Vacuum Casting Research Articles

Coarsening of needle-shaped precipitates in CoNiCrAl alloys during isothermal heat treatment: Kinetics in length and thickness

This paper investigated the coarsening kinetics of needle-shaped γ precipitates in CoNiCrAl alloys after isothermal heat treatments at 900 °C and 1100 °C. The CoNiCrAl alloys were prepared by vacuum induction melting and casting process. They were characterised to exhibit a two-phase γ + β structure and some needle-shaped secondary γ precipitates were formed within the primary β phase during isothermal heat treatments. The coarsening of the needle-shaped secondary γ precipitates occurred with heat treatment time and became more rapid at elevated temperatures. In particular, the coarsening kinetics of needle-shaped γ precipitates in length and thickness were specifically studied. It was found that the coarsening kinetics in length and thickness was a volume diffusion governed process and generally followed the classic Lifshitz-Slyozov-Wagner (LSW) theory. An analytical model was proposed to estimate the lengthening and thickening of the precipitates, which considered the aspect ratio and volume fraction of the precipitates. The calculated coarsening rate in thickness agreed well with the experimentally determined value. But some discrepancies were found between the predicted and measured coarsening rate in length. This might be due to the termination migration effects of the needle-shaped precipitates which restricted the coarsening rate in length.

Quantifying the effects of hydrogen concentration and cooling rates on porosity formation in Al–Li alloys

The addition of Li to Al alloys produces such benefits as a 6% increase of modulus and a 3% weight reduction upon adding 1 wt% Li, and yet it has led to difficulties for manufacturing due to the highly active Li and 25 times equilibrium [H] concentration in the liquid at elevated temperatures. In this study, the 3D porosity morphology was quantified using the X-ray computed tomography (X-CT) from both sand gravity and vacuum castings. A cellular automaton model has been adopted to predict porosity distribution as a function of equilibrium hydrogen concentration and thermal boundary conditions. Combining experimental and simulation results, it was found that the mechanical properties of vacuum casting Al–Li alloy have been improved significantly due to the reduction of hydrogen porosity. The prediction of porosity as a function of hydrogen levels and cooling conditions agrees well with experiments, and porosity has been found to decrease Young's modulus and initiating cracks in Al–Li alloys.

Effect of Nb content on mechanical reinforcement of the Cu-10Fe composites

The Cu-10Fe-based composites with different Nb content were fabricated by vacuum mold casting. The effect of Nb content on the solidification behavior and microstructure was investigated systematically and the optimal composition was determined as Cu-10Fe-1.0 Nb (wt%). The as-cast samples were rolled by 90% reduction at room and then aged at 250 ℃ for different time. The properties results showed that, after aging for 1800 min, microhardness, tensile strength and elongation of the Cu-10Fe-1.0 Nb samples reached 145 HV, 553 MPa and 21.5%, respectively. The microstructure results showed that the primary Fe-rich phases in the Cu-10Fe-1.0 Nb samples were significantly refined due to the heterogeneous nucleation induced by Fe2Nb phases, and then led to the refinement of the matrix. The enhanced mechanical properties could be attributed to the Orowan strengthening, refinement strengthening and work hardening resulted from the numerous submicron-/nano-sized Fe particles, fine sub-grains and high-density dislocation in the matrix formed during thermo-mechanical treatment.

Rheo‐kinetic study of 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB‐based composite propellant and evaluation of casting rate

AbstractThe flow behaviour of 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB‐based composite propellant (P01) and basic aluminized HTPB‐based propellant (P02) was investigated using shear rheometer. The experimental data were fitted to ‘power law’ for non‐Newtonian fluid flow, and the rheological parameters were expressed as consistency index (k) and pseudoplasticity index (n). For both the propellant compositions, a shear thinning nature (pseudoplasticity index; n < 1) has been observed. The study categorically showed that the incorporation of 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB has resulted in increased consistency index (k) and yield stress as compared to HTPB based compositions. In addition, the time–temperature cure‐kinetics study suggested that the rate of curing reaction is higher with toluene diisocyanate as compared to isophorone diisocyanate and the Arrhenius activation energy (Ea) corroborated with the observed trend. Furthermore, the Haegen–Poisseuille equation modified for non‐Newtonian fluid flow has been employed to determine the theoretical casting rate for 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB‐based composite propellant at different temperatures in a vacuum casting setup.

