Titanium Aluminide Powders Research Articles

Pressing and Sintering of Titanium Aluminide Powder after Ball Milling in Silane-Doped Atmosphere

Due to the high specific surface area of titanium aluminide powders, significant and unavoidable surface oxidation takes place during processing. The resulting oxides disrupt the conventional powder metallurgical process route (pressing and sintering) by reducing the green strength and sintered properties. Oxide-free particle surfaces offer the potential to significantly increase particle bond strength and enable the processing of difficult-to-press material powders. In this work, the effect of milling titanium aluminide powder in a silane-doped atmosphere on the component properties after pressing and the subsequent sintering was investigated. Ball milling was used to break up the oxide layers and create bare metal surfaces on the particles. With the help of silane-doped inert gas, the oxygen partial pressure was greatly reduced during processing. It was investigated whether oxide-free surfaces could be produced and maintained by milling in silane-doped atmospheres. Furthermore, the resulting material properties after pressing and sintering were analysed using density measurements, hardness tests, EDX measurements, and micrographs. It was concluded that ball milling in a silane-doped atmosphere produces and maintains oxide-free particle surfaces. These oxide-free surfaces and smaller particle sizes improve the component properties after pressing and sintering.

On the Temperature‐Induced Equilibration of Phase Distribution and Microstructure in a Gas‐Atomized Titanium Aluminide Powder

Powder production by gas atomization of γ‐TiAl based alloys typically yields a highly nonequilibrium material regarding the occurring phases and their microstructural appearance. In particular, the equilibration of the powder and the associated phase transformations during heating are of great importance for the subsequently applied densification techniques. The present work employs in situ high‐energy X‐ray diffraction to investigate how this thermodynamic equilibration manifests itself in the resulting phase distribution, the ordering behavior of the disordered α and β phase, both evidenced in the powder, and the change of the γ lattice parameters during heating of a Ti–46.3Al–2.2W–0.2B (at%) powder up to 850 °C. Complementary microstructural characterization of the gas‐atomized powder and the heat‐treated material condition reveals that the temperature exposure predominately affects the dendritic parts of the microstructure, especially when the α phase is transformed into γ phase with small embedded grains of α2 and βo.

Influence of Dwell Time and Pressure on SPS Process with Titanium Aluminides

Spark plasma sintering (SPS) or the field-assisted sintering technique (FAST) is commonly used to process powders that are difficult to consolidate, more efficiently than in the conventional powder metallurgy process route. During the process, holding time and applied holding pressure influence the product’s microstructure and subsequently its properties. In this study, in addition to the temperature impact, the influence of pressure and dwell time on the consolidation behaviour of titanium aluminide (TiAl) powders during the SPS process is investigated. Commercially available pre-alloyed TiAl48-2Cr-2Nb (GE48) and TiAl44-4Nb-0.7Mo-0.1B (TNM) powders were used, which have a high application potential in, for example, the aerospace industry. The results were evaluated based on microstructural analyses, hardness measurements and relative density calculations. It was shown that the investigated parameters significantly influence the sintering results, especially in the low temperature range. Depending on the temperature field in the sample, complete sintering is not achieved if the dwell time is too short in combination with too low a pressure. Above a certain temperature, the impact of holding pressure and holding time is significantly lower.

Prediction of the functional characteristics of plasma titanium aluminide coatings by computer simulation

The results of stochastic simulation (computer-aided design) of a layered structure formation and functional characteristics (porosity, roughness, adhesion) of metal coatings based on titanium aluminide powders (γ-phase TiAl) under conditions typical of atmospheric plasma spraying are given. Taking into account the stable formation of a metal splats and titanium aluminide coatings, as well as minimum porosity and maximum adhesive strength of coatings, the optimal plasma spraying mode has been obtained: the particle velocity Up = 250 m/s, the particle temperature Tp ≤ 2050 K, the particle diameter Dp = (30 ± 10) μm.

