Compression Sintering Research Articles

Effects of Y2O3 on the hot deformation behavior and microstructure evolution of Al2O3-cu/35Cr3TiB2 electrical contact composites

The Al2O3-Cu/35Cr3TiB2 and 0.5Y2O3/Al2O3-Cu/35Cr3TiB2 composites were prepared by a combination of fast hot compression sintering and internal oxidization. The effects of Y2O3 on the hot deformation behavior and microstructure evolution of the composites were investigated. According to the hot deformation data, the constitutive equations, hot processing maps, and critical dynamic recrystallization models were constructed for the two composites. The Y2O3 addition enhanced the flow stress, activation energy, and hot processing properties of the composites. This led to a reduction in the percentage of dynamic recrystallization structure from 25.3% to 19.4%, and decreased the amount of high-angle grain boundaries from 77.8% to 71.4%. Y2O3 was distributed at grain boundaries and phase interfaces, effectively impeding dislocation movement and grain boundary migration. Notably, the strain distribution within Y2O3 exhibited greater homogeneity compared to the Cu matrix. More twins and stacking faults were observed inside the 0.5Y2O3/Al2O3-Cu/35Cr3TiB2 composites, which synergistically strengthened the matrix.

Electrical/thermal conductivities of low-temperature sintered/Ag-decorated epoxy microspheres

The last decades composite production has benefited from additive manufacturing rendering production of special parts feasible and economical. Energy and time-consuming processes have improved significantly since the implementation of low temperature sintering methods. In this work, we prepare sub-micron powders in an attempt to produce conductive composites via compression sintering at a low overall production cost. Epoxy microspheres of glassy and rubbery type are synthesized in a controlled manner to inherit certain properties, and then decorated via a controlled deposition process of silver nanoparticles to form fine powders. The resulting fine powders are compressed at room temperature conditions to consolidate and hopefully sinter at post-cure. We study the structure-property relationship of the powder structure and the effect in the conductive properties that arise after consolidation. Remarkably, the compressed powders achieved DC conductivity with extremely low silver nanoparticle content (7.7 wt %, approx. 0.9 vol %) as compared with other literature reports and a promising increase in thermal diffusivity of about 18 % with just 4.2 wt % of silver nanoparticles.

Form-stable Na2CO3-NaCl/mullite phase change composite with SiC enhanced thermal conductivity for high temperature thermal storage

High-temperature energy storage technologies are gaining prominence to meet the needs of concentrating solar power plants and industrial waste heat recovery. In this study a series of form-stable phase change materials are prepared by a simple and efficient cold compression sintering method. In this method, Na2CO3-NaCl will be mixed with mullite ceramic powder; simultaneously, SiC nanoparticles are introduced to improve the thermal conductivity of the material. The leakage, microstructure, chemical compatibility and thermal physical properties of the prepared composites are systematically analyzed using Fourier-transform infrared spectroscopy, X-ray powder diffraction, Scanning electron microscope, Differential Scanning Calorimetry and Thermogravimetric. The results of the study show that good chemical compatibility of the components in the composites, and the latent heat of melting of the encapsulated composites as well as the sample with added SiC are 266.97 J/g and 217.63 J/g, respectively, while the latent heat of crystallization is 197.37 J/g and 151.13 J/g, respectively. Compared to the thermal conductivity of PCMs (0.41 W/(m·K)), the thermal conductivity of the sample with 20 % SiC added is 1.83 W/(m·K), an increase of 8.7 times. Thermal cycling and reliability tests show that even after 300 cycles, good chemical compatibility is maintained between the components in composites, and the phase change properties and quality remain stable. In addition, the thermal storage cost of FSPCM-M40-S20 is 1.90 $/MJ. Therefore, we believe that the prepared Na2CO3-NaCl/mullite/SiC FSPCM has promising applications in high-temperature thermal energy storage, especially in solar power generation and industrial waste heat recovery.

Comparative Study on the Compression Sintering Performance of Different Kinds of Copper-Chromium Powder Applied to Electrical Contact Materials

In this paper, the pressing and sintering properties of three kinds of copper-coated chromium composite powder and copper-chromium mechanical mixed powder with the same copper content were compared and studied. The copper-coated chromium composite powder was prepared by a diffusion sintering method, a liquid electroless plating method, and a diffusion sintering method with an added binder. The results show that with the increase in copper content, the pressing advantage of copper-clad chromium powder is more obvious. The density, hardness, and size shrinkage of the sintered sample are more stable. Moreover, the uniform distribution of Cu and Cr in the copper-coated chromium powder sintered sample can effectively improve the composition uniformity of Cu Cr electrical contact alloy.