Exploring the impact of configurational entropy on the design and development of CoNi-based superalloys for sustainable applications

A comprehensive literature review on recently rediscovered Co- and/or CoNi-based superalloys, strengthened by the γ' phase, revealed a relationship between the configurational entropy of the system and the γ' solvus temperature. This study was conducted on a high-Cr CoNi-based superalloy system with high configurational entropy to test our hypothesis based on the sustainable metallurgy framework. Thermodynamic calculations were performed to design the chemical compositions, followed by vacuum casting and heat treatments to produce the desired alloys. The microstructures were characterized using a scanning electron microscope, electron backscattered diffraction, transmission electron microscope, and differential thermal analysis. Microhardness and nanoindentation tests were employed to measure the mechanical properties. The results showed that both the configurational entropy and the type of alloying elements determine the final high-temperature performance of the alloys. We found that to enhance the higher γ' solvus temperature, the configurational entropy should be increased by adding γ' stabilizing elements. The microstructural and mechanical characteristics of the designed alloys before and after heat treatments are discussed in detail. The outcome of this study is beneficial for developing cobalt-based high-entropy superalloys with appropriate processing windows and freezing ranges for advanced sustainable manufacturing purposes, such as using powder bed fusion technologies.

Microstructure evolution of as-cast CoNiCrAl bond coat alloys after isothermal heat treatments

In this paper, the microstructure evolution of two as-cast CoNiCrAl bond coat alloys after various isothermal heat treatments were investigated. The CoNiCrAl bond coat alloys were prepared by vacuum induction melting and casting process. The as-cast alloys were subjected to heat treatments from 550 °C to 1300 °C for periods up to 100 h to study the effects of temperature on the microstructure and phase distribution. The microstructure of heat treated CoNiCrAl bond coat alloys was characterised by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The CoNiCrAl alloys exhibited a two phase γ + β structure, with the β phase acting as the primary phase. It was shown that the precipitation of needle-like secondary γ phase was slow at temperatures below 600 °C but became rapid above 900 °C. It was found that the morphology of the secondary γ phase changed from needle-like to rod-like at 1100 °C. A homogeneous γ + β two phase structure was obtained at 1300 °C even after 2 h heat treatment. It was revealed that the heat treatment temperature had a significant influence on the formation and distribution of the secondary γ phase. In addition, the precipitation of sub-micron Cr-rich particles occurred at 1300 °C in both CoNiCrAl alloys, which was due to the low solubility of Cr in the β phase and rapid coalescence of γ phase at elevated temperatures.

Deep drawing with unconventional tooling: impact of process parameters on a part accuracy

The analysis of influencing factors and their effects on the deep drawing process is essential for producing cost-effective, high-quality workpieces. In this study, the impact of deep drawing process variables, including die radius, blank holder force, and lubrication conditions, on the distribution of wall thickness and changes in radius for axisymmetric workpieces is explored. For the investigation, specialized tooling was created, with core components such as the punch, die, and blank holder made from a two-component resin and fabricated using rapid tooling technology - vacuum casting. The Taguchi method was employed as a statistical tool for planning the experiments, which allowed the impact of process factors to be determined with minimal variability.

Oxidation reaction kinetics of HTPB-boron carbide/polytetrafluoroethylene formulations as a solid fuel

A solid-fuel ramjet engine powered by boron carbide (B4C) can generate nearly the same amount of energy as boron. However, the inherent oxide layer on the B4C surface restricts the energy released during its oxidation. In this study, we examine the effect of polytetrafluoroethylene (PTFE) on the oxidation of B4C and the removal of the oxide layer during the oxidation reaction. The B4C/PTFE binary composite powder was prepared using a ball milling process at three different concentrations (5:20, 10:20, and 15:20). Hydroxyl-terminated polybutadiene (HTPB) loaded with binary composite powder was manufactured by vacuum casting technique. The pure HTPB and HTPB/PTFE fuels were manufactured as reference formulations. The B4C/PTFE binary composite powder was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and high-resolution scanning electron microscope (HRSEM). The thermal oxidation characteristics of prepared fuel formulations were studied using the thermogravimetric technique. The kinetics of the oxidation reaction was studied using both isothermal and non-isothermal methods. The thermogravimetric curves showed that the oxidation reaction of HTPB-based fuel occurred in four steps. When B4C/PTFE binary composite powder is added to HTPB, it decomposes faster and at a higher rate. The decomposed fluorine species of PTFE significantly improved the oxidation reaction of composite powder and increased the energy release rate of B4C. The kinetic studies of oxidation suggested that the addition of B4C/PTFE binary composite powder into HTPB lowered the activation energy (Ea: S1 > S2 > S3 > S4 > S5) required to prompt the oxidation reaction. Based on thermal and kinetic results, a potential oxidation promotion mechanism of B4C/PTFE composite powder was proposed. The initial stages of B4C oxidation resulted in a glassy layer of B2O3 oxide forming at the interface of B4C and PTFE powder. As a result of the oxidation reaction between B4C/PTFE and O2, CF4, Trifluoroboron (BF3) and CO2 were generated. At high temperatures, the oxide shell ruptured, allowing the O2 to diffuse into the core of the B4C particle and releasing a large amount of heat energy.

