High Relative Density Research Articles

Investigation of the wear resistance of in-situ Al-Ti composites fabricated by mechanical alloying and hot extrusion

ABSTRACT In this research, the wear behaviour of Al-20%Ti composites, fabricated by mechanical alloying and hot extrusion at different conditions, was investigated using the pin-on-disc method. A high-energy vibratory mill was applied to produce the nanocomposite (Al-20Ti-4hrV) and nanocrystalline (NC) Al samples, while a low-energy planetary mill was used to produce the other composites (Al-20Ti-20hrP and Al-20Ti-60hrP). To examine the microstructure and worn surface of specimens, optical microscopy and scanning electron microscopy were performed. To estimate the mechanical properties of the samples, their density and Brinell hardness were measured. The use of a high-energy vibratory mill caused the formation of an ultrafine aluminium matrix with in-situ nanometric intermetallic particles in the Al-20Ti-4hrV sample. As a result, the highest relative density and hardness and the best wear resistance were obtained in the Al-20Ti-4hrV sample. The application of the low-energy planetary mill led to the formation of flaky particles; accordingly, low relative density, poor mechanical properties and wear resistance in Al-20Ti-20hrP and Al-20Ti-60hrP samples were observed. The dominant wear mechanisms for Al-20Ti-4hrV and NC Al samples were identified as microploughing, adhesion and oxidation in the mild wear regime, whereas those of the Al-20Ti-20hrP and Al-20Ti-60hrP samples were mainly adhesion wear mechanism and inconsiderable delamination in the mild wear regime. The highest hardness and wear resistance were obtained for the nanocomposite sample owing to nanometric Al3Ti reinforcement, nanocrystalline Al matrix and good adhesion between particles and the matrix. This study confirmed that the nanocomposite production method presented in this research is suitable for wear-resistance applications.

Preparation, properties and microstructure of high hardness WC-Co cemented carbide tool materials for ultra-precision machining

WC-Co cemented carbides, with low binder content (Co content <4 wt.%), have become prospects as ultra-precision cutting tool materials as a result of their high hardness, which can be ground to a sharp cutting edge when machining tools. In this paper, three cemented carbides, with Co content of 1 wt.%, 2 wt.% and 3 wt.%, were systematically investigated. The mode of preparation, properties, microstructure and ultra-precision turning of these cemented carbides were studied. It has been researched that 0.1 wt.% VC could effectively refine the WC grains to exhibit excellent properties. The optimum sintering temperatures for WC-1Co-VC, WC-2Co-VC and WC-3Co-VC were 1350, 1300 and 1300 °C, respectively. The resultant cemented carbides displayed extremely high hardness (2450, 2377 and 2325 kg/mm2), high relative density (>99%), specific fracture toughness (8.89, 9.01 and 10.17 MPa·m1/2) and transverse rupture strength (1274, 1387 and 1474 MPa). During oxidation, from room temperature to 400 °C, there was a slight reduction in the strength of the cemented carbides with no oxide formed. From 400 to 600 °C, their strength decreased significantly with apparent oxides formed on the surface. At 800 °C, all the cemented carbides experienced a severe drop in strength and massive oxidation on the surface and fracture surface. The cemented carbides were used to make cutting tools used for ultra-precision turning of brass. The surface roughness after machining with the three modified cemented carbide tools, with increasing Co content, were 22, 14 and 17 nm, respectively.

Comparative Analysis of Helical Piles and Granular Anchor Piles for Foundation Stabilization in Expansive Soil: A 3D Numerical Study

This study investigates the performance of granular anchor piles and helical piles in expansive soils. Expansive soils pose challenges for engineering due to their significant swelling and shrinkage characteristics. Special considerations are required for constructing foundations on expansive soil to mitigate volumetric changes. While helical piles provide uplift resistance in light structures, they may not fully stabilize foundations in expansive soils. In contrast, granular anchor piles offer a simpler alternative for resisting uplift forces. A numerical study was conducted to analyze the pullout loads, compressive loads, and heave behavior of these anchor techniques. The results demonstrate that granular anchor piles outperform helical piles in terms of pullout and compressive performance, with improvements ranging from 17% to 22.5% in pullout capacity and 0.5% to 19% in compressive capacity, depending on specific pile lengths and diameters examined. However, both techniques show similar effectiveness in reducing heave, achieving reductions of over 90% when specific conditions are met. Additionally, the use of high-rise cap piles contributes to significant heave reduction, effectively minimizing heave to nearly negligible levels compared to low-rise cap piles. It is found that the relative density of the granular material has a more pronounced effect on the pullout load compared to the compressive load, and its impact varies depending on the length of the pile. Therefore, it is recommended to avoid high relative density when the pile is entirely within the expansive soil while utilizing higher relative density is beneficial when the pile penetrates and settles in the stable zone.

