Heating Sintering Research Articles

Evaluation of high-frequency induction heat sintering and conventional sintering in AlxCoCrFeMnNi high-entropy alloys

AlxCoCrFeMnNi high-entropy alloys with different aluminum concentrations (x = 0.5, 1, and 1.5 at%) were synthesized by mechanical alloying followed by consolidation using two different sintering methods, conventional (CS) and high-frequency induction heat + conventional (HFIHS + CS). The results show the presence of FCC, BCC, and B2ordered phases in all systems, regardless of the sintering method. The BCC phase exhibits morphological changes (cuboidal-type and plate-like) associated with the two sintering methods involving different diffusion rates and affecting the hardness values. The M23C6 carbide is identified in systems sintered by the CS method; meanwhile, the M7C3 carbide is identified in the HFIHS + CS method. Finally, the HFIHS + CS method results in a higher level of densification (~95%) than the CS method (~80%).

Synthesis of Ni-Cu Heterostructures with SPS to Achieve a Balance of Strength and Plasticity

The balance between strength and plasticity has always been an urgent problem for researchers to solve. In this experiment, Ni-Cu heterostructures (HSs) were synthesized by spark plasma sintering (SPS), rolling deformation, and subsequent heat treatment. The density of the Ni/Cu interface of Ni-Cu HS materials can be independently tuned, and thus the effect of hetero-deformation-induced (HDI) strengthening in Ni-Cu heterostructures can be tuned. The density of the Ni/Cu interface is tuned by adding Cu with different volume fractions to obtain the best combination of strength and plasticity. Compared with the previous HSs, the hardness differences between different regions of Ni-Cu HSs are more significant, and they are all composed of single substances. The hard Ni domain and the soft Cu domain are not only different in phase composition but also different in grain size. More interestingly, the density of the hard/soft domains can be adjusted independently, which provides a new way to explore the strength and plasticity balance of HS materials. The yield strength of Ni-Cu HS materials first increases and then decreases gradually with the increase in the Cu volume fraction. When the Cu volume fraction is less than 30%, the HDI strengthening effect in the Ni-Cu HS material can offset the effect of the yield strength reduction caused by Cu; with a further increase in the Cu volume fraction, the HDI strengthening effect is less than the yield strength reduction effect brought on by Cu.

Vat photopolymerization of low-titanium lunar regolith simulant for optimal mechanical performance

Recently additive manufacturing of lunar regolith to utilize in-situ resources of the Moon for deep space exploration has attracted attention. However, most previous works have been limited by low precision, inferior mechanical properties, and complex processes, such as ball grinding. Furthermore, the regional distribution difference of the lunar regolith which shows compositional diversity, demands the exploration of manufacturing of low-titanium lunar soil, which has not been comprehensively studied before. Herein, the vat photopolymerization and heat treatment of raw low-titanium lunar regolith simulant were investigated to achieve high dimensional precision and high mechanical properties. The influence of solid content and photoinitiator concentration on printability is carefully examined based on the characterization of rheological behaviors and curing depth. Then the vat photopolymerization is used to build green bodies with good interlayer bonding strength and high dimensional precision. Besides this, the effect of the debinding heating rate and sintering temperature on samples were optimized in air and nitrogen to enhance the mechanical properties of printed samples. Finally, the optimal sintered parts with a flexural strength of 108.8 MPa and compressive strength of 222.8 MPa were obtained.

Development and performance study of biomedical porous zinc scaffold manufactured by using additive manufacturing and microwave sintering

ABSTRACT Zinc (Zn) and its alloys are gaining popularity day by day in biomedical applications due to their acceptable biocompatibility and moderate degradation rate than magnesium and iron. However, the fabrication procedure for the metallic scaffold is still a challenging task. Hence, the present study aims to establish a new manufacturing route for fabricating Zn scaffold utilizing 3D printing and microwave sintering. The Central composite design (CCD) methodology was used to investigate the influence of sintering parameters like sintering temperature (St), heating rate (Hr), and soaking duration (Sd) on the compressive strength (C.S) & sintered density (S.D) values of the fabricated sample. It was found that the value of C.S and S.D increased with an increase in soaking duration and heating rate. Similar to Hr and Sd, C.S and S.D values increased with increasing sintering temperature, but the values of both properties declined after a critical temperature. Multi-objective optimization was performed utilizing Genetic algorithm (GA) methodology, a tool of MATLAB to obtain the optimum values of process input factors for maximum C.S (18.6MPa) and S.D (6.79 gm/cm3). In the end, a comparative study of the Zn scaffold was performed to evaluate the performance of developed fabrication method, and results were found satisfactory.

