Unreacted Ti Research Articles

Enhancing Interfacial Stability and Mechanical Strength of a CoSb3-Based Thermoelectric Junction Using Ti-Based Alloy Barrier Layers.

CoSb3-based filled skutterudites (SKDs) are among the most promising materials for power generation. However, the poor interfacial stability and mechanical strength severely limit their practical application when joined with Cu electrodes. In this study, we propose multiphase Ti-based alloy barrier layers for CoSb3-based thermoelectric junctions to prevent the continuous brittle TiCoSb phase formation. Following the principles of coefficient of thermal expansion matching, we designed three types of Ti80-xNbxCo20 (x = 0, 5, and 10, at.%) barrier layers with the thin intermetallic compound (IMC) layers (<20 μm). Transmission electron microscopy analysis revealed that the interfacial microstructure of the Ti75Nb5Co20/Ce-SKD junction comprises Ti5Sb3, Ti5CoSb3, TiCoSb, and TiSb2 phases, as well as unreacted TiCo, Ti2Co, and Ti(Nb)ss phases, demonstrating a uniform staggered distribution state. After aging tests, the IMC thickness increased gradually from 7 to 12 μm, and the interfacial contact resistivity increased from 7.59 to 15.46 μΩ·cm2. A Cu layer was chosen as a buffer during the brazing process to prevent the formation of cracks and holes. After aging for 360 h at 823 K, the shear strength of the brazed joints remained at ∼21 MPa. Our results demonstrate that the Cu/CuSnP/Cu/Ti75Nb5Co20/Ce-SKD brazed joint exhibits excellent interfacial stability and satisfactory mechanical strength.

Corrosion behavior of 7050 and 7075 aluminum alloys processed by reactive additive manufacturing

In this work, high-strength 7075 and 7050 aluminum alloys were processed by the laser powder bed fusion (LPBF) technique. Titanium and boron carbide particles were added to base 7050 and 7075 alloy feedstocks. These reacted in the melt to form inoculants in situ, resulting in a crack-free, refined, and textureless microstructure. X-ray diffraction, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectroscopy (EDS) techniques were used to characterize the process-induced microstructure of the alloys. Reactive Additive manufactured (RAM) alloys showed precipitation of various sub-micron to nanoscale phases such as Zn-Cu, Cu-Fe, Mg-Cu, Mg-Zn, and pure Zn. The corrosion response of RAM alloys was analyzed and compared with respective wrought alloys by various electrochemical measurements such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and atomic spectroelectrochemistry (ASEC) techniques. A reduction in corrosion resistance was observed in RAM alloys as compared to wrought counterparts due to thepresence of unreacted Ti and B4C particles and a higher cathodic activation attributed to the underlying microstructure. Time evolution surface imaging and post-corrosion microstructures were analyzed to support the understanding of underlying corrosion mechanisms.

Laser cladding of electroplated Ni-WC on surface of TA2：microstructure and mechanical properties

The combination of electroplating Ni/WC composite coating and laser cladding was utilized to modify surface of TA2 substrate. Microstructure of the Ni/WC composite coating was characterized by SEM and TEM. The composite coating consists mostly of TiNi-WC layer and Ti2Ni layer. The phases in the TiNi-WC layer include TiNi, unreacted Ti and uniformly dispersed WC, while Ti2Ni is the main phase in the Ti2Ni layer. The composite coating shows remarkable nano-hardness (9.5 GPa) compared to the TA2 substrate (2.5 GPa), which is contributed by residual WC particles in the laser remelted coatings. In addition, the hard phase WC particles facilitates the wear resistance of the laser remelted Ni/WC coating. Abrasive wear and adhesive wear mechanism are dominant in the friction and wear mechanism.

Preparation and characteristics of Ti3AlC2 -Al3Ti/Al composite materials synthesized from pure Al and Ti3AlC2 powders

A novel Ti 3 AlC 2 - Al 3 Ti/Al composite was fabricated by hot pressing Ti 3 AlC 2 and pure Al powders. One strong interfacial bonding appeared due to the formation of Al 3 Ti phase between Ti 3 AlC 2 and Al observed by HRTEM. Flexural strength, compressive strength, compressive yield strength and Vickers hardness of 30 vol% Ti 3 AlC 2 reinforced Al composite were measured to be 398 ± 5 MPa, 404 ± 17 MPa, 359 ± 12 MPa, and 1.91 ± 0.01 GPa, respectively. Transgranular fracture behavior occurred in unreacted Ti 3 AlC 2 particles in bending test, while no interfacial debonding was observed. The enhancement of mechanical properties were attributed to the load transfer strengthening, thermal mismatch strengthening and dispersion strengthening mechanism. • Prepared a novel Ti 3 AlC 2 - Al 3 Ti/Al composite. • Charactering the brilliant reaction process between Ti 3 AlC 2 and Al. • The prepared composite exhibited optimized microstructures and mechanical properties.

