Mechanical Properties Of TiAl-based Alloys Research Articles

The Effect of Heat Treatment on the Microstructure and Mechanical Properties of Powder Metallurgy Ti-48Al Alloy

Heat treatment is the critical step in achieving a refined microstructure and enhanced mechanical properties of TiAl-based alloys. This study investigated the influence of heat treatment temperature, cooling method, and heat treatment time on the microstructure and mechanical properties of an extruded powder metallurgy Ti-48Al alloy, and achieved the control of fully lamellar fine microstructures and the enhancement of performance through a simple heat treatment, rather than the traditional approach of homogenization followed by heat treatment. The results indicate that the heat treatment temperature determines the type of microstructure, while the cooling rate dictates the lamellar width. As the heat treatment temperature was increased from the two-phase region to the α single-phase region, the microstructure transitioned from duplex to near lamellar, and the alloy strength initially increased and then decreased, influenced by both the lamellar colony ratio and grain size. A rapid cooling rate (water quenching) induces a non-diffusive massive phase transformation, whereas a slow cooling rate (air cooling) gradually forms α2/γ lamellar colonies. Therefore, a suitable heat treatment regime for the powder metallurgy Ti-48Al alloy was determined to be 1340 °C/5 min/air cooling. The microstructure of the alloy was near lamellar, consisting of lamellar colonies approximately 50 μm and a small number of γ equiaxed grains of about 10 μm. Subsequently, the alloy exhibited a room temperature tensile strength of 784 MPa and a yield strength of 763 MPa, representing improvements of 17.0% and 38.7% over the extruded alloy, respectively. This research provides a reference for establishing a heat treatment process for powder metallurgy TiAl alloys.

Tailoring the Microstructure of Laser-Additive-Manufactured Titanium Aluminide Alloys via In Situ Alloying and Parameter Variation

Titanium aluminide (TiAl) alloys have emerged as promising materials for high-temperature applications due to their unique combination of high-temperature strength, low density, and excellent oxidation resistance. However, the fabrication of TiAl alloys using conventional methods is challenging due to their high melting points and limited ductility. Selective laser melting (SLM), an additive manufacturing technique, offers a viable solution for producing TiAl alloys with intricate geometries and the potential for tailoring their microstructure. This study investigates the effect of in situ copper alloying and multiple laser scans on the microstructure and mechanical properties of TiAl-based alloys fabricated using SLM. The results demonstrate that copper alloying enhances the formation of the α2-Ti3Al phase, refines the microstructure, and improves the mechanical properties of TiAl alloys. Multiple laser scans allow for the creation of distinct microstructural regions within a single component, enabling the tailoring of properties that are suitable for specific operating conditions. The findings provide valuable insights into the fabrication and optimization of TiAl intermetallic alloys with diverse applications.

ТЕМПЕРАТУРНА ТА ШВИДКІСНА ЧУТЛИВІСТЬ МЕХАНІЧНИХ ВЛАСТИВОСТЕЙ В ПЕРСПЕКТИВНИХ СПЛАВАХ TNM


 
 
 The temperature and velocity sensitivity of the mechanical properties of TiAl-based alloys were investigated. The structure was determined by scanning electron microscopy in SEI mode. Mechanical properties were determined by the results of tensile and bending tests. It was found that the temperature and velocity dependence of the mechanical properties in alloys with 47% Al is practically absent. This makes them promising for use as structural materials, due to the stability of their properties.
 
 

Effect of Y2O3 on physical and mechanical properties of TiAlbased alloys

Ti-45Al-5Nb alloy powders were used as the matrix, and added different contents of Y2O3. The TiAl-based alloys with excellent mechanical properties were prepared by vacuum hot pressing sintering technology. Analysed the effect about Y2O3 on the properties of the alloys. The results show that trace amounts of Y2O3 can effectively improve the physical and mechanical properties and refine the grain size of the alloys. When 0.25% Y2O3, the TiAl alloy exhibits excellent hardness, density, flexural strength and fracture toughness. TiAl-based alloys are mainly composed of brittle fracture.

First-Principles Study on the Impact of Antisite Defects on the Mechanical Properties of TiAl-Based Alloys

Microalloying is an effective approach to improve the mechanical properties of TiAl-based alloys which have been applied as high-temperature structure materials. The antisite defects may be regarde ...

High-throughput analysis of Al and Nb effects on mechanical behaviour of TiAl alloys using electromagnetic cold crucible continuous casting

To optimize the microstructure and mechanical properties of TiAl-based alloys, a novel high-throughput preparation method was developed using the electromagnetic cold crucible continuous casting (ECCCC) technique. Ti-48Al/Ti-44Al (at.%) and Ti-47Al-10Nb/Ti-47Al high-throughput gradient materials (HTGMs) were successfully fabricated using the ECCCC technique. Composition, microstructure and mechanical properties were systematically investigated. The results show that the HTGMs exhibit continuous and subtle variations in composition. The solute content at different pulling lengths was calculated, with the composition gradient controlled by the height of the molten pool. Using this method, the optimized composition of Ti-47Al-6Nb was determined by studying Ti-48Al/Ti-44Al and Ti-47Al-10Nb/Ti-47Al HTGMs. The ECCCC technique provides a new method to fabricate TiAl-based HTGMs; it is suitable for studying the effects of solute content on microstructure and mechanical properties.

