Titanium Aluminide Powders Research Articles

CO2 laser light absorption characteristics of metal powders

Absorption characteristics of metal powders for 10.6 μm CO2 laser radiation were examined. Using a calorimetric method, absorptance measurements were performed on four different powder materials, including aluminum, copper, iron, and titanium aluminide. The experimental results showed that laser absorptance depends on powder porosity and material. The measured absorptance values at low laser intensities ranged between 28% and 43%. The titanium aluminide powders showed the highest absorptance values, and aluminum powders the lowest. As laser intensity was increased, the copper and iron powders showed strong signs of oxidation when irradiated in air, resulting in an increase in absorptance. Neither oxidation nor increased absorptance were observed when helium or argon were used as shielding gas.

Toughening of TiAl composites by NiAl additions

Intermetallic alloys based on the TiAl or NiAl phases are promising as potential materials for high temperature structural applications. Limited ductility and toughness of these materials at ambient temperatures, however, has hampered their acceptance. Only modest improvements have been achieved by alloy and microstructural control, even though extensive investigations have been carried out in these areas. Evidence of room temperature ductility at unusually fine grain sizes has been observed in intermetallics and this could lead to further improvements. Mechanical alloying is a method known to produce ultrafine-grained materials. Although it is common to mechanically alloy elemental powders, there are few studies where prealloyed powders have been mechanically alloyed. In this study ultrafine-grained composite intermetallics are produced by milling mixtures of prealloyed titanium aluminide and nickel aluminide powders. Milling at cryogenic temperatures promotes fracture and suppresses inter-particle solid state welding. The low temperatures also suppress the formation of new phases and minimize the contamination that inevitably occurs during room temperature milling. Retaining the ultrafine grain size is difficult during consolidation. The conventional method for limiting grain growth is to incorporate inert dispersoids. Although this has been found to increase strength, a severe reduction in ductility generally results. An alternative is tomore » produce a multiphase material to limit grain growth. Ductility should not be affected to the same degree as for materials with fine brittle dispersoids. This is the rationale for milling and subsequently consolidating a mixture of two different prealloyed intermetallic phases.« less

Phase formation in cold-extruded and annealed titanium aluminide powder materials : T.J. Jewett et al (GKSS Research Centre, Geesthact, Germany)

Phase formation in cold-extruded and annealed titanium aluminide powder materials : T.J. Jewett et al (GKSS Research Centre, Geesthact, Germany)

Modeling the consolidation behavior of an alpha-two titanium aluminide powder

The consolidation of an alpha-two titanium aluminide powder was analyzed using an approach based on two density dependent variables: the apparent Poisson's ratio and a stress intensification (geometric hardening) factor. Uniaxial compression tests on samples with different relative densities were used to obtain the the apparent Poisson's ratio and constitutive behaviour. Microhardness tests on undeformed and deformed samples with different relative densities were used to obtain the stress intensification factor. With this information, a von Mises type yield function, modified for pressure effects, was developed and implemented into a finite element code and used successfully to model the densification of the alpha-two titanium aluminide powder.

Production of titanium aluminide powders by plasma rotating electrode process: K. Isonishi et al (Ibraki University, Mito, Japan)

Production of titanium aluminide powders by plasma rotating electrode process: K. Isonishi et al (Ibraki University, Mito, Japan)

Microstructure of rapidly solidified titanium aluminide powders: M. Cao et al (Academia Sinica, Shenyang, China), Acta Metallurgica Sinica, Vol 28, No 10, 1992, A428–A430. (In Chinese).

Microstructure of rapidly solidified titanium aluminide powders: M. Cao et al (Academia Sinica, Shenyang, China), Acta Metallurgica Sinica, Vol 28, No 10, 1992, A428–A430. (In Chinese).

