Zr–(Cu,Ag)–Al bulk metallic glasses

In this paper, we report the formation of a series Zr–(Cu,Ag)–Al bulk metallic glasses (BMGs) with diameters at least 20 mm and demonstrate the formation of about 25 g amorphous metallic ingots in a wide Zr–(Cu,Ag)–Al composition range using a conventional arc-melting machine. The origin of high glass-forming ability (GFA) of the Zr–(Cu,Ag)–Al alloy system has been investigated from the structural, thermodynamic and kinetic points of view. The high GFA of the Zr–(Cu,Ag)–Al system is attributed to denser local atomic packing and the smaller difference in Gibbs free energy between amorphous and crystalline phases. The thermal, mechanical and corrosion properties, as well as elastic constants for the newly developed Zr–(Cu,Ag)–Al BMGs, are also presented. These newly developed Ni-free Zr–(Cu,Ag)–Al BMGs exhibit excellent combined properties: strong GFA, high strength, high compressive plasticity, cheap and non-toxic raw materials and biocompatible property, as compared with other BMGs, leading to their potential industrial applications.     

A comparative study of microstructure,oxidation resistance,mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB₂, TiB, and TiB₂ targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB₂ coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB₂) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10^–6 mm3 N^–1 m^–1.     

Structure and properties of selected (Cr–Al–N,TiC–C,Cr–B–N) nanostructured tribological coatings

The paper will present the state-of-art in the process, structure and properties of nanostructured multifunctional tribological coatings used in different industrial applications that require high hardness, toughness, wear resistance and thermal stability. The optimization of these coating systems by means of tailoring the structure (graded, superlattice and nanocomposite systems), composition optimization, and energetic ion bombardment from substrate bias voltage control to provide improved mechanical and tribological properties will be assessed for a range of coating systems, including nanocrystalline graded Cr_1−xAl_xN coatings, superlattice CrN/AlN coatings and nanocomposite Cr–B–N and TiC/a-C coatings. The results showed that the superlattice CrN/AlN coating exhibited a super hardness of 45 GPa when the bilayer period Λ was about 3.0 nm. Improved toughness and wear resistance have been achieved in the CrN/AlN multilayer and graded CrAlN coatings as compared to the homogeneous CrAlN coating. For the TiC/a-C coatings, increasing the substrate bias increased the hardness of TiC/a-C coatings up to 34 GPa (at −150 V) but also led to a decrease in the coating toughness and wear resistance. The TiC/a-C coating deposited at a −50 V bias voltage exhibited an optimized high hardness of 28 GPa, a low coefficient of friction of 0.19 and a wear rate of 2.37 × 10⁻⁷ mm³ N⁻¹ m⁻¹. The Cr–B–N coating system consists of nanocrystalline CrB₂ embedded in an amorphous BN phase when the N content is low. With an increase in the N content, a decrease in the CrB₂ phase and an increase in the amorphous BN phase were identified. The resulting structure changes led to both decreases in the hardness and wear resistance of Cr–B–N coatings.     

Alloyed W–(Co,Ni,Fe)–C phases for reaction sintering of hardmetals

It has been shown that W–Co–C phases could dissolve a substantial amount of metals such as V, Cr and Ta, which are known to positively influence the microstructure of hardmetals with respect to uniform grain size distribution and fine grain size. This offers a tool to circumvent the conventional doping of hardmetals with individual carbides. In the present study we used double- and triple-alloyed κ-W₉Co₃C₄ (i.e. κ-(W,V,Cr)₉Co₃C₄ and κ-(W,V,Cr,Ta)₉Co₃C₄) and applied a variety of sintering experiments to obtain WC–Co, WC–(Ti,Ta,Nb)C–Co and WC–(Ti,Ta,Nb)(C,N)–Co hardmetals. We also prepared κ-W₉Fe₃C₄, alloyed κ-W₉Ni₃C₄, and κ-W₉(Fe/Ni)₃C₄, and used the latter for sintering.     

