L. A. Dobrzański

Influence of Heat Treatment on Structure and Properties of the Cast Magnesium Alloys

In this paper is presented the structure and proprieties of the cast magnesium alloys as cast state and after heat treatment cooled with different cooling rate, depending on the cooling medium (furnace, water, air). For investigations samples in shape of 250x150x25 mm plates were used. The presented results concern X-ray qualitative and quantitative microanalysis as well as qualitative and quantitative X-ray diffraction method, tensile tests, hardness measurement. In the analysed alloys a structure of α %solid solution and fragile phase β (Mg17Al12) occurred mainly on grain borders as well as eutectic and phase AlMnFe, Mg2Si. Investigation are carried out for the reason of chemical composition influence and precipitation processes influence to the structure and mechanical properties of the magnesium cast alloys with different chemical composition in as cast alloys and after heat treatment.

Predictive sensor guided robotic manipulators in automated welding cells

Abstract This paper presents an on-line tracking optimization scheme for sensor guided robotic manipulators by associating sensor information, manipulator dynamics and a path generator model. Feedback linearization-decoupling permits the use of linear SISO prediction models for the dynamics of each robot joint. Scene interpretation of CCD-camera images generates spline fitted segments of future trajectory. In the sensor vision field the proposed optimization criteria minimizes the error between state variables of the prediction model and the state variables of the spline trajectory generator. These techniques, allied with separation of disturbance rejection and path-tracking performance by the proposed feed-forward following model predictive (FMP) servo-controller design, permits very high path tracking dynamics (and consequently small errors). Experimental results on implementation of a CCD-camera guided hydraulic robot and a welding robot demonstrates the practical relevance of the proposed approach.

The modelling of hardenability using neural networks

Abstract This paper presents a novel method of the modelling of hardenability, its experimental-verification results, and comparison with the methods described in the literature. In addition, the potential of the new method of modelling the hardenability curves for the assessment of the effect of the chemical composition on steel properties is presented. Computer simulation was made of the influence of the particular alloying elements on hardenability and verification of the calculation results obtained was carried out using the experimental data.

Influence of Aluminium Content on Behaviour of Magnesium Cast Alloys in Bentonite Sand Mould

In this paper there is presented the structure and proprieties of the modeling cast magnesium alloys as cast state and after heat treatment, depending on the cooling medium (furnace, water, air), with different chemical composition. The improvement of the manufacturing technique and chemical composition as well as of heat treatment and cooling methods leads to the development of a material designing process for the optimal physical and mechanical properties of a new developed alloy. In the analysed alloys a structure of solid solution and fragile phase  (Mg17Al12) occurred mainly on grain borders as well as eutectic and AlMnFe, Mg2Si phase. The investigation is carried out to testy the influence of the chemical composition and precipitation processes on the structure and mechanical properties of the magnesium cast alloys with different chemical composition in its as cast alloys and after heat treatment.

Structure and Properties of the Wear Resistant Coatings Obtained in the PVD and CVD Processes on Tool Ceramics

The paper presents investigation results of structure and functional properties of the hard wear resistant coatings obtained in the PVD and CVD processes on the Si3N4 nitride tool ceramics. Examinations of coatings structures were made using the transmission (TEM) and scanning (SEM) electron microscopes, microhardness tests, coating adhesion to the substrate with the „scratch test”, and the coatings abrasive resistance „pin-on-disc” test. Machining tests results and roughness tests results for the machined grey cast iron surface are also presented. The research carried out proved that depositing the hard, anti wear, multilayer coatings based on the Al2O3 and TiN layers onto the Si3N4 nitride tool ceramics with the PVD method results in obtaining better functional properties like extension of the cutting tool life, than in case of the uncoated nitride ceramics or coated with the PVD coatings and some CVD ones.

