Sintered Tungsten Heavy Alloys Research Articles

Sintered tungsten heavy alloys: Review of microstructure, strength, densification, and distortion

Tungsten heavy alloys are fabricated using liquid phase sintering to form inertial, electrical, radiation, or structural components. The compositions, initially developed a century ago, are based on various W-Ni-(Fe/Cu/Co/Mo) alloys. Two classes, and W-Ni-Fe and W-Ni-Cu, remain the most popular. Nickel is key to sintering densification, producing the majority of sintering shrinkage prior to liquid formation. Sintering densification and distortion depend on the gravitational environment. Normal gravity induces distortion after densification, while sintering in microgravity fails to reach full density yet distorts. Mechanical properties are adjustable via changes to the composition, sintering cycle, or post-sintering treatment. Increased strength, with a loss of ductility, comes with post-sintering deformation and aging treatments. As shown here, a range of mechanical property combinations are possible. Processing options designed to improve strength invariably result in a loss of ductility, and vice versa. Peak property combinations are attainable over a broad tungsten content range, reflecting convergence to a self-similar microstructure.

Effect of Transition Metals Oxides on the Physical and Mechanical Properties of Sintered Tungsten Heavy Alloys

The addition of transition element oxides to tungsten heavy alloys (WHAs) fabricated by powder metallurgy technique provides new materials with higher density and electrical conductivity, which may be adequate in some applications such as kinetic energy penetrators. Additionally, materials with higher electrical conductivity are required for electrical contact applications such as electrical discharge machining (EDM) electrode materials. WHAs were fabricated by compacting its mixed constituents followed by sintering. Ni, Co and Fe are used as binding phases of the tungsten particles and oxides of Zr, Ti and Y are used as oxide dispersing strengthening (ODS) agents of the sintered materials. The results show that all of the chosen factors (i.e., pressure of compaction process, temperature of sintering, type of binding material and type of oxide) have clear effects on all properties of ODS tungsten heavy alloy specimens. The density and electrical conductivity increase with the increase in sintering temperature. Hardness and compression strength were also measured to evaluate the mechanical properties of sintered samples.

Substitution of Ni with NiB prevents shape distortion of liquid phase sintered 90W–6Ni–2Fe–2Co heavy alloys

The shape distortion of liquid phase sintered tungsten heavy alloys (WHAs) depends on different factors. Here, the effect of partial and full substitution of Ni with its monoboride (NiB) on distortion characteristics of 90W–6Ni–2Fe–2Co (wt.%) heavy alloy is investigated systematically without changing wt. fraction of W. The phase and microstructural evolution during sintering and effect of microstructural parameters on the distortion is studied. In order to understand the phase and microstructure evolution of the matrix phase of sintered samples, free-standing samples were prepared using the composition of the matrix phase under similar sintering conditions. XRD patterns of sintered sample show characteristic W-peaks along with austenitic matrix phase, whereas, in the case of free-standing samples majority of reflections corresponding to matrix phase (fcc, lattice parameter = 0.360 nm) eliciting a peak shift to slightly higher 2θ values as opposed to those of sintered samples. The FESEM micrographs of free-standing samples reveal microstructure resembling a hypoeutectic system with decreasing inter-lamellar and proeutectic spacing with the extent of NiB substitution. In the sintered 90W–6Ni–2Fe–2Co system, shape distortion resulted in elephant-foot formation (distortion parameter: 22.9). Owing to the partial and full substitution of Ni with NiB, the shape distortion is restricted by formation of uniformly contiguous microstructure, inherent microstructural changes of the matrix phase, increase in dihedral angle, and grain connectivity in partially (90W–3Ni–3NiB–2Fe–2Co) and fully (90W–6NiB–2Fe–2Co) NiB substituted samples, respectively. As a result, the distortion parameter reduces from 22.9 to 9.3 and to 3.7 for partially and fully substituted NiB samples.