Microstructure,mechanical properties and creep resistance of Mg–(8%–12%)Zn–(2%–6%)Al alloys

The microstructural characteristics, mechanical properties and creep resistance of Mg–(8%–12%)Zn–(2%–6%)Al alloys were investigated to get a better overall understanding of these series alloys. The results indicate that the microstructure of the alloys ZA82, ZA102 and ZA122 with the mass ratio of Zn to Al of 4–6 is mainly composed of α-Mg matrix and two different morphologies of precipitates (block τ-Mg₃₂(Al, Zn)₄₉ and dense lamellar ε-Mg₅₁Zn₂₀), the alloys ZA84, ZA104 and ZA124 with the mass ratio of 2–3 contain α-Mg matrix and only block τ phases, and the alloys ZA86, ZA106 and ZA126 with the mass ratio of 1–2 consist of α-Mg matrix, block τ precipitates, lamellar ?-Al₂Mg₅Zn₂ eutectics and flocculent β-Mg₁₇Al₁₂ compounds. The alloys studied with the mass ratio of Zn to Al of 2–3 exhibit high creep resistance, and the alloy ZA124 with the continuous network of τ precipitating along grain boundaries shows the highest creep resistance.     

Mechanical and Magnetic Properties of New(Fe,Co,Ni)–B–Si–Ta Bulk Glassy Alloys

The alloying effects of the like-atom substitution of Ni and Co for Fe on the various properties of Fe_(70)B_(16.7)Si_(8.3)Ta_5 metallic glass are investigated in this present work. New Fe-based bulk glassy alloys, namely Fe_(60–x)Co_xNi_(10)B_(16.7)Si_(8.3)Ta_5(at.%;x = 10, 20 and 30) with critical diameters up to 1.5 mm, were made by means of copper mold casting.A new glass-forming ability indicator, viz., the enthalpy of supercooled liquid, has been introduced for assessment of the glass-forming abilities(GFAs) of these Fe-based multi-component alloys. Nano-indentation results indicate that the calculated elastic modulus and hardness of the bulk glassy alloys are lower than those of the Fe_(70)B_(16.7)Si_(8.3)Ta_5 alloy.Among these bulk glassy alloys, Fe_(70)B_(16.7)Si_(8.3)Ta_5 exhibits the large elastic modulus and hardness with values of 178 ± 1GPa and 12.9 ± 0.1 GPa, respectively. All the bulk glassy alloys exhibit good soft magnetic properties with high saturation magnetization Bs~0.75–1.04 T but low coercive force Hc~0.2–5.2 A/m.     

The Influence of H,W, H/E,H 3/E 2, Structure and Chemical Composition on the Resistance of Ti–B–(N), Mo–B–(N), Cr–B–(N), and Zr–B–(N) Coatings to Cyclic Impact Loading

Protection of Metals and Physical Chemistry of Surfaces - Coatings based on transition metal borides (Ti, Mo, Cr, Zr) were obtained by magnetron sputtering of ceramic targets in Ar and Ar–15%...     

Microstructure and mechanical properties of Fe–Si–Ti–(Cu,Al) heterostructured ultrafine composites

The influence of partial substitution of Fe by Cu or Al in Fe_75?xSi₁₅Ti₁₀(Cu, Al)_x (x = 0 and 4) ultrafine composites on the microstructure and mechanical properties has been investigated. The Fe₇₁Si₁₅Ti₁₀Cu₄ ultrafine composite exhibits a favorable microstructural evolution and improved mechanical properties, i.e., large plastic strain of ～5% and pronounced work hardening characteristics. The mechanical properties of the ultrafine eutectic composite are strongly linked to the length scale heterogeneity and the distribution of the constituent phases.     

