Effect Of Tantalum Research Articles

Effect of Tantalum on the Impact Toughness of 12% Cr Steels Subjected to Thermomechanical Treatment

Effect of Tantalum on the Impact Toughness of 12% Cr Steels Subjected to Thermomechanical Treatment

Silicon Poisoning and Effects of Tantalum on AlSi Alloys

Grain refinement in Al-Si alloys is crucial for enhancing material castability and mechanical properties. Industrial practice involves adding inoculants, composed of TiB2 particles coated with metastable Al3Ti via adsorption, to the melt. This introduces essential free titanium for metastable phase formation and subsequent growth restriction. The superstoichiometric grain refiner Al-5Ti-1B, with 2.2 wt.% free titanium, is applied for this purpose. A peritectic reaction forms α-aluminium from this layer. However, when silicon content exceeds 3.5 wt.%, grain coarsening occurs due to silicon’s detrimental effect. This study quantified silicon poisoning in an Al-10Si alloy using stoichiometric and superstoichiometric grain refiners through ASTM-standardized TP1 tests. Adding 0.02 wt.% tantalum acted as an antidote to the τ1 phase, resulting in a finer microstructure. This was attributed to the formation of a Ta-rich layer on TiB2 particles, which causes α-aluminium formation via a peritectic reaction without generating ternary phases with Ti or Si. Correlating to the increasing particle size curves from the TP1 tests, phases were collected in the filter cake with the help of a PoDFA apparatus. These could be examined more closely on the SEM and identified as needle- or plate-shaped. By using an EDS unit, the phases found were assigned to the poisoning phase and further investigated. After the addition of tantalum, a solubility of tantalum could be detected in former poisoning phases. In combination with the gradients of the grain size, it can thus be assumed that tantalum is both an antidote for silicon poisoning in the Al-Si-Ti system and can itself have a grain-refining effect in this system.

Regulating the binder phase of polycrystalline diamond compact by adding tantalum to enhance the mechanical properties

In this study, PDC added with tantalum was successfully prepared via high pressure and high temperature (HPHT, 7.7GPa and 1650 °C) with the Cubic-Anvil Press. The effect of tantalum on the mechanical properties and thermal stability was systematically investigated by hardness, abrasion resistance, impact resistance and coefficient of thermal expansion (CTE) tests. The results showed that the hardness, wear ratio, total impact energy and initial expansion temperature increased by 21.7%, 45.5%, 55.2% and 20 °C with the addition of tantalum, respectively. The Ta-PDC material binder phase consisted of Ta-phases (TaC, (Ta,W)CX) and cobalt phase after sintering. In elemental quantification observe that the addition of Ta facilitated cobalt infiltration which was benefit to diamond-diamond bonding. The improvement of mechanical properties and thermal stability can be attributed to the reinforced binder, refined and deagglomerated WC grains at the interface between PCD layer and substrate, and better sintering quality. Further optimization of the Ta additive phase content, mixing methodology, or sintering conditions could be explored to further improve the mechanical properties and thermal stability of this novel PDC material.

Effect of tantalum and Ni[sbnd]Ta barriers on inter-diffusion between nickel coating and GH3535 alloy at 700 °C

Nickel-coated GH3535 alloy is suitable used for molten salt reactor at elevated temperature. However, coating failure caused by inter-diffusion is still problematic. In this study, tantalum and NiTa films were deposited as barriers between nickel coating and GH3535 alloy by magnetron sputtering, respectively. The diffusion behaviors of the coatings were investigated by micro-structure analysis and calculation of diffusion coefficient. The results indicate that a Ta barrier can inhibit the diffusion of Cr and Fe due to the formation of Ni3Ta phases, but Ni diffusion from the substrate to the barrier is promoted causing the formation of Kirkendall voids. However, a novel NiTa barrier exhibits excellent diffusion resistance for Cr, Fe, and Ni in the Ni/GH3535 system at 700 °C.

