new ternary compound T of composition Ti5Si1.2–1.6Sn1.8–1.4 was found to form with the crystal structure of W5Si3-type. The ternary eutectic equilibrium L↔〈β-Ti〉+〈Ti5Si3〉+〈Ti3Sn〉 was established to occur at 1460°C with the composition of the invariant point E at ∼77Ti–9Si–14Sn. Microhardness measurements were carried out for the primary grains of the alloys with 5 at.% Si.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Phase relations in the binary Ti–Ga system have been established experimentally by means of a study of alloy samples in the as-cast and annealed states. The alloys were prepared by arc melting. The investigation was carried out using physico–chemical methods of analyses (metallography, X-ray powder diffraction (XRD), differential thermal analysis (DTA) and electron probe microanalysis (EPMA)) over a composition range 0–75 at.% Ga. The refined phase diagram of the Ti–Ga system is presented as a result of this study.

Phase equilibria in Ti-rich corner of the Ti-Si-Sn-Al system were studied using differential thermal analysis, X-ray diffraction, microscopy, and electron microprobe analysis. Projections of solidus and liquidus surfaces, an isothermal section at 1300°C and an isopleth at 9Si-1Sn (at.%) were constructed. It was shown that in the concentration interval studied at the solidus and 1300°C temperatures two two-phase Ti5(Si,Sn,Al)3 + <β-Ti< and Ti5(Si,Sn,Al)3 + <α-Ti< regions are present. The liquidus surface is characterised by the regions of β and Z primary crystallisation, resulting in bivariant L ↔ β + Ti5(Si,Sn,Al)3 eutectic. The character of horizontal and vertical sections is similar to that for the Ti-Si-Al system.

By the methods of X-ray, microscopic and electron microprobe analysis the phase compositions of Ti-rich as-cast Ti-Si-Sn-Al alloys were studied. Projections of the solidus and liquidus surfaces at three Si/Sn ratios (9Si-1Sn, 7Si-3Sn, 5Si-5Sn in at.%) are discussed. The projections are similar to that for the Ti-Si-Al system, and differ in the width of the homogeneity range of the coexisting phases. Microhardness of the constituents (transformed beta-Ti, Ti-5(Si, Sn, Al)(3) (Z) and eutectic (beta + Z) was measured. The results are discussed on the basis of the above projections. Long-term and hot hardness of the alloys were examined. They strongly depend on the relative tin content in the alloys. All the alloys studied show higher strength at elevated temperature than VT-18 alloy. The alloy 75Ti-5Si-5Sn-15Al seems to be prospective in respect to workability.

The structure and mechanical properties of the Ti-Si-Ga and Ti-Al-Ga alloys (long-time and hot hardness, bending strength and bending diflection) with “in situ” and intermetalic structure over the temperature rang of 20-800C are presented. The samples were prepared by melting under an pure argon in arcfurnace from commercially available metals. The correlation between structure and mechanical properties is discussed. Mecanical properties of the alloys investigated in this work are given in comparision with properties of the industrial alloy VT-18 (Ti-7Al-11Zr-0.6Mo-1Nb (mass.%)). The investigated alloys are found to possess considerably more high strength at the medium and elevated temperatures than that of the industrial alloy VT-18, but they have a worse ductility at the room temperatures. Thus gallium can be used as effective element for the improving of the Ti alloys mechanical properties.

The structure and mechanical properties (bending strength and bending deflection) of three alloys with high content of eutectic constituents were investigated. The formation of the structure is considered according to the Ti-Ga-Si phase diagram presented by the sections through the points of compositions of the alloys investigated. The mechanical properties have been determined by means of bending test of the samples by a scheme of the three-point bend in the air in the temperature interval of 20–800°C. The correlation between the structure and mechanical properties is considered.

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti 5 (Si,Ga) 3 and β (Ti-base solid solution) and a narrow one of Ti 2 Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti 5 (Si,Ga) 3 and L↔β+Ti 2 Ga and to the L+Ti 5 (Si,Ga) 3 ↔Ti 2 Ga peritectic reaction. The three-phase region (β+Ti 5 (Si,Ga) 3 +Ti 2 Ga) results from the four-phase eutectic reaction L↔β+Ti 5 (Si,Ga) 3 +Ti 2 Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti 5 Si 3 and of both the elements in Ti are given.

