Application of phase diagram calculations to development of new ultra-high temperature structural materials

ln-situ refractory metal intermetallic composites（RMICs） based either on （Nb, Si） or （Mo, Si, B） are candidate materials for ultra-high temperature applications （〉1 400℃）. To provide a balance of mechanical and environmental properties, Nb-Si composites are typically alloyed with Ti and Cr, and Mo-Si-B composites are alloyed with Ti. Phase diagrams of Nb-Cr-Ti-Si and Mo-Si-B-Ti, as prerequisite knowledge for advanced materials design and processing development, are critically needed. The phase diagrams in the metal-rich regions of multicomponent Nb-Cr-Ti-Si and Mo-Si-B-Ti were rapidly established using the Calphad （Calculation of phase diagram） approach coupled with key experiments. The calculated isotherms, isopleths, and solidification paths were ：validated by experimental work. The important heterogeneous multiphase equilibria in both quaternary systems identified will offer engineers the opportunity to develop materials with a balance of properties for high-temperature applications.     

Stir casting process for manufacture of Al-SiC composites

Stir casting is an economical process for the fabrication of aluminum matrix composites.There are many parameters in this process,which affect the final microstructure and mechanical properties of the composites.In this study,micron-sized SiC particles were used as reinforcement to fabricate Al-3 wt% SiC composites at two casting temperatures(680 and 850 ℃) and stirring periods(2 and 6 min).Factors of reaction at matrix/ceramic interface,porosity,ceramic incorporation,and agglomeration of the particles were evaluated by scanning electron microscope(SEM) and high-resolution transition electron microscope(HRTEM) studies.From microstructural characterizations,it is concluded that the shorter stirring period is required for ceramic incorporation to achieve metal/ceramic bonding at the interface.The higher stirring temperature(850 ℃) also leads to improved ceramic incorporation.In some cases,shrinkage porosity and intensive formation of Al_4C_3 at the metal/ceramic interface are also observed.Finally,the mechanical properties of the composites were evaluated,and their relation with the corresponding microstructure and processing parameters of the composites was discussed.     

TiB2基陶瓷/42CrMo合金钢梯度纳米结构复合材料多尺度界面生成与组织演化

By taking 42CrMo alloy steel as the metal substrate and using (Ti-B4C) as the reactive system, the laminated composites of TiB2-based ceramic and 42CrMo alloy steel with the nano-structured gradient were achieved by centrifugal reactive casting processing. Based on XRD, FESEM, and HRTEM, it was considered that because of thermal explosion induced by centrifugal reactive casting processing, fusion-induced interdiffusion was initiated between the full-liquid ceramic and alloy steel, resulting in the formation of the intermediate liquid between the liquid ceramic and the steel substrate. Subsequently, the strong Stokes flow under high centrifugal force promoted the ceramic nuclei to collided with the others, thereby accelerating the coarsened ceramic particles to float up, meanwhile, the alloy-enriched liquid also flowed and converged toward the steel substrate. Finally, in the interlaminar region of the composite there developed nano-structured graded microstructure that the spatial size of ceramic/alloy phase boundary was continuously graded from the ceramic to the steel.     

Process Design for Hybrid Sheet Metal Components

The global trends towards improving fuel efficiency and reducing CO_2 emissions are the key drivers for lightweight solutions. In sheet metal processing, this can be achieved by the use of materials with a supreme strength-toweight and stiffness-to-weight ratio. Besides monolithic materials such as high-strength or light metals, in particular metal–plastic composite sheets are able to provide outstanding mechanical properties. Thus, the adaption of conventional, wellestablished forming methods for the processing of hybrid sheet metals is a current challenge for the sheet metal working industry. In this work, the planning phase for a conventional sheet metal forming process is studied aiming at the forming of metal–plastic composite sheets. The single process steps like material characterization, FE analysis, tool design and development of robust process parameters are studied in detail and adapted to the specific properties of metal–plastic composites. In material characterization, the model of the hybrid laminate needs to represent not only the mechanical properties of the individual combined materials, but also needs to reflect the behaviour of the interface zone between them.Based on experience, there is a strong dependency on temperature as well as strain rate. While monolithic materials show a moderate anisotropic behaviour, loads on laminates in different directions generate different strain states and completely different failure modes. During the FE analysis, thermo-mechanic and thermo-dynamic effects influence the temperature distribution within tool and work pieces and subsequently the forming behaviour. During try out and production phase,those additional influencing factors are limiting the process window even more and therefore need to be considered for the design of a robust forming process. A roadmap for sheet metal forming adjusted to metal–plastic composites is presented in this paper.     

