Differential thermal analysis (DTA) on the reaction mechanism in Fe–Ti–B4C system

Differential thermal analysis (DTA) was undertaken to determine the reaction mechanism in the Fe–Ti–B₄C system under argon. When the mixtures were heated to about 786 °C, Fe₂B and C appeared as a result of Fe reacting with B₄C. As the temperature continued to increase, FeTi formed by an interdiffusion between Fe and Ti. When the mixtures were heated to 1089 °C, FeTi reacted with Ti, leading to the formation of a Fe–Ti melt, into which the displaced C and B from B₄C dissolve, forming a Fe–Ti–C–B melt. Finally, when the concentration of C and B attained a certain value, Ti reacted with C and B, yielding TiC and TiB₂ in the melt, and simultaneously considerable heat released.     

Self-propagating high-temperature synthesis of TiCxNy–TiB2 ceramics from a Ti–B4C–BN system

An experimental study on direct formation of TiC_xN_y–TiB₂ ceramics by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–B₄C–BN system. The effects of the C/(C + N) ratio on the combustion behavior and reaction products were investigated. Experimental characterizations of quenched samples show that the combustion reaction started with the formation of highly substoichiometric TiN_y and TiB due to the solid-state reaction between Ti and BN; and then the TiN_y precursor and TiB dissolved back into the titanium melt, forming the Ti–B–N liquid, which in turn transformed to the Ti–B–N–C liquid due to the dissolution of the carbon atoms diffused away from B₄C. Finally, the TiC_xN_y and TiB₂ particles are formed from the melt through the dissolution-precipitation mechanism.     

Preparation of Ti–Al–Si alloys by reactive sintering

The isothermal section of the Dy–Co–Ti system at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. The only ternary phase DyTi_xCo_12−x is of ThMn₁₂-type structure, space group I4/mmm, and shows a small homogeneity range of 1 ≤ x ≤ 1.6. The lattice parameters for DyTi_xCo_12−x with 1 ≤ x ≤ 1.56 are a = 0.8336(4)–0.8402(1) nm and c = 0.4691(3)–0.4727(1) nm. Along a constant Dy concentration, the solid solubilities of Ti in the compounds Dy₂Co₁₇, DyCo₃, DyCo₂ and Dy₃Co are about 2.0, 2.0, 3.0 and 4.0 at.%, respectively. The TiCo phase has a homogeneity range of 50–54 at.% Co at 500 °C and dissolves up to 2.0 at.% Dy.     

Effect of composition and milling parameters on the critical ball milling of Ti–Si–B powders

The absence of brittle phases and elevated temperature during ball milling of a powder mixture containing a large amount of ductile component can contribute to reach an excessive agglomeration denoting a critical ball milling (CBM) behavior. This work reports in the effect of composition and milling parameters on the CBM behavior of Ti–Si–B powders. High-purity elemental Ti–Si–B powder mixtures were processed in a planetary ball mill in order to prepare the Ti₆Si₂B compound and two-phase Ti + Ti₆Si₂B alloys. TiH₂ chips instead of titanium powder were used as a starting material. To avoid elevated temperature in the vials during ball milling of Ti–Si–B powders the process was interrupted after each 10 min followed by air-cooling. Following, the milled powders were hot-pressed at 900 °C for 1 h. Samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Short milling times followed by air-cooling contributed to obtain a large amount of powders higher than 75% in the vials. Only Ti and TiH₂ peaks were observed in XRD patterns of Ti–Si–B and TiH₂–Si–B, respectively, suggesting that extended solid solutions were achieved. The large amount of Ti₆Si₂B and Ti + Ti₆Si₂B structures were formed during hot pressing from the mechanically alloyed Ti–Si–B and TiH₂–Si–B powders.     

