Effect of Potassium Phosphate Content in Aluminosilicate Matrix on Mechanical Properties of Carbon Prepreg Composites

Six matrices based on alkali-activated aluminosilicate with different amounts of potassium phosphate were prepared for the production of six-layer composite plates. The addition of potassium phosphate in the matrix was 2 wt%, 4 wt%, 6 wt%, 8 wt% and 10 wt% of its total weight. The matrix without the potassium phosphate was also prepared. The aim of this study was to determine whether this addition has an effect on the tensile strength or Young’s modulus of composites at temperatures up to 800 °C. Changes in the thickness and weight of the samples after this temperature were also monitored. Carbon plain weave fabric was chosen for the preparation of the composites. The results show that under normal conditions, the addition of potassium phosphate has no significant effect on the mechanical properties; the highest measured tensile strengths were around 350 MPa. However, at temperatures of 600 °C and 800 °C the addition of potassium phosphate had a positive effect, with the tensile strength of the composites being up to 300% higher than the composites without the addition. The highest measured values of composites after one hour at 600 °C were higher than 100 MPa and after 1 h at 800 °C higher than 85 MPa.     

Controlling the Thermal Stability of Kyanite-Based Refractory Geopolymers

The present project investigated the thermal stability of cold-setting refractory composites under high-temperature cycles. The proposed route dealt with the feasibility of using fillers with different particle sizes and studying their influence on the thermo-mechanical properties of refractory geopolymer composites. The volumetric shrinkage was studied with respect to particle sizes of fillers (80, 200 and 500 µm), treatment temperature (1050–1250 °C) and amount of fillers (70–85 wt.%). The results, combined with thermal analysis, indicated the efficiency of refractory-based kyanite aggregates for enhancing thermo-mechanical properties. At low temperatures, larger amounts of kyanite aggregates promoted mechanical strength development. Flexural strengths of 45, 42 and 40 MPa were obtained for geopolymer samples, respectively, at 1200 °C, made with filler particles sieved at 80, 200 and 500 µm. In addition, a sintering temperature equal to 1200 °C appeared beneficial for the promotion of densification as well as bonding between kyanite aggregates and the matrix, contributing to the reinforcement of the refractory geopolymer composites without any sign of vitrification. From the obtained properties of thermal stability, good densification and high strength, kyanite aggregates are efficient and promising candidates for the production of environmentally friendly, castable refractory composites.     

Effect of Age-Hardening Temperature on Mechanical and Wear Behavior of Furnace-Cooled Al7075-Tungsten Carbide Composite

In this study, aluminum alloy (Al7075) composites with a 4% weight fraction of tungsten carbide (WC) were manufactured using a stir casting process and the developed composites were subjected to various ageing temperatures. An attempt has been made to predict the age-hardening temperature with the enhanced mechanical and wear properties of Al7075-WC. The result shows that the composite specimen aged at 250 °C offered maximum tensile strength and the Brinell hardness number was increased by 37.1% and 50.5%, respectively; the maximum impact energy was observed to be 92.2% for the 450 °C aged composites, compared to the non-aged Al7075-WC composites. The strength properties of the Al7075-WC composite decreased to 30.86%, 4.7%, and 24.9% when the composite specimens aged at 350 °C. The mechanical properties of the Al7075-WC composite were increased at the age-hardening temperatures from 150 °C to 250 °C and decreased from 250 °C to 350 °C. The wear testing pin-on-disc setup utilized to determine the wear characteristics of the prepared MMC with wear parameters of load and sliding distance and the wear resistance of the composite specimens increased due to ageing. The fractography analysis of the composite samples carried out by scanning electron microscope (SEM) images revealed that the fracture of the composite during the tensile test is a mixture of ductile and brittle modes.     

