Ti2AlN Phase Research Articles

Analysis of microstructure and mechanical properties of alumina composites reinforced with Ti2AlN MAX phases

This study presents new findings on nitride MAX phases addition to ceramic matrix. Synthesised Ti2AlN was incorporated into alumina matrix with the use of powder metallurgy. Due to the low thermal stability and tendency of MAX phases for decomposition, Spark Plasma Sintering (as rapid sintering method) was utilized for composites consolidation. In order to evaluate the possibility of adopting Ti2AlN as reinforcing phase, the emphasis of the research was placed on microstructural analysis. Additionally, mechanical properties and tribological performance of produced sinters were examined. Successful synthesis of Ti2AlN phase was confirmed by XRD and FTIR analysis. Moreover, performed observations revealed that MAX phase preserved it layered structure in prepared composites. In addition, obtained results showed an improvement in the mechanical properties within entire range of Ti2AlN addition. Highest Vickers hardness (1974 HV) was measured for sinters with 2 and 2.5 wt% addition, while indentation fracture toughness reached maximum value of 4.84–5.13 MPa*m1/2 for shares in the range of 1.5–3 wt%. In case of composites with Ti2AlN content above 3 wt% decrease in mechanical properties was observed. For these sinters, adopted MAX phase undergoes phase transformation and reactions, resulting in presence of TiN, Ti2Al and Ti3AlN in microstructure. Additionally, composites with addition of 2, 2.5 and 5 wt% of Ti2AlN, when tested under the load of 60 N, where characterised by lower wear rate than reference pure alumina sinter.

Sample size dependence of high-temperature thermal stability of Ti2AlN MAX phase

The thermal stability of Titanium Aluminum Nitride (Ti2AlN) microcrystalline powder in vacuum has been studied by in-situ high-temperature X-ray diffraction. The limit of thermal stability for Ti2AlN phase is T < 850 °C. The process of thermal decomposition consists of the Al atoms sublimation and the formation of a new TiNx phase on the sample surface. An increase in sample size leads to an increase in thermal stability limit (850 °C for microcrystals and 1550 °C for dense bulk sample). Based on crystal chemical analysis and quantum chemical calculations, a mechanism of thermal dissociation was proposed. Kinetics of thermal dissociation of the Ti2AlN phase was modeled using the Avrami equation. Avrami exponent parameters (n = 1.09; 1.28) indicate that the process of germs formation occurs at a subgrain boundaries of the sample. The observed temperature dependence of the parameter n can be associated with a probability change of crosslinking formation during the growth of a new phase. The size dependence of Ti2AlN thermal stability was explained by the ratios of Al diffusion coefficients in the crystallite bulk and along the subgrain boundaries.

Fabrication and mechanical properties of Ti2AlN/TiAl composite with continuous network structure

Nitrogen was introduced into TiAl pre-alloyed powder using high-temperature gas nitriding, and Ti2AlN/TiAl composites with a continuous network structure of the reinforced phase were prepared via spark plasma sintering. The results show that the hardness of the composite is significantly higher than that of TiAl alloy, and increases with the increase of nitriding time. The strengthening effect is originated from the synergistic effect of the solid-solution strengthening caused by the nitriding of the powder, the continuous network of the Ti2AlN phase with high hardness and elastic modulus, and the increase of dislocation density. Additionally, the compressive strength of the Ti2AlN/TiAl composites is lower than that of the TiAl alloy, which is related to a part of Ti2AlN particles that are directly formed after nitriding and excessive reinforcement content.

3D Printing Using Ti-Al Nanopowders: Mechanisms of Structure Formation

In the presented research work, 3D materials were fabricated by additive moulding by means of extrusion of a mixture of high filled polymers and nanopowders of Ti-Al intermetallides with subsequent sintering at 1100 ± 20 °C, 1200 ± 20 °C and 1250 ± 20 °C (MEAM-HP process). Nanopowders of Ti-Al intermetallides were obtained by the electrical explosion of intertwined aluminium and titanium wires. It was found that the structure of the materials comprises an AlTi matrix with Ti2AlN MAX-phase particles distributed within it, surrounded by a composite layer of Ti3Al-Ti2AlN. Sintering temperature increases led to changes in the concentration of TiAl, Ti3Al and Ti2AlN phases in the samples. Besides that, aluminium oxide particles were discovered in the structure of the materials. It was found that as the sintering temperature was increased from 1100 ± 20 °C to 1250 ± 20 °C, the average microhardness of the samples increased from 193 to 690 HV0.1.

