The influence of the microstructure of high noble gold-platinum dental alloys on their corrosion and biocompatibility in vitro

The aim of this work was to compare the microstructures of two high noble experimental Au-Pt alloys with similar composition with their corrosion and biocompatibility in vitro. We showed that Au-Pt II alloy, composed of 87.3 wt.% Au, 9.9 wt.% Pt, 1.7 wt.% Zn and 0.5 wt.% Ir + Rh + In, although possessing better mechanical properties than the Au-Pt I alloy (86.9 wt.% Au, 10.4 wt.% Pt, 1.5 wt.% Zn and 0.5 wt.% Ir + Rh + In), exerted higher adverse effects on the viability of L929 cells and the suppression of rat thymocyte functions, such as proliferation activity, the production of Interleukin-2 (IL-2), expression of IL-2 receptor and activation — induced apoptosis after stimulation of the cells with Concanavalin-A. These results correlated with the higher release of Zn ions in the culture medium. As Zn²⁺, at the concentrations which were detected in the alloy’s culture media, showed a lesser cytotoxic effect than the Au-Pt conditioning media, we concluded that Zn is probably not the only element responsible for alloy cytotoxicity. Microstructural characterization of the alloys, performed by means of scanning electron microscopy in addition to energy dispersive X-ray and X-ray diffraction analyses, showed that Au-Pt I is a two-phase alloy containing a dominant Au-rich α₁ phase and a minor Pt-rich α₂ phase. On the other hand, the Au-Pt II alloy additionally contained three minor phases: AuZn3, Pt₃Zn and Au_1.4Zn_0.52. The highest content of Zn was identified in the Pt₃Zn phase. After conditioning, the Pt₃Zn and AuZn₃ phases disappeared, suggesting that they are predominantly responsible for Zn loss, lower corrosion stability and subsequent lower biocompatibility of the Au-Pt II alloy.     

Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use

The complex precipitation mechanisms related to the age-hardening of Cu-free Au-Ag-Pt-Zn-In alloy for multipurpose dental use was studied by means of hardness test, X-ray diffraction (XRD) studies, field emission scanning electron microscopic (FE-SEM) observations, energy dispersive spectrometer (EDS) analysis, and electron probe microanalysis (EPMA). The early diffusion and then clustering of the In-concentrated phase in the grain interior, together with the early diffusion and then ordering of the PtZn phase in the grain boundary, introduced the internal strains in the Au-Ag-rich α₁ matrix, resulting in the hardening process. As the Au-Ag-rich α₁^’ and PtZn β lamellarforming grain boundary reaction progressed, the phase boundaries between the solute-depleted face-centered cubic (FCC) α₁^’ matrix and the face-centered tetragonal (FCT) PtZn β precipitate reduced, resulting in softening. In the particlelike structures composed of the major Pt-Au-rich α₂ phase and the minor Pt-Zn-rich α₃ phase, the separation of In and Zn progressed producing the In-increased Pt-Au-rich α₂^’ phase and the Zn-increased PtZn α_3′ phase with aging time without restraining the softening. The miscibility limit by complex systems of Au-Pt, Ag-Pt, Au-In and In-Zn resulted in the phase transformation and related microstructural changes.     

Age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum

This study examined the age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum. The hardness increased rapidly in the initial stage of the aging process, reached the maximum value, then decreased continuously with aging time. The significant hardness increase resulted from the heterogeneous precipitation of the Pt-rich β phase from the grain boundary of the Au-rich α₁ matrix due to the miscibility limit of Au-Pt system. With increasing aging time, the fine Pt-rich β precipitates covered almost the whole matrix, and by further aging, the precipitates grew coarse. The microstructural coarsening reduced the interface between the Au-rich α₁ matrix and the Pt-rich β precipitates, which released the lattice strains between the two phases, resulting in a softening effect. In the later stage of aging process, the Au-containing Pt₃In particle-like structure was transformed into the Au-depleted particle-like structure containing relatively large amounts of Cu resulting from the overlapping miscibility limit of both Au-Pt and Ag-Cu systems, which was responsible for the slow decreasing rate in hardness in the later stage of aging.     