Balancing the strength and ductility of Ti2AlC/TiAl composite with a bioinspired micro-nano laminated architecture

In this work, the Ti, Al and graphene flake powders were used as raw materials, and a Ti2AlC/TiAl composite with the bioinspired micro-nano laminated architecture was successfully fabricated by spark plasma sintering and subsequent heat treatment. The as-fabricated composite mainly consists of the micro-laminated Ti2AlC with the length of 300 μm and thickness of 15 μm, the micro-nano γ-TiAl/α2-Ti3Al lamellar colony with the average lamellar spacing of 0.8 μm, and the nano-laminated Ti2AlC with the thickness of 10 nm. It was found that the composite possesses a good combination of compressive strength (1807 MPa) and ductility (25.5%) at room temperature due to its multiple plastic deformation features: i) dislocations and atomic-scale ripples could be easily nucleated on the (0001) basal plane of the micro-laminated Ti2AlC; ii) the micro-laminated Ti2AlC/TiAl interface could be the nucleation source for the dislocation and deformation twins; iii) high-density deformation twins could be formed in the γ-TiAl phase of γ-TiAl/α2-Ti3Al lamellar colony; iv) the pyramidal dislocation could be generated in the nano-laminated Ti2AlC. The aim of this work is to enrich the current understanding on the deformation behavior of TiAl matrix composites and open up a novel design direction for high-performance TiAl matrix composites.

In situ TEM observation of the microstructure characteristics of the vacuum sintering, sub-zero and heat treatments of Vanadis 23 high-speed steel by adding Cr3C2–TaC–TiC powders

ABSTRACT This research added different ratios of chromium carbides, tantalum carbide, and titanium carbide powders to Vanadis 23 high-speed steel powders. The composite powders utilised vacuum sintering at 1230, 1245, 1260, and 1275°C for 1 h, respectively, and the experimental results show that good mechanical properties were obtained by the addition of 0.6 mass% Cr3C2–0.2 mass% TaC–0.2 mass% TiC sintered at 1245°C for 1 h. Meanwhile, the apparent porosity was decreased to 0.23%, and the transverse rupture strength and hardness reached 2470.7 MPa and 78.5 HRA, respectively. When optimally sintered Vanadis 23 composites (0.2 T) underwent a series of heat treatments, the transverse rupture strength and hardness values were obviously enhanced to 2693.6 MPa and 84.0 HRA after quenching, and sub-zero and tempering treatments. The EBSD and TEM results confirm that the MC, M 6C, M 7C3, and M 23C6-type carbides appeared in the 0.2 T specimen after vacuum sintering and sub-zero heat treatments.

Sintering behaviors and thermal properties of Li2SiO3-based ceramics for LTCC applications

A series of new Li2SiO3+4 wt% Al2O3-xK2O–B2O3–SiO2 (x = 1–4 wt%) LTCC materials were prepared by standard traditional solid-state method and their bulk density, microstructure and crystalline phase composition were shown in detail. The sintering behavior, heat conduction and thermal expansion of the samples were all thoroughly studied. And their microwave dielectric properties were also demonstrated. The bulk density of the samples was enhanced with the addition of 3 wt% KBS glass, and the sintering temperature was reduced from 1020 °C to 900 °C. Meanwhile, the thermal diffusivity of the samples was determined using the LFA447 laser flash apparatus and the specific heat was calculated, according to the results of thermal diffusivity and specific heat, all samples possessed high thermal conductivity ranging from 5.5 ± 0.02 W/mK to 8.6 ± 0.08 W/mK. Furthermore, the attractive flexural strength and average coefficient of thermal expansion reach to 270 MPa and 15.7 × 10−6/K (at 100 °C), respectively. The reduction of the sintering temperature is attributed to the addition of KBS glass which reduces the crystallization activation energy of the samples. Besides, increasing bulk density can substantially reduce pores in the grain boundary, which has great effects on phonon scattering, improving the thermal conductivity.

