Tungsten-based alloys are the second largest category of tungsten-based products after cemented carbide, and their unique physical and mechanical properties make them useful in the defense industry and various areas of the national economy, but as future manufacturing industries require increasingly precise parts and more complex component designs, these requirements are difficult to achieve using traditional powder metallurgy method. Additive manufacturing（AM） offers unique geometric design freedom and rapid prototyping capabilities. This paper introduces the research progress of additive manufacturing tungsten-based alloys at home and abroad, and analyzes and outlooks the main problems and research trends facing the research.
The microstructure of cast duplex heat-resistant steel for pellet production was observed and its high-temperature oxidation characteristics at 900℃were studied by weight gain method.The morphology,element distribution and phase composition of the oxide film were characterized and analyzed by optical microscope,scanning electron microscope,energy spectrum analysis and X-ray diffraction.The results showed that the oxidation kinetics curve of the heat-resistant cast steel at 900℃followed the parabolic law,and the high-temperature oxidation resistance was excellent.The oxide film had an obvious double-layer structure.The inner layer was composed of protective flake Cr2O3,and the outer layer was composed of MnCr2O4 and FeCr2O4 spinel oxides.Local internal oxidation occurred.And there was a nickel rich layer and dispersed SiO2 particles in the internal oxidation region.The high temperature oxidation behavior of the heat-resistant cast steel at 900℃could be divided into three stages:the initial formation stage of oxide film,the rapid growth stage of Cr2O3oxide layer,and the rapid growth stage of MnCr2O4 and FeCr2O4 spinel oxide layer.
Scanning electron microscopy（SEM）, X-ray diffraction analyzer（XRD） and electron backscattering diffraction（EBSD） were used to investigate the effect of the original as-cast structure on the formation of reverse austenite during tempering of Cr13Ni4Mo martensitic stainless steel. The stepped castings with the thickness of 40 mm, 60mm and 80 mm were poured to obtain the original equiaxed crystal structure with different solidification rates. After normalizing and twice tempering treatment, the reverse austenite content in the structure increased with the decrease of the casting thickness, and the tensile strength and elongation of Cr13Ni4Mo steel increased. By the method of directional solidification, the original columnar crystal was obtained by changing the pull-down velocity to 1 μm/s, 5 μm/s and 50 μm/s. The results showed that with the increase of pull-down velocity, the columnar crystal was refined, the reverse austenite content increased, and the tensile strength and strong plastic deposition of Cr13Ni4Mo steel increased. The improvement of mechanical properties of Cr13Ni4Mo steel was due to the double effect of fine grain strengthening and reverse austenite TRIP effect.
By applying active screen plasma nitriding（ASPN） treatment, the use of nodular cast iron was expanded, and it can be expected to be used under special load conditions. In this study, we evaluated the effect of ASPN treatment on the mechanical properties of spheroidal graphite cast iron. With ASPN treatment, a nitride layer was formed on the sample surface and a diffusion layer was formed further inside the nitride layer. During the ASPN processing,the thickness of nitride layer increased as the treatment temperature increased. The hardness, wear resistance and fatigue strength of nodular cast iron will increase with the increase of treatment temperature.
The wear resistance of hypereutectic high chromium cast iron was improved by metal mold casting before and after Ce modification.By means of OM,SEM,XRD,hardness tester and wear testing machine,the microstructure and properties of hypereutectic high chromium cast iron before and after Ce modification were studied.The results show that the microstructure of hypereutectic high chromium cast iron before and after modification is composed of primary M7C3+eutectic M7C3+austenite+martensite.Compared with the pre-modification M7C3,the morphology of the primary M7C3 transformed from a long hexagon to a rounded hexagon,the size decreased by 44.9%,and the volume fraction increased by 30.2%.The Rockwell hardness,impact toughness and bending strength of cast iron are increased by 5.0%,43.4%and 39.2%respectively,and the weight loss is reduced by 50.7%.The compound Ce2O2S of Ce is moderately effective as the heterogeneous nucleation core of M7C3,and Ce can spherodize and purify the inclusions.The refined primary carbides protect each other with the matrix,which improves the surface wear resistance of cast iron.The wear mechanism of the cast iron is changed from micro-cutting mainly and fracture shedding as auxiliary.