Fabrication of in-situ Ni/Ni3Ti-NiTi-Fe2Ti-βCr2Ti reinforced Ti-based composite coating using tungsten inert gas processing

This study is an attempt to improve the surface micro-hardness and corrosion resistance of pure Ti by fabricating in-situ Ni/Ni3Ti-NiTi-Fe2Ti-βCr2Ti composite using TIG process and Inconel 718 filler alloy. Surface coating prepared by depositing of the filler rods on the surface of pure Ti substrate at various heat inputs ranging from 2.750 to 3.125 kJ/cm. Field emission scanning electron microscopy (FESEM) and X-ray diffraction spectroscopy (XRD) were carried out for detailed characterization of the elemental composition, surface morphology and phase analysis. X-ray diffraction via sin2ψ analysis and ASTM E384-HV were used to evaluate the residual stresses at the interface of prepared coating and micro-hardness of prepared samples, respectively. The corrosion behavior of the coatings was also investigated in NaCl 3.5 wt% electrolyte using potentiostat analysis. Results manifested that the Ni3Ti dendritic phase, NiTi needle-like phase, Fe2Ti and β-Cr2Ti rode-like phases mainly formed at the heat inputs ranging from 2.750 and 3 kJ/cm, whereas the Ni2Nb and Ni8Nb phases mainly generated at the higher heat input equal to 3.125 kJ/cm and the creation of micro-crack and micro-segregation was occurred. By increasing in the heat input up to 3 kJ/cm, creating of unreacted Ti particles and increasing in the size of dendrite and rode-like particles have been observed in the fusion zone. All of the prepared samples have much higher hardness than that of the pure Ti (in the range of 2.3–5.3 times higher than Ti). In this condition, based on the polarization and electrochemical impedance spectroscopy (EIS) tests, the prepared sample at the heat input equal to 2.875 kJ/cm has the highest corrosion resistance. The results of residual stresses determination of the optimum sample exhibited the tensile residual stress equal to 215 ± 40 MPa at the centerline of fusion zone.

Influence of composition and growth conditions on TiN nanocrystallite formation in TiN-metal films

The nanostructure of Ti in TiN-Cu films grown by Pulsed Layer Deposition (PLD) is investigated using Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy at the Ti-K edge. The TiN-Cu films were grown on Si (100) crystal wafers using either Ti (99.95%) and Cu (99.99%) elemental targets or a TiCu intermetallic target (99.95%), under flowing N2 (99.999 %). The influence of varying either the Ti concentration or the N2 partial pressure (PN2) was explored in a series of TiN-Cu films, in an effort to distinguish how these parameters affect the degree of TiN nanocrystalline formation. The Ti-K-EXAFS analysis results proposes that the growth of stoichiometric TiN nanocrystallites is favoured in all studied films, however the extent of TiN formation is strongly modulated as a consequence of changing growth conditions and film composition. In particular, when growth proceeds from a TiCu intermetallic target under constant PN2, decreasing the Ti concentration promotes the formation of a (Ti, Cu) solid solution at the expense of the formation of TiN nanocrystallites. Thus, PLD growth using intermetallic targets yields TiN-Cu films with extended TiN nanocrystalline regions embedded in a rich-amorphous Cu phase, where the excess of Ti atoms are also incorporated. When Cu and Ti elemental targets are used (Ti:Cu = 50:50), Ti preferentially bonds to N2 upon increasing PN2. The extent of TiN nanocrystalline formation is enhanced, while bond formation between the unreacted Ti atoms and the amorphous Cu regions is also revealed. Consequently, it can be proposed that a proper control of growth conditions and film composition can permit growth of TiN-metal films with improved mechanical response.

