Small Additions Of Ag Research Articles

High-temperature tribological behaviour and machining performance of self-lubricant CrAlNAg coatings for dry milling operations

Tribological and machining performance of CrAlNAg coatings having different Ag content tested against AISI 1045 medium carbon steel were assessed. Wear track was evaluated by scanning electron microscopy and energy dispersive spectroscopy. 3D topography of wear track and ball counterpart was determined by non-contact type profilometer. The formation of different oxide phases on track was confirmed using Raman spectroscopy. CrAlNAg9 and CrAlNAg12 coatings were found beneficial in reducing material adhesion from counterpart thus providing protective layers to counterpart, whereas small addition of Ag did not provide any improvement on CrAlN coating performance. CrAlNAg9 coated milling inserts demonstrated best results in terms of reduction in chip temperature (∼17.5 %), cutting forces, surface roughness (∼47 %) and chip thickness (∼12.7 %) compared to uncoated inserts.

Effect of Bactericidal Elements Addition on the Microstructure and Mechanical Properties of Ti34Nb Alloy

The functionalization of β-Ti alloys by the addition of small amounts of bactericidal elements is interesting for biomedical applications. Thus, alloying pure titanium with highly biocompatible elements such as Nb or Ta, stabilizes the β phase of the resulting alloy although they can also include difficulties during the fabrication process due to their refractory nature. This work studies the effect of small additions of Ag and Cu (1.5 to 3 wt.%) on the microstructure and mechanical properties of the Ti34Nb (wt.%) alloy processed by powder metallurgy. The blend elemental powders were mixed (30 rpm during 30 min). The samples were compacted at 600 MPa and sintered at 1250 oC during 3 hours. The microstructure was analyzed by X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscope with X-Ray Spectroscopy (FE-SEM/EDS). The mechanical properties were obtained by bending tests; the elastic modulus was measured by ultrasonic methods and the porosity by Archimedes test. Cu addition generates the appearance of α phase sheets inside the β phase grains. Cu also decreases the open porosity and increases the closed porosity of the material. On the contrary, Ag addition does not influence the stabilization of the β phase and it does not modify the density, thus the total porosity of the resulting material. With respect to the influence of the alloying elements on the elastic modulus (E) of the alloys, the E of the Ti34Nb (76.8 GPa) increases with the Cu addition (92.6 GPa) and decreases with the Ag one (68.9 GPa). Therefore, silver addition, which does not modify the microstructure and slightly decrease the mechanical properties of the Ti34Nb, can be considered a good alloying element to provide antibacterial features to the titanium alloy without losing performance.

Effects of Ag Addition on Precipitation and Fatigue Crack Propagation Behavior of a Medium-Strength Al–Zn–Mg Alloy

Effects of trace addition of Ag on the fatigue crack propagation behavior and microstructure of a medium-strength aged Al–Zn–Mg alloy were investigated in the present work. The results show that a combination of enhanced tensile strength and improved fatigue crack propagation resistance in Al–Zn–Mg alloys is achieved with small addition of Ag. The enhanced strength is attributed to the high density of η′ precipitates within the grains and narrow precipitate free zones in the vicinity of grain boundaries. The main contribution to the improvement of fatigue crack propagation resistance comes from the coarser precipitates within the grains. When subjected to two-step aging, Ag-added alloy shows larger semi-coherent matrix precipitates. These relatively coarser precipitates increase the homogeneity of deformation and therefore improve the fatigue crack propagation resistance. In addition, microstructure analysis indicates that the size and distribution of inclusions as well as the grain structures of Al–Zn–Mg alloys are independent of Ag addition.

Effect of Ag on the Hot Corrosion of NiAl Intermetallic Compound

AbstractThe low ambient tensile ductility and inadequate high temperature strength and creep resistance have limited the applications of intermetallic compound NiAl as a structure material at high temperatures. A small addition of Ag could increase the strength of NiAl. In this study, hot corrosion behavior of NiAl and NiAl-Ag containing 1 and 5%Ag (in weight percent), respectively, in molten (Na,K)2SO4 at 1173 K has been examined by thermogravimetry and physical analysis techniques. The experimental results indicated that the corrosion rates of NiAl and NiAl-Ag tended to increase with exposure time, accompanied with the formation of nodules. Fast localized corrosion is the typical feature of the corrosion of both NiAl and NiAl-Ag. The addition of Ag to NiAl accelerated its corrosion, with a higher corrosion rate observed for the 5%Ag addition. The two-phase microstructure of NiAl-Ag alloys accelerated the formation of nodules in the regions close to Ag phases.

