Manganese, serving as a cost-effective and potent stabilizer of the beta-phase, plays a pivotal role in the development of economically viable and easily deformable beta-type gamma-TiAl alloys. In this investigation, we focused on a low-cost and easily deformable Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C alloy (at%), which was rolled into 12 mm-diameter bars by vacuum induction melting and conventional hot rolling techniques. The effects of high-temperature treatments at 1270, 1220, and 1170 degrees C on the microstructure and mechanical properties of the alloy bars were studied by EPMA, TEM, and EBSD. The results show that the microstructure of the alloy contains gamma, alpha(2), and beta(o) phases after heat treatment. Decreasing the temperature of high-temperature treatment under identical aging conditions significantly reduces the alpha(2)/gamma lamellar content within the alloy. Moreover, both the size of the lamellar colonies and the spacing between lamellae exhibit pronounced reductions as the treatment temperature decreases. The tensile performance tests demonstrate that as the temperature of high-temperature treatment decreases, the tensile strength at room temperature and 800 degrees C of the alloys with different microstructures declines. At room temperature, the elongation of the heat-treated alloys shows a trend of first increasing and then decreasing, and the values are all within the range of 0.5%-1.0%. However, at 800 degrees C, significant variations in elongation are observed in the alloys. Specifically, an increase in equiaxed gamma phase content correlates with enhanced alloy elongation. Compared to samples treated at 1270 degrees C, those treated at 1220 degrees C exhibit a 280% increase in elongation, while those treated at 1170 degrees C show a 480% increase. This enhancement is attributed to the improved deformability of the equiaxed gamma phase at elevated temperatures. Additionally, greater activation of dislocations within the beta(o) phase occurs, while the gamma/gamma and alpha(2)/gamma interfaces impede the movement of twins and dislocations. This study provides a comprehensive discussion on the evolution behavior and patterns of different heat-treated alloys, emphasizing their correlation with mechanical properties.

Enhancing corrosion resistance in cast alloys using straightforward and cost-effective micro-alloying techniques has emerged as a key area of investigation in materials science. The challenge lies in applying this technique to further enhance the already excellent properties of CoCrNi medium-entropy alloys (MEAs) for casting applications. A micro-alloying approach was proposed to improve the corrosion resistance of as-cast CoCrNi MEAs by incorporating cerium (Ce). The corrosion resistance of CoCrNi MEAs firstly increases and then decreases as the Ce content increases in a 3.5wt.% NaCl solution. At a Ce content of 0.02at.%, the passivation current density reaches its minimum value (26.383 mu Acm(-2)), while the breakdown potential reaches its maximum (0.471 V-SCE), imparting exceptional corrosion resistance. The results indicate that the enhanced corrosion resistance is primary due to Ce micro-alloying, which affects inclusions by forming a non-conductive precipitated phase and modifying the passivation film. Ce micro-alloying presents a promising strategy for enhancing the corrosion resistance of as-cast CoCrNi MEAs.

Heat-treated Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1 C alloy with near-lamellar (NL) and equiaxed microstructures (EQ) underwent 100-hour cyclic oxidation at 750/800 degrees C and 100-3000 h isothermal oxidation at 750 degrees C. The microstructural evolution and oxidation behavior were characterized using SEM, EPMA, EBSD, EDS, XRD, and TEM. Results demonstrate that the oxidation kinetics of both microstructures approximately follow near-linear law during cyclic oxidation. The surface oxidation products primarily consist of a mixture of rutile and alpha-Al2O3, accompanied by minor amounts of TiNxOy (fcc) and alpha-Mn2O3. The EQ microstructure exhibits marginally superior oxidation resistance compared to the NL microstructure, with both forming intact oxide scales devoid of cracking or spallation. The transition layer primarily consists of Laves phases with minor beta o phases. Notably, under long-term isothermal oxidation, the NL microstructure demonstrates significantly enhanced oxidation resistance compared to the EQ structure. Phase transformation near the oxide layer in the NL structure generates a diffusion zone comprising (beta o+gamma+Laves) phases. This transformation facilitates the formation of a dense and structurally coherent transition layer with reduced beta o phase content, effectively suppressing outward Mn diffusion and substantially improving oxidation resistance. Conversely, the EQ microstructure shows no significant phase transformation near the oxide layer. Abundant beta o phases were found in the transition layer that compromise structural integrity, resulting in inferior oxidation performance.