Annealing Response of Additively Manufactured High-Strength 1.2709 Maraging Steel Depending on Elevated Temperatures

The present work describes the influence of different temperatures on mechanical properties and microstructure of additively manufactured high-strength 1.2709 maraging steel. For this purpose, samples produced by selective laser melting technology were used in their as-printed as well as their heat-treated state. Both samples were than exposed to temperatures ranging between 100 °C to 900 °C with a total dwell time of 2 h followed by water-cooling. The microhardness of the as-printed material reached its maximum (561 ± 6 HV0.1) at 500 °C, which corresponded to the microstructural changes. However, the heat-treated material retained its initial mechanical properties up to 500 °C. As the temperature increased, the microhardness of both the materials reduced, reaching their minimum at 900 °C. This phenomenon was accompanied by a change in the microstructure by forming coarse-grained martensite. This also resulted in a significant decrease in the ultimate tensile strength and an increase in the plasticity. TEM analysis confirmed the formation of Ni₃Mo intermetallic phases in the as-printed material when exposed to a temperature of 500 °C. It was found that the same phase was present in the heat-treated sample and it remained stable up to a temperature of 500 °C.     

The Effect of Reinforcement Preheating Temperatures on Tribological Behavior of Advanced Quranic Metal-Matrix Composites (QMMC)

The growing applications of iron/copper bimetallic composites in various industries are increasing. The relationship between the properties of these materials and manufacturing parameters should be well understood. This paper represents an experimental study to evaluate the effect of reinforcement (steel rod) preheating temperature on the mechanical properties (bond strength, microhardness, and wear resistance) of copper matrix composites (QMMC). In preparing the QMMC samples, the melted copper was poured on a steel rod that had been preheated to various temperatures, namely, room temperature, 600 °C, 800 °C, and 1200 °C. Properties of the QMMC (interface microstructure, interfacial bonding strength, microhardness, and wear) were investigated. The experimental results revealed that the best bond between the copper matrix and steel rod formed only in the composites prepared by preheating the steel rods with temperatures lower than the recrystallization temperature of steel (723 °C). This is because the oxide layer and shrinkage voids (due to the difference in shrinkage between the two metals) at the interface hinder atom diffusion and bond formation at higher temperatures. The microhardness test showed that preheating steel rod to 600 °C gives the highest value among all the samples. Furthermore, the QMMC’s wear behavior confirmed that the optimization of preheating temperature is 600 °C.     

Effect of Elevated Temperatures on the Mechanical Properties of a Direct Laser Deposited Ti-6Al-4V

In the present work, the mechanical properties of the DLD-processed Ti-6Al-4V alloy were obtained by tensile tests performed at different temperatures, ranging from 20 °C to 800 °C. Thereby, the process conditions were close to the conditions used to produce large-sized structures using the DLD method, resulting in specimens having the same initial martensitic microstructure. According to the obtained stress curves, the yield strength decreases gradually by 40% when the temperature is increased to 500 °C. Similar behavior is observed for the tensile strength. However, further heating above 500 °C leads to a significant increase in the softening rate. It was found that the DLD-processed Ti-6Al-4V alloy had a Young’s modulus with higher thermal stability than conventionally processed alloys. At 500 °C, the Young’s modulus of the DLD alloy was 46% higher than that of the wrought alloy. The influence of the thermal history on the stress relaxation for the cases where 500 °C and 700 °C were the maximum temperatures was studied. It was revealed that stress relaxation processes are decisive for the formation of residual stresses at temperatures above 700 °C, which is especially important for small-sized parts produced by the DLD method. The coefficient of thermal expansion was investigated up to 1050 °C.     

Surface Properties and Morphology of Boron Carbide Nanopowders Obtained by Lyophilization of Saccharide Precursors

The powders of boron carbide are usually synthesized by the carbothermal reduction of boron oxide. As an alternative to high-temperature reactions, the development of the carbothermal reduction of organic precursors to produce B₄C is receiving considerable interest. The aim of this work was to compare two methods of preparing different saccharide precursors mixed with boric acid with a molar ratio of boron to carbon of 1:9 for the synthesis of B₄C. In the first method, aqueous solutions of saccharides and boric acid were dried overnight at 90 °C and pyrolyzed at 850 °C for 1 h under argon flow. In the second method, aqueous solutions of different saccharides and boric acid were freeze-dried and prepared in the same way as in the first method. Precursors from both methods were heat-treated at temperatures of 1300 to 1700 °C. The amount of boron carbide in the powders depends on the saccharides, the temperature of synthesis, and the method of precursor preparation.     

