Cold Pressing Sintering Research Articles

Low-cost powder metallurgy Ti-Cu alloys as a potential antibacterial material

Ti and Ti alloys are extensively used in biomedical applications due to their excellent biocompatibility and mechanical properties but their high-cost of production is still a limiting factor. It has been reported that the addition of Cu to Ti enables the creation of Ti alloys exhibiting antibacterial properties. Therefore, in this study Ti-Cu alloys (Cu = 0.5, 2.5 and 5 in wt.%) with potential antibacterial activity were fabricated by powder metallurgy (i.e. cold press and vacuum sintering) to reduce the production costs. As many biomaterials are employed as structural components, the Ti-Cu alloys were also subjected to β forging in order to improve their mechanical properties. It is found that the studied Ti-Cu alloys have superior mechanical properties to other commonly used Ti-based materials and are, thus, potential candidate for biomedical applications. Moreover, among the tested materials, the β forged Ti-5Cu alloys has tensile strength of 904 MPa, elongation of 6.7%, and Vickers hardness of 302 HV, which are comparable to those of the Ti-6Al-4V, and comprises the Ti2Cu phase (confirmed by the XRD) as microstructural feature, which is fundamental to guarantee antibacterial properties.

Habanje legure aluminijuma LM4 ojačane sa WC i TA/NbC hibridnim nano kompozitima proizvedenim tehnikom praškaste metalurgije

The present investigation aims to understand the wear behavior of aluminum LM4 matrix reinforced with the different weight percentage of tungsten carbide and tantalum-niobium carbide (0.5, 1.0, 1.5 and 2wt %) hard particles. Composite Specimens prepared by powder metallurgy route followed by cold pressing and hot sintering process. The wear tests were carried out using pin-on-disc machine under varying load (10, 20, 30 and 40N) speed (1, 1.5, 2 and 2.5m/s) and sliding distance (400, 600, 800 and 1000m) at room temperature. Characterization was done on nanopowders, developed composites and worn out surfaces of tested samples using Transmission Electron Microscopy (TEM), X-ray diffractometer(XRD), Scanning electron microscopy (SEM), Energy Dispersion Spectroscopy (EDS). The obtained results indicate that higher content of hybrid nanoparticles up to 2wt% in the composite reduces the wear rate up to 43.75% as compared with pure aluminum LM4 alloy.

In situ synthesis of copper-modified graphene-reinforced aluminum nanocomposites with balanced strength and ductility

In this work, a novel copper nanoparticles-modified graphene (Cu-NPs@GN)-reinforced Al matrix composites were fabricated. The Cu-NPs@GN hybrids were firstly synthesized by an NaCl template-assisted in situ CVD method and then incorporated into the Al matrix to fabricate Cu-NPs@GN/Al bulk composites by cold-press sintering and hot extrusion. With the merit of the unique characteristic of Cu-NPs@GN hybrid, the Cu-NPs@GN/Al composites exhibited homogeneously dispersed GNs and a strong GN–Al interfacial bonding. It was found that the in situ grown Cu-NPs@GN showed much better strengthening effect than that of the ex situ grown counterparts, which might be attributed to the pinning effect of Al2Cu at the interface and thus promote the load transfer efficiency. Compared with pure Al, the composites with only 0.75 wt% Cu-NPs@GN exhibited a 68% increase in tensile strength (224 MPa) as well as had a total elongation of 17.5%.

Effect of Sintering Atmosphere on the Synthesis Process, Electrical and Mechanical Properties of NiFe2O4/Nano-TiN Ceramics

NiFe2O4/nano-TiN ceramics were fabricated by a two-step cold-pressing sintering process. Effect of sintering atmosphere (air, nitrogen, argon) on the synthesis process of NiFe2O4/nano-TiN ceramics was investigated. The DSC-TG and XRD analysis results indicated that besides principal phases of NiO and NiFe2O4, new-phase Ni3TiO5 formed in the sintered ceramics under the three sintering atmospheres, and metallic phase including iron and nickel appeared in the sintered samples with inert gas (nitrogen, argon) sintering condition. Microstructure analysis results showed that considerable quantity of micropores appeared in the ceramic samples sintered under inert gases (argon, nitrogen), but lower porosity (3.0, 3.6%) and higher densities (4.78 g/cm3, 4.51 g/cm3) can be obtained, comparing to the both values (14.4%, 4.17 g/cm3) for the ceramic samples sintered under air atmosphere. Besides, the average bending strength and elastic modulus of the samples sintered under argon is 113.75 MPa and 7.13GPa, which is higher than that of 75.12 MPa, 5.42GPa and 91.96 MPa, 6.26GPa for the samples synthesized under air and nitrogen, separately. When changing sintering atmosphere from air to inert gases (argon, nitrogen), the fracture model of the 4 wt.%nano-TiN/NiFe2O4 ceramics synthesized at 1400 °C for 4 h transformed from intergranular fracture to intergranular-transgranular fracture.

