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.     

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 obtained through cold compaction. The compacting behaviors in warm compaction and cold compaction are similar.Under the compacting pressure of 700 MPa, the warm compacted densities are 0.10 - 0.22 g/cm3 higher than the cold compacted ones, and the green strengths are 11.5%-50% higher. The optimal warm compacting temperature is 100 - 110℃. In the die wall lubricated warm compaction, the optimum internal lubricant content is 0.2%.     

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.     

Debinding and sintering of warm compacted and binder-treated complex iron-base part

Regular elemental powders were used in warm flow compaction instead of the expensive micron-sized powders to fabricate cross-shaped parts. Debinding behaviors, sintering properties and shape consistency of the sintered parts were studied. Binder removal was accomplished by heating green compacts at intermediate temperatures with optimal heating rates until the debinding temperature was reached. Results show that by controlling debinding process, complex parts with good shape consistence can be obtained by warm compaction of binder-treated powder. Fine and shiny surface was obtained and no surface defect can be observed for sintered parts debinded at 2 ℃/min, while defect can be observed in sintered parts debinded at 4 ℃/min.     

Mechanical properties of β-SiC fabricated by spark plasma sintering

The consolidation of SiC nanopowder synthesized by the mechanical alloying method was subsequently accomplished by spark plasma sintering of 1700 °C for 10 min under an applied pressure of 40 MPa. The SiC sintered compact with relative density of 98% consisted of nano-sized particles smaller than 100 nm. This phenomenon resulted in the ordering process of stacking disordered structure formed by mechanical alloying. In this work, the effect of grain size and relative density on the mechanical properties were studied. The mechanical properties of sintered compacts were evaluated and compared with the reference samples fabricated from the commercial SiC powder (β-SiC, 0.3 μm, IBIDEN Co., Gifu, Japan) with sintering additive (B–C mixture). The Vickers hardness and bending strength of those sintered compacts increased with the increment of the density. However, the mechanical properties were lower than those of reference samples in case of lower density, even though the mechanical property was close to that of reference sample in case of higher density. This phenomenon was considered for the difference of bond strength between grains because those sintered compacts were fabricated without any sintering additives, while those reference samples were fabricated by accelerating the grain bonding with a sintering additive of B–C mixture. In other words, those results indicated that the effect of sintering additive affected on mechanical properties directly. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee on October 18–20, 2004 in Columbus, OH.     

Warm compacted NdC particulate reinforced iron—base composite（Ⅱ）——Microstructure and properties

Effects of different sintering temperature and sintering time on the relative density of the sintered compacts were studied to obtain the optimal sintering parameters for the fabrication of NbC parti culate reinforced iron-base composite.With optimal sintering temperature of 1280℃ and sintering time of 80min,wear-resisting,high density NbC particulate reinforced iron-base composites can be obtained using warm compaction powder metallurgy.The microstructure,relative density,mechanical properties and tribological behaviors of the sintered composites were studied.The results indicate that the mechanical properties of the sintered compacts were closely related to the sintered density.The iron-base composite materials with different combinations of mechanical properties and tribological behaviors were developed for different applications.One of the developed composite,which contains 10%NbC,possesses a high strength of 815MPa with a remarkable friction and wear behaviors.The other developed composite,which contains 15%NbC,possesses a lesser strenth of 515MPa but with excellent friction and wear behaviors.     

Research of warm compaction technology on nylon bonded Nd-Fe-B magnets

Warm compaction and room temperature compaction were applied to prepare bonded Nd-Fe-B magnets. The results indicated that the density of magnet was determined by the compaction pressure and warm compaction temperature, whereas, the thermosetting temperature could hardly affect the density of magnet. The mechanical properties of magnets were the best when the thermosetting temperature was 200 ℃. The Br, Hcb, and (BH)max of warm compaction magnet were higher than those of room compaction. When the warm compa...     

Sintering behavior and properties of SiC/Si3N4 composite

SiC/Si3N4 composite was pressureless sintered using self-propagating high-temperature combustion synthesis a-Si3N4 powder and appropriate amount of b-SiC powder. Both of the sintering additive systems were used,which were YAN(Y2O3–Al2O3–AlN) and YN(Y2O3–AlN).The influences of b-SiC content on sintering behavior of SiC/Si3N4 composite were investigated. The results show that the density, shrinkage, bending strength, hardness, and fracture toughness of the samples with two sintering additive systems increase first with the increase of the contents of b-SiC and then decrease even when b-SiC contents continually increase. The tendency of weight loss of the samples is opposite. The b-SiC content of the samples with the best mechanical properties is different in two systems. For YAN system, the best mechanical properties of the samples are gained when b-SiC content reaches 10 %, while as for YN system it is 5 %. The properties of YN samples are superior to YAN samples. J phase(2Y2O3 Si2N2O) forms in YN system easily. A small amount of M phase(Y2O3Si3N4) is observed in YAN system.     

