Powder Mixtures Research Articles

Microstructural evolution and mechanical behavior of WC–4wt.%TiC–3wt.%TaC–12wt.%Co refractory cermet consolidated by spark plasma sintering of mechanically activated powder mixtures

The paper studied the structural features and physicomechanical properties of the WC–4wt.%TiC–3wt.%TaC–12wt.%Co composite refractory hard alloy system obtained by spark plasma sintering (SPS) from a preliminarily mechanically activated powder. It has been shown that preliminary mechanical activation in a planetary mill contributed to the comminution of agglomerates and the formation of a monomodal particle size distribution with a predominance of the submicron fraction, which intensifies the densification processes during subsequent consolidation by the SPS method. Kinetic analysis of the SPS process showed a two-stage sintering pattern with intense densification at temperatures above 790 °C due to rearrangement of WC, TiC, TaC particles and melting of the cobalt binder. It has been found that the SPS method does not lead to the formation of undesirable secondary phases in the entire sintering temperature range. A sintering temperature of 1200 °C is optimal for achieving the best structural homogeneity, density and mechanical properties, providing optimal distribution of carbide phases and the cobalt binder. The microstructure of the sample obtained at 1200 °C represents a refractory skeleton of WC grains with TiC and TaC carbide particles uniformly distributed throughout the volume. Improved fluidity of the melted cobalt binder and its mobile redistribution contribute to increased compactness of the structure and reduced porosity of the material. Samples sintered at 1200 °C possess high physicomechanical characteristics: relative density 99.99 %, hardness HV30 1623.2, bending strength 1125.1 MPa, fracture toughness 10.5 MN⋅m1/2. The abrasive wear resistance of a newly synthesized hard material was evaluated through a turning operation. Results showed durability, indicating promise for cutting tool applications and the need for further research to fully characterize the performance of this novel material.

Characterization of ZnWO4, MgWO4, and CaWO4 Ceramics Synthesized in the Field of a Powerful Radiation Flux

This paper presents the results of a study on the morphology, structure, and luminescent properties of ceramics synthesized in the radiation field of MeWO4 compositions (where Me is Mg, Ca, and Zn). The synthesis of ceramics was carried out by the direct action of the electron flux on an initial mixture of powders of the given stoichiometric composition. WO3, ZnO, MgO, and CaO powders with particle sizes in the range of 1–50 microns were used for the synthesis of the samples. It was found that the yield of the radiation synthesis reaction (the ratio of the mass of the sample and the charge used), when treated with an electron flux with an energy of 1.4 MeV and a flux power density of 15–18 kW/cm2, was in the range of 75–99%. The synthesis of all compositions was carried out under the same radiation treatment modes, although the melting temperatures of the starting materials varied significantly and ranged from 1473 °C (WO3) to 2825 °C (MgO). The study of the ceramic structure showed that under the radiation effect of powerful radiation fluxes on the charge, a crystalline phase of the appropriate composition formed, regardless of the synthesis modes. The results of XRD studies show that during the radiation treatment of the charge, ceramics are formed mainly with the crystalline phases ZnWO4, MgWO4, and CaWO4. These resulting MeWO4 ceramics can be used for the same purposes as crystals. Photoluminescence (PL) and cathodoluminescence (CL) were studied under excitation using stationary ultraviolet radiation and nanosecond pulses of electron flux. In general, the PL and CL of synthesized ceramic samples ZnWO4, MgWO4, and CaWO4 showed that their luminescent properties are similar to those of luminescence in corresponding crystalline materials. This indicates the formation of a crystalline phase in synthesized ceramic samples.