Effect of Synthesis Mode and Ni Particle Size on Microstructural Aspects and Hardness Properties of Combustion-Synthesized NiTi

NiTi intermetallic compound was fabricated via two modes of the combustion synthesis process, namely, thermal explosion (TE) and self-propagating synthesis (SHS). The effect of combustion synthesis mode as well as Ni particle size on the microstructure and microhardness of the final products was investigated. The phases in the products were determined using XRD technique, and microstructural investigations were performed using optical as well as SEM-EDS in order to make a comparison between microstructural evolutions in each mode, other conditions being constant. The analyses showed that the desired B2(NiTi) was successfully formed as the primary phase in all samples, and no unreacted Ni or Ti powders were present. The main secondary phase was NiTi2 which was invariably present in all samples; however, the percentage as well as the morphology of the detrimental NiTi2 phase was found out to be controllable by the mode of combustion as well as Ni particle size. A comparison between the two modes revealed that samples produced by TE showed coarse dendrites in the microstructure; they also presented higher average microhardness values. The SHS-synthesized samples exhibited microstructures similar to those observed in heat-treated and homogenized NiTi obtained from methods such as vacuum arc remelting and vacuum induction melting, and contained finely dispersed NiTi2 particles. It was shown that a decrease in Ni particle size presented a grain refining effect on NiTi2 in both modes.

Interface Structure and Mechanical Properties of 7075Al Hybrid Composite Reinforced with Micron Ti Metal Particles Using Pressure Infiltration

Micron Ti metal particles were incorporated into SiCp/7075Al composites using pressure infiltration. The interface structure between the Ti metal particles and the matrix during the casting processes were investigated. Results show that the dispersed unreacted Ti particles form mutual diffusion layer at the interface without the formation of low-temperature intermetallic phases during the solidification processes. The interaction between the micron Ti and the molten aluminum alloy is subject to the mutual diffusion coefficient of Ti–Al rather than the reaction activation energy. The tensile strength and plasticity of the composite were improved simultaneously due to the high interfacial bonding strength and released thermal misfit stress cause by the incorporated Ti metal particles.

Microstructure evolution of Cu-TiC composites with the change of Ti/C ratio

In this work, Cu-TiC composites have been successfully prepared by adding Ti and carbon black powder mixture into Cu melts. The microstructure evolution of the composites with the change of Ti/C ratio and its mechanism has been investigated. It is found that when Ti and carbon black powder mixture is added into Cu melts, Ti will react with carbon black to form TiC, which makes the carbon black be wetted. Then the unreacted Ti will be dissolved and further reacted with the wetted carbon black to form more TiC. However, the formed TiC particles are dispersed difficultly and tend to aggregate into agglomerations. Increasing the Ti/C ratio is an effective method to improve the distribution of TiC. It is found that, comparing with the Cu-4Ti-1C, non-stoichiometric TiCx with smaller x which has the better wettability with Cu melts can be synthesized in the Cu-5Ti-1C and Cu-6.67Ti-1C. As a result, TiC particles are more uniformly distributed in the prepared Cu-Ti-C composites with higher Ti/C ratio.

NiTi coating on Ti-6Al-4V alloy by TIG cladding process for improvement of wear resistance: Microstructure evolution and mechanical performances

A thick layer of NiXTiY (NiTi and NiTi2) was deposited on Ti-6Al-4V alloy by tungsten inert gas (TIG) cladding process using Ni and Ti powder mixture prepared by ball milling route as precursor. The analysis shows that the microstructure of the produced NiTi coating principally governs by the heat input, which was controlled through the employed processing current. The hardness of the NiTi clad layer measured by Vickers micro-indentation method was found reasonably higher as compared to Ti-6Al-4V alloy substrate. The XRD and EDS analysis of the clad layer revealed the formation of NiTi and NiTi2 as major phases along with some unreacted Ti and TiAl3 intermetallic. The sliding abrasive wear of the coating performed against abrasive disc shows upto 9.5 times reduction in the wear value as compared to the uncoated Ti-6Al-4V alloy as measured by its height loss. The experimental results revealed an ample effect of the TIG current on the hardness value and wear characteristic of the clad layer, which is predominantly dependent on the morphology and percentage of phase constituent formed. The produced NiTi coating has prospective applications in biomedical, where inadequate wear resistance of Ti-6Al-4V alloy is the major concern for its use.

Ti2Al(C, N) Solid Solution Reinforcing TiAl-Based Composites: Evolution of a Core-Shell Structure, Interfaces, and Mechanical Properties.

