Effects of Cr addition on glass-forming ability and mechanical properties of Cu–Zr–Al bulk metallic glass

Effects of a small amount addition of Cr on glass-forming ability (GFA) and mechanical properties of Cu–Zr–Al bulk metallic glass were investigated. The GFA of (Cu₄₆Zr₄₆Al₈)_100−x Cr _x (x = 0, 0.25, 0.5, 0.75, and 1 at%) alloys tends to decrease with the increasing Cr content. A good correlation between the GFA and the temperature interval of supercooled liquid region ΔT _x or parameter γ exists in these alloys. Addition of an appropriate amount of Cr can significantly improve the plasticity of the alloys. The bulk metallic glass with x = 0.5 exhibits promising mechanical properties with high fracture strength of 1870 MPa and obvious plastic strain of 2.23%.     

Microstructure evolution and mechanical properties of Nb-alloyed Cu–Zr–Al–Ni large-sized metallic glass composites

The effects of Nb on the microstructures and mechanical properties of large-sized (Cu_0.47Zr_0.47Al_0.06)_99???xNi₁Nb_x (x?=?0, 0.5, 1, 2?at.-%) bulk metallic glass composites were investigated. It is verified that the liquidus temperature (T_l) of the Nb-added alloys decreases to cause the increase of glass-forming ability (GFA). The addition of Nb adjusts the distribution and the volume fraction of B2-CuZr phase in the Cu–Zr–Al–Ni large-sized composites by changing the GFA of the alloys. The mechanical properties of the composites strongly depend on the volume fraction and distribution of B2-CuZr phase in the glassy matrix. The alloy with 0.5?at.-% Nb addition exhibits the high mechanical properties, which should be attributed to the uniform distribution and the proper volume fraction of B2-CuZr phase in the glassy matrix.     

Microstructure,mechanical and bio-corrosion properties of Mn-doped Mg–Zn–Ca bulk metallic glass composites

The effects of Mn substitution for Mg on the microstructure, mechanical properties, and corrosion behavior of Mg_69 ? xZn₂₇Ca₄Mn_x (x = 0, 0.5 and 1 at.%) alloys were investigated using X-ray diffraction, compressive tests, electrochemical treatments, and immersion tests, respectively. Microstructural observations showed that the Mg₆₉Zn₂₇Ca₄ alloy was mainly amorphous. The addition of Mn decreases the glass-forming ability, which results in a decreased strength from 545 MPa to 364 MPa. However, this strength is still suitable for implant application. Polarization and immersion tests in the simulated body fluid at 37 °C revealed that the Mn-doped Mg–Zn–Ca alloys have significantly higher corrosion resistance than traditional ZK60 and pure Mg alloys. Cytotoxicity test showed that cell viabilities of osteoblasts cultured with Mn-doped Mg–Zn–Ca alloys extracts were higher than that of pure Mg. Mg_68.5Zn₂₇Ca₄Mn_0.5 exhibits the highest bio-corrosion resistance, biocompatibility and has desirable mechanical properties, which could suggest to be used as biomedical materials in the future.     

Effect of grain refinement on the mechanical properties of Cu–Al–Be–B shape memory alloy

In this work, the mechanical properties of equal channel angular processing (ECAP)-processed fine- and coarse-grained Cu–11.42Al–0.35Be–0.18B shape memory alloys (wt.%) were evaluated using tensile testing. After eight passes of ECAP and subsequently quenching from 600 °C to RT, the mean grain diameter was refined from 227 μm to 42 μm with grain boundaries purified. The fine-grained alloy exhibited good mechanical properties with a high tensile strength (703 MPa) and featured deeper and closer dimples on its fracture surface. The micro cracks were more refined, and the cracks extension along the grain boundaries was improved in the fine-grained alloy. These changes can be attributed to improvement of martensite morphology, structural refinement and grain boundary purification.     

Influence of melt temperature on the compressive plasticity of a Zr–Cu–Ni–Al–Nb bulk metallic glass

Zr_63.78Cu_14.72Ni₁₀Al₁₀Nb_1.5 BMGs (bulk metallic glasses) were cast at the melt temperatures ranging from 1,073 to 1,313 K with the same interval of 40 K. The structure, thermal, and mechanical properties of the BMGs were investigated by XRD, DSC, HRTEM, dilatometric measurements, micro-hardness tests, and uniaxial compression. The results indicate that the higher the casting temperature, the fewer the nano-crystallites, the more the free volumes, and the lower the micro-hardness in the BMGs, leading to the larger plastic strains. The plasticity of BMGs deteriorates with the increase of nano-crystallites as decreasing the casting temperature. The free volume, instead of the nano-crystallites, favors the plastic deformation in Zr_63.78Cu_14.72Ni₁₀Al₁₀Nb_1.5 BMGs. The microstructures and mechanical performance of BMGs are closely affected by the casting temperature. The preparing parameters are important to improve the plasticity of the BMGs.     