Investigation of the Lithium-Containing Aluminum Copper Alloy (AA2099) for the Laser Powder Bed Fusion Process [L-PBF]: Effects of Process Parameters on Cracks, Porosity, and Microhardness

In order to widen the alloy spectrum for the laser powder bed fusion process, apart from the popular Al-Si-based alloys, AlSi10Mg and AlSi12, the precipitation-hardenable AA2099 wrought alloy has been considered in this work. The effect of varied laser power, scanning speed, a preheated base plate (in situ heat treatment) and post-heat treatments on porosity, cracks and microhardness was observed. The results indicate a successfully printed crack-free part with very minimal porosity at 90 W laser power and 550 mm/s scanning speed with microhardness of 72 HV0,1 at a 520°C preheat treatment temperature. The influence of added titanium aluminide powder in crack removal and grain refinement is also reported in this work.

Characteristics of laser metal deposited titanium aluminide

The unique properties of titanium and its alloys make them a continuous area of interest for the material researchers and high profile material industries. Titanium and its alloys possess high strength-to-weight ratio and excellent corrosion resistance properties which made them very useful for high temperature applications especially in areas such as energy generation, automobile and aeronautic industries. In this paper, the effect of deposition parameters on the properties of laser fabricated titanium aluminide alloy was studied. Titanium aluminide powder (Ti-4822-4) was deposited on pure titanium substrate using laser engineered net shaping (LENS) technique of additive manufacturing. Processing parameters like the laser power, scanning speed and powder flow rate were varied. Laser power was varied between 300 to 500 W, scanning speed varied between 3.174 to 7.406 mm s−1 and powder flow rate varied between 4.09 to 7.12 g min−1. The design and analysis of the results was carried out using design expert 6.0.8 software. The trends in deposits cracks, heights and microhardness in relation to the deposition parameters have been studied. The outcome of the study showed that cracks in the deposits reduced as the laser power increases and scanning speed reduces. It was also revealed that the overall microhardness increases as the laser power, scanning speed and powder flow rate increases. The height of the deposits increases as the laser power increases, scanning speed decreases and powder flow rate increases. Microscopic images of the deposits revealed massive presence of γ-TiAl and isolated lamellar region of γ-TiAl and Ti3Al.

Advances in the Systems and Processes for the Production of Gamma Titanium Aluminide Bars and Powder

A historical look at the melt processing of gamma titanium aluminides is presented first, followed by recent advances in melting equipment design by Retech to produce 50-mm and 100-mm-diameter ingots up to 1000 mm long. Equipment design for the economical production of gamma titanium aluminide powder is then discussed. The focus in industry has shifted away from basic research to cost-effective production of these titanium alloys for aerospace and automotive engine applications.

Fabrication and Properties of Gas Atomized Gamma Titanium Aluminide Powders and PM Processing

Pre-alloyed gamma titanium aluminide powders were fabricated by argon gas atomization. The powder was hot isostatic pressed (HIP) at 1200°Cand 150MPa for 3h to obtain full density compact. The properties of the powders and the HIP’ed compacts were investigated in this work. The microstructure of the powder exhibited dendrite and cellular mixed image, resulted from rapid solidification and independent of particle size. The microstructural transition from cell to dendrite could be readily represented in a droplet or the droplets of different size. The transition was the result of the decrease of undercooling. XRD analysis result showed that the powder consisted of α2 phase and γ phase, coarse powder was mostly γ phase, while fine powder mostly α2 phase. After HIP, the near gamma microstructure showed an average γ-TiAl grains of approximately 6μm.

Rapid Consolidation of Gamma Titanium Aluminide Powders Attrition Milled to Submicron Scale

Commercially available micron-sized gamma titanium aluminide powders with Ti-50%Al and Ti-48%Al-2%Cr-2%Nb (at%) composition were milled in an attrition mill for 5 hours and 8 hours, respectively, with 2 wt% stearic acid. Milling resulted in a decrease of the average powder particle size by 60%, which implies submicrometer range powders, with no change in the powder composition. The milled powders were consolidated to produce a near-gamma microstructure and fully lamellar microstructure for Ti-50%Al and Ti-48%Al-2%Cr-2%Nb composition samples, respectively. A significant decrease in grain size was realized for the samples consolidated from the milled powders as compared to samples consolidated from as-received powders. The decrease in grain size improved flexure strength and elongation.

