Ag-containing Alloy Research Articles

Dry tribological behavior of a cast Mg-Gd-Zr-Ag alloy at room and elevated temperatures

The hardness and wear resistance of cast Mg-6Gd-0.6Zr alloy were increased by the addition of 2 wt.% Ag. The microstructural studies of Mg-6Gd-0.6Zr–2Ag exhibited Ag-containing compounds within the α-Mg matrix. The addition of Ag increased the hardness by 20–30% at various temperatures up to 300 °C. The dry sliding wear behaviors of Mg-6Gd-0.6Zr and Mg-6Gd-0.6Zr–2Ag alloys were investigated under normal loads of 5, 20 and 40 N at wear temperatures of 25–325 °C against 52,100 steel using a pin-on-disk tribometer. Under a normal load of 5 N at various wear temperatures, Mg-6Gd-0.6Zr–2Ag alloy showed a higher wear resistance than Mg-6Gd-0.6Zr. However, under higher normal loads of 20 and 40 N at temperatures of 125–225 °C and 125–175 °C, respectively, the Ag-containing alloy showed a higher wear rate than the base alloy. The results also showed that the wear rates decreased with increasing temperature to critical temperatures of 225 °C for Mg-6Gd-0.6Zr and 275 °C for Mg-6Gd-0.6Zr–2Ag, which were then followed by a rise due to thermal softening and higher plastic deformation of the alloys.

Enhanced age-hardening response and mechanical properties of the Mg-Gd-Y-Zn-Zr alloy by trace Ag addition

In the present study, we have systematically investigated how the influence of silver (Ag) addition (0.3 wt%) on the microstructural and mechanical properties of Mg-6Gd-3Y-1Zn-0.4Zr (wt%) alloy. The results indicate that the Ag addition enhances the age-hardening response, especially at the early stage of aging. The improved age-hardening response of the alloy is associated with dense nanosized basal γ'' precipitates formed upon the Ag addition and the β’ phase. Furthermore, the presence of Ag also improves the tensile properties of the peak-aged alloy. The Ag-containing alloy exhibits higher ultimate tensile strength, yield strength, and elongation to failure than the Ag-free alloy at room and elevated temperatures. We suggest that the improved strength and ductility of the Ag-containing alloy originate from the coprecipitation of the nanosized basal γ'' precipitates and the β’ phase.

Microstructural evolution and superplastic behavior of a fine-grained Mg−Gd−Y−Ag alloy processed by simple shear extrusion

Abstract Two magnesium alloys with the nominal compositions of Mg−6Gd−3Y (GW63) and Mg−6Gd−3Y−1Ag (GW63−1Ag) were hot extruded and then processed by 6 passes of the simple shear extrusion (SSE) process at 553 K. Both SEM and EBSD studies confirmed the mean grain size reduction of the extruded base GW63 alloy from 10.1 to 2.9 μm by adding 1 wt% Ag. This decrease in the grain size was due to the formation of the Ag-containing precipitates with network-type morphology at the grain boundaries of the extruded GW63−1Ag alloy. Further grain refinement was achieved after SSE through the occurrence of DRX in both Ag-free and Ag-containing alloys. However, the GW63−1Ag alloy showed a higher fraction of DRX grains and HAGBs after SSE processing compared to the Ag-free alloy. The enhanced DRX behavior was attributed to the smaller initial grain size of the Ag-containing alloy in the as-extruded condition and the role of Ag addition in suppressing the solute drag effect of the segregated Gd and Y elements at the grain boundaries. The superplastic behavior of the alloys was assessed via the shear punch testing (SPT) method performed in the temperature ranges of 623–723 K for the extruded specimens and 573–673 K for the SSE processed alloys. It was revealed that none of the extruded alloys exhibited superplastic flow, because of their large grain sizes. The GW63 alloy processed by 6 passes of SSE displayed a maximum m-value of 0.38 at 648 K, while the high strain rate sensitivity (SRS) index of 0.5 was measured at 623 K for the Ag-containing alloy after SSE. This was accompanied with a superplastic deformation behavior of the latter alloy, for which an activation energy of 105 kJ mol−1 that is close to that of the grain boundary diffusion of pure Mg was obtained. Therefore, grain boundary sliding (GBS) associated with grain boundary diffusion was introduced as the dominant deformation mechanism during the superplastic flow of the Ag-containing alloy processed by SSE.

