粉末形状与松装密度对不锈钢烧结多孔材料制备工艺及其性能的影响

通过选用气雾化及水雾化两种工艺方法制备的不锈钢粉末来制取粉末烧结多孔材料。探讨了粉末形状及松装密度对不锈钢粉末烧结多孔材料制造工艺中的成形压力和烧结温度等工艺参数的影响;研究了原料粉末松装密度对不锈钢粉末烧结多孔材料的透气性、拉伸强度的影响。结果表明:成形压力、烧结温度和制品的透气性受粉末松装密度影响显著。粒度范围为0.18～0.90mm时,气雾化粉末的成形压力比水雾化粉末要高近1倍;当粉末的粒度相同时,采用松装密度大的球形粉末所需的烧结温度比松装密度小的不规则粉末的高60～70℃;粒度为0.45～0.60mm时,选用松装密度为4.13 g/cm3粉末所制备的多孔制品的透气性为3.16×10-10m2,而选用松装密度为2.67 g/cm3的粉末所制备的多孔制品的透气性仅为8.8×10-11m2。不锈钢多孔材料的强度受原料粉末的松装密度影响显著;粒度相同,制备工艺相同时,采用较低松装密度的粉末的制品,能够得到较高的强度。     

Homogeneity of the porous structure of permeable powder-metallurgy materials

Conclusions When the ratio of the mold diameter to the mean powder particle diameter is not less than 22 and the ratio of the thickness of the product to the moid diameter is not more than 11, then the homogeneity of the porous structure of material is not influenced by the wall effect or by the nonuniformity of stress distribution across the thickness during molding.When the thickness of the layer of material increases, its porous structure becomes statistically averaged on account of the smaller number of pores of maximal and minimal size and the larger number of average-size pores.With decreasing particle size of powder or increasing specific surface, the critical thickness of a layer of material characterizing the transition to homogeneous porous structure increases. Other conditions being equal, the shape of the powder particles has the decisive influence on the critical thickness.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 47–51, May, 1986.     

Porous powder-fiber materials based on copper

A theoretical and experimental investigation of porous powder—fiber materials based on copper powder and fibers with a layered distribution of components was carried out. Maximum and average pore sizes, permeability coefficients, and efficiency parameters as functions of pressing pressure, powder particle size, and relative thickness of the fiber layer were investigated. It was shown that the use of components with certain dimensions permits the fabrication of materials with a high pore size gradient (up to 12 times) in a thickness of material that considerably increases the efficiency parameter E relative to that in porous powder and porous fiber materials.     

Special features of the production of low-alloy powder steel for structural and antifriction purposes

Conclusions The use of a minimal amount of plasticizer (not more than 0.5%) in the compacted charge and molds with additional drainage make it possible with a single compaction and sintering to obtain highly dense powder products — (7.2-7.3)·10³ kg/m³ — with a compacting pressure of 1000 MPa. Sintering of highly dense powder material ZhGr0,8D2N1 for 3.6 ksec is accompanied by its decompaction in consequence of degassing; extending the sintering time to 10.8 ksec reduces the porosity and improves the mechanical porperties of the products.The combination of the processes of sintering and hardening of rollers made of powder steel ZhGr0,8D2N1 in the plant Degussa makes it possible to obtain great hardness (of the order of 50–53 HRC) of products with a porosity of 5–10% after their cooling in oil. In comparison with existing technological processes, this one is distinguished by high productivity and degree of automation and mechanization; all this meets perfectly the requirements of mass production.Study of the refrigerating capacity of compressors confirmed the possibility of successfully using porous components operating in dynamic regimes under conditions of liquid lubrication, using capillary phenomena and the effect of hydraulic obliteration of fine communicating pore channels for lubricating the surfaces of friction pairs.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 42–47, September, 1987.     

Porous structure of flame-arresting materials of metal powders

Conclusions A porous flame-arresting material is characterized by a critical thickness which provides the optimum structure and permeability of it. An increase in porosity and the use of nonspherical and coarsely dispersed powders increases the critical thickness of the material. It decreases as the result of addition to the original powder of a plasticizer (paraffin) in a quantity sufficient for formation on the surface of the particles of a continuous resistant layer. For powder metallurgy titanium with a porosity of 50% the optimum paraffin content is about 10 wt.%.Translated from Poroshkovaya Metallurgiya, No. 1(313), pp. 35–38, January, 1989.     

