We propose this topic because we predict that the low melting point characteristic of aluminum nanoparticles (ANP) is conducive to alleviating the problems of thermal deformation and internal stress in selective laser melting (SLM)3d printing. With the in-depth research, we further recognize that this characteristic of metal nanoparticles has potential not limited to this. There is a need to develop brand-new forms of 3d printing to expand its application scope. We conducted a comparative study on the molecular dynamics (MD) of ANP phase transitions in isolated and stacked states using LAMMPS software, observed the metallographic recombination before ANP melted to the melting point of aluminum structural components, and proved the feasibility of adjusting the printing temperature using the diameter of the metal powder. Based on the above research, we believe that the low-melting-point feature of nano-metal particles combined with the coating of succinic acid (flux) can be used to complete metal 3d printing through a smaller equipment improvement using the fused Deposition Modeling (FDM) platform. The phase transformation study of succinic acid composite ANP was carried out using the MD method, which proved the role of succinic acid passivation in further reducing the process difficulty. Based on this new 3d printing mode, the molecular dynamic simulation of the phase transition behavior of ANP with different succinic acid coating degrees was simulated.

The combustion behavior of Ti-Al-Mo-Zr-Sn-W alloy (TC25G) was studied in a high-temperature and high-speed air flow environment using the laser ignition method combined with ultra-high temperature infrared thermometer, scanning electron microscope, X-ray diffractometer, and transmission electron microscope. The burn-resistant performance of TC25G and TC11 alloys was compared. Meanwhile, the microstructural characteristics, crystal structure, and formation mechanism of the combustion products of TC25G alloy were analyzed in detail. The results show that the high-temperature and high-speed air flow promotes combustion within the air flow temperature range of 200-400 degrees C and the air flow velocity range of 0-100 m/s. The combustion path advances along the direction of the airflow. The combustion of TC25G alloy mainly relies on the diffusion of the oxygen and the expansion of the combustion area caused by the movement of the melt. Based on the microstructure and composition of combustion product, it can be divided into the combustion zone, the melting zone, and the heat affected zone. During combustion, the formation of microstructures is closely correlated with the behavior of alloying elements and their selective combination with O. The major oxidation products of Ti are TiO and TiO2. The oxides formed by Mo and W hinder the movement of the melt during the combustion. Al and Zr tend to undergo internal oxidation. Al2O3 precipitates on the surface of ZrO2, forming a protective oxide layer that inhibits the inward diffusion of O. Moreover, the element enrichment at the interface between the melting zone and the heat affected zone increases the melting point on the solid side, hindering the migration of the solid-liquid interface.

This study establishes a machine learning assisted optimization design framework for 600 degrees C high temperature burn resistant titanium alloys, integrating domain expertise and experimental data analysis. An high-precision predictive machine learning model(XGBoost) for oxidation resistance (R2 = 0.98) combined with genetic algorithm performed global compositional optimization in the Ti-V-Cr-Al-Si-C-Mo-Nb system, minimizing the parabolic oxidation rate (kp) to 1.02 x 10-6 mg2/cm4 & sdot;s. A representative composition of a burn resistant titanium alloy (TF600) capable of withstanding 600 degrees C was ultimately identified. This alloy exhibits well-balanced properties with a kp value as low as 1.02 x 10-6 mg2/cm4 & sdot;s. After optimization of the solution and aging treatment process, the room temperature and 600 degrees C tensile strengths of TF600 reached 1177 MPa and 970 MPa respectively. Through microstructural characterization of the TF600 alloy and cellular automata simulations, the strengthening mechanism was elucidated as being dominated by the pinning effect of 50-150 nm lath alpha phase interfaces and dispersion strengthening by 20-80 nm Cr/V-rich Laves phases. The burn resistant mechanism was attributed primarily to the barrier effect of a mixed oxide film composed of V2O5 and Cr2O3. This research provides a novel pathway for the machine learning assisted optimization and precise design of advanced high-temperature titanium alloys.