Al–Ti–B grain refiners via powder metallurgy processing of Al/K2TiF6/KBF4 powder blends

The response to thermal exposure of ball-milled Al/K₂TiF₆/KBF₄ powder blends was investigated to explore the potential of PM processing for the manufacture of Al–Ti–B alloys. K₂TiF₆ starts to be reduced by aluminium as early as 220 °C when ball-milled Al/K₂TiF₆/KBF₄ powder blends are heated. The reaction of KBF₄ with aluminium follows soon after. The Ti and B thus produced are both solutionized in aluminium before precipitating out as Al₃Ti and TiB₂. All these reactions take place below the melting point of aluminium. The ball-milled Al/K₂TiF₆/KBF₄ powder blends heat treated at approximately 525 °C can be compacted to produce Al–Ti–B pellets with in situ formed Al₃Ti and TiB₂ particles. These pellets are shown to be adequate grain refiners for aluminium alloys.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

Phase equilibria and chemical vapor transport in the system Mo–Ta–As

The phase diagram Mo–Ta–As was studied in two partial isothermal sections at 1050 °C (in the As-rich corner) and at 1400 °C (As-poor alloys) using powder X-ray diffraction and electron probe microanalysis. A complete solid solution was found to exist between isostructural Mo₅As₄ and Ta₅As₄ and the ternary solubility of Mo in Ta₃As at 1400 °C was determined. A ternary phase Mo_xTa_1−xAs with MnP-type structure was found to exist in the As-rich part of the system. Lattice parameters were investigated as a function of composition for (Mo,Ta)₅As₄ and for Mo_xTa_1−xAs. Additional experiments of chemical vapor transport (CVT) from 1000 °C to 900 °C using different ternary source compositions and I₂ and Br₂ (PtBr₂) as transport agents were performed. Only Ta compounds were found in the sink and no ternary transport was observed.     

Thermal property characterization of a Ti–4 wt.%Nb–4 wt.%Zr alloy using drop and differential scanning calorimetry

The thermal properties of Ti–4 wt.%Nb–4 wt.%Zr alloy, namely the enthalpy increment and heat capacity have been characterized as a function of temperature using drop and differential scanning calorimetry, respectively. The measured data clearly attested to the presence of a phase change from α (hcp) to β (bcc) phase at about 1100 ± 5 K. In fact, the alloy exhibited a transformation domain in the temperature interval 1100–1170 K. The enthalpy associated with the α → β phase change is estimated to be about 73 (±5%) J g⁻¹. The jump in the specific heat at the transformation temperature is 1714 (±7%) J kg⁻¹ K⁻¹. The drop and differential scanning calorimetry results are consolidated to obtain the first experimental data on the thermodynamic quantities of this alloy.     

The Yb–Zn–In system at 400 °C: Partial isothermal section with 0–33.3 at.% Yb

The phase relations in the ternary system Yb–Zn–In have been established for the partial isothermal section in the 0–33.3 at.% ytterbium concentration range at 400 °C, by researching of more than forty alloys. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to study the microstructures, identify the phases and characterize their crystal structures and compositions. The phase equilibria of this Yb–Zn–In partial section at 400 °C are characterized by the presence of three extended homogeneity ranges, indium solubility in Yb₁₃Zn₅₈ and YbZn₂ and of zinc solubility in YbIn₂, and the existence of one ternary intermetallic compound, YbZn_1−xIn_1+x, x = 0.3. This new compound crystallizes in the UHg₂ structure type (space group P6/mmm), with a = 4.7933(5) Å, c = 3.6954(5) Å. The studied partial isothermal section has eight ternary phase fields at 400 °C.     

Reinforcement of Al–Fe–Ni alloys with the in situ formation of composite materials

One of the most effective methods for the improvement of the mechanical properties of metals is their reinforcement with non-metallic materials. In the present work powder of K₂TiF₆ and KBF₄ was added in an Al–Fe–Ni alloy while the alloy was in liquid form at 1060 °C with a 5 wt.% mixture of powders and with simultaneous stirring for 30 min. The liquid was squeeze-casted at 150 bar. The as-cast specimens were examined with electron microscopy and X-ray diffraction. SEM analysis revealed that the as-formed material is composed by needle-like crystallites along with a dentritic form and an interdendritic phase. The composition of the needle-like crystallites may presumably be expressed by the formula (Fe-Ni)Al₃. The rest of the matrix consists of almost pure Al grown dentritically, while the interdendritic phase contains Fe and Ni dissolved in Al. EDS analysis also proved the existence of spots with high Ti concentration, which probably refer to the Ti–B compounds. Finally TEM verified the presence of nanocrystals in the matrix.     