Some characteristics of the reverse polymorphic transformations of sintered iron and cobalt

Conclusions The permanent compression exhibited by sintered iron during the reverse, transformation depends more on the particle size of the powder than on the porosity of the material. Filling the pores with copper at a residual porosity of 1.5% does not prevent this phenomenon, and enables internal stresses in the material to manifest themselves during the volume change accompanying the transformation. Thermal cycling in the region of the transformation temperatures, which leads to a substantial permanent compression buildup from the very first cycles, can be employed for improving the structure-sensitive mechanical properties of the material. The porous structure of sintered cobalt creates conditions facilitating the retention of its high-temperature phase at room temperature. The increase in the relative amount of the fcc phase brought about by an increase in porosity and hence in excess surface area and the sharp fall in the amount of the high-temperature phase induced by repressing the material with a very small reduction enable the inhibition of the reverse transformation to be attributed to the influence of the excess surface and stresses set up by dislocation pile-ups in the contact regions.Translated from Poroshkovaya Metallurgiya, No. 7 (259), pp. 61–65, July, 1984.     

Permeability of porous materials from refractory compounds

Summary A study was made of porous materials from spheroidized powders of refractory compounds. A relationship is established linking permeability with porosity and the particle size of the powder from which the materials were prepared. An empirical formula is proposed for determining the dependence of the coefficient of permeability on powder particle size and component porosity under linear filtration conditions. The integral and differential pore radius distribution curves obtained show that such materials are relatively homoporous and exhibit little scatter in pore radius size.Translated from Poroshkovaya Metallurgiya, No. 1(49), pp. 27–30, January, 1967.     

Cu基热管芯体多孔材料增孔补强的研究

对不同粒径Cu粉、不同造孔剂(CuCl2.2H2O、NaCl)及其含量的Cu基热管芯进行了对比试验,分别对其开孔隙度、渗透系数、压缩性能进行了测试;并用扫描电镜(SEM)观测芯体的孔洞特征及烧结颈的形成情况,进一步探讨了烧结强化机理。结果表明:球形Cu粉粒径越大,Cu基热管芯的孔隙度和渗透系数较大,但强度越低;添加造孔剂CuCl2.2H2O有造孔和强化基体的双重作用;添加NaCl增加孔洞效果明显,但仅有造孔作用。     

Superplastic behavior of powdered titanium nickelide during pressing

Conclusions In the process of pressing of a titanium nickelide powder a high level of "elastic" recovery is observed, due to the superelasticity of the material. The following characteristic features of the superelastic behavior of a titanium nickelide powder undergoing densification have been established: The maximum degree of volume recovery does not attain 100%; the degree of recovery diminishes with increasing degree of densification of material, and increases with rise in temperature up to 400C, the increase being the greater the higher the compact porosity; repeated application of the same pressure during the pressing of the powder markedly decreases the compact porosity.Translated from Poroshkovaya Metallurgiya, No. 2(266), pp. 13–17, February, 1985.     

Technology and properties of porous permeable aluminum-based materials

Results of the investigation of preparation conditions (pressure of powder pressing and time of sintering of compacts) and of the effect of aluminum additions (5–20 wt %) on the properties of a sintered porous material of an aluminum powder and its mixture with an Al₂O₃ powder are given. The possibility is shown of the production of porous (P = 30–35%), highly permeable (k = 2.0 to 2.5 × 10^?13 m²) aluminum-based sintered material with an addition of 20% Al₂O₃ and maximum size of pores equal to 1.3–1.5 μm in the following regime: p = 60 MPa, T = 723–823 K with an isothermal holding for 30–60 min.     

粉末粒度对Ti-35A1多孔材料孔结构的影响

粉末粒度是影响Ti-35Al多孔材料孔结构的主要因素之一.本文采用元素粉末反应合成工艺制备Ti-35Al 多孔材料,在其它制备参数一定的条件下,系统研究Ti/Al元素粉末的粒度与Ti-35Al多孔材料的孔隙度、孔径和透气度等孔结构参数之间的定量关系.结果表明:粉末粒度是决定Ti-A1合金多孔材料最大孔径的主要因素,多孔...     

Borided Hot-Worked Powder Materials Based on Iron. Part 1. Kinetics of Diffusion Boriding for Powder Materials

The effect of diffusion boriding temperature and time, hot-worked powder billet porosity, and the carbon content within them, on borided layer thickness is studied. A difference is established in impregnation at the temperature for eutectic formation in the system Fe B within the surface layer of a billet from boriding in the absence of a liquid phase. The processes are conditionally called liquid-phase and solid-phase boriding. The difference involves a higher impregnation rate and the possibility of porous billet infiltration with melt during liquid-phase boriding. Optimum production parameters are determined for boriding.     

Prediction of the filtering and mechanical properties of porous cold-worked stainless steel

Conclusions Additional cold plastic working makes it possible with a decrease in porosity and pore size to increase the tortuosity of the pore channels, to increase the strength, and to reduce the allowable bend radius of the sheet. Based on the mathematical models obtained, it is possible to establish the stainless-steel powder particle size and the compacting rolling method for providing the specified combination of filtering and mechanical properties.The coefficient of permeability of porous sheet may be calculated from the parameters of the internal structure of the pores using the capillary model of the porous medium.Cold compacting rolling of porous sintered sheet increases the sensitivity of the material to stress concentration.Translated from Poroshkovaya Metallurgiya, No. 9(261), pp. 88–91, September, 1984.     

