Ti3AlC2 Ceramics Research Articles

Preparation, mechanical properties, and corrosion resistance behavior of (Zr, Mo, Cr)-doped Ti3AlC2 ceramics

The corrosion resistance of Ti3AlC2 is an indispensable characteristic in its practical applications, and the focus of this study is to optimize its mechanical and corrosion properties by introducing metal ions at the M-sites of Ti3AlC2. Utilizing Ti/Al/C/Zr/Mo/Cr powders, (Ti0.8X0.2)3AlC2 solid solutions were synthesized via reactive hot pressing, with XRD and SEM analyses confirming the formation of MAX phases. Results revealed varying degrees of influence on the properties of Ti3AlC2 due to different doping elements. Among these, Zr-doped samples exhibited superior mechanical properties, boasting excellent hardness (511 Hv), flexural strength (386.57 MPa), and fracture toughness (10.24 MPa m1/2). Additionally, all (Ti0.8X0.2)3AlC2 samples formed n-type semiconductor passive layers in 3.5% NaCl solution, demonstrating outstanding corrosion resistance. Further investigation revealed that the enhancement in mechanical properties stems from solid solution strengthening and lattice distortion induced by different metallic elements. Meanwhile, the corrosion resistance is primarily attributed to alterations in electron distribution resulting from doping elements. These stable materials could find applications in electroplating wastewater treatment, where materials with excellent mechanical properties and corrosion resistance are required. It is anticipated that further modifications of MAX phase materials through doping will meet these additional requirements.

Damage mechanisms of Ti3AlC2 ceramics in pulsed laser processing

The damage mechanisms of Ti3AlC2 ceramics during laser processing in air and water were studied using the pulsed laser. The focused high-energy laser induced the melting of surface of Ti3AlC2 ceramics, causing the decomposition of Ti3AlC2 into TiC and Al with Al rapidly evaporating. During the laser processing in the air, oxygen diffused inward to form a solid solution of TiCxOy, and the rapidly heating and cooling of resolidified layer generated high thermal tensile stresses to result in a large amount of microcracks. When processing in the water, the thermal stresses were greatly weakened, and the outward diffusion of Al steam resulted in the voids on the sample surface. Additionally, it is determined that after treating in the air and water, the residual flexural strengths of Ti3AlC2 ceramics could retain the high values of 292 MPa and 484 MPa, and the Weibull moduli were kept at 7.2 and 16.0, respectively, exhibiting the excellent damage tolerance and high reliability.

Excellent ablation resistance of Ti3AlC2 ceramics up to 1900 °C in nitrogen plasma flame

In this work, the ablation behaviors of Ti3AlC2 ceramics were investigated in a nitrogen plasma flame at various temperatures. The ablation mechanisms were determined by analyzing phase compositions, macroscopic morphology, and microstructure. As the ablation temperature increased from 1500 to 1900°C, the linear ablation rate increased from − 0.725–8.7 µm/s, while the mass ablation rate increased from− 0.095–2.103 mg/s. At the ablation temperatures below 1900 °C, an oxide layer mainly consisting of Al2TiO5 was formed on the ablated surface owing to the decomposition and oxidation of Ti3AlC2, which adequately protected the matrix. When the ablation temperature reached 1900 °C, the oxide layer melted and was blown away by the plasma flow, resulting in the loss of protection and the rapid increase in ablation rates. The results indicate that Ti3AlC2 ceramic exhibits excellent ablation resistance below 1900 °C and is potentially used as thermal protection material.

