Effect of microstructure on the corrosion behaviour of dental gold alloys

The effect of microstructure on the corrosion behaviour of Au-Cu-11 at % Pd, Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys was studied by anodic potentiodynamic and potentiostatic polarization tests. The single-phase Au-Cu-11 at % Pd alloys had high corrosion resistance and their potentiodynamic polarization curves were simple. The high-nobility Au-Cu-11 at % Ag alloy displayed high corrosion resistance regardless of its microstructure. The two-phase Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys had lowered corrosion resistance compared with the single-phase alloys. Anodic potentiodynamic polarization curves of the two-phase alloys were complex, but they were explained by superimposing the curves of each phase using the principle of additivity. The potential at which the current density sharply increased corresponded with that of each phase, and the value of current density was calculated as the sum of the current density of each phase and taking account of their volume fractions. In the anodic potentiodynamic polarization, there was little galvanic effect between the two phases.     

Amorphous alloys resistant to corrosion in artificial saliva solution

The tailoring of new corrosion-resistant alloys with specific properties has recently been performed mostly by the sputter deposition technique. The aim of this work was to investigate corrosion resistance of aluminum–tungsten (Al–W) amorphous alloys in artificial saliva solution, pH=5.5, based on the electrochemical methods of cyclic voltammetry and linear polarization. Thin alloy films were prepared on a sapphire substrate by magnetron codeposition. Completely amorphous films were obtained in the Al₈₀W₂₀–Al₆₇W₃₃ composition range. Amorphous Al–W alloys exhibit very high corrosion resistance due to their homogeneous single-phase nature. The passive films spontaneously formed at their surface are uniform with characteristics of an insulator film and prevent corrosion progression in the bulk in a very demanding oral environment. The mechanism of increasing resistivity of Al–W alloys to pitting corrosion and generalized corrosion has been discussed in the view of increasing tungsten content in the alloy. Considering these exceptional corrosion properties and microhardness which falls in the range 7.5±1.6 Pa, Al–W alloys represent promising materials for dental applications.     

Phase transformation and age-hardening of Au-Cu-Pd ternary alloys

Phase transformations in Au-Cu-Pd single-phase alloys Were studied. Age-hardening of the alloys examined vvas attributed to the formation of fine domainu of long-range ordered (LRO) AuCuI type lattice in the interior of the grain. Prolonged ageing caused formation of large LRO domains of single variant at the grain boundary or microtwinning of LRo in the interior of the grain, depending on the ordering rate of the alloy. The electron-atom ratio (e/a) of the alloy and the axial ratio (c/a) of the ordered lattice seemed to playa part in the phase transformation behaviour in this alloy system. The effectiveness of rhodium addition on the grain refining was proved experimentally. These resuRs will be helpful in developing low nobility and high corrosion resistant dental alloys.     

Microstructure and Properties of As-Cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr Alloys at Different Extrusion Ratios

Herein, the effect of hot extrusion with different extrusion ratios (λ = 6, 8, 10, and 12) on the microstructure evolution and properties of as-cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr magnesium alloys, using optical microscopy (OM), scanning electron microscopy (SEM), immersion corrosion and electrochemical corrosion experiment, and tensile testing, is investigated. The results show that the Mg₁₄SnY and Mg₆SnY precipitated phases exist in the alloy before and after extrusion. After hot extrusion, the second phase of the alloy is broken into particles along the extrusion direction, whereas the grain size is significantly reduced, and dynamic recrystallization and deformed grains exist in the microstructure. The mechanical properties of the extruded alloy improve, but the corrosion resistance weakens. When the extrusion ratio is λ = 10, the extruded alloy exhibits relatively good mechanical properties and corrosion resistance. The corrosion behaviors of the extruded alloys are affected by both the grain size and galvanic corrosion. In the initial stage of corrosion, intergranular corrosion plays a major role in reducing the corrosion resistance of the extruded alloys. With prolonged corrosion time, galvanic corrosion has a more significant effect on weakening the corrosion resistance of the extruded alloys.     