EFFECT OF TANTALUM ON THE IMPACT RESISTANCE OF 12% CR STEELS SUBJECTED TO THERMOMECHANICAL TREATMENT

The effect of tantalum on the impact resistance of 12% Cr steels with different tantalum content (12CrTaNb and 12CrNb) was investigated in impact tests in the temperature range from -40 to +120°C with determining the brittle-ductile transition temperature as the temperature in the middle between the upper and lower shelf energies. Both 12% Cr steels were thermomechanically treated by alternating 1050°C annealing and forging in addition to standard normalizing treatment with high-temperature tempering. It was found that for Ta-alloyed 12% Cr steel, the entire fracture toughness versus temperature curve is 30-50 J/cm2 higher over the entire temperature range, including the upper and lower shelf energies, and the brittle-ductile transition temperature is 10°С lower. The main structural parameters of Ta-alloyed 12% Cr steel which can have a beneficial effect on toughness are a smaller initial austenite grain size, a larger average size but lower density of M23C6 carbide particles along low-angle martensite lath boundaries, and a larger volume fraction of VX carbonitrides.

Effect of Ta Doping on the Microstructure and Thermoelectric Properties of Bi2O2Se

In this study, Bi2−xTaxO2Se (x = 0, 0.02, 0.04, 0.06, and 0.08) ceramics were prepared using a synthesis method combining high-energy ball milling and cold pressing. Furthermore, the effects of tantalum (Ta) doping on the microstructure and thermoelectric properties of Bi2O2Se were systematically investigated. The results indicate that Ta doping effectively improves the carrier concentration and mobility, thus increasing the electrical conductivity from 8.75 S cm−1 to 39.03 S cm−1 at 323 K. Consequently, the power factor is improved, reaching a maximum value of 124 μW m−1 K−2 for the Bi1.92Ta0.08O2Se sample at 773 K. Moreover, the thermal conductivity of Bi1.96Ta0.04O2Se is reduced to 0.50 Wm−1 K−1. Finally, the maximum dimensionless figure of merit (ZT) value of the Bi1.94Ta0.06O2Se sample reached 0.18, which was 64% higher than that of Bi2O2Se (0.11). These results indicate that Ta doping and high-energy ball milling can optimize the electrical and thermal properties and thus improve the thermoelectric properties of ceramics.

Cu/Ta sheaths for iron-based superconductors: First experimental findings in Ca/K-1144 wires

Iron based superconducting wires (IBSCs) produced by the Powder in Tube (PIT) method rely on the use of silver sheaths as chemical buffer between the outer metal and the superconducting core. The adoption of silver entails however some limitations, such as the viable temperature range when coupled with copper, and the incompatibility with calcium-based IBSCs already at 600 °C, driving the research towards other wires architecture. Taking inspiration from the low temperature superconductors field, we decided to evaluate the adoption of tantalum as diffusion barrier in a layered Cu/Ta architecture, choosing a Ca/K-1144 IBSC as case study considering the high reactivity issues already reported in the case of silver sheaths for this compound. Squared wires were produced through a groove rolling lamination process coupled with a thermal treatment at 800 °C. The microstructural analyses show the absence of interdiffusion between the different parts of the wire, and the magnetic characterization shows performance in line with similar polycrystalline manufacts, with margin of enhancement to be pursued via the optimization of the mechanical process and other experimental variables. The reported results suggest thus the effectiveness of tantalum as diffusion barrier for Ca/K-1144 PIT wires.

