Binder Removal Research Articles

Influence of electrical discharge machining on the reciprocating sliding friction and wear response of WC–Co cemented carbides

Abstract The dry friction and wear behavior of a number of WC–Co cemented carbides, exhibiting 6 up to 12 wt.% cobalt as binder phase and average carbide grain sizes ranging from 0.3 up to 2.2 μm, combined with various surface finishing variants of wire electrical discharge machining (EDM), was evaluated by performing linearly reciprocating pin-on-flat sliding experiments against WC–Co cemented carbide using normal contact loads of 15 N up to 35 N and a sliding velocity of 0.3 m/s. Post-mortem obtained wear volumes and volumetric wear rates were correlated to real-time recorded penetration depth curves versus sliding distance. Consecutive execution of gradually finer EDM regimes onto the WC–Co alloys was found to considerably enhance the wear performance. Scanning electron microscopy on the worn surfaces revealed the occurrence of several wear mechanisms, i.e., grain polishing, abrasion, grain cracking and surface binder removal, mainly depending on the original surface finish EDM regime.

Effects of heat treatment on the properties of powder injection molded AlN ceramics

The effects of two different heat-treatment atmospheres, nitrogen atmosphere and reducing nitrogen atmosphere with carbon, on the properties of Y 2O 3-doped aluminum nitride (AlN) ceramics were investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compacts were fabricated by employing powder injection molding technique. The polymer-wax binder consisted of 60 wt.% paraffin wax (PW), 35 wt.% polypropylene (PP), and 5 wt.% stearic acid (SA). After the removal of binder, specimens were sintered at 1850°C in nitrogen atmosphere under atmospheric pressure. To improve the thermal conductivity, sintered samples were reheated. The result reveals that the heat-treatment atmosphere has significant effect on the properties and secondary phase of AlN ceramics. The thermal conductivity and density of AlN ceramics reheated in nitrogen gas are 180 W·m −1·K −1 and 3.28 g·cm −3 and the secondary phase is yttrium aluminate. For the sample reheated in reducing nitrogen atmosphere with carbon, the thermal conductivity and density are 173 W·m −1·K −1 and 3.23 g·cm −3, respectively, and the secondary phase is YN.

Borosilicate glasses with high softening points for glass-ceramic/copper multilayer substrates

We have developed borosilicate glasses with high softening points for glass-ceramic / copper multilayer substrates. The softening points of this glass ranged from 900°C to 1000°C. Glass-ceramics made using this glass barely sintered below 850°C, but sintered compactly at temperatures just below 1050°C. Green sheets made using this glass-ceramics could be fired around 850°C to remove the binder. Binder removal was caused very fast at this temperature. The glass-ceramics could be co-sintered with copper and had various advantages, such as easy binder removal, a coefficient of thermal expansion approximately equal to that of silicon, a low dielectric constant, sufficient flexural strength, and high water durability. These advantages helped make the manufacturing process of the substrate more productive.

Study on Solvent Debinding Process of Powder Injection Molded Ti(C, N)-Based Cermets

The solvent debinding processes of wax-based binders in powder injection molded Ti(C,N)-based cermets were studied. Effects of debinding temperature, debinding time, sample thickness, solvent types and solvent concentration on binder removal were investigated. Also, the dimension change of samples during the solvent debinding process was studied. It can be found that upwards of 70% paraffin waxes were removed and open pore channels were formed basically when the samples were immersed in heptane for 6 h at 50 °C.

Numerical and experimental investigations on thermal debinding of polymeric binder of powder injection molding compact

A mathematical model is established to describe the thermal debinding process of polymeric binder from a powder injection molding compact. The model takes into account of the thermal degradation of liquid polymer into liquid volatile fragment, the evaporation of liquid volatile fragment, the capillary driven liquid phase transport, the binary diffusion in solution, the convection and diffusion of gas phases, and the heat transfer in a porous medium. The proposed model is solved numerically based on a finite volume method and validated with experimental data. Based on the numerical results, the binder removal, the pressure buildup, the binder distribution, the mass transfers, and the removal mechanisms during thermal debinding are studied.