Influence of minor additions on characteristics of Cu–Al–Ni alloy

Abstract

The aluminium and nickel contents of Cu–Al–Ni alloy are varied to relate the parent phase chemistry to its shape memory behaviour. Rare earth and grain refining elements (titanium, zirconium, boron, etc.) are added in minor quantities to assess their effects on the grain refinement of the alloy and also on its shape recovery behaviour. It is observed that increasing the aluminium and nickel contents decreases the shape recovery temperature whereas minor additions are found to increase it. The alloys have been aged in the parent as well as the martensitic phase to investigate the influence of minor additions on their aging response. It is observed that precipitation of γ₂ phase occurs during the initial stage of aging of the ternary alloy. The aging behaviour is monitored via changes in resistivity and hardness of the alloys during aging. Minor additions are found to retard the precipitation of γ₂ phase during aging. Titanium and rare earths particularly reduce the tendency for grain coarsening in the alloy. It is further observed that two types of martensite, β′₁ and γ′₁, are produced in the alloys under investigation. The transformation temperatures of these martensites are also related to the aluminium content of the alloy.

MST/1744     

Microstructure,mechanical properties and shape memory effect of Cu–Hf–Al–Ni alloys

The influence of hafnium element’s incorporation on a Cu–xHf–13.0Al–4.0Ni (wt-%) (x?=?0.5, 1.0 and 2.0) high-temperature shape memory alloy was investigated systematically. The results show that the matrix of Cu–xHf–13.0Al–4.0Ni (x?=?0.5, 1.0 and 2.0) alloys is 18R martensite, and an orthorhombic-structured Cu₈Hf₃ phase is formed and distributed at the grain boundaries. The grain size is significantly reduced with increasing Hf content. The mechanical properties of Cu–xHf–13.0Al–4.0Ni (x?=?0.5, 1.0 and 2.0) alloys are improved by Hf doping due to the combination of refinement strengthening, solid solution strengthening and second phase strengthening. After heating under pre-strain of 10%, the shape memory effect of the Cu–1.0Hf–13.0Al–4.0Ni alloy reaches 5.6%, which is obviously higher than that of the Cu–13.0Al–4.0Ni alloy.     

Glass forming ability of Fe–Co–Zr–Nd–B alloys and bulk permanent magnets derived from amorphous precursor

The glass forming ability (GFA) and magnetic properties for Fe_48−x Co₂₇Zr₃Nd _x B₂₂ (x = 0–6) alloys were investigated. It was found that the proper addition of Nd (4–5 at.%) was very effective in improving GFA. The as-cast Fe₄₄Co₂₇Zr₃Nd₄B₂₂ and Fe₄₃Co₂₇Zr₃Nd₅B₂₂ alloys exhibited good soft magnetic behavior, while showed hard magnetic property after annealing at 760 °C for 10 min. Bulk permanent magnets were obtained from crystallization of amorphous alloys, which could provide a promising way for the bulk magnet produced by the simple process of copper mold casting and subsequent heat treatment.     

Effect of minor cerium additions on microstructure and mechanical properties of cast Al – Cu – Mg – Ag alloy

Abstract

A series of cast Al – Cu – Mg – Ag based alloys with minor cerium additions have been investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. It was found that increasing the cerium content from 0 to 0.45 wt-% increased the tensile strength at the test temperatures of 25°C and 300°C. The high strength of the casting alloys with cerium is attributed to the refined grains and the high density of fine ω precipitates. However, the addition of 0.2 wt-%Ce to the alloy with 0.25 wt-%Ti induced a detrimental effect on the mechanical properties. The cause of this was found to be the formation of the intermetallic compound Al_x Ti₆ Ce₃ Cu.     