Evaluation of the impact of Mn and Al on the microstructure of Fe–Co–Ni–Cr based high entropy alloys

ABSTRACT In this study, an equiatomic FeCoNiCrMn high entropy alloy (HEA) was examined and compared to two Al-containing variants, FeCoNi1.5CrMnAl0.5 and FeCoNi1.5CrAl0.5, in terms of microstructure, phase composition and hardness. The vacuum cast, hot isostatically pressed (HIP’d) alloys were evaluated using differential scanning calorimetry (DSC), SEM, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness testing. The DSC results indicated that the solidus and liquidus temperature of the base alloy on cooling are 1296.3 and 1314.8°C, respectively. Its microstructure exhibited a single-phase face centred cubic (FCC) structure, with a small amount of σ-phase. The two Al-containing alloys (FeCoNi1.5CrMnAl0.5 and FeCoNi1.5CrAl0.5) were observed to form a secondary phase, in a FCC matrix, along the grain boundaries and within the grains. FeCoNi1.5CrMnAl0.5 had a solidus and liquidus temperature at 1271.8°C and 1287.6°C upon cooling, while FeCoNi1.5CrAl0.5 exhibited a solidus at 1354.7°C and liquidus at 1376.1°C. The hardness of the base composition was measured at 142 HV while the addition of Al and increase of Ni content in FeCoNi1.5CrMnAl0.5 increased the hardness to 202 HV and the removal of Mn in FeCoNi1.5CrAl0.5 further enhanced the hardness to 217 HV. These results aim to form a basis for understanding the effects of HEA microstructure on the material performance in oxidising environments, such as supercritical-CO2.

Metallization of carbon-fibre reinforced composites via a metal-epoxy biphasic sublayer and low-pressure cold spraying

This study investigates the suitability of a sublayer-assisted low-pressure cold spraying for metallizing Carbon Fibre-Reinforced Polymer (CFRP) composites. The metal-based polymeric sublayer consists of a Cu-based epoxy sublayer, made of Cu spherical micron-sized powders and an epoxy phase, and which is embedded onto the CFRP composite surface using a vacuum moulding process. Then, a cold spray deposition onto the sublayer is performed to generate a coating. Different cold spray powders (copper, aluminium, zinc, and tin) were used to explore the optimal coupling powder/sublayer/CFRC substrate under different spraying conditions. The Cu powders require a high velocity so that they are difficult to be compatibilized with the CFRC structure without an erosion during the cold spray deposition. Soft powders like Al, Zn and Sn can lead to an onset of coating formation via the bonding of these powders onto the embedded sublayer. The Sn powders generate an adhesion onto the Cu-epoxy embedded sublayer via a metal-to-epoxy bonding (Sn-to-epoxy zone) and a metal-to-metal bonding (Sn-to-Cu), under the gas working condition of 9 bars and 25 °C. As conclusion, the present work demonstrates the feasibility of a sublayer-assisted cold spray process to metallize a CFRC structure partly made of metal-to-metal bonding.

EVALUATION OF THE WEAR OF AN FE-AL ALLOYTURBOCHARGER ROTOR SEAL RING UNDER SELECTEDOPERATING CONDITIONS

This publication presents the possibility of extending the service life of the rotor shaft seal ring in an automotiveturbocharger by using an intermetallic Al-Fe alloy. Comprehensive results of tribological, metallographic andprofilometric tests of this alloy (vacuum cast) operating in a sliding association on a T-05 bench allowedthe representation of a real friction node. Based on empirical tests, it will be possible to determine whichalloy (Al-Fe alloy or the one currently used for sealing rings of a car turbocharger rotor shaft) has bettertribological properties. For this purpose, the research was based on an experiment that assumes three mainfactors determining the wear of the tested association. The result of the experimental plan was to obtain threedimensionaldiagrams showing the influence of the wear factors on the friction force and surface topography.

Effect of B and Zr additions and homogenization treatment on the carbide morphology of a vacuum cast Co-Cr-W-Ni superalloy

The influence solution heat treatment (1200 °C) on the evolution of carbide morphology and creep tensile properties of a vacuum cast Co-Cr-W-Ni base superalloy with and without of B and Zr additions has been investigated. The experimental evidence, shows that compared to the as cast microstructure, the creep life at a temperature of 750 °C, the carbide morphology and distribution are affected by the B and Zr additions as well as the solution treatment. After solution treating the alloy without additions, a finer carbide distribution along the interdendritic arms was observed. On the contrary, the additions of B and Zr impact the carbide morphology as well as its distribution, precipitating within the dendrites and at interdendritic regions. Due to this, the creep life and creep deformation of sample with additions are 12.5 and 2.7 times higher compared to the sample without additions respectively.

