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.     

The isothermal section of the Ti–Co–Zr ternary system at 773 K

The phase equilibria of the Ti–Co–Zr ternary system at 773 K have been investigated mainly by powder X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive analysis (EDX). The isothermal section consists of 16 single-phase regions, 31 two-phase regions and 16 three-phase regions. There are 11 binary compounds, i.e. CoZr₃, CoZr₂, CoZr, Co₂Zr, Co₂₃Zr₆, Co₁₁Zr₂, TiCo₃, h-TiCo₂, c-TiCo₂, TiCo, Ti₂Co in the system. The existence of two ternary compounds Co₁₀Ti₇Zr₃ and Co₆₆Ti₁₇Zr₁₇ has been confirmed at 773 K. Co₂Zr, CoZr₃ and TiCo have a range of homogeneity. The solubilities of Ti in CoZr was determined to be up to 8.1 at.% Ti.     

Effect of Nb content on the microstructures and mechanical properties of Zr–Ti–Cu–Be–Nb glass-forming alloys

(Zr₃₅Ti₃₀Be_27.5Cu_7.5)_100?xNb_x (x = 0, 5, 8, 10, 12, 15 at.%) glass-forming alloys were prepared by copper-mould suction casting. The alloys with different Nb contents exhibited different microstructures and mechanical properties. The proper addition of Nb (x = 5, 8 at.%) to the Zr–Ti–Be–Cu system could ensure the formation of mostly amorphous phase. And excessive amount of Nb favored the formation of the bcc β-Zr solid solution. The alloys with Nb contents of 8 at.%, 10 at.%, and 12 at.% displayed the distinguished plasticity of 11.1%, 7.6%, and 11.0%, respectively.     

Beryllium-distribution in metallic glass matrix composite containing beryllium

The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites (MGMCs) containing beryllium (Be) with the nominal composition of Ti₄₇Zr₁₉Cu₅V₁₂Be₁₇ (mole fraction, %) were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS). Based on these findings, it has been obtained that the accurate chemical compositions are Ti_28.3Zr_19.7Cu₈V_6.4Be_37.6 (mole fraction, %) for glass matrix and Ti_62.4Zr_18.4Cu_2.6V_16.6 (mole fraction, %) for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.     

Formation of TiAl–Ti2AlC in situ composites by combustion synthesis

Preparation of TiAl–Ti₂AlC in situ composites with a broad range of composition was conducted by self-propagating high-temperature synthesis (SHS) with compressed samples from the mixture of elemental powders. When compared with SHS formation of monolithic TiAl, the addition of carbon particles to the Ti–Al powder mixture enhances the sustainability of the reaction. It was found that no prior heating was required for the samples prepared to produce the composites containing more than 20 mol% Ti₂AlC, in contrast to the need of preheating at 200 °C for single-phase TiAl formation. This is attributed to the fact that formation of Ti₂AlC is more exothermic than that of TiAl. As a result, the combustion temperature and combustion wave velocity increase with the content of Ti₂AlC formed in the TiAl–Ti₂AlC composite, and approach the values associated with formation of single-phase Ti₂AlC when considerable amounts of Ti₂AlC are yielded. The XRD analysis of the end products confirms formation of TiAl–Ti₂AlC in situ composites. Moreover, simultaneous formation of Ti₂AlC promotes the phase evolution of the aluminide compounds. That is, the secondary aluminide phase, Ti₃Al, was no longer detected in the TiAl–matrix composites containing Ti₂AlC of 30 mol% or above.     

Low temperature heat capacity and electrical resistivity of the Ti40Zr25Cu12Ni3Be20 glass forming alloy

Gaining knowledge of electronic structure provides useful information for understanding unique properties of metallic glasses. In this study, low temperature heat capacity and electrical resistivity of the glass forming Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ alloy with glassy, quasicrystalline, or crystalline states below 300 K were investigated. The precipitation of the I-phase was revealed in the initial crystallization process of the Ti₄₀Zr₂₅Cu₁₂Ni₃Be₂₀ BMG. The glassy state has higher state density at Fermi level than its quasicrystalline or crystalline counterparts, which could be interpreted by the electron localization in glassy state as well as a pseudo-Brillouin zone formed nearby Fermi surface in the quasicrystalline state. None of the three states showed superconductivity phenomenon down to 1.9 K. Temperature dependence of resistivity for both the glassy state and the quasicrystalline state exhibited negative temperature coefficient and was less sensitive to temperature than the crystalline state. The electrical resistivity showed a smaller value for the I-phase than that for the glass due to lower structural integrity of I-phase. Electrical resistivity as well as heat capacity measurements indicated that the electronic structure of the quasicrystalline state is quite similar to glassy state but far from crystalline state.     