Hardening and overaging Mechanisms in an Au-Ag-Cu-Pd alloy with In additions

Hardening and overaging mechanisms were examined in a semi-precious Au−Ag−Cu−Pd dental alloy with small amounts of In, Zn and Ir. The alloy showed maximum age-hardenability at the aging temperature of 400°C. The hardness value increased to reach the maximum value, and then decreased continuously with aging time. In the early stage of aging process, the matrix of the single α₀ phase separated into the α₁ and AuCu I phases, and the fine InPd-based precipitates containing Zn and Cu formed at the grain boundaries. During further aging, the grain boundary precipitates grew toward the grain interior. In overaged specimens, the original matrix was replaced by the coarse lamellar structure composed of the AuCu I phase containing Pd and Zn and the Ag−Au-based α₁ phase of Cu-, Pdand Zn-depleted. The hardness increase in the early stage of aging process was caused by the nucleation of the InPd-based phase and the AuCu I phase in the ga₀ matrix; this introduced significant lattice strains into the interface with the matrix. The hardness decrease in the latter stage of aging process was caused by the formation and coarsening of the lamellar structure composed of the α₁ phase and the AuCu I phase. The minor constituent, In formed InPd-based grain boundary precipitates prior to the lamellar structure formation of α₁ and AuCu I.     

Phase stability among the α(A1), β(A2), and γ(D83) phases in the Cu-Al-X system

The phase equilibria among the α(A1), β(A2), and γ(D8₃) phases in the Cu-Al-X systems (X: Ti, V, Mn, Fe, Co, Ni, Zn, Sn, and Sb) at 700 and 800 °C were investigated, and the effects of these alloying elements on the phase boundaries, homogeneous solid solution ranges, and tie-lines among the α, β, and γ phases were accurately determined by the diffusion couple method. The phase stabilities among α, β, and γ phases are discussed in terms of the partition coefficient. In addition, a modified Guillet’s method, which is used to estimate the effect of alloying elements on microstructure, is proposed by taking into account the change of equivalent coefficient with the phase fraction, and applied to predict the effect of alloying elements on the microstructure of the Cu-Al base alloy.     

Phase stability among the α(A1), β(A2), and γ(D83) phases in the Cu-Al-X system

The phase equilibria among the α(A1), β(A2), and γ(D8₃) phases in the Cu-Al-X systems (X: Ti, V, Mn, Fe, Co, Ni, Zn, Sn, and Sb) at 700 and 800 °C were investigated, and the effects of these alloying elements on the phase boundaries, homogeneous solid solution ranges, and tie-lines among the α, β, and γ phases were accurately determined by the diffusion couple method. The phase stabilities among α, β, and γ phases are discussed in terms of the partition coefficient. In addition, a modified Guillet’s method, which is used to estimate the effect of alloying elements on microstructure, is proposed by taking into account the change of equivalent coefficient with the phase fraction, and applied to predict the effect of alloying elements on the microstructure of the Cu-Al base alloy.     

Dislocation structure of the intermetallic alloy Ti-21.4 at % Al-5.6 at % Nb after room-temperature deformation

The dislocation structure of a two-phase α₂/β alloy of composition Ti-21.4 at % Al-5.6 at % Nb deformed at room temperature has been studied by electron microscopy. It has been established that the microstructure of the α₂ phase after deformation contains mobile a superdislocations in basal and prism planes. The initial stages of the formation of dislocation networks of a superdislocations have been observed. Mobile 2c + a superdislocations in pyramid planes have been revealed, as well as separate dislocations with a Burgers vector [0001]. The transfer of deformation from the α₂ into the β phase is effected only by a superdislocations whose Burgers vector enters into the Burgers orientation relationship between the α₂ and β phases. Factors responsible for the enhancement of plasticity in the two-phase alloys of Ti₃Al with Nb are discussed.     

Effect of Al addition on microstructure and mechanical properties of Mg−Gd−Zn alloys

The microstructure evolution and mechanical properties of Mg?15.3Gd?1Zn alloys with different Al contents (0, 0.4, 0.7 and 1.0 wt.%) were investigated. Microstructural analysis indicates that the addition of 0.4 wt.% Al facilitates the formation of 18R-LPSO phase (Mg₁₂Gd(Al, Zn)) in the Mg?Gd?Zn alloy. The contents of Al₁₁Gd₃ and Al₂Gd increase with the increase of Al content, while the content of (Mg, Zn)₃Gd decreases. After homogenization treatment, (Mg, Zn)₃Gd, 18R-LPSO and some Al₁₁Gd₃ phases are transformed into the high-temperature stable 14H-LPSO phases. The particulate Al?Gd phases can stimulate the nucleation of dynamic recrystallization by the particle simulated nucleation (PSN) mechanism. The tensile strength of the as-rolled alloys is improved remarkably due to the grain refinement and the fiber-like reinforcement of LPSO phase. The precipitation of the β′ phase in the peak-aged alloys can significantly improve the strength. The peak-aged alloy containing 0.4 wt.% Al achieves excellent mechanical properties and the UTS, YS and elongation are 458 MPa, 375 MPa and 6.2%, respectively.     

