Precision Casting Research Articles

Advanced β-Solidifying Titanium Aluminides – Development Status and Perspectives

ABSTRACTAfter almost three decades of intensive fundamental research and development activities intermetallic titanium aluminides based on the -TiAl phase have found applications in automotive and aircraft engine industries. The advantages of this class of innovative high-temperature materials are their low density as well as their good strength and creep properties up to 750°C. A drawback, however, is their limited ductility at room temperature, which is reflected by a low plastic strain at fracture. This behavior can be attributed to a limited dislocation movement along with microstructural inhomogeneity. Advanced TiAl alloys, such as β-solidifying TNM™ alloys, are complex multi-phase materials which can be processed by ingot or powder metallurgy as well as precision casting methods. Each production process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat-treatments. The background of these heat-treatments is at least twofold, i.e. concurrent increase of ductility at room temperature and creep strength at elevated temperature. In order to achieve this goal the knowledge of the occurring solidification processes and phase transformation sequences is essential. Therefore, thermodynamic calculations were conducted to predict phase fraction diagrams of engineering TiAl alloys. After experimental verification, these phase diagrams provided the base for the development of heat treatments to adjust balanced mechanical properties. To determine the influence of deformation and kinetic aspects, sophisticated ex- and in-situ methods have been employed to investigate the evolution of the microstructure during thermo-mechanical processing and subsequent multi-step heat-treatments. For example, in-situ high-energy X-ray diffraction was conducted to study dynamic recovery and recrystallization processes during hot-deformation tests. Summarizing all results a consistent picture regarding microstructure formation and its impact on mechanical properties in TNM alloys can be given.

Ni 基超合金 Inconel 718 の固相線温度近傍における力学特性値の引張速度依存性

Nickel-based superalloys have been applied to gas turbine and aircraft jet engine parts due to superior high temperature strength and corrosion resistance. However, casting defect such as solidification cracking often occurs. In order to increase productivity of precision casting and various shape casting processes, predicting the occurrence of solidification cracking by using CAE (Computer Aided Engineering) should be essential. Therefore, it is necessary to obtain mechanical properties in the state of solid-liquid coexistence. In the previous reports, high temperature mechanical properties were examined but tensile rate dependency wasn't examined. In this study, high temperature (around solidus temperature) mechanical properties and tensile rate dependency of their alloy were examined by using originally developed tensile test.

Influence of casting surface on creep behaviour of thin-wall Ni-base superalloy Inconel100

The conventionally cast nickel-base superalloy Inconel100 was investigated with the focus on the influence of the surface condition and the thin-section size on the creep properties. Flat samples with 0.9mm and 1.3mm thickness were wire eroded from precision cast ingots. Thin cast specimens with a remaining casting surface were compared with machined specimens which flat surfaces were subsequently ground to the final thicknesses. Microstructures were examined by optical and scanning electron microscopy. Creep tests in air at 980°C under a constant load of 150MPa revealed decreasing creep strength with decreasing sample thickness. However, thin cast samples and samples with a machined surface having the same thickness showed similar creep properties.

Research of Calcium Oxide Based Ceramic Cores in Titanium Casting

Ceramic cores are playing a more and more important role in the modern precision casting industry system; it could influence the internal structure and performance of the castings. Especially in the precision casting field, the internal structure directly influenced the ultimate properties. This paper investigated the calcium oxide ceramic cores used in titanium precision casting fields through changing the ratio of aggregate sizes and sintering process. The main properties as bend strength, sintering shrinkage, casting reaction layer and microstructure are performed using SEM, XRD and other measurement method. Results of this research showed that the calcium oxide ceramic cores could be used in titanium precision casting, provide a stable casting property and nearly without reaction pollution to the titanium castings.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys

AbstractAfter almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ‐TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high‐temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi‐phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo‐mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ‐TiAl based alloys, but concentrates on β‐solidifying γ‐TiAl based alloys which show excellent hot‐workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application‐oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro‐ and nanostructure during hot‐working and subsequent heat treatments.