Surface Modification of Ti6Al4V Using Tungsten Inert Gas Re-melting Process in the Presence of N2 in Shielding Gas

The surface modification of Ti6Al4V alloy using a TIG re-melting process with a non-consumable electrode under Ar and Ar + N2 shielding gases has been investigated. The re-melted layers were characterized using optical and scanning electron microscopy and x-ray diffraction. The corrosion behavior of samples was also examined by potentiostat analysis. Based on the results, the TIG surface re-melting process of Ti6Al4V alloy under Ar shielding gas has negative effects on hardness and corrosion behavior of coatings. In contrast, Ti6Al4V/TiN composite coatings were successfully formed during TIG re-melting process in the presence of N2 in shielding gas. The prepared coatings showed the hardness value of about 890-910 Hv which was over four times higher than the substrate (220 Hv). The hardness showed an increasing tendency by increasing the TIG current up to 115 A. By annealing the produced coatings, the metastable TiN phase was transformed into a stable Ti2AlN phase, and the hardness value increased to about 980 Hv. Moreover, the corrosion resistance of re-melted coatings was improved during the annealing process.

The Influence of Aluminum Nitride Nanoparticles on the Structure, Phase Composition, and Properties of TiB/Ti-Based Materials Obtained by SHS Extrusion

Compact ceramic long-dimensional materials based on titanium monoboride modified with aluminum nitride dopants (3 and 5 wt %) were obtained via SHS extrusion. Titanium monoboride was produced using azide technology of self-propagating high-temperature synthesis (SHS-Az). Small dopants of nanoscaled aluminum nitride powder exert a strong influence on the phase composition, structure, and physicomechanical properties of samples prepared by SHS extrusion. Scanning electron microscopy data reveal the refinement of the main titanium monoboride phase grains in modified samples. The most pronounced refinement of titanium monoboride grains is observed as the AlN nanopowder content is increased to 5 wt %. The combustion characteristics (temperature and combustion rate) are measured in an installation simulating the real SHS extrusion conditions. It is established that AlN at its content of 3 wt % in the initial charge interacts with the titanium matrix during combustion with the formation of the Ti2AlN and Ti4AlN3 MAX phases. AlN at a concentration of 5 wt % undergoes decomposition during combustion with release of titanium nitrides and pure aluminum, as well as the TiB, TiB2 and Ti2AlN phases. Modified compact ceramic materials are shown to exhibit higher microhardness in comparison with samples without using nanomodified AlN dopants.

Investigation on Tribological Behavior of Ti2AlN/TiAl Composite at Room and Elevated Temperature

In current investigation, tribological properties of TiAl matrix composite reinforced with 15 vol%Ti2AlN and TiAl alloy prepared through in situ reactive method of powder metallurgy were evaluated against Si3N4 balls at room and elevated temperature. The wear mechanism along with the variation of temperature was also systematically analyzed. The results reveal that Ti2AlN/TiAl presents lower friction coefficients and wear rates in comparison with TiAl alloy at all test conditions. Along with the increment of temperature, the primary wear mechanisms of two materials both transform from abrasion wear to adhesion wear. Particularly, more efficient formation of tribo-oxidation films with protective feature on the worn surface of Ti2AlN/TiAl plays a dominant role in the improvement in wear resistance at elevated temperature. Additionally, the excellent tribological properties of the composite attribute to the other advantages of additive Ti2AlN phase, such as the load-carrying role, inhibition on the slipping of wear debris, as well as the refined microstructure of TiAl matrix phase.

Reaction synthesis of the Ti2AlN MAX-phase

The Ti2AlN MAX-phase is synthesized by reaction sintering from Ti–AlN powder mixtures. The optimal synthesis mode of the compound containing less than 1% of the TiN impurity phase is established. It includes isothermal annealing at 1300°C for 2 h in argon at a pressure of 3 atm. The influence of the preliminary mechanical activation of the powder mixture and the reaction synthesis medium on the yield of the Ti2AlN phase are investigated. It is shown that the activation leads to an increase in the content of the secondary TiN phase. It is revealed that the vacuum synthesis also does not make it possible to form the singlephase Ti2AlN material.

Surface alloying of commercially pure titanium with aluminium and nitrogen using GTAW processing

In the present work, surface modification of pure titanium with aluminium and nitrogen during GTAW processing has been investigated. In this regard, Al wire (grade 1100) was deposited on commercially pure Ti surface by means of GTAW process under various N2/(N2+Ar) ratios (from 1/10 to 2.5/10) in shielding gas. The alloyed layers were characterized using X-ray diffraction (XRD), optical and scanning electron microscopy (OM & SEM). The corrosion behavior of the coatings was also examined in NaCl 3.5% electrolyte by potensiostat analysis. The results indicated that, Al/Ti3Al2N2-Ti3Al composite coating can successfully form on Ti surface during GTAW cladding process. All prepared coatings have much higher hardness (270–460Hv) than pure Ti substrate (160Hv) and the hardness has shown an increasing trend by increasing the N2/(N2+Ar) ratio up to 2.5/10. More increasing in this ratio, lead to the formation of high percentage of defects in alloyed layer. By annealing the produced coatings, the metastable Ti3Al2N2 phase was transformed to Ti2AlN phase and the coating/substrate interface was covered with a smooth and continuous layer of Ti2AlN. The hardness and corrosion resistance of the prepared coatings was also enhanced during annealing process.