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.     

Effect of adding methods of metallic phase on microstructure and thermal shock resistance of Ni/（90NiFe2O4-10NiO） cermets

Ball mixing and electroless plating were respectively used as the adding methods of metallic phase to prepare Ni/（90NiFe2O4-10NiO） cermets for the inert anode in aluminum electrolysis. The microstructure and thermal shock resistance of cermet samples were studied. The results show that, for the samples prepared by ball mixing method, aggregation of metallic phase is found in either the green blocks or sintered samples and the extent of aggregation increases with the increase of metal content. For 6.5Ni/（90NiFe2O4-10NiO） cermets prepared with electroless plating method, the homogeneous and fine metallic particles are found in either the green compacts or sintered samples, but the relative density and thermal shock residual strength decrease by 3% and 28%-58% respectively, compared with samples prepared with ball mixing method.     

Effect of sintering parameters on warm compacted iron-based material

1　INTRODUCTIONItiswellknownthatincreasingdensityisthebestwaytoincreasetheperformanceofpowdermet allurgy(P/M ) parts.ConventionalP/Mprocessingcanproduceiron basedpartswithdensitylessthan 7.1g/cm3(arelativedensityof 90 %approximately) .Theirmechanicalpropertiesaresubstantiallylessthanthoseoftheirfulldensitycounterpart .TherearemanymethodsthatcanproduceP/M partswithrela tivelyhighdensitysuchaswarmcompaction ,hightemperaturesintering ,doublepress/doublesinteringandforging .Warmcompactioni…     

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。     

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.     

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.     

C／CuPb复合轴承材料温压成形工艺的研究

用温压工艺制得了短碳纤维增强铜铅合金（Ｃ／ＣｕＰｂ）复合轴承材料,研究了温压工艺参数对温压压坯及烧结坯性能的影响,并对温压烧结与冷压烧结及二次压制烧结所得Ｃ／ＣｕＰｂ复合轴承材料的性能进行了分析对比。结果表明,温压压坯比冷压压坯具有更高的生坯密度,同时,温压烧结Ｃ／ＣｕＰｂ复合轴承材料的性能与二次压制烧结材料相当而明显高于冷压烧结材料。     

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…     

Warm compacted NbC particulate reinforced iron-base composite(Ⅱ)--Microstructure and properties

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｂｉｇｇｅｓｔｐｒｏｂｌｅｍｓｉｎｔｈｅｆａｂｒｉｃａｔｉｏｎｏｆｐａｒｔｉｃ ｕｌａｔｅｒｅｉｎｆｏｒｃｅｄｍｅｔａｌｍａｔｒｉｘｃｏｍｐｏｓｉｔｅｓ (ＭＭＣｓ)ａｒｅｔｈｅｅｖｅｎｄｉｓｔｒｉｂｕｔｉｏｎｓｏｆｒｅｉｎｆ     

Improving the uniformity in mechanical properties of a sintered Ti compact using a trace amount of internal lubricant

Large sintered powder compacts are likely to be associated with variability in mechanical properties; an improvement of the uniformity of the mechanical properties of sintered powder compacts is important for powder metallurgy. In this work 0.3–1 wt.% stearic acid (SA) or magnesium stearate (MgSt) was added to a 40 mm diameter Ti powder compacts with height to depth (H/D) ratio of unity to give a more uniform green density. Tensile test pieces were cut from selected positions in each sintered compact to obtain the distribution of mechanical properties. Results revealed that variations in mechanical properties are due to the pore morphology with respect to size, aspect ratio and preferred orientation. A trace amount of lubricant significantly improves the uniformity in mechanical properties by optimizing the porosity distribution and minimizing the pore size and aspect ratio of pores after sintering. Such an effect was achieved by reducing the initial green density inhomogeneity and the stress induced by the mismatch of sintering shrinkage. However a relatively high 1 wt.% SA addition with a large particle size created burnt-off pores in the top and bottom zones. MgSt is not recommended since it significantly increases the oxygen content. An addition of 0.6 wt.% SA is the best choice due to the even pore distribution, small pore size and acceptable level of oxygen pick up.