Microstructure and properties of WC-12Co cemented carbide fabricated via selective electron beam melting

In this study, we investigated the microstructure, mechanical and wear properties of WC-12Co cemented carbides fabricated via selective electron beam melting (SEBM). Subsequently, some of the samples were treated with vacuum sintering heat treatment at 1400 °C at 5 MPa under argon. Apart from the WC and Co phases, the Co3W3C phase was found in the SEBM-fabricated cemented carbides. After heat treatment, WC grain growth and the Co6W6C phase appeared. Interestingly, η phase content decreased after heat treatment. The longitudinal section of the samples exhibited a layered structure, which was interlaced with coarse and fine WC. A compressive strength value of 1839 MPa was achieved after heat treatment, while the compressive strength without heat treatment was 1770 MPa. The nanoindentation test showed that the microhardness of the heat-treated samples decreased compared to the SEBM- fabricated sample (18.92 GPa). The SEBM-fabricated WC-12Co cemented carbides had an average friction coefficient of 0.548 and a wear rate of 0.0055 mm3, which increased by 59.7% and 142% in the samples after heat treatment.

Effect of vacuum heat treatment on microstructure evolution and mechanical properties of 93W-4.9Ni-2.1Fe-(ZrB2) alloys

93W-4.9Ni-2.1Fe-(0.75ZrB2) alloys (wt%) were subjected to liquid phase sintering and vacuum heat treatment to optimize the microstructure and improve mechanical performance. Microstructural observations demonstrated that W–W continuity, dihedral angle and connectivity after heat-treatment remarkably decreased by 0.75, 10° and 0.7, respectively. Meanwhile, matrix phase volume fraction also increased by nearly 3%, which overcame the negative effects of non-homogeneous microstructure. However, densification and W grain size exhibited marginal changes. Mechanical properties strongly varied with the change of microstructural characteristics. Particularly, as matrix phase volume fraction increased and W–W contiguity decreased dramatically, elongation showed a distinct increasing tendency (from 18.6% to 22.4% in 93W alloys and from 17.5% to 19.5% in 93W-0.75ZrB2 alloys, respectively). Excellent W-matrix bonding strength improved the tensile property, while microstructure uniformity caused the decrease of hardness value (about 28 HV1). Furthermore, the relationship between mechanical properties and fracture mode was analyzed.

Adhesive wear performance of self-lubricating functionally graded cemented tungsten carbide prepared by spark plasma sintering

In order to encourage environment friendly manufacturing, dry machining is extensively explored and acknowledged. Consequently Functionally Graded Cemented Tungsten Carbide (FGCC) with solid lubricant was prepared by Spark Plasma Sintering at different heating rate and sintering temperature. The wear behavior of developed materials was explored by pin-on-disc tribological tests and dry machining. The attempts were made to analyze effect of key test parameters (such as load, ambient temperature, and sliding velocity) and solid lubricant over tribological behavior. The presence of solid lubricant resulted in reduced coefficient of friction (COF) and wear. The ambient temperature and load were displayed most significant influence over wear and COF respectively. Also samples prepared at high sintering temperature as well as heating rate demonstrated lower wear and COF. Additionally, the primary failure mechanism was identified as binder removal. These tribological examinations confirmed the suitability of self-lubricating FGCC as a cutting tool material for dry machining.

High-strength and tough bioactive Mg-doped hydroxyapatite bioceramics with oriented microchannels