Spark plasma sintering of hard wear‐resistant graphene nanoplatelet–reinforced TiB2 + SiC composites from TiC–B4C–SiC

AbstractGraphene nanoplatelet (GNP)–reinforced TiB2 + SiC composites were fabricated by reactive spark plasma sintering (SPS) from a TiC–B4C–SiC powder mixture with equal‐volume percentages, optimizing their SPS temperature and evaluating their unlubricated sliding wear against diamond. First, it is shown that during the heating ramp of the SPS cycle, TiC and B4C react according to the chemical reaction 2TiC + B4C → 2TiB2 + 3C, and that the thus‐formed C is graphenized as GNPs, leading to composites with microstructures consisting of a ceramic matrix of fine TiB2 and SiC grains with abundant randomly oriented GNPs at grain boundaries. It is also shown that this reactive SPS is optimal at 2000°C (under 75 MPa pressure and 5 min soaking), resulting in a very hard (∼28.5–29.9 GPa) and very tough (∼6.7(3) MPa m1/2) composite. And second, it is shown that these two properties and its proneness to develop an oxide tribolayer make this composite very resistant to unlubricated sliding wear against diamond (∼2.8(1)·108 (N m)/mm3), undergoing only very mild two‐body abrasion. Finally, opportunities for the fabrication of toughened and very hard ceramic composites for contact‐mechanical and tribological applications are discussed.

Influence of Chinese herbal plants on greenhouse gas emissions from pig manure composting and fermentation

To reduce greenhouse gas emissions during the composting of animal manure and promote the resource utilization of Chinese herbal plants, experiments on pig manure composting were conducted in a plastic greenhouse. A mixture of herbal powders (Radix isatidis and Radix Polygoni Multiflori, mixed in a 1:1 ratio) was added to the pig manure at concentrations of 0.05%, 0.1%, and 0.5% (w/w), respectively. The results showed that the emission peaks of greenhouse gases occurred in the early stages of composting. The addition of 0.5% of a mixture of Chinese herbal plant powders resulted in a significant reduction in cumulative emissions of CO2 (45.0%) and N2O (60.0%) compared to the control. This treatment also resulted in the lowest global warming potential, measured at 91.3 g kg−1, and significantly increased the germination index. The study concluded that adding 0.5% Chinese herbal plant powder to compost effectively mitigated greenhouse gas emissions during the composting process.

Smartphone video imaging: A versatile, low-cost technology for food authentication

This study presents a low-cost smartphone-based imaging technique called smartphone video imaging (SVI) to capture short videos of samples that are illuminated by a colour-changing screen. Assisted by artificial intelligence, the study develops new capabilities to make SVI a versatile imaging technique such as the hyperspectral imaging (HSI). SVI enables classification of samples with heterogeneous contents, spatial representation of analyte contents and reconstruction of hyperspectral images from videos. When integrated with a residual neural network, SVI outperforms traditional computer vision methods for ginseng classification. Moreover, the technique effectively maps the spatial distribution of saffron purity in powder mixtures with predictive performance that is comparable to that of HSI. In addition, SVI combined with the U-Net deep learning module can produce high-quality images that closely resemble the target images acquired by HSI. These results suggest that SVI can serve as a consumer-oriented solution for food authentication.

Microstructures and Mechanical Properties of TiC/Al–Si–Fe Composite with Ti–C Powder Mixture Prepared by Contact Reaction Method

Microstructures and Mechanical Properties of TiC/Al–Si–Fe Composite with Ti–C Powder Mixture Prepared by Contact Reaction Method

An interaction-based mixing model for predicting porosity and tensile strength of directly compressed ternary blends of pharmaceutical powders

Predicting the mechanical properties of powder mixtures without extensive experimentation is important for model driven design in solid dosage form manufacture. Here, a new binary interaction-based model is proposed for predicting the compressibility and compactability of directly compressed pharmaceutical powder mixtures based on the mixture composition. The model is validated using blends of MCC, lactose and paracetamol or ibuprofen. Both compressibility and compactability profiles are predicted well for a variety of blend compositions of ternary mixtures for the two formulations. The model performs well over a wide range of compositions for both blends and better than either an ideal mixing model or a ternary interaction model. A design of experiments which reduces the amount of API required for fitting the model parameters for a new formulation is proposed to reduce amount of API required. The design requires only three blends containing API. The model gives similar performance to the well-known Reynolds et al. model (2017) when trained using the same data sets. The binary interaction model approach is generalizable to other powder mixture properties. The model presented in this work is limited to curve-fitting of empirical compaction models for mixtures of common pharmaceutical powders and is not intended to provide guidance on the practical operating space (or design space) limits.