WC particle reinforced Ni-based composite coatings have excellent properties and can be widely employed to enhance the surface performance of metals by laser cladding technology. In this paper, the Ni60-WC composite coatings under different powder feeding rates are manufactured on H13 steel substrate using laser cladding (LC) technology. The morphology of the molten pool, interface between WC particles and the metal matrix, and the distribution of WC in laser-cladded Ni60-WC composite coatings have been thoroughly investigated. Additionally, the microstructure and microhardness of these coatings have been deeply studied. Moreover, special attention is paid to investigate the thermal damage forms of WC particles and its influence mechanism on the microstructure evolution. Due to the mismatch between laser energy input and powder mass addition, the dilution ratio is too high under the powder feeding rate of 5 g/min, and the mass fraction of WC in the composite coating is only 0.9 %, which is far lower than that of the original powder. In the Ni60-WC composite coating, gamma-(Ni, Fe) solid solution with some new precipitated carbides and borides such as FeW3C, CoW2B2, Ni4B3, Fe3B, M 23 C 6 and M12C can be found through XRD. The combined effects of fine grain hardening, solid solution hardening, precipitation hardening and dispersion hardening are the main reasons for the increase in micro- hardness of the Ni60-WC composite coating. When the powder feeding rate is 25 g/min, the maximum micro- hardness is 936HV, which is 2.4 times that of the H13 steel substrate. The microstructure characteristic is one of the main factors affecting microhardness, which is closely related to the mass fraction of WC, the thermal damage type of WC particles, and the solidification time of the composite coating. This paper provides an in-depth discussion of two thermal damage forms of WC particles, as well as the related microstructure characteristics and evolution mechanisms.

In beta-solidifying gamma-TiAl alloys, Mn serves as a crucial low-cost alloying element that significantly improves ductility and broadens potential applications. However, prolonged thermal exposure of Mn-containing gamma-TiAl alloys at service temperatures leads to the precipitation of detrimental Ti(Mn,Al)2 Laves phases that degrade mechanical properties and structural stability. While W addition has been shown to partially suppress the Laves phase formation [Intermetallics 2020; 126:106932]. In this study, the precipitation behavior of Laves phases in Ti42Al5MnxW (x = 0, 0.5, 0.8, 1.0 at%) alloys across 700-975 degrees C was systematically examined through comprehensive characterization using electron probe microanalysis (EPMA), thermodynamic calculations with PANDATTM, and first-principles density functional theory (DFT) computations. Results demonstrated that increasing W content reduced the maximum Laves phase fraction from 20 % (0 W) to 8.3 % (1.0 W) by elevating its formation energy while stabilizing beta o phase. Furthermore, a novel isothermal precipitation kinetics curves of Laves phase was established to quantitatively describe the precipitation behavior of the Laves phase under varying aging conditions and different W additions, offering a new analytical perspective for the study of Laves phase behavior.

The presented study addresses the technical challenges of contemporary nuclear research: realistic severe accident studies on the behavior of extremely aggressive chemically prototypic corium at high temperatures, which can reach the temperature level of more than 3000 degrees C. Though these experimental data are vital for the verification of safety models and codes, and for the nuclear engineering development in general, there are and have been just a few licensed experimental facilities, which can provide reliable data on critical stages of severe accident involving the interaction of highly aggressive and dangerous materials. One of the unique properties of chemically prototypic corium melt is liquid immiscibility of oxidic and metallic layers. Oxidic layer composition can be represented as a chemical formula (U,Zr,(Fe))O2-x in which Fe amount is smaller than 1 at.%. Metallic layer is Fe(Cr, Ni)-based melt, containing several at.% U, Zr and B, as well as <1 at.% C and O. These layers can have different relative densities resulting in their surface or bottom positions in case of different compositions and temperatures, ununiform partitioning of fission products (FPs) between them and different material properties of oxidic and metallic melts, such as heat conductivity, viscosity, surface tension and surface emissivity, having considerable effect on molten pool behavior, reactor pressure vessel failure mode, location and time, and corium ex-vessel progression. Development of uranium-free simulant material based on ZrO2-Fe and ZrO2-Zr-Fe systems to remove melt radioactivity and related experimental challenges, induction heating of oxidic melt to model volumetric decay heat of FPs and reliable melt retention in the cold crucible (IMCC technique) are presented in the current study to support experimental research of some severe accident phenomena, such as heat and mass transfer, miscibility gap and density stratification in molten corium pool, in conventional laboratories and universities. The reported experimental results are useful for better understanding of ZrO2-Fe and ZrO2-Zr-Fe melt behavior, phase equilibria between oxidic and metallic liquid, melt evaporation and aerosol formation, melt crystallization and corresponding phases transitions. The provided experimental data can also be used in the advanced material scaling and applied in the quantitative characterization of developed simulant material vs chemically prototypic compositions.