In-situ generated particle synchronous enhancement of strength and toughness in pressureless sintered Ti3AlC2 layered ceramics

Ti3AlC2 as a typical MAX phase has attracted extensive attention due to its advantages of both metals and ceramics. However, the decomposition of Ti3AlC2 during pressureless sintering leads to a low density, which restricts its application in complex-shaped components. To address this challenge, MgO, CeO2, Y2O3, and La2O3 were employed as additives to fabricate Ti3AlC2 ceramics with minimal decomposition via pressureless sintering. It was observed that these oxide additives reacted with aluminum and oxygen, forming MgAl2O4, CeAlO3, YAlO3, and LaAlO3, respectively. These in-situ generated aluminate particles effectively impeded the outward diffusion of aluminum and the inward diffusion of oxygen, thereby inhibiting the decomposition of Ti3AlC2. Furthermore, the thermal expansion mismatch between the in-situ generated particles and the matrix induced beneficial residual stresses. These combined effects contributed to the synchronized enhancement of both strength and toughness. Among the four additives, CeO2 displayed the best efficiency. Ti3AlC2-1.0 wt%CeO2 reached a flexural strength of 680.74 MPa and fracture toughness of 7.82 MPa m1/2, equivalent to those by pressure assisted sintering. The calculated toughness considering the residual stress was approximately 7.71 MPa m1/2, in good agreement with the measured value.

Ablation resistance of Ti2AlC ceramics at 1600 °C in nitrogen plasma flame

In this study, the ablation behaviors of high-purity and dense Ti2AlC ceramics were investigated using a nitrogen plasma flame at 1600 °C. The macromorphology, microstructure, and phase compositions of the Ti2AlC ceramics were systematically investigated at ablation times of 60–180 s. At the longest ablation time of 180 s, the linear ablation rate and mass ablation rate are 3.09 μm/s and −0.473 mg/s, respectively, which indicate noteworthy ablation resistance. The ablated cross-sections of the samples can be classified into three layers: a surface oxide layer, transition decomposition layer, and matrix layer. The surface oxide layers formed at different ablation times are composed of Al2TiO5 and TiO2, and the transition decomposition layer comprises mainly TiC and Al2O3 with pores and cracks. The high ablation resistance of the Ti2AlC ceramics is primarily due to the formation of the surface oxide layer, which effectively prevents oxidation and plasma flow erosion.

Formation mechanism of TiC/Al2O3 composite from porous Ti3AlC2 ceramics in 35 vol.% CO‐N2 atmosphere

AbstractThermal reaction and microstructure evolution of porous Ti3AlC2 ceramics in a graphite bed (65% N2 and 35% CO) between 1100 and 1500°C were investigated in this work. The main products of Ti3AlC2 in a graphite bed were titanium carbide and alumina. At 1100°C, a thin alumina layer formed on the Ti3AlC2 particles due to the outward diffusion of slight aluminum. As the temperature increased to 1300°C, more aluminum diffused outward from the Ti3AlC2 particles, and a partial of Ti3AlC2 transformed into titanium carbide. Consequently, the alumina layer formed on the surface of particles got thicker, and defects occurred inside the particles due to the Kirkendall effect. When the temperature was 1500°C, Ti3AlC2 was transformed entirely into alumina and titanium carbide, and visible pores were left inside the particles. The formation mechanism of TiC/Al2O3 composite from porous Ti3AlC2 ceramics in a graphite bed was proposed in detail.

Influence of cutting damage on the bending strength of Ti<sub>2</sub>AlC MAX phase machinable ceramics

Ti2AlC MAX phase ceramics are excellent candidates for high-temperature heat resistant materials. In addition, they are machinable using cemented carbide tools. However, heavy machining induces many surface cracks, reducing the mechanical strength and reliability of ceramic parts. Herein, we investigated the influence of the machining process on the bending strength and microstructure of Ti2AlC ceramics. Nearly fully dense Ti2AlC ceramics with elongated grains were machined using a carbide end mill in brittle mode, producing numerous cracks; however, the roughness of the ceramic was similar to that of tool steel cut in ductile mode. Despite its rough surface, the bending strength of the machined Ti2AlC was only slightly lower than that of polished Ti2AlC. The cracks in the machined Ti2AlC ceramics were induced with a kinking structure; however, they stopped at a length equivalent to one grain. The minimum strength of the machined Ti2AlC ceramics with a fracture toughness of 6.9 MPa·m1/2 was estimated by assuming a machining through-crack shape that was as deep as the maximum grain size. Cutting damage was limited to a single grain; thus, the bending strength of the machined Ti2AlC was not significantly reduced.