Determination of the 850 °C isothermal section in the Co-Ni-Ti system

The isothermal section of the Co-Ni-Ti system at 850 °C was determined by using diffusion couple specimens and equilibrated alloys, which were analyzed by optical microscopy, X-ray diffraction (XRD), and electron probe microanalysis (EPMA) techniques. This isothermal section consists of 9 single-phase regions, 12 two-phase regions, and 4 three-phase regions. The 9 single-phase regions include αTi solid solution, βTi solid solution, Ti₂(Co, Ni), Ti(Co, Ni), fcc-(Co, Ni) solid solution, and solid solutions based on TiCo₂(hexagonal), TiCo₂(cubic), TiCo₃, and TiNi₃. No ternary Co-Ni-Ti compound was found.     

Thermodynamic Interactions of Si and Ti in Liquid Cu

The activity coefficients of titanium in liquid Cu-Ti at 1623 and 1673 K were measured by equilibrating the liquids with Ti₃O₅ in a oxygen partial pressure controlled by C(s)/CO(g) equilibrium. Furthermore, the thermodynamic interaction parameter of silicon on titanium and the self-interaction parameter of titanium in liquid Cu-Ti-Si at 1773 K were determined by equilibrating the 58 mass% TiO₂-42 mass% CaF₂ slag with Cu-Si-Ti liquids. And the interaction parameters e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} and e_\textTi^\textSi e_{\text{Ti}}^{\text{Si}} obtained using a multiple regression were as large as −69.32 and 15.44 respectively. Based on the above determined value of e_\textTi^\textTi e_{\text{Ti}}^{\text{Ti}} , the relationship between Henrian constant of titanium in liquid Cu-Ti melt, \upgamma_{\textTi(\texts)}⁰ \upgamma_{{{\text{Ti}}({\text{s}})}}^{0} , from 1473 to 1923 K was evaluated, and is expressed as:

Low-temperature brazing of titanium by the application of a Zr–Ti–Ni–Cu–Bebulk metallic glass (BMG) alloy as a filler

Titanium (Ti) was successfully brazed at low temperatures below 800 °C by employing a Zr_41.2Ti_13.8Ni_10.0Cu_12.5Be_22.5 (at.%) bulk metallic glass (BMG) alloy as a filler. Through the use of this alloy filler, the detrimental segregation of Zr–Cu–Ni filler elements was completely eliminated by heating to well below 800 °C, so the resultant joint was quite homogeneous with a coarse acicular structure. The disappearance of the Zr–Cu–Ni segregated region was rate-controlled by the diffusion of the filler elements in the Ti base metal. Remarkably, the mechanical property and corrosion resistance of the homogeneous joint brazed at 800 °C for 10 min were mostly comparable to those of bulk Ti.     

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 heat treatment temperature on the microstructure and actuation behavior of a Ti–Ni–Cu thin film microactuator

Ti–Ni–Cu/SiO₂ two layer diaphragm-type microactuators were fabricated by sputter deposition and micromachining. The influence of heat treatment temperature on the actuation behavior was investigated under quasi-static conditions. The interfacial structure of Ti–Ni–Cu/SiO₂ and internal structure of the Ti–Ni–Cu layer were also investigated using transmission electron microscopy. The reaction layer formed between the Ti–Ni–Cu and SiO₂ layers, and preferentially grew into the SiO₂ side. The reaction layer formed at 1023 K mainly consisted of Ti₄(Ni,Cu)₂O. The maximum height of the diaphragm decreased with increasing heat treatment temperature. The growth of the reaction layer also affected the microstructure of the Ti–Ni–Cu layer. The density of fine platelets and Ti₂Ni precipitates decreased with increasing heat treatment temperature from 873 to 923 K, and they disappeared at 973 K due to the fact that the reaction layer mainly consisted of a Ti-rich phase. The microactuator heat treated at 973 K showed the highest transformation temperature with the lowest transformation temperature hysteresis, which is attractive for high speed actuation.     

Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO₂, Zr₃O, TiO₂ and TiO of different modifications, complex oxides such as Ni₅TiO₇, Ti_0.5Zr_0.5O_0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni₄Ti₃ and Ni₂Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti₂Ni, Ti–Ni and diffusion of Ti atoms in Zr₂Ni, Ni–Zr controls the later stages of sintering.     