Electrochemical and Reaction Bonding Processing of Thick ZrO_2/Al_2O_3 Composite Coatings

CERAMIC coatings are currently of much interest forapplications in high-temperature and highly corrosiveenvironments.Formation of ceramic coatings byelectrochemical processing is a relatively newtechnique.'1'It presents several advantages overalternative coating techniques.'2'Recently wedeveloped a novel fabrication technique for theproduction of ceramic/ceramic and metal/ceramiccomposite coatings by electrochemical processing.'31The technique combined two electrochemicaldeposition methods,…     

Characterizations on Mechanical Properties and In Vitro Bioactivity of Biomedical Ti–Nb–Zr–CPP Composites Fabricated by Spark Plasma Sintering

To alleviate the bio-inert of Ti alloys as hard tissue implants, Ti–35Nb–7Zr–xCPP(calcium pyrophosphate,x = 5, 10, 15, 20 wt%) composites were prepared by mechanical alloying(MA) and following spark plasma sintering(SPS). Mechanical behaviours and in vitro bioactivity of these composites were investigated systematically. Results showed that the composites consisted of β-Ti matrix, α-Ti, and metal–ceramic phases such as CaO, CaTiO_3, CaZrO_3, and Ti_xP_y. With increasing CPP content, the composites had higher strength(over 1500 MPa) and higher elastic modulus, but suffered almost zero plastic deformation together with lower relative density. When the CPP contents were 5 and 10 wt%,the compressive elastic moduli were 44 and 48 GPa, respectively, which were close to those of natural bones. However, the compressive elastic modulus of the composites increased significantly when CPP contents exceed 10 wt%, thus deteriorating the mechanical compatibility of the composites owing to more α-Ti and metal–ceramic phases. Besides, the surface of Ti–35Nb–7Zr–10CPP composite was deposited as a homogeneous apatite layer during soaking in simulated body fluid(SBF). It indicates a good bioactivity between the implant materials and living bones.     

INTERFACE MORPHOLOGIES AND SOLUTE SEGREGATION OF Al-Li ALLOY 8090 DURING UNIDIRECTIONAL SOLIDIFICATION

The solid-liquid interface morphology and solute segregation behaviour of AI-Li alloy 8090during unidirectional solidification were studied by the liquid metal quenehing method undervaried processing conditions.When solidification rate,RO.75 mm/min (temper-ature gradient,G_L=130℃/cm),the structure revealed of planar or dendritic interfacerespectively.With the increase of R,the interface morphology becomes cellular from planargradually,within a narrow range.And the greater the R,the,finer the dendrite.Segregationof element Cu and impurity elements Fe and Si are quite severe,the interface morphologymarkedly influences on solute segregation.During solidification at coarse dendrite interface,their segregation ratios are rather great and solidified structure is coarse.     

Recent progress in thermal/environmental barrier coatings and their corrosion resistance

Thermal/environmental barrier coatings(T/EBCs)play important roles in jet and/or gas turbine engines to protect the Ni-based superalloys and/or ceramic matrix composite substrates from the high-temperature airflow damage.Great efforts have been contributed to searching for enhanced T/EBC materials to improve the efficiency of the engines,which is the key of improving thrust-to-weight ratio and energy saving.The practical candidates,rare earth-contained materials,are widely used for T/EBCs in gas turbines due to their excellent properties such as low thermal conductivity,high melting point,hightemperature strength and durability as exhibited in yttriastabilized zirconia,pyrochlore oxides and rare earth silicates.In addition to the intrinsic properties,the microstructures obtained by different synthesis processes and the service performances,as well as the underlying failure mechanism,are also significant to this specific application.However,the main challenges for T/EBCs developments are T/EBC materials selection with balanced properties and their anti-corrosion performances at higher operating temperature.In this review,we summarized the progress in their fabrication techniques and mechanical/thermal properties of typically rare earth-contained T/EBCs,together with their anti-corrosion performance under the condition of molten salts or oxides(such as Na_2SO_4,V_2O_5and NaVO_3),calcium–magnesium–alumina–silicate(CMAS)and high-temperature water vapor.     

Development of Si_3N_4/Al composite by pressureless melt infiltration

1 Introduction Composites of ceramic/metal or metal/ceramic are expected to have properties superior to their constituents alone[1?4]. However, the fundamental difference in atomic bonding between metals and ceramics results in quite different physical a…     

Carbon Materials Reinforced Aluminum Composites:A Review

Carbon materials, including carbon fibers, graphite, diamond, carbon foams, carbon nanotubes, and graphene, are attractive reinforcements for aluminum matrix composites due to their excellent mechanical and/or physical properties as well as light weight. Carbon materials reinforced aluminum （C/Al） composites are promising materials in many areas such as aerospace, thermal management, and automobile. However, there are still some challenging problems that need to be resolved, such as interfacial reactions, low wettability, and anisotropic properties. These problems have limited the use of these composites. This review mainly focuses on the categories, fabrication processes, existing problems and solutions, coatings and interfaces, challenges and opportunities of C/Al composites so as to provide a useful reference for future research.     