Self-healing of indentation damage in Ti2AlC MAX phase ceramics

Although the crack-healing capacity of Ti2AlC ceramics has been sufficiently studied, the ability of Ti2AlC to self-heal large-scale damage, such as foreign object damage (FOD), remains unknown. This paper investigates the self-healing ability of Ti2AlC ceramics with large-scale damage (∼1000 μm in diameter). Extensive healing was observed even in the plastic damage and radial cracks. The damage and cracks caused by indentations made using a tungsten carbide sphere were filled and covered with newly formed oxides, such as titanium oxide and alumina, by the oxidation of Ti2AlC after heat treatment in air at 1000 °C. The strength, hardness, toughness, and elastic modulus of the Ti2AlC samples were measured before and after healing. The results show that the mechanical properties of Ti2AlC were similar or even slightly higher after the damage had been healed. Thus, Ti2AlC ceramics are attractive healing agents for foreign object damage in high-temperature applications.

Study on Ti2AlC/Mg Matrix Composites with Dual-scale Three-dimensional Network

The development of metal structural materials with low density, high specific strength and large internal friction is extremely urgent for the development of lightweight, high speed and high power of equipment and railway. The properties, microstructure and the evolution of interfacial bonding of composite materials are closely related. In this paper, the microstructure of Ti2AlC/Mg matrix composites with double-scale three-dimensional network is mainly studied. The prepared composite material presents a three-dimensional network in macro-micro scale, and the matrix and reinforcement are connected with each other. The mechanical properties and damping properties of the prepared dual-scale three-dimensional network Ti2AlC/Mg matrix composites and magnesium alloy matrix were tested. At the same time, the equivalent modulus of three-dimensional network Ti2AlC/Mg matrix composites on microscopic scale is predicted by finite element method according to the basic properties of Ti2AlC ceramics and AZ91D. The following conclusions are drawn: the ultimate bending strength of the composite material is increased by about 10% compared with its matrix magnesium alloy, and its ability to maintain strength is greatly improved compared with the matrix. Using the extracted information, the equivalent modulus of the composite microscopic model is calculated to be 31.25734 GPa, which is consistent with the experimental results. It provides data and theoretical support for similar research.

Interfacial Modification of Ti3AlC2/Cu Composites by Multi-Arc Ion Plating Titanium

Cu matrix composites reinforced with Ti3AlC2 ceramics can be applied for electrical contact materials, such as vacuum contact material or a pantograph slide plate. However, Ti3AlC2 particles substantially decomposed because lattice diffusion is the main way that Al atoms diffused into the Cu matrix and were uniformly distributed. In order to suppress the decomposition of Ti3AlC2 ceramics and improve the properties of Ti3AlC2/Cu composites, the surface of Ti3AlC2 was modified by multi-arc ion plating Ti. The results shows that, with the volume fraction increasing of Ti3AlC2, the decomposition of Ti3AlC2 is exacerbated and the lattice constant of Cu(Al) solid solution is bigger. In the meanwhile, the structure of Ti3AlC2 changes from dispersed granules to flakes, then to a continuous network. Multi-arc ion plating Ti effectively inhibits the diffusion of Al atoms into Cu matrix. The Ti coating reacts with Cu and generates CuxTi in the interface between the Cu and Ti coating, which inhibits the diffusion of Al atoms so as to inhibit decomposition., the inhibition of decomposition of Ti3AlC2 ceramics weakened solid solution strengthening and decreased the content of hard phase TiCx. Furthermore, the good mutual diffusion between CuxTi layer and Cu effectively improves the interfacial bonding strength.

