Warm compaction powder metallurgy of Cu

A series of experiments were carried out using different admixed lubricant contents, different compaction pressures and temperatures in order to study the warm compaction of copper powder. Results show that too much admixed lubricant will lead to the squeeze out of the lubricant from the compact during the warm compaction processing of Cu powder. Results also show that blisters can be found in sintered samples that contain lubricant less than 0.15%(mass fraction). Optimal warm compaction parameters for producing high density powder metallurgy copper material are obtained. Compacts with green density of 8.6 g/cm^3 and a sintered density of 8.83 g/cm3 can be produced by warm compacting the Cu powder, which contains 0.2% admixed lubricant, and is compacted at 145℃ with a pressure of 700 MPa.     

The densification of powder mixtures containing soft and hard components under static and cyclic pressure

The effect of pressure cycling on the densification and ejection of Pb–Al₂O₃ powder mixtures is investigated and compared to static loading. The volume fraction of Al₂O₃ is varied between 0 and 80%. The density of all mixtures increases with time under constant pressure even at room temperature. This mechanical behavior is the result of the creep of lead. This effect diminishes with increasing volume fraction of Al₂O₃. Pressure cycling does not have any influence on the final density of lead samples in the absence of Al₂O₃. The influence of cycling becomes, however, noticeable in the presence of Al₂O₃ in the mixture. In this case, the density and strength of specimens are higher than the corresponding ones obtained after static pressing for the same dwell time. This effect is enhanced with increasing Al₂O₃ percentage. A static pressure approximately 50–80% larger than the cyclic one is required to achieve the same density. Moreover, the strength of compacts with high Al₂O₃ content is substantially higher after cyclic pressing than under static pressing. The ejection force is higher after cyclic compaction at a given pressure level owing to the higher density achieved.     

Die wall lubricated warm compacting and sintering behaviors of pre-mixed Fe–Ni–Cu–Mo–C powders

Polytetrafluoroethylene (PTFE) emulsion was used as die wall lubricant. Die wall lubricating warm compacting and sintering behaviors of pre-mixed Fe–2Ni–2Cu–1Mo–1C powders were studied. Results show that green density and spring back effect of pre-mixed powders all gradually increased as the compacting pressure rose. The green density of pre-mixed powder increased with the rise of compacting temperature and then slightly fell, the maximal green density was obtained at 120–140 °C. The degree of effect of warm compaction conditions on green density in turn from big to small followed as compacting pressure, lubrication, compacting temperature, mixing method and compacting speed. Die wall lubrication in combination with warm compaction effectively increased the compact density of pre-mixed powder. Sintered density of pre-mixed Fe–2Ni–2Cu–1Mo–1C material first increased and then fell as the temperatures went up after compacts were sintered at different temperatures for 50 min, but the trends of sintering dilatation were quite the reverse. Sintered density first reduced and then increased with the going on of sintering time at 1300 °C, but the trends of dimension change after sintering were just the reverse.     

Warm compaction behaviors of iron-based powder lubricated by different kinds of graphite

1　INTRODUCTIONConventionalpowdermetallurgy(PM ) process ingcanproduceiron basedPM partswithadensitylessthan 7.1g/cm3(arelativedensityofapproxi mately 90 % ) .Theirmechanicalpropertiesaresub stantiallylessthanthoseoftheirfulldensitycounter part.IncreasingdensityisthebestwaytoincreasetheperformanceofthePM parts .Therearemanyprocessesthatcanproduceiron basedPM partswithhighdensitysuchaspowderforging ,doublepress/doublesinter(DP/DS)andCuinfiltration ,butwarmcompactionisthemosteconomical…     

Effect of compact structure on phase transformation kinetics from anatase phase to rutile phase and microstructure evolution during sintering of ultrafine titania powder compacts

The effect of compact structure both on phase transition kinetics and on the densification during sintering of n-TiO₂ compacts has been investigated. The compact structures varied from loose powder pack to very high density using different compaction pressures. The compact structure is verified to significantly affect phase transition kinetics and densification during sintering. The onset temperature of anatase -> rutile phase transition decreased with the increase of the compact density. The highest density compact of 86.9% showed phase transition at the lowest temperature and no detrimental effect on densification. The compact structure, i.e., the coordination number of particles in the compacts, is considered to significantly affect both the phase transition kinetics and the subsequent densification during the sintering of n-TiO₂ compacts.     