The Effect of Tantalum, Tungsten, and Rhenium Additions on the Tensile-Deformation Behavior of Model Nickel-Based Single-Crystal Superalloys at Intermediate Temperature

The Effect of Tantalum, Tungsten, and Rhenium Additions on the Tensile-Deformation Behavior of Model Nickel-Based Single-Crystal Superalloys at Intermediate Temperature

Molecular dynamics simulation of primary radiation damage in W-Ta alloys: Effect of tantalum

Tungsten (W) and W-based alloys are competitive candidates for plasma-facing materials in future fusion reactors. W-tantalum (Ta) alloys get the most attention amongst these materials. The present study uses molecular dynamics simulations to study the displacement cascades of pure W and W-Ta alloy systems with recoil energy up to 100 keV at 300 K and the further evolution of cascade defects at 1,000 K. The effects of Ta concentration on the generation and evolution of the defects, produced with primary knock-on atom energies, are quantitatively analysed. This study's results show that the presence of randomly distributed Ta atoms does not significantly affect the average number of surviving Frenkel pairs or the fractions of clustered vacancies and interstitials. In addition, there is no completed vacancy dislocation loop in all systems after cascading. The produced dislocation loops are mainly 1/2 〈111〉 loops companied with a small amount of 〈100〉 loops and mixed loops. However, the existence of Ta atoms slows down the motion of defects and defect mobility decreases as the Ta concentration increases in bulk W. This will affect the size and density of defects. In addition, the presence of Ta also inhibits the transition of the 〈100〉 dislocation loops to 1/2 〈111〉 dislocation loops under the high-temperature condition. This will affect the types of dislocation loops and the material performance.

Effects of Tantalum on the microstructure and properties of Ti-48Al-2Cr-2Nb alloy fabricated via laser additive manufacturing

To improve the mechanical properties of Ti48Al2Cr2Nb (TiAl) alloys, Ti48Al2Cr2Nb-xTa alloy specimens without metallurgical defects were obtained by a laser additive manufacturing (LAM) technique using Ti48Al2Cr2Nb/Ta mixed powders as raw materials. The effects of different Ta contents on the microstructures, phase compositions, and tensile properties of the TiAl alloys were systematically investigated, and the relationship between these properties was established. The results showed that the lamellar structure was composed of α2 (Ti3Al), γ (TiAl), and β/B2 (β ordered to B2) phases. With the increase of Ta content, the thickness of the lamellar structure increased, and the lamellar length gradually shortened. The morphology of the α2 phase changed from an ultra-fine continuous lamellar structure to a short lamellar and an equiaxed structure. On the other hand, the morphology of the γ phase changed from lamellar to an equiaxed crystal structure, while the morphology of β/B2 phase changed from ellipsoid shape to fine block to coarse block structure. When the amount of Ta added to the TiAl powders was 0 at.%, 2 at.%, and 5 at.%, respectively, the tensile strength gradually decreased with the increase of temperature, while the elongation increased. When the amount of Ta was 8 at.%, the tensile strength at room temperature dropped to the minimum (393 MPa), and the elongation reached its maximum value (21.2%). Thus, it can be concluded that the 5 at.%Ta alloy had the best comprehensive tensile properties. The maximum tensile strength of the TiAl-5 at.%Ta alloy at room temperature, 750 °C and 850 °C, was 677 MPa, 651 MPa, and 538 MPa, respectively, and the elongation was 2.0%, 2.0%, and 13%, respectively. Compared with the TiAl-0 at.%Ta alloy, the tensile strength of TiAl-5 at.%Ta at room temperature, 750 °C, and 850 °C increased by 1.66, 2.08, and 1.9 times respectively, and the elongation increased by 1.43, 1.43, and 9.29 times, respectively.

Effect of tantalum on the microstructure stability of PM Ni-base superalloys

The effect of Ta on the microstructure stability of powder metallurgy (PM) Ni-base superalloy was examined at standard heat treatment and after long-term thermal exposure. The results reveal that the previous particle boundary structure is eliminated with the addition of Ta. As Ta content increases, the γ' morphology changes from spheres to cuboids and begins to split, which is caused by the increase in the γ/γ' mismatch. Reversal coarsening of γ' particles in Ta-containing alloys are observed during exposure at 750 °C. The main reasons are related to γ/γ' lattice mismatch, elements partitioning and soft impingement. Besides, the increase of Ta content promotes the precipitation of σ phase at grain boundaries and in grains. • The PM Ni-based superalloys were fabricated by plasma rotation electrode process and hot isostatic pressing. • Systematical study on microstructure evolution of the PM superalloy with increase of Ta content. • The addition of Ta effectively inhibits the previous particle boundary structure in PM superalloy. • The addition of Ta changes the partitioning of alloying elements in γ and γ'. • Reversal coarsening of γ' particles occurred in the Ta-containing alloys during the aging at 750 °C.