Injection moulding of alumina with partially water soluble binder system and solvent debinding kinetics

A partially water soluble binder system was successfully derived and tested for injection moulding of alumina powder. The major binder of the binder system was comprised of poly(2-ethly-2-oxaline) and polyethylene glycol and these constituents formed the water soluble fraction of the system. The rheological properties of the feedstock were investigated systematically over a temperature range of 120 to 160°C and a shear rate range of 100 to 1000 s−1. Binder removal was accomplished using a two stage process. The water soluble constituents were removed by water leaching. The remaining binder constituents were removed by thermal pyrolysis. The solvent debinding kinetics of the water leaching process were studied as a function of temperature, ranging from 40 to 80°C. Solvent debinding is a two stage process consisting of dissolution and diffusion. In this study, dissolution was the rate limiting step during the first stage of water leaching over a leaching time of 90 min at 40°C. As the process proceeds, it is shown that diffusion becomes the rate limiting step.

Effects of Different Debinding Atmosphere on the Properties of Powder Injection Molded AlN Ceramics

In the present work the influence of two different thermal debinding atmosphere, vacuum and air, on the properties of 5wt% Y2O3-doped aluminum nitride (AlN) ceramics was investigated. The AlN powder as a raw material was synthesized by self-propagating high-temperature synthesis (SHS) and compact was fabricated by employing powder injection molding technique. The polymer-wax binder consists of 60wt% paraffin wax (PW), 35wt% polypropylene (PP) and 5wt% stearic acid (SA). The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. After the removal of binder, specimens were sintered at 1850˚С in nitrogen atmosphere at atmospheric pressure. The result reveals that debinding atmosphere has significant effect on the thermal conductivity and densification of AlN ceramics. The microstructure and secondary phase identification was determined by scanning electron microscopy and X-ray diffraction. The thermal conductivity and density of injection molded AlN ceramics are 177.3W·m-1·K-1 and 3.31g·cm-3 in the air and 200.8W·m-1·K-1 and 3.28g·cm-3 in the vacuum.

Injection Molding of Zirconia Ceramics Using Water-Soluble Binder

Water-soluble binder based injection molding of submicrometer-sized and stabilized zirconia was reported in this paper. The binder phase is chosen as the mixtures of polyethylene glycol, high-density polyethylene, polyvinyl butyral and stearic acid. Binder removal is accomplished by a two-steped process. The water-soluble constituent is firstly removed by dissolution in the water and the remaining is removed through the followed thermal treatment. The apparent viscosities of different kinds of feedstock were tested. The influences of water-leaching time and temperature on the efficiency of PEG removal were discussed.

Influence of microstructure on the abrasive edge wear of WC–Co hardmetals

Abrasive wear of the tool edge is a damage observed in various industrial applications. Although, the abrasive wear of flat specimens has been investigated thoroughly, still there are some challenges in the understanding of edge wear micromechanisms. In the present research, edge wear of coarse WC–6,9,14 wt.%Co and ultrafine/nano WC–5,6,9 wt.%Co hardmetals was examined using edge-on-disc abrasion test using P800 SiC abrasive paper. The specimens had an edge angle of 90° and were abraded in a direction perpendicular to the edge line. Experimental results demonstrated that Co content and WC grain size influenced wear resistance of the edge remarkably. Increase in Co content resulted in decrease of wear resistance in the coarse and in the ultrafine grades. Comparing to the ultrafine grades of the same Co content, the coarse grades demonstrated higher wear rates at the beginning of sliding, but lower wear rates at the final stages. This behaviour was associated with a transition of pullout of WC grains at the beginning to a binder removal followed by WC grains detachment at final stages. The ultrafine grades showed ploughing wear over all the sliding distances.

Fabrication and characterization of YSZ/Ni-YSZ bi-layered composites using thermoplastic coextrusion

The thermoplastic coextrusion process was used to fabricate YSZ/Ni-YSZ bi-layered composites. In this method, an initial feedrod was prepared by assembling YSZ and NiO-YSZ thermoplastic compounds to produce a monolithic body with a cross-section of 24 mm × 24 mm and then coextruded through various orifices having dimensions of 24 × 2, 1 and 0.6 mm at 120 °C. This simple process produced thin plates with a remarkable reduction in thickness, while preserving the YSZ:NiO-YSZ thickness ratio of 1:39. After binder removal, the samples were co-fired at 1350 °C for 3 h in air, followed by reduction at temperatures ranging from 700 to 900 °C for 5 h in an Ar-5% H 2 atmosphere. Using this method, it was possible to fabricate a YSZ/Ni-YSZ bi-layered composite without any noticeable defects, in which a 11-μm thick dense YSZ layer was coated onto a 400-μm thick Ni-YSZ cermet. Furthermore, the fabricated samples showed reasonable electrical conductivities, thus rendering them suitable for use as the basic components of planar solid oxide fuel cells (SOFCs).