On the remarkable fracture toughness of 90 to 97W-NiFe alloys revealing powerful new ductile phase toughening mechanisms

Tungsten is generally too brittle to serve a robust structural function. Here, we explore the fracture toughness of 90–97 wt%W Ni-Fe liquid phase sintered tungsten heavy alloys (WHAs). The room temperature (RT) maximum load fracture toughness (KJm ≈ 69–107 MPa√m) of the WHA, containing only 3–10 wt% of a Ni–Fe ductile phase (DP), is ≈ 9–13 times higher than KIc typical of monolithic W (≈ 8 MPa√m). All the WHAs show extensive stable crack growth, and increasing blunting line toughness averaging ≈ 170 MPa√m, prior to significant crack extension. In contrast to classical ductile phase toughening, that is primarily due to macrocrack bridging, the WHA toughness increase mainly involves new mechanisms associated with arrest, blunting and bridging of numerous dilatational shielding process zone microcracks in the macrocrack process zone. Tests down to –196 °C, to partially emulate irradiation hardening, show decreasing toughness and a transition to elastic fracture at a temperature of –150 °C for 90W to –25 °C for 97W. However, even at –196 °C, the leanest DP 97W WHA KIc is ≈ 3 times higher than that of monolithic W at RT. Possible effects of the small specimen size used in this study are briefly summarized.

Forced Circulation of Nitrogen Gas for Accelerated and Eco-Friendly Cooling of Metallic Parts

As nitrogen is nonreactive and non-flammable, it can provide a quick and simple medium of cooling and environment protection. One disadvantage of nitrogen cooling is its lower heat transfer coefficient than water. Despite its lower cooling capacity, nitrogen cooling can produce cleaner products, thereby eliminating the need to wash the parts and dispose of the contaminated water. In this study, an innovative nitrogen cooling system was developed for an accelerated and eco-friendly cooling of metallic parts. The dry nitrogen gas, transported via the nozzle of a cryogenic liquid nitrogen tank, is passed into the cooling chamber and exchanges heat with the workpiece. The heated nitrogen gas is forcibly transported to the chiller, where the heat is reduced, and the cooled gas is circulated again. The performance of this nitrogen cooling system has been evaluated with cooling experiments of sintered tungsten heavy alloys. The nitrogen-cooled product shows a clean surface with improved mechanical properties. Furthermore, nitrogen induces less distortion compared to water cooling, thus reducing the post-machining costs.

Effects of sintering temperature and Ni/Fe ratio on ballistic performance of tungsten heavy alloy fragments

The aim of this study was to investigate the effects of the sintering temperature and Ni/Fe ratio on the ballistic performance of liquid-phase sintered tungsten heavy alloys. The powder mixtures were pressed under 300 MPa and sintered at 1460, 1480, and 1500 °C for approximately 30 min in a reducing and protective atmosphere. Ballistic tests were performed by accelerating tungsten heavy alloy fragments with a velocity of ~900 m/s toward a 25 mm-thick Al 6061-T6 target. Simulation studies were performed using the finite-element method to model the deformation of the fragment and the target. The experimental results showed that the highest residual velocity and the best perforation performance for multiple-layered targets were obtained with a 93 W-4.67Ni-2.33Fe alloy sintered at 1480 °C, and the increase in the sintering temperature and plastic deformation of the fragments enhanced the damage on the target during the impact process via hole enlargement on the target. The simulation results showed that the mesh sizes of the fragment and the target affected the modeling of the fragment/target deformation and the residual velocity of the fragment. Additionally, the simulation results showed good correlation with test results with regard to the modeling of the deformation at the impact and rear surfaces of the target during perforation.

On the Remarkable Fracture Toughness of 90 to 97W-NiFe Alloys Revealing Powerful New Ductile Phase Toughening Mechanisms