Microstructure, mechanical properties and corrosion behavior of quaternary Mg−1Zn−0.2Ca−xAg alloy wires applied as degradable anastomotic nails

The microstructure, mechanical properties and corrosion behavior of quaternary degradable Mg−1Zn− 0.2Ca−xAg (x=1, 2, 4 wt.%) alloy wires, intended as anastomotic nails, were investigated. It was found that these Ag-containing alloy wires mainly consist of Mg matrix and Ag17Mg54 phase, characterized by SEM, EDS, XRD and TEM. Tensile and knotting tests results demonstrate the superior mechanical properties of these alloy wires. Especially, Mg−1Zn−0.2Ca−4Ag alloy exhibits the highest mechanical properties, i.e. an ultimate tensile strength of 334 MPa and an elongation of 8.6%. Moreover, with increasing Ag content, the corrosion rates of these alloy wires remarkably increase due to the formation of more micro-galvanic coupling between Mg matrix and Ag17Mg54 phase, shown by mass loss and scanning Kelvin probe force microscopy (SKPFM) results. The present alloy can be completely degraded within 28 d, satisfying the property requirements of anastomotic nails.

Effect of Ag Addition on the Hot Deformation, Constitutive Equations and Processing Maps of a Hot Extruded Mg-Gd-Y Alloy

Hot deformation behavior of the extruded Mg-6Gd-3Y (GW63) and Mg-6Gd-3Y-1Ag (GW63-1Ag) alloys was assessed by shear punch testing (SPT) method in the temperature range of 623 K to 723 K and shear strain rate of 1.6 × 10−2 to 1.3 × 10−1 s−1. Microstructural examinations showed that Ag addition decreased the initial grain size from 10.1 to 2.9 µm. According to the hot deformation results, hyperbolic-sine exponents (n-values) of 3.39 and 2.54 were obtained for the Ag-free and Ag-containing alloys, respectively. The corresponding activation energies were found to be 321 and 178 kJ mol−1 for these alloys. Therefore, the controlling deformation mechanisms were defined as viscous glide of dislocation for the Mg-6Gd-3Y alloy and grain boundary sliding for Mg-6Gd-3Y-1Ag. Processing maps were developed based on the dynamic material model (DMM) to determine the flow instability domains during hot deformation. Accordingly, the optimum hot working conditions were found to be in the temperature range of 655 K to 723 K and shear strain rate of 3.3 × 10−2 to 1.3 × 10−1 s−1 for the GW63-1Ag alloy, whereas the safe deformation window for the GW63 alloy was narrowed down to a temperature range of 665 K to 705 K and shear strain rate of 7.2 × 10−2 to 1.3 × 10−1 s−1. The Ag-containing alloy exhibited flow instability regions only at low temperatures and high strain rates. On the other hand, the Ag-free alloy demonstrated other instability domains comprising the formation of mechanical twins and cracking. Electron back-scattered diffraction analysis was utilized to correlate the microstructural evolution of the alloys after shear deformation to the hot working parameters. Continuous dynamic recrystallization was suggested as the main mechanism for generation of the dynamically recrystallized grains during hot deformation of both alloys.

Role of second-phase particles in the microstructural evolution and mechanical properties of extruded Mg-Gd-Y-Ag-Zr alloys

The role of coarse second-phase particles in the microstructural evolution and mechanical properties of as-extruded Mg-Gd-Y-Ag-Zr alloys was investigated. Results show that the volume fraction of coarse β particles was enhanced by the addition of Ag (0.5 and 1.0) (wt.%) in the Mg-10.5 Gd-5 Y-0.5 Zr (wt.%) alloy. These particles have a face-centered cubic structure phase. In addition to Gd and Y, Ag is also partitioned into particles in the Ag-containing alloys. β particles can promote the dynamic recrystallization via particle-simulated nucleation and effectively suppress grain growth by pinning effects, which are responsible for the grain refinement. With the increase of volume fraction of β particles, the texture and dislocation features have not been changed. Since the coarse β particles can greatly lead to the reduction of grain size, the grain boundary strengthening in Ag-containing alloys with high volume fraction of particles contributes to the significantly improvement of the tensile yield strength. The coupled effect of the increase in the coarse β particle fraction and the reduction in grain size causes a slight decrease in elongation for the Ag-containing alloy.