Mg-doped hydroxyapatite (MH) with oriented microchannels was prepared by hot-pressing sintering and pore-forming heat treatment using continuous carbon fibres (CFs) as the pore-forming agent to achieve balanced mechanical and biological properties. The proportion of MH and (Ca, Mg)3(PO4)2 in the microporous bioceramic with inter-microchannel spacing of 400 μm obtained by sintering at 900 °C (900-2P-MH) was 43.9/56.1 (wt%), which could promote degradation. The compressive strength of the MH bioceramics containing oriented microchannels with a suitable pore size (5–14 μm) did not decrease, but increased in comparison with that of a dense MH sample without microchannels. In particular, the compression strength of the MH bioceramic with oriented microchannels formed using single CF units was 53.31% higher than that of the dense ones. The fracture toughness of the MH bioceramics with oriented microchannels increased to 177.42% of that of the dense ones. The strengthening and toughening mechanism includes contributions from the combination of heating and pressing, uniform distribution of microchannels, and in situ formation of continuous micro/nano-MH ceramic tubes. Moreover, the microchannel-containing MH showed noticeably improved apatite mineralisation in simulated body fluid (SBF). Analysis of the rat tibial bone defect model revealed that the relative bone volumes in the cases of the dense MH without microchannels and the MH with microchannels increased by 23.18 and 40.14%, respectively, compared with that of hydroxyapatite. Furthermore, the MH bioceramics with oriented microchannels displayed a moderate reduction in strength owing to degradation after 8 weeks of implantation. The satisfactory osteogenic properties and degradability of the microporous bioceramic can be attributed to Mg2+ doping and oriented microchannels.

The improved strength and ductility of ZrCp/2024Al composites with a quasi-network microstructure fabricated by spark plasma sintering and T6 heat treatment

In this study, the 2024Al alloy improved by the various fraction of ZrC particles (ZrCp/2024Al composites) were constructed and processed through the spark plasma sintering (SPS) combined with T6 heat treatment in order to improve the strength and toughness simultaneously. The microstructure observations revealed that the interfacial bond between the ZrC and aluminum matrix was satisfactory and the quasi-network distribution of ZrC particles was demonstrated. The precipitates of Al2Cu and Al2CuMg, dissolved out from the 2024Al and ZrCp/2024Al composite during ageing process, exhibited little different in size and shape. With the introduction of ZrC particles, the ageing behavior was expedited and the time to achieve the aged hardness was prominently shortened from 12 h to 6 h as 5.0 wt% ZrC particles were introduced. The accelerated aging process benefited from dislocations, caused by the mismatch of thermal expansion coefficients between the ZrC and matrix. The ultimate hardness, yield strength, tensile strength and strain were all enhanced with the addition of ZrC particles. When 4.0 wt% ZrC particles were applied to the composites, the highest yield strength, tensile strength with superior ductility (332 MPa, 495 MPa and 12.0%) was obtained, which were 48.2%, 34.5% and 23.7% higher than that of pure 2024Al respectively. The improved tensile strength and strain are contributed to the particularly inhomogeneous quasi-network structure, which made the matrix deformation blocked, dislocation motion impeded and crack propagation path increased.

The effect of TiC on microstructure and mechanical properties of Ti-5553 beta phase titanium alloy

The presence of TiC in Ti alloys is ubiquitous, so, for the interest of exploring its effects, carbon is added in Ti-5553 (beta phase alloy). After fabrication, sintering and multi heat treatments are done to get desired microstructure (TiC in beta, alpha and alpha-matrix). Quasi-static compression, three-point bend test, nano-indentation, and abrasion tests are conducted to study the microstructural response. Different analyzing tools such as SEM, EDS, EBSD, and HRTEM are used to examine microstructural changes before and after fracture. Results showed that TiC crystals are hard and brittle, and favorite sites for crack nucleation and propagation. After comparing both the curves and their corresponding micrographs, it is concluded that the propagation speed of the crack is much faster in TiC as compared to the beta and alpha phases. Furthermore, an increase in the value of strain upon reaching a crack at the TiC/Tiᵦ, and TiC/Tiα interface justifies that these phases offer comparatively more toughness and ductility. In addition, the presence of these crystals in the beta phase initiate fracture almost within half of the elastic limit of Ti-5553 beta phase alloy. Conclusively, TiC has an adverse effect on titanium's mechanical properties if shape and size are not controlled.

Bicontinuous Nanoporous Nitrogen/Carbon-Codoped FeCoNiMg Alloy as a High-Performance Electrode for the Oxygen Evolution Reaction.

