High-porous materials made from alloy steel fibers: Production, structure, and mechanical properties

New high-porous corrosion-resistant materials are produced from steel fibers and a base porous material made by pressing and sintering of St.10 steel fibers. The materials obtained by chromizing (4.8–7.1 wt.%) and nickelizing (2.1–2.4 wt.%) a 60–90%-porosity base material have yield strength higher by a factor of 2 to 6 than that of the base material. The materials obtained by electrochemical coating of a base fibrous material with eutectic composite Ni-Ni₃B and subsequent liquid-phase sintering at 1120 °C contain 3.5–14.0 wt.% Ni. The yield strength of these materials at a porosity of 60–90% is higher by a factor of 2 to 3 than that of the base material.     

孔隙度对烧结不锈钢纤维多孔材料压缩性能的影响

采用丝径为100μm的不锈钢纤维经松装烧结工艺制备了孔隙度在70%～95%之间的金属纤维多孔板材.在MTS858材料试验机上检测压缩性能,结果表明:孔隙度在82.8%以下的试件的面内应力应变曲线大致分为三个阶段,应变很低情况下的线性弹性区、屈服平台区和应力急剧增大情况下的致密化区,其中屈服平台区较长,说明该材料具有较强的能量吸收能力;随着孔隙度的增加,不锈钢纤维多孔材料的卸载模量、屈服强度减小,其中孔隙度为70%的烧结不锈钢纤维多孔材料的平均卸载模量为5.2GPa,平均屈服强度达到了23MPa;孔隙度大于90.1%的试件屈服强度很低,能量吸收能力很小.     

Simulating the compaction of layered porous billets

An ideal rigid-plastic porous body is used as a rheological model to develop a mathematical model describing a closed matrix compacted by the axial force of porous two-layer cylindrical axisymmetric billets with different geometry, porosity of the layers, and yield stress of the base material for each layer. It is shown that the compaction rate of two-layer porous billets under deformation is determined by the combination of their parameters such as the yield stress of the base material, initial porosity, and thickness. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 16–21, 2007.     

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。     

模拟点蚀油气管线钢的拉伸性能

根据发生点腐蚀的油气管线基体有许多点蚀坑的特点,通过计算机产生随机数确定点蚀坑的位置,用小钻头打孔的方法模拟X60管线钢基体的多孔特征进行拉伸试验,测得其弹性模量、屈服强度和抗拉强度,并将理论计算值与前二者进行比较和修正,给出了多孔钢材的抗拉强度与孔隙率的函数关系.结果表明,多孔钢材弹性模量的实测值随孔隙率的变化与理论预测结果较为吻合;钢材实测屈服强度也随着孔隙率的增加而减少,但在较高孔隙率时其减少趋势变缓;衰减速率的实测值略大于理论预测值;实测抗拉强度随孔隙率的变化曲线与屈服强度相似,但对孔隙率更敏感.     

Forming porous fibrous materials by the pendant drop melt extraction

A method for forming porous material based on metallic fibers, which are obtained by pendant drop melt extraction (PDME) method, is proposed. An installation for forming porous fibrous materials by the PDME method is developed and fabricated. Samples of porous materials made of fibers of heat-resistant and corrosion-resistant steels, nickel alloys, zirconium, etc., are obtained. Mechanisms for forming the bonds between the fibers are investigated and an interaction model between the fibers in a formed material is proposed. The possibility of forming bonds between the fibers in a porous material based on copper and steel fibers at various extraction velocities is evaluated according to the proposed model.     

