Jenő Sólyom

Development of monotectic surface layers by CO2 laser

The aim of our work was to develop a monotectic surface layer for be arings by using laser surface-treatment technology. Two kinds of laser surface t reatment technology were used. In case of coating-melting technology a Pb layer was first develope d by galvanization, then the Pb layer was melted together with the matrix. In case of powder bl owing technology Bi powder was blown into the layer melted by laser beam, by Argon gas. The struct ure of monotectic surface layer was investigated by light microscope and a scanning electron micros cope. The volume fraction and size distribution of Pb and Bi particles were determined by image-analyzer. Introduction The essence of laser alloying is that only structure and propertie s of the surface layer of specimen are changed, the structure and properties of the bulk part remains unchang ed. During development of monotectic surface layer, the surface workpiece is heated to a temperature, where only a single homogenous melt remains, in the system after alloying and then – beca use of good heat-extraction ability of the basic material it is quickly cooled. As a conse quence of the high cooling rate (100010000 K/s), a very fine structure develops during solidification. Experiments Laser experiments were performed in the Bay Zoltán Institute of Materials Science and Technology using a CO2 laser with a power of 5 kW. The basic alloy was an Al-11Si eutec tic type alloy. The thickness of specimen was 15 mm and the surface area treated by the laser was 15x130 mm . Two kinds of technologies were used for surface treatment [1-4]. Duri ng the two-step technology (melting of the coating) (Fig. 1) a Pb layer having a thickness of 0.1 mm was taken to the surface by galvanizing, then the Pb layer was melted together with the basic material by using different laser power (2, 2.5, 3, 3.5 kW). The sample was shifted by a scan velocity of 300 mm /min. During the treatment, 8 melted bands were with 50% overlap. Diameter of the foc us was 2 mm. Samples were coated with graphite before treatment to increase the low absorption of aluminium. During the one-step (powder-blowing-in) technology (Fig. 2) Bi grains w ith a diameter of 40-60 μm were blown into the molten layer. The protecting gas was Ar and the laser power wa s chosen (2, 2.5, 3, 3.5 kW). The sample scan velocity was 300, 600 and 900 mm/min respectively. Fi bands were melted on each sample with an overlap of 50%. Materials Science Forum Online: 2003-01-15 ISSN: 1662-9752, Vols. 414-415, pp 147-152 doi:10.4028/www.scientific.net/MSF.414-415.147

Deforming Texture Effect on Phase Transformation in Stainless Steels

In stainless steels during the non-equilibrium transformation of aus tenite the deformed bcc α’ martensite and hexagonal, non-magnetic ε martensite also can form. These transformations can be induced by cooling (under critical temperature) and/or mechani cal deformation. The appearance of ε martensite has an effect on the deformation ability and other prope rties. The experimental results associate the ε martensite formation with the plastic deformation behaviour (TRIP effect), while the transformation of ε martensite into α’ martensite is accompanied with hardening. The present phases hardly determine the cold rolling properties. During the deforming of α’, ε, γ phases in stainless steels the texture also developes. The i nitial strong deforming γ texture changes with the appearance of α’ martensite. We suppose that the transformation takes place at certain places in an anisotropic wa y due to the deforming texture. The texture of α’ martensite develops by the initial anisotropy of parent phase a nd/or the phase deformation. Introduction Martensite has long been used to designate the hard microstructur e found in quenched carbon steel. If the steel with the carbon content higher than 0.6wt% is heated above the austeniti c range and than quenched at a sufficiently high cooling rate the fcc austenite tra nsforms into the metastable body centered tetragonal phase ( ). Perhaps the most important aspect in martensitic transformati n involves a special crystallographic relationship between the marte nsite and austenite, which allows a fast growth mechanism. The crystallography is very simil ar to the crystallography involved in deformation twinning. Thus in general when a martensitic transform ation is coupled with an externally applied stress other phenomena such as stress or strai n induced martensitic transformation, the generation of new nucleation sites, and transformat ion induced plasticity (TRIP) may occur. The most commonly used austenitic steel has a tendenc y to transform into α’ martensite and hexagonal ε martensite during thermomechanical treatment. The ε martensite has a well defined crystallographic relationship to the parent austenite phase, it forms close to the stacking faults with fine lathes on the {111} plate of austenite. The thickness of the ε lath is 300 nm or less. [1] Between Ms and Md temperatures the formation of martensite can be induced by ela stic and/or plastic deformation. Within this temperature intervals the driving force for the reaction consists of 1) the free energy difference between the martensitic and aust enitic states and 2) the externally applied stress. The authors propose to distinguish between the stress-i nduced and strain-induced formation of martensite. Martensite is considered to be stress induced when it forms as a result of elastic stresses from an external load (below the actual yi eld strength of austenite). Martensite is strain induced when the slip in the austenite precedes its format i n. (σA-M>σyield A, the lowest temperature is Ms σ ). The austenitic stainless steels have a wide range of usage i n th chemical industry and also in the processing of household goods. The most commonly used processing for the se goods is the cold working. So during the deformation of metastable austenitic CrNi st eels he and ε martensite can form. According to the chemical composition of steel and the condition of def rmation different transformations take place such as γ→ε, ε→α’ , γ→α’ , γ→ε→α‘. The deformation induced Materials Science Forum Online: 2003-01-15 ISSN: 1662-9752, Vols. 414-415, pp 281-288 doi:10.4028/www.scientific.net/MSF.414-415.281

Investigation of new type Cu-Hf-Al bulk glassy alloys

In the last years new type Cu-Hf-Al ternary alloys were developed with high glass forming ability and ductility. The addition of Al to Cu-Hf alloys results in improvements in glass formation, thermal stability and mechanical properties of these alloys. We have investigated new Cu-based bulk amorphous alloys in Cu-Hf-Al ternary system. The alloys with Cu49Hf42Al9, Cu46Hf45Al9, Cu50Hf42.5Al7.5 and Cu50Hf45Al5 compositions were prepared by arc melting. The samples were made by centrifugal casting and were investigated by X-ray diffraction method. Thermodynamic properties were examined by differential scanning calorimetry and the structure of the crystallising phases by scanning electron microscopy. The determination of liquidus temperatures of alloys were measured by differential thermal analysis.