To investigate the effects of alloying elements on the diffusion behavior of Mn and Al in TiAl alloys, a series of diffusion couples were prepared using a high-throughput diffusion multiple approach. The couples, which included Ti42Al5Mn-M (where M denotes 0, 0.8W, 0.8Mo, 2Nb, and 2Zr, at. %), Ti42Al, and Ti54Al, were aged at 1000 degrees C for 1000 h. The phase composition of the annealed samples and the concentration profiles of Al and Mn across the diffusion zones were systematically characterized by electron probe microanalysis (EPMA). Based on these profiles, the diffusion distances of Al and Mn were measured, and their interdiffusion coefficients in TiAl alloys containing W, Mo, Nb, or Zr were calculated according to Fick's second law. The influence of these alloying elements on the diffusion behavior of Mn and Al was comprehensively analyzed and discussed.

The influence of Ga doping on the structure and mechanical properties of B2-CuZr phase reinforced larger-size CuZrAlY metallic glass composites was investigated by experiments and simulations.The result showed that as Ga content increased,the glass-forming ability of CuZrAlY metallic glass composites was gradually enhanced.Section morphology and thermal analysis indicated that Ga doping induced the decreased content of the crystals and the enlargement of the super-cooled liquid region,and increased activation energy for crystallization.Ga also stabilized the B2-CuZr phase.Characterization of the microstructure and mechanical test results suggested that the B19'-CuZr phase disappeared in the as-cast samples after adding Ga,and the martensitic transformation of the B2-CuZr phase was hindered when Ga content increased.The evolution mechanism of mechanical behaviors of the CuZr-based metallic glass composites during Ga doping was clarified by first-principles calculation.The results would be beneficial to the development and application of large-size CuZr-based metallic glass composites.

An isothermal compression simulation experiment under conditions of 1100 similar to 1250 degrees C, 0.001-10 s(-1) was conducted to study the hot deformation behavior of the Ti-42Al-5Mn-0.3B (at. %) intermetallic compound, prepared by vacuum induction melting. A hot processing map and constitutive equation were established. Based on these findings, Ti-42Al-5Mn and Ti-42Al-5Mn-0.3B ingots were prepared using un-packing forging. The room temperature and high temperature tensile properties of the forged alloys were tested. The effects and mechanisms of trace B addition on the microstructures of the as-cast and forged alloys, hot-workability, as well as the mechanical properties of the forged alloys, were systematically analyzed. The results show that, regardless of the as-cast or forged conditions, the addition of 0.3 at. % B increases the alpha(2) phase content and decreases the gamma phase content, with the influence being more pronounced in the as-cast condition than in the forged condition. In the as-cast condition, 0.3 at. % B addition not only eliminates the coarse Widmanst & auml;tten lamellar structure to form an equiaxed lamellar structure, but also reduces the content and size of the beta(o) phase. These microstructural changes result in lower flow stress and apparent activation energy (Q) for the B-containing alloy compared to the alloy without B, leading to improved hot workability. In the as-cast condition, curved flaky TiB with orthorhombic B27 structure precipitates and coexists with the B2 phase, which can be fragmented into dispersed particles or short rods during hot forging deformation. This fragmentation significantly refines the lamellar colony size and lamellar spacing, thus enhancing the strength and ductility of the alloy at both room and high temperatures.