Preparation of a Porous Cermet SOFC Anode Substrate by Gelcasting of NiO–YSZ Powders

A porous NiO–YSZ substrate for anode‐supported solid oxide fuel cells has been prepared by gelcasting of NiO–YSZ powders using urea–formaldehyde monomers, followed by humidity‐controlled drying, binder removal, and sintering of the gelled bodies. The gelled bodies had sufficient strength to remove even 2‐mm‐thick samples from the mold immediately after gelation. A gelcast NiO–YSZ sample sintered at 1450°C for 2 h showed an open porosity of ∼53 vol%, and the porosity increased to ∼58% upon reduction with hydrogen. Pore sizes measured on the scanning electron microscopy photomicrograph of NiO–YSZ and Ni–YSZ cermet substrates are in the range of 2–5 μm. Urea–formaldehyde polymer, present in a high amount (∼13 wt%) in the gelcast body, acts as a template for pores.

Development of Compact Process using Microwave Heating

Conventionally the manufacturing of ceramic parts consists of various processes such as pulverization of raw materials, dispersion, mixing, drying, shape forming, removal of organic binder, sintering and machining. We proposed new manufacturing processes using microwave technique, a technique named “compact process,” for the significant enhancement of manufacturing speed and ultimate improvement of productivity of ceramics fabrication, in which the complicated operations are reduced to simplified processes. In this report, the effects on the characteristics of sintered body and decreasing of energy consumption by compact process will be discussed.

Degradation and the kinetics of binder removal

Manufacturing large anodes for aluminium smelting by PM processes is far from simple, and efficient binder removal from the green body is a primary requirement…

Factors Influencing Anisotropic Sintering Shrinkage in Tape‐Cast Alumina: Effect of Processing Variables

The effect of the processing variables shear rate, solids loading, and sintering temperature on the anisotropy of sintering shrinkage of aqueous tape‐cast alumina was studied. Higher shear rates and higher solids loading resulted in higher in‐plane shrinkage anisotropy, whereas the shrinkage anisotropy in the thickness direction was higher for low solids loadings. The in‐plane shrinkage anisotropy was found to be fairly constant above a certain critical shear rate (∼100 s−1) independent of the solids loading. The shrinkage anisotropy through the thickness was higher than in‐plane directions. A higher thickness direction sintering rate was observed and attributed to a greater number of interparticle necks in the thickness direction because of the platy nature of alumina particles and the greater thickness direction strains associated with binder removal. The binder did not significantly affect the in‐plane sintering shrinkage but significantly affected the shrinkage in the thickness direction. It was suggested that emulsion binder particles occupy sites in between layers of particles in the thickness direction. The degree of anisotropic shrinkage was quantified using edge orientation polarograms and a direct correlation was obtained between the processing variables, shrinkage anisotropy, and the edge orientation index.

Binder Removal from Ceramic‐Filled Thermoplastic Blends

Thermogravimetric analysis is used to examine the degradation of a multicomponent polymer binder consisting of a blend of a polyethylene co‐ethyl acrylate with a polyisobutymethacrylate polymer. In the polymer blends without ceramic powder, the methacrylate component degrades at a temperature lower than the ethylene copolymer. Minor additives polyethylene glycol, stearic acid, and paraffinic mineral oil are also considered. The thermal degradation of a five‐component blend is only approximately as expected from the individual components, with retardation of the methacrylate degradation. Oxide ceramic powder significantly alters polymer degradation, retarding degradation in the early stages but accelerating degradation in the later exothermic stages. Polymer–polymer interactions and oxide–polymer interactions make the degradation behavior of blends difficult to predict from single component behavior.

Hydroxyapatite (HA) bone scaffolds with controlled macrochannel pores

Hydroxyapatite (HA) macrochanneled porous scaffolds, with a controlled pore structure, were fabricated via a combination of the extrusion and lamination processes. The scaffold was architectured by aligning and laminating the extruded HA and carbon filaments. The macrochannel pores were formed by removing the carbon filaments after thermal treatments (binder removal and sintering). The porosity of the scaffolds was varied between 48 and 73% with a controlled pore size of approximately 450 microm, by adjusting the fractions of HA and carbon filaments. As the porosity was increased from 48 to 73%, the compressive strength decreased from 11.5 to 3.2 MPa. However, the osteoblast-like cell responses on the scaffold, such as the proliferation rate and alkaline phosphatase (ALP) activity, were significantly enhanced as the porosity was increased.