Influences of Al concentration and Nb addition on oxidation behavior of Ti2AlC ceramics at high temperatures

ABSTRACT A titanium aluminum carbide, Ti2AlC, which is classified among MAX phase ceramics, was studied as a potential candidate for various mechanical components used in high-temperature applications. The impact of its chemical composition on its high-temperature oxidation process was determined. Ti2AlC powders with various Al contents and with or without Nb addition were synthesized via a conventional reaction technique followed by 16 h of annealing in vacuum at 1300°C. The synthesized Ti2AlC powders were consolidated by means of 15 min of pulsed electric current sintering at a die temperature of 1300°C in vacuum under a uniaxial pressure of 30 MPa. In the presence of an aluminum reservoir in the form of TiAl3, Ti2AlC has excellent resistance against high-temperature oxidation. The promising results concerning the addition of Nb to TiAl provided the rationale for a similar modification of Ti2AlC. The results of oxidation tests on Nb-doped Ti2AlC likewise showed excellent oxidation resistance. Alloying with Nb can improve the oxidation resistance of Ti2AlC with low Al content, allowing the formation of a protective Al2O3 scale and inhibiting the growth of TiO2.

Ultra-Fast Thermal Shock Evaluation of Ti2AlC Ceramic.

In this work, the rapid thermal shock behavior of Ti2AlC ceramics was studied using induction heating. The present evaluation method possesses the merits of very rapid heating within tens of seconds and fast quenching in water of less than 0.1 s, removing the shortcomings of traditional thermal shock. For comparison, the samples were also quenched in the air to investigate the thermal shock mechanisms. The results showed that the abnormal shock occurred in the samples when quenching in water, ascribed to the formed oxide layer on the surface of Ti2AlC ceramic inhibited the water penetration into the substrate. The quenched Ti2AlC samples still had a high residual flexural strength above 167 MPa up to 1150 °C, exhibiting promising applications in the high-temperature fields.

Synthesis of MAX phase-based ceramics from early transition metal hydride powders

MAX phase ceramics are typically prepared by the reactive sintering of elemental powders that are often coarse, expensive, and prone to oxidation. The temperature-driven dehydrogenation of metal hydride powders offers an alternative synthesis approach, as the hydrides decompose into phase-pure, dimensionally fine elemental powder particles. The increased reactivity of these in situ formed, fine powder particles drastically reduces the formation temperature of the antecedent intermetallic phases, without forming excess binary carbides or facilitating powder oxidation in the Ti-Al-C and Zr-Al-C systems. This work elucidates the effect of metal hydrides on the sequence of formation reactions in MAX phase ceramics. In the Zr-Al-C system, the use of coarse, oxidation-prone elemental Zr powders prevented MAX phase formation, whereas spark plasma sintering of ZrH2 powders at 1500 °C produced ceramics containing 60 wt% Zr3AlC2. Similarly, in the Ti-Al-C system, spark plasma sintering of TiH2 powders at 1200 °C produced phase-pure Ti3AlC2 ceramics.

High-temperature microstructural evolution of Ti3AlC2 ceramics in a graphite bed

Microstructural evolution and chemical reactions of Ti3AlC2 ceramics in the range from 1100 °C to 1500 °C in a graphite bed were investigated in the present work. The electron probe microanalysis (EPMA) results indicated that only a thin but unbroken reaction layer was formed on the surface of Ti3AlC2 ceramics at 1100 °C. It was further confirmed as aluminum oxide, while aluminum oxide fine grains were distributed separately over the surface layer along a dozen microns scale. At 1300 °C, a continuous and dense reaction layer which was mainly composed of aluminum oxide and titanium carbide was detected. After heat-treated at 1500 °C, an obvious difference in metallic luster contrast between the interior and exterior layer of cross-sections of the sample was observed. The Kirkendall effect was proposed to elucidate the above results. Titanium carbide, instead of TiO2, became the main product phase in the reaction product layer. It was attributed to the weak oxidative condition in a graphite bed and low oxygen partial pressure, which was not considered in the previous study. Besides, thermodynamic calculations result was provided to elaborate on the reaction mechanism in detail.