Characterization of LaB6 particulate-reinforced eutectic Al-12.6 wt% Si composites fabricated via mechanical alloying and spark plasma sintering

In this study, x wt% LaB6 (x = 0, 2, 5 and 10) particulate-reinforced eutectic Al-12.6 wt% Si powders and composites were prepared from commercial Al, Si and LaB6 starting materials via powder metallurgy methods. Mechanical alloying (MA) was conducted on the blended powders using a high-energy ball mill (at 1060 cycles/min) for 2, 4 and 8 h. Mechanically alloyed (MA'd) powders were subjected to cold pressing (CP, under 450 MPa) and spark plasma sintering (at 450 °C for 180 s) processes. Powder particle morphologies changed from flaky to semi-equiaxial shape after MA duration of 4 h. Calculations performed through the XRD patterns of Al phase revealed that the average crystallite size increased and the average lattice strain decreased with increasing MA duration and LaB6 content. Spark plasma sintered (SPS'd) samples were examined in terms of composition, microstructure, densification and mechanical properties (hardness, yield strength, compressive strength and wear volume loss). Studies revealed that 4 h was the optimal MA duration and 10 wt% was the optimal reinforcement content for the LaB6particulate-reinforcedAl-12.6 wt% Si composites with respect to their mechanical properties. Al-12.6 wt% Si-10 wt% LaB6 sample had the highest hardness (1.72 ± 0.12 GPa), yield strength (373 MPa), compressive strength (578 MPa) and lowest wear rate (0.001 mm3/Nm) values among all SPS'd samples.

Laser additive manufacturing and homogeneous densification of complicated shape SiC ceramic parts

To improve the density of SiC ceramic components with complicated shape built by laser sintering (LS), cold isostatic pressing (CIP) and reaction sintering (RS) were incorporated into the process. In the process of LS/CIP/RS, Phenol formaldehyde resin (PF)-SiC composite powder was prepared by mechanical mixing and cold coating methods, with an optimized content of PF at 18 wt%. For the purpose of obtaining improved density of the sintered body after final reaction sintering, carbon black was added into the initial mixed powder. The material preparation, LS forming and densification steps were optimized throughout the whole fabrication process. The final sintered SiC bodies with the bending strength of 292 ~ 348 MPa and the density of 2.94–2.98 g cm− 3 were prepared using the PF coated SiC-C composite powder and the LS / CIP / RS process. The study further showed a positive and practical approach to fabricate SiC ceramic parts with complicated shape using additive manufacturing technology.

Influence of the milling process on TiB2 particle reinforced Al-7 wt.-% Si matrix composites

Abstract Al-Si metal matrix composites have generally been manufactured using casting methods. Powder metallurgy has been used as an alternative manufacturing technique to obtain more homogeneous and segregation-free products. In this study, 2 wt.-% TiB2 particle reinforced Al-7 wt.-% Si composites were manufactured using high energy ball milling, cold pressing (at 450 MPa) and pressureless sintering (at 570 °C for 2 h under Ar flow) techniques. The effects of different milling processes, such as mechanical alloying at room temperature and/or cryomilling in an isolated polycarbonate cylinder soaked in liquid nitrogen or sequential milling, on the Al-7 wt.-% Si-2 wt.-% TiB2 powders and corresponding bulk products were investigated. The microstructural, physical and mechanical properties of the composites sintered from the mechanically alloyed, mechanically alloyed and cryomilled, and sequentially milled powders were significantly improved as compared with those of as-blended ones. The highest density, the highest microhardness and the lowest wear rate were obtained in a composite sintered from mechanically alloyed and cryomilled powders at 92.38 %, 214.14 ± 41.17 HV and 3.8 × 10−3 mm3·N−1 × m−1, respectively.