Effect of Ti content on the microstructure and mechanical behavior of (Fe36Ni18Mn33Al13)100−xTix high entropy alloys

The microstructure and mechanical properties studies of a series of two-phase f.c.c./B2 (ordered b.c.c.) lamellar-structured, high entropy alloys (HEA) Fe₃₆Ni₁₈Mn₃₃Al₁₃Ti_x with x up to 6 at. % Ti have been investigated. X-ray microanalysis in a TEM showed that the Ti resided mostly in the B2 phase. The lamellar spacing decreased significantly with increasing Ti content from 1.56 μm for the undoped alloy to 155 nm with an addition of 4 at. % Ti, leading to a sharp increase in room-temperature yield strength,σ_y, from 270 MPa to 953 MPa, but with a concomitant decrease in ductility from 22% elongation to 2.3%. Annealing at 1173 K for 20 h greatly increased the lamellar spacing of Fe₃₆Ni₁₈Mn₃₃Al₁₃Ti₄ to 577 nm, producing a corresponding decrease in σ_y to 511 MPa. The yield strengths of all the doped alloys decreased significantly when tensile tested at 973 K with a concomitant increase in ductility due to softening of the B2 phase. The fracture mode changed from cleavage at room temperature to a ductile dimple-type rupture at 973 K. The results are discussed in terms of the Hall-Petch-type relationship.     

Zr–Ti-based Be-bearing glasses optimized for high thermal stability and thermoplastic formability

A new class of Zr–Ti-based Be-bearing (Vitreloy) glass-forming compositions that exhibit high thermal stability and good glass-forming ability is reported. Optimized ternary compositions were obtained by re-examining the Zr–Ti–Be phase diagram for regions that produce glasses having high thermal stability and modest glass-forming ability. By incorporating a fourth element in the optimized ternary compositions, quaternary alloys were obtained having thermal stabilities twice that of Zr_41.2Ti_13.8Ni₁₀Cu_12.5Be_22.5 (Vitreloy-1) while exhibiting good glass-forming abilities. Optimized quaternary alloys exhibiting critical casting thicknesses exceeding 15 mm and thermal stabilities as high as 165 °C are reported herein. The good thermal stability of these alloys renders them attractive for forming processes that can be performed thermoplastically in the supercooled liquid region, in a manner similar to the forming of polymers.     

Ordering process of Al5Ti3, h-Al2Ti and r-Al2Ti with f.c.c.-based long-period superstructures in rapidly solidified Al-rich TiAl alloys

Change in microstructure and stability of superstructural phases in Al-rich TiAl alloys containing 58.0–62.5 at.% Al were investigated using melt-spun ribbons. Ordering processes of long-period ordered phases such as Al₅Ti₃, h-Al₂Ti and r-Al₂Ti in the L1₀ matrix during annealing were examined. The presence of Al₅Ti₃ and h-Al₂Ti phases in the L1₀ matrix was confirmed in melt-spun Ti–60.0 at.% Al and Ti–62.5 at.% Al ribbons by electron diffraction patterns, while diffuse scattering corresponding to the Al₅Ti₃ superstructure appeared in Ti–58.0 at.% Al ribbon. In Ti–58.0 at.% Al ribbon, the Al₅Ti₃ phase developed as an island in the L1₀ matrix having an obscure coherent boundary at and below 800°C, while it dissolved during annealing above 800°C. Although the r-Al₂Ti phase was finally formed as an equilibrium phase, the ordering of Al₅Ti₃ and metastable h-Al₂Ti phases in Ti–60.0 at.% Al and Ti–62.5 at.% Al ribbons occurred prior to the precipitation of the r-Al₂Ti during annealing below 800°C. The priority for the ordering process is discussed on the basis of crystal symmetry and periodicity of Al layers parallel to the (002) plane. The anti-phase boundaries (APBs) based on the Al₅Ti₃-type ordering were observed along {110) planes in Ti–62.5 at.% Al ribbon annealed at 700°C and their energies were calculated using the interaction energy between neighbouring atoms.     