MAX相セラミックス製ボルト及びナットの強度評価

Ceramics are attracting attention in the aerospace and medical fields because of their high strength at high temperatures, good corrosion resistance, and good allergy resistance. However, in general, ceramics are hard and brittle and difficult to machine. In addition, since it is a brittle material, it is weak against tensile stress, so it is not suitable for bolts to which a tensile load acts. However, MAX-phase ceramics can be machined with cemented carbide tools like steel, and have excellent tensile strength. The purpose of this study is to develop an advanced ceramic bolt that has properties such as heat resistance, corrosion resistance, and non-allergenicity while having the high tensile strength required for fastening screw products. MAX-phase ceramics have excellent machinability and self-repairing properties in which cracks are filled with precipitates in a high-temperature environment, so higher tensile strength can be expected compared to other ceramics. In this study, M6 size bolts and nuts were fabricated by Ti2AlC ceramics, which is a kind of MAXphase ceramics, and their mechanical properties were evaluated. As a result, it was found that the breaking load of the Ti2AlC nut is lower than the guaranteed load of the JIS steel nut, but equal to or greater than that of the copper or aluminum alloy nut. It was also found that the failure mode of the Ti2AlC nut was due to tensile stress in the circumferential direction, not the usual shear failure of the threads. Also, the breaking load of Ti2AlC bolts is considerably lower than the guaranteed load of JIS steel bolts, but higher than other ceramic bolts such as Al2O3 and glass mica.

Oxidation and creep behavior of textured Ti2AlC and Ti3AlC2

The oxidation and creep behaviors of textured Ti2AlC and Ti3AlC2 ceramics were characterized. The oxidation behavior of the two materials, which was studied in air at temperatures ranging from1000 to 1300 °C, was observed to be anisotropic and the materials exhibited a better oxidation resistance along a direction transverse to the c-axis. The correlation between the overall parabolic rate constant and oxidation temperature of both textured materials was characterized, providing new insights into the oxidation kinetics. The results indicate that the texturing has a negligible influence on the creep behavior in the assessed temperature range of 1000−1200 °C in air, for the applied stresses ranging from 40 to 80 MPa. In this stress regime, the creep behavior of textured Ti2AlC and Ti3AlC2 appears to be controlled by grain boundary sliding. This behavior can be rationalized based on a model for superplastic deformation, indicating pure-shear motion under stationary conditions accommodated by lattice or grain-boundary diffusion.

Microstructure, properties and fracture mechanism of MAX phase Ti3AlC2 ceramics with Si doping via Ti–Al–C system by powder metallurgy

The key problems restricting the wide development of Ti3AlC2 material are the low hardness and strength. In this paper, MAX phase Ti3(Al,Si)C2 solid solutions with different Si doping were successfully synthesized using an in-situ reaction of Ti–Al–C system by powder metallurgy route. The phase structures and microstructures of the as-synthesized Ti3(Al,Si)C2 solid solutions were analyzed, the mechanical properties were tested, and the fracture surface morphologies were characterized. The results show that doping Si can prevent the lath-like structure of MAX phase from coarsening. When doping 0.2 mol Si, the as-synthesized Ti3Al1.0Si0.2C2 sample offers fine microstructure and has excellent performance. Its Vickers hardness, flexural strength and the fracture toughness are 5.52 GPa, 546 MPa, 7.51 MPa m1/2, respectively. The fracture mode is transgranular cleavage fracture. During propagation, the main crack deflects and branches obviously. The crack extends in a zigzag like path, accompanied by transgranular fracture. When suffering external force, the particular layered structure of Ti3(Al,Si)C2 can absorbs and dissipates more energy through hybrid deformation modes such as extrusion, kink, fold, interlaminar separation and tearing. With this complex and mixed fracture mode, the crack propagation were effectively prevented, and its flexural strength and fracture toughness were enhanced.

