Infiltration Sintering Research Articles

Effect of glass infiltration and modified cooling rates on color characteristics alteration of monochrome and multilayer high yttrium oxide containing zirconia.

Sintering technique impacted color of zirconia. This study examined the effect of glass infiltration and altering cooling rate on color alteration of monochrome (Mo) and multilayer (Mu) 5 mol% yttria-partially stabilized zirconia (5Y-PSZ). 180 specimens (width, length, thickness = 10, 20, 2 mm) were prepared from Mo and Mu (comprising cervical (C) and incisal (I) zone) 5Y-PSZ shade VITA-A2. Unintentionally categorized samples (n=15/group) were sintered with traditional (T) versus glass infiltrated (G) technique and cooled down with slow (S: 5°C/min), normal (N: 35°C/min), and fast (F: 70°C/min). CIE-L*a*b* color characteristics were determined for translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), and color difference (∆Ediff). Microstructures were investigated with SEM and XRD. ANOVA and Tamhane's comparisons were determined for significant differences (p<0.05). TP and OP were significantly higher for Mo than MuC and MuI, but no significant difference in CR among them. Comparable ΔEdiff between Mo and MuC were indicated, but both were significantly lesser than MuL. Glass infiltration and raising cooling rate significantly decreased TP and OP, whereas increased CR and ΔEdiff, which amplified color alteration. Glass infiltration sintering and modified cooling rate significantly altered color parameters of 5Y-PSZ. Monochrome demonstrated higher translucency and opalescence than multilayer, possibly due to colorant additives. Glass infiltration decreased translucency and opalescence due to different refractive indices. Increased cooling rate resulted in decreasing translucency and opalescence due to smaller grain size and t→m transformation. Nevertheless, altered sintering and cooling rates still rendered an acceptable color alteration. Key words:Cooling rate, glass infiltration, optical characteristics, translucency.

Synthesis and property enhancement of Ti-Si/SiC composites by reactive infiltration for semiconductor applications

Poor machinability and limited electrical conductivity present significant challenges for silicon carbide (SiC) composites used in the semiconductor industry. In this study, Ti-Si/SiC composites were synthesized by liquid infiltration of a Ti-Si eutectic alloy, using SiC and Carbon black as raw materials. The reactive sintering mechanism and properties of Ti-Si/SiC composites were investigated using the reactive infiltration sintering process. The relative density of Ti-Si/SiC composites reached 98.43 % at 1600 °C. The results indicate that continuous infiltration of the Ti-Si eutectic alloy and dissolution-reprecipitation are critical for synthesizing Ti-Si/SiC composites. The coefficient of thermal expansion for the composites is 5.16 × 10−6 °C−1. Remarkably, the exponential increase in electrical conductivity with rising temperature strongly supports the enhanced conductive properties of this composite semiconductor. The Ti-Si/SiC composites exhibit maximum flexural strength, indentation modulus, and hardness values of 310.4 MPa, 434.1 GPa, and 29.4 GPa, respectively. This research aims to advance the application of high-performance Ti-Si/SiC materials in semiconductor technology.

Microstructure evolution during oxidation of protruded NiCoCrAlYTa-Al2O3 abrasive coating produced by vacuum infiltration sintering

In this paper, protruded NiCoCrAlYTa-Al2O3 abrasive coatings were prepared by vacuum infiltration sintering, and the effect of the filler metal content on the microstructure before and after oxidation is investigated. The results show that, the Al2O3 grits are bonded to the coating matrix by a layer of Y-Al-O compound, and various types of G-phase are presented depending on the locations. Adjacent to the G-phase, larger γ' phase and γ/γ' eutectics are presented due to the expel of Al during the formation of G-phase. With the increase of the filler metal content, G-phase precipitation and the Si penetration depth into the single crystal superalloy substrate increase. After 1000 °C/100 h oxidation, the Y-Al-O intermediate layer between Al2O3 grits and the coating matrix is little changed, with an additional thermally grown oxide (TGO) layer between the Y-Al-O layer and the coating matrix presented. The selective oxidation of Al and Cr facilitates the formation of G-phase layer underneath the oxide film, and the rapid diffusion of Ti and the selective oxidation of Al yields the formation of γ' depletion region adjacent to the G-phase and on coating surface without Al2O3 grits.