In this work, Ti2Al(C, N) solid solution with lamellar structure-enhanced TiAl matrix composites was synthesized by vacuum arc melting, using bulk g-C3N4, Ti, and Al powders as raw materials. The phases, microstructures, interfaces, and mechanical properties were investigated. MAX phase of Ti2Al(C, N) solid solution with lamellar structure was formed. During the melting process, first, C3N4 reacted with Ti to form Ti(C, N) by Ti + C3N4 → Ti(C, N). Then Ti2Al(C, N) was formed by a peritectic reaction of TiAl(l) + Ti(C, N)(s) → Ti2Al(C, N). C3N4 is the single reactant that provides C and N simultaneously to final product of Ti2Al(C, N). The interfaces of TiAl//Ti2Al(C, N) and Ti2Al(C, N)//Ti(C, N) display perfect orientation relationships with low misfit values. The microhardness, compressive strength, and strain of best-performing TiAl-10 mol % Ti2Al(C, N) composite were improved by 45%, 55.7%, and 50% compared with the TiAl alloy, respectively. Uniformly distributed Ti2Al(C, N) and unreacted Ti(C, N) particles contributed to the grain refinement and reinforcement of the TiAl matrix. Laminated tearing, particle pull-out, and the crack-arresting of Ti2Al(C, N) are crucial for the improvement in compressive strength and plasticity of the composites.

Study of reaction sequences during MSR synthesis of TiC by controlled ball milling of titanium and graphite

During reactive ball milling of Ti and C, mechanically induced self-propagating reaction (MSR) synthesis of TiC is reported to occur via a process including initial formation of small amounts of TiC prior to exothermic ignition, followed by MSR and the formation of stiochiometric TiC (Dorofeev et al., 2011; Oghenevweta et al., 2016 [1, 2]). However, both the chemical evolution and mechanisms of reaction and growth of TiC both prior to, during and after ignition are not fully understood. This research focuses on fundamental understanding of the reaction sequences during MSR synthesis of TiC from elemental Ti and C (graphite).Magnetically controlled ball milling of stoichiometric (1:1) powder mixtures of titanium (Ti) and graphite (C) was performed under He gas with the exothermic ignition point by determined via in-situ temperature measurement. X-ray diffraction, Scanning Transmission Electron Microscopy (STEM) with electron energy loss spectroscopy (EELS), Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS) were employed to interpret the reaction sequences.The reaction sequence involved the following: During milling prior to ignition, severely deformed Ti, spheriodised graphite and amorphous carbon forms, and minor amounts of off-stiochiometric nano-TiC1−x crystals. In addition to the formation of TiC1−x, XPS revealed the formation of oxide skins coating the surface regions of the milled powders. There is also an evolution towards stiochiometric TiC with increasing milling time. Immediately after ignition, a reacted product comprising a mixture of multi-layer stacks of thin TiC plates form, in addition to a matrix comprising large TiC particles which have been liquid phase sintered under the high local heat of reaction by thin layers of unreacted Ti. MSR occurs via a dual mechanism involving rapid growth of existing TiC, plus nucleation and growth of new TiC. High spatially resolved EELS combined with STEM revealed additional information about the inhomogeneous chemical environment of the milled powders.

In-situ TiC-TiB2 coating on Ti-6Al-4V alloy by tungsten inert gas (TIG) cladding method: Part-I. Microstructure evolution

In order to improve the surface mechanical performance of Ti-6Al-4V alloy, in-situ TiC-TiB2 composite coating was deposited by tungsten inert gas (TIG) cladding process using Ti and B4C as precursor powder. Based on the available literature, SEM images of the blended precursor powder mixture and coating layer, electron probe micro analysis (EPMA) and corresponding XRD analysis of the produced coating, the formation mechanism of the present TiC-TiB2 composite coating during TIG cladding process was elucidated. The analysis shows that in the coating, TiB2 and TiB phases appeared as hexagonal or rectangular shape, whereas TiC as spherical shape within the matrix of unreacted Ti, Ti-6Al-4V alloy form the substrate and intermetallic phase like TiAl3 formed during the cladding process. The analysis also revealed that the TIG cladding processing current and scan speed have substantial effect on the coating morphology and the phases formed in the coating.

Effects of Unreacted Ti Particles on the Dry Sliding Tribological Behavior of Squeeze-Cast (SiCp + Ti)/7075Al Hybrid Composites Under Different Applied Loads

The effects of Ti particles on the dry sliding tribological behavior of squeeze-cast (SiCp + Ti)/7075Al hybrid composites were investigated. The incorporated Ti particles exerted significant influence on the tribological behavior of the composites except for the wear mechanism. Ti particles could hinder the crack of SiC particles on the contact surface of the composites, which made the composites show an obvious break-in stage at the beginning of the test. The friction coefficient showed varied amplitude and wave fluctuation trends due to the interactions among the debris, the composite and the counterpart without the influence of Ti particles. Moreover, the incorporated Ti particles exerted different effects on the wear resistance of the composites under different applied loads. Ti particles, which could hinder the fracture of SiC particles and the formation and propagation of the cracks in the subsurface deformation, improved the wear resistance of the composites under low applied load. The interfacial stresses in the vicinity of Ti particles increased sharply due to the different strains between the matrix and Ti particles under high applied load, which eventually invalidated the strengthening effects of the Ti particles. Finally, the wear resistance of the composites was deteriorated with the increase in applied load.