Ti150 powders were deposited on the as-forged Ti180 alloy by selective laser melting under different laser powers. The microstructure and mechanical properties of the Ti150/Ti180 bimetallic alloys were systematically studied. The results showed that the Ti150/Ti180 bimetallic alloy samples can be categorized into three regions: the forging zone, the bonding zone, and the deposition zone. The forging zone exhibited duplex microstructure. The bonding zone had no macroscopic defects. In the lower region, the Ti180 alloy underwent rapid melting and solidification, and formed a unique microstructure after undergoing multiple thermal cycles. In the upper region, there was a continuous variation in solute element concentrations, leading to the gradual transformation of the microstructure into Widmanst & auml;tten structure. The deposition zone consisted of Widmanst & auml;tten structure that was composed of alpha phase and residual beta phase. As the laser power increased, the density in the deposition zone initially increased and then decreased. The main defect type shifted from lack-of-fusion to pores. The tensile properties showed a trend of initial improvement followed by deterioration. When the laser power was 287 W, the deposition zone has the lowest defect content, with a relative density of 99.58%. The ultimate tensile strength and elongation of the sample at room temperature were 1151 MPa and 4.8%, and those at 450 degrees C were 969 MPa and 14.0%, respectively.

This study employs molecular dynamics (MD) simulations to explore the high-speed impact behavior of double conical tungsten (W) fragments on titanium (Ti) target plates, focusing on fragment cloud formation, Ti damage evolution, and the effects of temperature and impact velocity. High-speed impact converts W fragments’ kinetic energy into internal energy, causing W fragmentation and the formation of a mixed-phase fragment cloud, which induces severe damage to the Ti target. Under double-particle impacts, W fragments penetrate the Ti target to form a multi-source fragment cloud, with Ti target damage (characterized by amorphous phase distribution) undergoing initiation and extension stages. Higher temperatures broaden the high-temperature damage zone and increase crater size but do not change the impact penetration evolution mode or penetration depth. Impact velocity determines damage modes: low velocity causes non-through internal damage with a rear bulge, while high velocity leads to full perforation with mixed W-Ti fragment ejection, and lateral crater size is almost unaffected by velocity. This study innovatively reveals the atomic-scale damage evolution mechanism of Ti targets under dual conical W fragment impact, which fills the research gap in conventional single-fragment impact studies. These findings clarify the high-speed impact mechanism of Ti alloys, providing theoretical support for the design of Ti-based protective structures in engineering.

The pursuit of advanced structural materials for use in extreme environments, specifically those exceeding 1200°C in aerospace, energy, and defense applications, has exposed the fundamental limitations of conventional Ni-based superalloys. In this context, refractory complex concentrated alloys (RCCAs) have emerged as a transformative materials paradigm, promising a unique combination of ultra-high temperature strength, exceptional microstructural stability, and superior creep resistance. This review provides a comprehensive and critical examination of the rapid advancements in the design and development of RCCAs. It begins by synthesizing the evolution of alloy design methodologies, tracing the progression from empirical and semi-empirical criteria to the integration of sophisticated computational tools, including computational thermodynamics (CALPHAD), first-principles calculations (DFT), and data-driven machine learning (ML) techniques for accelerated discovery. The discussion then delves into the microstructural engineering of RCCAs, highlighting architected phases such as coherent BCC/B2 nanocomposites that mimic the strengthening mechanisms of superalloys yet extend their operational ceiling. A thorough analysis of mechanical and environmental properties, encompassing strength-ductility synergies, creep, fatigue, and oxidation resistance, is presented, underscoring both remarkable achievements and enduring challenges, particularly in room-temperature ductility and long-term environmental durability. The review further assesses scalable manufacturing pathways, such as additive manufacturing, and identifies critical roadblocks to industrial scalability and adoption. By converging fundamental insights with advanced design and processing strategies, this review aims to chart a course for realizing the full potential of RCCAs as next-generation materials for the most demanding technological applications.

Titanium nanoparticles are severely limited in practical applications in fields such as metal 3D printing due to their extremely high surface activity and strong oxidizing property. In this paper, the surface stability coating mechanism of titanium nanoparticles coated with succinic acid molecules was deeply explored through molecular dynamics simulation based on the ReaxFF reaction force field. The research has clarified that the most stable adsorption configuration of succinic acid is when the carbon chain is perpendicular to the metal surface, and the optimal adsorption distance is 3 & Aring;. Van der Waals interactions play a leading role in the adsorption process. In addition, spherical particle adsorption simulations confirm that succinic acid can form a dense and effective isolation layer on the titanium surface. This study demonstrates that succinic acid is a highly promising surface stabilizer for titanium nanoparticle materials, providing an important theoretical basis for high-performance metal 3D printing.