Tungsten is generally too brittle to serve a robust structural function. Here, we explore the fracture toughness of 90 to 97%W (by wt.) liquid phase sintered tungsten heavy alloys (WHAs). The room temperature (RT) maximum load fracture toughness (KIc or KJm ≈ 38 to 107 MPa√m) of WHA, containing only 3 to 10 wt.% of a NiFe-based ductile phase (DP), is ≈ 5 to 13 times higher than KIc typical of monolithic W (≈ 8 MPa√m). RT tests for a range of precracked bend bar sizes generally show extensive stable ductile tearing (DT), except in the case of the 97 wt.%W alloy, where elastic fracture occurs in all but the smallest specimen tests. Nevertheless, even in this case the KIc = 38 ± 4 MPa√m, which is still almost 5 times higher than that for monolithic W. Tests with the smallest specimens down to -196°C, to partially emulate irradiation hardening, show decreasing toughness and a transition to elastic fracture at a temperature of -150°C for 90W to -25oC for 97W. However, even at -196°C, the 97W KIc is ≈ 3 times that of monolithic W at RT. In contrast to classical ductile phase toughening by macrocrack bridging, WHA toughening mainly involves new mechanisms associated with arrest, blunting and bridging of numerous dilatationally shielding process zone microcracks.

Microstructure and mechanical properties of spark plasma sintered tungsten heavy alloys

The effect of cobalt (0.5wt%, 1.0wt%, 1.5wt% and 2.0wt%), as an alloying element, on the microstructure and mechanical properties of W-Ni-Fe tungsten heavy alloy (WNF) prepared through spark plasma sintering (SPS) process is investigated in this work. The sintering is performed at 1400°C with a heating rate of 100°C/min and holding time for a period of 2min. The properties of the cobalt added heavy alloys (WNFC) are found to be superior to that of the tungsten heavy alloy without cobalt addition. The 1.0% cobalt alloy is observed to give higher yield and tensile strengths compared to other alloys. As the mechanical properties of the alloys depend on the microstructural features, a detailed study on the influence of the microstructural parameters such as average grain size, contiguity and matrix volume fraction on the properties of the alloys is carried out. The average tungsten grain size of WNF alloy is 12.3µm and that of WNFC alloys is from 9.5µm to 11.5µm. The control of grain size is significantly evident in the case of spark plasma sintered alloys. The yield strength is found to be influenced by the W-grain size of the microstructure. The contiguity of the WNFC alloys is observed to decrease with increase in percentage of cobalt addition. The fractograph analysis of the tensile tested specimen helps in understanding the tensile behaviour of the alloys. The WNFC alloys show predominantly W-grain cleavage fracture compared to the WNF alloy, possibly due to the good cohesive strength of the matrix phase and W/matrix interface, because of cobalt addition and also due to the high heating rate followed in the SPS process.

Micro Structural Evolution of a 93 Wt% Tungsten Heavy Alloy: A Quenching Study to Understand the Evolution of Contiguity, Connectivity with Sintering Temperature and Time

Sintering temperature and time have an effect on the densification and distortion of liquid phase sintered tungsten heavy alloys. Quenching was used to observe the in situ microstructure at different temperatures and times. A 93 wt.% tungsten heavy alloy (WNi-Fe) was quenched from different temperatures and from 1500°C at different hold times and the micro structural parameters such as contiguity, connectivity, and grain size which define the critical sinter window for achieving full density without compromising dimensional control and mechanical properties are assessed. In situ measurements of Contiguity indicate that contiguity decreases at a rate of approximately 0.1/min during the initial minutes after liquid formation, indicating rapid dissolution of tungsten grains in the liquid matrix. The rate of penetration of the neck or grain boundaries is calculated as 0.018 μm/s, and this corroborates with drop in contiguity in the initial few minutes after liquid formation. The reduction in contiguity and connectivity is attributed to the dissolution of the necks between the tungsten grains, from the dissolution rate calculated in this study, it calculated that the grain boundaries dissolve within 3-4 minutes of liquid formation, which is validated by the experiments.