The kinetics of the oxygen evolution reaction (OER) in aqueous electrolytes is relatively slow, which seriously limits the energy efficiency of electricity-to-hydrogen conversion. Herein, a bicontinuous nanoporous FeCoNiMg alloy is prepared by high heat sintering method based on the nanoscale Kirkendall effect and the surface is codoped with nitrogen and carbon elements by the nitrocarburizing method (denoted NC-FeCoNiMg). The three-dimensional (3D) nanoporous NC-FeCoNiMg alloy electrode achieves superior electrocatalytic performance for the OER in alkaline media, delivering a low Tafel slope (34.6 mV dec-1) and small overpotentials (235 and 290 mV at 10 and 100 mA cm-2, respectively). Under consecutive high current densities, the NC-FeCoNiMg electrode still exhibits excellent long-term stability, and the OER activity even increases after testing for 100 h at a high current density of 1000 mA cm-2. Comprehensive studies reveal that the N/C codoping of the inner and outer surfaces dramatically improves the electrocatalytic activity of the NC-FeCoNiMg electrode. This work demonstrates an efficient nanoarchitectural construction and a surface modulation strategy to increase the electrocatalytic activity and stability of transition-metal-based electrodes for the OER, holding great promise for fulfilling the requirements for the large-scale production of clean hydrogen energy.

Optimal parameters of microwave sintering process on nickel based composite

Microwave sintering process is the most economical and feasible technique to fabricate composite with superior quality of products. Nickel, aluminium and titanium alloy were reinforced with silicon carbide particles. The different microwave sintering constraints like sintering temperature, heating rate and hold time were considered to fabricate the composite. The fabricated specimens were processed under the evaluation of tensile strength and hardness properties. Taguchi approach was used to optimize the microwave sintering process factor. The parametric effect on tensile strength and hardness were analyzed through contour plot and variance analysis. Tensile strength of 360 MPa was attained at sintering temperature of 1400 °C, holding rate of 20 °C/min and holding time of 80 min. It was observed that sintering temperature has produced 87.01% of effect on tensile strength.

Effect of precipitation hardening on wear behavior of premix Al7075 hybrid matrix composites

Al 7075 alloy is high strength alloy with excellent physical and mechanical properties. Though the alloy has capacity to work as structural material, many a times poor tribological properties limit its applications. Tribological properties can be improved by addition of hard ceramic reinforcement or by adding soft solid lubricants. But this solitary addition shows improvement at the cost of certain mechanical properties.In this study, premix alloy of Al 7075 was fabricated by blending elemental powders followed by Hot Press Sintering (HPS). The optimum operating window for HPS at 550 °C, 40 MPa for 6 min was used to obtain maximum densification. Al 7075–10 wt% B4C (ABC 10) was used as starting material for development of Hybrid Matrix Composites namely (HMC-G) and HMC-M containing solid lubricants viz. Graphite and MoS2 (1 to 5 % by wt.) respectively. Post sintering heat treatment consisting of solutionising at 480 °C followed by artificially ageing at 120 °C for 24 h was employed. The wear tests were carried out in Pin on Disc (POD) machine at various combination of sliding speeds (1, 1.5, 2, 2.5 m/s) and applied loads (10, 20, 30, 40 N) with constant sliding distance of 3000 m. These composites were then characterized for hardness and density measurement, microstructures, SEM-EDS and worn-out feature analysis. Surface response analysis was done to locate mild wear and severe regimes. Hybrid matrix composites containing 3 % wt. of MoS2/Graphite in ABC 10 shows improved wear resistance due to synergistic effect of dispersion and precipitation strengthening.

Microstructure and magnetic properties of nickel-zinc ferrite ceramics fabricated by spark plasma sintering

Dense nickel-zinc (NiZn) ferrite ceramics were successfully fabricated within tens of seconds via spark plasma sintering. The phase composition and microstructure of the sintered samples were characterized by X-ray diffraction and scanning electron microscopy, respectively. The static magnetic properties at room temperature and Curie temperature of the samples were investigated by vibrating sample magnetometry. The results indicated that the main phase of the sintered samples was Ni0.75Zn0.25Fe2O4 with spinal structure, and the sintering temperature and heating rate observably affected the microstructure and density, then the magnetic properties of the sample. The Joule heat generated by NiZn ferrite during spark plasma sintering was very important for the rapid preparation of the sample with high density and small grain size. The low sintering temperature and heating rate would be helpful to obtain samples with small grain size, high density, and then good magnetic properties. The samples sintered at 900 °C with the heating rate of 5–10 °C/s were characterized of the relative density above 95%, 4πMs value beyond 4000 Gs and coercivity below 27.7 Oe.