Electrodeposition of ternary Zn–Ni–Sn alloys from an ionic liquid based on choline chloride and their characterisation

Ternary Zn–Ni–Sn alloy coatings with a range of compositions were potentiostatically electrodeposited on steel substrates from a deep eutectic solvent-based electrolyte. The effect of electrodeposition potential on the morphology, chemical and phase compositions, and corrosion behaviour of the deposits was analysed. The co-deposition mechanism of Zn–Ni–Sn alloys was found to be normal whereby increasing the electrodeposition potential enhanced the ternary alloy Zn content (active element) and greatly suppressed the alloy Sn and Ni content (noble elements). The X-ray diffraction phase analyses showed that Ni in the deposits exists in the form of metal compounds including β-Ni₃Sn₂ as well as γ-NiZn₃. The improved corrosion resistance observed in all ternary alloys was attributed to their compact morphology, phase content and chemical composition. Comparison of corrosion performances shows that ternary Zn–Ni–Sn alloys are superior for sacrificial corrosion protection of steel metallic substrates compared to binary Zn–Sn and Zn–Ni alloys.     

Phase equilibria of the Au–Sn–Zn ternary system and interfacial reactions in Sn–Zn/Au couples

Phase equilibria of the Au–Sn–Zn ternary system and interfacial reactions between Sn–Zn alloys and Au were experimentally investigated at 160 °C. Experimental results reveal that no equilibrium-stated ternary phases were found and the ternary element solubility in the binary phase is insignificant. When the Zn content was less than 3 wt% in the Sn–Zn alloy, only the Au–Sn binary intermetallic compounds (IMCs), such as AuSn, AuSn₂ and AuSn₄ phases, were formed at the Sn–Zn/Au interface. When the Zn content in Sn–Zn alloys was greater than 7 wt%, the AuZn, AuZn₂ and Au₃Zn₇ phases were formed in the Sn–Zn/Au couples at 160 °C. However, both Sn–Zn and Au–Zn IMCs, and the Au–Zn–Sn ternary IMC (T phase) were observed between Au and the Sn–Zn alloys with 3–5 wt% added Zn. This T phase might be the metastable phase. The evolution of IMCs in the Sn–Zn/Au couples is very sensitive to the Zn content in Sn–Zn alloys.     

Zn对均匀化态Mg-3Sn-Ca镁合金腐蚀性能的影响

研究了Zn元素对均匀化态Mg-3Sn-Ca合金耐腐蚀性能的影响。通过XRD、金相、SEM、失重、析氢、电化学极化曲线和阻抗谱分析了Mg-3Sn-Ca(TX31)和Mg-3Sn-Ca-Zn(TXZ311)2种合金的耐蚀性能。结果表明,Mg-3Sn-Ca合金中主要由CaMgSn及Mg₂Sn相组成,加入Zn元素后晶粒得到显著细化,第二相体积分数增加并呈弥散分布,并有Mg₂Ca相析出。而Zn的添加可显著提高Mg-3Sn-Ca合金的耐蚀性能,这主要归因于TXZ311合金具有更细小的晶粒尺寸以及均匀密集分布的CaMgSn相,使合金在腐蚀过程中形成的钝化膜更加均匀。因此,TXZ311合金的耐蚀性远高于TX31合金。     

Effect of silicon on the phase formation in mechanically activated systems based on Fe(75)C(25): Temperature-induced transformations in mechanosynthesized composites

Transformations realized in mechanosynthesized amorphous-nanocrystalline Fe(75)C(25 − x)Si(x) (0 ≤ x ≤ 10 at %) alloys during heating have been studied using dynamic magnetic susceptibility measurements, X-ray diffraction, and metallography. In contrast to mechanosynthesized alloys consisting of α-Fe, Fe₃C, and amorphous phases, the annealed alloys with x > 5 at % were found to exhibit the formation of an additional phase such as Fe₅SiC. After heating to 700 and 800°C, the powder particles of alloys contain a large amount of uniformly distributed graphite particles of ∼0.5 μm in size. The formation of particles results from the cementite decomposition, which is accelerated at the expense of partial silicon dissolution in cementite and in the presence of α-Fe nanograins as well.     

