Effect of Die Wall Lubrication on Warm Compaction Powder Metallurgy

Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials. Iron-based samples were prepared by die wall lubricated warm compaction at 135 ℃ and 175 ℃, using polytetrafluoroethylene (PTFE) emulsion as die wall lubricant. A compacting pressure of 700 MPa and 550 MPa were used. The admixed lubricant concentration ranging from 0 to 0.6 wt.% was used in this study. Compared with non-die wall lubricated samples, the die wall lubricated samples have higher green densities. Results show that in addition to the decrease in ejection forces, green density of the compacts increased linearly with the decrease in admixed lubricant content. Mechanical property of the sintered compacts increase sharply when the admixed lubricant concentration reduced to 0.125 wt.% or less. Ejection force data indicated that samples with die wall lubrication show lower ejection forces when compared with samples without die wall lubrication. No scoring was observed in all experiments even for samples contain no admixed lubricant. Our results indicated that under experimental condition used in this study, no matter at which compaction pressure, compaction temperature, graphite and lubricant contents in the powder the die wall lubricated warm compaction would give the highest green density and lowest ejection force. It can be concluded that combination of die wall lubrication and warm compaction can provide P/M products with higher density and better quality. It is a feasible way to produce high performance P/M parts if suitable die wall lubrication system was applied.

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 550 MPa. 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 lubricant 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.

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/cm^3 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.

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

The correct use of lubricant is the key of warm compaction powder metallurgy. Different lubricants produce different lubrication effects and their optimal application temperature will be different. Three different lubricants were used to study the effects of friction coefficient on warm compaction process. Friction coefficients of these lubricants were measured at temperatures ranging from ambient temperature to 200 ℃. Iron-base samples were prepared using different processing temperatures and their green compact densities were studied.

Warm compaction of Al_2O_3 particulate reinforced powder metallurgy iron-base composite

Mechanical properties of the warm compacted alumina particulate reinforced powder metallurgy composite materials was compared with those of the materials obtained by conventional cold compaction. Factors affecting the properties of the warm compacted material such as compaction temperature, lubricant content and alumina content were studied. A 3%(mass fraction) alumina particulate reinforced iron-base composite with a green density of 7.0 g/cm 3 can be obtained by pressing the powder with a pressure of 700 MPa at 175 ℃. The sintered materials have a density of 6.88 g/cm 3, a tensile strength of 512 MPa and an elongation of 1.3%. Results show that as alumina content increases, density and mechanical properties of the composite decrease.

Structure of Grading a Resistor-Heated System of Warm Compaction in Powder Metallurgy

We present the scheme of the structure of grading a resistor-heated system ofwarm compaction in powder metallurgy. The structure has the first heater and the second heater thatare heated by electrical tubes. Powder is heated in turn in the first heater and the second heater,where there is the mass fluidity of powder under gravity. The dimensions of the first heater andthe second heater were calculated from the Fourier equation of heat conduction, and the boundarycondition was constant temperature. The drawings of the first heater, the second heater and thepowder-delivering device were given. The structure of the heat equipment is simple and easy tomanufacture. Finally, an exact warm compaction press system HGWY- II was developed for the heatingsystem.

Densification Mechanism of Warm Compaction and Powder Mixture Designing Rules

By phenomenological analysis of warm compaction, it is found that, compared with the contribution of particle plastical deformation to densification of powder compact,the particle rearrangement is a dominant densification mechanism for powder warm compaction, and the plastical deformation of particles plays an important role in offering accommodating deformation for particle rearrangement and densifying powder compact at the final stage of pressing.In order to attain density gain as high as possible during warm compaction, six rules for designing warm compacting powder mixtures were proposed in detail.

Die wall lubricated warm compaction behavior of non-lubricant admixed iron powders

The phenomena of die wall lubricated warm compaction of non-lubricant admixed iron powders were researched, and its mechanism of densification was discussed. Water atomized powder obtained from the Wuhan Iron and Steel Corporation was used. With compacting and sintering, compared with cold compaction, the density of warm compacted samples increases by 0.07 - 0. 22 g/cm^3 at the same pressed pressure. The maximum achievable green density of warm compacted samples is 7.12 g/cm^3 at 120℃, and the maximum sintered density is 7.18 g/cm^3 at 80℃. Compared with cold compaction, the ejection force of warm compaction is smaller; the maximum discrep- ancy is about 7 kN. The warm compacted mechanism of densification of iron powders can be obtained： heating the powder contributes to improving plastic deformation of powder particles, and accelerating the mutual filling and rearrangement of powder particles.