Effect of Cr Content on the Compression Properties and Abrasive Wear Behavior of the High-Volume Fraction(TiC–TiB_2)/Cu Composites

The(TiC–TiB2)/Cu composites with 50 vol% Ti C–Ti B2 ceramic particles were successfully fabricated by the combustion synthesis and hot press consolidation in a Cu–Ti–B4C–Cr system. The effects of the Cr content on the microstructures, hardness, compression properties, and abrasive wear behaviors of the composites were investigated. The final products consist of only Cu, Ti C, and Ti B2 phases, and the ceramic particles are distributed uniformly in these composites. The size of the ceramic particles decreases with Cr addition. As the Cr content increases, the yield strength,ultimate compression strength, microhardness, and abrasive wear resistance of the composites increase, and the fracture strain decreases.     

Recent progress in carbon/lithium metal composite anode for safe lithium metal batteries

Owing to their very high theoretical capacity,lithium(Li) metal anodes regain widespread attentions for their promising applications for next-generation highenergy-density Li batteries(e.g., lithium–sulfur batteries,lithium–oxygen batteries, solid-state lithium metal batteries). However, the inherent bottleneck of Li metal anodes,especially the growth of Li dendrites and the related safety concerns, should be well addressed. Owing to their featured micro-/nano-porous structures and intriguing physical properties, nanocarbon materials have been applied as host materials for Li metal anodes. This review summarizes the recent progress in the development of porous nanocarbon materials for safe Li metal anodes. The perspectives regarding the challenges and future development of employing micro-/nano-porous carbon materials in Li metal anodes are also included.     

Plasma spray-physical vapor deposition toward advanced thermal barrier coatings:a review

Plasma spray–physical vapor deposition(PS–PVD) is a unique technology that enables highly tailorable functional films and coatings with various rare metal elements to be processed. This technology bridges the gap between conventional thermal spray and vapor deposition and provides a variety of coating microstructures composed of vapor, liquid, and solid deposition units. The PS–PVD technique serves a broad range of applications in the fields of thermal barrier coatings(TBCs), environmental barrier coatings(EBCs), oxygen permeable films, and electrode films. It also represents the development direction of high-performance TBC/EBC preparation technologies.With the PS–PVD technique, the composition of the deposition unit determines the microstructure of the coating and its performance. When coating materials are injected into a nozzle and transported into the plasma jet,the deposition unit generated by a coating material is affected by the plasma jet characteristics. However, there is no direct in situ measurement method of material transfer and deposition processes in the PS–PVD plasma jet,because of the extreme conditions of PS–PVD such as a low operating pressure of * 100 Pa, temperatures of thousands of degrees, and a thin and high-velocity jet.Despite the difficulties, the transport and transformation behaviors of the deposition units were also researched by optical emission spectroscopy, observation of the coating microstructure and other methods. This paper reviews the progress of PS–PVD technologies considering the preparation of advanced thermal barrier coatings from the perspective of the transport and transformation behaviors of the deposition units. The development prospects of new high-performance TBCs using the PS–PVD technique are also discussed.     

Simulation of microstructure evolution in fused-coating additive manufacturing based on phase field approach

The mechanical properties of metal components are determined by the solidification behavior and microstructure. A quantitative phase field model is used to investigate the microstructure evolution of fused-coating additive manufacturing, by which to improve the quality of deposition. During the fused-coating process, the molten metal in a crucible flows out of a nozzle and then reaches the substrate. The solidification happens at the moment when the molten metal comes into contact with substrate moving in three-dimensional space. The macroscopic heat transfer model of fused-coating is established to get the temperature field considered as the initial temperature boundary conditions in the phase field model. The numerical and experimental results show that the morphology of grains varies with different solidification environments. Columnar grains are observed during the early period at the bottom of fused-coating layer and the equiaxed grains appear subsequently ahead of the columnar grains. Columnar dendrites phase field simulations about the grains morphology and solute distribution are conducted considering the solidification environments. The simulation results are in good agreement with experimental results.     