EFFECT OF ALLOY COMPOSITION ON THE MECHANICAL PROPERTIES AND FRACTURE BEHAVIOR OF TUNGSTEN HEAVY ALLOYS

ABSTRACT The objective of this experimental study is to investigate the effect of the alloy composition on the mechanical properties and the fracture behavior of the liquid phase sintered tungsten heavy alloys. Tungsten alloy with three different compositions 93%W-4.9%Ni-2.1%Fe,91%W-6%Ni-3%Co and 90.5%W-5.6%Ni-2.4%Fe-1.5%Co were prepared and used in this investigation. Elemental powders were mixed using planetary mixer for 5 hours to ensure suitable homogeneity. Uni-axial compaction pressure of 200 MPa was applied to obtain standard tensile and impact specimens. Vacuum liquid phase sintering was carried out under different temperatures from 1470ᵒC up to 1530ᵒC for 90 minutes.The effect of changing the alloy composition particularly, the binder constituents was characterized in terms of density, hardness, impact resistance and tensile properties for samples in the as sintered state. Fracture behavior of the used tensile fracture specimens having different compositions was studied, and the relation between the obtained fracture modes and tensile properties of these alloys was indicated.The obtained results indicated that hardness increases with increasing the cobalt content, Moreover, the tensile strength increases, in a first stage, by adding cobalt up to 1.5wt.%, due to the strengthening effect of cobalt. Further increase in cobalt content decreases strength. On the contrary, the ductility and impact resistance showed a continuous decrease with increasing the cobalt content. The results, also, clearly showed that the addition of cobalt to tungsten heavy alloy has a great beneficial hardening effect. On the other hand, it causes embrittlement due to the formation of brittle intermetallic compounds, particularly, with tungsten at the tungsten-matrix interface leading to degradation of alloy properties, which makes the dissolution of these intermetallics by a post sintering heat treatment of great importance.It was also shown that the strength of the matrix or the bonding strength of the interface (between tungsten particles and matrix) was the controlling criterion of thenature of final fracture. Poorer matrix strength or interfacial strength was found to initiate the fracture by separation of tungsten particles either by matrix failure or by interface failure. On the other hand, tensile fracture takes place predominantly by cleavage fracture of tungsten particles, if both the matrix and interface are stronger than the tungsten particles. The tensile fracture surfaces clearly indicated that failure in case of W-Ni-Fe based heavy alloys was due to matrix or interface failure. Whereas, W-Ni-Fe-Co heavy alloys were failed predominantly by cleavage fracture of tungsten particles. While, in case of W-Ni-Co based heavy alloys, the dominant fracture mode was intergranular tungsten separation. This fracture behaviour was in good correlation with the obtained mechanical properties , and indicates that the cobalt content in the binder plays a key role in dictating the failure behaviour.

Tensile and impact properties of microwave sintered tungsten heavy alloys

The present study investigates the interrelationship between microstructure, tensile and impact properties of microwave sintered tungsten heavy alloys. Alloys of two different compositions were microwave sintered and conventionally liquid phase sintered using similar heating rate, followed by microstructure and mechanical property evaluation. The tensile properties of microwave sintered alloys were significantly superior to those of liquid phase sintered alloys in both the compositions. Excellent impact properties were obtained in microwave sintered alloys, without any subsequent heat treatment or processing. In order to understand the reasons for the improvement, a detailed comparative study of microstructural features in both microwave and conventionally sintered alloys was carried out and it was observed that both tensile and impact properties of these alloys were largely influenced by tungsten–tungsten contiguity; the weakest link in the microstructure. Microwave sintered alloys were found to exhibit substantially lower contiguity as compared to the conventionally sintered alloys and consequently their properties were found to be superior as compared to the conventionally sintered alloys.

Study on the solid-phase sintering of the nano-structured heavy tungsten alloy powder

Recently, the high performance W–Ni–Fe–Co heavy tungsten alloy has become as the major core material of armor piercing ammunition. Since the melting temperature of tungsten element is too high to be fabricated by the melting process, that the W–Ni–Fe–Co alloy only can be synthesized by powder metallurgy process. In this study, two compositions of alloy powders, 93W–3Ni–2Fe–2Co and 93W–3.5Ni–1.5Fe–2Co, were selected for investigating their microstructure and mechanical properties after solid-phase sintering. These pre-alloyed powders with crystal cell size about 16 nm were synthesized by mechanical alloying (MA) the mixture of appropriate composition of pure elements in the Spex mill for 8 h. Then, the MA powders were compressed by cold isostatic pressing (CIP) and vacuum sintered at various temperature below 1400 °C for different time. Microstructure characterization of the sintered tungsten heavy alloys was conducted by means of SEM with EDS capability, X-ray diffraction (XRD), and TEM techniques. The result reveals that the microstructure of these sintered alloys was found to consist of the tungsten matrix phase and the Fe–Ni solid solution phase. The hardness of these sintered tungsten heavy alloy presents a trend with increasing sintering temperature and sintering time.

