Kształtowanie mikrostruktury i własności stopów na osnowie fazy Heuslera Co₂NiGa

Stopy na osnowie faz Heuslera, którym przypisuje się wzór A₂BC z uwagi na występujący w tych stopach magnetyczny efekt pamięci kształtu związany z przemianą martenzytyczną lub reorientacją wariantów płytek martenzytu pod wpływem zewnętrznego pola magnetycznego, są obecnie przedmiotem intensywnych badań wielu czołowych ośrodków naukowych. Istotą procesu reorientacji płytek martenzytu jest nakładanie się pasm utworów bliźniaczych w płytkach martenzytu z ferromagnetycznymi domenami Weissa. Przyłożenie pola magnetycznego wywołuje przemieszczenie się granic domen i bliźniaków w płytce martenzytu korzystnie zorientowanej w stosunku do przyłożonego zewnętrznego pola magnetycznego kosztem wariantu o niekorzystnej orientacji. Zatem magnetyczny efekt pamięci kształtu związany jest z ruchem granic bliźniaczych, stąd wymaganiem jest niska wartość naprężeń konieczna dla przemieszczenia się granic bliźniaczych w płytce martenzytu. Największy efekt magnetycznej pamięci kształtu ok. (10%) uzyskano jak dotąd w jednofazowych monokrystalicznych stopach na osnowie Ni₂MnGa. Jednak praktyczne zastosowanie tych stopów w stanie polikrystalicznym jest znacznie ograniczone ze względu na ich kruchość. Poszukiwania stopów o wyższych własnościach plastycznych wykazały, że można ją osiągnąć w stopach na osnowie Co₂NiGa przy obecności cząstek fazy γ

Microstructure, phase transformations, and properties of hot-extruded Ni-rich NiTi shape memory alloy

Processing of NiTi shape memory alloys strongly influences their microstructure, phase transformations, mechanical, and shape memory properties. Hot forging, hot swaging, or hot rolling are efficient techniques for obtaining the desired shape, but during multiple operations the material must be heated and worked in the temperature range from 700 to 900 C. During these processes, intense oxidation takes place. In order to reduce it, the hot-pack working is applied. The hot extrusion is more effective for reduction of ingot, billet, and rod diameters than hot forging, hot swaging, or hot rolling. Also, during hot extrusion the material surface undergoes considerably less oxidation. In the present work, results of the characterization by differential scanning calorimetry, low-temperature x-ray powder diffraction, and three-point bending and free recovery ASTM F2082-06 tests of the samples after hot direct extrusion and heat treatment are presented. The obtained alloy after hot direct extrusion exhibits desired shape memory effect. The phase transformations during cooling and heating cycle occur with the presence of the R phase. The range of the characteristic temperatures for the obtained material gives possibility for further medical applications. After annealing at 400 and 500 C, the characteristic temperatures shift to higher values

Mechanical properties of Ni-Fe-Cu-P-B alloy produced by two component melt spinning (TCMS)

The aim of this work was to investigate the microstructure and mechanical properties of the two-component melt-spun (TCMS) alloy produced from Ni40Fe40B20 and Ni70Cu10P20 melts. The Ni40Fe40B20, Ni70Cu10P20, Ni55Fe20Cu5P10B10 alloys were arc-melted. Then the alloys were melt-spun in the two different ways i.e.: by casting from a single-chamber crucible and from the two-chamber crucible. All of the above mentioned alloys were processed in the first way and the Ni40Fe40B20 and Ni70Cu10P20 were simultaneously cast on the copper roller from the two-chamber crucible. The microstructure of the alloy was studied using transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) and light microscopy. The mechanical properties were investigated using tensile testing and nanoindentation. The two-component melt-spun (TCMS) amorphous Ni55Fe20Cu5P10B10 alloy present hardness, tensile strength and Young modulus on the significantly higher level than for a single phase amorphous Ni55Fe20Cu5P10B10 alloy and slightly below the corresponding values for the Ni40Fe40B20

Role of the molybdenum addition on the mechanical properties and structure of the NiCoMnIn alloys

In this paper, the influence of Mo addition on the structure and mechanical properties of the NiCoMnIn alloys have been studied. Series of polycrystalline NiCoMnIn alloys containing from 0 to 5 mas.% of Mo were produced by the arc melting technique. For the alloys containing Mo, two-phase microstructure was observed. Mo-rich precipitates were distributed randomly in the matrix. The relative volume fraction of the precipitates depends on the Mo content. The numbers of the Mo rich precipitates increases with the Mo contents. The structures of the phases were determined by the TEM. The mechanical properties of the alloys are strongly affected by Mo addition contents. Brittleness of the alloys increases with the Mo contents