The grinding balls used in coal mills have the problems of excessive wear and low coal breaking efficiency. The wear status of ZQCr5 grinding balls was characterized by scanning electron microscopy, X-ray diffraction, laser confocal microscopy, and other instruments. The ball diameter ratio was adjusted by EDEM software. The optimal scheme was determined by a quantitative comparison of three indicators: the failure rate of the coal block bond,the crushing force, and the energy borne by the lining plate. The results showed that low hardness and toughness were the reasons for the high wear of the grinding balls. It is suggested to increase Cr content and control residual austenite content to improve wear resistance. In the process of crushing bituminous coal, the tangential grinding was the main way of crushing bituminous coal, and the surface grinding wear was the main failure mode of the grinding ball. While changing the grinding ball gradation relationship to: Φ60 mm∶Φ30 mm∶Φ20 mm=16 ∶3 ∶1,the grinding ball consumption was reduced by 35%, the crushing efficiency was increased by 9%, and the loss of the liner was greatly reduced. The work could provide the reference for improving coal grinding efficiency and reducing grinding ball loss.
A certain type of gray cast iron cylinder produced by our company use the low sulfur nitrogen recarburizer for molten iron smelting, and the scrap rate of castings is high, mainly including blowholes and depression. The high sulfur nitrogen recarburizer and low sulfur nitrogen recarburizer are added to the molten iron in a certain proportion,while increasing the carbon content of the molten iron, the tensile strength of the casting did not decrease, the blowhole and depression rejection rate decreased significantly, and the rejection rate of the casting decreased significantly. The main reason is that the nitrogen content in the high sulfur nitrogen recarburizer is high, the addition of high sulfur nitrogen recarburizer increases the nitrogen content of liquid iron, nitrogen can make the length of graphite sheet shorter, the bending degree increased, the end is inactive, and can refine pearlite, strengthen the matrix structure, improve the mechanical properties of the casting, which is greatly beneficial to improving the quality of the cylinder casting, stabilizing the casting material, and reducing the production cost.
The effect of solution treatment on the microstructure and mechanical properties of Mg-2Nd-1Gd-0.5Zn-0.5Zr magnesium alloy was studied using optical microscopy,scanning electron microscopy,transmission electron microscopy,and room temperature tensile machines.The results showed that the microstructure of the as-cast alloyswas mainly composed of α-Mg matrix and eutectic microstructure at grain boundaries.During solution treatment,the eutectic β phaseswith high Zn contentwere disappear,whilethe second phases with low content of Zn were observed,it was completely disappeared after solution treatment at 540℃for 20 h.Therefore,the optimal solution treatment system was 540℃×20 h.After solution and subsequent aging treatment,anew fine precipitateswere observed within the α-Mg matrix,and its habit plane was {1120}MG crystal face,which helped to achieve more better strengthening effect.The optimum mechanical properties of the alloy could be gained after heat treatment at 540℃×20 h+200℃×18 h,the average tensile strength,yield strength,and elongation after fracture were 274.58 MPa,155.94 MPa,and 4.94%.
In order to further explore the influence of Cu content on the precipitated phase and properties of Al-Mg-SiCu-La alloy,thermodynamic simulation of Al-Mg-Si-Cu-La alloy was carried out by using material phase diagram and property simulation software JMatPro,and the contents of equilibrium phase and metastable phase were obtained under different Cu addition levels.The results showed that with the increase of Cu content,the content of enhanced β（Mg2Si） phase and Q（Al5Cu2Mg8Si6） phase had no change at room temperature,the content of θ （Al2Cu） phase increased gradually,the content of metastable β'（Mg9Si5） phase decreased gradually,and the content of θ'（Al2Cu） phase and GP zone increased gradually.Q'(Al3.8Mg8.6Si7Cu)phase content increased first and then decreased.The mechanical property model of the alloy showed that increasing the Cu content would improve the mechanical properties of the alloy.When the Cu content was4wt.%,the tensile strength （Rm） and hardness （HV） of the alloy reached the maximum,but when the Cu content was 5wt.%,the tensile strength and hardness of the alloy began to decrease.
Through in-situ tensile test of aluminum alloy under scanning electron microscope, the damage mechanism of A356-T6 aluminum alloy at strain stage was obtained. Through quantitative analysis of microstructure and insitu study of damage mechanism, the distribution law of Si particles and eutectic was described, and finally used to control ductility. The in-situ test showed that, with the increase of strain, the damage accompanied by brittle fracture of Si particles was formed due to the cleavage of eggs, and the adjacent microcracks were generated. At the same time, the addition of Si microcracks caused the nucleation of microcracks on the dendrite boundary. Finally, the crack grewalong the dendrite boundary until instability occurs. The research showed that the quantitative data about the damage mechanism could be obtained through the in-situ mechanical test, which was very useful for predicting the engineering characteristics of cast alloys.