Modification of Powder Compaction Equation of Kawakita

Based on an analysis of the validity of the powder compaction equation of Kawakita,a modified compaction equation is proposed.It is shown by the statistical analysis on the experimental compaction data of various powders that in most cases the proposed equation provides a better description of the compaction data than Kawakita's equation,especially in the cases of the compaction of hard material powders.

Possibility of utilizing water-atomized Fe-Ni-Mo steel powder as base materials for warm compaction process

Water atomized Fe Ni Mo steel powder, was utilized as base powder for designing powder mixtures for warm pressing. The warm pressing and sintering behaviours of the powder mixtures were studied. The results show that, compared with the pressing at room temperature, the green density gain by warm pressing is within a range of 0.10 0.19 g/cm 3 and reduction in spring back is 30% 40% of the ambient, and maximum green density of 7.32 g/cm 3 at 735 MPa is obtained as the graphite mass fraction is 0.8%. It was found that sintered densities of the compacts were reduced slightly due to releasing of elastic stress stored in the compacts during sintering. The warm pressing of steel powders gives evidence for substituting the traditional double pressing and double sintering process.

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

Warm compaction behaviors and their affecting factors such as compaction temperature, compaction pressure and lubricant concentration were studied. Effect of die wall lubrication on the powder’s warm compaction behavior was also studied. The use of smaller size colloidal graphite investigated can give a higher compact density and lesser spring back effect than the use of flake graphite.

Warm compacting behavior of stainless steel powders

The warm compacting behaviors of four different kinds of stainless steel powders,304L,316L,410L and 430L,were studied. The results show that warm compaction can be applied to stainless steel powders. The green densities and strengths of compacts obtained through warm compaction are generally higher than those obtai ned through cold compaction. The compacting behaviors in warm compaction and col d compaction are similar. Under the compacting pressure of 700 MPa,the warm co mpacted densities are 0.100.22 g/cm^3 higher than the cold compacted o nes,and the green strengths are 11.5%50% higher. The optimal warm compa cting temperature is 100110 ℃. In the die wall lubricated warm compact ion,the optimum internal lubricant content is 0.2%.

Effects of temperature on the mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase of partial welding is found among the junctions of particles inside the compacts; there is no obvious grain growth inside the compacts within the temperature range.

Microstructure and mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

Ti6Al4V powder compaction was performed by using magnetic pulse compaction in air at 200℃.Effects of process parameters such as voltage,capacitance,discharge times on the microstructure,compressive strength,hardness and relative density of compacts were investigated.The experimental results show that the relative density,hardness and compressive strength of compacted specimens increase with increasing voltage.In addition,the relative density and compressive strength of compacted specimens increase with the augmentation of capacitance in the range investigated.The relative density increases,the hardness firstly increases and then tends to be a fixed value;and the compressive strength firstly increases and then decreases from one to five times compaction.Both values of the hardness and compressive strength reach the maxima of HRA 69.1 and 1 062.31 MPa,at three times compaction,respectively.There are pores in and between particles.

Lubrication effectiveness of composite lubricants during P/M electrostatic die wall lubrication and warm compaction

The lubrication effectiveness of the composite lubricants, 50wt% ethylene bis-stearamide （EBS） wax ＋50wt% graphite and 50wt% EBS wax ＋ 50wt% BN, during the powder metallurgy （P/M） electrostatic die wall lubrication and warm compaction was studied. The results show that the combination of 50wt% EBS wax and 50wt% graphite has excellent lubrication performance, resulting in fairly high green densities, but the mixture of 50wt% EBS wax and 50wt% BN has less beneficial effect. In addition, corresponding die temperatures should be applied when different die wall lubricants are used to achieve the highest green densities.

Phenomenological Modeling of Warm Compaction and Experimental Verification

A phenomenological modeling approach to establishing the warm compaction equation and curves by modifying the regression equation of the room-temperature compaction curve is presented. An enhanced factor of compacting pressure is introduced into the equation in order to reveal the effects of powder/die temperature and filling height of powders on green density. Compaction curves yielded from this equation are consistent with the experimental data of ATOMET grade iron powders. The curves show that the powder/ die temperature should reduce as the filling heights of powders increase and that in some cases warm compaction can not give rise to a higher green density.