Influence of Ag content on microstructure and intermetallic phases of AlSi12 alloy

The main objective of this study is to examine the influence of trace additions of silver on the morphology and composition of the complex microstructure of the intermetallic phases in AlSi12 alloy. Intermetallics were found in short or long rod, or ‘Chinese Script’, forms containing Si, Fe, Mn, Ag and Mg, These compounds became richer towards the grain boundaries. It was observed that the high Ag content intermetallics were created in the form of short rods. In all samples with added Ag, the dendritic structures had transformed into non-dendritic ones. The addition of Ag, in addition to the degeneration of the dendritic structures, enhanced the transformation from rosette form to globular morphologies. The results showed that the amount of eutectic Si increased with small additions of Ag to the AlSi12 alloy. It was established that in general the Ag is distributed within the eutectic structure.

Coating of Cr–V ledeburitic steel with CrN containing a small addition of Ag

Samples made from Vanadis 6 PM ledeburitic tool steel were surface machined, ground, and mirror polished. They were heat treated and coated with CrN with and without Ag addition by reactive magnetron sputtering. The CrN film grew in a typically columnar manner. A small addition of 3% Ag did not lead to alterations in the growth mechanism. The hardness of the CrN coating was 16.79 ± 1.49 GPa compared to 15.97 ± 1.44 GPa for the coating with Ag addition. The Ag addition in the CrN improved adhesion of the coating, which can be attributed to the capability of CrAgN coating to accommodate higher deformation energy before failure. The CrAgN coating exhibited superior tribological properties at intermediate temperatures. Compared to pure CrN the friction coefficient is lowered to 70–75% when measured at 400 and 500 °C, respectively. This is reflected in a reduction in the volume wear, which was found to be three times lower for the coating containing Ag. Flexural strength decreased slightly for the CrN- or CrAgN-coated material compared to uncoated steel. However, as the decrease in flexural strength is very weak there is practically no risk of significant embrittlement of the investigated material due to the CrN coating with or without Ag addition.

Effects of small addition of Ag and/or Cu on the microstructure and properties of Sn–9Zn lead-free solders

In the present study, the effects of separate and dual addition of small amount of Ag and Cu on the microstructure and mechanical properties of the eutectic Sn–9Zn solder alloy were investigated. Results indicate that alloying of Ag and/or Cu resulted in refine the coarse needle-like Zn-rich phase and formation of intermetallic compounds (IMCs) with the eutectic solder. Single addition of Ag led to formation of AgZn, Ag 5Zn 8 and ɛ-AgZn 3 IMCs, which results in significant increase in both ultimate tensile strength (UTS) and ductility, while, the flower shaped and rod shaped Cu 6Sn 5, γ-Cu 5Zn 8 and ɛ-CuZn 5 IMCs produced by Cu alloying, results in small increase in UTS and ductility. The dual addition of Ag and Cu suppressed the appearance of Ag 5Zn 8 IMCs due to the competition for Zn between Cu and Ag, which results in slight decrease in UTS and ductility of Sn–9Zn–1.5Ag solder. Worthy of notice is that all alloys demonstrated an increase in both UTS and yield stress with increasing strain rate and/or decreasing testing temperature, indicating that the tensile behavior of the four alloys often exhibits a strain rate and temperature dependence.

Microstructure and mechanical properties of Al–Cu–Mg–Mn–Zr alloy with trace amounts of Ag

The microstructure and mechanical properties of Al–Cu–Mg–(Ag)–Mn–Zr alloys were studied by means of tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that small additions of Ag to Al–Cu–Mg–Mn–Zr alloy can accelerate the hardening effect of the aged alloy and reduce the time to peak-aged. The mechanical properties can be improved both at room temperature and at elevated temperatures, which is attributed to the fine and uniform plate-like Ω precipitates. Meanwhile the ductility of the studied alloys remains at relatively high level. The major strengthening phases of the Ag-free alloy are θ′ and less S′, while that of Al–Cu–Mg–Mn–Zr alloy containing trace amounts of Ag are Ω and less θ′.