Microstructures and Mechanical Properties of Alumina and/or Yttrium Oxides Strengthened 9Cr Steel Fabricated by Vacuum Casting

The oxides with Al2O3‐containing and/or Y‐containing are introduced into 9Cr ferritic/martensitic steel fabricated by vacuum casting to modify its microstructures and improve its mechanical properties. The results show that the micron nonmetallic particles are refined, and the number of submicron particles is increased after the introduction of Al2O3‐containing oxides, while the number of submicron particles is decreased when both Al2O3‐and Y‐containing oxides are introduced. The average grain size, the width of martensite, and the M23C6 phases in the tempered steel are optimized when the Al2O3‐containing oxides are introduced. However, with the further introduction of Y‐containing oxides, these tempered microstructures do not change much, except for the precipitation of the δ‐Fe phase. Due to the grain refinement and second‐phase particle strengthening after the introduction of Al2O3‐containing particles, the tensile strength is improved not only at room temperature but also at 550 °C, but the impact energy drops significantly, which is caused by a large number of TiN particles promoted by Al2O3 particles through heterogeneous nucleation. At the same time, the further introduction of Y‐containing oxides reduces the tensile strength and increases the elongation at room temperature, which is attributed to the precipitation of soft δ‐Fe promoted by the addition of Y.

Microstructure and mechanical properties of multi-scale α-Fe reinforced Cu–Fe composite produced by vacuum suction casting

Cu–10Fe composites were produced by the vacuum suction casting and traditional vacuum mold casting, respectively. The evolution of microstructure and properties of the composites during cold rolling and aging processes was analyzed. Compared with the traditional mold-casted Cu–Fe composites, the suction-casted Cu–Fe composite had better mechanical properties, with microhardness, tensile strength and elongation of 146 HV, 526 MPa and 23.7%, respectively. The softening temperature of the suction-casted Cu–Fe composite was 520 °C, which was 220 °C higher than that of traditional mold-casted Cu–Fe composite. The good performance of the suction-casted Cu–Fe composite was mainly attributed to the refinement of the Cu matrix and the formation of the multi-scale α-Fe particles caused by the effect of solute trapping during vacuum suction casting. The yield strength of the composites was mainly attributed to the contribution of Orowan strengthening, refinement strengthening and dislocations strengthening, which count for 31.1%, 25.8% and 24.1%, respectively.

Universal eco-friendly biodegradable packaging for storage and transportation of food and industrial goods based on shives of bast plants

Integrated processing of plant raw materials refers to the primary areas of use of natural resources and their rotection. During the primary processing of bast plants, a large amount of waste remains – a shives. Part of the shives is burned, the rest goes into the dump. Due to its chemical composition, high content of cellulose shives can be used in the production of eco-friendly packaging. Packaging can be obtained with the complete or partial replacement of waste paper in its composition. Thanks to this, the issue of the shortage of waste paper at the enterprises of recycling of secondary raw materials will also be resolved. The purpose of the work is the production of eco-friendly biodegradable packaging from flax shives in industrial conditions. The paper presents the results of samples of lumpy egg packaging obtained by vacuum casting with the use of flax production waste. In industrial conditions, it was possible to replace part of the waste paper on the fire. For more efficient use, the shives was pre-ground to the consistency of wood flour M-560. The following indicators were determined: humidity, strength, moisture absorption capacity, antibacterial properties. The obtained results showed the optimal ratio of the mixture components, processing modes. According to all indicators, the packaging with a bone is not inferior, and in the case of tensile strength and antibacterial properties exceeds the normalized values.

Casting technology with the formation of a uniform fine-grained metal structure

The paper is devoted to the development of vacuum casting technology, which ensures the formation of a casting with a uniform fine-grained metal structure. This effect is achieved by the slow filling of the cooled cavity of the mold with a cooling liquid due to the difference in the flow rate of the liquid at the inlet and outlet. At each moment of time, the cooling of metal is carried out in a thin layer of the casting, which ensures the uniformity and fine-grained structure of the casting material, the absence of shrinkage and internal stresses.

