Herbert Danninger, Vassilka Vassileva and Christian Gierl-Mayer
In ferrous powder metallurgy, both boron and phosphorus have been known to be sintering activators for a long time. However, the use has been widely different: while P is a standard additive to sintered iron and steels, boron has been frequently studied, but its use in practice is very limited. Both additives are also known to be potentially embrittling, though in a different way. In the present study the differences between the effects of both elements are shown: while P activates sintering up to a certain threshold, in part by stabilizing ferrite, in part by forming a transient liquid phase, boron is the classical additive enhancing persistent liquid phase, being virtually insoluble in the iron matrix. The consequence is that sintered steels can tolerate quite a proportion of phosphorus, depending on composition and sintering process; boron however is strongly embrittling in particular in combination with carbon, which requires establishing a precisely defined content that enhances sintering but is not yet embrittling. The fracture mode of embrittled materials is also different: while with Fe-P the classical intergranular fracture is observed, with boron a much more rugged fracture surface appears, indicating some failure through the eutectic interparticle network but mostly transgranular cleavage. If carbon is added, in both cases transgranular cleavage dominates even in the severely embrittled specimens, indicating that no more the grain boundaries and sintering necks are the weakest links in the systems.
K. Sülleiová, B. Ballóková, M. Besterci and T. Kvačkaj
The development of the nanostructure in commercial pure copper and the strength and ductility after severe plastic deformation (SPD) with the technology of equal channel angular pressing (ECAP) are analysed. Experimental results and analyses showed that both strength and ductility can be increased simultaneously by SPD. The final grain size decreased from the initial 50μm by SPD to 100-300 nm after 10 passes. An increase of the ductility together with an increase of strength caused by SPD are explained by a strong grain refinement and by a dynamic equilibrium of weakening and strengthening, and it is visible on the final static tensile test stress-strain charts.
M. Kupková, M. Hrubovčáková, M. Kabátová and M. Kupka
Elemental iron and manganese powders were blended to form mixtures containing 25, 30 and 35wt.% Mn. Mixtures were compressed into prismatic bars and sintered. Some of the bars were repressed and resintered. Compared to a bar pressed and sintered once, the bar pressed and sintered twice possessed a higher relative density, a higher bending stiffness, and a grid microindentation data set with a lower variance. Bars were immersed in Hank's solution for eight weeks. After this procedure, the bending stiffness were found reduced for all bars except for those pressed, sintered and only repressed, the bending stiffness of which remained unchanged. The repressing has most likely closed up throats connecting the clusters of pores with the free surface of a bar, reducing thus a surface area exposed to a corrosive attack. The resintering has opened up those throats, the electrolyte could fill accessible pores and corrosion weakened the near-surface material, reducing thus a bar's bending stiffness.
A new inert gas fusion method has been developed for determining oxygen and nitrogen in Al and Mg powders. The approach, the methods and some results are discussed. Dissociation of AlSi10Mg powder, 99.9 % Mg powder, Mg alloy powder and MgO p.a. are presented.
H. Bruncková, Ľ. Medvecký, E. Múdra, A. Kovalčiková, J. Ďurišin, M. Šebek and V. Girman
Samarium niobate SmNbO4 (SNO) and tantalate SmTaO4 (STO) thin films (~100 nm) were prepared by sol-gel/spin-coating process on alumina substrates with PZT interlayer and annealing at 1000°C. The precursors of films were synthesized using Nb or Ta tartrate complexes. The improvement of the crystallinity of monoclinic M′-SmTaO4 phase via heating was observed through the coexistence of small amounts of tetragonal T-SmTa7O19 phase in STO precursor at 1000°C. The XRD results of SNO and STO films confirmed monoclinic M-SmNbO4 and M′-SmTaO4 phases, respectively, with traces of orthorhombic O-SmNbO4 (in SNO). In STO film, the single monoclinic M′-SmTaO4 phase was revealed. The surface morphology and topography of thin films were investigated by SEM and AFM analysis. STO film was smoother with roughness 3.2 nm in comparison with SNO (6.3 nm). In the microstructure of SNO film, small spherical (~50 nm) and larger cuboidal particles (~100 nm) of the SmNbO4 phase were observed. In STO, compact clusters composed of fine spherical SmTaO4 particles (~20-50 nm) were found. Effect of samarium can contribute to the formation different polymorphs of these films for the application to environmental electrolytic thin film devices.