Microstructure and mechanical properties of Al–Si cast alloy with additions of Zr–V–Ti

The microstructure and tensile properties at temperatures up to 300 °C of an experimental Al–7Si–1Cu–0.5Mg (wt.%) cast alloy with additions of Ti, V and Zr were assessed and compared with those of the commercial A380 grade. The microstructure of both alloys consisted of Al dendrites surrounded by Al–Si eutectic containing, within its structure, the ternary Al–Al₂Cu–Si phase. Whereas the Al₁₅(FeCrMn)₃Si₂ phases were present in the A380 alloy, Ti/Zr/V together with Al and Si phases, Al(ZrTiV)Si, were identified in the experimental alloy. As a result of chemistry modification the experimental alloy achieved from 20% to 40% higher strength and from 1.5 to 5 times higher ductility than the A380 reference grade. The role of chemistry in improving the alloy thermal stability is discussed.     

Synthesis and mechanical behavior of ternary Mg–Cu–Dy in situ bulk metallic glass matrix composite

In situ Mg phase reinforced Mg₇₀Cu₁₇Dy₁₃ bulk metallic glass (BMG) matrix composite with diameter of 3 mm was fabricated by conventional Cu-mold casting method. The results show that the Mg-based BMG matrix composite exhibits some work hardening except for initial elastic deformation, a high fracture compressive strength of 702 MPa, which is 1.125 times higher than single-phase Mg₆₀Cu₂₇Dy₁₃ BMG and some plastic strain of 0.81%. The improvement of the mechanical properties is attributed to the fact that the Mg phase distributed in the amorphous matrix of the alloy has some effective load bearing and plastic deformation ability to restrict the expanding of shear bands and cracks and produce its own plastic deformation, which was proved by the shear deforming and fracturing mode and the fracture surfaces characterized by the vein pattern, severe remelting, and the very rough and bumpy region of the alloy.     

Effect of predeformation on microstructure and mechanical properties of Al–Cu–Li–Zr alloy containing Sc

Abstract

The effects of prior cold deformation on the microstructures and the room temperature mechanical properties of an Al–3·5Cu–1·5Li–0·22(Sc + Zr) alloy have been observed by using TEM and tensile test at room temperature. The results show that the alloy has the character of aging hardening, and the major phase of precipitation and strengthening is T₁ phase. The result also show that prior cold deformation leads to more dispersive and uniform distribution of T₁ precipitations. It accelerates aging response, causes earlier aging peak occurrence, and enhances strength greatly. However, the plasticity of the alloy is declined with prior cold deformation. In contrast, excessive prior cold deformation causes coarsening and heterogeneous distribution of T₁ phase. It also reduces the strength of the alloy, therefore, influences the composite properties of the alloy. The favourable prior cold deformation is about 3·5% under the experimental condition.     

Effect of CeLa addition on the mechanical properties of Al–Cu–Mn–Mg–Fe alloy

The rapid development of new energy automobiles leads to an increasing demand for high-strength lithium battery shell alloy. The microstructures, electrical conductivity and mechanical properties of CeLa-containing Al–Cu–Mn–Mg–Fe alloys were investigated with scanning electron microscopy (SEM), X-ray diffraction, Eddy Current conductivity tester, tensile testing and Erichsen cup testing. Experiment results indicate that Al₆(Mn, Fe) particles could be refined by CeLa alloying and AlCuCeLa phase nucleates and grew up at the surface of Al₆(Mn, Fe) particle. Major texture of the CeLa-containing alloys was different from that of the CeLa-free alloy. The electrical conductivity decreased with increase of the CeLa content. CeLa addition could greatly enhance the tensile strength of the alloy at temperatures ranging from –40°C to 300°C.     

Molecular dynamics simulations of critically percolated,cluster-packed structure in Zr–Al–Ni bulk metallic glass