Vacancy–solute interactions during multiple-step ageing of an Al–Cu–Mg–Ag alloy

Small additions of Ag and Mg stimulate nucleation of the Ω phase in artificially aged Al–Cu alloys, after which these elements segregate to the Ω/matrix interfaces. In this work, positron spectroscopy results show that vacancies accompany the Ag (and Mg) atoms at the interface during precipitate formation, after which they are released back into the matrix and facilitate secondary ageing at ambient temperature.

Formation and thermal stability of Pd-based bulk metallic glasses

The glass-forming ability and thermal stability of bulk glassy Pd79Cu6Si10P5 alloy were studied by substitution of Cu with Ag and with Au+Ag from 0 to 6at.%. The results indicated that the small addition of Ag strongly affects the thermal stability and glass-forming ability of the Pd79Cu6Si10P5 alloy. The alloy doped with 4at.% Ag (Pd79Cu2Ag4Si10P5) exhibits the largest glass-forming ability among the Pd79Cu6−xAgxSi10P5 (x=0–6at.%) alloys. The critical diameter for glass formation of this alloy reaches as large as 7mm by copper mold casting. On the other hand, the multi-addition of Au+Ag does not increase the glass forming ability though the Ag and Au are similar in atomic size. The largest glass forming ability is obtained at 1at.% Au+2at.% Ag among the Pd79Cu6−x−yAuxAgySi10P5 (x=1–4at.%, y=1–3at.%) alloys. The critical diameter of this alloy is 5mm by copper mold casting.

Improvement of Bake-Hardening Response of Al-Mg-Cu Alloys by Means of Nanocluster Assist Processing (NCAP) Technique

In this work, the bake-hardening (BH) response of an Al-3.0Mg-1.0Cu (in mass%) alloy has been improved by the small addition of Ag as a good example of our proposed Nanocluster Assist Processing (NCAP) technique. From the detailed observation through high resolution transmission electron microscopy (HRTEM), it is found that the origin of the increased hardness in the Ag-added alloy is attributed to the densely and uniformly formed Z phase at the expense of Guinier-Preston- Bagaryatsky (GPB) zones and the S’ phase. It is new findings that the Z phase is formed even in the ternary alloy although the chemical composition lies in the (α+S+T) phase field. Based on the threedimensional atom probe (3DAP) results, furthermore, it is suggested that nanoclusters of Mg, Ag and/or Cu provide effective nucleation sites for the Z phase, whereas nanoclusters of Mg and Cu do less. Such unique characteristics of Ag are clearly seen in the newly constructed interaction energy map (IE map).

Ａｌ‐３％Ｍｇ‐１％Ｃｕ合金の時効硬化およびナノ析出組織に及ぼすＡｇ添加の影響

In this work, the bake-hardening (BH) response of Al–3.0%Mg–1.0%Cu alloys with and without Ag has been investigated by a hardness test, and related to the nano-scale precipitate microstructures observed by high resolution transmission electron microscopy (HRTEM) and a three-dimensional atom probe (3DAP). The small addition of Ag increased hardness under a BH condition (e.g. 443 K for 1.2 ks) due to the rapidly formed nanoclusters containing Mg, Ag and/or Cu. The formation of the equiaxed Z phase was also accelerated by the Mg/Cu/Ag clusters, resulting in the more increased second-stage hardening. This strongly suggests that Mg/Cu/Ag clusters provide effective nucleation sites for the Z phase, whereas Mg/Cu clusters formed in the ternary alloy do less.