Effect of Tantalum on the Microstructure and Mechanical Properties of M2 High‐Speed Steel Prepared by Laser Additive Manufacturing

Herein, M2 high‐speed steel (HSS) samples with different Ta contents are prepared on #45 steel substrates by a laser additive manufacturing process. The microstructure and mechanical properties of the samples are systematically studied under five different Ta contents. Scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), and X‐ray diffraction (XRD) analyses show that the microstructures of the samples comprise equiaxed crystals, cellular dendritic structures, and reticular eutectic carbides. The samples are mainly composed of supersaturated martensite, retained austenite, and MxCy‐type carbides. The microstructures and mechanical properties of the samples are greatly affected by Ta alloying. After the M2 HSS is alloyed with 1 and 2 wt% Ta, obvious grain refinement occurs and the amount of retained austenite decreases; as a result of these microscale changes, the microhardness increases by 2.9% and 7.2%, the impact toughness increases by 12.4% and 17.4%, and the wear resistance increases by 75.74% and 25%.

Effect of tantalum on short-term creep of a 12%Cr-3%Co-0.07%Ta martensitic steel for steam blades

9-12%Cr martensitic steels are prospective materials for elements of boilers, tubes, pipes, heaters and steam blades for fossil power plants, which are able to work at ultra-supercritical parameters of steam. Decreasing N content and increasing B content together with increasing Cr content required the optimization of ferrite-stabilizing and austenite-stabilizing elements to avoid the formation of δ-ferrite at high temperatures. Addition of 3-4%Co, 0.01%B, 0.80%Cu and 0.07%Ta as austenite-stabilizing elements can compensate increasing Cr content up to 12% at decreasing N content to 0.003% and provides the δ-ferrite in the amount less than 10%. Two Co-containing 12%Cr steels were developed and investigated. The main difference between these steels is Ta addition; one of the 12%Cr steel studied contains 0.07%Ta, other 12%Cr steel is Ta-free one. Creep tests at 650°C and the applied stresses ranging 180-80 MPa with a step of 20 MPa for both Co-containing 12%Cr steels were carried out. Addition of Ta in the Co-containing 12%Cr steel provide the increment in the creep time to rupture at both high and low applied stresses. This increment in the creep properties due to Ta addition was explained by decrease in coarsening rate of Ta-rich MX carbonitrides during creep at 650°C.

Effect of tantalum on phase transition and thermal stability of metastable tungsten tetra-boride

Decomposition of WB4 into WB2 at temperature higher than 1200 °C makes the preparation of pure bulk WB4 ceramic difficult. Doping of the third element was reported to be an effective way for thermal stability improvement of ceramic materials. In the present work, the nearest element of W, tantalum (Ta), was introduced into tungsten boride synthesized by a combination of high energy ball milling and thermal treatment with (W:Ta):B= (2/3:1/3):4.5 & 5. The phase composition, chemical state of each element, and thermal stability of the as-synthesized samples were investigated. Results show that, with W:Ta molar ratio of 2/3:1/3, ei, 2:1, when the (W + Ta):B = 1: 4.5, about 49.5% mass fraction of WB4 phase was maintained successfully after being thermal treated at 1500 °C for 1 h, compared with pure WB22 phase obatined by the Ta-free sample. Increasing B content in raw materials to (W + Ta):B = 1:5, the mass fraction of WB4 phase was increased to 97%, while the only phase can be detected in the Ta-free samples is also WB2. The significantly improved thermal stability of WB4 can be mainly attributed to the completely dissolve of Ta into the W-B system. It was also found that the oxidation resistance of the W-B system was increased with the introduction of Ta.