轧钢铁皮制备多孔不锈钢化学成分及孔隙控制

 为了充分发挥氧化铁皮含铁品位高、杂质元素含量低、产生量大的优势和特点,并开发高附加值的金属制品,采用真空还原烧结的方法制备了316多孔不锈钢,并确定了适宜的制备工艺以及孔隙率的影响因素。研究过程中采用高温真空管式炉对试样进行还原烧结制备;采用直读光谱、氧氢氮联合检测仪、X射线衍射分析仪、扫描电镜等设备对试样的化学成分、物相组成和微观形貌进行了分析。研究结果表明,以轧钢铁皮为主要原料,配入还原剂及其他合金粉末,通过高温真空还原可以得到成分合格的316多孔不锈钢,确定最佳制备工艺为10-3Pa真空度、1 200 ℃下保温3 h;还原烧结过程中,锰合金的收得率仅为61%。制备出的试样为单一的奥氏体组织,同时有Cr₇C₃在晶内析出,晶界附近存在σ相析出。保温0~3 h内,试样的孔隙率由37.26%增加至40.27%,延长保温时间至4 h,金属颗粒之间的烧结更加完全,孔隙率降低至35.16%;将制坯压力由76.43增加至152.87 MPa,多孔不锈钢的孔隙率由42.07%降低至34.44%,呈现逐渐降低趋势。当制样压力大于152.87 MPa时,发生了造孔剂偏聚的现象,导致孔隙率略微增加至35.76%。造孔剂碳酸氢铵每多增加10%,多孔不锈钢的孔隙率增加9.3%。通过对正交试验分析发现造孔剂加入量对多孔不锈钢孔隙率的影响最为显著,制样压力次之,保温时间对孔隙率的影响最小。     

Fracture of high-nitrogen 05Kh20G10N3AMF steel during impact loading

Specimens with V- and U-shaped notches made of austenitic high-nitrogen corrosion-resistant 05Kh20G10N3AMF steel are subjected to impact tests in the temperature range from +20 to ?196°C, and stress-strain diagrams are recorded. The test data are used to estimate impact toughness KCV and KCU, dynamic fracture toughness J _id at the stage of crack nucleation, and crack propagation energy A _p. The microrelief of the fracture surfaces is studied. As compared to forging, quenching from 1100°C is found to increase the impact toughness and the dynamic cracking resistance of the steel during impact loading and to decrease the ductile-brittle transition temperature. The steel is shown to exhibit the cold brittleness behavior characteristic of bcc materials. A model is proposed for the formation of cleavage facets in austenitic steels. It is based on easy slip along lattice planes under the low shear stress at a notch tip and the development of fracture at a stress lower than the yield strength of the material.     

Effect of porosity on microplastic deformation of iron base powder materials

Conclusions By the method of subjecting beams of uniform strength to bending tests we measured the modulus of elasticity of sintered iron base materials in a broad interval of porosity (0–40%).With porosity from 10 to 25% the curves of microyield are reduced to a single curve of strain-hardening of compact material by normalization to the coefficients K = E_o/E_gq.Deviations from similarity are found in the region of small (<10%) and high (>25%) porosity. The authors bring these effects into connection with the change of the structural state of the material.In the region of microplasticity (_pl = 10^–6-10^–3) a characteristic feature of iron base sintered materials with porosity of less than 25% is parabolic strengthening: ^1/2. An analysis of the curves of microyield in coordinates -^1/2 revealed that strengthening proceeds in stages.For materials with porosity of more than 25% the yield stress and strain are correlated by a dependence of the type ln .Translated from Poroshkovaya Metallurgiya, No. 7(319), pp. 79–84, July, 1989.     

Microstructure and Properties of Ti and Ti+Nb Ultra-Low-Carbon Bake Hardened Steels

Hot rolling, cold rolling and continuous annealing processes of Ti bearing and Ti+ Nb stabilized ultra-low-carbon bake hardened steels were experimentally studied. The microstrueture and texture evolution, as well as the morphology, size and distribution of second phase precipitates during hot roiling, cold rolling and continuous annea-ling were also analyzed. The results showed that the size of NbC precipitates in Ti+ Nb stabilized ultra-low-carbon bake hardened steel was smaller than that of TiC precipitates in Ti bearing ultra-low-carbon bake hardened steel, which made the average grain size of Ti+ Nb stabilized ultra-low-carbon bake hardened steel finer than that of Ti bearing ultra-low-carbon bake hardened steel; for the yield strength, the former was higher than the latter; but for the γ value which reflects the deep-drawing performance, the former was lower than the latter.     