Characterization of titanium aluminide powder made by plasma rotation electrode process (PREP): L. Tao et al (Northwest Inst of Non-Ferrus Metal Research, China)

Characterization of titanium aluminide powder made by plasma rotation electrode process (PREP): L. Tao et al (Northwest Inst of Non-Ferrus Metal Research, China)

Phase transformation effects during hip of TiAl

The densification of titanium aluminide powders during hot isostatic pressing has been measured in situ by an eddy-current sensor. The samples were found to experience enhanced densification as they transformed from an initial metastable α 2 structure to an equilibrium structure consisting mostly of the γ phase. The temperature at which the enhanced densification occurred corresponded closely to the temperature at which an exotherm is observed by differential thermal analysis. Evaluation of several possible explanations for this enhanced densification indicates that it is most probably the result of transformation plasticity.

Thermochemical processing of titanium aluminide powders and compacts

Thermochemical processing of titanium aluminide powders and compacts

Production of titanium and titanium aluminide powders by calciothermic reduction of oxides : R. Suzuki et al. (Kyoto University, Japan.) Zairyo to Purosesu, Vol 2, No 2, 1991, 322–323, (In Japanese.)

Production of titanium and titanium aluminide powders by calciothermic reduction of oxides : R. Suzuki et al. (Kyoto University, Japan.) Zairyo to Purosesu, Vol 2, No 2, 1991, 322–323, (In Japanese.)

The Deformation and Dynamic Recrystallization in a Hot Isostatically Pressed Ti-48A1-2W Powder Alloy

Titanium aluminide powder of composition Ti-48A1-2W (at%) was consolidated by hot isostatic pressing (HIP) at 200 MPa and 1050°C, 1100°C, 1150°C and 1250°C, respectively. The as-HIP'ed microstructure and substructure were characterized by optical microscopy and transmission electron microscopy (TEM). The densified powder alloy possesses an inhomogeneous microstructure consisting of fine-grained prior dendrites and coarse-grained interdendritic regions. The former contain the , 2 and phases. The HIP processing induced substantial deformation in the latter regions where dislocation segments and tangles, deformation twins and dislocation sub-boundaries were formed, indicative of plastic yielding and creep deformation. Both 1/2

Shock densification/hot isostatic pressing of titanium aluminide

Consolidation of rapidly solidified titanium aluminide (Ti3Al) powders employing explosive shock pressure followed by hot isostatic pressing (“hipping”) was carried out successfully. Shock densification was achieved by using a double tube design in which the flyer tube was explosively accelerated, impacting the powder container. Elemental mixtures of Ti (15 wt pet) and Al (15 wt pct) powders were added to intermetallic compound powders (Ti3Al). Hipping was used to chemically induce bonding between Ti3Al particles. The highly exothermic reactions were activated by hipping at 1000 ‡C and enhanced the bonding between the inert intermetallic powders. Compression tests indicated strong bonding between Ti3Al particles. Well-bonded Ti3Al compacts having an average ultimate compressive strength of 2 GPa and compressive fracture strain of 20 pct were produced by this technique. The ultimate tensile strengths, due to the presence of flaws in the microstructure (microcracks and voids) and intergranular fracture observed in the reacted regions, were much lower (~250 MPa).

Production of amorphous titanium aluminide powder by vibratory ball milling

Production of amorphous titanium aluminide powder by vibratory ball milling

Dynamic compaction of titanium aluminides by explosively generated shock waves: Experimental and materials systems

Different approaches to compact cylinders of titanium aluminide powders by explosively generated shock waves were explored. Two basic compositions of the titanium aluminide powders produced by the rapid solidification rate (RSR) technique were used: Ti-21 wt pct Nb-14 wt pct Al and Ti-30.9 wt pct Al-14.2 wt pct Nb. A double-tube design utilizing a flyer tube was used in all experiments. Experimental parameters that were varied were initial temperature, explosive quantity, and explosive detonation velocity. The major problem encountered with shock consolidation of titanium aluminides was cracking. Titanium aluminide powders were also mechanically blended with niobium powders in one case and elemental mixtures of aluminum and titanium powders in the other case. Enhanced bonding and decreased cracking were observed in both cases. In the former case, the addition of niobium powder provided a ductile binder medium which assisted in consolidation. In the latter case, due to the additional heat generated and melting produced by the shock-induced reactions between Ti and Al, significant improvements in bonding of the titanium aluminide powders were observed.