A new refractory Ti-Nb-Hf-Al high entropy alloy strengthened by orthorhombic phase particles

This study reports the structure and mechanical properties of a new refractory Ti₄₀Nb₃₀Hf₁₅Al₁₅ (at.%) high entropy alloy. The alloy was fabricated by vacuum arc melting and had a density of 7.07 ± 0.03 g/cm³. After annealing at 1200 °C for 24 h, the alloy possessed a single-phase B2 structure. Further annealing at 600 °C for 24 h resulted in the formation of Widmanstatten (Ti, Al)-rich orthorhombic particles (O-phase) in a bcc matrix. The single-phase B2 alloy demonstrated high (>50%) compressive ductility and a pronounced work hardening capacity. The precipitation of the O-phase particles led to a 50% strength increment at 22 and 600 °C, with some sacrificing in the compressive ductility at 22 °C. The obtained results suggest new approaches to the development of precipitation-strengthened refractory high entropy alloys with a balanced combination of the room- and high-temperature properties.     

High hydrogen permeability in the Nb-rich Nb–Ti–Ni alloy

The microstructure and the hydrogen permeability of the Nb-rich Nb–Ti–Ni alloy, i.e., the Nb₅₆Ti₂₃Ni₂₁ alloy were investigated and compared with those of the Nb₄₀Ti₃₀Ni₃₀ alloy. The Nb₅₆Ti₂₃Ni₂₁ alloy consisted of a combination of the primary phase bcc- (Nb, Ti) solid solution with the eutectic phase {bcc- (Nb, Ti) + B2-TiNi}. The volume fraction of the former and the latter phases were 62 and 38 vol.%, respectively. The Nb₅₆Ti₂₃Ni₂₁ alloy showed the higher Φ value of 3.47 × 10⁻⁸ (mol H₂ m⁻¹ s⁻¹ Pa^−0.5) at 673 K, which is 1.8 times higher than that of the Nb₄₀Ti₃₀Ni₃₀ alloy, which has been reported to be highest in the Nb–Ti–Ni system. The present work demonstrated that the Nb-rich Nb–Ti–Ni alloys consisting of only the primary phase bcc- (Nb, Ti) and the eutectic phase {bcc- (Nb, Ti) + B2-TiNi} are promising for the hydrogen permeation membrane.     

Corrosion behavior of select MAX phases in NaOH, HCl and H2SO4

In this paper we report on the electrochemical corrosion of select MAX phases, namely Ti₂AlC, (Ti,Nb)₂AlC, V₂AlC, V₂GeC, Cr₂AlC, Ti₂AlN, Ti₄AlN₃, Ti₃SiC₂ and Ti₃GeC₂ in 1 M NaOH, 1 M HCl and 1 M H₂SO₄ solutions. Polarization characteristics recorded in 1 M NaOH show that V₂AlC, V₂GeC and Cr₂AlC undergo active dissolution at potentials more positive than the corrosion potential, while Ti₂AlC, (Ti,Nb)₂AlC, Ti₃SiC₂ and Ti₃GeC₂ passivate. In the 1 M HCl solutions, Ti₂AlC, V₂AlC and V₂GeC actively dissolve; Ti₃SiC₂ and Ti₃GeC₂ passivate. Depending on potential, (Ti,Nb)₂AlC and Cr₂AlC showed trans-passive behavior. In 1 M H₂SO₄ solutions, Ti₂AlC, (Ti,Nb)₂AlC, Ti₃SiC₂ and Ti₃GeC₂ passivate, V₂AlC and V₂GeC show active dissolution, while Cr₂AlC exhibits trans-passive behavior. Ti₂AlN and Ti₄AlN₃ were passive in all solutions except in 1 M HCl, where Ti₂AlN showed trans-passive behavior. Given that the corrosion behavior of (Ti,Nb)₂AlC is unlike either Ti or Nb, the behavior of the former cannot be predicted from that of the latter.     

Preparation of Ti3AlC2 by mechanically activated sintering with Sn aids

The mechanically activated sintering process was adapted to synthesize Ti₃AlC₂ using 3Ti/Al/2C/0.05Sn powder mixtures. The result showed that the powders containing TiC, Ti₃AlC₂ and Ti₂AlC were obtained by mechanical alloying (MA) 3Ti/Al/2C powders. Addition of appropriate Sn reduced the content of Ti₂AlC and enhanced the synthesis of Ti₃AlC₂ significantly. The powders with highest content of Ti₃AlC₂ were obtained by MA 3Ti/Al/2C/0.05Sn powders. Through pressureless sintering the mechanical alloyed powders at 900–1100 °C for 2 h, the high purity Ti₃AlC₂ material with fine organization was produced.