Combustion synthesis of TiC–TiB2 composites

An experimental study on formation of TiC–TiB₂ in situ composites with a broad range of compositions was conducted by self-propagating high-temperature synthesis (SHS) using the reactant compacts from different combinations of Ti, B₄C, C, and B powders. Direct reaction of Ti with B₄C at stoichiometry of Ti:B₄C = 3:1 yields a TiB₂-rich composite with TiC:TiB₂ = 1:2. Formation of the products containing 20, 33.3, and 50 mol% of TiB₂ was achieved by the Ti–B₄C–C reactants. In addition, the test specimen composed of Ti, B₄C, and B was employed for the synthesis of a composite with 80 mol% TiB₂. Among three different types of the powder compacts, the boron-containing sample was characterized by the fastest combustion wave and the highest reaction temperature. The lowest combustion temperature and wave velocity were observed in the Ti–B₄C compact. When fine Ni particles were added to the Ti–B₄C reactant, it was found that the propagation rate of the reaction front was increased and the densification of the end product was enhanced significantly. This was attributed to formation of the Ti–Ni eutectic liquid during the reaction. As a result, the relative density of a TiC + 2TiB₂ composite increases from 30 to 86% with the Ni content from 0 to 20 mol%. Based upon the XRD analysis, small amounts of TiNi₃ and TiB were detected in the Ni-reinforced TiC–TiB₂ composites.     

Experimental determination of phase equilibria in the Fe–Nb–V ternary system

The phase equilibria in the Fe–Nb–V ternary system were investigated by means of optical microscopy, electron probe microanalysis and X-ray diffraction. Four isothermal sections in the Fe–Nb–V ternary system at 1000 °C, 1100 °C, 1200 °C and 1300 °C were firstly experimentally established. Present experimental results indicate that: (1) there is a large (Nb, V) continuous bcc solid solution; (2) there are the larger solubilities of V in the FeNb and Fe₂Nb phases. The newly determined phase equilibria in this system will provide important support for the development of hydrogen storage materials and microalloyed steels.     

The 473 K isothermal section of the Cu–Ti–Sn ternary system

The phase relationships of the Cu–Ti–Sn ternary system at 473 K have been investigated mainly by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM) and differential thermal analysis (DTA). The isothermal section consists of 17 single-phase regions, 33 two-phase regions and 17 three-phase regions. The existence of 12 binary compounds and 2 ternary compounds, namely Cu₄Ti, Cu₃Ti₂, Cu₄Ti₃, CuTi, CuTi₂, Cu₃Sn, Cu₆Sn₅, Ti₃Sn, Ti₂Sn, Ti₅Sn₃, Ti₆Sn₅, Ti₂Sn₃, CuTi₅Sn₃ and CuTiSn, are confirmed in the Cu–Ti–Sn ternary system at 473 K. No new ternary compound is found. The maximum solid solubility of Cu in Ti₆Sn₅ was approximately 10 at.% Cu.     

A novel Al–Ti–B alloy for grain refining Al–Si foundry alloys

Al–Ti–B refiners with excess-Ti (Ti:B > 2.2) perform adequately for wrought aluminium alloys but they are not as efficient in the case of foundry alloys. Silicon, which is abundant in the latter, forms silicides with Ti and severely impairs the potency of TiB₂ and Al₃Ti particles. Hence, Al–Ti–B alloys with excess-B (Ti:B < 2.2) and binary Al–B alloys are favored to grain refine hypoeutectic Al–Si alloys. These grain refiners rely on the insoluble (Al,Ti)B₂ or AlB₂ particles for grain refinement, and thus do not enjoy the growth restriction provided by solute Ti. It would be very attractive to produce excess-B Al–Ti–B alloys which additionally contain Al₃Ti particles to maximize their grain refining efficiency for aluminium foundry alloys. A powder metallurgy process was employed to produce an experimental Al–3Ti–3B grain refiner which contains both the insoluble AlB₂ and the soluble Al₃Ti particles. Inoculation of a hypoeutectic Al–Si foundry alloy with this grain refiner has produced a fine equiaxed grain structure across the entire section of the test sample which was more or less retained for holding times up to 15 min.     

Thermal stability and primary phase of Al–Ni(Cu)–La amorphous alloys

Thermal stability and primary phase of Al_85+xNi_9−xLa₆ (x = 0–6) and Al₈₅Ni_9−xCu_xLa₆ (x = 0–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. It is revealed that replacing Ni in the Al₈₅Ni₉La₆ alloy by Cu decreases the thermal stability and makes the primary phase change from intermetallic compounds to single fcc-Al as the Cu content reaches and exceeds 4 at.%. When the Ni and La contents are fixed, replacing Al by Cu increases the thermal stability but also promotes the precipitation of single fcc-Al as the primary phase.     