Ni-Al多孔材料的研究进展

多孔材料是有别于致密材料的特殊功能材料,由于其特殊的孔结构,使其具有致密材料难以胜任的用途,发挥着特殊的功能.以NiAl多孔材料为研究对象,综述了近几年NiAl多孔材料在价电子结构与性能的关系、NiAl多孔材料孔率的影响因素、多孔材料的力学性能和化学性能的研究成果.     

Control of Mechanical Properties of Three-Dimensional Ti-6Al-4V Products Fabricated by Electron Beam Melting with Unidirectional Elongated Pores

Aligned, unidirectional, elongated pores were incorporated in Ti-6Al-4V products fabricated by electron beam melting in order to control the mechanical properties of the products such that they became suitable for biomedical applications. Unidirectional pores were successfully produced when the scan spacing of the electron beam was greater than the diameter of the beam. By changing the scan spacing of the electron beam, the size of the unidirectional pores could be varied. As a result, both the Young’s moduli and the yield stresses of the products with unidirectional pores decreased linearly with an increase in their porosity, owing to the stress concentration coefficient being 1 in the equation representing the relation between strength and porosity for porous materials. Further, low (<35 GPa) Young’s moduli were obtained when the scan spacing was 1 mm or higher, with these values being were close to the typical Young’s modulus of human cortical bone. This suggested that these porous materials could be used to fabricate customized bone implants that exhibited desired mechanical properties and suppressed the stress shielding of bone that is normally noticed when implants made of Ti alloys are used.     

添加升华性造孔剂的放电等离子法制备多孔铝块体材料

为解决高孔隙率多孔金属材料制备过程中的污染问题,以升华性萘颗粒为造孔剂,采用放电等离子脉冲烧结法(SPS)进行多孔铝块体材料的制备。结果表明,升华性造孔剂可在实现多孔铝材料高孔隙率的同时,有效提高其洁净度。采用该方法在350℃时可以制备出结构与尺寸可控性好、开孔效果好、孔隙率(63.33%)较高、粉体颗粒无明显长大的多孔金属铝块体材料。升华性造孔剂可对孔隙体积进行有效调节,实现多孔铝材料体内小孔与大孔的合理搭配,进一步改善多孔铝材料孔隙之间的连通性,该方法与SPS烧结技术相结合后,对于开孔性与颗粒连接性要求较高的多孔金属材料制备具有技术优势。     

Variation of the yield stress of a porous metal during cold deformation

Conclusions An examination is made of individual factors involved in the variation of the yield stress of a porous material during deformation, and a method is proposed for determining them using empirical relationships between the mechanical properties and density of porous materials and information concerning the true variation of the yield stress of the relevant nonporous metal. The method proposed, which allows for the variation of density during deformation and gives values of yield stress which are in good agreement with experimental results, may be recommended for the determination of deformation forces in various production processes for the plastic working of porous materials.Translated from Poroshkovaya Metallurgiya, No. 1(193), pp. 7–13, January, 1979.     

Character of porosity of compact materials obtained from metalorganics

The possibility of obtaining highly porous (60–80% pores) materials by combining techniques of powder metallurgy with chemical-metallurgical processes of formation of nanodimensional activators of sintering during the thermal destruction of metalorganics is shown. It is noted that, irrespective of the composition of starting charges, the surface porosity of such materials is represented by pores <30 μm, the fraction of which does not exceed 1%. The basis (86–89%) is represented by pores <4 μm. The character of porosity inside the sintered articles is determined by the sizes and shape of the powderlike skeleton material introduced into the starting charge to prevent the outflow of metalorganics during thermal treatment. When using powders with highly developed particle surfaces as such, the character of the internal porosity is similar to the surface porosity. The combination of scale particles up to 100 μm in size and highly dispersed (<10 μm) particles promotes the formation of long porous channels (100–350 μm) 10–50 μm in width.     