Reactive sintering of coaxial Yb3+:YAG/YAG transparent ceramics

15 at.% Yb3+:YAG/YAG transparent composite ceramics with a coaxial geometry were synthesized by a ceramic forming method combined with the reactive sintering at 1800 °C. Densification peculiarities, microstructure, optical properties, and laser characteristics of composite ceramic samples were studied. Powder mixtures of Yb3+:YAG and YAG stoichiometric compositions demonstrate almost the same densification enabling uniform shrinkage of composite without differential sintering. It was shown that in-line optical transmittance of 15 at.% Yb3+:YAG/YAG composite ceramics reaches 80 % at 1030 nm wavelength. The effective diffusion coefficient of Yb3+ ions in garnet structure has been determined. Efficient laser emission was generated from Yb3+:YAG/YAG composite ceramics with a slope efficiency of ηsa = 0.30.

Exploring the Elemental Interactions of Melamine with Binder–Metal Powder Mixtures: A Pathway to Enhanced Catalytic Debinding and Rheological Control

Exploring the Elemental Interactions of Melamine with Binder–Metal Powder Mixtures: A Pathway to Enhanced Catalytic Debinding and Rheological Control

Investigation of microstructure and thermal expansion behaviour of a functionally graded YSZ/IN718 composite produced by laser-powder bed fusion

Yttria-stabilized zirconia (YSZ) has been extensively used as a thermal barrier coating (TBC) for high-temperature alloys. In this research, the microstructural attributes and thermal expansion behavior of an additively manufactured functionally graded composite (YSZ/IN718 FGC) were investigated. First, a powder mixture of IN718 and YSZ (ranging from 1 wt% to 4 wt%) was achieved via low-energy ball-milling at 100 rpm. Differential scanning calorimetry (DSC) analysis depicted the melting behaviour of the powder mixtures of different YSZ content. The endothermic peaks in the DSC curve, at ∼1360 ℃, suggested that the energy needed to melt the powder mixture increases with increasing YSZ content. These varying powder compositions were used to fabricate FGC samples using L-PBF. The study investigated the effects of laser power variation along the YSZ gradient, successfully mitigating the fusion defects that had been initially observed in FGC samples. Microscopic analyses, comprising scanning electron microscopy (SEM) and transmission electron microscopy (TEM), depicted the elemental segregation of Nb and Mo at the solidification subgrain boundaries (SSBs). Furthermore, the electron backscattered diffraction (EBSD) results demonstrated the refinement of grains and a reduction in textural intensity, particularly along the YSZ gradient. Energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA) were used to validate the uniform dispersion of YSZ particles throughout the composite matrix, with the EPMA line scan affirming a predominantly linear YSZ content variation. Lastly, the coefficients of thermal expansion (CTEs) were evaluated, both parallel and perpendicular to the build direction. A decrease of approximately ∼6 % in CTE was noted along the building or gradation direction. Notably, perpendicular to the building direction, the CTE values for specimens containing 4 wt% and 2 wt% YSZ witnessed significant reductions of ∼32 % and ∼12 %, respectively. This research significantly contributes to the understanding of the microstructural intricacies and thermal behavior of YSZ/IN718 FGC produced by L-PBF process.

