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 discrepancy 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.     

Study on mechanical properties of warm compacted iron-base materials

Mechanical properties of the warm compacted iron-base powder metallurgy materials were compared with those of conventional cold compacted materials. Factors such as compaction temperature, lubricant concentration and lubricant′s property were studied. A lubricant for warm compaction powder metallurgy was developed. An iron-based powder metallurgy material with a green density of 7.31 g/cm3 (a relative density of 92.5%) can be obtained by pressing the powder at 700 MPa and 175 ℃. The sintered materials have a density of 7.2 g/cm3, an elongation of 2.1% and a tensile strength of 751 MPa compared to 546 MPa using conventional cold compaction with the same lubricant and 655 MPa using warm compaction with other lubricant. Compact density and mechanical properties were influenced strongly by the compacting temperature. Although the best quality compacts can be obtained at 175 ℃, warm compaction within 165 to 185 ℃ can give high density compacts. Evidence shows that compact density depends on the friction coefficient of the lubricant.     

原料合金化及烧结方式对NiTi合金性能的影响

镍钛形状记忆合金因具有优良的形状记忆效应、超弹性和良好的生物相容性而被广泛地运用于各个领域。本文研究原料粉末合金化及烧结方式对烧结体结构和性能的影响,分别以金属镍/钛混合粉及镍钛合金粉为原料,通过凝胶注模成形得到生坯,再以不同的烧结方式获得NiTi合金,利用X射线衍射仪和扫描电镜等设备,对原料粉末及烧结体的结构和性能进行分析。结果表明:相对于镍钛混合粉,以NiTi合金粉为原料制备出的NiTi合金组织中NiTi相含量更多;采用热等静压方法在1 050 ℃、9 MPa气压值的条件下,烧结4 h,制备出致密度达到91.5%、密度为5.9 g/cm3的合金,比真空烧结制备出的合金的密度值高出约0.5 g/cm3;同时热等静压烧结出合金的平均硬度值为226.2 HV,比真空烧结出合金硬度高出约33.6 HV。采热等静压的烧结方式能促进烧结过程中合金的致密化,大幅度提高凝胶注模成形制备NiTi合金的密度。     

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

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.     

Densification mechanism of warm compaction and powder mixture designing rules

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Simulation of pressure effects on hot isostatic pressing of stainless steel powder

To investigate the effects of pressure on the hot isostatic pressing (HIP) process of a stainless steel powder, density distribution and deformation of the powder at four different applied pressure levels were predicted and compared by using finite element method (FEM). Constitutive relations of porous compacts during HIP process were derived based on the yield criterion of porous metal materials. Thermo-mechanical coupling calculations were carried out by the MSC.Marc. Densification mechanisms were studied through evolutions of relative density, equivalent plastic strain and equivalent viscoplastic strain rate for compacts. The simulation results were also compared with experimental data. The results show that the densification rate and final density of compacts increase dramatically with the increase in the applied pressure level when it is below 100 MPa during HIP process, and the creep for compacts evolves into steady stage with the improvement of density.     

Key parameters for low temperature warm compaction of high density iron-based P/M materials

In order to reduce powder temperature to lower than 100℃ in warm compaction by changing polymer lubricant design, powder flowability, warm compacting behavior, lubricating mode as well as ultimate tensile strength after sinter-hardening and tempering were investigated systematically. By means of low temperature warm pressing and sintered hardening technique, samples with the sintered densities of 7.40 - 7.45 g/cm^3 and the strengths of 950 -1 390 MPa are achieved as the early compacting pressure is 686 - 735 MPa.     

Rapid Sintering of Alumina in Low Pressure RF Plasma

PlasmashowsmanypeculiarPrOPertiesforspecimenheating.Manyparaxneters,suchasgeneratingmethods,workingpressure,andgasspeciesofplasmaaffectheatingcharacteristicstospecimens.TheplasmasinteringofoxideceramicswasexaminedtOhavethecharacteristicsofrapidheatin...     