A NEW WELDING MATERIAL FOR REGENERATION IN THE WELDING TECHNOLOGY BASED ON NICKEL. ANALYSIS OF THE PROCESSABILITY OF APPLICATION OF THE EXPERIMENTAL FILLER IN THE REGENERATION OF SUPERALLOY CASTINGS VIA TIG WELDING AND OTHER TECHNOLOGIES

This work involves an analysis of high-chromium high-temperature deformable wieldable nickel alloys for use in GTE repair assemblies. It is shown that the alloys EP868 (VZh98) and Haynes 230 can be used in welded assemblies with an operating temperature of 800-1100 °C. The alloys Nimonic 81, Nimonic 91, IN 935, IN 939, and Nicrotan 2100 GT also have a high potential for use in welded assemblies. They are characterized by a combination of good weldability, high-temperature strength, and resistance to scaling. There have been conducted studies on high-temperature salt corrosion of model nickel alloys. They allowed establishing the patterns of the impact of base metal alloying with chromium, aluminum, titanium, cobalt, tungsten, molybdenum, niobium, tantalum and rare earth metals on the critical temperature of the start of salt corrosion Tcor and the alloy mass loss. It has been established that alloys with a moderate concentration (13-16%) of chromium can possess satisfactory hightemperature corrosion resistance (HTC resistance) under the operating conditions of ship GTE. The HTC resistance of CrAl-Ti alloys improves upon reaching the ratio Ti/Al ˃ 1. Meanwhile, the ratio Ti/Al ˂ 1 promotes the formation of corrosion products with low protective properties. The positive effect of tantalum on the HTC resistance of alloys is manifested at higher test temperatures than that of titanium, and the total content of molybdenum and tungsten in alloys is limited by the condition 8Mo2 – 2W2 = 89. The presence of refractory elements stabilizes the strengthening phase and prevents formation of the ɳ-phase. However, their excess promotes formation of the embrittling topologically close packed (TCP) phases and boundary carbides of an unfavorable morphology. Based on the studies of the HTC resistance, there has been identified a class of model high-temperature corrosionresistant nickel alloys with a moderate or high chromium content (30%), Ti/Al ˃ 1, and a balanced content of refractory and rare-earth elements.

A NEW WELDING MATERIAL FOR REGENERATION IN THE WELDING TECHNOLOGY BASED ON NICKEL. DEVELOPMENT OF A NEW HIGH-TEMPERATURE AND CORROSION-RESISTANT WELDING MATERIAL FOR THE REGENERATION OF DEFECTS IN HNA CASTINGS. ANALYSIS OF EXISTING FUELLING STATIONS TYPES AND VEHICLES USING HYDROGEN, HYDROGEN PRODUCTION AND STORING METHODS

This work involves an analysis of high-chromium high-temperature deformable wieldable nickel alloys for use in GTE repair assemblies. It is shown that the alloys EP868 (VZh98) and Haynes 230 can be used in welded assemblies with an operating temperature of 800-1100 °C. The alloys Nimonic 81, Nimonic 91, IN 935, IN 939, and Nicrotan 2100 GT also have a high potential for use in welded assemblies. They are characterized by a combination of good weldability, high-temperature strength, and resistance to scaling. There have been conducted studies on high-temperature salt corrosion of model nickel alloys. They allowed establishing the patterns of the impact of base metal alloying with chromium, aluminum, titanium, cobalt, tungsten, molybdenum, niobium, tantalum and rare earth metals on the critical temperature of the start of salt corrosion Tcor and the alloy mass loss. It has been established that alloys with a moderate concentration (13-16%) of chromium can possess satisfactory hightemperature corrosion resistance (HTC resistance) under the operating conditions of ship GTE. The HTC resistance of CrAl-Ti alloys improves upon reaching the ratio Ti/Al ˃ 1. Meanwhile, the ratio Ti/Al ˂ 1 promotes the formation of corrosion products with low protective properties. The positive effect of tantalum on the HTC resistance of alloys is manifested at higher test temperatures than that of titanium, and the total content of molybdenum and tungsten in alloys is limited by the condition 8Mo2 – 2W2 = 89. The presence of refractory elements stabilizes the strengthening phase and prevents formation of the ɳ-phase. However, their excess promotes formation of the embrittling topologically close packed (TCP) phases and boundary carbides of an unfavorable morphology. Based on the studies of the HTC resistance, there has been identified a class of model high-temperature corrosionresistant nickel alloys with a moderate or high chromium content (30%), Ti/Al ˃ 1, and a balanced content of refractory and rare-earth elements.

