Ti Al Si Research Articles

Effects of carbon addition on Ti–Al–Si coatings synthesized by self‐generated gradient hot‐dipping infiltration method

AbstractThe effects of carbon addition on the microstructure and oxidation resistance of Ti–Al–Si coatings synthesized by the self‐generated gradient hot‐dipping infiltration method were studied. The microstructure, phase structure, as well as composition of the coating, were observed by using X‐ray diffraction, scanning electron microscope, and energy dispersive spectrometer. It was found that when carbon was added into the Al‐SiO2 system, the coating was composed of L‐(Al,Si) phase and Ti(Al,Si)3 phase. The thickness of the Ti(Al,Si)3 phase layer increased along with the dipping time. The cycle oxidation tests at 900°C for 160 h showed that the weight gains of the coating samples were only 8.1% of that of the Ti–6Al–4V alloy samples. This result indicates that the coatings remarkably enhanced the oxidation resistance of Ti–6Al–4V alloy, which could be ascribed to two reasons: (1) the mixed oxidation zone of Al2O3, Ti(Al,Si)3, and Ti5Si3 on top of the oxidized coating could act as a barrier to retard the diffusion of oxygen to the substrate; and (2) several new phase layers (Ti3Al, TiAl, and Ti5Si3 + TiAl2) near the substrate during oxidation could reduce the cracks at the bottom of the oxidized coating.

Structure and Phase Formation of a Ti–Al–Si Based Alloy Prepared by Self-Propagating High-Temperature Synthesis Compaction

Structure and Phase Formation of a Ti–Al–Si Based Alloy Prepared by Self-Propagating High-Temperature Synthesis Compaction

Experimental investigation of Ti–Al–Si phase equilibria at 800–1200 °C

Five partial isothermal sections of the Ti–Al–Si system up to 70 at% Al and 40 at% Si have been determined experimentally between 800 and 1200 °C. Seven alloys were heat-treated for 24–1504 h and characterized utilizing scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and differential thermal analysis. No ternary phase was found and αTi, βTi, Ti3Al, TiAl, TiAl(1d-APS), TiAl2, TiAl3 are in equilibrium with Ti5Si3. A partial vertical section at 9 at% Si shows that all determined data are consistent with each other.

Atomic diffusion mechanism and interface nanomechanics in the Al/Ti composite structures

In this work, Al/Ti composite structures are obtained by isothermal compression at 550 °C and then annealed at 500–650 °C, respectively. The microstructure, elemental diffusion behavior , bonding characteristic and nanomechanics at the Al/Ti interface are systematically investigated by different material characterization methods. A nanoscale Al–Ti solid solution is formed at the contact interface between AA6063 and Ti–6Al–4V sheet, and TiAl 3 is generated after annealing. Si-enriched clusters at the Ti/TiAl 3 interface and Mg-enriched clusters at the Al/TiAl 3 interface are observed, which retards the growth of the TiAl 3 layer. With an increase in the annealing temperature, the average thickness of the TiAl 3 layer dramatically increases and the enrichment of Si and Mg decreases. Ordered TiAl 3 is gradually formed through the atomic rearrangement in the Ti–Al–Si–V structures at the three-dimensional Ti/TiAl 3 interface, accompanied by the transformation of an order–disorder–order structure. The nanomechanics at the interface is closely related to the annealing temperature, elemental diffusion and microstructure characteristic, which is also discussed. • Si-enriched and Mg-enriched clusters are observed at the Al/Ti interface, which retards the growth of TiAl 3 . • With an increase in temperature, the thickness of the TiAl 3 layer increases and the enrichment of Si and Mg decreases. • TiAl 3 is formed by the atomic rearrangement in Ti–Al–Si–V structures and the transformation of a disorder–order structure. • Differences of the nanomechanics at the interface cause the deformation incompatibility and interfacial debonding.

Structure and Phase Composition of Ti–Al–Si Powder Composites at Different Synthesis Conditions

Structure and Phase Composition of Ti–Al–Si Powder Composites at Different Synthesis Conditions

Changes in the structural and textural state of titanium alloy VT41 after hot upsetting and annealing

A study of the structure of titanium alloy VT41 (Ti–Al–Si–Zr–Sn– β-stabilizers) was carried out on a sample subjected to hot upsetting in the (α+β)-region – conditions simulating the stamping of a disk of a gas turbine engine (GTE). The features of the formation of the textural state of primary and secondary globular grains, as well as the kinetics of their dissolution with an increase in the annealing temperature, have been determined. As a result of heat treatment at 995°C, the homogeneity of the alloy structure significantly increases comparing to the deformed state, which is associated with the recrystallization of lamellar and small-globular grains and the retention of primary globular grains of the α-phase. The sequence of structural changes has been established during the annealing within the temperature range from 950 to 1040°C.