Role of Liquid-Phase Amount in Ceramization of Silicone Rubber Composites and Its Controlling

The reliable mechanical properties of ceramizable silicone rubber composites during pyrolysis are necessary for their application in the fire-resistant fields. The effects of liquid-phase amount on the mechanical properties of silicone rubber composites are investigated. The results show a positive correlation between the liquid-phase amount and the flexural strength of the residual products pyrolysis below 800 °C. The nano-γ-Al₂O₃ in the fillers reacts with liquid B₂O₃ to form aluminum borate above 800 °C, which consumes the liquid phase and strengthens the residual products to a certain extent. Increasing the B₂O₃ addition and introducing nano-γ-Al₂O₃ can control the liquid-phase amount in the range of 15% to 30%, which makes the composites have better residual strength and support performance. The residual strength of composites pyrolysis at 500 °C to 1000 °C is higher than 2.50 MPa, and the maximum is up to 18.7 MPa at 1000 °C.     

Infill Density Influence on Mechanical and Thermal Properties of Short Carbon Fiber-Reinforced Polyamide Composites Manufactured by FFF Process

In three-dimensional (3D) printing, one of the main parameters influencing the properties of 3D-printed materials is the infill density (ID). This paper presents the influence of ID on the microstructure, mechanical, and thermal properties of carbon fiber-reinforced composites, commercially available, manufactured by the Fused Filament Fabrication (FFF) process. The samples were manufactured using FFF by varying the infill density (25%, 50%, 75%, and 100%) and were subjected to tensile tests, three-point bending, and thermal analyses by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). It was shown that the samples with 100% ID had the highest values of both tensile, 90.8 MPa, and flexural strengths, 114 MPa, while those with 25% ID had the lowest values of 56.4 MPa and 62.2 MPa, respectively. For samples with infill densities of 25% and 50%, the differences between the maximum tensile and flexural strengths were small; therefore, if the operating conditions of the components allow, a 25% infill density could be used instead of 50%. After DSC analysis, it was found that the variation in the ID percentage determined the change in the glass transition temperature from 49.6 °C, for the samples with 25% ID, to 32.9 °C, for those with 100% ID. TGA results showed that the samples with IDs of 75% and 100% recorded lower temperatures of onset degradation (approximately 344.75 °C) than those with infill densities of 25% and 50% (348.5 °C, and 349.6 °C, respectively).     

Effects of Preparation Methods on the Microstructure and Mechanical Properties of Graphene-Reinforced Alumina Matrix Composites

Recent years have witnessed a growing research interest in graphene-reinforced alumina matrix composites (Al₂O₃-G). In this paper, to better achieve the dispersion of graphene in composites, a ball milling method for adding raw materials step by step, called stepwise feeding ball milling, was proposed. The Al₂O₃-1.0 wt % graphene composites were prepared by this stepwise feeding ball milling and hot pressing. Then, the effects of sintering temperature and sintering pressure on the microstructure and mechanical properties of composites were studied. Results showed that the bending strength, fracture toughness and Vickers hardness of composites increased firstly and then decreased with increasing sintering temperature. The mechanical properties of composites were all at their maximum with the sintering temperature of 1550 °C. For example, the bending strength of composites reached 754.20 MPa, which was much bigger than 478.03 MPa at 1500 °C and 364.01 MPa at 1600 °C. Analysis suggested that the strength of composites was mainly related to the grain size, microflaw size and porosity.     