Simulation of Electrical Conductivity of Porous Composite Electrodes for Solid Oxide Cells Using a Monte Carlo 3D Equivalent Electronic Circuit Networks

Solid oxide cells (SOCs) show high potential in energy conversion applications necessary for the decarbonization of the economy. Their advantage consists in ability to operate at high temperatures, reaching up to 900 °C. Firstly, it results in accelerated electrode reactions kinetics, secondly, in favorable thermodynamic conditions decreasing the equilibrium voltage of the water splitting. As a result, SOCs are attractive candidates for both efficient electrolysis and fuel cell applications, offering a robust solution in the pursuit of clean energy. However, the elevated operational temperature also introduces material challenges that hinder the competitiveness of SOCs.Porous gas diffusion electrodes are used to accomplish the desired electrode reactions. Considering conventional exclusively electron-conductive electrode materials, triple phase boundary (TPB) is required for the reactions to take place – a simultaneous contact of electron-conductive, ion-conductive and gaseous phase. While the electrode and electrolyte phases are solid, the gaseous phase is represented by open porosity in the electrode body. TPB is located exclusively at the contact area of electrode and electrolyte components in the case of single-phase electrodes, limiting the electrode electrocatalytic performance. To avoid the limitation by TPB length, composite electrodes are frequently used. Due to the involvement of the ionically conductive phase, they exhibit improved electrocatalytic capabilities.Electrolyte phase, however, usually exhibits 4 orders of magnitude lower electrical conductivity than the electron-conductive phase, while gaseous phase is electrically non-conductive. Thus, an improper phase composition and morphology of the composites can lead to a significant drop in their electrical conductivity and thus in the cell performance. Simple and reliable method for the conductivity value prediction is up to now missing. At the same time, experimental determination is both expensive and time-consuming. The goal of this study was to develop simple, fast and reliable method for prediction of electrical conductivity of the porous electron-ion conductor composites.The key feature of the presented approach lies in the minimal requirements for input parameters. Only electrode phase composition and bulk electrical conductivity of each phase are required. Based on the input composition, the model generates a 3D artificial specimen, a domain discretized into cubic voxels each assigned randomly to a specific phase. The resulting structure is substituted with an equivalent circuit network with electric elements corresponding to the electrochemical properties of the material components: specific resistivity of electrical conductors and polarization resistance / capacitance of electrochemical reaction at material interface. In-silica electrochemical impedance spectroscopy measurement is performed by solving charge balance following Kirchhoff’s current law for multiple frequency values. Resulting impedance spectrum is fitted in order to obtain Ohmic and polarization resistance and the capacitance of the artificial specimen. This procedure is averaged over a large number of artificial specimens in a Monte Carlo manner.Conventionally used oxygen electrode composite material lanthanum strontium manganite (LSM) mixed with yttria-stabilized zirconia (YSZ) was used to produce validation dataset. LSM:YSZ powder mixtures of compositions between 1:0 and 0:1, chosen to produce samples of various degree of LSM percolation, were homogenized. The mixtures were fired at 1150 °C. Electrical conductivity of the pellets was determined at temperatures between 600 and 800 °C using electrochemical impedance spectroscopy.Experimental data obtained were confronted to the model results. The model demonstrated very good accuracy for a porosity value of up to 55%. Significant error was observed in the porosity range between 55% and 68%. Finally, the model failed to generate an artificial specimen with a porosity of 75%. As it was found, the limited applicability of the model for the materials characteristic for high porosity was caused by the coalescence of the void phase. This shortcoming of the model was solved by implementing morphological parameter describing degree of void phase coalescence in the electrode structure. Due to this modification, model allows to gain valuable information on the microstructure of the studied composite material on the base of the experimentally determined conductivity data.This work introduces a novel modelling approach with minimal amount of input parameters, streamlining the prediction of electrical conductivity of porous electron-ion conductor composites. This simplified yet effective methodology holds great promise for efficiently characterizing and optimizing materials for energy conversion applications, offering a valuable tool for advancing research in the field.This publication was supported by the project "The Energy Conversion and Storage", funded as project No. CZ.02.01.01/00/22_008/0004617 by Programme Johannes Amos Commenius, call Excellent Research.

Thermally Sprayed Coatings for the Protection of Industrial Fan Blades.