Structure and hydrogen sorption properties of (Ti,Zr)–Mn–V alloys

The present investigation is a part of the series of works on the development of new materials as highly efficient hydrogen accumulating media. Earlier we reported on the investigation of Ti–Mn–V alloys of Laves phase type. This work is the continuation of these studies. The work was aimed on the determination of concentration boundaries of Laves phase and investigation of hydrogen sorption properties of alloys. Using X-ray, EDXA and electron microscopy methods the phase compositions of over 50 alloys were studied. The Laves phase concentration boundaries were determined to extend up to 26 at.% of vanadium. Compared to ternary Ti–Mn–V system the region of λ₁-phase is about 2 at.% wider for Ti–Mn side of concentration triangle. Depending on metal concentrations lattice parameters were determined to increase proportionally with increasing titanium or vanadium concentration according to Vegard rule. The interaction of alloys with hydrogen was studied by PC-isotherm method. The isotherms were measured at three different temperatures and thermodynamic parameters of reaction were calculated using the vant Hoff equation. The hydrogen sorption properties were analysed in view of overall alloy composition. The enthalpy of desorption was found to depend proportionally on unit cell volume of alloy.     

Structure of martensite in sputter-deposited (Ni,Cu)-rich Ti–Ni–Cu thin films containing Ti(Ni,Cu)2 precipitates

The martensite structure in sputter-deposited thin films of Ti_48.6Ni_35.9Cu_15.5 was studied. The Ti(Ni,Cu)₂ phase precipitates during the annealing process. Fine Ti(Ni,Cu)₂ precipitates can be deformed by the shear deformation of martensitic transformation, but they obstruct the movement of the twin boundaries to some extent. Coarse Ti(Ni,Cu)₂ precipitates seriously impede the growth of martensite plates and lead to a rectangular-cell-like structure of martensite in the film annealed at 873 K. The resistance of Ti(Ni,Cu)₂ precipitates to the growth of the martensite plates enhances with the coarsening of Ti(Ni,Cu)₂ precipitates, which is one of the reasons for the decrease in the maximum recoverable strain with increasing annealing temperature. B19′ martensite with (0 0 1) compound twinning is frequently observed near coarse Ti(Ni,Cu)₂ precipitates and grain boundaries in films annealed at 873 and 973 K. The local stress concentration should be responsible for the presence of B19′ martensite.     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.     

Microstructures and Mechanical Properties of Mg–xAl–1Sn–0.3Mn( x = 1, 3, 5) Alloy Sheets

The influence of Al alloying on the microstructures and the mechanical properties of Mg–x Al–1 Sn–0.3 Mn alloy sheets was investigated. The microstructure of Mg– x Al–1 Sn–0.3 Mn consisted of α-Mg and Mg 17 Al 12 precipitates. Alloying with Al increased the amount of Mg_(17)Al_(12) and the average grain size. Uniaxial tensile tests were carried out along the extrusion direction(ED), the transverse direction(TD) and 45° toward the ED. Mg–5 Al–1 Sn–0.3 Mn alloy sheet exhibited the best combination of mechanical properties along the ED: a yield strength of 142 MPa, an ultimate tensile strength of 282 MPa and an elongation of 23%. The good performance of Mg–5 Al–1 Sn–0.3 Mn sheet was mainly attributed to the large quantity of Mg_(17)Al_(12) precipitates and a weak basal texture. Annealing caused static dynamic recrystallization, refined the grain size and enhanced the mechanical properties: yield strength of 186 MPa, ultimate tensile strength of 304 MPa, elongation of 21% along ED. Both strength and ductility were enhanced by Al alloying.     

Secondary precipitation in Al–Zn–Mg–(Ag) alloys

Secondary ageing of age-hardenable aluminium alloys occurs at temperatures below the solvus of GP zones after a preliminary ageing at a higher temperature. The phenomenon has technological interest, as it may be included in heat treatments giving a substantial benefit on the mechanical properties. In the present work, positron annihilation lifetime spectroscopy (PALS) is applied in combination with Vickers hardness measurements for an investigation on secondary ageing of Al–4wt.%Zn–3wt.%Mg–xAg, where x=0, 0.1, 0.2, 0.3, 0.5 wt.%. Ageing regimes have been characterised by the substantially different evolutions that are observed. The results shed light on the interplay between the formation of coherent solute aggregates (clusters or GP zones) and the precipitation of semi-coherent or incoherent precipitates, which are in competition to control the hardening effects. PALS data show that secondary ageing in the ternary Al–Zn–Mg alloys produces coherent aggregates even in the presence of a well-developed stage of semi-coherent or incoherent precipitation that is obtained if the alloys are first aged to peak hardness. In the presence of Ag, on the contrary, the effects of coherent aggregation during secondary ageing are observed only if the preliminary ageing is interrupted well before reaching peak hardness.     