Microhardness and morphologic characteristics of rapidly solidified Al-12Si-8Ni-5Nd alloy

Al-Si-Ni-Nd alloys with a nominal composition of Al-12 wt.% Si-8 wt.% Ni-5 wt.% Nd alloy are prepared by a conventional casting (ingot) and melt spinning technique at different cooling rates (ν). The effects of the rapid solidification rate on the microstructures and microhardness performances of the specimen alloys are investigated in detail. The results obtained by the XRD, SEM and DSC show that the ingot and melt spun alloys have a multiphase structure. When ν is 5 m/s, the alloy consists of four phases namely α-Al, intermetallic Al₃Ni, Al₁₁Nd₃, and fcc Si. The melt-spun ribbons are completely composed of α-Al and eutectic Si phases, and primary silicon is not observed when ν increases to 20 m/s, 25 m/s, 30 m/s and 35 m/s. The XRD analysis indicated that the solubility of Si in the α-Al matrix increases greatly with the rapid solidification. The change in microhardness is discussed based on the microstructural observations. The microhardness values of the melt spun ribbons are about three times higher than those of ingot counterparts.     

Effect of heat treatment and plastic deformation on the structure and elastic modulus of a biocompatible alloy based on zirconium and titanium

Transmission electron microscopy and X-ray diffraction analysis have been used to study the phase composition and structure of an IMP-BAZALM (Zr-31Ti-18Nb (at %)) biocompatible medical alloy depending on the heat-treatment conditions. An interrelation between the values of the electron concentration of phases normalized to the volume (e/a _norm = e/a _alloy(ν_β/ν_phase)) and the phase composition of the alloy has been found to exist. It has been established that the appearance of the α″ and ω phases in the structure of the alloy leads to an increase in the modulus of elasticity. The greatest increase in the modulus is observed under the conditions corresponding to the formation of the ω phase.     

Electrochemical codeposition of typical α＋β phases Mg-Li alloys from the molten LiCl-KCl-MgC2 system

Electrochemical codeposition of Mg-Li alloys on molybdenum electrodes was investigated in LiCl-KCl (50 wt.%:50 wt.%) melts containing different concentrations of MgCl₂ at 973 K. Cyclic voltammograms show that the underpotential deposition of lithium on pre-deposited magnesium leads to the formation of liquid Mg-Li alloys. The deposition potentials of Mg(II) and Li(I) ions gradually near each other with MgCl₂ concentration decreasing. Mg-Li alloys with typical α + β phases could be obtained by potentiostatic electrolysis from LiCl-KCl melts containing 5 wt.% MgCl₂ at −2.25 V vs. Ag/AgCl (cathodic current density 1.70 A·cm⁻²) for 2.5 h. α phase, α + β phases, and β phase Mg-Li alloys with different lithium contents were obtained by potentiostatic electrolysis from LiCl-KCl melts with the different concentrations of MgCl₂. The samples were characterized by X-ray diffraction and scanning electron microscopy.     

磁兼容Au-25Pt合金的组织结构及综合性能

Au-Pt合金具有优异的MRI磁兼容性、良好的生物兼容性、高的耐蚀性等优点,在医用材料领域具有巨大的应用前景。采用X射线衍射仪、金相显微镜、维氏显微硬度仪和综合物性测量系统等,研究冷加工过程Au-25Pt合金丝材的组织结构演变及其对体积磁化率和维氏硬度的影响,为制备综合性能优异的Au-Pt合金探索有效途径。结果表明,固溶处理后的Au-25Pt合金为面心立方结构的单相固溶体,经30%～70%冷变形后,没有其它相产生。冷加工变形显著增加了Au-25Pt合金的维氏硬度,尤其在冷加工初期(<30%变形量),但对磁化率影响很小。冷变形Au-25Pt合金不仅具有接近人体组织的体积磁化率(-8.5×10-6),还有较高的维氏硬度(HV0.1=160)。     

Electrodeposition and characterization of Zn-Mn alloy coatings obtained from a chloride-based acidic bath containing ammonium thiocyanate as an additive