A NEW WELDING MATERIAL FOR REGENERATION IN THE WELDING TECHNOLOGY BASED ON NICKEL. PRINCIPLES OF DOPING OF HIGH-TEMPERATURE NICKEL ALLOYS RESISTANT TO HIGH-TEMPERATURE CORROSION

This work involves an analysis of high-chromium high-temperature deformable wieldable nickel alloys for use in GTE repair assemblies. It is shown that the alloys EP868 (VZh98) and Haynes 230 can be used in welded assemblies with an operating temperature of 800-1100 °C. The alloys Nimonic 81, Nimonic 91, IN 935, IN 939, and Nicrotan 2100 GT also have a high potential for use in welded assemblies. They are characterized by a combination of good weldability, high-temperature strength, and resistance to scaling. There have been conducted studies on high-temperature salt corrosion of model nickel alloys. They allowed establishing the patterns of the impact of base metal alloying with chromium, aluminum, titanium, cobalt, tungsten, molybdenum, niobium, tantalum and rare earth metals on the critical temperature of the start of salt corrosion Tcor and the alloy mass loss. It has been established that alloys with a moderate concentration (13-16%) of chromium can possess satisfactory hightemperature corrosion resistance (HTC resistance) under the operating conditions of ship GTE. The HTC resistance of CrAl-Ti alloys improves upon reaching the ratio Ti/Al ˃ 1. Meanwhile, the ratio Ti/Al ˂ 1 promotes the formation of corrosion products with low protective properties. The positive effect of tantalum on the HTC resistance of alloys is manifested at higher test temperatures than that of titanium, and the total content of molybdenum and tungsten in alloys is limited by the condition 8Mo2 – 2W2 = 89. The presence of refractory elements stabilizes the strengthening phase and prevents formation of the ɳ-phase. However, their excess promotes formation of the embrittling topologically close packed (TCP) phases and boundary carbides of an unfavorable morphology. Based on the studies of the HTC resistance, there has been identified a class of model high-temperature corrosionresistant nickel alloys with a moderate or high chromium content (30%), Ti/Al ˃ 1, and a balanced content of refractory and rare-earth elements.

Effect of tantalum on the temperature dependent electrical characteristics of NaNb1−xTaxO3 (0.0 [formula omitted] x [formula omitted] 0.3) ceramics between 400 and 560 °C

NaNb1−xTaxO3 (x = 0.0, 0.1, 0.2 and 0.3) (NT0, NT1, NT2 and NT3) ceramics are synthesized by conventional solid state reaction technique at high sintering temperature 1150 °C for 4 h. The crystallinity and surface morphology are studied by X - ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM) at room temperature, respectively. XRD analysis of Ta ion doped sodium niobate ceramics confirms the formation of single phase with orthorhombic symmetry. In FE - SEM analysis, the effect of tantalum (Ta) ion on the grain growth of NT ceramics is clearly noticeable. With increasing the amount of Ta ion in NT ceramics, size of grains get diminished. The dielectric and impedance behavior of NT material are studied as a function of frequency (100 Hz - 5 MHz) at selected temperature (400 °C - 560 °C). The maximum value of real permittivity (ε') is obtained in NT3 ceramics at 560 °C temperature. The impedance analysis of NT ceramics confirms that the relaxation peaks shift toward higher frequency with a rise in temperature. Such type of change in relaxation peak is attributed to the temperature dependent time relaxation phenomenon present in material.