Emergence of mixed quintet superfluidity in the chain of partially polarized spin-3/2 ultracold atoms

The system of ultracold atoms with hyperfine spin F=3/2 might be unstable against the formation of quintet pairs if the interaction is attractive in the quintet channel. We have investigated the behavior of correlation functions in a model including only s-wave interactions at quarter filling by large-scale density-matrix renormalization-group simulations. We show that the correlations of quintet pairs become quasi-long-ranged when the system is partially polarized, leading to the emergence of various mixed superfluid phases in which BCS-like pairs carrying different magnetic moment coexist.

Analysis of Cu-Zr-Ag Amorphisable Alloys Produced by Centrifugal Casting

Bulk Metallic Glasses (BMGs) have been widely investigated due to their excellent physical and chemical properties [1]. The copper based BMG occupies a special place in the family of BMGs since they are relatively low priced. The Cu-Zr-Ag ternary system has been examined on the basis of the ternary phase diagram [2]. We have changed the concentration of the alloys from the Cu58Zr42 to the concentration of the deep eutectic point. Wedge-shaped samples have been cast from the master alloys by centrifugal casting into a copper mould, consequently analyse the influence of the cooling rate on the crystallization. The cooling rate has been estimated from the secondary dendrite arm distances by using a Cu-Sn crystalline alloy. Near the tip of the wedge the samples were amorphous and near the base of the wedge the samples were fully or partially crystallized. The structures of the samples have been characterized by scanning electron microscope and X-ray diffraction.

Laser Alloying of the Surface Layer of Al4.5Cu1Si Alloy with TiC and WC Particles

The surface layer of the samples of Al4.5 %Cu1.0% Si alloy was deve loped by CO2 laser using TiC and WC particles. Because the oxide film on the surface it was impossible to introduce the TiC particles into the melt, as the WC particles could broken th oxide film and could penetrate to the melt. The microstructure of resolidified layers were c ellular or dendritic with cast texture. The bands were overlaped and so the resolidified structure was partl y hea treated. The carbide particles reacted with the melt.

Investigation of thermomechanical treated austenitic stainless steel

During thermomechanical treatment of austenitic stainless steel a’ martensite and e martensite form in the austenite matrix. The martensitic transformation and deforming existing together result a high elongation at the investigated steel belonging to the TRIP grades. The amount of a’and e martensite depends on the strain level as well as on the deforming temperature in this steel. In the course of thermomechanical treatments we measured the amount and texture of the existing phases at different temperature and strain. It has been stated that the martensites are dominant in low temperature range, they have a considerable amount, and the transformation from e martensite to a’ martensite also takes place. The amount of a’ martensite increases by increasing the strain while the amount of e martensite shows a maximum. By investigating the relationship between the quantity of existing phases and the effect of texture, it has been stated that the transformation takes place in certain given plates in the textured matrix.

Superficial remelting of cast iron by laser radiation

A rarely applied technology of surface modifications is the remelting of surfaces by a laser beam. This is so because in the case of laser remelting of surfaces, similarly to other processes used in production, such a competitive alternative surface modification technology is searched for in which the value in use of the component with new properties created by the new procedure is in proportion with the costs and time requirement needed for its production. According to such a point of view, a laser remelting of a surface is in general not worth applying this expensive technology, since the change, the improvement in the properties as a result of remelting is not sufficiently large. However, the laser remelting of cast iron surfaces represents a specific case, since the nature of the surface of this relatively cheap (as compared to cast steel) material of advantageous properties can be changed significantly by this technology. In addition, by the treatment with laser beam, an extraordinarily particular material structure unknown in mass production can be developed. This is why we turned our attention to the specificities and properties of this structure formed during laser beam treatment of cast iron surfaces.

Characterization of the Solidifying Microstructure in Ti60(NixCu40-x)40 Alloys

Ti60(NixCu40-x)40 x = 5 - 40 at% ternary alloys were prepared by arc-melting followed by a centrifugal casting into a wedge-shaped copper mould in order to examine glass forming of these compositions. Microstructure of the master alloys and wedge-shaped samples were studied. Among the master alloys, which solidified under non-equilibrium conditions, the sample with 15 at% Ni content displayed clear eutectic structure and its wedge-shaped sample had the finest structure but still crystalline. Microstructure of the other compositions was far from amorphous state.

Microstructure and Phase Analysis by TEM in Cu-Hf-Ti Alloys

There are no data about the equilibrium phases in the Cu-Hf-Ti system, in the Cu-rich corner which is a glass former region. Phases and solidifying microstructures were examined in the master alloy (cooling rate: ~150 K/s) and in slowly cooled (5 K/min) samples in case of different compositions. Unknown ternary phases were found by SEM and XRD analysis and one of them with the highest Ti content could be identified by TEM study.