Preparation of TiAl Intermetallic Alloy by Gelcasting

TiAl intermetallic alloy was prepared by gelcasting. The alloy powders were synthesized through reaction diffusion. The microstructure was investigated by XRD and SEM. The results showed that titanium aluminide powders were synthesized from elemental powders under the condition of 600°C for 3h. The solid loading of metal slurry was 45%. After gelcasting, drying and sintering at 1480°C for 2h, TiAl with the relative density of 93% was successfully prepared.

The effect of microstructure on creep behavior of a powder metallurgy (PM) beta gamma alloy

Pre-alloyed beta gamma titanium aluminide powder with a nominal composition of TiAl-2Nb-2Mo (G2) is consolidated by hot isostatic pressing. After consolidation, a step cooled heat treatment is performed to homogenize the material and produce a fully lamellar microstructure. Various aging heat treatments are then performed to form interfacial beta phase precipitates along lamellar interfaces. The step cooled heat treatment produces a relatively fine microstructure with an average lamellar grain size of 40 μm. The aging heat treatments generate beta phase precipitates along lamellar grain boundaries as well as along lamellar interfaces, and result in limited lamellar degradation and grain growth. However, coarse intergranular grains consisting of beta and gamma grains form during aging. Constant load tensile creep tests are performed on step cooled heat treated and aged specimens. Primary creep resistance, generally, improves with aging time, even with interfacial precipitation, and the limited lamellar degradation occurs with aging. However, total creep life of aged samples decreases with aging time. The microstructures of the tested specimens are characterized and related to the creep behaviour of the TiAl-2Nb-2Mo alloy in the un-aged and aged conditions.

The Microstructure, Creep, and Hardness Properties of Powder Metallurgy Beta Gamma TiAl-4Nb-3Mn Alloy

Pre-alloyed beta gamma titanium aluminide powder with a nominal composition of TiAl-4Nb-3Mn is consolidated by hot isostatic pressing. After consolidation, a step cooled heat treatmentis performed to homogenize the material and produce a fully lamellar microstructure. Various agingheat treatments are then performed with the goal of forming interfacial beta phase precipitates alonglamellar interfaces. The step cooled heat treatment produces a relatively fine microstructure with alamellar spacing of 0.04 μm and an average lamellar colony size of 60 μm. The aging heat treatmentsgenerate beta phase precipitates along lamellar colony boundaries but not along lamellar interfaces,and result in lamellar degredation and grain growth. Constant load tensile creep and room temperaturehardness tests are performed on step cooled heat treated and step cooled heat treated and aged specimens.Creep resistance, generally, improves with aging time, even with no interfacial precipitation,and the lamellar degredation that occurs with aging. The microstructures of the as-tested specimensare characterized and related to the creep properties. The hardness values are also compared as afunction of selected heat treatment condition and microstructural features.

Pressureless Reaction Sintering and Characterization of TiAl-TiC and Ti3Al-TiC Composites

Dense TiAl- and Ti3Al-based composites reinforced with 10–50 vol. % of TiC particles were fabricated by pressureless reaction sintering of reaction mixtures consisting of commercial titanium aluminide powders (TiAl with traces of Ti3Al and the single phased Ti3Al) blended with the appropriate amount of ceramic reinforcement and sintering agents (Al and Ti powders). The microstructures of the as-sintered composites were studied by scanning electron microscopy and X-ray diffraction analysis. The sintered samples of as-received TiAl and Ti3Al powders were within 10–15 vol. % of the retained porosity, while in samples with 10 vol. % of TiC particles, pressureless sintered without sintering agents, the retained porosity was reduced below 5 vol. %, according to the chemical reactions between TiAl or Ti3Al and TiC. On the contrary, the complete pressureless densification of composite samples with more than 10 vol. of TiC was achieved only by the addition of 5–10 vol. % of free aluminium and 5 vol. % of titanium, particularly involved in final stages of pores closuring. The tensile properties and Vickers hardness of composite samples were measured at room temperature. The improvement in tensile properties (except elongation) and Vickers hardness was found to correlate with the amount of TiC reinforcement in the matrix.