Optimal Performance of Mg-SiC Nanocomposite: Unraveling the Influence of Reinforcement Particle Size on Compaction and Densification in Materials Processed via Mechanical Milling and Cold Iso-Static Pressing

Achieving uniformly distributed reinforcement particles in a dense matrix is crucial for enhancing the mechanical properties of nanocomposites. This study focuses on fabricating Mg-SiC nanocomposites with a high-volume fraction of SiC particles (10 vol.%) using cold isostatic pressing (CIP). The objective is to obtain a fully dense material with a uniform dispersion of nanoparticles. The SiC particle size impact on the compressibility and density distribution of milled Mg-SiC nanocomposites is studied through the elastoplastic Modified Drucker-Prager Cap (MDPC) model and finite element method (FEM) simulations. The findings demonstrate significant variations in the size and dispersion of SiC particles within the Mg matrix. Specifically, the Mg-SiC nanocomposite with 10% submicron-scale SiC content (M10Sµ) exhibits superior compressibility, higher relative density, increased element volume (EVOL), and more consistent density distribution compared to the composite containing 10% nanoscale SiC (M10Sn) following CIP simulation. Under 700 MPa, M10Sµ shows improvements in both computational and experimental results for volume reduction percentage, 2.31% and 2.81%, respectively, and relative density, 4.14% and 3.73%, respectively, compared to M10Sn. The relative density and volume reduction outcomes are in qualitative alignment with experimental findings, emphasizing the significance of particle size in optimizing nanocomposite characteristics.

Fabrication of hypereutectic Al–Si alloy with improved mechanical and thermal properties by hot extrusion

Silicon phase in hypereutectic AlSi powders appears as primary Si and eutectic Si. Due to the poor thermal stability of eutectic Si, the material suffers from pores, stress concentration and dislocation packing during hot extrusion process, resulting in low density and poor thermal properties. In order to eliminate the eutectic Si, a heat treatment is conducted on Al20Si powders before hot extrusion. Because of the Ostwald ripening effect, the eutectic Si and dislocations in the powders are replaced by isolated Si lumps and a clear Al matrix. As a result, the formability and thermal properties of the material are greatly improved. The extruded samples made from the treated powder present high relative densities 99.7–100%, ultimate tensile strength (UTS) 167–170 MPa, elongations 8.8–10.8% and thermal conductivities (TCs) 191–195 Wm−1 K−1 and low coefficient of thermal expansions (CTEs) 13.8–14.5 × 10−6/K. The excellent mechanical and thermal properties are attributed to the elimination of eutectic Si from the treated powders and as-extruded alloys. In addition, hot extrusion introduces in-situ Al2O3 in the Si surface, Al grain boundary and Al grains, which is beneficial to reducing and stabilizing the CTE of the material. Moreover, it hinders Ostwald ripening and thus growth of the Si particles during the service of the material.

Experimental and numerical studies on mechanical properties of TPMS structures

Due to their exceptional lightweight and mechanical properties, triply periodic minimal surface (TPMS) based lattice structures have been widely studied. In this paper, the energy absorption performance of eight TPMS structures under large deformation was thoroughly studied, and five meshing strategies were evaluated comprehensively for the first time. The research objectives include three parts. First, the mechanical properties of eight TPMS structures, namely Primitive (P), Gyroid (G), Diamond (D), I-Wrapped Package (I-WP), Fischer-Kock (F-K), Neovius (N), I2-Y⁎⁎ and F-Rhombic Dodecahedra (F-RD) lattices, were investigated by utilizing experimental and numerical methods. These TPMS structures were fabricated using 316 L stainless steel powder by selective laser melting (SLM) and compared experimentally under compression in terms of the stress-strain curve, deformation and energy absorption. The results showed that F-RD and D lattice structures exhibit the best energy absorption capacity at relative densities less and greater than 30%, respectively. Second, to evaluate different meshing strategies for these complex structures, five finite elements (FE) models based on the shell, solid, and voxel elements were compared in terms of modeling ease, computational efficiency, data management, and simulation accuracy. It was demonstrated that the quadrilateral shell model shows satisfactory results for lattice structures with low relative densities or thin walls. In contrast, the voxel model shows the best results for structures with higher relative densities or thicker walls. Last, the voxel model was applied to the F-RD and D lattice structures. The numerical results showed that the stress distribution was more uniform in the F-RD, and the internal self-contact occurred later in the D lattice structure, further confirming the experimental observation and revealing the energy absorption mechanisms of TPMS structures.