Microstructural characterizations and mechanical properties of NbB2 and VB particulate-reinforced eutectic Al-12.6 wt% Si composites via powder metallurgy method

Mechanical alloying of elemental Al, Si, NbB2 and VB powder mixtures constituting the matrix alloy composition of Al-12.6 wt% Si and particulate-reinforced compositions of Al-12.6 wt% Si-x NbB2 and Al-12.6 wt% Si-x VB (x = 1, 2 and 5 wt%) were carried out for 2, 4 and 8 h in a high-energy ball mill. Mechanically alloyed (MA’d) powders were subjected to cold pressing (450 MPa), cold isostatic pressing (400 MPa) and pressureless sintering (570 °C/2 h) processes. Powder particle morphologies changed from flaky to equiaxed shape after the optimum MA duration of 4 h. 1 wt% NbB2 and 1 wt% VB particulate-reinforced Al-12.6 wt% Si based composites exhibited better mechanical properties than the Al-12.6 wt% Si matrix alloy and Al-12.6 wt% Si-x NbB2 and Al-12.6 wt% Si-x VB (x = 2 and 5 wt%) composite samples. In particular, Al-12.6 wt% Si-1 wt% NbB2 had the highest yield strength (378 MPa), compressive strength (491 MPa) and hardness (1.86 GPa) values. Investigations on the wear behaviors of the composites revealed that significant amount of wear loss occurred as a result of debris formation due to pull-outs of reinforcing boride (NbB2 and VB) and oxidized Al (Al2O3) particles.

Thermoelectric properties of lower concentration K-doped Ca3Co4O9 ceramics**Project supported by the National Key R&D Program of China (Grant No. 2016YFB0601101) and the National Natural Science Foundation of China (Grant No. 51476173).

The tuning of electron and phonon by ion doping is an effective method of improving the performances of thermoelectric materials. A series of lower concentration K-doped Ca3−xKxCo4O9 (x = 0, 0.05, 0.10, 0.15) polycrystalline ceramic samples are prepared by combining citrate acid sol-gel method with cold-pressing sintering method. The single-phase compositions and plate-like grain morphologies of all samples are confirmed by x-ray diffraction and field emission scanning electron microscope. The effects of lower concentration K doping on the thermoelectric properties of the material are evaluated systematically at high temperatures (300–1026 K). Low concentration K doping causes electrical conductivity to increase up to 23% with little effect on the Seebeck coefficient. Simultaneously, the thermal conductivity of K-doped sample is lower than that of the undoped sample, and the total thermal conductivity reaches a minimum value of approximately , which may be suppressed mainly by the phonon thermal conduction confinement. The dimensionless figure-of-merit ZT of Ca2.95K0.05Co4O9 is close to 0.22 at 1026 K, representing an improvement of about 36% compared with that of Ca3Co4O9, suggesting that lower concentration K-doped Ca3Co4O9 series materials are promising thermoelectric oxides for high-temperature applications.

Effect of tungsten disilicide addition on tungsten boride based composites produced by milling-assisted pressureless sintering

In this study, tungsten boride (WB and W 2 B) based composites with various amounts of tungsten disilicide (WSi 2 ) addition were fabricated by using a combined method of mechanical milling (MM), cold isostatic pressing (CIP) and pressureless sintering (PS). MM was conducted for 4 h in ethanol (wet milling) and Argon atmosphere (dry milling) using a high-energy ball mill. WSi 2 was used with different amounts (0, 5, 10 and 20 wt.%) in order to investigate its effect on the resultant products. MM’d powders were compacted using CIP under a pressure of 450 MPa, and were consecutively sintered at 1600 °C for 2 h and 1770 °C for 2 h under Ar atmosphere. Compositional, physical and microstructural characterizations of the samples were performed using stereo and optical microscopes, X-ray diffractometer, TOPAS software, scanning electron microscope coupled with an energy-dispersive spectrometer, particle size analyzer and gas pycnometer. Sintered products were also characterized in terms of Archimedes density and Vickers microhardness. Moreover, the oxidation studies of the samples were performed at 500 and 1000 °C via thermogravimetric analyzer. The results showed that the highest density, microhardness and oxidation stability values amongst the fabricated composites were obtained for the dry milled and sintered WB-20 wt.% WSi 2 sample.

Thermal-fluidic transport characteristics of bi-porous wicks for potential loop heat pipe systems

With the miniaturization of electronic components, thermal management of electronic devices and systems becomes a crucial problem. A Loop Heat Pipe (LHP) is a promising solution for many contemporary and future thermal management problems. A LHP is a passive, flexible and robust two-phase heat transfer device which utilizes the latent heat of phase-change to transfer heat and the capillary force generated by porous wick to circulate the working fluid. The porous wick is the heart of LHP which strongly controls its thermal performance. The main aim of the present research is to develop a bi-porous wick and analyze its thermal performance. Bi-porous copper wicks are fabricated with cold press sintering using naphthalene as the pore former. The effect of pore former content and sintering temperature on porous characteristics has been studied. It is observed that porosity and permeability increase with an increase in pore former content and decreases with increase in sintering temperature. The local heat transfer characteristic of the porous wick is studied using Infrared Thermography. Both infrared thermography and digital videography show that the liquid-vapor interface in the porous wick moves away from the heated fin as heat load increases. A change in slope of temperature profile in the porous wick is observed at the liquid-vapor interface. The evaporative heat transfer coefficient at fin-wick interface decreases with increase in heat load.