Compressive Behavior of Porous Titanium Fiber Materials

Porous titanium fiber materials with the fiber sizes of 70-120μm in diameter were prepared by vacuum sintering technology.The morphology and compressive properties of porous titanium fiber materials were investigated by using a scanning electron microscope(SEM)and an MST 858 compression testing machine in quasi-static condition.The results show that porous titanium fibers form complex micro-networks.The stress-strain curves of porous titanium fiber materials exhibit elastic region,platform region and densification region and no collapse during platform region.The yield strength of porous titanium fiber materials decreases with increasing the porosity and increasing the fiber diameter.     

Microplasticity behavior of porous nickel

We have used a physical and structural approach to study the mechanical behavior of monoporous И=5–45%) and biporous (И=45–70%) nickel powder at room temperature within the strain range 10^?5 to 5·10^?3. We have shown that for both low porosity and high porosity materials, the true microyield curves depend on the hardening provided by grain boundaries or interparticle boundaries. We found effects connected with the geometrical structure of the materials under investigation. The increase in the deforming stresses in the base metal material when the porosity is greater than 25% can be explained by the peculiarities of the stress states in the interparticle connections. The softening effect, which depends mainly on the porosity of the powder subsystem, is related to initiation of cracks in the initial phases of microyield.     

Induction Hardening vs Conventional Hardening of a Heat Treatable Steel

This study focuses on the comparison of mechanical and microstructural properties of induction and conventionally heat-treated steels in the as-quenched state. The investigated steel is a heat treatable 42CrMo4 steel. In order to characterize the mechanical properties, tensile tests and Vickers hardness tests are performed. The yield strength and hardness of the induction hardened condition turn out to be slightly lower compared to the conventionally hardened one. Light optical and scanning electron microscopy show no differences in the martensitic structure of the induction and conventionally hardened condition. However, electron back scatter diffraction investigations reveal a smaller block size within the conventionally hardened specimen. Carbon mappings by electron probe micro analysis show a homogenous carbon concentration in the conventionally hardened and a non-uniform distribution in the induction-hardened case. The segregation of the carbon exhibits line-type features in the induction hardened condition, lowering the total amount of carbon in the matrix. Therefore, the carbon content in the matrix of the conventionally hardened condition is slightly higher, which causes a smaller block size. The smaller block size is believed to be the reason for the higher hardness and yield strength.     

Stainless-steel porous-layered and framework fiber-powder composites

Porous layered and framework composites have been made from stainless-steel fibers and powders in the form of sheets. Measurements have been made on the electrical conductivity, elastic modulus, and ultrasound speed as dependent on the porosity, fiber and powder dispersions, and the structural features of the composites. Framework composites are better than layered ones throughout the porosity range, while purely fiber materials are better with porosity less than 60%. __________ Translated from Poroshkovaya Metallurgiya, Nos. 1–2(447), pp. 45–50, January–February, 2006.     

Heat transfer performance of porous titanium

Porous titanium fibre materials with different structural parameters were prepared by vacuum sintering method. The thickness,porosity and wire diameter of prepared materials were investigated to understand the effects of structural parameters on pool heat transmission performance of titanium fibre porous material. As a result,better heat transfer performance is obtained when overheating is less than 10 °C. In addition,when the wire diameter is smaller,the heat transfer is better. However,when superheating is above 10 °C,heat transfer performance can be improved by increasing the wire diameter. Moreover,thickness influences the superficial area of the prepared material and affects the thermal resistance when bubbles move inside the material; superficial area and thermal resistance are the two key factors that jointly impact the heat transfer in relation to the thickness of the materials. Experimental results also show that the materials of 3 mm in thickness exhibit the best performance for heat transmission. Furthermore,changes in porosity affect the nucleation site density and the resistance to bubble detachment; however,the nucleation site density and the resistance to bubble detachment conflict with each other. In summary,the titanium fibre porous material with a 50% porosity exhibits suitable heat transfer performance.