Effect of Nb addition on oxidation resistance during cyclic oxidation at 800 degrees C of a Mn-containing gamma-TiAl alloy was explored. Nb addition reduces the oxidation reaction rate constant and thus enhances the oxidation resistance. Density functional theory calculations and experiments show that Nb stabilizes Ti(Mn, Al)2 Laves phase in the intermediate layer, and results in the disappearance of Z phase and then lower crack nucleation tendency. Nb enriched in the intermediate layer could replenish the consumption during oxidation and then inhibit rapid oxygen diffusion.

The introduction of laser beam oscillation in directed energy deposition (DED-LBO) significantly influences the thermal-fluid behavior and molten pool formation during the process. This study presents a high-fidelity CFD model, integrated with a ray-tracing algorithm, to investigate the laser-material interaction and molten pool behaviors under linear and circular oscillation mode during the DED-LBO process of 316 L stainless steel. The results show that both the average interaction angle between the laser rays and the molten pool surface, as well as the laser absorptivity, vary periodically over time due to the periodic movement of the oscillating laser. This periodic heat input condition induces fluctuations in both temperature and fluid velocity within the molten pool. A higher oscillation frequency leads to the reduced temperature and fluid velocity. Compared to the circular oscillation mode, the fluid velocity is larger under the linear oscillation mode, primarily due to the larger temperature gradient. However, the surface area of the molten pool is larger under the circular oscillation mode, resulting in the capture of more powder particles. Moreover, the calculated Peclet number and Marangoni number are both larger than unit, indicating that thermal convection is the dominant heat transfer mechanism and Marangoni force is the primary driving force during the DED-LBO process. A good agreement is achieved between the simulated and experimental dimensions of the deposited tracks, with a relative error of <11.2 %. This study could enhance the understanding of thermal-fluid transport behavior of the molten pool during the DED-LBO process and provide insights for optimizing process parameters.

gamma-TiAl based alloys are advanced structural materials use in the automotive and aerospace industries. Their notable characteristics, including low density, high specific yield strength, and exceptional resistance to creep and oxidation, make them highly viable for being used as structural components in high-temperature applications of internal combustion engines. The novel beta-solidifying gamma-TiAl alloy designed in this study demonstrated excellent oxidation resistance at temperatures of 750, 800, and 850 degrees C. However, research regarding the solid-state phase transformations and microstructure control of this alloy is lacking. The study of the phase transformation behavior and microstructural evolution of alloys is crucial for developing appropriate thermal processing and heat treatment techniques for beta-solidifying gamma-TiAl alloys. This work introduces a novel Ti-Al-Mn-Nb alloy, with a nominal composition of Ti-43Al-1.5Mn-3Nb-0.2Si-0.2C-0.1B (atomic fraction, %). Using Pandat software for thermodynamic calculations, along with techniques such as EPMA, TEM, EBSD, and XRD, an extensive and meticulous investigation of the microstructural transformations within the range from 1440 degrees C to 1000 degrees C for this innovative alloy was undertaken. The results indicate that the as-cast microstructure of the alloy comprises a lamellar colony (alpha(2)/ gamma), grain gamma phase, and a small amount of beta(o). The solidification pathway of the alloy can be determined as follows: liquid -> liquid + beta ->beta ->beta + alpha ->alpha ->alpha + gamma ->(alpha(2) + gamma)->(alpha(2) + gamma) + beta(o)->(alpha(2) + gamma) + beta(o) + gamma(g). The temperature at which the alloy exists as a single beta phase (T-beta) is approximately 1420 degrees C, while the decomposition temperature of gamma phase (T-gamma,T-solv) is approximately 1280 degrees C; additionally, the eutectoid transformation temperature (T-eut) is approximately 1160 oC. Slightly below T-gamma,T- solv, the gamma precipitated from the alpha phase exhibits a lamellar structure. The alpha and gamma phases consistently demonstrate a Blackburn orientation relationship: (111)(gamma)//(0001)(alpha 2) and <1<(1)over bar>0>(gamma)//<11<(2)over bar>0>(alpha 2), respectively. The secondary beta(o) phase precipitated from the alpha phase appears as a block shape and follows the Burgers orientation relationship: (110)(beta O)//(0001)(alpha 2) and <111>(beta O)// <11<(2)over bar>0>(alpha 2). The Vickers hardness of the quenched microstructure of the novel alloy ranges between 385 and 512 HV. With an increase in the quenching temperature, there is an observable enhancement in the microhardness of the quenched microstructure. The martensite microstructure formed after quenching in the beta single-phase area contributes to the hardness of 512 HV. This novel alloy encompasses the beta and alpha single-phase areas; thereby holding significant implications for the development of novel, highly deform-able, and high-temperature-resistant beta-solidifying gamma-TiAl alloys characterized with fully lamellar structures.

