Halina Garbacz

Structural and mechanical properties of nanocrystalline titanium and 316LVM steel processed by hydrostatic extrusion.

The aim of the present study was to examine the potential of hydrostatic extrusion for the fabrication of high‐strength materials for medical applications. The materials examined were 316LVM steel and technically pure titanium. The microstructures and mechanical properties of the materials before and after hydrostatic extrusion were analysed. It was found that the hydrostatic extrusion process resulted in a substantial refinement of the material microstructures. The refinement of the microstructure was accompanied by an improvement of the mechanical properties, such as the microhardness and yield stress.

Comparative Laser Spectroscopy Diagnostics for Ancient Metallic Artefacts Exposed to Environmental Pollution

Metal artworks are subjected to corrosion and oxidation processes due to reactive agents present in the air, water and in the ground that these objects have been in contact with for hundreds of years. This is the case for archaeological metals that are recovered from excavation sites, as well as artefacts exposed to polluted air. Stabilization of the conservation state of these objects needs precise diagnostics of the accrued surface layers and identification of original, historical materials before further protective treatments, including safe laser cleaning of unwanted layers. This paper presents analyses of the chemical composition and stratigraphy of corrosion products with the use of laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy. The discussion of the results is supported by material studies (SEM-EDS, XRF, ion-analyses). The tests were performed on several samples taken from original objects, including copper roofing from Wilanów Palace in Warsaw and Karol Poznański Palace in ŁódŸ, bronze decorative figures from the Wilanów Palace gardens, and four archaeological examples of old jewellery (different copper alloys). Work has been performed as a part of the MATLAS project in the frames of EEA and Norway Grants (www.matlas.eu) and the results enable the comparison of the methodology and to elaborate the joint diagnostic procedures of the three project partner independent laboratories.

Structure and Properties of Ti-Al Intermetallic Layers Produced on Titanium Alloys by a Duplex Treatment

The rapid progress in engineering enhances the demands set on materials requiring better mechanical properties, resistance to frictional wear, corrosion and erosion etc. These demands can be also satisfied by e.g. applying various surface engineering techniques which permit modifying the microstructure, phase and chemical composition of the surface layers produced on the treated parts. A prospective line of the development is the production of the intermetallic layers by combining various methods aimed to improve essentially the performance properties and service life of the treated parts. The paper presents properties of the Al2O3+TiAl3+TiAl+Ti3Al type layer produced on titanium alloy Ti6Al2Cr2Mo by duplex method combined with magnetron sputtering process of aluminium coating with a glow discharge assisted treatment. The results of the examinations: microstructure, chemical and phase composition, frictional wear resistance and mechanical properties are discussed. Produced composite surface layers have the diffusion character and a precisely specified structure, chemical and phase composition and good wear and corrosion resistance what can widen significantly application range of treated parts.

Nanocrystalline Titanium Rods Processed by Hydrostatic Extrusion

The potential application range of coarse-grained commercial purity titanium is limited by its low mechanical properties. A reduction of the grain size of titanium leads to a significant increase in its strength and hardness. This paper is concerned with application of hydrostatic extrusion (HE) for fabrication nano-grained titanium. In the present study titanium rods were subjected to hydrostatic extrusion with the aim to reduce the grain size to the nano-metric scale and thereby improve the mechanical properties. The obtained material can be an equivalent and compete with the commonly used Ti6Al4V alloy. The results were compared with those other SPD techniques reported in the literature and refered to Hall-Petch relationship.

Homogeneity of Bulk Nanostructured Titanium Obtained by Hydrostatic Extrusion

The aim of this study was to investigate the homogeneity of the bulk nanocrystalline titanium rods obtained by Hydrostatic Extrusion (HE). The investigated material was commercially pure titanium grade 2. The final products of extrusion were nanocrystalline rods with diameters of 7 and 10 mm and lengths of about 250 mm. The size and shape of the grains were examined on transverse sections using transmission electron microscopy (TEM). The grain size was determined by the average grain equivalent diameter d2. The grain size diversity was quantified in terms of the equivalent diameter coefficient of variation CV (d2). The samples for the microscopic analyses were cut from various regions of the rods i.e. top, end, centre, and from surface of the rods. In all the samples, the average grain size determined on transverse sections was about 70 nm and the nano-grains in the various regions of the rods were similar in the shape. The examinations demonstrated that the nanostructure of the extruded rods was homogeneous. This observation was confirmed by the results of microhardness measurements.