MECHANICAL PROPERTIES AND HIGH TEMPERATURE OXIDATION BEHAVIOR OF Ti–Al COATING REINFORCED BY NITRIDES ON Ti–6Al–4V ALLOY

Ti–Al alloyed coating reinforced by nitrides was fabricated by laser surface alloying technique to improve mechanical properties and high temperature oxidation resistance of Ti–6Al–4V titanium alloy. Microstructures, mechanical properties and high temperature oxidation behavior of the alloyed coating were analyzed. The results show that the alloyed coating consisted of Ti3Al, TiAl2, TiN and Ti2AlN phases. Nitrides with different morphologies were dispersed in the alloyed coating. The maximum microhardness of the alloyed coating was 906[Formula: see text]HV. The friction coefficients of the alloyed coating at room temperature and high temperature were both one-fourth of the substrate. Mass gain of the alloyed coating oxidized at 800[Formula: see text]C for 1000[Formula: see text]h in static air was [Formula: see text][Formula: see text]mg/mm2, which was 1/35th of the substrate. No obvious spallation was observed for the alloyed coating after oxidation. The alloyed coating exhibited excellent mechanical properties and long-term high temperature oxidation resistance, which improved surface properties of Ti–6Al–4V titanium alloy significantly.

Reaction synthesis of Ti2AlN MAX-phase

Ti2AlN MAX-phase was synthesized from the powder mixtures of Ti–AlN using the reactionary sintering method. The optimal synthesis mode for the compound containing less than 1 % of TiN impurity phase was determined: isothermal annealing at 1300 °C for 2 hours in argon at a pressure of 3 atm. The preliminary mechanical activation and the reaction synthesis environment were investigated as the factors that can influence the yield of the Ti2AlN phase. It is shown that the activation increases the level of TiN secondary phase. It was also found that the vacuum synthesis does not enable obtaining of single-phase Ti2AlN.

Oxidation and Decomposition of Ti&lt;sub&gt;2&lt;/sub&gt;AlN MAX Phase Coating Deposited on Nickel-Based Super Alloy IN718

In this work, the oxidation behavior of Ti2AlN coating deposited on nickel super alloy IN718 was investigated. The coating was obtained by DC-magnetron sputtering at 540°C and subsequent vacuum annealing at 800°C for 1h. The coating morphology as well as the chemical composition were analyzed using SEM, EDS and XRD, respectively. The XRD results revealed that the coating mainly composed of Ti2AlN MAX phase. Cycling oxidation was performed at 700 °C and 800 °C in air. The XRD and SEM results proved the interaction between substrate and coating and the formation of the quaternary Ti3NiAl2N phase during oxidation at the interface. Due to the Ni diffusion towards the surface, the Ti3NiAl2N phase grew continuously and the Ti2AlN phase decomposed gradually resulting in a coating failure. The results indicate that the oxidation behavior of the coating is essentially controlled by the interdiffusion of Ni from substrate into the coating.

Mechanical properties and microstructure of in situ formed Ti2AlN/TiAl(WMS) composites

The Ti2AlN-reinforced TiAl (WMS) composites with different contents of Ti2AlN were prepared by an in situ method of reactive arc-melting technique. According to the results of X-ray diffraction (XRD) analysis, the Ti2AlN-reinforced WMS composites consist of γ-TiAl, α2-Ti3Al, and Ti2AlN phases. Microstructure analysis results indicate that Ti2AlN reinforcements with rod-like in shape form in the WMS matrix with a α2/γ lamellar structure containing some bulk γ phases. With volume fraction of Ti2AlN increasing, the grain size of the composites decreases significantly and the elasticity modulus (E) increases. The compressive strength and compressive fracture strain of the composite with 3 vol% Ti2AlN have a maximum value of 1,654 MPa and 22.5 %, respectively, which are approximately improved by 45.84 % and 29.31 %, respectively, compared with that of the unreinforced WMS alloy.

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

Ti2AlN/TiAl composites with different volume fractions of reinforcement were successfully fabricated by hot-pressing sintering method (reaction hot pressing) using Ti, Al and TiN powders as starting materials. The synthesis process includes four stages: first, the reactions between Al and Ti powers and between Al and TiN powders respectively occur and result in TiAl3 phase; secondly, Al powders in the sample are exhausted; the remaining Ti cores react with TiAl3 layer to form Ti-Al intermetallics; moreover, a few Ti2AlN particles precipitate from the TiAl3 phase; thirdly, Ti-Al intermetallics react with the remaining Ti cores to form Ti3Al and TiAl phases. TiAl phase and original TiN powers are in direct contact each other; finally, the residual TiN powers react with TiAl phase and result in a plenty of Ti2AlN phase. Compared with TiAl matrix, the hardness, elastic modulus and high-temperature compressive strength of Ti2AlN/TiAl composite are improved obviously and they are all enhanced with increasing the volume fraction of Ti2AlN phase.