Processing defect, microstructure evolution and mechanical properties of laser powder bed fusion Al-12Si alloys

The laser power and scan speed are significant processing parameters influencing the defects and microstructures due to affecting the thermal state within the melt pool during laser powder bed fusion (LPBF). To this end, these process parameter combinations under a constant laser energy density are correlated with defects (balling phenomenon and pores) and microstructures (melt pool arrangement and cell morphology). Setting the parameter combination (laser power and scan speed are 200 W and 910 mm/s, respectively) yields large balling droplets (average size of 150 μm) due to the relatively high melt viscosity resulting from the low melt pool temperature. In this case, a limited surface tension difference acting on a liquid surface cannot provide sufficient driving forces against viscous drags to promote the efficient spreading of the molten alloy. Cavity regions are formed between the large balling droplets and the previous layer, forming lack-of -fusion pores. By increasing the laser power and scan speed gradually, samples with relative densities greater than 99.5% are produced. This phenomenon can be attributed to the increases in laser power and scan speed, which improves the spreading ability of the molten alloy. With increasing laser power and scan speed, the cell size decreases (from 0.51 μm to 0.42 μm) because of the increase in the cooling rate. The sample (laser power and scan speed are 350 W and 1590 mm/s, respectively) has the highest performance (310 MPa yield strength, 470 MPa ultimate tensile strength, and 6.6% fracture strain) due to its highest relative density (greater than 99.5%) and fine microstructure (average cell size of 0.45 μm). All four samples exhibit anisotropic mechanical properties resulting from the combination of the melt pool boundary and lack-of-fusion pores.

Structure and electrical properties of cold-sintered strontium-doped potassium sodium niobate

Cold sintering is an attractive method for sintering ferroelectric ceramics at temperatures at or below 300 °C. While we can practically obtain bulk samples by introducing a transient liquid and applied pressure, the mechanisms of sintering and final functional properties of cold-sintered ceramics are far from being understood. Here, we investigate the influence of grain size and sintering parameters on the microstructure and ferroelectric properties of 0.5 % Sr-doped K0.5Na0.5NbO3 ceramics. By comparing with the conventionally-sintered samples, we find that cold-sintered ceramics have higher dielectric permittivity and lower dielectric losses, which we attribute to smaller grains and higher relative density. Using atomic-scale analysis, we point out the presence of numerous lattice dislocations that likely act as pinning sites and thus inhibit any significant polarization-switching behaviour. Due to the slim P–E loop and high dielectric breakdown fields of the cold-sintered ceramics we consider its potential for energy storage applications.

Mechanical and tribological behavior of a hybrid WC and Al2O3 reinforced Al–4Gr composite

Abstract The development of aluminum (Al) based composites has been an interesting subject to sustain technological developments in the defense, automotive, and aerospace industries. In this study, the microstructure, mechanical, and tribological performances of hybrid Al composites reinforced with fixed ratio (4 %) graphite (Gr) and two different reinforcement materials such as tungsten carbide (WC) and aluminum oxide (Al2O3) at different ratios were investigated. The impact of hybrid reinforcement and its ratios on the relative density value and hardness performance were investigated. The results of three different loads (1, 2, and 3 N) and three different sliding distances (200, 300, and 400 m) on wear performance were analyzed using Taguchi’s L18 experimental design. High relative density (94.39 %) and hardness (74.26) values were achieved by hot pressing. It has been determined that hybrid reinforcements have positive effects on wear performance. The lowest SWR value was recorded as 7.82 × 10−5 mm3/N.m in composite no Al-6. As the applied load raised, the friction coefficients decreased. On the other hand, the sliding distance and the increased applied load caused the temperatures to rise. With Al–4Gr/WC–Al2O3 composite material, a new AMMC has been presented to the literature, which has remarkable hardness and wear properties, and can show better ductility and machinability compared to equivalent materials.