Sequence of phase evolution during mechanically induced self-propagating reaction synthesis of TiB and TiB2 via magnetically controlled ball milling of titanium and boron powders

Mechanically induced self-propagating reaction synthesis of titanium boride and diboride was investigated for elemental mixtures of titanium and amorphous boron in starting atomic ratios of Ti50B50 and Ti34B66. Samples were milled for different periods leading up to and after an ignition point which was determined by in-situ monitoring of the mill temperature. Methods of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy were used to determine product evolution.For both compositions, a partial crystallisation of amorphous boron commences during the early stages of milling and progresses through to the ignition point. At later stages and prior to ignition, HRTEM combined with electron diffraction revealed the formation of nanocrystalline titanium diboride, which was confirmed by Raman spectroscopy to be of an off-stoichiometric, boron-lean composition; TiB2-x. This phase is believed to have formed by solid-state reaction at the interface of the heavily deformed Ti and amorphous B via a mechanism which parallels the formation of nanocrystalline off-stoichiometric Ti1+xC1-x prior to the self-propagating synthesis of TiC from Ti and graphite. After ignition, the product for Ti34B66 comprised relatively large facetted grains of TiB2, liquid phase sintered by thin regions of unreacted Ti which had melted due to high heat of reaction. In contrast, the product of Ti50B50 comprised platelike TiB particles, and spheroidal dispersions of TiB2 in unreacted Ti and B. Likely mechanisms for the different product evolution routes for the two compositions are proposed and discussed.

Synthesis of high-purity Ti2SC powder by microwave hybrid heating

A novel simple method is presented to synthesize high-purity Ti2SC powder using Ti/C/S and Ti/C/TiS2 systems by microwave hybrid heating at different temperatures in argon atmosphere. It was confirmed that the synthesis temperature is strongly dependent on the starting composition. For Ti/C/S system, Ti2SC with small amounts of TiS and TiC was synthesized at 1200 °C. For Ti/C/TiS2 system, high-purity Ti2SC was synthesized at 800 °C and above. The synthesis of Ti2SC powder at low temperature was attributed to the combination of microwave effect by microwave hybrid heating and the introduction of TiS2 as sulfur source. Scanning electron microscopy (SEM) analysis indicated that the layered structure of Ti2SC particles is perfectly formed at 1100 °C, and the crystal particle size approaches to homogeneity which is about 2–5 μm. It was presumed that the formation mechanism of Ti/C/TiS2 system is that TiS2 firstly reacts with Ti to form Ti–S intermetallics, then Ti–S intermetallics reacts with un-reacted Ti and graphite to produce Ti2SC.

Accelerated Degradation of Ag-Cu-Ti Alloy in Molten Sodium Via Dissolution of Sliver