Mo70Cu30 composites synthesized by infiltration sintering and hot rolling with simultaneously improved mechanical and electrical properties

In this study, Cu@Mo composite powders, prepared using an electroless plating method, were applied to synthesize Mo70Cu30 composites using infiltration sintering and hot rolling technologies. Microstructure, mechanical properties and physical properties of the synthesized Mo70Cu30 composites were studied. Results showed that the prepared Cu@Mo composite powders have a core-shell structure with Mo particles uniformly coated with Cu layers. Density values of Mo70Cu30 composites before and after the hot rolling process are 98.45% and 99.79%, their tensile strengths are 517 MPa and 753 MPa, and their thermal conductivities are 179.7 W/(m·K) and 214.6 W/(m·K), respectively. Formation of network Cu channels in the Mo70Cu30 composite is beneficial for achieving uniform microstructures, increased density, and enhanced thermal conductivity. Rolling process deforms the Cu phase into a fibrous shape, forming a good thermal conductivity channel and refining the Mo phase grains. The enhancement in the mechanical properties of the composites is attributed to the combined mechanisms of deformation strengthening and fine grain strengthening.

Unusual ablation behaviors of tungsten graded network reinforced copper composites synthesized by 3D printing and infiltration sintering at ultra-high temperatures

Tungsten network reinforced functionally graded copper composites were prepared using an integrated 3D printing and infiltration technology to improve high temperature ablation properties of nuclear fusion divertor materials. The composites' ablation behavior was systematically investigated using an argon arc welding torch. Results showed that mass loss of composites was increased firstly but then decreased with the increase of ablation time. During ablation, evaporation of the melted copper reduces the local temperature of tungsten skeleton, whose high melting point also restrict the further evaporation of copper. These mechanisms significantly improve the ablative resistance of CuW gradient composite. Tungsten twinning structures were identified to form during ultra-high temperature (at 6273.15 K) ablation process in a cold environment in air. The formation of distinctive W twinning structures and gradient distribution of copper and tungsten skeleton were identified as the key mechanisms for the significantly enhanced ablation performance of the graded composite.

Optimizing infiltration parameters of nanostructured anode electrode in solid oxide fuel cells

This study focuses on the development and optimization of nanostructured anode electrodes for solid oxide fuel cells (SOFCs) by infiltration method. Ni (nickel) catalyst in the form of a nickel nitrate solution is infiltrated into porous YSZ (yttria stabilized zirconia) backbone fabricated by tape casting. Numerous electrolyte-supported cells are fabricated to investigate the effects of several significant infiltration fabrication parameters such as catalyst loading and infiltration sintering temperature. Conventional cell with screen printed Ni-YSZ anode is also fabricated for comparison. Electrochemical performances and microstructural properties of the cells are examined and evaluated. The best peak performance of 0.398 W/cm2 at 800 °C is obtained from the cell, which is infiltrated 9 times with 2 M solution followed by firing at 800 °C. The conventional cell, on the hand, exhibits only 0.174 W/cm2 under the same testing conditions in spite of the relatively higher Ni catalyst content in the anode. Furthermore, the optimized cell produces 0.169 W/cm2 maximum power density at 700 °C. The overall results reveal that nickel catalyst infiltration is a very effective method to improve the cell performance by providing increased number of electrochemical reaction zones within the anode electrode due to nanostructured nickel catalyst formed around the main YSZ phase.

Effect of carburized time on microstructure and properties of W[sbnd]Cu composites fabricated by vacuum pulse carburization

In this study, gradient WCX ceramic particle-reinforced WCu composites were successfully fabricated by vacuum pulse carburization and an infiltration sintering process. The effects of carburization time on the microstructure, hardness, compressive strength, wear resistance, and electrical conductivity were investigated in detail. With an increase in carburization time, the edges of the W particles became coarse until a large number of cracked structures appeared. The WC phase and a small amount of the W2C phase were the primary carbides generated upon carburization for 60 to 100 min. The WCX gradient microstructure significantly improved the mechanical properties of the WCu composites. The gradient structure also ensured the electrical conductivity of the WCu composites.