Optimization of thermodynamic and surface properties of ternary Ti–Al–Si alloy and its sub-binary alloys in molten state

Thermodynamic and surface properties of the ternary system were studied at different higher temperatures (1973 K, 2073 K, 2173 K and 2273 K). The thermodynamic properties were studied using the Chou, Kohler and Toop models. Meanwhile, the surface properties were investigated using the same models plus the Butler model. The thermodynamic and surface properties of the ternary alloys computed from different models were compared with one another. The surface concentration of the components of the ternary Ti–Al–Si alloy was computed using Butler's equation.

Development of TiAl-Si Alloys-A Review.

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods.

Joining of Silicon Particle-Reinforced Aluminum Matrix Composites to Kovar Alloys Using Active Melt-Spun Ribbons in Vacuum Conditions

The vacuum brazing of dissimilar electronic packaging materials has been investigated. In this research, this applies silicon particle-reinforced aluminum matrix composites (Sip/Al MMCs) to Kovar alloys. Active melt-spun ribbons were employed as brazing filler metals under different joining temperatures and times. The results showed that the maximum joint shear strength of 96.62 MPa was achieved when the joint was made using Al-7.5Si-23.0Cu-2.0Ni-1.0Ti as the brazing filler metal at 580 °C for 30 min. X-ray diffraction (XRD) analysis of the joint indicated that the main phases were composed of Al, Si and intermetallics, including CuAl, TiFeSi, TiNiSi and Al3Ti. When the brazing temperature ranged from 570 °C to 590 °C, the leakage rate of joints remained at 10−8 Pa·m3/s or better. When the joint was made using Al-7.5Si-23.0Cu-2.0Ni-2.5Ti as the brazing filler metal at 580 °C for 30 min, the higher level of Ti content in the brazing filler metal resulted in the formation of a flake-like Ti(AlSi)3 intermetallic phase with an average size of 7 µm at the interface between the brazing seam and Sip/Al MMCs. The joint fracture was generally in the form of quasi-cleavage fracture, which primarily occurred at the interface between the filler metal and the Sip/Al MMCs. The micro-crack propagated not only Ti(AlSi)3, but also the Si particles in the substrate.

Modification of the Structure of Ti–Al–Si–Cu–N Gradient Coatings by Mechanical Tests

The structural state in the zones of indentation and scratch testing of Ti–Al–Si–Cu–N gradient coatings has been studied using dark-field electron microscopy for analyzing the bending-torsion of a crystalline lattice. It has been found that the strength properties of a substrate, which determine the degree of plastic relaxation of the applied load, are important for modifying the structure of coatings. An increase in the bending of a crystalline lattice with respect to the undeformed state, heterogeneity, and anisotropy of its values with respect to the point and axis of applied load have been found for the material under the indenter top. The formation of strips of localized deformation, in which an increase in crystal sizes, a decrease in the bending of a crystalline lattice, and residual local stresses are observed, has been shown.

Thermodynamics of Nitrogen Solubility and Nitride Formation in Fe–Cr–Ti–Al–Si–N Alloy Melts

Thermodynamics of Nitrogen Solubility and Nitride Formation in Fe–Cr–Ti–Al–Si–N Alloy Melts

Micrographic Properties of Composite Coatings Prepared on TA2 Substrate by Hot-Dipping in Al–Si Alloy and Using Micro-Arc Oxidation Technologies (MAO)

A composite coating composed of intermetallic compounds, Al–Si alloys, and an oxide ceramic layer was prepared on TA2 substrate by hot-dipping Al–Si alloy and micro-arc oxidation (MAO) methods. The microstructure and composition distribution of the resulting hot-dipped Al–Si alloy layer and MAO-caused ceramic layer were studied by scanning electron microscope (SEM) and energy dispersive spectrum (EDS). In addition, the phase composition of the diffusion layer obtained by the Al–Si alloy hot-dipping procedure was investigated by electron backscattered diffraction (EBSD), and the phase structure of the MAO-treated layer was studied by X-ray diffraction (XRD) analysis and X-ray photoelectron spectroscopy (XPS). The MAO method can make the hot-dipped Al–Si alloy layer in-situ oxidized to form a ceramic layer. Finally, a three-layer composite coating composed of a diffusion layer formed by the Ti–Al–Si interdiffusion, an Al–Si alloy layer and a ceramic layer was prepared on TA2 substrate. Compared with TA2 substrate, the TA2 sample with a three-layer composite coating has larger friction coefficient and less abrasion loss. The three-layer composite coating can significantly improve the wear resistance of TA2. A technical composite method was developed to the low cost in-situ growth of alumina-based ceramic wear-resistant coatings on TA2 substrate.