The effect of hot isostatic pressing（HIP） on the microstructure and properties of ZL116 alloy casting was studied by comparing the tensile properties and structural defects of the alloys before and after HIP. The results showed that the HIP could significantly improve the mechanical properties of the castings（tensile strength increased by 15%,elongation increased by 100%, hardness increased by 16%）. After HIP, shrinkage, porosity and other defects in the castings could be effectively repaired.
In order to improve the corrosion resistance of aluminum alloy for sports equipment, the（La+Yb）/ZL105 alloy was prepared by solution treatment. The effects of solution temperature on the microstructure and corrosion resistance of the（La+Yb）/ZL105 alloy were studied and analyzed by OM, SEM, EDS, corrosion weight loss and electrochemical testing techniques. The results show that the solution treatment and the addition of mixed rare earth La+Yb can improve the microstructure of the alloy, and the rare earth phase presents discontinuous acicular shape.When the solution temperature was 520 ℃, the microstructure of the（La+Yb）/ZL105 alloy was refined more obviously,and the Si phase was granular, the Fe-rich phase was small or granular, the corrosion loss rate was the smallest,the corrosion potential was the largest, and the corrosion current density was the smallest. When the solution temperature was too high, the microstructure of the alloy was coarsened, overburning occurs, micro-cracks appear,and the corrosion resistance of the alloy was reduced. The mechanism of improving the corrosion resistance of the solution treated（La+Yb）/ZL105 alloy was the effect of fine grain strengthening.
In this paper, the inclusion detection and analysis of 1060 industrial pure aluminum rods in a factory were carried out in terms of the purity of aluminum melt. The samples were made by mechanical polishing and electrolytic polishing, and various types of inclusions such as Al2O3, iron-containing intermetallic compounds,chlorine salts and fluorides were observed by SEM/EDS. The inclusion distribution, total quantity and average diameter of inclusion in qualified and unqualified aluminum rods were statistically analyzed. The most abundant inclusions were Al2O3 inclusions, which were in the range of 0-20 μm. The total number of inclusions in the unqualified rod was nearly twice that of the qualified rod. A large number of inclusions easily accumulate on the wall of the continuous shunt extrusion mold, resulting in surface abrasion of the processed aluminum tubes, which was the main reason for the failure of the unqualified pipe fitting.
In this paper, the invention patents of Ti2AlNb alloy were retrieved, counted statistically, classified and analyzed from multi-aspects. It could be found that since the alloy was discovered, the related material optimization, processing technics and application research have been continuously carried out. As the potential application value of the Ti2AlNb alloy has been explored, the number of relevant patent applications increased rapidly. So far, the Ti2AlNb alloy has progressed to the second generation, the alloy composition design is more close to the actual engineering application, and the preparation process research objective is also developed from materials to structural parts. With the improvement of technology readiness levels, the scope of application research expands. Due to the high technological threshold in this research field, the global innovation bodies are concentrated in a few countries such as China, the U.S., France and Japan. In China,universities and research institutes are the main innovation bodies of the Ti2AlNb alloy.
Aiming at the iterative efficiency in the casting process design stage, an agile digital gating system design method was proposed. Using database development technology, the data and experience in the process design process were converted, constructed and stored in digital form to form digital assets, which were organically integrated into process structure analysis and gating system design practice. The rapid design mode integrating contextual design, parametric design, intelligent recommendation and real-time verification were investigated,and an agile digital design framework with unified processes, methods, tools, and information was formed to improve gating system design efficiency, which accelerated the digital transformation capabilities of foundry enterprises in R＆D. The design ideas and systematic practice methods of this paper can be effectively guided and extended to other casting process designs, providing guidance for the realization of a complete, efficient,and easy-to-use digital and intelligent design system for casting processes.