Formation of Ti2AlN phase after post-heat treatment of Ti–Al–N films deposited by pulsed magnetron sputtering

Ti–Al–N films with different compositions were prepared by varying the nitrogen flow rate using pulsed magnetron sputtering and subsequently annealed in air at 700°C. The microstructure and microhardness of the films were investigated before and after heat treatment. The XRD results indicate that no Ti2AlN MAX phase occurs in all the as-deposited films. Ti2AlN phases could be acquired only after annealing via solid state reaction. The formation condition of Ti2AlN phase is strongly dependent on the film composition. It has been found that the nitrogen concentration in the films plays a key role for the phase formation, and the critical value is in the range of 22.5–29.6at.%. The fractured cross-section SEM images show that all the as-deposited films exhibit a fine columnar morphology. The annealed films with Ti2AlN phase components change the morphology from columnar to fine equiaxed polycrystalline. In addition, the microhardness of the films containing Ti2AlN phase is also explored, which is within the range of 18–24GPa.

Synthesis of high-purity Ti 2AlN ceramic by hot pressing

High-purity Ti 2AlN ceramic was prepared at 1300 °C by hot pressing(HP) of Ti/Al/TiN powders in stoichiometric proportion. The sintered product was characterized using X-ray diffraction(XRD) and MDI Jade 5.0 software (Materials Data Inc, Liverpool, CA). Scanning electron microscopy(SEM) and electron probe micro-analysis(EPMA) coupled with energy-dispersive spectroscopy(EDS) were utilized to investigate the morphology characteristics. The results show that Ti 2AlN phase is well-developed with a close and lamellar structure. The grains are plate-like with the size of 3–5 μm, thickness of 8–10 μm and elongated dimension. The density of Ti 2AlN is measured to be 4.22 g/cm 3, which reaches 97.9% of its theory value. The distribution of Ti 2AlN grains is homogeneous.

Synthesis of high-purity bulk Ti 2AlN by spark plasma sintering (SPS)

Single-phase bulk Ti 2AlN was prepared by spark plasma sintering (SPS) at 1200 °C of Ti/Al/TiN powders in stoichiometric proportion. Investigated by X-ray diffraction (XRD) of samples and the sintering process parameter, the reaction procedure could be analyzed. Scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA) coupled with energy-dispersive spectroscopy (EDS) were utilized to investigate the morphology characteristics. When sintered at 1200 °C, Ti 2AlN phase was well developed with a close and lamellated structure. The distribution of Ti 2AlN grains was homogeneous.

Tribological performance of plasma nitrided gamma based titanium aluminides

Ti–48Al–2Nb–2Mn (at.%) alloy was plasma nitrided to investigate the effect of this thermochemical surface modification on the tribological behaviour of gamma based titanium aluminides. The effects of nitriding temperature, nitriding time and H 2/N 2 gas ratio were investigated. Characterisation of the microstructure and phases formed within the nitrided surface layers was performed using optical and electron microscopy, X-ray diffraction (XRD) and glow discharge spectroscopy (GDS). The wear resistance of the plasma nitrided samples increased considerably against ball bearing steel (AISI 52100). Experimental results indicated that time controls the thickness and nitriding temperature, and H 2/N 2 ratio is responsible for the crystal structure of the nitrided layers. The nitrided compound layers consist of TiN and Ti 2AlN phases. The diffusion zone, in most cases comprises of recrystallised gamma grains beneath the compound layer.

Ion nitriding of titanium aluminides with 25–53 at.% Al I: Nitriding parameters and microstructure characterization

Titanium aluminides with Al contents of 25, 40, 50 and 53 at.% were ion nitrided to modify the surface conditions. The effects of four process parameters, namely nitriding temperature, nitriding time, working pressure and [N 2] [H 2] ratio, were investigated by the orthogonal test. The phases and microstructures of the nitrided surface were studied by X-ray diffraction (XRD), electron probe microanalysis, optical microscopy and scanning electron microscopy. Experimental results indicate that nitriding temperature and time are the primary parameters responsible for improving surface hardness. The nitrided compound layer consists of TiN and Ti 2AlN phases. As the Al content in titanium aluminides increases, the XRD intensity of Ti 2AlN phase becomes stronger. The diffusion layer in all the cases has little nitrogen, allowing this layer to be easily attacked by the etching reagent. A mechanism to explain the formation of the ion-nitrided layer in titanium aluminides is also proposed in this study.