Deformation and fracture mechanisms of selective laser melted tungsten skeleton reinforced copper matrix composites at varied temperatures

Tungsten skeleton reinforced copper matrix composites (TRC) were designed and fabricated using a selective laser melting (SLM) method followed by infiltration sintering. Deformation and fracture mechanisms were investigated at 25, 300 and 500 °C. Compressive and tensile tests of the tungsten skeletons showed brittle fracture mode, whereas tensile tests of the TRC exhibited a mixed mode of ductile and brittle fracture. Fracture mechanisms of the TRC were identified as cleavage of tungsten and separation between copper and tungsten at 25 °C. Whereas at 300 and 500 °C, its fracture mechanisms were identified as intergranular fracture of tungsten particles, tearing of copper and separation between copper and tungsten.

Microstructure and properties of silver-added W-Cu prepared by infiltration sintering

A dense and uniform W-15Cu composite material was successfully prepared by adding different amounts of silver as the active agent followed by direct sintering and infiltration. The effects of silver additive content on the microstructure and properties of W-15Cu composites under the prefabricated tungsten skeleton re-osmosis copper process and direct sintering infiltration were studied by scanning electron microscopy (SEM), X-ray diffractometer and laser thermal conductivity analyzer. When using direct infiltration sintering, adding an appropriate amount of silver eliminated pores and promoted densification, thereby increasing the relative density of tungsten copper composites. When the silver content was 2.0 wt%, the relative density was 96.58%, the thermal conductivity was up to 203.43 W/m.K, and the conductivity was 31.2% IACS. Compared with the W-15Cu composite material (26.4% IACS) prepared at the same process temperature, the conductivity of W-2.0Ag13Cu was increased by about 18.2%, and the Vickers hardness was 262 HV. The fracture morphology analysis of the tungsten‑copper composites showed that the addition of Ag enhanced the interfacial bonding of the sintered composite materials and formed an ideal tungsten‑copper network structure. The fracture modes were the ductile fracture of the Cu-Ag matrix and the brittle fracture of the W phase.

Lattice-structured SiC ceramics obtained via 3D printing, gel casting, and gaseous silicon infiltration sintering

In view of technical difficulties in preparing ceramics with complex shapes, gel casting combined with 3D printing was here adopted to prepare silicon carbide ceramic green body, and gaseous silicon infiltration sintering was used to prepare 3D lattice-structured ceramics. The preparation of the slurry, gel curing, and ceramic molding was investigated. Results demonstrate that the ratio of components affects the fluidity and stability of slurry. However, when volume fraction of the solid phase of the slurry reaches 56%, the viscosity of slurry is only 300 mPa s, and drying shrinkage rate of green body is 6.6%; these characteristics make slurry suitable for 3D complex model injection molding. Furthermore, both the temperature and the initiator affect gel curing speed. As the temperature and initiator content increase, the induction and gel time are rapidly shortened. When demolding at 300 °C and when gaseous silicon infiltration sintering is carried out at 1550 °C, a 3D lattice-structured ceramic with relative density of 87% and average compressive strength of 433 MPa can be obtained.

Combination of electrophoretic and electroless depositions to fabricate Ni/TiC cladding

ABSTRACT A novel method is established that improves the shortcoming of embedding low volume fraction of reinforcements in Ni–P electroless coating. Experimental design of the present study is based on 5 steps: (1) electrophoretic deposition (EPD) of titanium carbide core inside the Ni–P shell particles (2) pre-sintering of as-EPD layer (3) electroless deposition of Ni–P top layer on as-EPD layer (4) heating the multilayer structure and (5) infiltration of the Ni–P melt phase through porous EPD layer. Anchoring TiC particles inside a Ni–P shell was done for catalyzing electroless Ni–P deposition on as-EPD layer and improving the high-temperature wettability of the EPD layer. By infiltration sintering on EPD layer (20 V for 2 min) a composite coating of Ni–P/TiC with a volume fraction of ∼49% TiC was successfully produced. According to wear test results, embedding TiC into Ni–P significantly increases hardness (972–1460 VHN) and reduces friction coefficient (0.45–0.23).