A large number of droplets and their products produced by titanium fire combustion in aeroengine compressor will cause burn through and non-inclusiveness failure of titanium alloy casing. This has shown great harm. In this study, a quantitative evaluation method for titanium fire inclusiveness of compressor was explored based on the mechanism of titanium alloy melt drop ablation and laser ignition technology. A test and evaluation method was established with the characteristic parameters of the melt drop penetration resistance of two configurations of TC4 titanium alloy casing, namely horizontal expansion and vertical drip. Meanwhile, the diffusion behavior of titanium fire and the critical failure conditions under simulated airflow environment were varified by experiments as well. Those results show that the mechanism of titanium alloy droplet burning through the casing lies in the local high heat concentration formed at the droplet contact interface. Under the action of heat transfer, the kinetic energy of the atoms in the base of the titanium alloy cartridge increases rapidly, forming a penetrating liquid phase, and finally causing burn- through, that is, titanium non-inclusiveness failure. When the droplet moves horizontally in the process of extended combustion, it will be affected by some mechanism such as reverse airflow, which will weaken the expansion effect. When the droplet is adhered to the surface of the casing simulation for a long time under the action of gravity or centrifugal force, the heat released is enough to burn through the titanium alloy casing. Its critical thickness is between 1. 5-2 mm.

With the improvement of thrust-to-weight ratio and other properties of future aero-engine，the high temperature mechanical property and structural stability of titanium alloy components are required. The limitation of traditional experiments in time and space scale has become increasingly prominent，and it is difficult to deeply study the microscopic transient phenomena and mechanisms. Moreover，the molecular dynamics（MD）calculation method takes the atomic/molecular model as the calculation object，on the basis of Newton classical mechanics and empirical parameters，the calculation efficiency is greatly improved compared with the quantum calculation method. Therefore，MD has become an important method to optimize the process parameters and calculate the microstructure properties of aero-engine titanium alloy. Based on an overview of the basic principle of MD computing space and time scale advantages，this paper reviews the relevant domestic and foreign achievements in the study of molding，microstructure characterization and performance testing of aero-engine titanium alloys by MD method in recent years，as well as representative conclusions that contribute to the improvement of high temperature resistance of aero-engine titanium alloys. Finally，the future prospect is discussed based on the demand for MD computing technology for aircraft engine titanium alloys，thus pointing out the challenges faced on the following aspects，including high-throughput composition design based on MD computing method，training molecular force fields for mature titanium alloy systems，and introducing the new ReaxFF（Reactive Force Field）into the study of combustion mechanisms.

The heat transfer and oxygen transport behaviors of Ti-6Al and Fe-12Cr alloys directly affect their aeronautical material application. In order to investigate the flame retardant mechanism in atomic scale, molecular dynamic (MD) simulations were performed to study the heat transfer and oxygen transport performances of Ti-6Al and Fe-12Cr alloys in the linear and uniform heating treatment. Next, the ignition performances of Ti-6Al and Fe-12Cr alloys were further verified by the frictional ignition tests. Therefore, this is a multi-scale research with a novel combination of MD simulations and ignition tests. Those obtained results show that the heat is more concentrated at the heating edge of Ti-6Al alloy while at the same heating rate. This leads to the intensification of atomic motion at the heating edge, and reduces the structural thermal stability of Ti-6Al alloy’s heating edge. Therefore, the heat transfer performance of Fe-12Cr alloy at the same state is better than that of Ti-6Al alloy. When there is an oxide layer on the surface of these two alloys, Fe-12Cr alloy can inhibit the oxygen transfer more effectively than Ti-6Al alloy, and further improve its flame retardant property. In addition, the frictional ignition tests with Ti alloy rotor under the same airflow environment show that the critical airflow velocity of the Fe-12Cr alloy stator is about 114[Formula: see text]m/s higher than that of Ti-6Al-4V alloy stator at 384∘. Generally, according to MD simulations and frictional ignition tests, it could be concluded that the flame retardancy of Fe-12Cr alloy is higher than Ti-6Al alloy.

The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine, and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating. Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field, molecular dynamics (MD) simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys. The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation, and the temperature field of the molten pool is normally distributed from the center to the edge. When the center temperature reaches the critical point of ignition, the extended combustion occurs, and the extended combustion path advances along the direction of the air flow. Compared with Ti6Al alloy, Ti-48Al alloy has higher fire retardancy under laser ablation. This is due to the better heat transfer performance of Ti-48Al, which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field. So it is necessary to increase the partial pressure of oxygen, and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source. In the aspect of extended combustion path, the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow. That is, the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction, resulting in a concentration of heat near the boundary. So the combustion path also tends to expand along this direction.