Heating rate effects on microstructural properties of liquid phase sintered tungsten heavy alloys

Dimensional precision is one of the prime concerns in forming net-shape bodies by liquid phase sintering. The factors that lead to densification can also cause distortion, leaving a narrow processing window in which to achieve densification without distortion. This paper reports the effect of heating rate on liquid phase sintering of W–Ni–Fe heavy alloys. Heavy alloys with compositions of 83, 88, and 93 wt.% W, balance Ni–Fe in the ratio 7:3, were sintered at heating rates of 1, 5, 10, and 15 °C/min. Over this range, heating rate did not have a significant effect on densification nor distortion. Critical values of contiguity and connectivity were identified that separate distortion from shape preservation. The grain size distributions produced by different heating rates are self-similar. A previously proposed cumulative intercept grain size distribution function gives a good fit to the grain size data. The mean grain growth rate constant is 2.8 μm3/s. The grain growth rate constant varies inversely with the volume fraction of liquid to the 2/3 power.

Heating rate effects on microstructural properties of liquid phase sintered tungsten heavy alloys

Dimensional precision is one of the prime concerns in forming net-shape bodies by liquid phase sintering. The factors that lead to densification can also cause distortion, leaving a narrow processing window in which to achieve densification without distortion. This paper reports the effect of heating rate on liquid phase sintering of W–Ni–Fe heavy alloys. Heavy alloys with compositions of 83, 88, and 93 wt.% W, balance Ni–Fe in the ratio 7:3, were sintered at heating rates of 1, 5, 10, and 15 °C/min. Over this range, heating rate did not have a significant effect on densification nor distortion. Critical values of contiguity and connectivity were identified that separate distortion from shape preservation. The grain size distributions produced by different heating rates are self-similar. A previously proposed cumulative intercept grain size distribution function gives a good fit to the grain size data. The mean grain growth rate constant is 2.8 μm 3/s. The grain growth rate constant varies inversely with the volume fraction of liquid to the 2/3 power.

Combination of mechanical alloying and two-stage sintering of a 93W–5.6Ni–1.4Fe tungsten heavy alloy

Abstract The microstructural evolution and mechanical properties of a mechanically alloyed and two-stage sintered tungsten heavy alloy were investigated. Elemental powders of tungsten, nickel and iron of a composition corresponding to 93W–5.6Ni–1.4Fe were mechanically alloyed in a tumbler ball mill for 72 h. Mechanically alloyed powders were solid-state sintered at 1300 °C for 1 hr in a hydrogen atmosphere followed by secondary sintering at 1445–1485 °C for a sintering time ranging from 4 to 90 min. Solid-state sintered tungsten heavy alloys exhibited full densification (above 99% in relative density) due to the enhanced sintering resulting from mechanical alloying. Secondary sintering with a rapid heating rate changed the microstructures of the solid-state sintered alloy with contiguous tungsten phases into a dispersion alloy with spherical tungsten particles embedded in the W–Ni–Fe matrix, maintaining fine tungsten particle due to the combination of a mechanical alloying and a short sintering time. The two-stage sintered tungsten heavy alloy from mechanically alloyed powders showed finer tungsten particle (about 6 μm in diameter) than in conventional liquid-phase sintered tungsten heavy alloys. The mechanical properties of a tungsten heavy alloy were found to be dependent on the microstructural parameters such as tungsten particle size, matrix volume fraction and tungsten/tungsten contiguity which are controllable through the two-stage sintering process.

Effects of sintering conditions on mechanical properties of mechanically alloyed tungsten heavy alloys

The effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20∶1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300°C for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470°C with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 μm in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6–15 μm and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix.