Synthesis, characterization and applications of 3D porous graphene hierarchical structure by direct carbonization of maleic acid

This work reports the synthesis of a novel 3D porous graphene (PG) from maleic acid (HO2CCH=CHCO2H) used as a carbon source through a simple one-step carbonization process. The sodium carbonate (Na2CO3) was used as the skeletal substrate for 3D PG preparation and we observed that the ideal mass ratio of maleic acid (MA) to Na2CO3 is 1:4, which gives the highest yield and net carbon content for 3D PG preparation. The Na2CO3 decomposition temperature is greater than 550 °C which causes the release of CO2 and hence ultimately it produced 3D porous graphene (PG). The prepared 3D PG was characterized by X-Ray Diffraction (XRD), Raman Spectra, Transmission Electron Microscope (HRTEM), Scanning Electron Microscope (SEM), X-Ray Photoelectron Spectroscopy (XPS), and Brunauer Emmett Teller (BET) Surface area. The synthesized 3D architectural frameworks of graphene offered well-defined pores with a large surface area amounting to 567.56 cm2g-1. However, with increasing temperature above 700 °C, there is a decrease in surface area which can be attributed to the heat shrinkage and sintering or collapse of smaller diameter pores. Also at higher temperatures, Na2CO3 decomposes quickly which impart less effect on the morphology of synthesized graphene. In addition, electrochemical and adsorptive properties were also studied and a comparison is made with 3D rGO synthesized separately. The unique porous structure of 3D PG showed an excellent adsorption capacity of 433.3 (mg g-1) towards emerging pharmaceutical compound Atenolol and it further increases up to 642.4 (mg g-1) towards organic dye Rhodamine B, which is much higher than the 3D reduced graphene oxide rGO obtained by the chemical reduction process. Similarly, the as-synthesized 3D PG depicted enhanced oxidation and reduction properties as compared to 3D rGO as is evident from sharp anodic and cathodic peaks for the 3D PG prepared at 700 °C.

Statistical optimization of the elaboration of ceramic membrane support using Plackett-Burman and response surface methodology

The effect of Sintering temperature (ST), Particle size (PS), Starch content (SC) and Heating rate (HR) of the Ceramic Support Membrane Elaboration based on wet clay were evaluated using Plackett-Burman Design (PBD) and investigated by porosity and mechanical strength measures. Response Surface Methodology based on Central Composite design (CCD) was used for further optimization. The supports have been prepared from a clay with a two fraction 2 and 30 µm and a starch to enhance the performance of the support. The supports sintered between 900 °C and 1200 °C with a different heating rate (1 °C/min and 10 °C/min). By using PBD, it was found that the sintering temperature (ST) and starch content (SC) are the main controlling factors of the physical properties of ceramic support membrane. The increase of ST had a positive effect on Mechanical strength and negative effect on porosity, on other hand the increase of SC had a positive effect on porosity and negative effect on Mechanical Strength. The optimal factors to elaborate the membrane support by using CCD include a sintering temperature of 1014.36 °C and starch content of 4% predicting the porosity of 38.79% and Mechanical strength of 12 MPa.

Clay Ceramic Support Membrane Optimization Using Factorial Design Approach

In the present study, the effect of Sintering temperature, Particle size and Heating rate of the ceramic support membrane Elaboration based on dry clay were evaluated using full factorial design and investigated by porosity and mechanical strength measures. The flat supports have been prepared from 5 g of the material with a two fraction 2 and 30 µm, the extrusion was performed using the uniaxial pressing in applicant a pressure of 12 tones, the supports sintered between 900° C and 1200°C with a different heating rate (1°C/min and 10°C/min). By using full factorial design 23, it was found that the sintering temperature is the main controlling factors of the physical properties of dry ceramic support membrane, and its increase had a positive effect on Mechanical strength and negative effect on porosity. The interactions between the factors were relatively less important, and they had different (antagonistic/synergetic) influence on the properties. The optimal factors to elaborate the support membrane include a particle size of 2 µm, sintering temperature of 950°C, Heating rate of 1°C predicting the porosity of 40, 8% and Mechanical strength of 12 MPa.