Influence of the Rate of Gas Pressure Growth during Vacuum Compression Sintering on the Structure and Properties of the VK6M Hard Alloy

Influence of the Rate of Gas Pressure Growth during Vacuum Compression Sintering on the Structure and Properties of the VK6M Hard Alloy

Increased wear resistance of subsoiler bits

Purpose. Improve wear resistance of subsoiler bits by coating with new wear-resistant materials. Methods. Graphic, micrometer, comparative and field tests of locally hardened experimental parts of tillage machines. Results. A technology has been developed for restoring and strengthening subsoiler bits using new wear-resistant materials. Conclusions 1. According to the results of laboratory comparative tests of samples of wear-resistant materials deposited by detonation and plasma methods, compression sintering and surfacing, it was found that materials made of tungsten carbides Kutrite Carbide size and VK-8 have the highest relative wear resistance, respectively, 96.15 and 50 times higher, compared with hardened steel 65G, and titanium, chromium and nickel carbides – 54.34 times higher. 2. Based on the results of a production inspection of a batch of restored and strengthened deep-rippers bits in the soil conditions of UPI-AGRO LLC, it was found that the operating time of experimental deep-rippers bits is at the level of original parts and their resource is about 480 hectares per TG Gaspardo Artiglio R17820721 unit and 240 hectares on the Dante Macchine unit. Keywords: hardening, wear resistance, subsoiler bits.

The Effect of Physical-Chemical Nature of UHMWPE and PPS Thermoplastic Matrices on the Formation of Mechanical and Tribological Properties of their Carbon Fiber Filled Composites

The effect of carbon fiber dimensions on mechanical and tribological properties of the composites based on two thermoplastic matrices of different physical-chemical nature (polyphenylene sulfide, PPS, and ultrahigh molecular weight polyethylene, UHMWPE) is compared. It is shown that the supermolecular structure formed by compression sintering of PPS and UHMWPE controls the distribution pattern of carbon fibers in the matrix, which affects the level of tribological properties. The composites on a high-strength PPS-matrix, designed for structural/tribotechnical applications and loaded with short carbon fibers (70 μm), can be fabricated at a high loading degree (40 wt.%), which provides a five-fold increase in wear resistance and a 1.7-fold decrease in friction coefficient. The wear resistance increases due to the formation of a third body consisting of wear debris, which essentially reduces the friction coefficient. Loading the PPS with carbon nanofibers modifies the polymer matrix structure through the dispersion hardening mechanism but does not improve its tribological properties. Adding chopped carbon fibers (with a length of a few millimeters) into the PPS matrix gives rise to substantial hardening but significantly degrades the tribological properties. The UHMWPE composites can be manufactured via filling the matrix with 10 wt.% chopped carbon fibers evenly distributed in it. Carbon nanofibers are thought to be the most efficient fillers for the UHMWPE matrix of a spherulitic supermolecular structure in terms of increasing its wear resistance. They play the role of a solid lubricant medium (wear resistance increases 2.7 times, the friction coefficient is decreased twice). Comparatively long chopped carbon fibers of the millimeter range (2–3 mm) play a reinforcing role in contrast to the short carbon fibers measuring tens and hundreds of micrometers (70, 200 μm). They neither increase the friction coefficient nor result in the abrasive wear of the steel counterpart. The role of interphase adhesion, polymer matrix hardness, its chemical reactivity and supermolecular structure in forming the tribomechanical properties of carbon composites based on thermoplastic matrices of different physical-chemical nature is discussed.

Taguchi Optimization of Parameters for Feedstock Fabrication and FDM Manufacturing of Wear-Resistant UHMWPE-Based Composites.