What controls the antibacterial activity of Ti-Ag alloy, Ag ion or Ti2Ag particles?

Antibacterial metal materials, including Cu- and Ag-containing alloy, have attracted much attention worldwide. As for the antibacterial mechanism of the antibacterial alloys, there are two different views: metal ions sterilization and contact sterilization. For the purpose of revealing the key control factor, Titanium-silver (Ti-Ag) alloys with different silver contents were prepared and a surface acid etching was applied to change the silver ion release and the volume fraction of Ti2Ag on the surface. The microstructure, phase composition, elemental composition, surface roughness, hydrophilicity, silver ion release and antibacterial properties of Ti-Ag alloys were studied comprehensively by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), contact angle and roughness test, silver ion dissolution test and antibacterial test. The results have shown that the increasing of Ag content did not bring about any change to the surface roughness and hydrophilicity but enhanced the Ag ion release while the surface acid etching improved the hydrophilicity, enhanced the Ag ion release and made more Ti2Ag particles appear on the surface. The antibacterial experiments have shown that the antibacterial properties increased with the increasing of Ag content in Ti-Ag alloys and that the surface acid etching improved the antibacterial activity significantly. The calculated results and surface microstructure observation and XPS analysis demonstrated that the antibacterial activity of Ti-Ag alloys was mainly controlled by Ti2Ag particle in a contact sterilization mode. Silver ion release from Ti-Ag alloy also contributed to antibacterial activity of Ti-Ag, but the Ag ion sterilization was not the key antibacterial mechanism. Finally, the CCK-8 results showed that all Ti-Ag alloys exhibited good cell compatibility.

Influence of Ag replacement on supercooled liquid region and icosahedral phase precipitation of Zr65Al7.5Ni10Cu17.5-xAgx (x = 0–17.5 at%) glassy alloys

The glass transition phenomenon for Zr65Al7.5Ni10Cu17.5-xAgx (x = 5–17.5 at%) glassy alloys was observed in the Ag content range below about 15% and the icosahedral phase precipitated as the heating-induced primary phase in the limited Ag content range. In the higher Ag content range where glass transition is not clearly observed, the primary precipitation phase changed to mixed phases of tetragonal Zr3Ag + tetragonal Zr2Ni + hexagonal Zr4Al3. The good correspondence between the appearance of glass transition and the icosahedral phase precipitation was recognized in the multicomponent glassy alloys containing the immiscible type atomic pairs of Ni-Ag and Cu-Ag. Although neither glass transition nor supercooled liquid region is observed for Zr65Al7.5Ni10Ag17.5 and no icosahedral phase is formed, a modified Zr65Al7.5Ni17.5Ag10 alloy with higher Ni/Ag content ratio exhibits glass transition and supercooled liquid region and the primary precipitates also changes to an icosahedral phase. The good correspondence can be interpreted on the basis of the previous knowledge that the appearance of glass transition and supercooled liquid state originates from icosahedral-like medium range ordered atomic configurations. Besides, the 6%Ag-containing alloy keeps high glass-forming ability which is high enough to form a bulk glassy alloy rod of 6 mm by suction casting. The close correlation between the appearance of glass transition phenomenon and the primary precipitation of icosahedral phase is expected to provide a useful knowledge on the role of icosahedral-like atomic configuration in the achievement of bulk glass-forming ability through the stabilization of supercooled liquid.

