Reaction Sintering Of Powders Research Articles

Physical properties of TiMn2 and interaction with refractory TiN (system Ti-Mn-N)

Mechanical (elastic) properties have been derived for polycristalline TiMn2 from micro-indentation and thermal expansion measurements. With a room temperature (RT) Vicker's hardness of ∼11 GPa, TiMn2 is a rather hard intermetallic material. The elastic modulus is E = 217 ± 4 GPa at RT. Physical properties (from 1.8 K to 300 K) including specific heat, electrical resistivity and magnetic susceptibility reveal temperature independent paramagnetism and metallic conductivity consistent with a Bloch-Grüneisen behavior.Based on experimental data (X-ray powder diffraction, metallography, SEM and EMPA on 30 alloys prepared by various methods employing arc melting, powder reaction sintering in closed crucibles as well as nitriding binary master alloys in 105 Pa nitrogen gas) phase relations in the ternary system Ti-Mn-N have been established and calculated for the isothermal section at 900 °C. The thermodynamic modelling relies on existing thermodynamic assessments of the Mn-N and Ti-N binary systems and on our recent modelling of the Ti-Mn system, which is characterized by a significantly higher thermodynamic stability of the C14-type Laves phase Ti1-xMn2+x than hitherto assumed in the literature. It is this higher stability, which is consistent with the experimental phase triangulation in Ti-Mn-N: as the most important consequence of the higher stability of Ti1-xMn2+x, compatibility exists between the only two congruently melting compounds Ti1-xMn2+x and TiN1-x. The high melting refractory solution TiN1-x dominates the liquidus surface pushing all monovariant melting lines close to the Ti-Mn binary.

The ternary system cerium–iridium–silicon

Phase relations in the ternary system Ce–Ir–Si have been established and the isothermal section at 950 °C was constructed based on X-ray powder diffraction, scanning electron microscopy, and electron probe microanalysis techniques on 83 alloys, which were prepared by arc melting under argon or powder reaction sintering. Among the 15 ternary compounds observed at 950 °C 8 phases have been reported earlier. Based on powder X-ray diffraction data the crystal structures for 6 new ternary phases were assigned to known structure types: τ6 – Ce3IrSi3 (Ta3B4-type), τ8 – Ce3Ir4Si4 (U3Ni4Si4-type), τ10 – Ce6Ir30Si19 (Sc6Co30Si19-type), τ12 – Ce2Ir12Si7 (Ho2Rh12As7-type), τ13 – Ce3Ir2−xSi2+x (Sm3Ir2Si2-type), and τ14 – Ce3Ir3Si2 (Ce3Rh3Si2-type). For another new compound τ1 – Ce4Ir27Si69 (at.%), which has homogeneity region along 27 at.% of Ir, the reflections were indexed in hexagonal lattice symmetry with cell parameters close to high-temperature IrSi3−x phase.

The ternary system cerium–rhodium–silicon

Phase relations have been established in the ternary system Ce–Rh–Si for the isothermal section at 800 °C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 °C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ 7—Ce 3RhSi 3, (Ba 3Al 2Ge 2-type), τ 8—Ce 2Rh 3− x Si 3+ x (Ce 2Rh 1.35Ge 4.65-type), τ 10—Ce 3Rh 4− x Si 4+ x (U 3Ni 4Si 4-type), τ 11—CeRh 6Si 4 (LiCo 6P 4-type), τ 13—Ce 6Rh 30Si 19.3 (U 6Co 30Si 19-type), τ 18—Ce 4Rh 4Si 3 (Sm 4Pd 4Si 3-type), τ 21—CeRh 2Si (CeIr 2Si-type), τ 22—Ce 2Rh 3+ x Si 1− x (Y 2Rh 3Ge-type) and τ 24—Ce 8(Rh 1− x Si x ) 24Si (Ce 8Pd 24Sb-type). For τ 25—Ce 4(Rh 1− x Si x ) 12Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ 3—CeRhSi 2 (CeNiSi 2-type) and τ 6—Ce 2Rh 3Si 5 (U 2Co 3Si 5-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ 4—Ce 22Rh 22Si 56, τ 5—Ce 20Rh 27Si 53 and τ 23—Ce 33.3Rh 58.2−55.2Si 8.5−11.5 are unknown. High temperature compounds with compositions Ce 10Rh 51Si 33 (U 10Co 51Si 33-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 °C.

On the system cerium–platinum–silicon

Phase relations in the ternary system Ce–Pt–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ 18-Ce 5(Pt,Si) 4 ( Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ 3-Ce 2Pt 7Si 4 ( Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ 10-CePtSi 2 ( Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm 5Ge 4-type, the Ce 2Pt 7Ge 4-type and the CeNiSi 2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt 3Si (Pt 3Ge-type, C2 /m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ 16-Ce 3Pt 5Si (Ce 3Pd 5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ 17-Ce 3PtSi 3 (Ba 3Al 2Ge 2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce–Pt–Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ 13-Ce(Pt x Si 1− x ) 2, τ 6-Ce 2Pt 3+ x Si 5− x or τ 7-CePt 2− x Si 2+ x .