Die wall lubricated warm compaction of iron-based powder metallurgy material

Lubricant is harmful to the mechanical properties of the sintered materials,Die wall lubrication was applied on warm compaction powder metallurgy in the hope of reducing the concentration level of the admixed lubricant.Iron-based samples were prepared by die wall lubricated warm compaction at 175℃,using a compacting pressure of 550MPa.Emulsified polytetrafluoroethylene(PTFE) was used as die wall lubricant.Admixed lubricant concentration ranging from 0 to 0.5% was tested.Extremely low admixed lubricant contents were used.Results show that in addition to the decrease in ejection forces,the green density of the compacts increases with the decrease of admixed lubricant content until it reaches the maximum at 0.06% of lubrcant content,then decreases with the decrease of admixed lubricant content.The mechanical properties of the sintered compacts that contain more than 0.06% admixed lubricant are better than those of the samples that contain lesser lubricant.No scoring was observed in all die wall lubricated experiments.     

Experimental and numerical investigation of idealized consolidation: Part II: Cyclic compaction

Prior studies have shown that the cyclic application of pressure can be far more effective in consolidating composite compacts than monotonic compaction. To study a simple system, pure aluminum and hardened steel rods were assembled in arrays and consolidated under cyclic pressure at room temperature. Idealized experiments and finite element simulations showed similar results for enhanced densification under cyclic pressure. Both inter-particle friction and pressure amplitude were shown to have important and predictable effects. Inter-particle friction hinders monotonic consolidation but assists cyclic compaction. Consolidation is enhanced with increasing numbers of pressure cycles and pressure-cycle amplitude, while the maximum pressure is fixed.     

润滑剂含量不同时W-Ni-Fe合金的温压行为

研究90W-7Ni-3Fe合金的温压成形工艺,探讨润滑剂含量不同时温压行为对硬粉的作用,并比较温压工艺与常温压制工艺的不同。结果表明：在相同单位压制压力下,温压压坯密度明显高于常温压制的;润滑剂含量为0.6%（质量分数）时压坯密度达到最大值,温压压制与常压压制相比,压坯密度增加0.26 g/cm3;润滑剂含量超过0.6%后,压坯密度又逐渐下降;添加润滑剂后合金的脱模力明显降低,其温压脱模力较常压脱模力小;试样的抗拉强度、伸长率在润滑剂含量为0.6%时达最大值,这与烧结体的密度随润滑剂含量的变化一致;同时温压烧结坯的密度与常压试样的区别不明显,但抗拉强度和伸长率都高于同批的常压试样。     

Influence of preparation process on sintering behavior and mechanical properties of ultrafine grained Ti（C, N）-based cermets

The influences of forming and sintering processes on distortion, cracking as well as mechanical properties of sintered bodies of ultrafine grained Ti（C, N）-based cermets were investigated. The results show that lubricant is indispensable to fabrication of ultrafine Ti（C, N）-based cermets, however, with low binder content in powder mixture, the lubrication action of paraffin is attenuated. A appropriate level of 2% （mass fraction） paraffin is determined for a cermet with binder content of 36% （mass fraction）. It is also found that the influence of compaction pressure on distortion and cracking of sintered bodies presents a complex relationship. A relatively lower or higher compaction pressure, less than 100 MPa and more than 400 MPa respectively, favors uniform density distribution in green compact. The heating rate of sintering should be strictly controlled. Too fast heating rate results in enclosed pores to burst and forms large size pores in sintering body. A heating rate of 3 ℃/min is recommended.     