Development of Aluminum Die Casting Products with High Accuracy as Well as Superior Die-to-Casting Transcriptional Capability by Using Semi-Solid Method

Despite the lightweight demands, precision die casting products with high dimensional/ die-transcriptional accuracy is still made by zinc die-casting, because the conventional aluminum die-casting cannot satisfy the requirement. While light weight precision die casting demand for electric devices /automobile parts has been encouraging the material replacement from zinc to aluminum, it cannot be realized yet. We applied the Semi-Solid die casting technique to the precision casting, and verified possibility of replacement of the material from zinc to aluminum

Consideration of the influence of contamination from oxide crucibles on TiAl cast material, and the possibility of achieving low-purity TiAl precision cast turbine wheels

In order to promote the development of low-cost TiAl precision cast turbine wheels, consideration was given to the influence of reduced purity. In the research reported here, the contamination behavior of Ti–46 at%Al cast material from various oxide crucibles was examined, and the influence of impurities and inclusions on material properties of Ti–46 at%Al cast material was evaluated. As a result, it was found that oxygen concentration had the greatest effect on properties, although it was observed that a relatively high concentration of up to approx. 0.4 wt% did not reduce room temperature tensile strength. Next, upon attempting the precision casting of TiAl turbine wheels, it was confirmed that items produced from an yttria crucible and having oxygen concentration of 0.17 wt% had greater room temperature tensile strength than turbine wheels from a conventional water-cooled copper crucible, together with comparable toughness required in practical use. Accordingly, the upper limit for oxygen concentration in TiAl castings, formerly considered to be 0.1 wt%, can be revised upward, which is extremely beneficial from the standpoint of reducing production costs.

Analysis for the Influence of the Admixture on the Solidification Rate of Expansion of the α-High-Strength Gypsum Plaster

The α-type high-strength gypsum with its superior strength and performance is widely used in precision casting, ceramic molds, arts and crafts as well as plaster and GRG self-leveling and other industries that have higher demands to the dimensional stability of the products. Solidification rate of expansion is an important characterized parameters of gypsum volume stability, and also an important indicator of α-High-Strength gypsum plaster. The common adjustment method of Solidification rate of expansion is to add additives to change the gypsum hydration process. But the influences of different types of additives on setting expansion have not been studied yet, therefore, this paper studied on the influences of citric acid, tartaric acid and sodium pyrophosphate on the solidification rate of expansion of the α-High-Strength gypsum plaster. The results indicate that the gypsum expansion rate was decreased with the increase of gypsum set retarder, the expansion rate was firstly increased and then decreased when the citric acid and sodium pyrophosphate increased; however, when the tartaric acid increased, the expansion gradually decreased, and the tartaric acid and the expansion of the gypsum by and large are in an inverse proportion.

Analysis for the Influence of the Admixture on the Solidification Rate of Expansion of the α-High-Strength Gypsum Plaster

The α-type high-strength gypsum with its superior strength and performance is widely used in precision casting, ceramic molds, arts and crafts as well as plaster and GRG self-leveling and other industries that have higher demands to the dimensional stability of the products. Solidification rate of expansion is an important characterized parameters of gypsum volume stability, and also an important indicator of α-High-Strength gypsum plaster. The common adjustment method of Solidification rate of expansion is to add additives to change the gypsum hydration process. But the influences of different types of additives on setting expansion have not been studied yet, therefore, this paper studied on the influences of citric acid, tartaric acid and sodium pyrophosphate on the solidification rate of expansion of the α-High-Strength gypsum plaster. The results indicate that the gypsum expansion rate was decreased with the increase of gypsum set retarder, the expansion rate was firstly increased and then decreased when the citric acid and sodium pyrophosphate increased; however, when the tartaric acid increased, the expansion gradually decreased, and the tartaric acid and the expansion of the gypsum by and large are in an inverse proportion.

ИССЛЕДОВАНИЕ КАЧЕСТВА МЕРНЫХ СЛИТКОВ, ПОЛУЧЕННЫХ ИЗ 100 % ТЕХНОЛОГИЧЕСКОГО ВОЗВРАТА, РАФИНИРОВАННОГО МЕТОДОМ ТЕМПЕРАТУРНО-ВРЕМЕННОЙ ОБРАБОТКИ

The macro and microstructure, mechanical properties at normal and elevated temperatures of ВЖЛ12Э-ВИ and ЭИ868Л heat-resistant alloy small bars produced of 100 %-recycled material were researched. Test results showed that the small bars entirely meet the requirements of standards and may be used for precision casting.

Ni基超合金Inconel 718の固相線温度近傍における力学特性取得に関する検討

Nickel-based superalloys have been applied to gas turbine and aircraft jet engine parts due to superior high temperature strength and corrosion resistance. However, casting defect such as solidification cracking often occurs. In order to increase productivity of precision casting and various shape casting processes, predicting the occurrence of solidification cracking by using CAE(Computer Aided Engineering) should be essential. Therefore, it is necessary to obtain mechanical properties in the state of solid-liquid coexistence. In this study, we try to get high temperature (around solidus temperature) mechanical properties of the nickel-based superalloy such as Inconel 718 by using originally developed tensile test. In the previous reports, flat distribution of temperature in the gage length, and crack initiation strain were not ensured. On the other, the developed device ensured within 3℃ of the temperature distribution in the gage length as to the Inconel 718. Tensile strain was measured by using in-situ observation of marker on the surface of the specimen. As a result, Stress-Strain curve, crack initiation stress, and crack initiation strain of Inconel 718 were obtained.