This paper presents a study on thermally sprayed coatings. Coatings produced by high-velocity oxygen-fuel spraying HVOF and plasma spraying deposited on the A03590 aluminum casting alloy are tested. The subject of this research concerns coatings based on tungsten carbide WC, chromium carbide Cr3C2, composite coatings NiCrSiB + 2.5%Fe + 2.5%Cr, mixtures of tungsten and chromium powders WC-CrC-Ni, mixtures of carbide powders with the Cr3C2-NiCr + the composite 5% NiCrBSi and WC-Co + 5% NiCrBSi. The aim of this research is to find a coating most resistant to the erosive impact of particles contained in the medium centrifuged by industrial rotors. The suitability of the coating is determined by its high level of microhardness. The hardest coatings are selected from the coatings tested and subjected to abrasion tests against a sand particle impact jet and the centrifugation of a medium with corundum particles. It is found that the most favorable anti-erosion properties are demonstrated by a coating composed of a mixture of tungsten carbide and chromium carbide WC-CrC-Ni powders. It is concluded that the greatest resistance of this coating to the erosive impact of the particle jet results from the synergistic enhancement of the most favorable features of both cermets.

Achieving efficient hardfacing on stainless steel using single SiC powder in laser directed energy deposition

Generally, in a laser hardfacing process, a mixture of ceramic and metal powder is used to clad a hard surface, resulting in enhanced wear characteristics of metal parts. This study proposes an efficient hardfacing process that uses a single and minimal amount of ceramic powder (0.079 g/min in this work). This process, named as Laser Directed Energy Deposition of Minimal Ceramic Powder (LDED-MCP), features that the melt pool is generated inwardly because only the substrate participates in forming the melt pool. Furthermore, due to the minimal powder flow rate used and sparse particle-melt pool collision events, ripple formations leading to the convective melt pool flow and inhomogeneous microstructures would be suppressed. Consequently, the produced layer is nearly flat and free of incompletely melted metallic particles, thus minimizing post-machining. For a 316 L substrate and SiC powder material combination, a crack-free layer about 560 μm thick with an average hardness of about 417 HV was created through process parameter optimization. This layer showed a eutectic structure composed of γ-austenite and chromium carbides, partially melted SiC particles between dendrites, and in-situ synthesized SiC nanoparticles decorating the cell walls. Through this work, near-net-shape hardfacing of stainless steels is realized through LDED-MCP process minimizing powder pre-processing and post surface machining.

How Does the Powder Mixture of Ibuprofen and Caffeine Attenuate the Solubility of Ibuprofen? Comparative Study for the Xanthine Derivatives to Recognize Their Intermolecular Interactions Using Fourier-Transform Infrared (FTIR) Spectra, Differential Scanning Calorimetry (DSC), and X-ray Powder Diffractometry (XRPD).

Molecular interactions between active pharmaceutical ingredients (APIs) and xanthine (XAT) derivatives were analyzed using singular value decomposition (SVD). XAT derivatives were mixed with equimolar amounts of ibuprofen (IBP) and diclofenac (DCF), and their dissolution behaviors were measured using high-performance liquid chromatography. The solubility of IBP decreased in mixtures with caffeine (CFN) and theophylline (TPH), whereas that of DCF increased in mixtures with CFN and TPH. No significant differences were observed between the mixtures of theobromine (TBR) or XAT with IBP and DCF. Mixtures with various molar ratios were analyzed using differential scanning calorimetry, X-ray powder diffraction, and Fourier-transform infrared spectroscopy to further explore these interactions. The results were subjected to SVD. This analysis provides valuable insights into the differences in interaction strength and predicted interaction sites between XAT derivatives and APIs based on the combinations that form mixtures. The results also showed the impact of the XAT derivatives on the dissolution behavior of IBP and DCF. Although IBP and DCF were found to form intermolecular interactions with CFN and TPH, these effects resulted in a reduction of the solubility of IBP and an increase in the solubility of DCF. The current approach has the potential to predict various interactions that may occur in different combinations, thereby contributing to a better understanding of the impact of health supplements on pharmaceuticals.