A comparison between the properties of natural hydroxyapatite produced by cold isostatic pressing and spark plasma sintering techniques

The natural hydroxyapatite (HA) extracted from cattle bone was produced by cold isostatic pressing (CIP) and spark plasma sintering (SPS) techniques and sintered at 1350 and 1150 °C, respectively. Scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, X-ray fluorescence (XRF) analysis, Fourier transform infrared spectroscopy (FTIR), and mechanical testing were carried out to characterize the microstructure and chemical and mechanical properties of developed materials. The bioactivity of samples was also studied by immersing the samples in simulated body fluid for 28 days. The results indicated that the density of bulk HA produced by SPS technique was higher than that of the CIP samples, where the density of bulk HA produced by SPS reached theoretical density. In addition, the hardness of the SPS sample was higher than the hardness of the CIP samples.

Infiltration sintering of WCu alloys from copper-coated tungsten composite powders for superior mechanical properties and arc-ablation resistance

W70Cu30(W-30 wt.% Cu) alloys were fabricated using cold pressing and infiltration sintering methods from two types of powders, i.e., mixed copper-tungsten (M-Cu-W) powders and our newly developed copper-coated tungsten composite (Cu@W) powders. Microstructure, mechanical and arc-ablation properties of the W70Cu30 alloys were investigated, and the mechanism of enhanced physical/mechanical properties and arc-erosion resistance of the W70Cu30 alloys was discussed. For the W70Cu30 alloys prepared using the Cu@W powders, their physical properties, including hardness, electrical conductivity and relative density were much better than those prepared from the M-Cu-W powders. The W70Cu30 alloys fabricated from the Cu@W powders were free of cracks, and showed homogenous distributions of W and Cu network structures. Whereas for the alloys prepared from the M-Cu-W powders, segregation of Cu was observed and the segregation size was about 40–100 μm. Characterization of arc-erosion morphologies of the W70Cu30 alloys prepared with the Cu@W powders revealed the occurrence of evaporation of Cu phase; whereas that of W70Cu30 alloys prepared with the M-Cu-W powders revealed the occurrence of the sputtering of Cu. After arc breakdown for 200 times, mass loss of alloys made using the mixed powders was twice as much as those made using the coated composite powders. Based on the experimental results and theoretical analysis, an arc breakdown mechanism of the WCu-C alloys using the composite powders was proposed which is attributed to the formation of a homogeneous Cu-Cu network structure to uniformly disperse arc energy and dissipate the generated heat, thus prolonging the service life of the WCu alloy contacts.

Microstructural evaluation and mechanical properties of Al-CNT nanocomposites produced by different processing methods

In this research, the semi-wet (SW) and slurry based (SB) methods were applied to synthesize Al-1.5 wt.%CNT nanocomposites powder. The initial 30 mm diameter compacted billets were produced through cold pressing and pressure-less sintering at 550 °C for 2 h for both types of nanocomposites. The billets were hot extruded at 400 °C to produce 10 mm diameter rods. The synthesis parameters of composites were investigated through experiments of tension, compression, FTIR, XRD, STA and Raman. The dispersion of CNTs within Al powder and fracture surface analysis was studied through FE-SEM.The yield and tensile strength of pure Al sample were measured as 90 and 136 MPa, respectively. These values were increased to 110 and 170 MPa for SW sample and improved to 152 and 203 MPa for SB product, by adding 1.5 wt.% CNT to pure Al. The strengthening effect of fibers was investigated using load transfer mechanism with fiber length less than critical value (l < lc) for SW and long fiber issue (l > lc) for SB samples. According to the fracture surface analysis, the bridging and CNTs fracture phenomena were observed in SB specimen and CNTs pull out was detected for SW sample. These results showed good agreement with strengthening efficiency of fibers (R) versus shear stress diagram including R = 25.6 in CNTs fracture and R = 13 in pull out regions. The Al4C3 interphase formation was characterized by XRD and Raman spectroscopies whereas end-contact and side-contact of carbides around CNTs were suggested as preferred sites for SB and SW products, sequentially.