It is believed that the structure and properties of parts fabricated by additive (i.e., non-stationary) manufacturing are slightly worse compared to hot pressing. To further proceed with improving the quality of Fused Deposition Modeling 3D-printed parts, the ‘UHMWPE + 17 wt.% HDPE-g-SMA + 12 wt.% PP’ composite feedstock fabrication parameters, by the twin-screw extruder compounding and 3D printing (the Fused Deposition Modeling (FDM) process), were optimized using the Taguchi method. The optimization was carried out over the results of mechanical tests. The obtained results were interpreted in terms of (1) the uniformity of mixing of the polymer components upon compounding and (2) the homogeneity of the structure formed by the 3D printing. The values of the main factors (the processing parameters) were determined using the Taguchi method. Their application made it possible to improve the physical, mechanical, and tribological properties of the samples manufactured by the FDM method at the level of neat UHMWPE as well as the UHMWPE-based composites fabricated by compression sintering. A comparative analysis of the structure, as well as the mechanical and tribological properties of the composite obtained by the FDM method, and the hot pressing from ‘optimized’ feedstock was performed. The ‘UHMWPE + 17 wt.% HDPE-g-SMA + 12 wt.% PP’ composites fabricated by the optimal compounding and 3D printing parameters can be implemented for the additive manufacturing of complex shape products (including medical implants, transport, mining, and processing industries; in particular, in the Far North).

Comparative Analysis of Tribological and Mechanical Properties of Extrudable Polymer–Polymer UHMWPE Composites Fabricated by 3D Printing and Hot-Pressing Methods

Abstract—A comparative analysis of the structural, tribological, and mechanical properties of polymer–polymer composites with the optimized composition UHMWPE + 15 wt % HDPE-g-SMA + 15 wt % PP, obtained by FDM (fused deposition modeling) and compressive sintering (hot-pressing) methods has been performed. It is shown that the tribomechanical characteristics (wear resistance, friction coefficient, elasticity modulus, yield limit, strength, elongation at break) of 3D-printed extrudable polymer–polymer UHMWPE composites exceed those of hot-pressed composites due to a more homogeneous supramolecular structure with enlarged crystallinity. Tribotests of extrudable UHMWPE composites in different friction modes (PV) demonstrates their applicability in joints operating in a wide range of loads and sliding rates.

Microstructure and Properties of Co@RGO/Cu Composites by One-Step <i>In Situ</i> Reduction Method

In order to improve the interfacial bonding between graphene and copper and improve the dispersibility of graphene in the copper matrix, a novel method was used to prepare graphene. Firstly, graphene oxide (GO) was prepared by the modified Hummer's method, and then the reduced graphene oxide-supported cobalt nanoparticle composite powder (Co@RGO) was prepared by one-step in-situ reduction method. The fabricated materials were mixed with copper powder to obtain various volume fractions. The powder mixture was subjected to compression and discharge plasma sintering (SPS) to prepare a bulk copper-based composite material. The microstructure and its comprehensive properties were studied by SEM, TEM, XRD, FTIR and Raman. The results show that the agglomeration of graphene can be effectively inhibited after the cobalt nanoparticles supported on the graphene surface. The proper amount of Co@RGO could be uniformly dispersed in the copper matrix. The composite material showed a high electrical conductivity (>86% IACS), and the Vickers hardness also increased by about 30% compared with pure copper.

Effect of Adhesion on Mechanical and Tribological Properties of Glass Fiber Composites, Based on Ultra-High Molecular Weight Polyethylene Powders with Various Initial Particle Sizes.

The aim of this study was to assess the effect of adhesion between the non-polar, ultra-high molecular weight polyethylene (UHMWPE) matrix and the glass fiber fillers of various lengths treated with the commercially available “KH-550” agent, on the mechanical and tribological properties of the UHMWPE-based composites. The motivation was to find the optimal compositions of the polymer composite, for the compression sintering manufacturing of lining plates for the protection of marine venders and construction vehicles, as well as transport equipment. It was shown that the initial powder size at equal molecular weight determined the distribution patterns of the glass fibers in the matrix, and, as a consequence, the mechanical and tribological properties of the composites. Based on the obtained experimental data and the results of the calculation by a developed computer algorithm, control parameters were determined to give practical recommendations (polymer powder size and glass fiber length), for the production of the UHMWPE-composites having specified mechanical and tribological characteristics. The “GUR4022 + 10% LGF” composite, loaded with the chopped 3 mm glass fibers treated with the “KH-550”, was recommended for severe operating conditions (high loads, including impact and abrasive wear). For mild operating conditions (including cases when the silane coupling agent could not be used), the “GUR2122 + 10% MGF” and “GUR2122 + 10% LGF” composites, based on the fine UHMWPE powder, were recommended. However, the cost and technological efficiency of the filler (flowability, dispersibility) and polymer powder processing should be taken into account, in addition to the specified mechanical and tribological properties.