Microstructure and mechanical properties of TiC reinforced TZM composites prepared by spark plasma sintering

In this paper, TiC (1 wt%, 5 wt%, 10 wt%, 15 wt%)-reinforced TZM composites with high relative density and good mechanical properties were prepared by high energy ball milling and spark plasma sintering. The microstructure, element distribution, and phase composition of TZM-TiC composites were systematically analyzed and characterized. The mechanical properties of TZM-TiC composites were evaluated by microhardness test, room temperature compression test and high temperature compression test. The results proved that with the increase of TiC content, the size of Mo grains in TZM-TiC composites was significantly inhibited, and the morphology of the reinforcement phase changed from a spherical shape to a long stripe shape. Mo was found to be partially amorphous in TZM-TiC composites, and various second phases (TiC, Ti and Mo2C) were found in the TZM-TiC composites. Through two-dimensional mismatch theory and first-principle calculations, the strengthening effect of Mo-Mo2C interface was much higher than that of Mo-TiC and MoTi interface. The generation of amorphous Mo, the grain refinement and the second phase strengthening together significantly improve the micro-Vickers hardness and compressive strength of TZM-(10%, 15%)TiC composites, which contributes to the Vickers hardness of TZM-15%TiC reaching 885.77 HV, and the compressive yield strength of TZM-10%TiC composite reaching 2169.7 MPa. Besides, the TZM-10%TiC composite exhibits excellent thermal stability, and its compressive yield strength at 600 °C reaches 1880.7 MPa.

Optimizing Li1.3Al0.3Ti1.7(PO4)3 Particle Sizes toward High Ionic Conductivity.

NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) has attracted a lot of attention because of its high ionic conductivity and stability to air and moisture. However, the size effect of LATP primary particles on ionic conductivity is ignored. In this study, different sizes of LATP particles are prepared to investigate the morphology, relative density, and ionic conductivity of the LATP solid electrolyte. The influences of particle size and sintering temperature on the microstructure, phase composition, and electrical properties of LATP ceramics were systematically studied. The medium-sized LATP particle (2 μm) presents a great microstructure with a high relative density of over 97%, the highest ionic conductivity of 6.7 × 10-4 S cm-1, and an activation energy of 0.418 eV. The Li-Li symmetric cells and Li-LFP batteries delivering good electrochemical performance were fabricated with highly conductive LATP ceramics. These results make significant strides in elucidating the relationship between the particle sizes of LATP and its electrochemical performance.

Synergetic effect enabling high thermal conductivity in Cu/diamond composite

Diamond has a superior thermal conductivity, but the diamond particles reinforced Cu matrix composites exhibit thermal conductivities far from expected. Here an ultrahigh thermal conductivity of 1050 W/mK is realized in a Cu/diamond composite via a discrete in situ carbide interlayer and a bimodal diamond particle strategy. The high thermal conductivity stems from a synergetic effect of high interfacial thermal conductance, large diamond particle size, high diamond content, and high relative density in the composite, which are obtained simultaneously. The study highlights the fundamental role of synergetic effect in attaining high thermal conductivity in Cu/diamond composites. This methodology also provides guideline for preparing other diamond particles reinforced composites for thermal management applications.

Strengthening Mo2BC ceramic by a two-step sintering process

Mo2BC ceramic has potential application value in structural fields due to its high strength and hardness. However, the microstructures and mechanical properties of ceramics are greatly depended on the sintering process. In this paper, the effect of sintering temperature on microstructures and mechanical properties of Mo2BC ceramics has been studied. Mo2BC ceramic bulks were fabricated at the temperature varying from 1300 °C to 1600 °C under a pressure of 50 MPa by fast hot-pressing sintering method. It is well confirmed that the sintering temperature can remarkably influence microstructural evolution and mechanical properties. The results presented here provide an optimal sintering process to prepare Mo2BC ceramic bulks. It is established that the two-step sintering process is an effective method to refine the microstructures and improve the mechanical properties. Based on the two-step sintering process, the relative density of as-prepared Mo2BC ceramic bulk is as high as 98.5 %. Besides, the Vickers hardness, compressive strength, flexural strength and fracture toughness are all evidently improved, of which the values are 20.1 GPa, 4.95 GPa, 511.5 MPa and 4.7 MPa m1/2, respectively. The enhanced mechanical properties are mainly attributed to the refinement strengthening effect and high relative density.