Ag-Cu-Ti alloys are widely used in active metal brazing (AMB) to bond between heterogeneous metal-ceramic joints. This is mainly because brazed joints with the alloys show acceptable bonding strength and good oxidation resistance at high temperatures of 400~600 oC through a simple but low cost bonding process. For example, a brazed joint between 304 stainless steel and α-Al2O3 with a commercial Ag-35.2Cu-5.4Ti (in wt.%) alloy showed excellent shear bonding strength of 100~200 MPa, and the oxidation kinetics of the alloy in air obeys the parabolic rate law with the rate constant of about 10-10~10-12 g2 cm−4 s−1 in the temperature range of 400~600oC. Previous studies showed that the alloy formed slowly growing protective Cu- and/or Ti- oxide layers. However, when the brazing alloys are applied to applications associated with molten sodium (Na) environments, such as cooling pipe joints in nuclear power plants and heterogeneous joints of high temperature sodium beta-alumina batteries, the joints show poor bonding performance resulting in failure in less than 100 hours at 350oC. In order to elucidate the phenomena different from a general expectation, there is a need to investigate the effect of molten sodium on the degradation kinetics of Ag-Cu-Ti alloys. In this study, disk shaped coupon specimens (10 mm in diameter, 5 mm in thickness) made of 430 stainless steel and α-Al2O3 were prepared and the heterogeneous specimens were brazed with a Ag-35.2Cu-5.4Ti alloy. The bonded assemblies were exposed to molten sodium at 350oC. Their degradation behaviors were characterized via (1) cross-sectional observation through optical microscopy (OM), secondary electron microscopy (SEM), transmission electron microscopy (TEM), and field-emission electron probe micro analyzer (FE-EPMA), and (2) kinetics analysis with Na penetration depth measurements at different exposure times. As the exposure proceeds, it was characterized that Ag in the Ag-Cu-Ti alloy continuously dissolves into the Na melt at the alloy-Na interface leaving the unreacted Cu and Ti to be a porous structure. The kinetics of the Na penetration depth into the alloy is governed by the linear rate law. It turns out that (1) no continuous and protective layer at the reaction front between the Na melt and alloy is formed and (2) Ag concentration in the melt in the vicinity of the reaction front is maintained below its maximum solubility in molten Na by sufficiently rapid homogenization of the Na melt (with a small amount of dissolved Ag) at this temperature. It was concluded that rapid degrdation of Ag-Cu-Ti in molten Na is not via corrosion but via dissolution of alloying element(s) in the melt although its resulting microstructure is hardly distinguishable from that formed by corrosion process. Since the reaction front is continuously refreshed, the velocity of the reaction front, i.e., the penetration depth of Na into the alloy as a function of time, is governed by the linear rate law which is analogous to gaseous corrosion forming porous or discontinuous corrosion products.

Thermal Conductivity and Interface Thermal Conductance of Titanium Silicide Films on Si

Titanium silicide films were prepared by magnetron sputtering of Ti on B-doped Si (100) and annealing at different temperatures up to 700 °C in argon atmosphere. Films were also prepared by laser physical vapor deposition (LPVD) of Ti at 500 °C and 600 °C on B-doped Si (100) followed by in situ annealing. The films were characterized by X-ray diffraction for phase identification, scanning electron microscopy for interface microstructure and oxygen level, atomic force microscopy for interface roughness, transient thermoreflectance for thermal conductivity and interface thermal conductance of the interface with Si. Annealing at 700 °C for 1 h was responsible for the complete formation of C54 phase. LPVD at 500 °C and 600 °C was responsible for C54 formation with smaller grain size, but unreacted Ti and other silicide phases were also present. The interface in all the films was continuous with the absence of voids. The thermal conductivity of the films increased for higher processing temperature. The interface thermal conductance for films prepared below 700 °C was lower. Film annealed at 700 °C significantly showed higher interface thermal conductance and lower effective thermal resistance. Comparison of thermal properties of the TiSi2 films with that of WSi2 films prepared previously showed that the effective thermal resistance of the C54 phase is lower.

Formation of in-situ Al3Ti particles from globular Ti powders and Al alloy melt under ultrasonic vibration

The formation process of Al3Ti was studied based on the in-situ reaction between globular solid Ti powders with almost uniform size and 2024 Al melt under ultrasonic vibration. The microstructures of the Al3Ti/Al composite were examined at different reaction time. The reaction mechanism was analyzed based on the phase diagram and empirical reaction kinetics. Moreover, the effects of ultrasonic vibration on the formation of Al3Ti were discussed. The results show that the Al3Ti formed a layer around the unreacted Ti particle and was ruptured as the reaction continuing. An empirical reaction kinetics model of in-situ Al3Ti was established. The kinetic exponent n is determined to be 0.86, which is much higher than that of the standard diffusion-controlled growth (n = 0.5). The ultrasound assisted reaction follows an interface-controlled growth which means a higher reaction rate. The comprehensive effects of instantaneous pressure, high-intensity shock waves and local high-temperature caused by acoustic streaming and cavitation, are responsible for the high reaction rate and fine Al3Ti particles during the reaction process under ultrasonic vibration.

Microstructural Studies on Ti–Y2O3 Interface Reaction Products

Ti and Y2O3 reaction products find application in flash memory drives, in ODS steels as dispersion strengthening constituent and in Ti castings. The solid state reaction between Ti and Y2O3, was studied using a suitable experimental setup. The reaction product was investigated by a variety of electron microscopy techniques including SEM, TEM and EBSD. Surface characterisation revealed islands of the reaction product and step like structure for the un-reacted Ti matrix, typical of thermal etching. The reaction product was identified as Y2TiO5 by analysis of selected area electron diffraction pattern.