Evolution of microstructure and high temperature tensile strength of gray cast iron HT250: The role of molybdenum

The present work investigated the influence of molybdenum (Mo) content on the microstructure and high temperature tensile strength (HTTS) of gray cast iron (GCI) to achieve improvement of the HTTS of GCI brake drum for heavy-duty trucks and extension of their service life. The specimens of GCI with Mo (0.024%, 0.22%, 0.51%, 0.8%) have been prepared by smelting in a 25 kg vacuum induction furnace and casting in a standard mold. The microstructure was observed by scanning electron microscopy and optical microscopy, while physical properties tested by microcomputer-controlled testing machine and micro hardness tester. The results show that increasing the Mo content from 0.024% to 0.8%, the length of graphite flake decreased from 400 μm to 288 μm; the pearlite interlayer spacing decreased from an average of 619 nm–439 nm. However, the pearlite content also decreased with the increase of the Mo content. A portion of the Mo is in solution in the matrix; this contributes to solution strengthening of the matrix. The remainder of the Mo precipitates in the austenite grains, or the grain boundaries, as carbides. This results in the refining of the pearlite grains. Eutectic cell density increased from 217 cm−2 to 286 cm−2. Both room temperature tensile strength and HTTS increased with increasing Mo content. The findings suggest adding Mo to GCI is an effective way to improve the microstructure and increase its HTTS.

A comprehensive study on using expanded silica gel size as hollow sphere material in different aluminum alloy-based syntactic foams

PurposeMetal foams are a structural and functional composite materials that have received wide attention due to their specific structures and properties. The aim of this study is to investigate the mechanical properties of syntactic foam by using expanded silica gel with the spacer technique.Design/methodology/approachIn this research paper, the vacuum casting production method was used to produce metal syntactic foams including AlSi12 and AlSi8Cu3 matrix and expanded silica gel fillers with diameters of 2–4.75 mm and 4.75–5.6 mm.FindingsAs a result of the study, it was observed that as the foam densities increased, the compressive strength values of the samples increased due to the increasing volume fraction of the metallic matrix. Samples with the AlSi12 matrix showed higher compressive strength than samples with the AlSi8Cu3 matrix.Originality/valueThe originality of the study is the comparison of two different main matrix alloys (AlSi12 and AlSi8Cu3) and different pores using expanded silica gel.

Microstructure and thermophysical properties of as-cast CoNiCrAl bond coat alloys at different Al contents

In this paper, the microstructure and thermophysical properties of two CoNiCrAl bond coat alloys with differing Al contents were investigated. Two CoNiCrAl alloys with compositions of Co-31.7%Ni-20.8Cr-10Al and Co-31.7%Ni-20.8Cr-12Al (all in wt%) were prepared by vacuum induction melting and casting. The microstructure of the as-cast CoNiCrAl alloys was characterised by scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD). The phase changes of the CoNiCrAl alloys as a function of temperature were studied by differential scanning calorimetry (DSC). Thermophysical properties such as thermal conductivity, thermal diffusivity and thermal expansion were evaluated. The as-cast CoNiCrAl alloys exhibited a two-phase structure, consisting of the Al-rich BCC β phase and Co and Ni-rich FCC γ phase. It was found that the β-phase fraction increased with the overall Al content in the alloy. A two-stage thermal expansion was noted for both CoNiCrAl alloys. In addition, it was shown that the CoNiCrAl alloy with the higher Al content exhibited a lower thermal expansion coefficient at high temperatures. This is because more β phase was formed in the CoNiCrAl-12 alloy, resulting in a reduced thermal expansion coefficient.

Infiltration of aluminum in 3D‐printed metallic inserts

AbstractAluminum structural composites through the infiltration process can be performed by vacuum, centrifugal, or squeeze casting, involving the infiltration of molten Al into fibers, particles, foams, or even porous preforms. This methodology creates hybrid structures of two distinct metal alloys that can be used to locally strengthen components or even to improve the properties of bulk materials, such as ultimate tensile strength and thermal conductivity. New approaches involve the infiltration of liquid Al into a three‐dimensional (3D)‐printed structure of the more rigid metal, such as steel, that the Al matrix. In the current study, stainless steel and copper inserts were produced by fused filament fabrication techniques with various geometries. Moreover, some 3D inserts were electrochemically coated with pure copper to enhance the wettability of the steel insert by Al. Then, the infiltration of these inserts was evaluated by gravity casting, centrifugal casting, and low‐pressure sand casting (LPSC). Evaluations involved microstructural characterization using optical microscopy and SEM for interface analysis. It is revealed that centrifugal casting is highly reliable to infiltrate the inserts with Al, filling detailed cavities in depth. The copper coating aided in the creation of intimate interfaces. The infiltration at the insert's surfaces, curved‐like topography, is obtained through LPSC though it is affected by the direction in respect of material flow.