진공 다이캐스팅 공법의 사출조건에 따른 연료전지용 분리판 성형 해석 및 제조 공정

The vacuum die casting is a promising candidate of the stamping process for fabrication of fuel cell bipolar plate due to its advantages, such as precision casting, mass production and short production time. This study proposes vacuum die casting process to fabricate bipolar plates in fuel cell. Bipolar plates were fabricated under various injection conditions such as molten metal temperature and injection velocity. Also, according to injection velocity conditions, simulation results of MAGMA soft were compared to the experimental results. In case of melt temperature <TEX>$650^{\circ}C$</TEX>, misrun occurred. When the melt temperature was <TEX>$730^{\circ}C$</TEX>, mechanical properties were low due to dendrite microstructure. Injection velocity has to set at more than 2.0 m/s to fabricate the sound sample. When melt temperature, injection velocity (Fast shot), and vacuum pressure are <TEX>$700^{\circ}C$</TEX>, 2.5 m/s and 30 kPa respectively, sample had good formability and few casting defects. Simulation results are mostly in agreement with experimental results.

Study on Rapid Casting for Complex Parts

A rapid casting method for complex parts is presented. In this method, casting moulds with complex cavity are manufactured by self-created rapid prototyping approach which called Selected Laser Partitioning for Prototyping. After surface coating treatment for moulds, complex parts are obtained by centrifugal casting. As application cases, metal impeller was casted by this method. A self-developed five-axis coordinate measurement machine was used to process the surface measuring of impeller. The Dimension accuracy grade of impeller is CT-3 and the surface roughness is Ra 6.3µm through making comparisons directly between CAD model and point cloud data of impeller surface. The result shows that this rapid casting method which has the characters of simple technology and low production cost reaches the level of precision casting.

Casting of MOD inlay using rings with holes on both sides: 12∼18 wt%Au–20∼26Pd–14.48∼26.48Cu–40Ag–1.5Zn–0.02Ir alloys

Using a casting ring with openings on both sides and a water-absorbent polymer, heterogeneity is maintained in a single casting and a precise MOD inlay can be produced. We produced 9 different kinds of gold-silver-palladium (Au-Ag-Pd) alloys by changing the ratio of palladium, gold, and copper and investing them, and changing parameters such as the angulation of the casting ring openings and the water:powder ratios to produce MOD inlay castings. We measured the expansion and shrinkage percentage of the castings in both the buccolingual and mesiodistal directions. From this experiment, we learned that precise MOD inlay castings can be produced using rings with 240° openings when invested in a thick mix having a standard water:powder ratio or using rings with 200° openings when invested in a thick mix having a water:powder ratio for a 12 wt%Au-20∼26Pd-20.48∼26.48Cu-40Ag-1.5Zn-0.02Ir alloyes.

Modelling of bead filling process in lost foam casting based on gas–solid two-phase fluid simulation

Lost foam casting (LFC), the new generation of precision casting process, is called to be the representation of advanced casting technology. In the LFC, the foam pattern is the key qualification, and the bead filling process is quite crucial to ensure the high quality of the foam pattern. Filling without uniformity and denseness will cause various defects and affect the quality of the casting. Numerical simulation of the bead filling process is carried out to optimise the process, enhance the efficiency and decrease the waster. Based on molecular dynamics simulation, the discrete element method is established to analyse the flow of discrete particles. A universal programme of simulating the LFC bead filling process is developed, which can forecast the movement law and character of foam beads in the die cavity. By comparing the results of visual experiments with simulation results, the rationality of such physics concept and the correctness of the computational method can be tested. Furthermore, the force distribution on the beads and the movement mechanism of the filling process can be analysed at the same time. Factors that may influence the filling process, including the position of the bead inlets, the amount and position of outlets, the initial pressure of the gas phase, etc., are studied respectively.

Coring micron- and milli-scale holes in metallic glasses

Metallic glasses (MGs) combined with copper cores possess many advantages in precision casting and coring of alloys. In this study, inner holes with different dimensions and complex sectional shapes were fabricated through direct casting and coring in MGs. The MG castings show good surface finish and the cored inner holes exhibit high aspect ratios larger than 80 while holding a tight dimension tolerance. The dimensional deviation was proved to originate mainly from the contraction disagreement between castings and copper cores by comparing their thermal expansion coefficients and simulating the solidification and cooling processes, while other factors may also contribute to it. The results are expected to provide a convenient and economical way in the near net-shape fabrication of inner holes in metallic devices and in the assembly of MG components.

