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Abstract A study was carried out to evaluate the wear properties of Binder Jet 3D Printed (BJ3DP) WC-12% Co per the ASTM B611 and G65 test methods. The printed samples were sintered under a pressure of 1.83 MPa at 1485 °C for 5 min to achieve near theoretical densities. A dual WC grain size was observed in the microstructure of the sintered parts. The microstructure largely consists of 1.4–2.0 μm WC grains and clusters of coarse grains ranging in size up to ~ 20 μm in the Co matrix. The samples showed a volume loss of 140.48 ± 2.73 mm3during the B611 testing. The wear resistance of the samples was found to be superior to that of standard cemented carbides with similar amount of Co. The superior wear resistance is attributed to the dual grain size microstructure. The SEM micrographs of the wear surfaces after B611 testing showed the fragmentation and pull out of WC and substantial wear of the Co matrix. The G65 wear testing showed a volume loss of 3.67 ± 0.66 mm3. The SEM micrographs of the wear surfaces after the G65 testing showed wear occurring primarily in the Co matrix. The results from the present study confirm the feasibility of the BJ3DP process to fabricate WC-12%Co parts with superior wear resistance properties. Highlights • Wear properties of Binder Jet 3D Printed (BJ3DP) WC-12%Co was evaluated. • The samples showed a volume loss of 140.48 ± 2.73 mm3 during the B611 testing. • The G65 wear testing showed a volume loss of 3.67 ± 0.66 mm3. • The superior wear resistance is attributed to the dual grain size microstructure. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) is a promising technique for the fabrication of complex net shaped parts of many metals. However, the high melting temperature of tungsten makes fabricating complex parts via SLM difficult. A study was undertaken to understand the effect of process parameters like hatch spacing and scan speed on the densification of tungsten by the SLM technique. Experiments were conducted at hatch spacing of 15 and 30 μm and scan speeds in the range 200–1400 mm/s. A constant laser power of 90 W and a powder layer thickness of 30 μm were used. Rectangular cuboids of 7.8 ± 1.4 mm × 10.1 ± 0.1 mm × 10.1 ± 0.04 mm were printed using various process parameters and analyzed for densification. The densification of tungsten was found to increase with an increase in energy density. A maximum density of 75% theoretical was achieved at energy density of 1000 J/mm 3 . [ABSTRACT FROM AUTHOR]

A study was carried out to evaluate the sintering densification, shrinkage and mechanical properties of WC-12%Co powders processed by binder jet 3D printing (BJ3DP). After debinding, vacuum sintering at 1435–1485 °C for 45 min yielded low sintered densities in the range of 13.1–13.5 g/cm 3 . Near theoretical densities of 14.1–14.2 g/cm 3 were achieved by sintering the parts under a pressure of 1.83 MPa at 1485 °C for 5–30 min. Shrinkage in the range of 22.2–24.4% and 20.9–26.2% was observed in the parts sintered in vacuum and under pressure, respectively. The samples densified to near theoretical density showed hardness of 1256 HV30 and fracture toughness of 17 ± 1 MPa m 1/2 . The hardness and fracture toughness are in line with the properties of conventionally produced WC-12%Co with medium grain size. The results from the present study confirm the suitability of the binder jet 3D printing (BJ3DP) process to manufacture WC-Co parts with good mechanical properties. [ABSTRACT FROM AUTHOR]

The capability of thermal plasma technique to produce nanocrystalline tungsten powder from tungsten oxide and tungsten carbide powder form a mixture of tungsten oxide and carbon in a single step process was investigated. The amount of tungsten and tungsten carbide powders formed strongly depended on the hydrogen flow and power. Due to short exposure time of tungsten oxide and carbon to plasma, complete reduction or carburization was not achieved. The crystallite size of the reduced W and the resulting W 2 C was under 70 nm. The free carbon, total carbon and surface area of the powders decreased with increase in hydrogen flow rate and power. The results from the study highlight the challenges involved in obtaining successful reduction and carburization of the tungsten oxide in a one step process. Near complete carburization was achieved after heating the plasma treated powders at significantly lower temperature of 1000 °C for 1 h in hydrogen atmosphere. The results from the study introduce a potential two-step process to economically manufacture nano size tungsten carbide powder. [ABSTRACT FROM AUTHOR]

Abstract: The development of methods to increase sintered density and improve dimensional tolerances is a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of starting powders is one effective route to achieve high sintered density and dimensional precision. The current paper presents an in-depth study on the effect of nanoparticle addition on the powder content of SiC and AlN powder–polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder volume fraction (solids loading) in the mixtures for injection molding. This observation to increasing packing density by using nanoparticles is surprising and novel since nanoparticles are known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the monomodal μ-suspensions. The ability to lower the suspension viscosity by adding nanoparticles to micron-sized particles has important implications for processing of particulate suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting. Samples made from bimodal powders exhibited slower polymer removal during debinding and higher densification with lower shrinkage on sintering compared to the corresponding samples made from monomodal powder mixtures. [Copyright &y& Elsevier]