Phase transformation mechanisms occurring during spark plasma sintering elaboration of new duplex composite stainless steels

This study focuses on the elaboration of duplex stainless steels (DSS) from powder mixtures using spark plasma sintering (SPS). Different mass fractions of an austenitic 316L powder and a ferritic 410L one were blended and then sintered by SPS. Microstructural characterizations of the sintered samples obtained from different powder mixtures were performed. They were coupled with marking experiments of the powder particles’ surface. The results showed the formation of martensite within the ferritic powder and at the austenite/ferrite interfaces, following two different mechanisms. In addition, it was found that the width of the martensitic regions is mainly influenced by the diffusion of Cr and Ni from the austenitic to the ferritic powder during sintering. The characterizations revealed that the originality of this approach lies in the particular microstructure obtained after sintering. The characteristic size of the ferritic and austenitic domains in the final material is that of the initial powder particles (up to some hundred microns). Moreover, each domain is formed by equiaxed and isotropic grains, having a size ranging from some microns to some tens of microns. This particular microstructure justifies the use of the term “composite duplex stainless steels” (COMPLEX) for this kind of new DSS.

Study of magnetic phase transitions by helium-3 in DyF3 nanoparticles

The spin kinetics of liquid 3He in contact with a mixture of LaF3 (99.7 %) and DyF3 (0.3 %) powders at temperatures of 1.5–3 K was studied by pulsed nuclear magnetic resonance. DyF3 particles have ellipsoidal shape and average size 225 × 153 nm with the magnetic phase transition at temperature Tc = 2.45 K. The temperature dependence of the longitudinal and transverse magnetization relaxation rates of 3He nuclei with a mixture of LaF3 and DyF3 powders has a broad maximum near Tc, which is related to the magnetic phase transition. It is shown that the adsorbed layer of 3He is extremely sensitive to magnetic phase transitions. Preplating the particles surface with adsorbed nitrogen layers allowed to vary the distance from 3He nuclei to the surface of particles in a controlled way. Calculations of the nuclear magnetic relaxation rates with a change in the distance of helium-3 from the particle surface have been carried out, which is in good agreement with experimental data. It was shown that helium-3 is extremely sensitive to surface magnetism and can be used to study surface effects and surface magnetism.

Solution of the plane problem of thermoelasticity with variable properties with a new variant of the derivation of equations in stresses

The interaction of thermal and mechanical fields in modern technologies for the synthesis and processing of materials attracts more and more attention. This is due to the need to predict the behavior and properties of new materials and products depending on the conditions of their creation. In the present work, attention is focused on the comparison of the solutions to the thermoelasticity plane problems with and without accounting for the temperature dependence of the material properties. It is assumed that an external heat source traveling over the surface with a specific velocity and following a given trajectory is responsible for a significant temperature increase. It may correspond to a laser source, for example. The new way of problem formulation in stresses is used. The temperature dependence of the characteristics leads to nonlinear thermoelasticity equations when the equilibrium equations, the requirement of strain compatibility, and the Duhamel-Neuman relation for the plane stress state case are combined. To determine the temperature field, a nonlinear thermal conductivity equation is used. To solve the problem numerically, the use of an implicit finite-difference scheme and coordinate splitting for the thermal conductivity equation and the finite-difference method of successive over-relaxation with Chebyshev acceleration for the equations for stresses was made. As a result, the difference in the solution of linear and nonlinear problems is demonstrated for the considered cases. Using the example of a mixture of titanium and aluminum powders, numerical modeling demonstrated that some stress components can reach values up to 3.5 times higher than those obtained in the case of temperature-independent material properties when there is a 500-degree local temperature increase.