Manufacturing porous materials from metalorganic mixtures: Report 2

The morphology of the surface and fracture of highly porous materials obtained during the thermal destruction of metalorganic mixtures (MOM) was investigated. The size and shape of pore channels in the finished product were shown to be determined through the fractional composition and the particle shape in MOMs. The effect of the porosity on the permeability and strength of sintered materials was considered. The permeability was demonstrated to depend not only on the value, but also on the shape of pore channels. Combining the techniques of powder metallurgy with chemical-metallurgical processes allows us to obtain materials with a porosity of 70–80% and a strength of no less than 5–25 MPa. If the pore size was from 10 to 100 μm, the permeability of materials was (in 10⁻¹² m²) 1–3 for Mo, 0.5–6 for Mo-Ni, and 2–6 for Ti-Mo.     

Pressing behavior of atomized iron powders

Conclusions The porous structure of the particles of an atomized iron powder depends on the chemical composition and sieve analysis of the starting powder and also, to a smaller extent, on its own sieve analysis, as determined by the conditions of milling of the sponge produced by annealing. In our study of various powder batches the best combination of degree of particle sponginess and agglomeration and hence pressing characteristics was found to be ensured by the use of a cast iron starting powder containing about 50% of a fine fraction, < 0.063 mm, with a comparatively low oxygen content (6.5%). With the atomized powders, the transition from the first stage of pressing to the second took place more gradually and at a higher pressing pressure (600 MPa) than with the reduced powder (450 MPa). It is shown that the compressibility of an iron powder is the better the greater the contribution from the first stage and hence the smaller the role of the volume plastic deformation of the particles in the attainment of a given density. The best compressibility with a low degree of contanimation with carbon and oxygen can be attained at minimum values of specific surface, degree of sponginess , and degree of agglomeration and also a maximum apparent density resulting from the use of powders of equiaxed particle shape close to spherical. The steady increase in compressibility with increasing apparent and tap densities that is characteristic of reduced iron powders is not always observed with powders pro-duced by atomization and annealing.Translated from Poroshkovaya Metallurgiya, No. 2(218), pp. 23–29, February, 1981.     

人工髋关节用复合多孔钛股骨头制备方法的研究

本研究采用等离子旋转电极制取的Tc4钛合金球形粉末,涂覆在致密芯杆上,制成柄部表面多孔层厚度约2mm的复合多孔钛股头。本文着重研究了原始粉末粒度、烧结制度、基体表面粗糙度对复合多孔层的孔径、孔隙度以及多孔层与基体间结合强度的影响,同时还测定了复合多孔钛股头的机械性能。研究结果表明,材料的最大孔径主要取决于原始粉末粒度,并随粉末粒度的增大而线性增加。影响结合强度的主要因素是烧结制度、原始粉末粒度和基体表面粗糙度。其结合强度随烧结温度的提高、保温时间的延长、原始粉末粒度的下降和基体表面粗糙度的增加而增加。孔隙度仅取决于粉末的堆积状态。所获得的复合多孔钛股头的机械性能为σ_b=830~880 MPa,σ_0.2=810~840 MPa,σ=9.5~12.0%,ψ=26.0~33.0%。     

Special features of the structure of powdered high-speed steel after sintering in the presence of liquid phase

Conclusions Sintering of powdered high-speed steels to the poreless state proceeds under conditions of short-term appearance of liquid phase; this entails the formation of low melting phases in consequence of the segregation of the alloying elements and carbon on the surface of the powder particles. To obtain material with less than 1% porosity it is necessary to use powder with mean particle size not exceeding 80 m.Translated from Poroshkovaya Metallurgiya, No. 3(279), pp. 40–44, March, 1986.     

Use of low-temperature plasma for the production of ultrafine copper powders

Conclusions In an investigation of the hydrogen reduction of copper chloride in a stream of arc-discharge argon plasma ultrafine (d<0.1 m) copper powders of spherical particle shape were obtained characterized by comparatively narrow particle size distribution functions. Their oxygen content was 0.1 wt. %. It was found by experiment that the mean particle size of such a copper powder and its particle size distribution vary as functions of the rate of supply of copper chloride, but are independent of the rate of feed of the plasma-forming gas, which is in accord with the proposed model of frontal reaction of copper chloride with hydrogen on the scale of turbulent globules. Ultrafine copper powders produced by the method described can be pressed at room temperature to a residual porosity of not more than 5%.Translated from Poroshkovaya Metallurgiya, No. 11(263), pp. 23–28, November, 1984.