铜及铜合金在泥沙海水中的腐蚀研究

介绍了 9种铜及铜合金在舟山海域暴露 1、2、4、8a的腐蚀结果 ,并通过室内模拟泥沙海水的加速腐蚀试验 ,研究了这些铜及铜合金在泥沙含量分别为 0 ,0 .75‰ ,1 .5‰的海水中的冲刷腐蚀行为及海水的泥沙含量对铜及铜合金的腐蚀形貌和腐蚀率的影响。结果表明 ,海水中泥沙的存在会加剧铜及铜合金的腐蚀 ,海水的泥沙含量对铜及铜合金腐蚀的影响程度随合金的不同有很大变化。     

Biocompatibility of Dental Alloys

Modern dental alloys have been used for 50 years to produce prosthetic dental restorations. Generally, the crowns and frames of a prosthesis are prepared in dental alloys, and then veneered by feldspar ceramics or composites. In use, the alloys are exposed to the corrosive influence of saliva and bacteria. Metallic dental materials can be classified as precious and non‐precious alloys. Precious alloys consist of gold, platinum, and small amounts of non‐precious components such as copper, tin, or zinc. The non‐precious alloys are based on either nickel or cobalt, alloyed with chrome, molybdenum, manganese, etc. Titanium is used as Grade 2 quality for dental purposes. As well as the dental casting alloys, high purity electroplated gold (99.8 wt.‐%) is used in dental technology. This review discusses the corrosion behavior of metallic dental materials with saliva in “in vitro” tests and the influence of alloy components on bacteria (Lactobacillus casei and Streptococcus mutans). The test results show that alloys with high gold content, cobalt‐based alloys, titanium, and electroplated gold are suitable for use as dental materials.     

机械镀Zn-Al合金镀层的耐腐蚀性能研究

为了增强机械镀镀层的耐腐蚀性能,采用机械镀方法,以含铝5%(质量分数)的Zn-Al合金粉为原料,在Q235钢材基体表面制备了Zn-Al合金镀层。利用扫描电镜(SEM)表征了合金镀层的截面和断面形貌;采用极化曲线、电化学阻抗谱(EIS)分析了合金镀层在3.5%NaCl溶液中的电化学行为;通过中性盐雾腐蚀实验分析了合金镀层的耐蚀性,并采用XRD分析了镀层的盐雾腐蚀产物。结果表明,Zn-Al合金镀层由葫芦状的Zn-Al合金颗粒交错互嵌堆积而成,镀层颗粒之间以类似隼接的连接方式搭接“卡锁”;与机械镀Zn层相比,Zn-Al合金镀层的腐蚀电位正移了209 mV,腐蚀电流密度仅为纯Zn镀层的7.1%左右,极化电阻为纯Zn镀层的14倍;Zn-Al合金镀层的容抗弧半径明显大于纯Zn镀层的弧半径,且Q_dl较纯锌层减小;纯Zn镀层出现白锈和红锈的时间分别为24和362 h,而Zn-Al合金镀层出现白锈和红锈的时间为48和504 h。Zn-Al合金镀层的耐中性盐雾腐蚀性能明显优于纯Zn镀层,合金镀层对电荷转移具有更好的抑制作用,且Zn-Al合金镀层的腐蚀产物结构致密,可增强物理屏蔽功能。     

Electrochemical impedance spectroscopy study of high-palladium dental alloys. Part I: Behavior at open-circuit potential*

Electrochemical impedance spectroscopy (EIS) was used to study the in vitro corrosion of three representative high-palladium alloys and a gold–palladium alloy for comparison. The corrosion resistances (measured as the charge transfer resistance R _CT from an equivalent circuit) of the high-palladium alloys and the gold–palladium alloy were comparable in simulated body fluid and oral environments, and under simulated dental plaque. The great similarity in corrosion behavior for the three high-palladium alloys is largely attributed to their substantial palladium content and passivity in the laboratory test media, and possibly to their similar structure at the submicron level. Differences in composition and microstructure at the micron level and greater, including the effects of heat treatment simulating the firing cycles for dental porcelain, do not have noteworthy effects on the in vitro corrosion of the three high-palladium alloys. Good accuracy and convenience of extracting corrosion characteristics from equivalent circuit modeling, along with the capability of providing intrinsic information about the corrosion mechanism, enable EIS to be an excellent alternative method to conventional potentiodynamic polarization for evaluating the corrosion behavior of noble dental alloys.     