Effects of warm compaction on mechanical properties of sintered P/M steels

The green and sintered densities,and tensile strength of sintered P/M steels produced by cold compaction,warm compaction,warm compaction combined with die wall lubrication(DWL)were measured under various compaction pressures using polytetrafluoroethylene(PTFE)emulsion as the die wall lubricant.The effects of warm compaction on the mechanical properties were studied.The tensile fracture behaviors of cold compaction and warm compaction were studied using scanning electron microscope(SEM).The results show that the density of sintered P/M steel prepared by warm compaction or warm compaction with DWL is higher than that by cold compaction under all compaction pressures.Meanwhile,the highest tensile strength is obtained by combination of warm compaction and die wall lubrication under all compaction pressures.The SEM results show that the fracture modes of the sintered samples prepared by cold compaction and warm compaction at 700 MPa are the mixed mode of ductile fracture and brittle fracture,and obvious dimples can be found in some regions.The fracture of sample prepared by cold compaction is uneven and has irregular and big pores,but that by warm compaction is relatively even and the pores are round mostly,and the samples have many obvious dimples on the whole fracture surface.

Coupled mechanical and thermal simulation of warm compaction

Warm compaction process of pure iron powder was investigated. Due to the existence of elastic, plastic and thermal strains, a coupled mechanical and thermal model was applied. The elasto-plastic constitutive equations for powder material were developed based on ellipsoidal yield criterion and continuum theory. The constitutive equations were integrated into the constitutive integral arithmetic and solved employing incremental iterative solution strategy. The yield strength of iron powder was obtained according to the tensile experiments. When the compaction temperature was raised to 130 ℃, the yield strength of iron powder metal drops to 85% of room temperature value. Modified coulomb friction law is applied and the simulation results show that friction was an important factor resulting in the inhomogeneous relative density and reverse-density distribution phenomena in the regions near the die wall and the symmetrical axis.

Sinter-hardening properties of partially-diffuse alloyed Fe-Cu-Ni-Mo-C material prepared by die wall lubricated warm compaction

The sinter-hardening properties of a partially-diffuse alloyed Fe-2Cu-2Ni-1Mo-1C material were investigated. Samples were formed by die wall lubricated warm compaction method,then,sintered in hydrogen atmosphere at 1 150 ℃ for 1 h and cooled at 4.6,2.9 and 1.5 ℃/s,respectively,from 900 ℃ down to 600 ℃. Effects of cooling rate on mechanical properties and microstructure of the material were discussed. The results show that when the cooling rate increases,the tensile strength of the material increases,while,the elongation shows opposite result. The sintered material has a tensile strength of 872 MPa and an apparent hardness of HB 257 at a cooling rate of 4.6 ℃/s. Slight shrinkage is observed. Heterogeneous microstructures containing martensite,bainite,pearlite and nickel-rich retained austenite are observed in the material. Higher martensite content can be obtained at higher cooling rate,while,at lower cooling rate,pearlite and retained austenite dominated the microstructure.

Development of Powder Metallurgy （PM） Compacted Cu-TaC Electrodes for EDM

The main aim of this paper is to investigate the properties of Cu-TaC electrodes produced by Powder Metallurgy （PM） method. The design of Experiment （DOE） method was used to plan the investigation. Two different compositions of the powders （Cu-TaC with 30 and 55 % wt TaC） were used. The major properties which determine suitability of electrodes for Electro Discharge Machining （EDM） are electrical conductivity, therrnal conductivity and to some extent density. These properties were measured for the green compacted electrodes, analyzed and compared with their sintered counterparts. This is the initial stage to determine the suitability or otherwise of the compacted electrodes. The results showed that the compacted electrodes in green form can be suitable for EDM, since the electrical conductivities are very high （94.96-189.92Ω^-1m^-1）. The thermal conductivity is good （29.70-33.20W/m K）. The density ranges between 6.13 and 9.80 g/cm3. The sintered electrodes were found to be unsuitable at the specified conditions, because they became non-conductive electrically after sintering. Current efforts are geared towards improving these properties for the sintered ones and also determining their optimum levels.