Ultrafine WC-Co cemented carbide with enhanced mechanical properties prepared by oscillating sinter forging

A novel oscillating sinter forging (OSF) was used to prepare ultrafine WC-Co cemented carbides for the first time. The mechanical properties of the resultant samples were characterized and compared with those of cemented carbides prepared by conventional sinter-forging (CSF). The results show that the samples prepared by OSF have higher hardness and fracture toughness. The sample prepared by OSF at 1125 °C has a hardness of 1911 kg/mm2 and fracture toughness of 17.52 MPa·m1/2. These values are much higher than those obtained from the sample prepared by CSF and outperform the general trade-off between hardness and toughness observed in cemented carbides processed by other processes. Microstructural analysis suggests that OSF samples exhibited much better microstructure, such as higher relative density, finer grains, more uniform microstructure, more fcc-structured Co phase, and more ∑2 low-energy grain boundaries. The effects of microstructure on the mechanical properties were discussed. The current study suggests that OSF has excellent synergistic hardening and toughening effects and is a promising technique for preparing high-performance cemented carbides.

Cold sintering assisted two-step sintering of potassium sodium niobate (KNN) ceramics

Potassium sodium niobate (KNN) ceramics were densified using a multiple-stage sintering process in which initially applied cold sintering process (CSP) was followed by the solid-state sintering between 1100 and 1120 °C. Comparative assessments demonstrated that multi-step sintered samples yielded better properties than conventionally sintering ones. The highest relative density (94.7%) and the best electrical properties were obtained from the sample subjected to cold sintering at 120 °C/1 h using 5 wt% deionized water subsequently heat-treated at 1120 °C/2 h, resulting in a monolithic KNN ceramic having a piezoelectric coefficient of 120 pC/N.

The effect of spark plasma sintering parameters on the densification and mechanical properties of TiB2‐TiC‐TiB composites

AbstractSpark plasma sintering (SPS) tests were designed using the Taguchi method to create high‐performance composites consisting of 60 wt% TiB2, 30 wt% TiC, and 10 wt% Ti. The effects of SPS parameters on the microstructure and mechanical properties of TiB2‐TiC‐TiB composites were systematically investigated. Additionally, the evolution of phase and microstructure during the densification of the composites was analyzed in detail. It has been demonstrated that composites can achieve a high relative density of 99.8%, a hardness of 22.2 GPa, a strength of 739 MPa, and a fracture toughness of 7.07 MPa m1/2, as well as a dense structure and small grain size. These properties can be obtained by sintering at a temperature of 1500°C, a pressure of 50 MPa, and a holding time of 5 min. Sintering temperature is the primary factor that promotes the densification of the composite and influences its relative density, grain size, and morphology. Holding time and sintering pressure are relatively minor factors, but they play important roles at different stages of the sintering process.

Microstructural Evolution, Mechanical Properties and Tribological Behavior of B4C-Reinforced Ti In Situ Composites Produced by Laser Powder Bed Fusion.

Based on the advantage of rapid net-shape fabrication, laser powder bed fusion (LPBF) is utilized to process B4C-reinforced Ti composites. The effect of volumetric energy density (VED) on the relative density, microstructural evolution, tensile properties and wear behaviors of B4C-reinforced Ti composites were systematically investigated. The LPBF-ed samples with high relative density (>99%) can be achieved, while the pores and un-melted powders can be observed in the sample owing to the low energy input (33 J/mm3). The additive particulates B4C were transformed into needle-like TiB whiskers with nano-scale while C dissolved in the Ti matrix. Fine-scale grains (<10 μm) with random crystallographic orientation can be achieved and the residual stress shows a downtrend as the VED increases. Through the analysis of the tensile and wear tests, the sample at 61 J/mm3 VED showed a good combination of strength and wear performance, with an ultimate tensile strength of 951 MPa and a wear rate of 3.91 × 10-4 mm3·N-1m-1. The microstructural evolution in VED changes and the corresponding underlying strengthening mechanisms of LPBF-ed Ti + B4C composites are conducted in detail.