The non-isothermal oxidation behaviors of TiAl and Ti3Al alloys at 1450-1570 ℃ in a pure oxygen atmosphere were studied by using TGA/DSC simultaneous thermal analysis, SEM and EPMA characterizations and theoretical calculation. The results show that a continuous dense Al2O3 barrier layer is formed on the melt surface of TiAl alloy, when the oxidation temperature is higher than the melting point of TiAl alloy. The Gibbs free energy of Al reacting with O in the melt is 50-150 kJ∙mol-1 lower than that of Ti, Cr and Nb. The diffusion coefficient(D) of Al atom in the melt of TiAl alloy is about 1.7 times that of Ti atom. The Al atoms continue to diffuse to the melt surface and preferentially react with O to form a continuous and dense Al2O3 layer. The Al2O3 barrier layer effectively hinders the diffusion of oxygen and metal ions inside and outside the matrix. TiAl alloy melts and absorbs heat to reduce the matrix temperature and slows down the oxidation rate, resulting in the non-isothermal oxidation resistance of TiAl alloy is better than that of Ti3Al alloy in range of 1450-1570 ℃.

In this research, molecular dynamic (MD) simulations computation is applied to generally study the coating behavior of palmitic acid molecules and aluminum (Al) nanoparticle (ANP) surface through single and multi-molecule models. Changes and comparisons of adsorption distance, energy, effectiveness and stability are generally discussed in this study. Those obtained results indicate that the adsorption configuration of palmitic acid and Al has shown the adsorption polarity clearly. For carboxyl terminal of palmitic acid and Al surface, when their critical adsorption angle is around 60∘, its distance is within 9 Å. Besides, the decisive atomic group of palmitic acid molecule is carboxyl, whose oxygen atom with double bond can adsorb the Al atom stably. This adsorption effect and formation is close to the covalent bond. During the adsorption process, van der Waals force acts on the long-distance attraction, and the Coulomb force acts more critically as the short-range adsorption force. Finally, the gas coating has proper advantages over the liquid coating, as the erosion of Al surface is much lower when it is surrounded by gas-phased palmitic acid.

For the issues of high temperature performance affected by the alloying elements content in Ti-V-Cr and Ti-V-Cr alloys, the thermodynamic calculation method based on JMatPro program was applied in this study. The research is mainly focused on the analysis of phase composition, thermodynamic parameters and mechanical properties of Ti-Al-V and Ti-V-Cr series alloys with different element proportions under high temperature environment. Those obtained results show that the proportion of Al in Ti-Al-V alloys has a great influence on the high temperature properties. Increasing the content of Al not only increases the transformation temperature of β single-phase structure and delays the transformation process of α/β microstructure to β single-phase structure, but also helps to improve the high temperature thermal conductivity and elastic deformation resistance of the alloy. In Ti-V-Cr alloys, the influence of V element on high temperature properties is mainly focused on the improvement of thermal conductivity and high temperature deformation properties, while the influence of Cr element is relatively weak. Besides, adding a small amount of Al element to Ti-V-Cr alloy can further improve the thermal conductivity of the alloy. The Young’s modulus of the Ti-V-Cr alloy increases when 0.3%-1% of C element is added. Finally, the effect of Si element on the high temperature elastic deformation of the alloy is relatively weak.

Aluminum nanoparticle (ANP) in liquid Cellulose dinitrate decamer sol was investigated by ReaxFF molecular dynamics simulations. The mechanism of nitrocellulose (NC) single chain adsorption was researched as a chemisorption process. New Al–O bonds are formed by dehydrogenation and denitrification of the nitrate ester groups. The adsorbed part of the NC chain drags other parts to the surface as a horizontal adsorption state. We also simulated the processes of liquid Cellulose dinitrate decamer sol (ethanol, diethyl ether, and NC three components) coating the ANPs at different temperatures. The results indicate that the organic coating near surface is mainly consisted of ethanol and diethyl ether molecules. The NC chains are adsorbed on the ANPs surface in two states, including the horizontal adsorption or the nearly vertical adsorption. Heating can increase the coating rate without significantly changing the composition of the coating. Finally, the oxidation simulation shows that the organic layer can maintain good stability and oxidation resistance.