A NEW WELDING MATERIAL FOR REGENERATION IN THE WELDING TECHNOLOGY BASED ON NICKEL. ANALYSIS OF THE COMPOSITION AND PROPERTIES OF DEFORMABLE HEAT-RESISTANT HIGH-CHROMIUM NICKEL-BASED ALLOYS FOR WELDED PARTS. ANALYSIS OF EXISTING FUELLING STATIONS TYPES AND VEHICLES USING HYDROGEN, HYDROGEN PRODUCTION AND STORING METHODS

This work involves an analysis of high-chromium high-temperature deformable wieldable nickel alloys for use in GTE repair assemblies. It is shown that the alloys EP868 (VZh98) and Haynes 230 can be used in welded assemblies with an operating temperature of 800-1100 °C. The alloys Nimonic 81, Nimonic 91, IN 935, IN 939, and Nicrotan 2100 GT also have a high potential for use in welded assemblies. They are characterized by a combination of good weldability, high-temperature strength, and resistance to scaling. There have been conducted studies on high-temperature salt corrosion of model nickel alloys. They allowed establishing the patterns of the impact of base metal alloying with chromium, aluminum, titanium, cobalt, tungsten, molybdenum, niobium, tantalum and rare earth metals on the critical temperature of the start of salt corrosion Tcor and the alloy mass loss. It has been established that alloys with a moderate concentration (13-16%) of chromium can possess satisfactory hightemperature corrosion resistance (HTC resistance) under the operating conditions of ship GTE. The HTC resistance of CrAl-Ti alloys improves upon reaching the ratio Ti/Al ˃ 1. Meanwhile, the ratio Ti/Al ˂ 1 promotes the formation of corrosion products with low protective properties. The positive effect of tantalum on the HTC resistance of alloys is manifested at higher test temperatures than that of titanium, and the total content of molybdenum and tungsten in alloys is limited by the condition 8Mo2 – 2W2 = 89. The presence of refractory elements stabilizes the strengthening phase and prevents formation of the ɳ-phase. However, their excess promotes formation of the embrittling topologically close packed (TCP) phases and boundary carbides of an unfavorable morphology. Based on the studies of the HTC resistance, there has been identified a class of model high-temperature corrosionresistant nickel alloys with a moderate or high chromium content (30%), Ti/Al ˃ 1, and a balanced content of refractory and rare-earth elements.

Effects of Tantalum on Microstructure Evolution and Mechanical Properties of High-Nb TiAl Alloys Reinforced by Ti2AlC.

Experiments have been carried out to study the relationship between the addition of tantalum and microstructure, especially the formation of the B2 phase in lamellar colonies. The mechanical properties, with different contents of Ta, were also measured. Ti46Al8Nb2.6CxTa alloys were prepared by casting with the content of Ta varying from zero to 1.0 at.%. Experimental results show that the B2 phase forms in lamellar colonies with the addition of Ta, and its content increases when the content of Ta increases. Meanwhile, the γ phase decreases and the lattice parameter of the α2 phase increases. The size of the lamellar colony decreased from 29.9 to 21.6 μm. Ta dissolves into Ti2AlC by substitution, and its solubility is more than 1.1% tested by EDS. Nb, which is necessary for the formation of the B2 phase, comes from two aspects. The first is that Ta dissolves into the Ti2AlC and partly replaces the Nb atom and the second is the decrease in the γ phase because it has higher solid solubility for Nb. The increase in Nb in the liquid phase increases the composition supercooling and heteronucleation at the solidification front, which accounts for refining the lamellar colony. Room temperature compressive testing showed that the compressive strength and the strain increased when the Ta content increased up to 0.8% and then decreased. Improvement of the compressive properties resulted from the grain boundary strengthening and their decrease induced by more content of the B2 phase. Tensile properties, at elevated temperature, were improved with testing temperature increasing from 750 to 950°C, because solid solution strengthening is a major influence factor.