Effects of small additions of Ag, Al, and Ga on the structure and properties of the Sn–9Zn eutectic alloy

The effects of a third elements, i.e., Ag, Al, and Ga, on melting temperature, microstructures, and mechanical properties of the Sn–9Zn lead-free solders were investigated. The results indicate that Ga is uniformly distributed in the Sn-matrix, Al is detected in the grain boundaries and Zn-rich phases, and Ag combines with Zn to form an Ag–Zn compound. The adding of 0.5 wt% Ag, results in decreasing the UTS and ductility. By the addition of Al the UTS and elongation of the Sn–9Zn–0.45Al alloy can be decreased due to the Al element precipitated in the grain boundaries. The Sn–9Zn–0.5Ga alloys have very good UTS and elongation, which are better than both those of the Sn–9Zn–0.5Ag and Sn–9Zn–0.45Al alloys.

Fundamental considerations for the development of oxidation-resistant alloys and coatings based on γ-TiAl

Alloys based on γ-TiAl are promising high-temperature materials that may replace conventional heat-resistant steels and superalloys in applications where high strength in combination with low density is required. However,an important hindrance to the use of γ-TiAl alloys at high temperatures is their relatively poor oxidation resistance and sensitivity against environmentally induced embrittle-ment. This material degradation is related to the poor protective properries of the mixed TiO 2 /Al 2 O 3 suface scales which form on the surface during high-temperature exposure. Recently, it was shown that protective alumina scale formation on γ-TiAl can be obtained by small additions of Ag. This effect was found to be related to the formation of Z phase in the subscale depletion layer at the expense of α 2 -Ti 3 Al. It was found that the beneficial effect of Ag can be suppressed if the alloys contain additional α 2 -stabilizing elements, such as Nb, as is the case for most (semi)commercial, high-strength alloys. Therefore, recent efforts have concentrated on developing Ag-containing γ-TiAl alloys as oxidation-resistant coatings for high-strength titanium aluminides. Preliminary results using magnetron sputtering have shown that, due to the similarities in chemical and physical properties of the coating and base material, the Ag-containing material offers promising potential to be qualified as a coating material for reducing the oxidation-induced degradation of titanium aluminides.

Effect of Ag addition on cold-seeded melt-growth of Gd–Ba–Cu–O superconductor using Nd123 seed crystal

We investigated the effect of Ag addition on cold-seeded melt-growth of Gd–Ba–Cu–O superconductors using Nd123 seed crystal. We found that a small addition of Ag enlarged the temperature window for stable single-grain growth, since the decomposition temperature of Gd123 decreased with Ag addition. However, Ag addition of more than 5 wt.% restricted the temperature window due to the melting of Nd123 seed crystal which reacted with Ag. The employment of a double layered precursor, which composed of two layers with and without Ag, solved the problem of the diffusion of Ag into the seed crystal. As a result, single grain Gd–Ba–Cu–O/Ag bulks could be obtained in a wide temperature window.

Coprecipitation of Ω and σ phases in Al-Cu-Mg-Mn alloys containing Ag and Si

The individual influence of small additions of Ag and Si on the nucleation of the Ω (i.e., a chemically modified coherent form of ϑ-Al2Cu) and σ (Al5Cu6Mg2) phases, respectively, in Al-Cu-Mg alloys has been known. These phases nucleate directly and exhibit reduced rates of coarsening at the commercial aging temperatures. Alloys containing a uniform and fine distribution of these phases may, therefore, be of interest for further investigation for applications at temperatures below 200 °C. In a recent study, using an Al-Cu-Mg-Mn-Ag-Si alloy aged at 180 °C, it was shown that the Ω phase formed as a major precipitate nucleated predominantly upon the Mn-bearing dispersoids, while the σ phase was present as a minor one. This article describes the conditions under which widespread nucleation of σ phase may occur at unidentified sites in the matrix as well as upon the Mn-bearing dispersoids in the alloy. Widespread nucleation of σ phase begins in the alloy following the onset of dissolution of Guinier-Preston-Bagaryatski (G-P-B) zones that form early in the aging cycle as the major precipitate. It is established that nucleation of σ as a major phase precipitate requires a critical minimum supersaturation of Si in the solid solution. This article further points out that several constituent phases (implying those which form as solidification products and survive the homogenization treatment) together with the Mn-bearing dispersoids dissolve Si, thereby considerably reducing the Si supersaturation in the solid solution. The implications of these observations are discussed in view of the available data on the nucleation of σ phase in such alloys.