Effect of Solution Temperature on Microstructure and Properties of Thixotropic Back-Extruded Tin–Bronze Shaft Sleeve

To study the heat-treatment process of a semi-solid copper alloy, a thixotropic back-extruded tin–bronze shaft sleeve was heat-treated at 630 °C, 660 °C, 690 °C and 720 °C for 1 h, respectively. Microstructure changes and mechanical properties under different solution temperatures of shaft sleeve were characterized using a metallographic microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), hardness tester, and tensile tester. The results show that the tensile strength first increases and then decreases; the elongation decreases; and the Brinell hardness increases gradually with increasing solution temperature. When the solution treatment is at 690 °C, the tin–bronze shaft sleeve’s microstructure and comprehensive mechanical properties are the best. The shape factor is 0.75, the average grain size is 82.52 μm, the Brinell hardness is 122 HBW, the tensile strength is 437 MPa, and the elongation is 17.4%, which is 3.4 times higher than that before solution treatment.     

Microstructure,Mechanical Properties,and Corrosion Behavior of Boron Carbide Reinforced Aluminum Alloy (Al-Fe-Si-Zn-Cu) Matrix Composites Produced via Powder Metallurgy Route

In this paper, Al-Fe-Si-Zn-Cu (AA8079) matrix composites with several weight percentages of B₄C (0, 5, 10, and 15) were synthesized by powder metallurgy (PM). The essential amount of powders was milled to yield different compositions such as AA8079, AA8079-5 wt.%B₄C, AA8079-10 wt.%B₄C, and AA8079-15 wt.%B₄C. The influence of powder metallurgy parameters on properties’ density, hardness, and compressive strength was examined. The green compacts were produced at three various pressures: 300 MPa, 400 MPa, and 500 MPa. The fabricated green compacts were sintered at 375 °C, 475 °C, and 575 °C for the time period of 1, 2 and 3 h, respectively. Furthermore, the sintered samples were subjected to X-ray diffraction (XRD) analysis, Energy Dispersive Analysis (EDAX), and Scanning Electron Microscope (SEM) examinations. The SEM examination confirmed the uniform dispersal of B₄C reinforcement with AA8079 matrix. Corrosion behavior of the composites samples was explored. From the studies, it is witnessed that the rise in PM process parameters enhances the density, hardness, compressive strength, and corrosion resistance.     

Intermediate-Temperature Tensile Behavior of a Hot-Rolled Mg-Li-Al-Cd-Zn Alloy

Developing light structure materials that work stably at elevated temperatures is a long-standing challenge for many application fields, particularly in the development of aerospace equipment. Zn/Cd alloying elements were prospected to improve the stability of the lightest Mg-Li based alloys; however, little is known about the intermediate-temperature mechanical properties of such alloys. The present work investigated the tensile behaviors of a cold-rolled Mg-Li-Al-Cd-Zn alloy in a temperature range of 30–150 °C. The results indicate that the alloy can host a tensile strength σ_UTS of 108~121 MPa, a yield strength σ_YP of 97~109 MPa and elongation ε_B of 14–15 % at 150 °C, dependent on the tensile direction. The mechanical properties intensively are modulated by temperature through the competition between work hardening and softening. Work hardening due to dislocation blocking by the precipitated MgLi₂X phase dominated the deformation at low temperatures, while softening that resulted from dynamic recrystallization was the main effect at high temperatures. Correspondingly, a quasi-cleavage mechanism dominated the fracture at temperatures near room temperature, and microvoid coalescence worked at high temperatures above 100 °C. Our results offer a new experimental understanding of the elevated-temperature mechanical behaviors of Mg-Li alloys and will advance the development of new light magnesium alloys with high stability.     

In-Situ Synthesis,Microstructure, and Mechanical Properties of TiB2-Reinforced Fe-Cr-Mn-Al Steel Matrix Composites Prepared by Spark Plasma Sintering

