Mariusz Kulczyk

Enhancement of mechanical properties of biocompatible Ti–45Nb alloy by hydrostatic extrusion

Abstractβ-Type titanium alloys are promising materials for orthopaedic implants due to their relatively low Young’s modulus and excellent biocompatibility. However, their strength is lower than those of α- or αxa0+xa0β-type titanium alloys. Grain refinement by severe plastic deformation (SPD) techniques provides a unique opportunity to enhance mechanical properties to prolong the lifetime of orthopaedic implants without changing their chemical composition. In this study, β-type Ti–45Nb (wt%) biomedical alloy in the form of 30xa0mm rod was subjected to hydrostatic extrusion (HE) to refine the microstructure and improve its mechanical properties. HE processing was carried out at room temperature without intermediate annealing in a multi-step process, up to an accumulative true strain of 3.5. Significant microstructure refinement from a coarse-grained region to an ultrafine-grained one was observed by optical and transmission electron microscopy. Vickers hardness measurements (HV0.2) demonstrated that the strength of the alloy increased from about 150 to 210 HV0.2. Nevertheless, the measurements of Young’s modulus by nanoindentation showed no significant changes. This finding is substantiated by X-ray diffraction analyses which did not exhibit any phase transformation out of the bcc phase being present still before processing by HE. These results thus indicate that HE is a promising SPD method to obtain significant grain refinement and enhance strength of β-type Ti–45Nb alloy without changing its low Young’s modulus, being one prerequisite for biomedical application.

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 hydrostatic extrusion on the properties of an austenitic stainless steel

The paper presents the results of investigations into the mechanical properties and tribological characteristics of 316 LVM processed by hydrostatic extrusion (HE). The mechanical properties were characterized by microhardness measurements and compression tests. The wear properties were investigated using a pin-on-disc tribometer under dry and lubricated conditions. The friction coefficient was measured as a function of the time of the wear test. The results indicate that the hydrostatic extrusion process significantly improves the mechanical properties and the wear resistance of 316 LVM stainless steel. The results are discussed in terms of the microstructural changes induced during processing by hydrostatic extrusion.

Development of high-strength pure magnesium and wrought magnesium alloys AZ31, AZ61, and AZ91 processed by hydrostatic extrusion with back pressure

Abstract Cold hydrostatic extrusion with and without back pressure of commercial Mg 99.5+% and AZ31, AZ61, and AZ91 wrought magnesium alloys has been performed on a press operating up to 2000 MPa with a back pressure reaching up to 700 MPa. Application of back pressure extended the formability of Mg, and AZ-type magnesium alloys, which decreases with the increase in the Al content. Fibrous and elongated grains above 1 micrometre and nanometre scale sub-grains and grains were observed. The strength of all materials was significantly higher in comparison to materials conventionally and hydrostatically hot-extruded, hot ECAP-ed or after hot wire drawing. In comparison to materials processed by traditional methods the ultimate tensile strength increment after hydrostatic extrusion with back pressure increases gradually with an increase in Al content reaching for AZ91 almost 40%. The potential application of AZ-type magnesium alloys as semi-products for degradable medical implants or high strength structural components is indicated.

UFG and nanocrystalline microstructures produced by hydrostatic extrusion of multifilament wires

Abstract Aluminium, Al-4Cu-0.5Mg-1Mn aluminium alloy (AA2017), copper, iron and nickel in the form of a bundle of wires placed in appropriate capsules were subjected to cumulative hydrostatic extrusion to form 3 mm wires with total true strain above 10 in Al, the aluminium alloy and Cu and above 7 in Ni and Fe. The deformation was first induced in single wires which were then assembled and further deformed to form a multifilament wire. The final product had a nanocrystalline (grain size below 100 nm in Fe and the 2017 Al alloy) and ultra-fine grain (below 130 nm in Ni and below 270 nm in Cu and Al) microstructure. The grain refinement resulted in the microhardness being increased, with the greatest increase to 3.5 GPa being achieved in iron. During hydrostatic extrusion, the severe deformation was possible due to the high applied pressures of up to 1.7 GPa. The hydrostatic extrusion of multifilament wires broadens the application range of this process extending it to the fabrication of ultra-fine grain and nanocrystalline microstructures.