Effects of foaming parameters on microstructure and compressive properties of aluminum foams produced by powder metallurgy method

Semi open-cell aluminum foams having channels between individual cells were produced using low cost CaCO₃ foaming agent and applying the powder compact melting process. To this end, the aluminum and CaCO₃ powder mixtures were cold compacted into dense cylindrical precursors for foaming at specific temperatures under air atmosphere. The effects of several parameters including precursor compaction pressure, foaming agent content as well as temperature and time of the foaming process on the cell microstructure, linear expansion, relative density and compressive properties were investigated. A uniform distribution of cells with sizes less than 100 μm, which form semi open-cell structures with relative densities in the range of 55.4%–84.4%, was obtained. The elevation of compaction pressure between 127–318 MPa and blowing agent up to 15% (mass fraction) led to an increase in the linear expansion, compressive strength and densification strain. By varying the foaming temperature from 800 to 1000 °C, all of the investigated parameters increased except compressive strength and relative density. The results indicated the optimal foaming temperature and time as 900 °C and 10–25 min, respectively.     

Simulation of Aluminum Powder in Tube Compaction Using Equal Channel Angular Extrusion

Aluminum powder in tube compaction with a 25 mm front plug through equal channel angular extrusion (ECAE) at room temperature was modeled using the finite element analysis package ABAQUS. The Gurson model was used in modeling this process. 2-D simulations in a 90° angle die showed better consolidation of powder near the inner edge of the die than the outer edge after one pass of ECAE but almost full densification occurs after two passes. The effect of hydrostatic pressure on densification of the powder was investigated by using two plugs varying in length dimension. The results obtained from the simulations were also compared with experiments conducted to compact aluminum powder with mean particle diameter of 45 μm. Optical microscopy, microhardness test, and density measurements confirmed the simulations. The simulations were extended to powder compaction in a 60° and 120° angle die. It was found that one pass of ECAE is sufficient to consolidate the aluminum powder completely and uniformly in a 60° angle die, whereas the material is still porous in a 120° angle die.     

Warm die compaction and sintering of titanium and titanium alloy powders

A study has been made of the effect of non-lubricated warm die (200 °C) compaction on the densification of hydride–dehydride (HDH) Ti powder, pre-alloyed (PA) Ti-6Al-4V and Ti-10V-2Fe-3Al powders, and HDH Ti and V-Fe-Al master alloy powder blends, compared to cold die compaction. Depending on the compaction pressure, which was varied from 200 to 1000 MPa, non-lubricated warm die (200 °C) compaction was very effective for −100 mesh HDH Ti powder, increasing the green density by 5.0–9.4% theoretical density (TD). Die wall lubrication with stearic acid showed no influence on the green density when compacted at 800 MPa. With warm die (200 °C) compaction, achieving a green density of greater than 90%TD was straightforward for HDH Ti powder when compacted at ≥750 MPa. Accordingly, near pore-free (≥99.5%TD) Ti microstructures were obtained after sintering at 1300 °C for 120 min in vacuum when compacted at 1000 MPa. The resulting increment in the sintered density was between 2.0%TD and 4.4%TD. Warm die (200 °C) compaction showed no effect on PA Ti-10V-2Fe-3Al powder and only a small effect on PA Ti-6Al-4V powder when compacted at 1000 MPa. However, it was still virtually effective for Ti-10V-2Fe-3Al powder blends made of HDH Ti powder and V-Fe-Al master alloy powder. The observations were compared with literature data and discussed in accordance with the yield strength of Ti, Ti-6Al-4V, Ti-10V-2Fe-3Al and Al₃V as a function of temperature.     

