Barbara Romelczyk

The Strength and Ductility of 5483 Aluminium Alloy Processed by Various SPD Methods

Grain size refinement is an efficient way to improve mechanical strength and thus make light metals even lighter in terms of specific strength. However, the strength improvement is at the expense of ductility. Therefore, a better understanding of microstructural factors influencing both parameters is of prime importance for further development of ultrafine grained materials. In this work, we report results obtained for 5483 aluminium alloy which was subjected to several severe plastic deformation (SPD) methods, i.e. equal channel angular pressing (ECAP), Hydrostatic Extrusion (HE) and the combination of the two. Detailed microstructural analysis revealed significant difference in the grain size and grain boundary characteristics between samples obtained following different routes. It was found that although the grain size is a prime microstructural parameter determining mechanical strength, second order factors such as grain size distribution and distribution of grain boundary misorientation angles also play a significant role.

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite

The influence of hot pressing conditions on mechanical properties of nickel aluminide/alumina composite has been investigated in the present paper. In particular, effect of the process parameters, viz. compacting pressure, sintering temperature and sintering time on the evolution of density, elastic constants and tensile strength properties of the intermetallic-ceramic composite has been studied. Elastic constants, the Youngs modulus and Poissons ratio, have been evaluated using an ultrasonic testing method, and the tensile strength has been determined by a Brazilian-type splitting test. Microscopic observations of microstructure evolution complemented the experimental procedure. Experimental results have been confronted with theoretical models showing a good agreement between the data compared.

Fatigue Crack Growth Rates and Tensile Strength of Titanium Produced by Means of Selective Laser Melting

Mini-samples technique was utilized to determine mechanical properties of technically pure titanium produced by means of selective laser melting (SLM). Full-field digital image correlation (DIC) measurements and inverse method were applied for crack tip position and stress intensity factors calculations in the case of fatigue crack growth rate tests. DIC was also used for strain measurement during tensile tests on sub sized samples. There was studied the influence of samples orientation on the mechanical properties of mini-samples. Samples were cut out from rectangular cubes and were oriented with 0°, 45° or 90° angle to the direction of laser beam travel. There were also tested samples directly produced via SLM. Additionally microstructure observations were performed to verify the quality of SLM processed materials and explain mechanical properties variations.

A study of densification and microstructure evolution during hot pressing of NiAl/Al2O3 composite

Evolution of the density and the microstructure during hot pressing of NiAl/Al2O3 composite has been investigated in the present paper. In particular, the effect of the process parameters, viz. compacting pressure, sintering temperature and sintering time, on the evolution of the density of the intermetallic–ceramic composite has been studied. Evolution of the density has been related to microstructure changing. Porosity, pore structures and grains rearrangement have been analysed in microscopic observations.

Fatigue Crack Growth in Fe Mini-Samples Consolidated by Means of Impact Sintering

The paper presents the results of fatigue crack growth rate test of iron sinters. The samples were produced by means of the impact sintering. Applied production method allowed to obtain dense sinters with fine grain size resulted from large shear strains. Due to the limited size of the final products the mechanical tests were carried out in mini-samples. Optical, non-contact method of displacement measurement, namely Digital Image Correlation (DIC), was applied for determination of the displacement fields near the crack tip at the maximal force of selected loading cycles. The results of DIC measurement were utilized in the calculations of stress intensity factors and crack tip coordinates by means of the iterative procedure based on inverse method. These parameters were used for measuring crack development rate. There were investigated two types of materials produced by the consolidation of two different kinds of Fe powders and sintered in different temperatures. The results of crack growth rate tests were correlated with the microstructure changes, as well as yield and ultimate strength of the materials.

Magnesium AZ91 Alloy Cast Mechanical Properties Measured by the Miniaturized Disc-Bend Test

Miniaturized Disc-Bend Test (MDBT), also called the Small Punch Test (SPT) is used for characterizing the mechanical properties of metals, when only a small volume of material is available. This study was dedicated to investigating the mechanical properties of AZ91 magnesium cast alloy. The casts were prepared via gravity sand casting and have sections with different wall thickness. The examined samples were cut out of 30 mm and 10 mm thick walls. The correlation between results obtained from the tensile tests and MDBT was determined.

Fatigue Crack Growth of Thin Wall Magnesium AZ91 Alloy Cast

The paper presents the results of fatigue crack growth rate tests performed in magnesium AZ91 alloy cast of different wall thicknesses. Due to the limited size of investigated cast the tests were carried on mini-samples of 4x4x1 mm gauge section dimensions. The samples were cut from the 5, 10 and 30 mm thick walls. The optical displacement measurement technique, namely Digital Image Correlation, and inverse method were applied for determination of the stress intensity factors and the crack tip coordinates during tests. There were also performed uniaxial tensile tests in mini-samples for the determination of the mechanical properties changes related to different cast thicknesses. The relation between the microstructure and the results of mechanical tests was discussed.

The Effect of the Polyamide Reinforcement on Mechanical Properties of Fluorocarbon Rubbers Exposed in Aggressive Environment

The aim of presented study was to select a proper material for caterpillar application in mobile robots. The fluorocarbon rubbers were chosen for investigation. The samples hardness of 40 and 50 Sh⁰A either without or with polyamide reinforcement were prepared. The uniaxial tensile tests on mini-samples were carried out. The tests were performed on virgin samples as well as on previously exposed for one hour in aggressive liquids. The changes of the surface before and after the exposition were observed via SEM. The relation between the surface changes and the mechanical properties were described