Microstructure characterization and mechanical properties of TiAl-based alloys prepared by mechanical milling and spark plasma sintering

High Nb containing TiAl alloy powders with or without mechanical milling were consolidated by spark plasma sintering (SPS) technique. The effects of SPS temperature and mechanical-milling treatment on phase constitution and microstructure were studied, and the mechanical properties at room temperature were tested. The phases in the as-atomized powder are composed of major α2 phases, a few γ phases and a trace of β phases. After milling, the diffraction peaks for α2 phase are obviously broadened, and the intensities of diffraction peaks for both γ phase and β phase are decreased. Similar phase constitution including a large quantity of γ phases and a few α2 phases are exhibited in the alloys sintered by either as-atomized powder or as-milled powder. At a sintering temperature of 1200°C, the microstructure of the alloy sintered by using as-atomized powder consists of inhomogeneous γ and α2 phases as well as a few α2/γ lamellar colonies. By contrast, the densities increase and the microstructures are apparently refined for the alloys sintered by using as-milled powder. Fully dense alloys with uniformly distributed γ and α2 grains can be obtained at extending milling time or increasing rotating speed. The nucleation of γ phase during SPS of the powders is dependent on recrystallization. The heterogeneity of deformation should be responsible for the formation of heterogeneous γ grains in the alloys sintered by using as-atomized powder. The heterogeneous grain size for the alloys sintered by using as-milled powders is mainly derived from the inhomogeneous nucleation of γ phase and the uneven distribution of α2 grains. Good mechanical property accompanied by a fine grain size and a dense microstructure can be achieved by optimizing the process parameters.

Effect of Y Addition on Microstructure and Mechanical Properties of TiAl-based Alloys Prepared by SPS

Abstract TiAl alloys with a composition of Ti-45Al-2Cr-2Nb-1B-0.5Ta(at%) (TA alloy) and Ti-45Al-2Cr-2Nb-1B-0.5Ta- 0.225Y(at%) (TAY alloy) were prepared by double mechanical milling and spark plasma sintering (SPS). The effect of Y addition on microstructure and mechanical properties of TiAl-based alloys was studied. The results show that the morphology of double mechanical milling powder is regular with sizes in the range of 20∼40 μm. The main phases of TiAl and Ti3Al and few phases of Ti2Al and TiB2 were observed in the SPS bulk samples of TiAl-based alloys. The equiaxed crystal grain microstructure was achieved with sizes in the range of 100∼400 nm in TA alloy samples. The samples exhibited compressive properties at room temperature with a compressive strength of 2614 MPa and a compression ratio of 20.57%. For TAY alloy, the sizes of equiaxed crystal grain obviously decreased. The samples exhibited compressive properties at room temperature with a compressive strength of 2677 MPa and a compression ratio of 22.91%. The micro-hardness of the SPS bulk samples of TA alloy was obviously higher than that of the SPS bulk samples of TAY alloy. On the base of analysis of fractographs, it showed that the compression fracture transform of the SPS TiAl-based alloys samples was intergranular rupture.

Effect of Isothermal Forging on Microstructure and Mechanical Properties of TiAl-Based Alloys

The effect of isothermal forging on microstructure and mechanical properties of Ti-44Al-4Nb-4Zr-0.2Si-1B alloys were investigated by means of BSE, TEM, tensile and the high cycle fatigue test at room temperature. The results showed that the lamellar thickness and volume fraction of equiaxed γ phases and B2+ω phases decreased, the grain size and volume fraction of lamellar α2+γ colonies was raised after isothermal forging. The lamellar was bending. The tensile strength and yield strength was increased by 80MPa although the total elongation hardly changed. The fatigue limit was increased by 230MPa. The effect of boride, lamellar thickness and B2+ω phases on the mechanical properties were studied.