Manufacture of Nano-Sized Particle-Reinforced Metal Matrix Composites:A Review

Compared to the micro-sized particle-reinforced metal matrix composites, the nano-sized particle-reinforced metal matrix composites possess superior strength, ductility, and wear resistance, and they also exhibit good elevated temperature properties. Therefore, the nano-sized particle-reinforced metal matrix composites are the new potential material which could be applied in many industry fields. At present, the nano-sized particle-reinforced metal matrix composites could be manufactured by many methods. Different kinds of metals, predominantly A1, Mg, and Cu, have been employed for the production of composites reinforced by nano-sized ceramic particles such as carbides, nitrides, and oxides. The main drawbacks of these synthesis methods are the agglomeration of the nano-sized particles and the poor interface between the particles and the metal matrix. This work is aimed at reviewing the ex situ and in situ manufacturing techniques. Moreover, the distinction between the two methods is discussed in some detail. It was agreed that the in situ manufacturing technique is a promising method to fabricate the nano-sized particle-reinforced metal matrix composites.     

RESEARCH AND DEVELOPMENT OF HIGH TEMPERATURE STRUCTURAL MATERIALS FOR AERO-ENGINE APPLICATIONS

The status of research, development of superalloys and materials processing ＆ fabrication technologies for aero-engine applications in China Aviation Industry, with an emphasis on recent achievements at BIAM including directionally solidified and single crystal superalloys for blade and vane applications, wrought superqlloys for aero-engine disks and rings, and powder metalurgy （PM） superalloys for high performance disk applications were described. It was also reviewed the development of new class of high temperature structural materials, such as structural intermetallics, and advanced material processing technologies including rapid solidification, spray forming and so on. The trends of research and development of the above mentioned superalloys and processing technologies are outlined. Cast, wrought and PM superalloys are the workhorse materials for the hot section of current aero-engines. New high temperature materials and advanced processing technologies have been and will be the subject of study. It is speculated that high performance, high purity and low cost superalloys and technologies will play key roles in aero-engines.     

Fabrication of cast carbon steel with ultrafine TiC particles

The carbon steels dispersed with ultrafine TiC particles were fabricated by conventional casting method. The casting process is more economical than other available routes for metal matrix composite production, and the large sized components to be fabricated in short processing time. However, it is extremely difficult to obtain uniform dispersion of ultrafine ceramic particles in liquid metals due to the poor wettability and the specific gravity difference between the ceramic particle and metal matrix. In order to solve these problems, the mechanical milling (MM) and surface-active processes were introduced. As a result, Cu coated ultrafine TiC powders made by MM process using high energy ball milling machine were mixed with Sn powders as a surfactant to get better wettability by lowering the surface tension of carbon steel melt. The microstructural investigations by OM show that ultrafine TiC particles are distributed uniformly in carbon steel matrix. The grain sizes of the cast matrix with ultrafine TiC particles are much smaller than those without ultrafine TiC particles. This is probably due to the fact that TiC particles act as nucleation sites during solidification. The wear resistance of cast carbon steel composites added with MMed TiC/Cu-Sn powders is improved due to grain size refinement.     

Effect of Surface Layer Structural-Phase Modification on Tribological and Strength Properties of a TiC–(Ni–Cr) Metal Ceramic Alloy

This paper reports TiC–(Ni–Cr) metal ceramic alloy(ratio of components 50:50) with nanoscaled components formed in the surface layer and smoothly transformed into the initial inner structure throughout the material under pulsed electron irradiation of the alloy surface. Principal changes in the surface layer are ascribed to the formation of gradient structure leading to the increase in wear resistance of the surface layer, drop of friction coefficient and improvement of specimen bending resistance when stressing on the irradiated surface side. The above changes of tribological and strength properties in the surface layer under pulsed electron irradiation become more apparent with increasing atomic mass of a plasma-forming inert gas.     

Manufacturing of Long Products Made of Innovative Lightweight Materials

The processing of innovative lightweight materials to sheet metal components and assemblies with globally or locally defined properties is the object of this work. It takes a load-dependent design of components and assemblies, for example, based on the composition of different construction materials or a targeted setting of component areas with specified characteristics to fully exploit the lightweight potential when substituting conventionally used materials. Different process chains for the manufacturing of roll-formed long products made of magnesium alloys and high-strength steels with locally defined properties will be presented in this paper. Depending on the kind of material to be formed and the desired product characteristics, different temperature managements are needed for capable processes. Due to limited formability at room temperature, magnesium alloys require a heating of the forming zones above 200–225 °C throughout the bending process in order to activate additional gliding planes and to avoid any failures in the radii. The realization of local hardening effects requires at least one process-integrated heat treatment when roll forming manganese–boron steels. For both processes, it is imperative to realize a heating and cooling down or quenching appropriate for the manufacturing of long products with the required quality. Additionally, proper line speeds that allow a continuously operated economical production have to be considered. Research results including design, FEA, realization and experimentation of the mentioned process chains and strategies will be described in detail.