Tailoring Morphology and Size of Microstructure and Tensile Properties of Sn-5.5 wt.%Sb-1 wt.%(Cu,Ag) Solder Alloys

Transient directional solidification experiments, and further optical and scanning electron microscopy analyses and tensile tests, allowed the dependence of tensile properties on the micromorphology and length scale of the dendritic/cellular matrix of ternary Sn-5.5Sb-1Ag and Sn-5.5Sb-1Cu alloys to be determined. Extensive ranges of cooling rates were obtained, which permitted specific values of cooling rate for each sample examined along the length of the casting to be attributed. Very broad microstructural length scales were revealed as well as the presence of either cells or dendrites for the Ag-containing alloy. Hereafter, microstructural spacing values such as the cellular spacing, λ c, and the primary dendritic spacing, λ 1, may be correlated with thermal solidification parameters, that is, the cooling rate and the growth rate. While, for the Cu-containing Sn-Sb alloy, the β-Sn matrix is characterized only by the presence of dendritic arrangements, the Ag-containing Sn-Sb alloy is shown to have high-velocity β-Sn cells associated with high cooling rate regions, i.e., positions closer to the bottom of the alloy casting, with the remaining positions being characterized by a complex growth of β-Sn dendrites. Minor additions of Cu and Ag increase both the yield and ultimate tensile strengths when compared with the corresponding values of the binary Sn-5.5Sb alloy, with a small reduction in ductility. This has been attributed to the homogeneous distribution of the Ag3Sn and Cu6Sn5 intermetallic particles related to smaller λ 1 characterizing the dendritic zones of the ternary Sn-Sb-(Cu,Ag) alloys. In addition, the Ag-modified Sn-Sb alloy exhibited an initial wetting angle consistent with that characterizing the binary Sn-5.5Sb alloy.

Antibacterial Titanium Produced Using Selective Laser Melting

Titanium and titanium alloys used in current medical and dental applications do not possess antibacterial properties, and therefore, postoperative infection remains a significant risk. Recently, the addition of silver and copper to conventional biomaterials has been shown to produce a material with good antibacterial properties. In this article, we investigate selective laser melting as a method of producing antibacterial Ti-6Al-4V containing elemental additions of Cu or Ag. The addition of Ag had no effect on the microstructure or strength, but it did result in a 300% increase in the ductility of the alloy. In contrast, the addition of Cu resulted in an increase in strength but in a decrease in ductility, along with a change in the structure of the material. The Cu-containing alloy also showed moderate antibacterial properties and was superior to the Ag-containing alloy.

Influence of a Trace Alloying of Ag on the Ageing Behavior and Mechanical Properties of AZ80M Magnesium Alloys

The ageing behavior of AZ80+xAg (x=0;0.3;0.5) magnesium alloys at different temperature were systematically investigated using optical microscopy, scanning electron microscopy and X-ray diffraction analysis. Experimental results demonstrate that the trace amount of Ag accelerated the precipitation of Mg17Al12 phase during ageing at 200°C, AZ80+0.5Ag achieved the peak hardness of 89.7HV after holding for 12h, compared with 80.8HV after 28h for the Ag-free alloy. However, when ageing at high temperature (250°C), the promotion response of Ag was totally vanished. The tensile property of the peak aged alloys at ambient temperature increased with Ag addition, as well as the tensile property at elevated temperature. Further investigation indicates that Ag addition suppresses the discontinuous precipitates, which account for the enhanced property of Ag-containing alloy.

Effect of Ag addition on microstructure and mechanical properties of Mg–14Gd–0.5Zr alloy

Microstructure and mechanical properties of the Mg–14Gd–0.5Zr (wt.%) alloy and Mg–14Gd–2Ag–0.5Zr (wt.%) alloy in homogenized, extruded and aged conditions have been investigated. Addition of 2% Ag enhances the tensile ultimate strength of the homogenized Mg–14Gd–0.5Zr alloy due to producing a larger strain field in magnesium crystal lattice. For the hot extruded alloys, the Ag-containing alloy shows a different type of texture, finer grains, higher hardness and a weak age-hardening response compared with the extruded Mg–14Gd–0.5Zr alloy, which are influenced by more Mg5Gd phases precipitating during extrusion in the Ag-containing alloy. The extruded Ag-containing alloy in peak-aged condition exhibit a lower yield strength due to a lower density of the prismatic β′ precipitate, while its better elongation is ascribed to the finer grain size and the basal precipitate.