Metallic Nano-Materials and Nanostructures: Development of Technology Roadmap

Current and prospective trends in application of metallic nanomaterials have been studied. The study has been conducted within the Nanoroad SME European project – as the first step for a roadmap for industrial application of nanomaterials. The web page of the project is http://www.nanoroad.net/. The present report presents an analysis of patents, papers, national and European projects in the field of nano-metals, and also an analysis of the present state of research and expected trends in this domain. Based on the performed analysis a data base of nanomaterials has been developed as well as roadmaps with expected time to applications. It can be found under http://bourgogne.arist.tm.fr/nanoroadsme/home/. The roadmap is mainly addressed to SMEs to help them to decide about applications or production of nanomaterials.

Densification of Nd-Fe-B Powders by Hydrostatic Extrusion

Hydrostatic extrusion is a modern method of densifying materials. This method is rapid and permits extruding materials of various properties. In the present experiments, Nd-Fe-B powder, provided by Magnequench, was subjected to densification by hot pressing and subsequent hydrostatic extrusion. The powder was initially pressed mechanically and subsequently placed in a copper capsule. The densification was conducted at room temperature and at temperatures above and below the melting point of the Nd-rich phase (TNd), respectively. When densified at a temperature below TNd, the sample was strongly porous and the powder particles were not well bonded, whereas at the temperature above TNd the interparticle bonds were good. In scanning electron microscopy images we can see solid regions which are fragments of the starting powder particles and, between them, porous regions which also contain small fragments of the powder particles. It seems that, during the deformation, the surface layer of the polycrystalline powder particles is segmented into smaller particles. After the extrusion new regions appear, containing the Nd-rich phase which has been forced out from the intergranular spaces just as it is the case of die-upset forging. The extrusion, even at room temperature, affects the magnetic properties of the material, whereas when conducted at higher temperatures, it resulted in a slight decrease of the coercivity. This can be due to the grains growth when the powder is heated prior to extrusion. No anisotropy of the magnetic properties was observed in the extruded materials.

Combination of ECAP and Hydrostatic Extrusion for UFG Microstructure Generation in Nickel

An ultra-fine grained microstructure was obtained in high purity nickel by a combination of (a) equal-channel angular pressing (ECAP) and (b) hydrostatic extrusion (HE) with a cumulative true strain of ~11.2. The resulting microstructure was examined by light and TEM microscopy. Mechanical properties have been measured by tensile and hardness tests. It was found that HE of ECAP-ed samples leads to a significant grain size refinement (from 330 to 160nm) and to an increase in microstructural homogeneity. SPD nickel, made by a combination of the ECAP and hydrostatic extrusion methods, has high strength and ductility (i.e.: YS=1120MPa and εf = 11%). The microstructure transformation was accompanied by a strength increase of 78% compared to ECAP alone. The results obtained fit well with the Hall-Petch relationship. A combination of ECAP and HE has achieved much better properties than either single process and show it to be a promising procedure for manufacturing bulk UFG nickel.

The Influence of Hydrostatic Extrusion on the Microstructure of 6082 Aluminium Alloy

Hydrostatic extrusion can be viewed as one of the methods of Severe Plastic Deformation, SPD, for the fabrication of ultra-fine grained alloys which causes a significant increase in the mechanical properties such as tensile strength and hardness. In the present study the microstructure of 6082 aluminium alloy after hydrostatic extrusion was investigated. Hydroextrusion was performed in three steps with accumulated true strains of 1.34, 2.73 and 3.74 respectively. Microstructural observations were carried out using SEM, TEM and light microscopy. Grain and inclusion sizes, shapes and distribution were investigated in the HE processed samples. The study has shown that the hydrostatic extrusion process results in a profound refinement of both the grain size and the inclusions in 6082 aluminium alloy.

Microstructure and Texture Evolutions of Biomedical Ti-13Nb-13Zr Alloy Processed by Hydrostatic Extrusion

A biomedical β-type Ti-13Nb-13Zr (TNZ) (wt pct) ternary alloy was subjected to severe plastic deformation by means of hydrostatic extrusion (HE) at room temperature without intermediate annealing. Its effect on microstructure, mechanical properties, phase transformations, and texture was investigated by light and electron microscopy, mechanical tests (Vickers microhardness and tensile tests), and XRD analysis. Microstructural investigations by light microscope and transmission electron microscope showed that, after HE, significant grain refinement took place, also reaching high dislocation densities. Increases in strength up to 50 pct occurred, although the elongation to fracture left after HE was almost 9 pct. Furthermore, Young’s modulus of HE-processed samples showed slightly lower values than the initial state due to texture. Such mechanical properties combined with lower Young’s modulus are favorable for medical applications. Phase transformation analyses demonstrated that both initial and extruded samples consist of α′ and β phases but that the phase fraction of α′ was slightly higher after two stages of HE.