Structural chemistry and phase relations in intermetallic systems Ti–{Pd,Pt}–Al

Phase relations in the ternary systems Ti–{Pd,Pt}–Al have been experimentally established for the partial isothermal sections at 950°C in the Pd/Pt-poor region (<25 at.% Pd/Pt). The investigation is based on X-ray powder diffraction, metallography, SEM and EMPA techniques on about 45 alloys, which were prepared by various methods employing arc melting, levitation melting under argon or by powder reaction sintering in closed crucibles. Three ternary compounds were observed at 950°C in the Ti–Pd–Al system: τ 3-(Ti,Pd)(Ti,Pd,Al) 2 with Laves-MgZn 2-type, τ 2-(Ti,Al) 6(Ti,Pd,Al) 23+1 with a filled Th 6Mn 23+1-type and τ 1-(Ti,Pd,Al)(Ti,Pd,Al) 3 with AuCu 3-type. Due to the wide extension of the Laves phase field, there is no compatibility among γTiAl and τ 2-(Ti,Al) 6(Ti,Pd,Al) 23+1. The Ti–Pt–Al system at 950°C contains three ternary compounds: τ 3-(Ti,Al)(Ti,Pt,Al) 2 with Laves-MgZn 2-type, τ 2-(Ti,Al) 6(Ti,Pt,Al) 23+1 with the filled Th 6Mn 23+1-type and τ 1-(Ti,Pt,Al) with Cu-type. Compatibility exists for Al-rich γTiAl and τ 2-(Ti,Al) 6(Ti,Pt,Al) 23+1. The typical feature for both alloy systems studied is the three-phase equilibrium: α 2Ti 3Al+γTiAl+τ 3-(Ti,Pd/Al)(Ti,Pd/Pt,Al) 2. The solid solubility of palladium and platinum in the binary titanium aluminides, as observed from EMPA and X-ray data, is rather small and at 950°C accounts to about 2.5 at.% Pd and 2.0 at.% Pt. Two new oxide compounds Ti 3PdAl 2O x and Ti 3PtAl 2O x with a filled Ti 2Ni-type are observed in both quaternary systems.

Microstructural Characterization of Reactively Sintered Mullites

Mullite ceramics have been produced by reaction sintering of powders prepared using pseudoboehmite–colloidal silica and aluminum sulfate–colloidal silica mixtures. The microstructural development of these mullites was studied by a number of transmission electron microscopy based techniques including diffuse dark field, Fresnel fringe defocus imaging, and high‐resolution transmission electron microscopy. This characterization procedure showed that mullite ceramics free from glassy phases at triple junctions and grain boundaries could be produced from both mixtures using suitable sintering temperatures and alumina/silica ratios. The wetting of grain boundaries by glass, occurring in the mullite ceramics from either incomplete reaction between alumina and silica components or release of silica from the mullite structure with increasing temperature, was found to depend on the prior thermal history of the ceramics.

The influence of FeTi and NiTi intermetallide additions on high-temperature oxidation of permalloy alloy

As a rule powder metallurgy Permalloy alloys are used in production of parts for electronic instruments. For the purpose of controlling the magnetic and electrical properties and also the wear (in the case of production of magnetic heads) and corrosion resistance appropriate additions of metals or such compounds as carbides and oxides are added to the alloy. In this work use of FeTi and NiTi intermetallides produced by reaction sintering of powders of pure metals in a protective atmosphere as alloying additions to Permalloy is recommended. The size of the original powders is less than 100 {mu}m. For reaction sintering at temperature 50{degrees}C above the eutectic temperature in the Ti-TiFe and TiNi-Ni systems was selected. The contents of titanium, iron, and oxygen in the FeTi alloy is 51.9, 45.7, and 2.4 wt.%, respectively, and of titanium, nickel, and oxygen in the NiTi alloy 59.6, 31.9, and 4.6 wt.%. High-temperature oxidation in air up to 1300{degrees}C with a rate of change in temperature of 15{degrees}C of type 78N Permalloy with additions of FeTi and NiTi alloys was investigated with use of methods of differential thermal and differential thermogravimetric analyses on an OD-103 derivatograph under nonisothermal conditions. The reaction products were studiedmore » by x-ray diffraction phase analysis on a DRON-3 instrument in CoK{sub {alpha}}-radiation. Pure 78N alloy powder with a composition of 78.1% Ni + 19.3% Fe (specimen 1) and also with additions of 1% FeTi (specimen 2) and 1% NiTi (specimen 3) were subjected to oxidation.« less

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Phase relations in the ternary system Ce–Pt–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce–Pt–Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ13-Ce(PtxSi1−x)2, τ6-Ce2Pt3+xSi5−x or τ7-CePt2−xSi2+x.

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Phase relations in the ternary system Ce–Pt–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce–Pt–Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ13-Ce(PtxSi1−x)2, τ6-Ce2Pt3+xSi5−x or τ7-CePt2−xSi2+x.