Application of fused deposition in controlled microstructure metal‐ceramic composites

PurposeAl‐alumina interconnected phase composites were processed using the direct fused deposition process. These materials with tailored microstructures can find applications as structural materials with gradient properties.Design/methodology/approachIn this process, feedstock material with fused silica as a starting material was compounded at a high shear mixer and then extruded as a filament using a single screw extruder. Extruded filaments were used with a commercial fused deposition modeler, FDM 1650, to process controlled porosity green ceramic structures. Porous green ceramic preforms were subjected to binder removal and sintering cycles in furnace air. Controlled porosity sintered ceramic structures were infiltrated with Al 5052 metal by pressureless reactive metal infiltration to form an in situ Al‐alumina structured composite.FindingsThe main advantage for this approach is to control distribution of both metal and ceramic phases in the composite. During metal infiltration good bonding was observed between the metal and the ceramic phases. Composites were tested under both quasi‐static and dynamic shock loading to evaluate their mechanical properties. Compression strength of these composites was 689±95 MPa.Originality/valueThis paper describes application of the direct fused deposition process for fabrication of ceramic/metal composites where both macrostructure as well as microstructure can be controlled simultaneously. The paper also focuses on one of the potential application area for 5052‐Al alloy.

Wear surface studies on coal water slurry nozzles in industrial boilers

In this study, Al 2O 3/(W,Ti)C ceramic, WC/Co cemented carbide, and 1Cr18Ni9Ti stainless steel were produced to be used as nozzle materials in coal water slurry (CWS) industry boilers. Coal water slurry burning tests with these nozzles were carried out. The wear surface features of the nozzles made from these materials were examined. The results showed that the wear mechanisms of nozzles varied from entry to exit. The material removal of Al 2O 3/(W,Ti)C ceramic nozzle in CWS atomizing and burning is attributed to a mixed mode damage by brittle fracture, polishing, thermal cracking and chipping. The nozzle entry section appears to be entirely brittle in nature with evidence of large scale-chipping. The centre bore area showed a polishing effect with a very smooth surface. While the exit section exhibits cracking owing to the large thermal shock. Examination of the eroded bore surface of the WC/Co cemented carbide nozzles demonstrated that the wear occurred through preferential removal of the metal binder (Co) followed by pluck-out of the exposed WC grains at the entry zone, while the center and the exit zone showed polishing action. The primary wear mechanisms of 1Cr18Ni9Ti stainless steel nozzle exhibited plastic deformation at the entry zone, and plowing and micro-cutting at the other zones by the eroded particles.

Heat Transfer in Porous Green Bodies During Binder Removal by Minimum Time Heating Cycles

Heat transfer in ceramic green bodies is examined during rapid binder removal cycles predicted by a variational calculus algorithm. Both the heat transfer and the mass transfer problems are described by one‐dimensional spatial models, for which analytical solutions are available. During the minimum time heating cycles, the temperature difference within the green body is shown to depend on the thermal diffusivity, on the permeability, on the threshold pressure at which failure of the green body occurs, and on a number of other kinetic and transport parameters. The temperature difference within the green body is smallest during the early part of the minimum time heating cycle, when the constraint on pressure buildup within the green body limits the rate at which the temperature can be increased.

Microporous alumina substrate with porosity >70% by gelcasting

Microporous alumina membrane substrate in tubular and planar configurations have been prepared by gelcasting of alumina powder slurry using high amount of urea–formaldehyde as gelling agent followed by humidity controlled drying, binder removal and sintering of the gelled bodies. Porosity of the substrate samples sintered at 1350 °C was more than 70% as measured by mercury porosimeter. More than 51% porosity could be retained even after sintering of the samples at 1450 °C. Average pores size of the membrane substrate samples sintered at temperature in the range from 1250 to 1550 °C varied between 0.42 and 0.56 with a maximum at 1350 °C. More uniform pores were observed in sample sintered at 1450 °C. Urea-formaldehyde polymer present in the gelcast body acts as template for micropores.