Leo Brewer (1919–2005)

In Memoriam

Leo Brewer (1919–2005)     

Recrystallization behavior,microstructure evolution and mechanical properties of biodegradable Fe–Mn–C(–Pd) TWIP alloys

In this study the interplay between recrystallization and precipitation in a biodegradable TWIP (twinning-induced plasticity) steel developed for use in temporary implants was investigated. Microstructural and mechanical properties were studied and a thermomechanical treatment was designed with the aim of achieving an overall performance suitable for the intended application as temporary implant material. The formation of Pd-rich precipitates in the cold-worked state was found to considerably retard recrystallization during an annealing treatment. The formation, morphology and interaction with dislocations of these precipitates were studied by means of scanning and transmission electron microscopy. Grain boundary pinning by Pd-rich precipitates (Zener drag) and reduced dislocation mobility due to a solute drag effect caused by the enrichment of dislocation cores with Pd were both identified as mechanisms which impede recrystallization. A model is reported which explains the interplay between recrystallization and precipitation, and provides the basis for the optimized thermomechanical treatment then presented. The resulting mechanical properties, in particular the combination of high strength and ductility with a pronounced strain-hardening response, exceed the performance of other TWIP steels and alloys typically used in biomedical implants, such as stainless steel, titanium or cobalt–chromium alloys. The specific property profile developed is especially advantageous for the production and deployment of cardiovascular stents.     

Oswald kubaschewski (1912–1991)

In Memoriam

Oswald kubaschewski (1912–1991)     

Horizontally Solidified Al–3 wt%Cu–(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters,Microstructure, Microhardness,and Corrosion Behavior

In the present experimental investigation, Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(G_R), cooling rate(C_R), secondary dendrite arm spacing(λ_2), Vickers microhardness(HV), and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures, that is, h-Al_2Cu, S–Al_2CuMg, and x-Al_7Cu_2 Fe, are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software, optical microscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Moreover, electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings. Hall–Petch-type equations are proposed to represent the HV dependence on λ_2. It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV; however, the Al–Cu binary alloy is shown to have lower corrosion current density(i_(corr)) as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.     

Glass-forming ability of RE–Al–TM alloys (RE=Sm,Y; TM=Fe,Co, Cu)

The glass-forming ability (GFA) of RE–Al–TM (RE=Sm, Y; TM=Fe, Co, Cu) upon melt-spinning and die-casting into a copper mold has been studied. Melt-spun ribbons for both Sm- and Y-based alloys show a fully amorphous structure. However, die-casting revealed that Sm-based alloys exhibit a higher GFA than Y-based alloys. The as-cast Sm₇₀Fe₂₀Al₁₀, Sm₆₀Fe₂₀Al₁₀Co₁₀ and Sm₆₀Fe₂₀Al₁₀Co₅Cu₅ cylinders (3 mm×50 mm) contain a mixture of amorphous and crystalline phases after copper-mold casting. A new bulk metallic glass was obtained for the Sm₆₀Fe₁₀Al₁₀Co₁₅Cu₅ alloy, which shows ferromagnetic behavior. In contrast, as-cast Y-based alloys are completely crystalline. Based on the data of the activation energy for crystallization of the amorphous phase, E_x, and the crystallization temperature, T_x, together with magnetic measurements, it is concluded that the as-cast Sm₆₀Fe₁₀Al₁₀Co₁₅Cu₅ cylinder displays a tendency for clustering. The improved glass-forming ability of Sm-based alloys is interpreted in terms of classical nucleation theory.