A newly low-cost beta-solidifying gamma-TiAl alloy Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C (in at. %, named as TMMW) was invented. The rolled bars with a diameter of 12 mm were successfully fabricated by conventional hot rolling process, directly carrying out from the ingot without the pre-forging or hot-packing. The heat-treated TMMW rolled bar, which had a fine-grained nearly lamellar (NL) microstructure, was then air-exposed at 750 degrees C for up to 3000 h. The changes of the microstructure during this exposure were characterized using electron probe X-ray micro-analyzer (EPMA), transmission electron microscope (TEM), electron backscattered diffraction (EBSD) and high-energy X-ray diffraction (HEXRD). The tensile properties of the samples before and after thermal exposure were also tested. The fine-grained NL microstructure is found to be thermodynamically stable during the exposure. Meanwhile, the combined addition of Mo and W shows a positive effect on the stabilization of beta(o) phase at colony boundaries, with only slight precipitation of the nanometer beta(o) phases with no other brittle phases, such as Laves, in the metastable alpha 2 lamellae. It is found that the thickness of the alpha(2) lamellae decreases after 500 h exposure, while remains basically unchanged from 500 h to 3000 h, which is contributed by the effective pinning effect of the precipitated beta o phase in alpha(2) lamellae. As a result, the exposure-induced embrittlement under room temperature and elevated temperature does not take place. Interestingly, the ductility tested at 800 degrees C improves significantly after exposure. As for the tensile strength, it is only reduced by less than 10 % after 500 h exposure, while it remains essentially unchanged when increasing the exposure time from 500 h to 3000 h. Finally, the mechanisms of the precipitation of beta(o) phases in the alpha(2) lamellae and the tensile properties evolution during the exposure were carefully discussed.

This paper aims to improve the density and thermal shock resistance of Y2O3 ceramics for the preparation of ultra-pure high-temperature alloy crucible materials. The doping effect of MgF(2 )content on the densification behavior, physical properties, and thermal shock resistance of Y2O3 ceramics was systematically investigated in this paper. The results suggested that the presence of MgF2 greatly promoted the growth of Y(2)O(3 )grains and the transformation of the pore structure by liquid-phase sintering. And the mechanical properties of the MgF2-doped Y2O3 ceramics were significantly improved. Besides, the marked improvement in the thermal shock resistance of MgF2-doped Y2O3 ceramics was attributed to the synergistic action resulting from the growth of grain size and the enhancement of the crack deflection effect. In particular, the relative density of Y(2)O(3 )ceramics doped with 1.5 wt% MgF2 reached 96.4% and the residual flexural strength ratio after thermal shock achieved 45.0%, showing an excellent application prospect.

The effect of varying amounts (1.0–5.0wt.%) of TiO2 as an additive on the interfacial behavior between the MgAl2O4 crucible materials and molten K417G superalloys during the vacuum induction melting has been characterized. Experimental results indicate that the phases of the TiO2-doped MgAl2O4 materials were identified as MgAl2O4 and minor amounts of MgTiO3 after sintering at 1680°C for 1h. When the TiO2-doped MgAl2O4 crucibles were in contact with K417G melt, a reaction layer of MgTiO3 was formed at the inner wall of the crucible. Moreover, some Al3+ and O2- were expelled toward the alloy side from MgTiO3 near the interface to form Al2O3 phases, and even form a continuous aluminum oxide layer in the 5wt.%TiO2-doped crucible after the melting experiment. Furthermore, only MC carbide with MgAl2O4 as the core (MgAl2O4-(Ti, Mo)C hybrid-type) in the K417G alloy after the melting experiment can be observed, indicating that physical erosion predominates.