Dielectric properties of silicon nitride ceramics produced by free sintering

Abstract The silicon nitride ceramics with a beneficial combination of low dielectric losses and improved physical properties was fabricated by cold isostatic pressing and pressureless sintering. The fine grain microstructure, three-phase composition based on the β-SiAlON, the small amount of the glass phase and relatively small porosity promote a unique combination of a low thermal conductivity 14.51 W m −1 K −1 and low dielectric loss 1.4·10 −3 . A novel method is proposed to overcome the main drawbacks of the commercial and high-cost technologies.

Influence of Milling Atmosphere on the Controlled Formation of Ultrafine Dispersoids in Al-Based MMCs

Properties of compacts made from aluminium powder, milled under different atmospheres, were evaluated. The duration of all the milling processes was 10 h, although different atmospheres were tested: vacuum, confined ammonia, and vacuum combined with a short-time ammonia gas flow (5 min). Milled powders were consolidated by cold uniaxial pressing and vacuum sintering.

Novel Sodium-Rich Anti-Perovskites Via Conventional Sintering and Spark Plasma Sintering

We experimentally investigated the effects of two processing techniques: conventional cold pressing and spark plasma sintering, on Na3OBr, a sodium-rich antiperovskite solid-state electrolyte. We demonstrated that the electrolyte can be synthesized via a single-step solid-state reaction from readily available sources. We compared the differences between CP and SPS processing using XRD, SEM, and EIS and determined that SPS reduced the grain boundary impedance contribution by three orders of magnitude, which translated into an increase in the overall Na ionic conductivity. Additionally, the SPS sample had activation energy of 0.837 eV, lower than the 1.142 eV of the CP sample. DFT was also undertaken to gain insight on the Na ion conduction behavior of Na3OBr. Figure 1

Effect of wrapped Zn plate on the densification of Al-MWCNTs composites produced by cold pressing and liquid phase sintering

To produce highly dense and cost-effective Al-multi-walled carbon nanotube (Al-MWCNT) composites, the composite powders are wrapped by a Zn plate and then cold-pressed. The green compacts are then sintered at 550°C, which shows ~99%density after sintering for 24h. During sintering, Zn atoms fill the voids at the powder boundaries by capillary action and are then dissolved into the Al matrix because of the high solubility of Zn in Al, thus assisting densification of the composite powder. The Al/Zn-based composites containing 4vol% MWCNTs show compressive yield strength (~380MPa) and high work hardening capacity.

Effect of the Cooling Ways on the Properties and Microstructure of ZrO&lt;sub&gt;2&lt;/sub&gt;/ZrW&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt; Ceramic Composites

ZrO2 has been widely used due to its good physical and chemical properties and the ZrO2/ZrW2O8 ceramic composites with adjustable thermal expansion coefficient can be prepared by mixing and sintering the ZrO2 and ZrW2O8 powders. In this paper, the ZrO2/ZrW2O8 ceramic composites have been prepared by mixing, cold isostatic pressing and atmospheric sintering, and then being cooled in air or in water. We focus on the effect of the cooling ways on the properties and microstructure of the ZrO2/ZrW2O8 ceramic composites. The results show that the relative density of all samples is more than 98%. For the in-situ method, the density and flexural strength of the samples cooled in air and in water are 98.1% and 98.4%, 112.96MPa and 45.23MPa, respectively. The ZrW2O8 content and thermal expansion coefficient of the samples cooled in the air are less and higher than those in the water, respectively. For the direct mixture method, the density and flexural strength of the samples cooled in air and in water are 98.9% and 99.3%, 195.99MPa and 58.71MPa, respectively. For the four groups of the composite samples, they behave better mechanical properties after cooled in air, and lower thermal expansion coefficients after cooled in water.

Investigation of Application Possibilities of Re-Ni Alloy Powder to Tungsten Heavy Alloys Production

The experiments results connected to possibilities of use of Re-Ni alloy powder for tungsten heavy alloys production were presented in the paper. This powder was obtained by nickel (II) perrhenate reduction under dissociated ammonia atmosphere. The optimal conditions for the thermal reduction for nickel (II) perrhenate were determined. The production process of investigated sinters contained, among others, cold isostatic pressing and two-staged sintering. Selected results of microstructure investigation and mechanical properties of obtained sinters were shown. Performed research indicated that the application of nickel (II) perrhenate to manufacture tungsten heavy alloys resulted in material with the microstructure typical of tungsten heavy alloys and characterized by high mechanical properties.