Influence of thermal cycling on shear strength of Cu–Sn3.5AgIn–Cu joints with various content of indium

This work presents an investigation on the influence of thermal cycling of Cu–Sn3.5AgIn–Cu joints for various content of indium. Solders Sn–3.5Ag containing 0, 6.5 and 9 mass% In were prepared by rapid quenching of appropriate alloys. Joints Cu–solder–Cu were prepared in furnace at 280 °C and 1800 s. Thermal cycling was in the interval room temperature (RT)–150 °C up to 1000 cycles and in the interval RT–180 °C for 500 cycles. The shear strength of the joints with indium-free solder decreases with increasing number of cycles. On the contrary shear strength of joints with indium containing solders increases with increasing number of cycles. It is related with the thickness of Cu₆Sn₅ phase which makes the interface between Cu substrate and solder. In the first case the thickness of this phase is growing with increasing number of cycles, in the second case the amount of this phase is reducing with increasing the number of cycles due to the support of dissolution of copper from Cu₆Sn₅ phase into the Sn–Ag–In solder by indium. X-ray diffraction analysis of original solders as well as of uncycled and 1000 times cycled joints made with all three kinds of solders is given.     

Effect of Zn concentration on the microstructure and phase formation of Mg–5Gd alloy

The effect of Zn additions (0, 1 and 2 wt%) on the microstructure and phase formation of Mg–5Gd alloy has been investigated using X-ray diffraction (XRD), differential thermal analyzer (DTA) and scanning electron microscope (SEM) techniques. Zinc free alloy shows the negligible amount of Mg₅Gd phase formation whereas 1 wt% Zn addition leads to formation of more volume of Mg₅Gd phase having dissolution temperature at 518 °C. Two weight percentage of Zn addition yielded more volume of MgZn₂ phase having the dissolution temperature at 333 °C but less volume of Mg₅Gd phases. Moreover, 1 wt% Zn addition is found to be more favorable to the age hardening behavior as compared to 2 wt% Zn added alloy.     

Experimental study of Ti–Sn–Y system phase equilibria at 473 K

The phase equilibria of the Ti–Sn–Y ternary system at 473 K have been investigated mainly by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The existences of 10 binary compounds, Ti₃Sn, Ti₂Sn, Ti₅Sn₃, Ti₆Sn₅, Ti₂Sn₃, Sn₃Y, Sn₂Y, Sn₁₀Y₁₁, Sn₄Y₅ and Sn₃Y₅ were confirmed. The 473 K isothermal section was found to consist of 13 single-phase regions, 23 two-phase regions and 11 three-phase regions. There is no new ternary compound found in the work. None of the phases in this system reveals a remarkable homogeneity range at 473 K.     

Effect of nickel addition on the exothermic reaction of the Ti–C–BN system

The effect of Ni addition on the exothermic reaction in the Ti–C–BN system was investigated using differential thermal analysis (DTA). Based on DTA and X-ray diffraction (XRD) analyses, a reaction path for the formation of TiC_xN_y and TiB₂ in the Ni–Ti–C–BN system was proposed in which the reaction initiated with the solid-state diffusion between Ti and BN. The resultant TiN_x then reacted with Ni to form Ni–Ti compounds (e.g., Ti₂Ni). With increasing temperature, a Ni–Ti–N eutectic liquid phase formed between the Ni–Ti compounds and TiN_x at about 1110 °C, enabling the dissolution of C and B in the melt to form Ni–Ti–N–C–B liquid. Finally, TiC_xN_y and TiB₂ formed and precipitated out of the liquid.     

A convenient thermal reduction–nitridation route to nanocrystalline molybdenum nitride (Mo2N)

Nanocrystalline molybdenum nitride (γ-Mo₂N) was synthesized via a thermal reduction–nitridation route by the reaction of metallic sodium with anhydrous molybdenum pentachloride and ammonium chloride in an autoclave at 550 °C. X-ray powder diffraction pattern indicated that the product was cubic Mo₂N, and the cell constant was a = 4.161 Å. Scanning electron microscopy image showed that it consisted of particles with an average size of about 30 nm. The product was also studied by BET and TGA. It had good thermal stability and oxidation resistance below 400 °C in air.