Pressure consolidation of amorphous ZrO2–Al2O3 by plastic deformation of powder particles

Amorphous ZrO₂–Al₂O₃ powders undergo densification at low temperatures (<650°C) and moderate uniaxial pressures (~750 MPa). It is established that large pressure dependent densification and little time dependent densification occur. Viscous sintering is not the dominant densification mechanism. Study of the particle size effect in densification of amorphous ZrO₂–40% Al₂O₃, and comparison with hot pressing of borosilicate glass powder at 500 and 550°C and cold compaction of silver powder, clearly indicate the possibility of compaction of amorphous ZrO₂–Al₂O₃ by plastic deformation. Good agreement was seen between a model for the compaction of ductile metal powders and the observed hot pressing behaviour.     

Hot consolidation of mechanically alloyed nanocrystalline powd in Ni-, Fe- and Mo-Based systems

The sinterability and hot-pressing behavior of mechanically milled metastable powders with nanocrystalline structures were examined in Ni-, Fe- and Mo-based systems. The nanocrystalline powders exhibited a poor sinterability in spite of very high grain boundary energy induced during mechanical milling. High applied pressures in the order of several GPa are likely to be necessary for achieving full density. The addition of third metals to mechanically alloyed powders can markedly improve both compressibility and densification in pressureless sintering or in hot pressing with re1atiw:ly low pressures below 60 MPa. Near full densification was obtained by the proper selection of the additive metals and their content while retaining a nanocrystalline structure in the inner layer. In Mo₃₃Si₆₇ retarded grain growth was observed when applying pressure during hot consolidation.     

An Investigation on the Sinterability and the Compaction Behavior of Aluminum/Graphene Nanoplatelets (GNPs) Prepared by Powder Metallurgy

In the present study, the densification response of Al matrix reinforced with different weight percentages (0, 0.5, 1.0, 1.5 and 2.0 wt.%) of graphene nanoplatelets (GNPs) was studied. These composites were produced by a wet method followed by a conventional powder metallurgy. The Raman spectrum of graphene indicates that preparation of the composites through the wet mixing method did not affect the disordering and defect density in the GNPs structure. The nanocomposite powder mixture was consolidated via a cold uniaxial compaction. The samples were sintered at different temperatures (540, 580 and 620 °C) under nitrogen flow so as to assess the sinterability of the nanocomposites. X-ray diffraction (XRD) has been carried out to check the possible reaction between GNPs and aluminum. According to the XRD patterns, it seems that Al₄C₃ did not form during the fabrication process. The relative density, compressibility, sinterability and Vickers hardness of the nanocomposites were also evaluated. The effects of GNPs on the consolidation behavior of the matrix were studied using the Heckel, Panelli and Ambrosio Filho, and Ge equations. The outcomes show that at early stage of consolidation the rearrangement of particles is dominant, while by increasing the compaction pressure, due to the load partitioning effect of GNPs, the densification rate of the powder mixture decreases. Moreover, the fabricated nanocomposites exhibited high Vickers hardness of 67 HV₅, which is approximately 50% higher than monolithic aluminum. The effect of graphene addition on the thermal conductivity of Al/GNPs nanocomposites was evaluated by means of thermal diffusivity measurement, and the results showed that the higher thermal conductivity can be only achieved at lower graphene content.     

3-D profiles and surface topography of alumina compacts

A non-contacting laser scanning profilometer, with associated hardware and software, is used for the determination of the overall shape and surface topography of cylindrical alumina compacts. The change in the shape distortion of the cylinder, defined as (R_max-R_min)/R_min (R is the radius of the compact), was monitored, as a function of the ambient temperature, during sintering.During sintering, an increase in the diameteral distortion values were observed. Certain surface topographic characteristics , also obtained by the laser scanning of the surfaces of the green compacts, were used to characterise the agglomerate deformation and breakdown. The deformation of agglomerates starts at very low compaction pressures. However, the inter-agglomerate pores are not eliminated until a compaction pressure of 37 MPa.     