粉末法生产Mn-Al中间合金

介绍了利用粉末冶金工艺生产MnAl25和MnAl15中间合金的过程及方法。通过试验得出粉末冶金生产MnAl25合金的最佳工艺条件为：压制压力650MPa,粘结剂用量0．6％。润滑剂用量0．6％;生产MnAl15中间合金的最佳工艺条件为：压制压力650MPa,粘结剂用量0．8％,润滑剂用量0．6％。MnAl25中间合金的粉化率为0．01％,密度可达4．41g／cm^3;MnAl15中间合金的粉化率为0．02％,密度可达4．8g/cm^3,且中间合金的成分均匀。     

Shape memory effect during preparation of alumia ceramic tubes

Pure alumina ceramic tube and 95 alumina ceramic(the ceramic with 95.84% alumina) tube were prepared by using self-prepared alumina micrometer powder without agglomeration as raw material. The ceramic green was shaped by isostatic pressing and sintered at different temperature from 800 to 1 600 ℃ for 2 h. The 95 ceramic tube sintered at 1 550 ℃ for 2 h had mean particle size of 4 μm, bend strength of 437 MPa and volume density of 3.714 g/cm3. Shape memory effect during sintering was observed. XRD results showed that no phase transition occurred during shape memory process, which indicated that shape memory effect was not caused by phase transition. Several probable causes of the alumina ceramic shape memory effect were discussed in this paper.     

包覆法添加烧结助剂制备A12O3/SiCp复相陶瓷

通过包覆的方法将烧结助剂Y2 O3均匀地加入到陶瓷粉体中 ,用无压烧结制备Al2 O3-SiCp 复相陶瓷材料。在Al2 O3 SiC混合粉体上覆一层Y (OH) 3后 ,素坯结构均匀 ,且有利于提高素坯致密性。在较佳条件下 ,材料的相对密度和强度分别达到96 8%和 364MPa。     

固相配位反应法制备Cu0．30Ni0.66Mn2．04O4超细粉体

以乙酸盐和草酸为原料,采用室温固相配位反应制得Cu0.30Ni0.66Mn2.04（C2O4）·nH2O复合草酸盐,将该草酸盐在800℃煅烧2h,得到尖晶石相Cu0.30Ni0．66Mn2.04O4复合氧化物粉体。该氧化物粉体粒径均匀细小,一次粒径为-150nm;烧结活性较高,在1050℃烧结5h制得的热敏陶瓷相对密度高达-97％。     

Powder Extrusion Molding of Nanocrystalline WC-10Co Composite Cemented Carbide

The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 （ wt% ） composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing （CIP） technology was used before or after debinding. Specimens were siutered by vacuum siutering and hot isostatic pressing （HIP）. The density, Rockwell A hardness, magnetic coercivity , and magnetic saturation induction of siutered specimen were measured. The microstructure of the green bodies and the siutered specimens was studied by scanning electron microscopy （SEM）. Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be siutered to 99.5% density of composite cemented carbide rods with an average grain size of about 200- 300 nm, magnetic coercivity of 30.4 KA / m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85% . Superfine WC- 10 Co cemented carbide rods with excellent properties were obtained.     

Preparation of precursor for stainless steel foam

The effects of polyurethane sponge pretreatment and slurry compositions on the slurry loading in precursor were discussed： and the,performances of stainless steel foams prepared from precursors with different slurry loadings and different particle sizes of the stainless steel powder were also investigated. The experimental results show that the pretreatment of sponge with alkaline solution is effective to reduce the jam of cells in precursor and ensure the slurry to uniformly distribute in sponge, and it is also an effective method for increasing the slurry loading in precursor; the mass fraction of additive A and solid content in slurry greatly affect the slurry loading in precursor, when they are kept in 9%-13% and 52%-75%, respectively, the stainless steel foam may hold excellent 3D open-cell network structure and uniform muscles; the particle size of the stainless steel powder and the slurry loading in precursor have great effects on the bending strength, apparent density and open porosity of stainless steel foam; when the stainless steel powder with particle size of 44 μm and slurry loading of 0.5 g/cm^3 in precursor are used, a stainless steel foam can be obtained, which has open porosity of 81.2%, bending strength of about 51.76 MPa and apparent density of about 1.0 g/cm^3.     