Modern production methods for superalloy and titanium aluminide powders

For well over a decade, fully dense superalloy and corrosion resistant nickel base alloy components have been produced for rotating aircraft turbines as well as critical oil well service by powder metallurgy (PM). Over the next decade, the compounded annual growth rate for aircraft products is expected to reach 9–10%. While the growth rate for oil field products is more volatile and difficult to predict, the need for these products is also increasing. Following is an overview of a fully integrated powder plant that has undergone a capacity upgrade to meet the challenges of a growing market for high quality full dense PM products. As part of a continuing development programme, efforts to commercialize refractory free melting and atomization for production of titanium and titanium aluminide powders is also described.

Microstructure Control of Titanium Aluminide Powder Compacts by Thermochemical Processing.

Powder metallurgy of ordered alloys is not only a method to obtain net-shape products but is also an effective approach to microstructural refinement for improvement of some properties such as tensile ductility and fatigue strength. In the present study, prealloyed plasma rotating electrode process (PREP) powder was used to produce compacts with an ultrafine grain structure by employing conventional and hydrogen thermochemical processing routes. These processes are capable of producing a wide range of alpha-2 (α2) structures, including an ultrafine microstructure with a grain size on the order of a micron. This paper will discuss some of the mechanisms leading to microstructure refinement with an emphasis on the role of hydride formation.

Densification of rapidly solidified titanium aluminide powders—II. The use of a sensor to verify hiring models

An eddy-current sensor was used to monitor consolidation of γ-titanium aluminide powder, in situ, during hot isostatic pressing (HIP). The resulting data was then compared with predictions generated from a model developed by Helle, Easterling and Ashby. A major finding was that significant densification occurred during the pressurization phase of the HIP cycle. Agreement was extremely good between experiment and theory, although asymptotic errors were found in the model when approaching full density. Discrepancies also arose at 1223 K and short times, between the continuous sensor data and interrupted cycle density measurements. The transformation from metastable α 2-γ powders to a single phase γ microstructure was suggested as the origin of the discrepancy, which is not currently considered in the models. A useful method is also suggested by which the sensor may estimate the sample density on-line, using mathematical models to filter the sensor data.

Densification of rapidly solidified titanium aluminide powders—I. Comparison of experiments to hiping models

Rapidly solidified γ-titanium aluminide powders were characterized and subjected to consolidation by hot isostatic pressing (HIP). Primary solidification of h.c.p.-α phase followed by formation of interdendritic γ-segregate prevails in both REP (Ti-50% Al-1.8% Nb) and RSR (Ti-48% Al-2.4% Nb-0.3% Ta) powders, except for a minor fraction of fine powders that form b.c.c.-β phase from the liquid. The evolution of these microstructures and their subsequent solid state transformations are in line with previous observations on binary titanium aluminide droplets solidified with and without supercooling. In the consolidation experiments, the influences of time, temperature and pressure on final densification were experimentally determined and compared with predicted HIP maps using best estimates of input data on material properties. Experimentally it was found that the densification rate is independent of average mean particle diameter. Best agreement between predictions and experiments were obtained for power-law creep as the dominant consolidation mechanism at high pressure, i.e. 182 MPa. Modifications of the model are suggested for consolidation during the pressurization.

Matrix/reinforcement interactions in shock-wave consolidated titanium aluminide reinforced with SiC

Explosive shock-wave consolidation has been used to fabricate a composite consisting of gamma phase titanium aluminide matrix reinforced with paniculate silicon carbide. Although the consolidation process takes less than a microsecond to complete, melting of the surfaces of the titanium aluminide powder particles results in a reaction with the silicon carbide. Titanium suicide and titanium carbide form in the molten zone, depleting it of titanium to the extent that its final composition is TiAl3. In addition, a second titanium suicide phase forms on the surfaces of the silicon carbide particles.