The electrodeposition of Zn-Mn alloys was performed using a chloride-based acidic bath containing ammonium thiocyanate (NH₄SCN) as an additive. An electrochemical study using cyclic voltammetry (CV), performed for each of the metal ions (Zn(II) and Mn(II)), showed that neither metal ion forms complexes with NH₃, and that Mn(II) but not Zn(II) forms complexes with SCN⁻. The influence of NH₄SCN on the morphology, composition and crystallographic structure of the electrodeposited Zn-Mn alloys was studied using scanning electron microscopy (SEM), glow discharge spectroscopy (GDS) and X-ray diffraction (XRD). The results show that the presence of NH₄SCN in the solution induces an increase in the Mn content of the alloy, from 3% in the Zn-Mn alloy obtained in the absence of additive to 6.2% in the alloy obtained in the presence of additive. In addition, the presence of NH₄SCN favors the formation of coatings comprised of a mixture of ε-phase Zn-Mn(002) + α-phase Zn-Mn(111) alloys. These coatings were compact and smooth and exhibited a lower corrosion rate compared to the coatings obtained in the absence of NH₄SCN, which where comprised of a mixture of Zn, ε-phase Zn-Mn and α-phase Zn-Mn alloys.     

Effect ofβ volume fraction on the dynamic grain growth during superplastic deformation of Ti3Al-based alloys

The superplastic deformation behavior of Ti₃Al based(α ₂+β alloy was studied with respect to the volume fraction of α₂/β. Three alloys containing 21, 50 and 77% in volume fractions ofβ exhibited large tensile elongations of over 500% at 970°C with a strain rate of 2.5x10^-4 sec^-1. The largest elongation was observed in the alloy with 21% ofβ. As the volume fraction ofβ phase increased, the flow stress and correspondingly, the strain-rate sensitivity values decreased. Due to the higher diffusivity of Ti in,β phase than in α₂ phase, the increase inβ volume fraction from 21 % to 77% accelerated the dynamic grain growth, and degraded the superplasticity of the Ti₃Al-based alloys. The strain-based grain growth behavior was quantitatively analyzed and incorporated into a constitutive equation. The calculated flow curves are in agreement with the experimental ones in the stable deformation region.     

Phases and microstructures of high Zn-containing Al–Zn–Mg–Cu alloys

Phases and microstructures of three high Zncontaining Al–Zn–Mg–Cu alloys were investigated by means of thermodynamic calculation method, optica microscopy(OM), scanning electron microscopy(SEM)energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), and differential scanning calorimetry(DSC) analysis. The results indicate that similar dendritic network morphologies are found in these three Al–Zn–Mg–Cu alloys. The as-cast 7056 aluminum alloy consists of aluminum solid solution, coarse Al/Mg(Cu, Zn, Al)_2 eutectic phases, and fine intermetallic compounds g(MgZn_2). Both of as-cast 7095 and 7136 aluminum alloys involve a(Al)eutectic Al/Mg(Cu, Zn, Al)_2, intermetallic g(MgZn_2), and h(Al_2Cu). During homogenization at 450 °C, fine g(MgZn_2) can dissolve into matrix absolutely. After homogenization at 450 °C for 24 h, Mg(Cu, Zn, Al)_2 phase in 7136 alloy transforms into S(Al_2Cu Mg) while no change is found in 7056 and 7095 alloys. The thermodynamic calculation can be used to predict the phases in high Zncontaining Al–Zn–Mg–Cu alloys.     

Structural properties in flame quenched Cu−9Al−4.5Ni−4.5Fe alloy

The flame quenching process has been employed to modify the surfaces of a commercial marine propeller material, aluminum bronze alloy (Cu−9Al−5Ni−5Fe), and the material’s microstructure and hardness properties have been studied. The thermal history was accurately monitored during the process at various surface temperatures and holding times. XRD and EDX analyses have shown that aboveT _β temperature the microstructure consisting of α and κ phases changes into α and β’ martensite due to an eutectoid reaction of α+β→κ and a martensitic transformation of β→β’. The β’ martensite phase formed has a face-centered cubic (FCC) crystal structure with typical twinned structure. The hardness of the flame-quenched layer having the α+β’ structure is similar to or lower than that of the α+κ structure, depending highly on the size and distribution of β’ and κ phases. It is noted that the sliding wear resistance of the flame-quenched layer is enhanced with the formation of β’ martensite.