Lightweight Design and Verification of Gantry Machining Center Crossbeam Based on Structural Bionics

The lightweight and high efficiency of natural structures are the inexhaustible sources for engineering improvements. The goal of the study is to find innovative solutions for mechanical lightweight design through the application of structural bionic approaches. Giant waterlily leaf ribs and cactus stem are investigated for their optimal framework and superior performance. Their structural characteristics are extracted and used in the bio-inspired design of Lin MC6000 gantry machining center crossbeam. By mimicking analogous network structure, the bionic model is established, which has better load-carrying capacity than conventional distribution. Finite Element Method (FEM) is used for numerical simulation. Results show better specific stiffness of the bionic model, which is increased by 17.36%. Finally the scaled models are fabricated by precision casting for static and dynamic tests. The physical experiments are compared to numerical simulation. The results show that the maximum static deformation of the bionic model is reduced by about 16.22%, with 3.31% weight reduction. In addition, the first four natural frequencies are improved obviously. The structural bionic design is a valuable reference for updating conventional mechanical structures with better performance and less material consumption.

CAD/CAM systems available for the fabrication of crown and bridge restorations

Dental biomaterials are widely used in all areas of routine dental practice. There are mainly two methods for their application. Firstly, dental biomaterials are placed into living tissues, such as teeth, to fill the space. Secondly, dental devices such as crown and bridge restorations and dentures are fabricated using various materials to restore the morphology and function of the dentition. Crown and bridge restorations are one of the main treatment methods used by general practitioners to achieve lifelike restoration of form and function. The recent introduction of osseointegrated implants has expanded the application of crown and bridge restorations for partially edentulous patients. Mechanical durability and precision fit are mandatory requirements for crowns and bridges. The development of various casting alloys and precise casting systems has contributed to the successful use of metal-based restorations. However, patient requests for more aesthetic and biologically 'safe' materials has led to an increased demand for metal-free restorations. There is also a growing demand to provide all-ceramic restorations more routinely. New materials such as highly sintered glass, polycrystalline alumina, zirconia based materials and adhesive monomers, will assist dentists to meet this demand. In addition, new fabrication systems combined with computer-assisted fabrication systems (dental CAD/CAM) and various networks are now available. Dental technology was centred on lost-wax casting technology but we now face a revolution in crown and bridge fabrication. This article reviews the history and recent status of dental CAD/CAM, the application of CAD/CAM fabricated tooth-coloured glass ceramic crowns, and the application of all-ceramic crowns and bridges using CAD/CAM fabricated zirconia based frameworks.

Design factors influencing weldability of the Mg-4Y-3RE cast magnesium alloy

Due to low density and good strength properties, magnesium alloys are increasingly used as a structural material They are used, amongst others, for large-size castings in sand moulds, pressure and precision castings. Welding and pad welding is used to repair casting defects, such as misruns, micro-shrinkage, cracks, etc. The most frequent reason for disqualifying of welded joints made to repair the castings is hot cracking which occurs as a result of tensile stresses formed in the material during welding. The Mg-4Y-3RE (WE43) alloy with addition of yttrium and rare earth and zirconium elements used for testing is creep resistant to 300°C. The alloy is used in the automotive industry, for example for engine blocks and in aerospace industry for gearbox housings. This paper describes the welding and remelting tests of the Mg-4Y-3RE (WE43) castings in conditions of constant and variable stiffness. It has been concluded that hot cracks are formed as a result of eutectic melting in the areas of contact of α - Mg solid solution crystals.

고융점 금속의 미소형상 정밀주조를 위한 탄소몰드의 적용성에 관한 연구

Carbon material shows relatively high strength at high temperature in vacuum atmosphere and can be easily removed as CO or <TEX>$CO_2$</TEX> gas in oxidation atmosphere. Using these characteristics, we have investigated the applicability of carbon mold for precision casting of high melting point metal such as nickel. Disc shape carbon mold with cylindrical pores was prepared and Ni-base super alloy (CM247LC) was used as casting material. The effects of electroless Nickel plating on wettability and cast parameters such as temperature and pressure on castability were investigated. Furthermore, the proper condition for removal of carbon mold by evaporation in oxidation atmosphere was also examined. The SEM observation of the interface between carbon mold and casting materials (CM247LC), which was infiltrated at temperature up to <TEX>$1600^{\circ}C$</TEX>, revealed that there was no particular product at the interface. Carbon mold was effectively eliminated by exposure in oxygen rich atmosphere at <TEX>$705^{\circ}C$</TEX> for 3 hours and oxidation of casting materials was restrained during raising and lowering the temperature by using inert gas. It means that the carbon can be applicable to precision casting as mold material.