We have studied the local atomic arrangements of a Zr_0.60Al_0.15Ni_0.25 bulk metallic glass (BMG) with molecular dynamics (MD) simulations based on a plastic crystal model (PCM). We have utilized features of orientationally disordered state of a molecule in plastic crystals. A Zr_0.618Al_0.146Ni_0.236 alloy with an approximated composition to the Zr_0.60Al_0.15Ni_0.25 has been created using MD–PCM from a Zr_0.73Ni_0.27 glassy alloy that possesses critically percolated Ni atoms. The MD–PCM dealt with icosahedral and tetrahedral clusters with 13 and five atoms, respectively, with a Ni, Al, or Zr atom at each center site of the clusters. After the Zr_0.73Ni_0.27 glassy alloy had been created with monatomic MD simulation by quenching from a liquid, the Zr and Ni atoms in the Zr_0.73Ni_0.27 glassy alloy were replaced with randomly oriented icosahedral and tetrahedral clusters, respectively. Subsequently, structural relaxation was performed after adjusting the density to that of the Zr_0.618Al_0.146Ni_0.236 alloy. Total pair-distribution and interference functions revealed that the Zr_0.618Al_0.146Ni_0.236 alloys created with MD–PCM exhibit the characteristics of a non-crystalline phase. Further, Voronoi polyhedra analysis revealed that the Ni-centered polyhedral clusters used as initial atomic arrangements for MD–PCM tend to reproduce the features of the conventional MD results. The origin of the excellent glass-forming ability of the Zr_0.618Al_0.146Ni_0.236 alloy is attributed to the critically percolated cluster-packed structure.     

Microstructural and mechanical properties of Sn–Ag–Cu lead-free solders with minor addition of Ni and/or Co

The effects of minor additives, that is, Co and Ni, on the microstructural and mechanical properties of Sn–3.0 mass%Ag–0.5 mass%Cu (SAC305) bulk solder were investigated. The addition of Co and/or Ni resulted in microstructural changes of the SAC305 solder, such as the formation of new intermetallic compounds (IMCs) and the refinement of grain size, as well as the suppression of undercooling. The single addition of Co in SAC305 solder resulted in the formation of CoSn₂ IMCs and undercooling suppression, whereas the single addition of Ni accelerated the appearance of rod-shaped (Cu,Ni)₆Sn₅ IMCs inside the β-Sn dendrites during the solidification process. The dual addition of Co–Ni resulted in refined β-Sn grains and suppression of undercooling, as well as the formation of CoSn₂ IMCs. In tensile tests, Co and/or Ni additives had little effect on the tensile strength of SAC305 solder, but obviously suppressed the elongation ratio and reduction of area. During tensile deformation in samples with existing thin plate-like CoSn₂ IMCs, micro-cracks or cavities were easily initiated through the interface between CoSn₂ and the solder matrix, which was responsible for the decrease of ductility.     

Effect of thermal cycling on martensitic transformation temperatures in Ti–Ni–Cu shape memory alloys

Abstract

Changes in martensitic transformation temperatures during thermal cycling in Ti–Ni–Cu shape memory alloys have been investigated by means of electrical resistivity measurements, thermal cycling tests under constant load and transmission electron microscopy. During thermal cycling without applied stress, the B2→B19′ transformation temperature M _s decreased, while the B2→B19 transformation start temperature M _s′ kept almost constant. During thermal cycling with applied stress, in solution treated Ti–45Ni–5Cu alloy, changes in M _s depended on the amount of applied stress. That is, M _s decreased when the applied stress was 39.2 MPa, while its value kept almost constant when a stress of 117.2 MPa was applied. It was also found that M _s′ increased during thermal cycling in the solution treated Ti–35Ni–15Cu and Ti–30Ni–20Cu alloys, irrespective of the amount of applied stress. All changes in M _s and M _s′ during thermal cycling with applied stress in Ti–Ni–Cu alloys were explained well by a combination of the thermal cycling effect and the structural refinement effect.     

Effect of Fe and Mn additions on microstructure and mechanical properties of spray-deposited Al–20Si–3Cu–1 Mg alloy

Spray deposition is a novel process which is used to manufacture rapidly solidified bulk and near-net-shape preforms. In this paper, Al–20Si–3Cu–1 Mg alloy was prepared by spray deposition technique. The effect of Fe and Mn additions on microstructure and mechanical properties of spray-deposited Al–20Si–3Cu–1 Mg alloy was investigated. The results show that two kinds of intermetallics, i.e. δ-Al₄FeSi₂ and β-Al₅FeSi, is formed in the microstructure of spray-deposited Al–20Si–5Fe–3Cu–1 Mg alloy. With additions of 5% Fe and 3% Mn to Al–20Si–3Cu–1 Mg alloy, the needle shape of Al–Si–Fe intermetallic phases is substituted by the particle shape of Al₁₅(FeMn)₃Si₂ phases. The presence of the intermetallic phases (δ-Al₄FeSi₂, β-Al₅FeSi and Al₁₅(FeMn)₃Si₂) improves the tensile strengths of the alloy efficiently at both the room and elevated temperatures(300 °C).