The Effect of Natural Pre-Ageing on the Mechanical Properties of Rheo-High Pressure Die Cast Aluminium Alloy 2139

Near-net shape casting of wrought aluminium alloys has proven to be difficult due to hot tearing. The Council for Scientific and Industrial Research (CSIR) has successfully processed wrought aluminium alloy 2139 into plate castings using the Rheo-high pressure die casting process (R-HPDC). Alloy 2139 is a Ag-containing aluminium alloy from the Al-Cu-Mg 2xxx series family. The addition of Ag enhances the age hardening response through the formation of co-clusters that act as precursors to the formation of plate-like Ω precipitates. These co-clusters typically form during natural ageing and 12-24 h of natural pre-ageing is normally specified before artificial ageing in Ag-containing Al-Cu-Mg alloys. The T6 hardness and tensile properties of R-HPDC 2139 alloy were investigated with and without natural pre-ageing. It is shown that there is no significant difference in both peak hardness and tensile properties in R-HPDC alloy 2139 with and without natural pre-ageing. The possible precipitation phenomena in both cases are discussed.

Enhanced superplasticity in an extruded high strength Mg–Gd–Y–Zr alloy with Ag addition

The effect of 2wt% Ag addition on the superplastic behavior of an extruded Mg–8.5Gd–2.5Y–0.5Zr (wt%) alloy was investigated by impression testing in the temperature range of 523–598K. The average sizes of the dynamically recrystallized grains of the Ag-free and Ag-containing alloys were about 8 and 3μm, respectively. Analysis of electron backscattered diffraction (EBSD) data confirmed the higher fractions of high-angle grain boundaries (HAGBs) in the Ag-containing alloy. The deformation response of this alloy in proper temperature range conforms to regions I, II and III, typical of superplastic deformation behavior. The addition of Ag to the base alloys led to enhanced superplasticity in region II by increasing the strain rate sensitivity (SRS) indices (m-values) from 0.25 to 0.51 and 0.36 to 0.46 at 573 and 598K, respectively. These high m-values together with the activation energy of 181kJ/mol suggest that the major mechanism involved in superplastic deformation is grain boundary sliding (GBS) accommodated by lattice diffusion at temperatures above 573K.

Effect of Ag addition on the elevated-temperature mechanical properties of an extruded high strength Mg–Gd–Y–Zr alloy

Elevated-temperature mechanical properties of the extruded Mg–8.5Gd–2.5Y–0.5Zr (wt%) and Mg–8.5Gd–2.5Y–0.5Zr–2Ag (wt%) alloys were investigated by the shear punch test (SPT) in the temperature range of 25–300°С. The average sizes of the dynamically recrystallized grains of the Ag-free and Ag-containing alloys were about 8 and 3µm, respectively. Addition of Ag to the base alloy led to the formation of a new intermetallic phase with a composition close to Mg16Gd2YAg, and increased the volume fraction of the second phase particles from 2.5% to about 13%. This together with the refinement of microstructure resulted in superior mechanical properties of the Ag-containing alloy over the base material in the whole temperature range studied.

Indentation Creep of Lead-Free Sn-5Sb Solder Alloy with 1.5 wt% Ag and Bi Additions

Creep behavior of the ternary Sn-5Sb-1.5Ag and Sn-5Sb-1.5Bi alloys was studied by indentation testing at 298 and 370 K, and compared to that of the binary Sn-5Sb base alloy. Among all tested materials, as indicated by their minimum creep rates, Sn-5Sb-1.5Bi showed the highest creep resistance followed by Sn-5Sb-1.5Ag and Sn-5Sb. The superiority of the Bi-containing alloy is mainly due to the microstructural refinement and solid solution hardening effects of Bi in the Sn matrix, while the improvement in the creep resistance of the Ag-containing alloy is caused by the formation of spherical and rod-shaped Ag3Sn particles. The stress exponent values in the range 11.0–12.2 are close to those determined by tensile and impression creep testing of the same alloys reported in the literature. These high stress exponents together with the activation energies of 58–70 kJ/mol may suggest that the dominant creep mechanism is dislocation creep.