添加固体废弃物的硅藻土基多孔材料的制备

硅藻土作为主要基料,白云石为添加剂,加入其他固废物,制备了一种新型多孔材料。通过X射线衍射、扫描电镜及强度、吸水率等测试手段对制品进行了分析,探讨了硅藻土、白云石不同固体废弃物对多孔材料形成和性能的影响。研究表明,在硅藻土、白云石、粉煤灰、熟污泥的质量分数分别为45%、35%、10%、10%时,经1 020℃烧成并保温30min形成的多孔材料的密度为1.36g/cm3,孔隙率45%,吸水率为25%,抗折强度达12.43MPa,通过物相分析其多孔材料的成分主要晶相为莫来石与钙长石及透辉石。     

粉末冶金制备铝青铜/钢双金属材料

通过铝青铜酸洗和添加低熔点硅青铜粉以提高铝青铜的相对密度和铝青铜/钢界面结合强度.研究结果表明:铝青铜/钢双金属材料的制备工艺为烧结温度980～1 000℃,保温时间1h,添加低熔点硅青铜粉的质量分数10％～30％,提高烧结温度和添加低熔点硅青铜粉能显著提高铝青铜的相对密度和界面结合强度.     

粉末冶金法制备梯度多孔Mg-Ca合金

采用粉末冶金法以碳酸氢铵为造孔剂、镁粉和钙粉为原料,制备了梯度多孔Mg-Ca合金。研究了造孔剂含量、分布和烧结温度对梯度多孔Mg-Ca合金孔隙特性的影响。测量了烧结产物的弯曲性能。研究结果表明随着中间层造孔剂含量的降低,孔隙梯度分布加大,试样的平均孔隙度降低,但梯度孔隙结构导致试样的抗弯强度增加。此外,随着烧结温度的升高,梯度多孔Mg-Ca合金的平均孔隙度降低,抗弯强度增加。XRD和SEM观察结果都表明,烧结产物中没有造孔剂碳酸氢铵的残留,主要有Mg和Mg2Ca两相组成。     

Kinetic characteristics of liquid phase sintering of mechanically activated W-15wt% Cu powder

The kinetic characteristics of W grain growth operated by diffusion controlled Oswald ripening （DOR） during liquid phase sintering were studied. A liquid phase sintering of W-15wt%Cu was carried out by pushing compacts into a furnace at the moment when the temperature increased to 1340℃ for different sintering times. The results show that liquid phase sintering produces the compacts with considerably low relative density and inversely, rather high homogeneity. On the basis of the data extracted from the SEM images, the kinetic equation of W grain growth, G^n = G0^n ＋ kt, is determined in which the grain growth exponent n is 3 and the grain growth rate constant k is 0.15 μm^3/s. The cumulative normalized grain size distributions produced by different sintering times show self-similar. The cumulative distribution function is extracted from the curves by non-linear fitting. In addition, the sintering kinetic characteristics of W-15wt%Cu compacts were also investigated.     

Effects of activated sintering process on properties and microstructure of W-15Cu alloy

The effects of activated sintering technology of H2 atmosphere sintering on the microstructure and properties of W-15Cu alloy using ultrafine W-15Cu composite powder fabricated by spray drying calcining-continuous reduction technology were investigated.The experimental results showed that W-15Cu alloy,consolidated by activated sintering technology of H2 atmosphere sintering for 1 h at 1300 ℃,with 98.5 % relative density,transverse rupture strength 1218 MPa,Vickers hardness HV0.5 378,average grain size about 1.2 μm and thermal conductivity 192 W/m·K,was obtained.In comparison to the normal sintering process,activated sintering process to W-15Cu alloy could be achieved at lower sintering temperature.Furthermore,better properties in activated sintered compacts were obtained,and activated sintering process resulted in finer microstructure and excellent properties.     

抑制剂对W-15Cu合金性能与结构影响研究

以喷雾干燥-共还原法制备的W-15Cu超细复合粉末为原料,采用氢气活化烧结制备了W-15Cu高比重合金,研究了晶粒生长抑制剂Y2O3对合金性能与结构的影响。利用扫描电镜、维氏硬度仪、密度测试仪、金相显微镜等,观察烧结体显微结构,测试其硬度、密度与断裂强度。结果表明,在最佳烧结温度下,添加质量分数0.3%Y2O3的W-15Cu合金抗弯强度达到最大值1 128.6 MPa,添加质量分数0.5%Y2O3的W-15Cu维氏硬度达到最大值2.78 GPa,优于未添加抑制剂的W-15Cu合金。Y2O3可以细化W晶粒。