Simulations are continuously becoming more and more important to predict the behaviour of materials, components and structures. Porous materials, such as PM, put special demands on the material models used. This paper investigates the application of the Gurson material model to PM steels. It is shown how the model can be calibrated to material data. The results are also applied to an indentation test, where it’s demonstrated that experimental results can be reproduced with some accuracy. Limitations of the model, and the potential to use more advanced material models are also discussed.
L. Medvecky, R. Stulajterova, M. Giretova and M. Faberova
Prepared powder polyhydroxybutyrate – chitosan - calcium phosphate composite system with 10 wt % of biopolymer component can be utilized as biocement which is characterized by the prolonged setting time and achieves wash out resistance after 5 minutes of setting. The origin powder tetracalcium phosphate/nanomonetite agglomerates were coated with the thin layer of biopolymer which decelerates both the transformation rate of calcium phosphates and hardening process of composites. The porosity of hardened composite was around 62% and the compressive strength (8 MPa) was close to trabecular bone. No cytotoxicity of composite resulted from live/dead staining of osteoblasts cultured on substrates.
The aim of the study was to evaluate the effect of chemical composition on the structure and mechanical properties of Mn-Ni-Mo and Ni-Mo-Cu PM steels. Pre-alloyed powder Astaloy 85Mo, diffusion alloyed powders Distaloy AQ and Distaloy AB produced by Höganäs, low carbon ferromanganese, carbonyl nickel powder T255 with three-dimensional filamentary structure and graphite CU-F have been used as the basic powders. Three mixtures with compositions of Fe-1%Mn-(0.5/1.75)%Ni-(0.5/0.85)%Mo-0.8%C and Fe-1.75%Ni-0.5%Mo-1.5%Cu-0.8%C were prepared in a Turbula mixer. Green compacts were single pressed in a steel die at 660 MPa according to PN-EN ISO 2740 standard. Sinterhardening was carried out at 1250°C in a mixture of 95% N2+5% H2 for 60 minutes. Mechanical tests (tensile, bend, hardness) and microstructural investigations were performed. Additionally, XRD and EDS analysis, fractographic investigations were carried out. The microstructures of steels investigated were mainly bainitic or bainitic-martensitic. Addition 1% Mn to Distaloy AQ based steel caused increase of tensile properties (YS from 422 to 489 MPa, UTS from 522 to 638 MPa, TRS from 901 to 1096 MPa) and decrease of plasticity (elongation from 3.65 to 2.84%).
Beáta Ballóková, Katarína Sülleiová, Michal Besterci, Oksana Velgosová and Song-Jeng Huang
The micromechanisms of fracture of AZ61 + 1 wt. % Al2O3 composite in the zone of superplastic deformation was analysed and quantified in this work. The specimens were tested at temperature of 200°C at different strain rates. Changing the strain rate, from 1x10-2 s-1 to 1x10-4 s-1, a significant growth of ductility was observed. At maximum value of superplasticity the fracture was transcrystalline ductile with dimples of two size categories. Based on the statistical analysis of fracture micromechanisms at the elevated temperature and strain rates of 10-0- 1x10-4 s-1 hyperbolic dependency was depicted according to Gurland - Plateau theory.
Magdaléna Strečková, Mária Fáberová, Radovan Bureš and Pavel Kurek
The fields of soft magnetic composites and powder metallurgy technologies have a powerful potential to redesign the way of electric motor preparation, and will continue to grow for years to come. A design of the novel soft microcomposite material composed of spherical FeSi particles and Ni0.3Zn0.7Fe2O4 ferrite nanofibers is reported together with a characterization of basic mechanical and electrical properties. The needle-less electrospinning method was used for a preparation of Ni0.3Zn0.7Fe2O4 ferrite nanofibers, which has a spinel-type crystal structure as verified by XRD and TEM analysis. The dielectric coating was prepared by mixing of nanofibers with glycerol and ethanol because of safe manipulation with fumed fibers and homogeneous distribution of the coating around the FeSi particle surface. The final microcomposite samples were prepared by a combination of the traditional PM compaction technique supplemented with a conventional sintering process of the prepared green compacts. The composition and distribution of the secondary phase formed by the spinel ferrite fibers were examined by SEM. It is demonstrated that the prepared composite material has a tight arrangement without any significant porosity, which manifest itself through superior mechanical properties (high mechanical hardness, Young modulus, and transverse rupture strength) and specific electric resistivity compared to the related composite materials including resin as the organic binder.