Fabrication of boron carbide ceramics reinforced with silicon carbide fibers

In the present study, the boron carbide ceramics reinforced with silicon carbide fibers (B4C-SiCf) were fabricated by incorporating various contents of SiCf ranging from 2.5 to 10 wt%. The B4C-SiCf powder mixtures were sintered using the Field Assisted Sintering Technique (FAST), also known as Spark Plasma Sintering (SPS), at temperatures of 1800 °C and 2000 °C for 5 min by applying a pressure of 70 MPa in argon atmosphere, while heating and cooling rates were maintained at 100 °C/min and 50 °C/min, respectively. The influence of the initial powder ratio on the sintering behavior, relative density, microstructural development, and mechanical properties of the obtained B4C-SiCf composites was investigated. The results indicated that the sintered ceramic materials contained only the initial compounds, i.e. B4C and SiC phases. Scanning Electron Microscopy (SEM) showed that the sintered composites consisted of densely compacted B4C grains. The highest relative density (>99 %) was achieved for the sample with 95 wt%B4C and 5 wt%SiCf, sintered at 2000 °C. Depending on the constituent content and the densification temperature the obtained composites demonstrated hardness values ranging from 29 to 43 GPa. The maximal hardness was attained in the composite with 95 wt%B4C sintered at 2000 °C. To assess the performance of the composites under extreme conditions, the ablation resistance was evaluated using a flowing oxyacetylene torch test. The material containing 5 wt%SiCf exhibited superior ablation resistance when compared to the other compositions. The attained results of this study showed that the SPS technique is a highly effective method for the densification of additive-free B4C-SiCf ceramic composites, showcasing promising properties for applications in extreme environments.

Complex-shaped titanium components fabricated via metal injection molding using hydride-dehydride titanium powder

Metal injection molding (MIM) is a net-shape manufacturing method that lessens the costs of production and increases the affordability of titanium goods. A range of CP-Ti specimens was prepared to confirm the primary manufacturing parameters for titanium metal injection molding utilizing affordable hydride-dehydride (HDH) powders. Mixture of powder and polyformaldehyde-based binder was injection molded, debonded, and then sintered. The optimum powder loading is 55 vol%. The ideal conditions of catalytic debinding were attained by placing the specimens in the catalytic debinding system at 120 °C temperature. Samples with minimal deformation and low impurity content were obtained when thermal debinding was carried out at a modest heating rate of 1.0 K/min and a holding time of 1.5 h. All the sintered samples have a similar microstructure, that is, lamellar α + β structure. The sample exhibits a strength of 739 MPa and an elongation of 6.1 % at the optimum sintering conditions (sintering at 1250 °C for 2 h). The samples prepared by MIM have excellent wear resistance. This process provided a straightforward and cost-effective means of producing complex-shaped titanium components from HDH Ti powder.

Behavior of free-standing atmospheric plasma sprayed Al2O3–Cr2O3 solid solution-based coatings under cyclic heating at 1000 °C

This paper investigates the cyclic heating behavior of free-standing atmospheric plasma sprayed Al2O3 - Cr2O3 coatings containing a solid-solution phase. The coatings are deposited on steels by spraying mechanically blended Al2O3 - Cr2O3 powder mixture with variable Cr2O3 content (2–6 wt%) in the feedstock. The tests are performed up to 50 cycles at 1000 °C temperature in a muffle furnace in a normal atmosphere. After each cycle, the weight gain of the coatings is measured, and the oxidation rate constant (Kp) for each material is estimated. The microstructure and phases of the coatings are studied by using scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques respectively. The porosity and crack length are estimated by image analysis (Image J) technique. The hardness of the coatings is measured by Vickers microhardness tester. After 50 cycles, all the free-standing coatings are found to be intact without fragmentation. At higher cycles, the Al2O3 - Cr2O3 coatings form α-Al2O3 and (Al0.9Cr0.1)2O3 solid-solution phase only. The Al2O3 - Cr2O3 coatings gain much less weight than the pure Al2O3 coating due to the major presence of oxidation resistant α-Al2O3 phase in the former. However, among the Al2O3 - Cr2O3 coatings with an increase in Cr2O3 content, the Kp value tends to increase due to the high presence of metastable (Al1.8Cr0.05)2O3 solid-solution phase. On the other hand, the (AlxCr1-x)2O3 phase helps to reduce crack formation due to its high fracture toughness properties. With the highest amount of solid-solution phase content, the Al2O3-4 wt% Cr2O3 coating shows the highest fracture toughness among all. The micro-porosity of the coatings is increased with an increase in the heating cycle, and the coating hardness is reduced accordingly.