The Effects of Hot Isostatic Pressing Conditions on the Microstructure of Beta-Gamma Titanium Aluminide Powder Alloys

The effects of hot isostatic pressing temperature and cooling rate on the microstructure of two powder metallurgy beta-gamma titanium aluminide alloys with nominal compositions TiAl 4Nb 3Mn (G1) and TiAl-2Nb-2Mo (G2) are investigated. Particular attention is placed on the volume fraction of the beta phase, which is known to improve the hot workability. The alloys are consolidated by hot isostatic pressing at 1200 °C, 1250 °C, and 1300 °C, and cooled at rates between 3.0 °C/min and 17.5 °C/min. The volume fraction of beta phase in both alloys was unaffected by the change in cooling rates. The volume fraction of the beta phase in G2 decreased linearly from ~9.5 vol.% to ~3.5 vol.% with increasing HIP temperature from 1200 °C to 1300 °C.

Synthesis of ultrafine titanium aluminide powders and their catalytic enhancement in dehydrogenation kinetics of NaAlH 4

Titanium aluminide powders with various sizes have been synthesized using four different mechanochemical reactions. While the reaction between TiCl3, AlCl3 and Mg produces TiAl3 nanopowder with a primary particle size of about 50 nm, the use of LiH instead of Mg results in the formation of Ti2Al5. These titanium aluminide powders reveal a considerable catalytic effect on dehydrogenation of NaAlH4. It is also found that the catalytic effect is particle-size dependent.

Effect of Properties of Titanium Aluminide Powders and Detonation Spraying Conditions on Phase and Structure Formation in Coatings

We have studied phase formation in detonation coatings sprayed from Ti - 50 at.% Al powders. The powders of the alloy were obtained by various methods: crushing an ingot and mechanical alloying of Ti and Al. Using polyphase nanostructural materials activated by mechanical alloying makes the process of phase formation in the gas-thermal sprayed coatings based on them more general-purpose and controlled due to the more active and more subtle reaction of the material with the gaseous atmosphere. We have shown that from mechanically alloyed Ti - 50 at.% Al powder, using the detonation-gas spraying method we can consolidate a coating based on Al2TiO5 by oxidizing action of the working gas on the powder and also a coating based on titanium aluminides with TiN inclusions by nitriding action. The phase composition of the cast microstructural γ-TiAl powder is inherited by the coating.

Utilization of gas atomized titanium and titanium aluminide powders

Utilization of gas atomized titanium and titanium aluminide powders

Characterization of titanium aluminide powder made by reduction

Characterization of titanium aluminide powder made by reduction

Utilization of gas-atomized titanium and titanium-aluminide powder

A gas-atomization process has been developed producing clean, high-quality, prealloyed spherical titanium and titanium-aluminide powder. The powder is being used to manufacture hot-isostatically pressed consolidated shapes for aerospace and nonaerospace allocations. These include gamma titanium-aluminide sheet and orthorhombic titanium-aluminide wire as well as niche markets, such as x-ray drift standards and sputtering targets. The powder is also being used in specialized processes, including metal-matrix composites, laser forming, and metal-injection molding.

Synthesis conditions for obtaining fine powders of pure and alloyed titanium aluminide without milling

We have studied processes not involving milling for obtaining fine powders of either pure titanium aluminide or titanium aluminide alloyed with chromium and manganese. We consider the effect of heat treatment, pressing pressure, and also the degree of dilution of the starting mixture with titanium aluminide. We show that manganese and chromium form solid solutions based on AlTi that cause an elevation in microhardness by 50% and 80% respectively. We have investigated treatment of titanium aluminide powder particles with an Al2O3 coating.