Abstract: The effects of nanoparticle addition on the multi-step debinding of injection molded aluminum nitride (AlN) samples were studied. Experiments varying the solvent debinding conditions (time, temperature and aspect ratio) were performed on monomodal, microscale (μ) and bimodal, micro-nanoscale (μ-n) AlN samples. Variations in the solvent debinding kinetics as a result of the reduced particle size and increased powder content were examined. The bimodal μ-n AlN samples showed a slower solvent extraction of binder components compared to monomodal μ-AlN samples. The activation energy for solvent extraction estimated from diffusion coefficients (Arrhenius equation) was in close agreement with the value estimated by the master debinding curve (MDC) method. An activation value around 50kJ/mol was estimated by both the methods for μ and μ-n AlN samples. The thermal debinding behavior of dewaxed samples was also studied and the trends correlated with the solvent debinding behavior. [Copyright &y& Elsevier]

Abstract: Field assisted sintering (FAST) has emerged as a useful technique to densify ultra high temperature ceramics like HfB2-20SiC to a high density at relatively low temperatures and shorter times. The effect of various process variables on the densification during spark plasma sintering of HfB2-20SiC was studied using Taguchi analysis. The statistical analysis identified sintering temperature as the most significant parameter affecting the densification of HfB2-20SiC material. A density of 99% was achieved on sintering at 2373K for 8min at 30kN pressure and heating rate of 100K/min. [Copyright &y& Elsevier]

Abstract: Ammonium dimolybdate ((NH4)2Mo2O7) or molybdenum trioxide (MoO3) is used as starting raw materials for manufacturing Mo powders. In the initial step, usually carried out in rotary calciners, (NH4)2Mo2O7 or MoO3 is reduced to MoO2. Agglomeration of powder due to melting of eutectic formed between MoO3 and Mo4O11 and due to melting of MoO3 occurs during this reduction step resulting in several manufacturing issues. The reduction from (NH4)2Mo2O7 involves an endothermic reaction however, reduction of MoO3 occurs only by exothermic reaction. It is hypothesized that addition of (NH4)2Mo2O7 to MoO3 will decrease agglomeration of powders due to the endothermic reaction involved in the reduction process. The current paper details experiments carried out to verify the hypothesis. MoO3 containing varying amounts (NH4)2Mo2O7 were reduced at 550°C, 650°C and 750°C in hydrogen atmosphere. The results show lower agglomeration of powder with addition of (NH4)2Mo2O7. The thermal analysis results confirm reduction of MoO3 at lower temperatures with the addition of (NH4)2Mo2O7. [Copyright &y& Elsevier]

Abstract: Molybdenum powder is manufactured in a two step process starting from MoO3. The first step reduction of MoO3 to MoO2 is carried out in rotary calciners. Agglomeration of powder occurs during this reduction stage resulting in several manufacturing issues. The evolution of agglomeration during the reduction of MoO3 was investigated in the current study. As-received MoO3 and MoO3 milled for 0.5h were used as the starting powders. The powders were reduced at 550°C, 650°C and 750°C in a hydrogen atmosphere. The starting and reduced powders at various temperatures were analyzed using BET surface area, XRD, and SEM techniques. The surface area of the reduced powders was monitored for quantifying the degree of agglomeration. The surface area was found to be minimum for the samples reduced at 650°C. SEM observations confirmed the agglomeration of powders during reduction process. XRD analysis showed complete reduction of MoO3 to MoO2 at 650°C and 750°C. The agglomeration of the powders was either due to melting of eutectic formed between MoO3 and Mo4O11 or due to partial melting of MoO3. The reduction of MoO3 is recommended to be completed at a low temperature to prevent agglomeration of the oxide powders. [Copyright &y& Elsevier]

Printed parts displaying good green/handling strength are vital for the Binder Jet 3D Printing (BJ3DP) process to succeed in manufacturing complex parts with thin sections and tiny intricate features. A study was carried out to understand the effect of the binder saturation and powder layer thickness on green strength of the printed samples. The ability of using the green strength data of the samples to identify the optimum processing conditions for printing was examined. The strength of the parts were evaluated after printing at binder saturation levels of 45–75% and powder layer thickness of 50-70 μm. For any given powder layer thickness, the strength of the samples increased with increase in binder saturation. The samples printed at 60 and 75% saturation showed similar strengths at 50 and 60 μm layer thickness. However, the strength decreased with further increase in powder layer thickness to 70 μm. Doubling the binder set time and increasing the binder saturation options were evaluated to minimize the difference in the strength of the parts printed at 60 and 70 μm thickness. Increasing the binder saturation was found beneficial in minimizing the difference in the strength of the parts printed at 60 and 70 μm thickness compared to doubling the binder set time. • Ability of green strength to identify optimum conditions for BJ3DP was examined. • The strength of the samples increased with increase in binder saturation. • Samples printed at 60&75% saturations showed low strength at 70 μm layer thickness. • High binder amount lowered strength changes in printed parts at 60&70 μm thickness. [ABSTRACT FROM AUTHOR]