A design of self-generated Ti–Al–Si gradient coatings on Ti–6Al–4V alloy based on silicon concentration gradient

A new method, referred to as Self-generated Gradient Hot-dipping Infiltration (SGHDI), was proposed to prepare Ti–Al–Si gradient coatings on Ti–6Al–4V alloy. The coating samples with different dipping time (20, 30, 40, 50 and 60 min) were prepared at the dipping temperature of 800 °C. The microstructure, phase structure and composition of the coating were observed by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results demonstrated that the silicon concentration gradient coatings were in the sequence of Ti(Al,Si)3 phase, τ2 (Ti(AlxSi1-x)2) phase + Liquid-(Al,Si) phase, and Liquid-(Al,Si) phase from the substrate. The high temperature oxidation kinetics data of samples with a hot-dipping time of 60 min showed that the coating exhibited good high temperature oxidation resistance. The main advantage of this design of coatings lies in that in addition to the dense Al2O3 layer formed at high temperature to block oxygen atoms, the newly formed dense alloy layers during high temperature oxidation would stop crack growth in the coatings, further preventing oxygen atoms from entering the substrate.

Constitutive behavior and microstructural evolution in Ti–Al–Si ternary alloys processed by mechanical milling and spark plasma sintering

Severe plastic deformation is closely related to the microstructural behaviors of intermetallics or grain refinement by mechanical milling and subsequent rapid sintering process, i.e. high energy ball milling and spark plasma sintering. In this study, the Ti–Al–Si ternary powders were synthesized to investigate their phase transformation by plastic deformation during the mechanical milling in each process time and composition. The sintered-bodies Ti–Al–Si ternary alloys were fabricated by spark plasma sintering among the rapidly consolidated powders, except for the distribution of single phases in accordance with the Al-melting. The microstructures of intermetallics in Ti–Al–Si ternary alloys were composed of titanium aluminides and titanium silicides, and even ternary compounds as a τ1-phase. In particular, the twining or stacking faults induced by severe plastic deformation were revealed through crystallographic patterns and microstructural evidence. These defects were caused by the slip system for TiAl3 (fcc) or Ti5Si3 (hcp) phases, depending on the grain refinement and generation of ambient intermetallics. To estimate the possibility of these defects, various approaches were taken to obtain experimental measurement of the twin probability and stacking fault energy derived from TEM and XRD analyses.

Thermal Stability of Structure and Properties of Gradient and Gradient-Layered Coatings of the Ti–Al–Si–Cu–N System

Using the methods of dark-field electron microscopy analysis, energy-dispersive X-ray microanalysis, hardness measurements and scratch testing, the variations of elemental composition, structure and mechanical properties of gradient and gradient-layered coatings of the Ti–Al–Si–Cu–N system are investigated during annealing in vacuum at the temperatures within the range 973–1373 K. It is found out that at the annealing temperatures up to 1173 K such structural changes as equalization of the nitride-phase lattice parameter throughout the coating thickness and decreased lattice bending are due to the diffusion-induced redistribution followed by a drop in the concentration of the nitride-doping elements and precipitation of the nanosized copper crystals. For the annealing temperature 1373 K, a several-fold (compared to the state after deposition) decrease in the nitride-phase crystal lattice bending and a change in the concentration of the elements of a few tens of percent are revealed, as well as the formation of heterophase nanocrystalline structure during their localization at the interfaces. A similarity of the defect microstructure in the crystals of both coatings after annealing at 1373 K is determined. The influence of the structural-phase transformations on the variations in the hardness and adhesion strength values of the coatings is discussed.

Corrosion mechanism and behavior of high‐velocity arc‐sprayed Al–Ti–Si–RE coating in a simulated deep sea

AbstractThe corrosion protection of deep‐sea equipment using the economical method of thermal spraying has become a research hotspot. This study investigated the corrosion behavior of high‐velocity arc‐sprayed Al–Ti–Si–RE coating in a simulated deep sea with regard to microstructures, compositions, and electrochemical measurements. Results showed that the Al–Ti–Si–RE coating has excellent corrosion resistance at high hydrostatic pressure (HP). HP plays an important role in the anodic reaction of the coating, whereas dissolved oxygen (DO) mainly affects the cathodic reaction. HP accelerates the dissolution of the coating's passive film, which results in steady corrosion. The amount of corrosion products depends on DO. The corrosion of the self‐sealing coating is inhibited in low DO when steady corrosion is achieved.