Wear-resistant electrophoretic deposition (EPD) layer of titanium carbide

A wear-resistant EPD layer of TiCsub (i.e. sub micrometer titanium carbide) was synthesized by pressureless infiltration sintering. EPD is an ideal technique to form a porous layer that could be thickness modulated by easily change of applied voltage/current. Full melt spreading of NiCrBSiFe on TiCsub EPD layer and suppression of TiCsub grain growth can be achieved by substituting TiCsub with core-shell structure of NiP electroless plated on TiCsub. In an infiltrated layer, lowering of TiCsub pushing by solidification front hence homogeneous distribution of TiCsub along with eliminating porous TiCsub solid skeletons are essential factors to improve the wear properties. Wear measurement results showed decrement in friction coefficient of NiCrBSiFe (0.29–0.17), amplitude of acoustic emission signals and wear coefficient (variation between 10−5 and10−6) by embedding TiCsub into the NiCrBSiFe layer. It is postulated that melt infiltration of an EPD layer is a practical way to clad wear-resisting layers on the surface.

W-Cu composites reinforced by copper coated graphene prepared using infiltration sintering and spark plasma sintering: A comparative study

In order to solve problems of significant interfacial reactions and agglomeration in graphene reinforced WCu composites, powders of copper coated graphene (Cu@Gr) were pre-mechanically mixed with tungsten and copper powders, and then graphene doped WCu composites were sintered using two different methods, e.g., spark plasma sintering (SPS) and infiltration sintering. Microstructural analysis showed that the doped Cu@Gr powder can effectively inhibit the interfacial reaction between graphene and tungsten, prevent the segregation of graphene, and evenly distribute the copper in the binder phase. When the mixed concentration of Cu@Gr was 0.45 wt%, uniform distributions of W phase and Cu phase were obtained in the composite, and the mechanical properties and conductivity of this composite achieved their best results. When the doping content was further increased to 0.8%, WC phase was found in all alloys, thus resulting in poor mechanical and physical properties. Comparing the microstructures produced using these two methods, the composites prepared using the infiltration sintering method showed network distribution of copper phase and segregation of copper, whereas the composites prepared using the SPS method showed network skeleton phase of tungsten. Although the SPS process was performed in a much shorter time, the mechanical properties of the composites sintered using the SPS process did not show much differences with those sintered using the infiltration sintering method.

The preparation of SiC-based ceramics by one novel strategy combined 3D printing technology and liquid silicon infiltration process

SiC-based ceramics with periodic structure were successfully fabricated by extrusion freeforming 3D printing technology and liquid silicon infiltration process. The ceramic slurries containing SiC, carbon black, chopped carbon fiber were firstly prepared with the appropriate viscosity and rheological properties, then were formed by extrusion freeforming 3D printing technology and densified by liquid silicon infiltration sintering successively, to acquire SiC ceramic composites components. The microstructure and morphology of green parts and sintered bodies were observed. Chopped carbon fibers were found to be oriented distribution in SiC ceramic composites parts. The sintered bodies exhibited maximum flexural strength of 300 MPa and sintered linear shrinkage below 2%. The manufacturing method has demonstrated big potential to fabricate ceramic components with personalized complex structure.

Infiltration sintering properties of Ni-4B-4Si(wt.%) alloy powders

The Ni-4B-4Si(wt.%) alloy powders were infiltrated into the nickel skeletons, the effects of sintering temperatures (1050-1150 °C) and skeletons (loose and compact nickel powders) on the microstructures and hardness of the sintered alloys were investigated. The Ni-B-Si alloy sintered at 1100 °C consisted of γ-Ni and Ni3B, and Si mainly solid soluted in the γ-Ni. The loose nickel powders favored to the infiltration of Ni-B-Si liquid alloy into the nickel skeletons, the sintered alloys exhibited dense microstructures and good interfacial bonding with Ni substrates. The interfacial hardness was equal to that of the sintered alloys and Ni substrates. Loose nickel powders ensured the density and interfacial bonding of the sintered alloys, the infiltration sintering process can be simplified and easily applied to practice.