In-situ synthesis, microstructure, and mechanical properties of four TiB₂-Reinforced Fe-Cr-Mn-Al Steel Matrix Composites have been researched in this work. The microstructure and phases of the prepared specimens have been characterized by using scanning electron microscopy (SEM), X-ray diffraction technique, and transmission electron microscopy (TEM). The sintered specimens consisted of Fe₂AlCr, CrFeB-type boride, and TiB₂. The mechanical properties, such as hardness and compression strength at room temperature (RT) and at elevated temperatures (600 °C and 800 °C) have been evaluated. The compressive strength and Vickers hardness of the sintered specimens increase with the volume fraction of TiB₂ in the matrix, which are all much higher than those of the ex-situ TiB₂/Fe-15Cr-20Mn-8Al composites and the reported TiB₂/Fe-Cr composites with the same volume fraction of TiB₂. The highest Vickers hardness and compressive strength at room temperature are 1213 ± 35 HV and 3500 ± 20 MPa, respectively. As the testing temperature increases to 600 °C, or even 800 °C, these composites still show relatively high compressive strength. Precipitation strengthening of CrFeB and in-situ synthesis of TiB₂ as well as nanocrystalline microstructure produced by the combination of mechanical alloying (MA) and spark plasma sintering (SPS) can account for the high Vickers hardness and compressive strength.     

Environment-Friendly Preparation of Reaction-Bonded Silicon Carbide by Addition of Boron in the Silicon Melt

Reaction-bonded silicon carbide ceramics were sintered by infiltration of Si and B–Si alloy under an argon atmosphere at different temperatures. The element boron was added to the silicon melt to form a B–Si alloy first. The mechanical properties of samples were improved by infiltration of the B–Si melt. The samples infiltrated with the Si-only melt were found to be very sensitive to experimental temperature. The bending strengths of 58.6 and 317.0 MPa were achieved at 1530 and 1570 °C, respectively. The sample made by infiltration of B–Si alloy was successfully sintered at 1530 °C. The relative density of the sample was more than 90%. The infiltration of B–Si alloy reduced the sintering temperature and the bending strength reached 326.9 MPa. The infiltration mechanism of B–Si alloy is discussed herein.     

Design,Fabrication, and Mechanical Properties of T-700TM Multiaxial-Warp-Knitting–Needled–C/SiC Composite and Pin

In this paper, the 12k T-700^TM Multiaxial-Warp-Knitting–Needle (MWK–N) C/SiC composite and pin were designed and fabricated using the isothermal chemical vapor infiltration (ICVI) method. The composite’s microstructure and mechanical properties were examined by subjection to tensile and interlaminar shear tests. Three types of double-shear tests were conducted for C/SiC pins, including shear loading perpendicularly, along, and at 45° off-axial to the lamination. The fracture surface of the tensile and shear failure specimens was observed under scanning electronic microscope (SEM). The relationships between the composite’s microstructure, mechanical properties, and damage mechanisms were established. The composite’s average tensile strength was σ_uts = 68.3 MPa and the average interlaminar shear strength was τ_u = 38.7 MPa. For MWK–N–C/SiC pins, the double-shear strength was τ_u = 76.5 MPa, 99.7 MPa, and 79.6 MPa for test types I, II, and III, respectively. Compared with MWK–C/SiC pins, the double-shear strength of MWK–N–C/SiC pins all decreased, i.e., 26.7%, 50.8%, and 8% for test types I, II, and III, respectively. The MWK–N–C/SiC composite and pins possessed high interlaminar shear strength and double-shear strength, due to the needled fiber in the thickness direction, low porosity (10–15%), and high composite density (2.0 g/cm³).     

Enhanced Crystallinity and Luminescence Characteristics of Hexagonal Boron Nitride Doped with Cerium Ions According to Tempering Temperatures

Hexagonal boron nitride was synthesized by pyrolysis using boric acid and melamine. At this time, to impart luminescence, rare earth cerium ions were added to synthesize hexagonal boron nitride nanophosphor particles exhibiting deep blue emission. To investigate the changes in crystallinity and luminescence according to the re-heating temperature, samples which had been subjected to pyrolysis at 900 °C were subjected to re-heating from 1100 °C to 1400 °C. Crystallinity and luminescence were enhanced according to changes in the reheating temperature. The synthesized cerium ion-doped hexagonal boron nitride nanoparticle phosphor was applied to the anti-counterfeiting field to prepare an ink that can only be identified under UV light.     