Three-Component Composite Based on Ultra-High Molecular Weight Polyethylene for Additive Manufacturing

A comparative analysis on structure, mechanical and tribological properties of a multicomponent extrudable polymer composites "UHMWPE + 17 wt. % HDPE-g-SMA + 12 wt. % PP" fabricated by i) FDM (fused deposition modeling) as well as hot pressing of ii) powder mixture, and iii) granules of the same composition has been conducted. It is shown that UHMWPE composites obtained by the 3D–printing over a complex of tribomechanical properties (wear resistance, friction coefficient, elastic modulus, yield point, tensile strength, elongation at break) are comparable with those of composites fabricated by compression sintering of granules (this is associated with formation of more homogeneous permolecular structure, first of all, due to the compounding with the help of a twin-screw extruder) and significantly exceed those for hot pressing of powder mixtures. The obtained results allow one to recommend this composite for manufacturing complex shape products for tribotechnical application at employing 3D-printing technologies.

Coal Waste as a Promising Raw Material for the Production of Heat-Resistant Refractory β-Sialon Ceramics

The β- and 15R-sialons were obtained from coal waste (carbonaceous rocks) at the Institute of Fossil Fuels (IGI) for the first time in the world. Ceramics based on β-sialon powder made from carbonaceous rock by compression sintering possessed increased cracking resistance, as compared to that of known analogues, even when heated in a plasma flow at 2000°C. In this case, other characteristics of the ceramics, such as strength and thermal coefficient of linear expansion, are also in the acceptable ranges of characteristics for such materials. The full-scale tests of odd-shaped products at temperatures to 1420–1450°C did not cause destruction and cracking; this fact demonstrates the applicability of carbonaceous rocks of a certain composition as raw materials for the production of heat-resistant refractory nitride ceramics based on β-sialon. Technical requirements imposed on the composition of carbonaceous rocks suitable for the production of β-sialon found in the course of this study and technical characteristics of β- and 15R-sialon ceramics obtained from carbonaceous rocks are reported.

Preparation, structure and flame retardancy of poly(butylene terephthalate) with gradient intumescent flame retardant distribution

In this manuscript, the content-gradient distributions of an intumescent flame retardant (IFR) island-shaped structure in poly(butylene terephthalate) (PBT) were prepared using compression sintering processing technology inspired by powder metallurgy, to achieve efficient flame retardancy and mechanical properties with low flame retardant dosage. The PBT/IFR master-batch was first prepared by extrusion and then pulverized into powder. At low temperature (20 °C below the melting temperature) and high pressure (≥ 50 MPa) sintering processing conditions, two PBT/IFR powders with different levels of IFR content were fabricated into restricted island-like structure composites. The island with a higher IFR content exhibited flame retardancy, while the island with lower IFR content maintained the mechanics of the matrix. Compared with the uniform dispersion PBT/20 wt% IFR composite, the combustion of the PBT/IFR (25 wt%:15 wt% = 1:1) gradient content composite improved from V-1 to V-0 using a UL-94 test, while the tensile strength increased by 10%. The performance of the flame retardant was improved by periodically changing its distribution in the polymer matrix via restricted island-like structures fabricated using compression sintering processing technology inspired by powder metallurgy.

Low‐Temperature Sintering of Stereocomplex‐Type Polylactide Nascent Powder: From Compression Molding to Injection Molding

AbstractStereocomplex (SC) crystallization between poly(l‐lactide) (PLLA) and poly(d‐lactide) (PDLA) exhibits tremendous potential to improve the properties of polylactide (PLA), but the practical processing of SC‐type PLA (SC‐PLA) is significantly hindered by the insufficient melt stability and serious degradation after complete melting of SC crystallites over 240 °C. In a previous work, powder metallurgy inspired low‐temperature (180–210 °C) compression sintering is proposed to fabricate SC‐PLA products from its nascent powder. However, its industrial application is still challenging mainly due to the low production efficiency (half an hour is required) as well as the weak ability to fabricate products with complex shapes. In this work, an effort to rapidly fabricate complex‐shaped SC‐PLA products using low‐temperature injection molding technology is reported, where SC‐PLA nascent powder is partially melted. To ensure appropriate powder flowability, small amounts of glyceryl monostearate are incorporated as a lubricant. The results show that, both the self‐nucleation and flow‐induced nucleation effects facilitate the SC crystallization across the interfaces between adjacent unmelted powder particles, which considerably shortens the sintering cycle to about 2 min. In this way, complex‐shaped SC‐PLA products (such as gears) with superb performance are successfully fabricated by injection molding for the first time.