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.

Synthesis of Ni/TiC composite coating by infiltration sintering of electrophoretic deposited layers

In this study, electrophoretic deposition (EPD) was employed as a practical way to form porous structure of TiC-based layer. The porous medium was infiltrated successfully by a Ni-based melt phase at 1060°C to fabricate Ni/TiC composite coatings. It was revealed that EPD parameters such as voltage affect the volume fraction of TiC particles in the sintered layer. It was indicated that electroless deposition of Ni-P shell on TiC core particles before EPD was necessary to enhance the melt penetration into the TiC porous matrix and hence to densify the porous medium. Microstructure and phase characterization were studied by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The results showed that TiC particles were well distributed through a matrix composed of primary γ-Ni phase. The average hardness of the sintered composite coating was 1540 Vickers, which is sufficiently high to make them good candidates for wear resistance applications.

Effects of SiC whiskers on the mechanical properties and microstructure of SiC ceramics by reactive sintering

As-received and pre-coated SiC whiskers (SiCw)/SiC ceramics were prepared by phenolic resin molding and reaction sintering at 1650°C. The influence of SiCw on the mechanical behaviors and morphology of the toughened reaction-bonded silicon carbide (RBSC) ceramics was evaluated. The fracture toughness of the composites reinforced with pre-coated SiCw reached a peak value of 5.6MPam1/2 at 15wt% whiskers, which is higher than that of the RBSC with as-received SiCw (fracture toughness of 3.4MPam1/2). The surface of the whiskers was pre-coated with phenolic resin, which could form a SiC coating in situ after carbonization and reactive infiltration sintering. The coating not only protected the SiC whiskers from degradation but also provided moderate interfacial bonding, which is beneficial for whisker pull-out, whisker bridging and crack deflection.

Fabrication of Fe-Based Diamond Composites by Pressureless Infiltration.

A metal-based matrix is usually used for the fabrication of diamond bits in order to achieve favorable properties and easy processing. In the effort to reduce the cost and to attain the desired bit properties, researchers have brought more attention to diamond composites. In this paper, Fe-based impregnated diamond composites for drill bits were fabricated by using a pressureless infiltration sintering method at 970 °C for 5 min. In addition, boron was introduced into Fe-based diamond composites. The influence of boron on the density, hardness, bending strength, grinding ratio, and microstructure was investigated. An Fe-based diamond composite with 1 wt % B has an optimal overall performance, the grinding ratio especially improving by 80%. After comparing with tungsten carbide (WC)-based diamond composites with and without 1 wt % B, results showed that the Fe-based diamond composite with 1 wt % B exhibits higher bending strength and wear resistance, being satisfactory to bit needs.

On the Preparation of Advanced Materials via Pulsed Electric Current Sintering Procedures

A general overview on the processing of a series of advanced engineering materials, synthesized via pulsed-electric-current-sintering related techniques, and the similarities in between those techniques are introduced in this work. This paper is focused on two major techniques; namely, the Spark Plasma Extrusion (SPE) and Current Assisted Infiltration Sintering (CAIS), which in turn are derived from the Spark Plasma Sintering (SPS) technique, all widely used by this research group. Not only the geometry but also the microstructure of thus prepared specimens might vary depending on the selected technique. The resulting specimens can be under the forms of discs (flat or thick coin-like), rivets (enlarged cylindrical bars)-like and/or disclosing interpenetrated periodic networks with regular or irregular (either coin or rivet/screw)-like specimens, respectively. As for the CAIS technique, either 3D printed ceramic frameworks or naturally synthesized porous substrates (such as bone-like structures), can be infiltrated with virtually any metal or alloy. Among the series of produced materials we can include, for example: biomaterials such as: Ti-and Mg-hydroxyapatite, pure hydroxyapatite HA, composites, e.g., Al5083-CNT ́s, just to name a few. The expanding possibilities of SPS, SPE and CAIS techniques are briefly indicated here.