Microstructures and Mechanical Properties of TiAl-Based Alloys Prepared by High-Energy Ball Milling and Hot-Pressing Sintering

TiAl-based alloy with a composition of Ti-47%Al-3%Cr (mole fraction) was prepared by high-energy ball milling and hot-pressing sintering. The relationship between microstructure and mechanical properties of Ti-47%Al-3%Cr alloy was studied by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and mechanical testing. The results showed that the TiAl-based alloy with high density and uniform microstructure could be obtained by high-energy ball milling and hot-pressing sintering. The compactibility and sintering densification of the element powder could be promoted efficiently by high-energy ball milling. The main phase TiAl and few phases Ti3Al were observed in the hot pressing sintering bulk samples. In addition, the microstructure changed with ball milling times, as a result, the mechanical properties changed with the microstructure. The finer the microstructure was, the higher the strength at room temperature became. After the element powder was milled for 20 hours and hot-pressing sintered at 1300 °C for 2 hours, TiAl-based alloys were found to have good room temperature mechanical properties with the compressive strength of 2870 Mpa and the relative compressive ratio of 27.3%. Keywords: TiAl-based alloys; hot-pressing sintering; microstructure; mechanical properties

Effects of microalloying and ceramic particulates on mechanical properties of TiAl-based alloys

Micro-alloyed titanium aluminides and TiAl-based composite with a fully dense structure have been synthesized by a powder metallurgical method. X-ray diffraction and EDX studies show that the monolithic TiAl-based alloy and its composite consist of TiAl and Ti3Al compounds with the former as the major phase. Additions of Nb and/or (Mo + Cr) exert remarkable effects on the resultant phase compositions and mechanical properties of TiAl-based alloys. Both the added Mo and Cr elements are dissolved into the TiAl-based compounds to exhibit solid solution strengthening effect whereas Nb is only partially dissolved and the rest appears in the Nb-rich compound, Nb2Al. In general, the micro-alloyed TiAl and the composite exhibit superior flexural strength and fracture toughness to TiAl-based monolithic compound.

Effect of composition and cooling rate on the transformation of α to γ phase in TiAl alloys

Microstructure controls mechanical properties of TiAl-based alloys and it does so in three ways: alloy composition, thermomechanical (dynamic), and static heat treatments. This study considers the effect of composition and cooling rate in the transformation temperature from hcp-α phase to fct-γ phase in the α and γ phase field. The data for three Ti–46Al–4–8Nb alloys show that α and γ transformation temperature varies by 70 °C by changing the cooling rate over a factor of 40. Compared to the effects of cooling rate, the effect of composition on the α–γ transformation is minimal. Microstructural examination following a change in cooling rate from the post-extrusion heat treatment reveals differences in the desired lamellar structure and suggests the alloy composition and heat treatment cooling rate for optimal properties.

The application of transformation matrices on the determination of γ/γ interface types in a γ-TiAl alloy

The domain orientations and lamellar interfaces play a key role in the mechanical properties of TiAl-based alloys. All six domain orientations in the lamellar structure of a modern (α 2+γ) two-phase alloy were therefore measured by means of convergent-beam electron diffraction. The transformation matrices necessary for indexing crystallographically differently oriented γ lamellae were systematically calculated. Based on these calculated matrices, the interface types between neighboring γ laths could be determined unambiguously. The frequency of different interface types was measured systematically and compared with the frequency distribution in binary TiAl alloys.

Directional Solidification of TiAl-based Alloys and Properties of Directionally Solidified Ingots

The mechanical properties of TiAl-based alloys with lamellar microstructure are extremely anisotropic. However, if the lamellar microstructure can be aligned parallel to the growth direction, the resulting material should possess a good combination of mechanical properties. Unfortunately, simple casting operations often lead to a solidification texture with the lamellar boundaries perpendicular to the heat flow direction. This difficulty can be overcome by directionally solidifying TiAl-based alloys. We have been performing directional solidification experiments with and without using a seeding technique. The current status of directional solidification of TiAl-based alloys is reviewed.

Microstructural control in Ti-Al for enhanced mechanical properties

A study was initiated to understand the effect of grain refinement on mechanical properties of TiAl-based alloys at room and elevated temperatures. The following was found in that study. Utilizing a processing approach that includes homogenizing annealing or deformation in the α-phase field, followed by multi-step isothermal forging in the γ+ α2 phase range at relatively low strain rates and a continuously decreasing temperature, homogeneous submicro-crystalline structures were produced in titanium aluminides, facilitating further processing such as superplastic forming at temperatures below 1,000°C. Also described in this paper is a fully lamellar structure with a colony size as small as 15 µm, produced in gamma TiAl-based alloys containing borides by the fast-heating of an initially submicro-crystalline structure in the alpha-phase range followed by air cooling.

Atom-probe determination of interstitial element concentration in two-phase and single-phase TiAl-based alloys

Interstitial elements (O, C, N) seem to have a key role with respect to mechanical properties of TiAl-based alloys. This paper presents an atom-probe study of the distribution of interstitial elements in the α 2 and γ phases of two-phase TiAl alloys. These elements are found to preferentially segregate in the α 2 phase. This effect is particularly important for oxygen. Measurements of oxygen concentration in the γ phase of two-phase and of single-phase alloys were performed. This allows the maximum solubility of oxygen in the γ phase to be determined. The result shows that the poor low-temperature ductility of single-phase TiAl alloys cannot be simply due to the presence of oxygen in the γ phase.