Using differential thermal analysis, X-ray diffraction, microscopy and electron microprobe, phase equilibria in the Ti-rich corner of the Ti-Si-Ge-Al system were studied. Projections of the solidus and liquidus surfaces were constructed. At the solidus temperatures Ti-5(Si,Ge,Al)(3) (Z) phase coexists with <beta-Ti>-based solid solution (beta), resulting in a wide two-phase beta + Z region. The solidus surface has a temperature maximum at 1540 degrees C for 70Ti-5Si-5Ge-20Al. The isopleth at 5 at.% Si + 5 at.% Ge is given. The liquidus surface is characterised by the bivariant eutectic surface L <-> beta + Z. Microhardness of the primary phases, corresponding to the boundaries of the homogeneity ranges, and eutectic mixtures was measured. Partial substitution of silicon for germanium does neither change the character of the phase equilibria nor the temperatures of phase transformations.

Phase equilibria in the Ti–Si–Ga system were investigated by physico-chemical analysis methods (metallography, XRD and EPMA) in a limited composition range of below 31 at.% Ga and above 62 at.% Ti at 1350°C for the first time. The Ti5(Si,Ga)3 phase on the Ti5Si3 compound base exists up to about 25 at% Ga. It coexists with the phases of the Ti–Ga system (β, Ti2Ga and Ti5Ga3) and forms an extended two-phase region β+Ti5(Si,Ga)3, a narrow region Ti2Ga+Ti5(Si,Ga)3, and two three-phase fields, Ti2Ga+Ti5(Si,Ga)3+Ti5Ga3 and β+Ti5(Si,Ga)3+Ti2Ga. The solubility of silicon in Ti2Ga and in Ti-based phases is small.

The microhardness of the constituents (transformed beta-Ti, Z and eutectic (beta + z)) was measured for Ti-rich Ti-Si-Al alloys. It depends both on the aluminium content in the alloy as well as on the character of mutual substitution of the atoms in the phases at the boundaries of the homogeneity ranges. The results are discussed on the basis of the Ti rich part of the Ti-Si-Al phase diagram.

Alloys on the basis of titanium aluminides are very important for modern industry. The influence of β-stabilizer of titanium on the structure and properties of Ti–Al alloys has been studied by many authors. The alloying of titanium by α-stabilizers has almost not been investigated. The purpose of this investigation was to determine the influence of gallium on the structure of Ti–Al based alloys at 50 at.% Ti. The TiAl–TiGa section has been investigated by means of metallographic, electron microprobe, differential thermal and XRD analyses. The alloys were prepared by arc-melting from pure metals with an unconsumable tungsten electrode on a water-cooled copper hearth and studied in both as-cast and annealed state. It is shown that continuous solid solutions γ are formed between the equiatomic phases TiAl and TiGa with the same crystal structure (tetragonal CuAu-type) and similar lattice parameters.

By the methods of differential thermal, X-ray. microscopy and electron microprobe analysis phase equilibria in the Ti-rich corner of the Ti-Si-Al system were studied. Projections of solidus and liquidus surfaces as well as an isothermal section at 1300 degrees C were constructed. It was shown that at the solidus and 1300 degrees C Ti-5(Si,Al)(3) (Z) phase coexists with all of the Ti-Al-based phases, resulting in wide two-phase (beta + Z, alpha + Z, gamma + Z) and narrow three-phase (alpha + beta + Z, alpha + gamma + Z) regions. The last two ones result from invariant four-phase peritectic and eutectic reactions, respectively. Coordinates of peritectic (U-1) and eutectic (E) points were determined to be: U-1-1420 degrees C, similar to 49Ti-4Si-47Al: E-1415 degrees C, 48Ti-4Si-48Al. The solidus surface has its temperature maximum at 1545 degrees C corresponding to the invariant pseudobinary eutectic L <-> beta + Z with eutectic point at 65Ti-8Si-27Al. The isopleth at 10 at.% Si is given. The shape of the Ti-5(Si,Al)(3) homogeneity range is discussed.