The present problem aims to study the scattering behavior of SH-waves by a circular cavity near two symmetrically permeable interface cracks in the piezoelectric bi-material half-space. The steady-state response of the problem is obtained, with the aid of the Green’s function method and the complex function method. Above all, the essential expression of Green’s function is constructed by the mirror method. This expression satisfies the conditions of being stress-free and electric insulation on the horizontal boundary of the orthogonal space where the circular cavity is located, and the condition of bearing a harmonic out-plane line source force on the vertical boundary. Next, on the basis of dividing the bi-material medium into two parts along the vertical boundary, the first kind of Fredholm integral equation with uncertain anti-plane forces is established by using the conjunction method and the crack-division technology. Then, the solution is obtained by solving an algebraic equation with finite terms, which is an effective truncation of the integral equation. Finally, the dynamic stress concentration factor around the edge of the circular cavity and the dynamic stress intensity factor at the crack tip are calculated numerically. On this basis, the effects of incident wave frequency, crack length, crack location and circular cavity position on the dynamic stress concentration factor and dynamic stress intensity factor are discussed.

Aluminum (Al) nanoparticle (ANP), as a metal fuel agent, has excellent combustion rate and energy density. However, several critical research gaps of ANP still exist. This study is focused on the annealing properties of ANP and its coating performances under the mixture of ethanol and ether molecules. According to those obtained molecular dynamic (MD) simulation results, the microstructure of ANP in the annealing process and the formation of ethanol–ether binary coating are discussed in this paper. During the melting process, the melting point of ANP could be analyzed by the inflection point of its atomic potential energy and the mean square displacement, then the accuracy of EAM force field could be verified. Because surface atoms have lower potential energy than inner atoms, it seems that the melting of ANP started from the particle surface and diffuses from surface to the core. When the melted Al cluster is solidified until 300 K, the microstructure of the crystallized particle is largely affected by the cooling rate. If the cooling rate if too fast, it is not enough for the Al cluster to recrystallize, which is called as the “freezing effect” for ANP. Next, the binary “competitive adsorption” behavior of ethanol and ether on the surface of ANP was simulated according to different ethanol–ether molecular ratios. Analyses of ethanol–ether binary coating layer show that the main component of binary coating is ethanol, but not ether. This competitive superiority of ethanol is caused by its own adsorption mechanism and molecular migration in this mixture of ethanol and ether.

Sintering is one of the key factors limiting the application of aluminum nano particles (ANPs) as additives in solid propellant. Because of its high specific surface area and the surface is covered by atoms with low coordination number, ANPs are prone to aggregate or sinter even during the production process which blocks the energy release of ANP during combustion. We perform reactive molecular dynamics simulations to study sintering behaviors for bare and ethanol coated ANPs. Several parameters including shrinkage ratio, gyration radius and moment of inertia are responsible for judging the progress of particle sintering process. A three-stage sintering process has been observed. ANPs follow different sintering laws below and above their melting temperatures. At the same temperature, the smaller the ANP size, the faster the sintering process ends. Before melting, the effect of raising temperature on the sintering degree is not obvious. The coated ANPs show an excellent anti-sinter behavior even when temperature is above their melting point. Different heating rates (1012 K/s–1014K/s) are used to simulate different ignition environments and results show a slow heating rate can make ANPs enter sintering process earlier. For the organic coating layer, carbon and oxygen atoms hinder the formation of the neck region which is an important step in the sintering process. Hydrogen atoms tend to diffuse into the interior of ANPs rather than stay on the surface.

Studies on nitrocellulose (NC) mixtures with little solubilities were neglected in many cases previously. This investigation was performed to provide supplemental characterizations of NC and its soaked state with pure liquid ethanol or diethyl ether by simulations and practical methods. Above all, a short-chained NC model (polymerisation degree: 8) and a dried NC specimen were characterized for their substitution of nitrate and microstructure. It was confirmed that both the numerical model and practical specimen belonged to low-nitrated NC. The bonding information of a glycosyl unit and nitrate ester were summarized via first-principle calculations. Then, ReaxFF potential based Molecular Dynamic (MD) simulations and soaking tests on binary organic mixtures demonstrated that both ethanol and diethyl ether had limited solubility for our specified NC. However, potential energies and diffusion coefficients of both computational models showed that the interactions from ethanol molecules were relatively stronger than diethyl ether molecules. The viscosities of saturated NC solutions also proved this consequence, as the difference between pure ether and its filtered NC solution was only 0.02 mm 2 s −1 . Finally, the strong volatility of diethyl ether itself could keep the wetness of NC upper surface shortly, because this was an upward volatilization effect. Due to this effect, the penetration of NC-diethyl ether mixture was higher in the early period of penetration tests.