Mn-containing beta-solidifying gamma-TiAl alloy, Ti-42Al-5Mn-0.8W (at%, similarly hereinafter) was prepared by a vacuum induction furnace. Then the effect of trace W addition on the hot workability of the alloy was investigated. Hot deformation behavior of the alloy was studied under the temperature of 1100 similar to 1250 degrees C, strain rate of 0.001 similar to 10 s(-1) and maximum deformation degree of 70% with thermal simulator. The results show that the range of appropriate thermal processing parameters are 1150-1250 degrees C/0.001-10 s(-1) and 1100-1145 degrees C/0.001-1 s(-1). 0.8at% W addition can obviously reduce the peak flow stress (sigma(p)) of Ti- 42Al-5Mn alloy and steady-state flow stress (sigma(0.7)), and the steady-state flow stress decreases more significantly. The main reason why 0.8at% W improves the hot workability of Ti-42Al-5Mn alloy is that on the one hand, the W content is relatively low, and the segregation degree of W element is not obvious under the vacuum induction melting mode with strong electromagnetic stirring; on the other hand, the beta-stabilizing effect of W is stronger than that of Mn, which extends the region of beta single phase zone, and thus the alloy possesses a wider processing window that can be thermally deformed.

The thermal conductivity and expansion properties of materials are important factors affecting their application. The effects of W, B addition on the thermo- physical properties such as thermal diffusion rate, thermal conductivity and thermal expansion of Ti-42Al-5Mn alloy (at%, the same below) with low cost and good hotworkability were systematically studied. The results show that with the increase of W content to 1.0at%, the thermal diffusivity of the alloy decreases slightly. On the contrary, after the B content increases to 0.3at%, that of the alloy increases slightly. The promotion of beta(o) phase in microstructure by W addition is the main reason for decreasing the thermal conductivity of the alloy. It is observed that these phases in beta-solidifying gamma-TiAl alloys are followed by gamma, alpha(2), and beta(o) in deceasing order of thermal conductivity. On the other hand, B improving the thermal conductivity of the alloy might be related to the B-containing precipitates in the alloy. W addition (0.5at%-1.0at%) has little effect on the average linear expansion coefficient of Ti-42Al-5Mn alloy. In the range of 100-300., with W content increasing to 1.0at%, the average linear expansion coefficient of the alloy decreases slightly. On the contrary, the influence decreases gradually at higher temperature. The thermal expansion coefficient of TiAl alloy is equivalent to that of cast iron, and lower than that of steel, nickel base superalloy and other materials. It would have certain application value in components requiring very low thermal expansion coefficient such as piston.

A novel thermal- deformable Ti- 43Al- 3.5Mn-0.5W (at%) alloy was designed and fabricated. The microstructure characterization, room and elevated temperature tensile mechanical properties, oxidation resistance, and deformation capacity of the alloy were investigated. The results indicate that compared with Ti-42Al- 5Mn, the developed alloy has better strength, high temperature oxidation resistance and thermal deformation ability. The alpha(2) and beta(o) phases of the alloy have lower Mn content, which reduces the precipitation tendency of Mn-rich Laves phase near the service temperature. The evolution of the phases in the alloy can be generalized as follows: beta ->beta+alpha ->beta +alpha +gamma ->beta +beta(o)+alpha +alpha(2)+gamma ->beta(o)+alpha(2)+gamma, with the T gamma- solv approximate to 1250 degrees C, T-beta approximate to 1360 degrees C. The microstructure of the forged alloy is lamellar structure and a large number of beta(o) and gamma mixed phases at the lamellar interface. The high temperature strength of the forged alloy decreases obviously. Through two-step heat treatment, the high temperature strength and stability of the forged alloy are improved to a certain extent, which is mainly attributed to the increase in lamellar structure content and the refinement size of lamellar colonies. At 800 degrees C, the yield strength, tensile strength, and elongation of the forged alloy treated with 1260 degrees C/ 0.5 h/AC+ 800 degrees C/3 h/FC were 320 MPa, 555 MPa, and 16%, respectively.