The microstructures and mechanical properties of the Sn-Zn-Ag-Al-Ga solder alloys—the effect of Ag

The microstructures and mechanical properties of Sn-8.55Zn-xAg-0.45 Al-0.5Ga (wt.%) lead-free solders were investigated. The x content of the solders investigated were 0.5-3.0 wt.%. The results indicate that Ag plays an important role not only in the structure but also in the mechanically properties. The mechanical properties and differential scanning calorimetry (DSC) behavior has been compared with that of 63Sn-37Pb solder. Small additions of Ag decreased the melting point of the Sn-8.55Zn-xAg-0.45Al-0.5Ga solders while maintaining the same strength and ductility as the 63Sn-37Pb solder.

Compositional characterization of Cu-rich phase particles present in as-cast Al-Cu-Mg(-Li) alloys containing Ag

The effects of small additions of Ag on the aging of wrought Al-Cu-Mg(-Li) alloys, involving widespread nucleation of Cu-rich Ω (and T1) phase precipitates, are known. This article examines the influence of small additions of Ag on the nature of Cu-rich θ-Al2Cu, S-Al2CuMg, and T1-Al2CuLi phases present in appropriate as-cast Al-Cu, Al-Cu-Mg, and Al-Cu-Li-Mg alloys. Using a combination of light microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA), it is shown that neither independent nor combined additions of Ag and Mg to the binary Al-Cu alloy alter the composition of the θ phase; however, there are differences in the ways the θ phase is evolved in Al-Cu-Mg alloys with and without Ag. Ag additions to the Al-Cu-Mg alloy result in the formation of an Al-Cu-Mg-based ternary phase, having a Cu content similar to that of the θ phase and containing small amounts of Mg; rapid rates of cooling cause the retention of this phase in the as-cast alloy. Relatively large amounts of both Ag and Mg are always located in the peripheral regions of such a phase. This phase is readily replaced by θ phase upon annealing at 450 °C. The S phase of the ternary Al-Cu-Mg system is identified in this alloy and is found to dissolve small amounts of Ag. In the case of the Al-Cu-Li-Mg-Ag alloy, two major changes are observed: both Ag and Mg are always present in relatively large amounts in the peripheral regions of the T1 phase, and the S-phase particles are once again found to dissolve small amounts of Ag. These results are discussed in light of the known compositional features of the precipitates formed in the artificially aged Al-Cu-Mg(-Li)-Ag alloys, to reveal that examination of phases present in the as-cast microstructure is a contributory step toward determining the locations of trace alloy additions in the phase precipitates of interest.

Nucleation of <I>Ω</I> Phase in an Al–Cu–Mg Alloy Containing Small Additions of Ag

The role of small additions of Ag in increasing the nucleation frequency of a plate shaped precipitate having {111} A1 habit plane, designated Ω, in an Al-Cu-Mg alloy has been investigated using transmission electron microscopy (TEM), electron diffraction and energy dispersive X-ray spectroscopy. The results provide for the first time direct evidence showing association of Ω plates with small Ag-rich precipitates of the constituent binary Al-Ag system during the early stages of artificial aging. Given the strong attraction between Ag and Mg owing to the large difference in electronegativity between them, Mg simultaneously combines with the Ag-rich precipitates formed on the {111} A1 matrix planes, and makes such sites suitable for the heterogeneous nucleation of Ω phase.

ＰｂＳｒ（Ｍｇ１／３Ｎｂ２／３）Ｏ３−ＰｂＺｒＯ３−ＰｂＴｉＯ３の焼結挙動に及ぼすＡｇとＰｂＯの影響

The effect of Ag and PbO on the sintering behavior and the piezoelectric properties of PbSr(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3 system has been studied. A small addition of Ag enhances the value of er. and Kr. In the specimen with Ag addition, the grain growth was observed by use of SEM. The shrinkage vs temperature curves showed that the shrinkage of the specimen with Ag addition abruptly increases from 900°C and the value of shrinkage at 1100°C is as twice as the additive-free specimen. The shrinkage vs time plots revealed that the grain boundary diffusion is dominant on the sintering of PMN-PZT with Ag and Pb addition.