High-speed steels with addition of niobium or titanium

Abstract It was found that about 0.5% Nb or 0.3% Ti may be employed as partial substitutions for vanadium in the W Mo V high-speed steels of the 11-0-2, 11-2-2 and 9-2-2 types, with concentration of Si increased to 0.7%. Additions of niobium or titanium introduced into these steels result in change of the chemical compositions of the MC type primary carbides. This makes possible transition of vanadium, in a sufficient concentration, into the solid solution, and obtaining the secondary hardness effect not lower than in the steels without niobium or titanium, even with lower vanadium concentration in the steel. Additions of the 0.5% Nb or 0.3% Ti secure the highest secondary hardness of about 66 HRC in the investigated steels. The main reason of the secondary hardness effect in the investigated steels with the additions of niobium or titanium is dispersive precipitation of the M4C3 carbides in the tempered martensite matrix and the martensitic transformation of the retained austenite.

Phases and Structure Characteristics of the Near Eutectic Al-Sl-Cu Alloy Using Derivative Thermo Analysis

For determining of the micro-structural changes taking place in a near eutectic Al-Si-Cu aluminium cast alloy during heating and cooling process the UMSA device (Universal Metallurgical Simulator and Analyzer) was used. In this work the dependence between the regulated cooling speed and structure on the basis of the thermo-analysis was carried out. The thermal analysis was performed at a cooling rate in a range of 0,2 °C to 1,25 °C. The changes were examined and evaluated qualitatively by optical and electron scanning microscopy methods and the EDS microanalysis. During the investigation the formation of aluminium reach (α-Al) dendrites was revealed and also the occurrence of the α+β eutectic, the ternary eutectic α+Al2Cu+β, as well a iron and manganese containing phase was confirmed. The performed investigation are discussed for the reason of an possible improvement of thermal and structural properties of the alloy. The achieved results can be used for liquid metal processing in science and industry – for example foundry for developing and obtaining of a required alloy microstructure and properties influenced by a proper production conditions.

Hot-Rolling of Advanced High-Manganese C-Mn-Si-Al Steels

The high-manganese austenitic steels are an answer for new demands of automotive industry concerning the safety of passengers by the use of materials absorbing high values of energy during collisions. The chemical compositions of two high-manganese austenitic steels containing various Al and Si concentrations were developed. Additionally, the steels were microalloyed by Nb and Ti in order to control the grain growth under hot-working conditions. The influence of hot-working conditions on a recrystallization behaviour was investigated. Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light microscopy. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. The obtained microstructure – hot-working relationships can be useful in the determination of powerful parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures.

The structure and properties of W–Mo–V high-speed steels with increased contents of Si and Nb after heat treatment

Abstract The results of experiments carried out have confirmed the possibility of partial substitution of V by Nb in W–Mo–V high-speed steels of the 9–2–2, 11–2–2 and 11–0–2 types with the concentration of Si increased to 0.7%. It has been found that with the addition of 0.5% Nb, the steels investigated have the highest secondary hardness after austenitizing at 1240°C and tempering at 540–570°C. The 9–2–2+Si+0.5% Nb-type steel quenched at 1240°C and tempered at 540–570°C acquires the highest secondary hardness of about 66 HRC of all of the investigated steels. The main reason for the secondary hardness effect in all of the steels investigated is the precipitation of the dispersive M4C3 carbides in the martensite matrix and the martensitic transformation of the residual austenite.

Silicon solar cells with Al2O3 antireflection coating

The paper presents the possibility of using Al2O3 antireflection coatings deposited by atomic layer deposition ALD. The ALD method is based on alternate pulsing of the precursor gases and vapors onto the substrate surface and then chemisorption or surface reaction of the precursors. The reactor is purged with an inert gas between the precursor pulses. The Al2O3 thin film in structure of the finished solar cells can play the role of both antireflection and passivation layer which will simplify the process. For this research 50×50 mm monocrystalline silicon solar cells with one bus bar have been used. The metallic contacts were prepared by screen printing method and Al2O3 antireflection coating by ALD method. Results and their analysis allow to conclude that the Al2O3 antireflection coating deposited by ALD has a significant impact on the optoelectronic properties of the silicon solar cell. For about 80 nm of Al2O3 the best results were obtained in the wavelength range of 400 to 800 nm reducing the reflection to less than 1%. The difference in the solar cells efficiency between with and without antireflection coating was 5.28%. The LBIC scan measurements may indicate a positive influence of the thin film Al2O3 on the bulk passivation of the silicon.