Studies of aluminium coatings deposited by vacuum evaporation and magnetron sputtering

The paper presents the results of investigations of the microstructures and properties of the aluminium coatings deposited by vacuum evaporation and magnetron sputtering. These coatings generally have a very refined microstructure with elongated nano‐grains. However, the surface topography of the aluminium coating deposited by vacuum evaporation is more developed, its microstructure is less homogeneous and more porous. The residual tensile stresses in the aluminium coating deposited by magnetron sputtering are close to 130 MPa, and the texture is relatively pronounced. Vacuum evaporation does not induce residual stresses in the coatings and the texture is very weak. The results obtained indicate that the aluminium coatings produced by magnetron sputtering are more suitable for the diffusive Ti‐Al intermetallic layers.

The Influence of the Initial State on Microstructure and Mechanical Properties of Hydrostatically Extruded Titanium

Titanium was subjected to hydrostatic extrusion, a method of producing Severe Plastic Deformation (SPD). The experiments were aimed at refining the microstructure of the titanium in order to improve some of its mechanical properties. The effect of the initial state of titanium on the process of extrusion process and the final product was investigated. The results of these investigations are used to establish the optimum conditions for the hydrostatic extrusion process and more easily selecting the initial condition of the material according to the intended application of the extruded product.

Ti – Al Intermetallic Layers Produced on Titanium Alloy by Duplex Method

The paper presents the results concerning the microstructure of Ti – Al intermetallic layers produced on a TA6V titanium alloy by the “duplex method”. This method combines vacuum evaporation coating of aluminum with glow discharge assisted heat treatment of the deposited films. It has been found that this combination of surface engineering techniques yields multi – layered films of the diffusive character. The films contain intermetallic phases from Ti – Al system which ensure a high microhardnes and good wear resistance. It is finally suggested that these properties can significantly widen application range of titanium alloy parts in aerospace.

Microstructural refinement under high plastic strain rates during hydrostatic extrusion

High strain rates have a similar influence to large deformations on the refinement of microstructure. In both cases, at large strains and high deformation rates, a strong tendency to form microbands is observed. It was found, that the width of the microbands is very sensitive to changes of the deformation parameters. It has been observed particularly, that in severely deformed materials, the width of the microbands is reduced to nanometric dimensions. Hydrostatic extrusion, which has been used in for the deformation of copper in the current work, strain rates exceeding 2 1 3.84 10 − ⋅ ε = × s were employed. In all the samples investigated, numerous microbands were found in the microstructure. The width of microbands varied from 20 to about 400 nm. Thus, the width of some of the microbands exhibited dimensions typical of nanometric materials. Additionally, a special feature was the appearance of large areas of subgrains with an average dimension of about 200 nm. These areas were identified as recrystallized dynamically, or post-dynamically. Large misorientations were found between the microbands and the surrounding “matrix’. Such misorientation facilitates the formation of high angle boundaries, which in turn contribute to the changes of microstructure and mechanical properties. The mechanism for the creation of high misorientation in the microband areas is probably different from that operating during the process of dynamic recrystalization. The results confirm the possibility of obtaining a nanometric structure at lower deformation, but at higher strain rates.

Processing by Hydrostatic Extrusion of Titanium Coated with Aluminides

The material examined was commercially pure titanium with intermetallic Ti-Al layers produced by magnetron sputtering followed by glow discharge assisted treatment. This material was subjected to hydrostatic extrusion at room temperature. This resulted in substantial grain size refinement in the titanium accompanied by significant property improvement. The intermetallic Ti- Al layers reduced the pressure required during hydroextrusion and also increased the microhardness and frictional wear resistance of the material.