Densification Behavior, Microstructural Development and Mechanical Properties of Spark Plasma Sintered α/β-Silicon Nitride Ceramics with Different Rare Earth Oxide Additives

ABSTRACT Monolithic Si3N4 ceramics were fabricated by spark plasma sintering at 1750°C for 15 min under 50 M Pa applied pressure using α-Si3N4 powder with 2 wt% Y2O3, 2 wt% Dy2O3, 2 wt% Eu2O3 and 8 wt% Y2O3 as single rare earth oxide additives. It aimed to investigate the effects of the composition and content of rare earth oxide additives on densification, microstructural development, and mechanical properties of α/β-silicon nitride ceramics via XRD and SEM analyses, temperature and displacement curves obtained through spark plasma sintering and mechanical tests. Addition to 2 wt% Y2O3 as an additive into composition resulted in high relative density (98%), hardness (14.9 GPa), and fracture toughness (9.8 M Pa.m1/2). The use of Dy2O3 instead of Y2O3 decreased β-Si3N4 phase ratio and densification rate. This behavior continued further with Eu2O3 addition. The increment of Y2O3 content to 8 wt% provided the same relative density and fracture toughness (98% and 9.8 M Pa.m1/2), whereas hardness was reduced to 12.6 GPa. As a result, densification was achieved only by Y2O3 addition regardless of additive content, and both high hardness and fracture toughness were obtained using only 2 wt% Y2O3 as a single additive.

Study on the microstructure and properties of Cu-graphite-Cr3C2 composites prepared by in-situ reactive synthesis

Cu-graphite-Cr3C2 composites were synthesized via spark plasma sintering (SPS) using different gas environments, including argon and air, to blend the raw materials consisting of Cr2AlC, Cu-coated graphite, and pure Cu. The microstructure and physical properties of the composites were thoroughly investigated. The findings revealed that Cr3C2, synthesized in situ from Cr2AlC, was firmly embedded in the Cu matrix. Additionally, a layer of Cr3C2 was formed at the interface between the Cu matrix and graphite. The composites showed a high relative density, which above 96 %. The composites fabricated with the raw materials mixed in an argon gas environment had a hardness of 72.6 HSD and an electrical conductivity of 1.102 × 106 S·m−1. Whereas, the hardness and electrical conductivity of the composites fabricated with the raw materials mixed in an air gas environment increased to 75.6 HSD and 1.314 × 106 S·m−1, respectively. Furthermore, Cu-graphite-Cr3C2 composites fabricated with the raw materials mixed in air rather than argon exhibited better lubrication performance and wear resistance, the average friction coefficient and wear rate were measured to be 0.4644 and 2.682 × 10−7 mm3/N·m, respectively.

Microstructure evolution and reactive diffusion behavior of highly dense TiNi alloy prepared from Ti2Ni and TiNi3 intermetallic compound powders

Powder metallurgy (PM) fabricated TiNi alloy is suffering from the reaction between Ti and Ni preferentially generates Ti2Ni and TiNi3, which inhibits the growth of the TiNi phase and extremely prolonging the sintering duration required for phase homogenization. In this case, we propose a novel strategy for preparing TiNi alloy utilizing Ti2Ni and TiNi3 intermetallic compound powders. This approach simplifies the reaction process by transforming the multi-step reactions (2Ti+NiTi2Ni, Ti+3NiTiNi3, and 2Ti2Ni+TiNi3 =5TiNi) into a one-step reaction (2Ti2Ni+TiNi3 =5TiNi). Consequently, the reaction process is shortened, and the growth rate of the TiNi phase is improved. Furthermore, results reveal that Ti2Ni-TiNi3 diffusion couple exhibits 8 times higher efficiency than the Ti-Ni diffusion couple in generating the TiNi phase. The as-prepared TiNi alloy exhibits high relative density, homogeneous phase distribution, and a fine grain size of 0–4.5 µm. These findings provide valuable insights into the efficient preparation of TiNi alloy through the PM method, with potential benefits for various applications.