Effects of lubricant''''s friction coefficient on warm compaction powder metallurgy

1　INTRODUCTIONWarm compaction is a relatively simple and e conomical process that can produce sintered partswith density up to 94% of the theoretical pore freedensity[1 3], and its potential is tremendous. Withminor modification on the conventional powdermetallurgy equipment and approximately 20%higher cost than conventional cold compaction,green compact density of 7.5 g/cm3 can be obtainedby single press. The only difference between thewarm compaction and th…     

Analysis of density and mechanical properties of high velocity compacted iron powder

A new method for producing higher density PM parts, high velocity compaction (HVC), was presented in the paper. Using water atomized pure iron powder without lubricant admixed as the staring material, ring samples were compacted by the technique. Scanning electron microscopy (SEM) and a computer controlled universal testing machine were used to investigate the morphologies and the mechanical properties of samples, respectively. The relationships among the impact velocity, the green density, the sintered density, the bending strength and the tensile strength were discussed. The results show that with increasing impact velocity, the green density and the bending strength increase gradually, so the sintered density does. In addition, the tensile strength of sintered material is improved continuously with the sintered density enhancing. In the study, the sintered density of 7.545~g/cm³ and the tensile strength of 190~MPa are achieved at the optimal impact velocity of 9.8 m/s.     

Prediction of effect of volume fraction, compact pressure and milling time on properties of Al-Al2O3 MMCs using neural networks

An artificial neural network (ANN) model was developed to predict the effect of volume fraction, compact pressure and milling time on green density, sintered density and hardness of Al-Al₂O₃ metal matrix composites (MMCs). Al-Al₂O₃ powder mixtures with various reinforcement volume fractions of 5, 10, 15% Al₂O₃ and milling times (0 h to 7 h) were prepared by mechanical milling process and composite powders were compacted at various pressure (300, 500 and 700 MPa). The three input parameters in the proposed ANN were the volume fraction, compact pressure and duration of the milling process. Green density, sintered density and hardness of the composites were the outputs obtained from the proposed ANN. As a result of this study the ANN was found to be successful for predicting the green density, sintered density and hardness of Al-Al₂O₃ MMCs. The mean absolute percentage error for the predicted values didn’t exceed 5.53%. This model can be used for predicting Al-Al₂O₃ MMCs properties produced with different reinforcement volume fractions, compact pressures and milling times.     

Influence of Applied Pressure on Tensile Behaviour and Microstructure of Squeeze Cast Mg Alloy AM50 with Ca Addition

The development of alternative manufacturing processes is essential for the success in applying Ca-containing magnesium alloys for automotive applications due to their relatively poor die castability. Squeeze casting with its inherent advantages has been demonstrated capable of minimizing the formation of casting defects in Mg-Al-Ca alloys. In this study, the effect of applied pressures on tensile behavior and microstructure of squeeze cast Mg-5wt.%Al-1%wt.%Ca alloy (AMX501) was investigated with the applied pressure varying from 3 to 90 MPa. The results of tensile testing indicate that the tensile properties of AMX501 alloy including ultimate tensile strength, yield strength, and elongation (E _f) increase from 153.7, 80 MPa and 3.26% to 183.7, 90.5, and 5.42% with increasing applied pressure levels from 3 to 90 MPa, respectively. The analysis of true stress versus strain curves shows that an increase in applied pressure levels result in high straining hardening rates during the plastic deformation of the alloy. Microstructural analysis and density measurements indicate that, as the applied pressure increases, the porosity levels of the alloy decrease considerably, despite of almost no significant reduction in grain sizes of the squeeze cast alloys due to their high aspect ratio of cylindrical castings. Hence, the improvement in tensile properties should be primarily attributed to casting densification resulting from applied pressures. The scanning electron microscopy observation on fractured surfaces reveals that the fracture modes of the squeeze cast alloys transit to ductile from brittle with increasing applied pressures.