Multiple grain growth events in liquid phase sintering

Sintered tungsten heavy alloys consist of a solidified liquid alloy matrix phase which interpenetrates a solid tungsten skeletal structure. A consequence of liquid phase sintering is considerable grain growth while the compact densifies. The driving force for grain growth is a decrease in the interfacial surface energy, and the process itself is the combined result of liquid diffusion, solid diffusion, and vapor diffusion if porosity is present. In this study, we utilized microgravity sintered samples to avoid solid-liquid segregation to study the multiple diffusion processes. Coupled with the diffusion event through the liquid phase, there is simultaneous solid-state sintering such as coalescence. The dihedral angle determines the contiguity and the grain growth rate. The liquid diffusion grain growth rate constant is at least one order of magnitude larger than the solid diffusion grain growth rate constant. As composition changes, the ratio of grain growth contributions from these three components also changes, which, in turn, causes grain size, grain size distribution, and contiguity variations.

Microstructure and mechanical properties of mechanically alloyed and solid-state sintered tungsten heavy alloys

The mechanical properties of solid-state sintered 93W–5.6Ni–1.4Fe tungsten heavy alloys fabricated by mechanical alloying were investigated. Blended W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm employing a ball-to-powder ratio of 20:1 and a ball filling ratio of 15%. A nanocrystalline size of 16 nm and fine lamellar spacings of 0.2 μm were obtained in mechanically alloyed powders at a steady state milling stage. Mechanically alloyed powders were consolidated into green compacts and solid-state sintered at 1300°C for 1 h in a hydrogen atmosphere. The alloys sintered from mechanically alloyed powders showed fine tungsten particles (about 3 μm in diameter) and a relative density above 99%. The volume fraction of the matrix phase was 11% and the tungsten/tungsten contiguity was determined to be 0.74. The alloys exhibited high yield strengths (about 1100 MPa) due to their fine microstructures, but exhibited reduced elongation and impact energy due to a large area fraction of tungsten/tungsten boundaries and the low volume fraction of matrix phase.

Effects of Sintering Conditions on Mechanical Properties of Mechanically Alloyed Tungsten Heavy Alloys

The effects of sintering conditions on the microstructural evolution and mechanical properties of mechanically alloyed tungsten heavy alloys were investigated. W, Ni and Fe powders were mechanically alloyed in a tumbler ball mill at a milling speed of 75 rpm, ball-to-powder ratio of 20∶1 and ball filling ratio of 15%. The mechanically alloyed powders were compacted and solid-state sintered at a temperature of 1300°C for 1 hour in a hydrogen atmosphere. The solid-state sintered tungsten heavy alloy was subsequently liquid-phase sintered at 1470°C with varying sintering times from 4 min to 90 min. The solid-state sintered tungsten heavy alloy showed fine tungsten particles of 3 μm in diameter and high relative density above 99%. The volume fraction of the W-Ni-Fe matrix phase was measured, as 11% and tungsten/tungsten contiguity was 0.74 in solid-state sintered tungsten heavy alloys. Mechanically alloyed and two-step sintered tungsten heavy alloys showed tungsten particles of 6–15 μm and a volume fraction of the W-Ni-Fe matrix phase of 16% and tungsten/tungsten contiguity of 0.40. The solid-state sintered tungsten heavy alloy exhibited a yield strength of about 1100 MPa due to its finer tungsten particles, while it showed low elongation and impact energy due to its large tungsten/tungsten contiguity. The yield strength of two-step sintered tungsten heavy alloys increased with the decreasing of tungsten particle size and volume fraction of the W-Ni-Fe matrix.

The effect of porosity on distortion of liquid phase sintered tungsten heavy alloys

Porosity effects on distortion during liquid phase sintering were investigated experimentally. W–Ni–Fe alloys with compositions ranging from 78 to 93 wt% tungsten were liquid phase sintered at 1500°C for 30 min. Surprisingly, the results show that porosity has no appreciable effect on distortion. After sintering, similar distortion profiles were obtained for compacts with both high and low green porosities. On the other hand, distortion reduced with increasing solid:liquid ratio. No distortion occurred for samples with 93 wt% tungsten. Quenching experiments showed the onset of slumping was delayed until densification neared completion. In high liquid content samples, this means slumping occurred within a few minutes after melt formation, corresponding to liquid exudation. The results are in agreement with model predictions by German. The sintered microstructures were quantitatively measured for solid volume fraction and contiguity. No apparent effects of green porosity on microstructural evolution were observed.