Effect of Sintering Method on Surface Fatigue of Carbide Composites

In this work the influence of sintering method on the surface fatigue of carbide composite was studied. The research focuses on WC-15wt%Co hardmetals prepared using different powders and different sintering techniques and as a result different microstructure: conventional WC+Co powder and novel reactive powder type W+C+Co are sintered using vacuum furnace, compression sintering (sinterhipping) and spark plasma sintering (SPS method). As tungsten carbide is a common material for cold forming punches and surface degradation causes punch failure [1], the tool life can be significantly extended by material surface fatigue life improvement. It is expected that SPS production route of WC-15wt%Co hardmetal will conclude in better microstructure, more even average grain size distribution and smaller residual porosity, and respectively better mechanical and surface fatigue properties compared to conventional production routes. There are some expectations related to the reactive sintering production routes, as this technique promotes the fine microstructure and better mechanical properties.

In-vitro elution of cisplatin and fluorouracil from bi-layered biodegradable beads

This study developed biodegradable bi-layered drug-eluting beads and investigated the in-vitro release of fluorouracil and cisplatin from the beads. To manufacture the drug-eluting beads, poly[(d,l)-lactide-co-glycolide] (PLGA) with lactide:glycolide ratios of 50:50 and 75:25 were mixed with fluorouracil or cisplatin. The mixture was compressed and sintered at <TEX>$55^{\circ}C$</TEX> to form bi-layered beads. An elution method was employed to characterize the release characteristic of the pharmaceuticals over a 30-day period at <TEX>$37^{\circ}C$</TEX>. The influence of polymer type (i.e., 50:50 or 75:25 PLGA) and layer layout on the release characteristics was investigated. The experiment suggested that biodegradable beads released high concentrations of fluorouracil and cisplatin for more than 30 days. The 75:25 PLGA released the pharmaceuticals at a slower rate than the 50:50 PLGA. In addition, the bi-layered structure reduced the release rate of drugs from the core layer of the beads. By adopting the compression sintering technique, we will be able to manufacture biodegradable beads for long-term drug delivery of various anti-cancer pharmaceuticals.

Peculiarities of Compacting during Sintering of VH8M Alloy with Addition of Nanosized Tungsten Carbide

There were introduced shrinkage curves of alloys obtained from hard-alloy mixtures based on WC-8%Ni, activated by means of introduction of 10 % nano-sized WC, and charging material without additives over the ranges of temperature 800–1500 °C. There was investigated pore structure and microstructure of specimens on the different stages of sintering. There was uncovered peculiarity of modified alloy’s compression that involves disalign- ment of shrinkage curve in field of more low temperatures. This is allows decrease temperature of its vacuum compression sintering, obtain more fine- grained structure and attain high indices of hardness/enduring quality, without decreasing of strength characteristics. There were investigated physi- cal and mechanical properties and microstructure of compression sintering specimens from activated alloy VN8M and standard VH8 without additives

Interaction between phase transformation and compression sintering in a TiAl-based intermetallic alloy

Interaction between phase transformation and compression sintering in a TiAl-based intermetallic alloy

Spark Plasma Sintering: A Useful Technique to Develop Large-Sized Bulk Metallic Glasses

Metallic glasses exhibit unique combination of physical, chemical and mechanical properties due to their amorphous nature which lacks long range order and defects such as grain boundaries and dislocations [1,2]. In the past two decades, they have been rapidly developed for application in many fields. However, the disadvantages such as poor plasticity and limited dimensions hamper their large-scale industrial applications [3,4]. The most common method to improve plasticity of the monolithic bulk metallic glasses (BMGs) is to produce glassy composites by introducing nanoor micro-scale crystalline phases into the metallic glassy matrix [5-9]. On the other hand, intensive efforts have been made to overcome dimension limitation. Powder metallurgy process is an alternative route to produce large-size metallic glassy alloy parts. It is also favor to fabricate the glassy composites by dispersing crystalline particulates into the glassy matrix. Spark plasma sintering (SPS) as a newly developed rapid sintering technique, has a great potential for producing glassy composites while crystallization of the glassy alloy and coarsening of the dispersed particles are avoided. Furthermore, it is also a type of solid-state compression sintering technique which is similar to hot pressing sintering process, so that the sintered samples with the large-size and complicated shape can be produced [10,11].