Based on the casting forming of large complex thin-walled JG4247 alloy turbine rear casing, the shrinkage porosity and hot tearing tendency of the casing were comparatively simulated and analyzed by ProCAST software under different casting systems conditions. The results showed that compared with the top gating system, the riser and sprue realized the feeding of the multiple variable cross-section hot spots of the casing during the solidification process simultaneously by using the bottom gating system, which was a suitable casting system design for the turbine rear casing. Although the hot tearing tendency of the bottom gating system casing was slightly greater than that of the top gating system. While the further research revealed that the hot tearing tendency of the casing decreased with the reducing of pouring temperature or the increase of shell temperature under the condition of the bottom gating system, the latter factor played an important role in the system. Therefore, the hot tearing tendency of the casting with the condition of the bottom gating system could be reduced by increasing the shell temperature under the bottom gating system, and finally the high metallurgical quality JG4247 alloy turbine rear casing casting without crack and macro shrinkage inside could be obtained. The simulation results were consistent well with the actual casting results of the casing.
It is very difficult to prevent and control the inner reminder for the casting with complicated pipeline. This paper summarized the types of the reminder in the inner pipeline, and analyzed the causes and evaluated the removal difficulty. Meanwhile, this paper presented the all-flow prevention and control strategy including casting structure design, manufacture process optimization, process-flow improvement and production management. This study was helpful for the prevention and control of reminder for casting with the complicated inner structure.
The design case of S415 vermicular graphite cast iron crankcase casting core is introduced. The core is made of precoated sand, supplemented by mold coating. The horizontal core shooting mode is adopted, and the complicated cavity cores are all cut to avoid the core pulling structure of the die. The annular lock catch and bayonet are used for mutual positioning, and finally the cast iron splint is used for locking. While meeting the process requirements,a number of design measures were taken in terms of core thickness, positioning, sealing, exhaust, etc. The actual production has proved that the design of S415 crankcase body core meets the requirements of casting process, can reduce the consumption of molding sand, ensure the dimensional accuracy of castings, and avoid defects such as sand inclusion and blowholes.
High-pressure turbine blades are the core components of aerospace engines, and their casting quality is one of the main factors affecting engine performance. Due to the complex structure of blade, many casting defects and low qualified rate of finished product, it is necessary to carry out high-precision nondestructive testing. In this paper,micro-focus industrial CT was used to conduct CT scanning and reconstruction of cast high-pressure turbine blades.Three-dimensional data and tomography images of blades were obtained through projection images and filtered back projection algorithm. The influence of transmittance interval Angle on defect identification was analyzed, and the internal structural defects such as porosity were visually analyzed.
The quality of camshaft castings is affected not only by the combination of multiple casting process parameters,but also by the error fluctuation caused by noise factors in the environment. Based on this, the concept of signalto-noise ratio in Taguchi method and TOPSIS in multi-objective decision-making were applied to the optimization of process parameters in camshaft casting process, so as to realize the robust design of casting quality. Combined with the computer numerical simulation technology of the casting process, the optimal combination of process parameters with strong anti-interference ability was obtained from the simulation test scheme. The test results show that the casting process parameters of casting mould temperature 35 ℃, pouring time 12 s and pouring temperature 1446 ℃ make the performance of camshaft casting reliable and robust, which provides an idea for the optimization method of casting process parameters in actual production.
The iron Buddha in Fuzhou Kaiyuan Temple is one of the biggest ancient ones, existing both at home and abroad.In this paper, the construction of cast object, the state of inner surface, the chaplets with their affected zones, the gridding stripes, the metallographic structure, and the chemical composition were exhaustively characterized. The observation illustrated that there was no any sign of cold steam existed in the main structure of the iron Buddha.The chemical calculation exhibited that the carbon equivalent is 4.3%, falls into eutectic composition. The metallographic analysis displayed that there is white cast iron on the surface, but mottled cast iron in the substrate.We try to discuss the advantages, causes and related technologies of the three important technological characteristics observed.
This paper introduces the main revision contents of GB/T 2100—2017 standard, the brand, chemical composition, mechanical properties, heat treatment, welding repair, test methods and acceptance rules of general corrosion resistant steel castings, and the characteristics, typical application cases of the standard.The standard covers 27 kinds of stainless steel castings in three categories: martensite, austenite and duplex（austenite-ferrite）, which can meet the requirements of corrosion resistance and mechanical properties of castings in various corrosive working conditions. When selecting materials, it is necessary to combine the characteristics of stainless steel and the service environment, and comprehensively consider the material cost, manufacturing cost and process difficulty degree, so as to optimize the brand of corrosion resistant steel castings with high price-performance ratio, which improve the safety and reliability of equipment.