Effect of Heat Treatment Temperature on Microstructure and Properties of PM Borated Stainless Steel Prepared by Hot Isostatic Pressing

Borated stainless steel (BSS) with a boron content of 1.86% was prepared by a powder metallurgy process incorporating atomization and hot isostatic pressing. After solution quenching at 900–1200 °C, the phase composition of the alloy was studied by quantitative X-ray diffraction phase analysis. The microstructure, fracture morphology, and distributions of boron, chromium, and iron in grains of the alloy were analyzed by field-emission scanning electron microscopy with secondary electron and energy-dispersive spectroscopy. After the coupons were heat treated at different temperatures ranging from 900 to 1200 °C, the strength and plasticity were tested, and the fracture surfaces were analyzed. Undergoing heat treatment at different temperatures, the phases of the alloy were austenite and Fe_1.1Cr_0.9B_0.9 phase. Since the diffusion coefficients of Cr, Fe, and B varied at different temperatures, the distribution of elements in the alloy was not uniform. The alloy with good strength and plasticity can be obtained when the heat treatment temperature of alloy ranged from 1000 to 1150 °C while the tensile strength was about 800 MPa, with the elongation standing about 20%.     

Fracture Behavior of Long Fiber Reinforced Geopolymer Composites at Different Operating Temperatures

The aim of this article was to analyze the fracture behavior of geopolymer composites based on fly ash or metakaolin with fine aggregate and river sand, with three types of reinforcement: glass, carbon, and aramid fiber, at three different temperatures, approximately: 3 °C, 20 °C, and 50 °C. The temperatures were selected as a future work temperature for composites designed for additive manufacturing technology. The main research method used was bending strength tests in accordance with European standard EN 12390-5. The results showed that the addition of fibers significantly improved the bending strength of all composites. The best results at room temperature were achieved for the metakaolin-based composites and sand reinforced with 2% wt. aramid fiber—17 MPa. The results at 50 °C showed a significant decrease in the bending strength for almost all compositions, which are unexpected results, taking into account the fact that geopolymers are described as materials dedicated to working at high temperatures. The test at low temperature (ca. 3 °C) showed an increase in the bending strength for almost all compositions. The grounds of this type of behavior have not been clearly stated; however, the likely causes of this are discussed.     

Properties of Titanium Zirconium Molybdenum Alloy after Exposure to Indium at Elevated Temperatures

Titanium zirconium molybdenum (TZM) is a high strength at high temperature alloy with favorable properties for use in high temperature structural applications. Use of TZM in high pressure, gas-containing autoclave systems was recently demonstrated for the ammonothermal method. Use of indium (In) in the system is desired, though there is a general lack of literature and understanding on the corrosion and impact of In on the mechanical properties of TZM. This study reports for the first time the mechanical properties of TZM after exposure to metallic In at temperatures up to 1000 °C. Static corrosion testing of TZM in In were performed at 750 °C and 1000 °C for 14 days. A microstructure analysis was performed suggesting no visible alteration of the grain structure. Differential thermal analysis (DTA) was performed to investigate compound formation between In and the primary constituents of TZM yielding no measurable reactions and hence no noticeable compound formation. X-ray energy dispersive spectroscopy (EDS) line scans across the TZM-In interface revealed no measurable mass transport of In into the TZM matrix. These results were confirmed using X-ray diffraction (XRD). Given the apparent inertness of TZM to In, mechanical properties of TZM after exposure to In were measured at test temperatures ranging from 22 °C to 800 °C and compared to unexposed, reference TZM samples from the same material stock. Tensile properties, including ultimate tensile strength, yield strength and total elongation, were found to be comparable between In-exposed and unexposed TZM samples. Impact fracture toughness testing (Charpy) performed at temperatures ranging from −196 °C to 800 °C showed that TZM is unaffected upon exposure to In. Tensile testing indicated ductile behavior at room temperature (slow strain rate) whereas impact testing (high strain rate) suggested a ductile to brittle transition temperature between 100 °C and 400 °C. Given these results, TZM appears to be a promising candidate for use as a force bearing material when exposed to In at high temperature.