Effects of Ag addition on the microstructure and thermal stability of 6156 alloy

The effects of Ag addition on the microstructure and thermal stability of 6156 Al–Mg–Si–Cu alloy were investigated by means of hardness measurement, tensile tests, differential scanning calorimetry, and transmission electron microscopy. The results showed that addition of small amount of Ag to 6156 alloy did not change the precipitation sequence mainly β″ and Q′ strengthening phase but slightly accelerated the age-hardening rate and increased peak hardness at the same aging condition. The tensile properties enhanced about 30 MPa at the room temperature or thermal exposure at lower temperature (<100 °C). With the exposed temperature and time increased to 150 °C for 1000 h, almost no difference between the Ag-containing and Ag-free alloys. When exposed at 200 °C, the tensile strength of Ag-containing alloy became lower than that of Ag-free alloy because of the coarsening precipitations in matrix and boundary observed by TEM observed. For both alloys, thermal exposure at temperatures 100 °C for long time periods had no significant effect on tensile properties. Loss in strength was small and large with prolonging the exposure time at 150 and 200 °C, respectively.

Atom probe tomography of nanoscale microstructures within precipitate free zones in Al–Zn–Mg(–Ag) alloys

Solute distributions in the vicinity of grain boundaries in Al–Zn–Mg(–Ag) alloys were studied using a three-dimensional atom probe, in order to elucidate the mechanism of formation of precipitate free zones (PFZs) and the fundamental role of Ag in controlling PFZ width. It is shown that nanoscale clusters are formed within the PFZ in Al–Zn–Mg, despite the solute concentration remaining at the levels in the as-quenched state. Such observations have not previously been possible, and show unambiguously that vacancy depletion is the dominant mechanism of formation of PFZs in this alloy. In the Ag-containing alloy, a narrower PFZ is observed, with a reduced solute level, showing that here the dominant mechanism of PFZ formation is solute depletion. The role of Ag in this change of mechanism appears to be due to its favorable interactions not only with Mg and Zn atoms but also with vacancies.

Effect of Ag micro-alloying on the microstructure and properties of Cu–14Fe in situ composite

This paper studied Ag micro-alloying in the deformation-processed Cu–14Fe in situ composite, by a comparison of Cu–14Fe and Cu–14Fe–0.06Ag. Each alloy was prepared by casting and processed into an in situ composite by hot and cold working. The microstructures were documented using light microscopy and scanning electron microscopy (SEM). The mechanical properties were measured with a tensile-testing machine. The electrical conductivity was measured with a micro-ohmmeter. For both alloys, the as-cast microstructure consisted of a Cu matrix and Fe dendrites; after hot and cold working the microstructure consisted of a Cu matrix containing Fe fibres elongated in the working direction. The as-cast Ag-containing alloy contained finer Fe dendrites. The Ag-containing in situ composite had thinner Fe fibres, higher tensile strength, higher ductility, and higher conductivity. The cold worked Cu–14Fe–0.06Ag in situ composite with cumulative cold deformation strain η=7.8 (where η=ln(A0/A) and A0 and A are the original and final cross-section areas, respectively), achieved a tensile strength of 930MPa and a conductivity of 56%IACS (International Annealed Copper Standard; 17.241nΩm is defined as 100%IACS). The Ag micro-alloyed in situ composite had a combination of properties comparable to that of a much more expensive alloy containing much more Ag. After 1h heat treatment at 300°C, the tensile strength was increased to 950MPa and the conductivity was increased to 56.4%IACS.

Influence of Ag micro-alloying on the microstructure and properties of Cu–7Cr in situ composite

This paper studied the influence of Ag micro-alloying on the deformation-processed Cu–7Cr in situ composite, by a comparison of Cu–7Cr and Cu–7Cr–0.07Ag. For both alloys, the as-cast microstructure consisted of a Cu matrix and Cr dendrites; after hot and cold working the microstructure consisted of a Cu matrix containing Cr fibres elongated in the working direction. The as-cast microstructure of the Ag-containing alloy contained finer Cr dendrites. The Ag-containing in situ composite had thinner Cr fibres, higher tensile strength, higher ductility, and slightly higher conductivity. The Cu–7Cr–0.07Ag in situ composite had a good combination of properties: a tensile strength of 772 MPa and a conductivity of 77.3%IACS.