Structure of the Extruded and Thermally Treated Ni54.3Fe16.2Ga29.5 Alloy

Hot extrusion process was applied to Ni54:3Fe16:2Ga29:5 polycrystalline alloy. Then the rod was annealed subsequently for 1 h at 700, 800, 900, and 1100 C. In this paper the effect of annealing on the microstructure of the polycrystalline extruded Ni–Fe–Ga alloy were analyzed. The structure of the alloys was determined by the X-ray and transmission electron microscopy. The electron backscattering diffraction technique was applied to obtain the texture of the extruded rods after heat treatmen

Effect of the Boron Addition on the structure of the Ni-Mn-Co-In alloys

Series of Ni45:5xCo4:5Mn36:6In13:4Bx (at.%, x = 0, 0.05, 0.1, 0.5, 1.0) polycrystalline magnetic shape memory alloys produced by the induction melting were examined in terms of the structure and transition temperatures. The structure of the alloys was determined by the X–ray diffraction and transmission electron microscopy. Scanning electron microscopy and electron backscattering diffraction techniques were applied to obtain the microstructure and texture of alloys. Boron addition promotes nucleation of the second Co–rich and In–poor phase as well as causes decrease of the martensitic transformation temperatures

Influence of high energy milling time on the Ti-50Ta biomedical alloy structure

Nickel-free titanium alloys are a promising research direction in the field of biomedical materials. Current literature reports indicate that there is a possibility of using the Ti–Ta alloys in medicine since these alloys have had satisfactory results as far as biocompatibility, resistance to corrosion and mechanical properties are concerned, which is an important aspect while considering the use of this alloy for long-lasting bone implants. This article presents the results of a high-energy milling process with the use of Ti and Ta powders. The ball-milling process was carried out for various times, including 20, 40, 60, 80, and 100 h. The samples were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The research confirmed partial synthesis of the materials during the process of high energy ball milling

Preparation and magnetic characteristics of Co1−δZnδFe2O4 ferrite nanopowders

In the present paper the Co1 Zn Fe2O4 (0 1) ferrite nanopowders with a spinel type structure were synthesized using a chemical co-precipitation technique with constant flow rate FR = 120 cm3/min at three different reaction temperatures i.e. Tr = 50 C, 70 C and 90 C. Magnetic and structural characteristics of the obtained materials were investigated by means of X-ray diffraction method, transmission electron microscopy and vibrating sample magnetometer. In the course of studies hysteresis loops M( 0H) and the relations of magnetization M7T (determined at 0H = 7 T), squareness ratio S and the Néel temperature TN versus Zn content were determined and discussed in detail. It was shown that for < 0:6 the increase in reaction temperature Tr results in a significant increase of the measured magnetic characteristics. In particular, in the case of Co0:8Zn0:2Fe2O4 ferrite nanopowder magnetization M7T reaches maximal value of about 80 emu/g

Magnetic hardening induced in RCo5 (R = Y, Gd, Sm) by short HEBM

The paper is focused on the magnetic and structural properties of RCo5 (R = Y, Gd, Sm) intermetallics fabricated by high energy ball - milling (HEBM). The investigated samples were first produced by arc-melting as bulk materials and then were milled for 1h in dimethylformamide with balls to powder ratio 10:1. The influence of the HEBM parameters on the microstructure was investigated by a variety of complementary measurement methods. The Rietveld refinement was performed to estimate the dependence of crystallite size and microstrain on type of sample. The hysteresis loops were recorded by SQUID magnetometer at 2 K and 300 K and at magnetic field up to 0H 7 T. The impact of short HEBM process is visible as the enhancement of coercivity and simultaneous reduction of the saturation magnetization[…

Magnetic properties of Tb(Ni1-xFex)3 (x = 0.2,0.6) crystalline compounds and powders

In the paper we present and discuss magnetic properties of the Tb(Ni1xFex)3 (x = 0:2, 0.6) crystalline compounds and their ball-milled powders. The investigated samples are polycrystalline and crystallize in the rhombohedral PuNi3 type of crystal structure. The Curie temperature of the material seems to be independent of particle size and is constant. The coercivity depends on the amount of iron dopant. The saturation magnetization decreases after mechanical grinding which is connected with the reduction in particle size. After 6 h milling time the SEM results show the presence of nano akes with thickness up to 100 nm or even smaller. Moreover, the pulverization leads to the observed decrease of magnetocaloric e ect