Obrada metala intenzivnom plastičnom deformacijom (IPD) – odgovarajuća struktura i mehanička svojstva

SPD methods are used to convert coarse grain metals and alloys into ultrafine grained (UFG) materials. Obtained UFG materials then possess improved mechanical and physical properties which destine them for a wide commercial use. This paper, in one direction, looks into historical development of SPD processes and their effect at obtaining fine crystalline structure, and on the other side also partially focuses on development of UFG structure and its stability in commercial pure aluminium as a function of strain and post-deformation annealing applied.Obrada metala intenzivnom plastičnom deformacijom (IPD) – odgovarajuća struktura i mehanička svojstva. IPD je postupak pretvorbe krupno u ultrafino zrnate (UFZ-a) metale i legure. Dobiveni UFZ materijal posjeduje oplemenjena mehanička i fizikalna svojstva, te su namjenjeni za široko komercijalno rabljenje. Ovaj članak s jedne strane daje osvrt na povijesni razvitak IPD-a postupka, a s druge strane djelomice ishodište za razvitak UFZ-a i njezine stabilnosti u trgovački čistom aluminiju, kao funkcija preoblikovanja i poslije deformacije primjenjenog žarenja

Recent Progress in High Strength Low Carbon Steels

Advanced High Strength (AHS) steels, among them especially Dual Phase (DP) steels, Transformation Induced Plasticity (TRIP) steels, Complex Phase (CP) steels, Partially Martensite (PM) steels, feature promising results in the field. Their extraordinary mechanical properties can be tailored and adjusted by alloying and processing. The introduction of steels with a microstructure consisting at least of two different components has led to the enlargement of the strength level without a deterioration of ductility. Furthermore, the development of ultra fine-grained AHS steels and their service performance are reviewed and new techniques are introduced. Various projects have been devoted to develop new materials for flat and long steel products for structural applications. The main stream line is High Strength, in order to match the weight lightening requirements that concern the whole class of load bearing structures and/or steel components and one of the most investigated topics is grain refinement

Nanostructures by Severe Plastic Deformation of Steels: Advantages and Problems

The aim of this paper is to consider the features of structure evolution during severe plastic deformation (SPD) of steels and its influence on mechanical properties. The investigation have been carried out mainly on low carbon steels as well as on austenitic stainless steels after SPD by torsion under high pressure (HPT) and equal channel angular (ECA) pressing. Structure formation dependencies on temperature deformation conditions, strain degree, chemical composition, initial state and pressure are considered. The role of phase transformations for additional grain refinement, namely, martensitic transformation, precipitation of carbide particles during SPD and heating is underlined

Effect of multiaxial forging on microstructure and mechanical properties of Mg-0.8Ca alloy

It was shown that multiaxial forging with continuous decrease of temperature from 450°C to 250°C turns coarse structure of the Mg-0.8Ca alloy in homogenized state with grain size of several hundreeds μm into fine structure with average grain size of about 2.1 μm. Refinement of structure is accompanied by drastic increase of mechanical properties: tensile yield strength increases from 50 MPa to 193 MPa, ultimate tensile strength increases from 78 to 308 MPa and elongation to fracture increases from 3.0% to 7.2%. The microstructural evolution during multiaxial forging is studied using optical microscopy, scanning electron microscopy and EBSD analysis. The mechanisms responsible for refinement of microstructure are discusse

Hot deformation and dynamic recrystallization of 18%mn twinning-induced plasticity steels

The deformation behavior of 18%Mn twinning-induced plasticity (TWIP) steels with 0.4%C or 0.6%C is studied by means of isothermal compression tests in the temperature range of 973-1373 K at the strain rates of 10³-10¹ s¹. The hot working is accompanied by the development of discontinuous dynamic recrystallization (DRX), which is commonly advanced by an increase in deformation temperature and/or a decrease in strain rate. A decrease in the carbon content promotes the DRX development, though the flow stresses scarcely depend on the carbon conten

Low Carbon Steel Processed by Equal Channel Angular Warm Pressing

Low carbon steel AISI 10 was subjected to a severe plastic deformation technique called Equal Angular Channel Pressing (ECAP) at different increased temperatures. The steel was subjected to ECAP with channel’s angle j = 90°, at different temperature in range of 150 - 300 °C. The number of passes at each temperature was N = 3. Light, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of thin foils were used to study the formation of substructure and ultrafine grains in deformed specimens. The size of newly born polygonized grains (subgrains and/or submicrocrystalline grains) is in range of 300 - 500 mm. The formation of such of predominant submicrocrystalline structure resulted in significant increase of yield stress [Re] and tensile strength of the steel [Rm]

Rationale for Processing of a Mg-Zn-Ca Alloy by Equal-Channel Angular Pressing for Use in Biodegradable Implants for Osteoreconstruction

Widespread use of Mg-Zn-Ca alloys in clinical orthopedic practice requires improvement of their mechanical properties—in particular, ductility—and enhancement of their bioactivity for accelerated osteoreconstruction. The alloy was studied in two structural states: after homogenization and after equal-channel angular pressing. Immersion and potentiodynamic polarization tests showed that the corrosion rate of the alloy was not increased by deformation. The mass loss in vivo was also statistically insignificant. Furthermore, it was found that deformation did not compromise the biocompatibility of the alloy and did not have any significant effect on cell adhesion and proliferation. However, an extract of the alloy promoted the alkaline phosphatase activity of human mesenchymal stromal cells, which indicates osteogenic stimulation of cells. The osteoinduction of the deformed alloy significantly exceeded that of the homogenized one. Based on the results of this work, it can be concluded that the alloy Mg-1%Zn-0.3%Ca modified by equal-channel angular pressing is a promising candidate for the manufacture of biodegradable orthopedic implants since it stimulates osteogenic differentiation and has greater ductility, which provides it with a competitive advantage in comparison with the homogenized state

The effect of equal-channel angular pressing on microstructure, mechanical properties, and biodegradation behavior of magnesium alloyed with silver and gadolinium

The effect of equal channel angular pressing (ECAP) on the microstructure, texture, mechanical properties, and corrosion resistance of the alloys Mg-6.0%Ag and Mg-10.0%Gd was studied. It was shown that ECAP leads to grain refinement of the alloys down to the average grain size of 2–3 μm and 1–2 μm, respectively. In addition, in both alloys the precipitation of fine particles of phases Mg$_{54}$Ag$_{17}$ and Mg$_{5}$Gd with sizes of ~500–600 and ~400–500 nm and a volume fraction of ~9% and ~8.6%, respectively, was observed. In the case of the alloy Mg-6.0%Ag, despite a significant grain refinement, a drop in the strength characteristics and a nearly twofold increase in ductility (up to ~30%) was found. This behavior is associated with the formation of a sharp inclined basal texture. For alloy Mg-10.0%Gd, both ductility and strength were enhanced, which can be associated with the combined effect of significant grain refinement and an increased probability of prismatic and basal glide. ECAP was also shown to cause a substantial rise of the biodegradation rate of both alloys and an increase in pitting corrosion. The latter effect is attributed to an increase in the dislocation density induced by ECAP and the occurrence of micro-galvanic corrosion at the matrix/particle interfaces