Constructing an ultrahard layer on the surface of Ti3AlC2 ceramics via electron beam surface remelting

The present work investigated the surface irradiation and remelting effects of Ti3AlC2 ceramics by electron beam surface remelting (EBSR). The effects of electron beam current and irradiation times on the microstructure and thickness of the irradiated layer on Ti3AlC2 were studied. The original coarse lamellar Ti3AlC2 grains were refined and a graded structure consisting of remelted layer and heat-affected zone was formed on the surface of Ti3AlC2 matrix. Near-spherical TiC particles with diameters of 300 nm were obtained in the remelted layer. Vickers hardness of more than 21 GPa was achieved in the EBSR-treated Ti3AlC2 ceramics, which could be attributed to the formation of TiC particles coupled with crystallite refinement. This work provides a simple and low-cost route for surface hardening of structural ceramic materials.

Experimental investigation and mathematical modelling of water vapour corrosion of Ti3SiC2 and Ti2AlC ceramics and their mechanical behaviour

Commercially available Ti3SiC2 and Ti2AlC ceramics were used in this study to investigate their wet corrosion and mechanical behaviour as they were under investigation for years for their applications in the field of nuclear as cladding materials and aerospace. The test coupons of dimension 3 × 4 × 40 mm3 and 3 × 4 × 20 mm3 were machined out from commercially available samples for the 3-pt bend test and wet corrosion test, respectively. The water vapour corrosion studies of these samples were carried out at 800 ℃, 1000 ℃, 1200 ℃ for 10, 20 and 100 h in gas flow condition containing 50 % steam + 50 % air. Phase analysis of the as-received Ti3SiC2 and Ti2AlC ceramics revealed the presence of other impurity phases such as TiC and TiSi2. The XRD patterns of the oxidised samples show the formation of rutile as the major phase in both materials. The oxidation layer formed on Ti3SiC2 sample was measured to be 280 μm after exposing the sample in steam for 100 h at 1200 °C. The water vapour corrosion studies reveal that Ti2AlC has high oxidation resistance compared with the Ti3SiC2 due to the formation of protective layers of TiO2 and Al2O3 which resulted in reduced weight gain and oxidation layer thickness. Three-point bend tests were conducted at room temperature for the samples after the water vapour corrosion test at 1000 °C/100 h. The TAC samples showed no degradation in the bending strength (244 MPa) whereas the TSC samples showed reduced strength of 320 MPa. The tensile strength of the samples was measured at room temperature and hydrothermal condition (250 °C and 250 bars pressure) and it was observed that Ti3SiC2 had high tensile strength (190 MPa) in hydrothermal conditions. The tensile strength results were validated using Finite element analysis (FEA) using ANSYS and the FEA results showed a negligible variance of 7 % compared with experimental method. Mathematical modelling based on one dimensional solution of diffusion equation combined with Deal-Grove model was employed to study and compare the oxidation thickness for the linear and parabolic models for the ceramics. The model was effective in validating the oxidation thickness of Ti3SiC2 showing that the experimental thickness was closer to that of mathematical model.

Pressure-assisted direct joining of Ti3AlC2 ceramics in air

We introduced a novel strategy for direct joining Ti3AlC2 ceramics in air without the need for any interlayer and vacuum/ inert gas protection. This was achieved by applying constant external pressure to manipulate the amount of available oxygen for oxidation at the Ti3AlC2―Ti3AlC2 interface. The shear strength of the joints bonded under a pressure of 10 MPa was approximately 3 times higher than that without pressure. The joining mechanisms were addressed based on the atomic interdiffusion and preferential oxidation of Al in lamellar Ti3AlC2 grains.