High-temperature oxidation of Ti–Al–Si alloys prepared by powder metallurgy

The Ti–Al–Si alloys are promising materials for high-temperature use in automotive, aerospace or cosmic industry. The main advantages of these alloys are their low density (approximately 4 g/cm3), good oxidation resistance, and mechanical properties at elevated temperatures. Addition of silicon into the Ti–Al alloys improves the high-temperature behaviour and improves compactness and adhesion of the oxide layer. The resistance against oxidation can be effectively improved also by an appropriate technology of preparation. In this work, the high-temperature cyclic and isothermal oxidation resistance of the Ti–Al–Si alloys are described. The effect of powder metallurgy production route (reactive sintering, mechanical alloying, Spark Plasma Sintering) on high-temperature behaviour was compared. Cyclic and isothermal oxidation tests were carried out at 800 °C and 1000 °C, well above the air-operating limit for TiAl. It was confirmed, that the Ti–Al–Si alloys are resistant at temperature 800 °C, where only very thin oxide layer was formed. Mechanical alloying followed by Spark Plasma Sintering improved the high-temperature behaviour of these alloys, the oxide layer was even thinner.

Oxidation Behavior of Ti-Al-Si-N-O Nanocomposite Films Deposited by Filtered Arc Ion Plating Technique.

Oxidation behavior of nanocomposite films is very important characteristics for application of machining and cutting tools. In this study, Ti-Al-Si-N-O nanocomposite films were fabricated onto WC-Co and Si wafer substrates. The composition of the Ti-Al-Si-N-O films was analyzed by X-ray photo-electron spectroscope (XPS). Also X-ray diffactometer (XRD) analysis was conducted to investigate the crystallinity and phase transformation of the films. As a result of XRD, Ti-Al(18 at.%)-Si-N-O films showed the great oxidation resistance of 950 °C for 30 min in air. Based on glow discharge optical emission spectroscopy (GDOES) depth profiles, Ti-Al(18 at.%)- Si-N-O film annealed at 950 °C for 30 min shows formation of aluminum oxide layer on the film surface. On the other hand, Ti-Al(7.56 at.%)-Si-N-O film had a titanium oxide layer on the surface after annealing at 950 °C for 30 min.

Microstructure and Mechanical Properties of Functional Graded Ti–Al–Si–N–O Nanocomposite Films Deposited by Filtered Arc Ion Plating Technique

Functional graded Ti-Al-Si-N-O nanocomposite films were deposited onto WC-Co substrate by a filtered arc ion plating system using TiAl and TiSi composite targets under N₂/Ar atmosphere. XRD and XPS analyses revealed that the synthesized Ti-Al-Si-N-O films were nanocomposite consisting of nanosized (Ti, Al, Si)N crystallites embedded in an amorphous Si₃N₄/SiO₂ matrix. The hardness of the Ti-Al-Si-N-O films exhibited the maximum hardness values of ~47 GPa at a Si content of ~5.63 at.% due to the microstructural change to a nanocomposite as well as the solid-solution hardening. Besides, Ti-Al-Si-N-O film with Si content of around 5.63 at.% also showed perfect adhesive strength value of 105.3 N. These excellent mechanical properties of Ti-Al-Si-N-O films could be help to improve the performance of machining tools and cutting tools with application of the film. A comparative study on microstructural characteristics among Ti-Al-Si-N-O films with various Si contents is reported in this paper.

Preparation of TiAl15Si15 intermetallic alloy by mechanical alloying and the spark plasma sintering method

ABSTRACTThis work is devoted to the preparation of alloys based on intermetallic compounds in the Ti–Al–Si system by powder metallurgy using mechanical alloying and the spark plasma sintering (SPS) method. The aim was to describe the formation of intermetallic phases during mechanical alloying of TiAl15Si15 (wt-%) alloy and to consolidate the powder prepared by optimised conditions. Phase composition, microstructure and hardness of compacted alloy were determined. Four hours of mechanical alloying is sufficient time for preparation of pure elements free material composed only of intermetallic phases. After consolidation, the TiAl15Si15 alloy has a homogeneous structure composed of silicide (Ti5Si3) in aluminide (TiAl) matrix. The hardness of the material reaches 865 ± 42 HV 5.