Superconductivity of copper containing small amounts of niobium

Superconductivity of copper containing small amounts of niobium has been investigated by measuring the electrical resistivity, superconducting volume fraction and by metallographic studies. Small amounts of niobium added to copper has a drastic effect on the low temperature resistivity of the alloys, The annealed alloy Cu_99.5Nb_0.5 shows zero resistance at a current density of 200 A cm^–2 below 3K. The estimated superconducting volume fraction of this alloy at 2K is about fifty times the physical volume fraction of the Nb in the alloy.When more Nb is added these effects unexpectedly become much smaller than those observed in the dilute alloys (< 1.5 at. % Nb). Metallographic results indicate that in all the Cu-Nb alloys studied there are two distinct types of Nb particles in the Cu matrix. The large particles (average size 10 m) randomly distributed in the alloy are probably formed at high temperature when the bulk of the alloy is still in the liquid state. The small Nb particles (size 1 m, interparticle distances < 0.2 m) probably form through a solid state precipitation. It has been found that the large precipitates are more abundant in the alloy containing more than 1.5 at. % Nb, than in alloys containing less than 1.5 at. % Nb. The observed superconducting properties of alloys Cu_99.8Nb_0.2 and Cu_99.5Nb_0.5 have been attributed to the proximity effect of the small Nb particles whose interparticle distances are compatible with the coherence length in the Cu matrix. The very wide superconducting transition shown in both the resistivity and the inductance measurements suggested a distribution in the Nb particle sizes as well as in the interparticle distances.     

Electrical resistivity and thermoelectric power of copper-germanium films

CuGe films over the whole composition range were prepared by the vapour quenching of the alloys onto glass substrates held at 300 K. The electrical resistivity, thermoelectric power and temperature dependence of the films were studied in the temperature range 100–500 K. The observed behaviour of the electrical resistivity and thermoelectric power is understandable on the basis of transmission electron microscopy and electron diffraction observations which indicate three structural regions. Up to 5 at.% Ge in copper the films are single phase with a structure similar to that of pure copper; in the range 5–80 at.% Ge in copper the films consist of a mixture of Cu₃Ge, copper and germanium; beyond 80 at.% the CuGe films are single-phase amorphous.     

硼对铜合金组织和性能的影响

研究了加硼铜合金的组织以及力学、腐蚀、腐蚀磨损和冲蚀性能。结果表明：硼能明显细化铜合金的组织，提高其强度、硬度，改善其耐蚀、耐腐蚀磨损及耐冲蚀能力；并确定硼在铜合金中的最佳含量范围。     

Comparative corrosion study of Ag-Pd and Co-Cr alloys used in dental applications

The electrochemical behaviour of two Ag-Pd alloys (Unique White and Paliag) used in dental prosthetics construction for crowns and bridges and one Co-Cr alloy (Vitallium 2000) was studied in artificial saliva using the polarization curves and electrochemical impedance spectroscopy (EIS). The corrosion resistance was evaluated by means of the corrosion currents value and by coulometric analysis. The open circuit potential of Ag-Pd are attributed to dealloying followed by surface enrichment with Ag and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. Our results have shown that these alloys have a somewhat good corrosion resistance in artificial saliva. The corrosion current densities of Unique White and Vitallium 2000 alloys were very low (∼100 nA/cm²). For Ag-Pd alloys, when increasing the content of Cu, corrosion resistance decreases. The passivation of all samples occurred spontaneously at the open circuit potential. The electrochemical properties of the spontaneously passivated electrodes at the open circuit potential were studied by EIS. The polarization resistance (R _p) and the electrode capacitance (C _dl) were determined. The polarization resistance of all the samples increases with the immersion time. The polarization resistances are largest for Unique White (Ag-Pd) and Vitallium 2000 (Co-Cr) alloys. Because the electrochemical behaviour of the Co-Cr alloy was compared with that of Ag-Pd alloy, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses. The present study, though limited, has shown that electrochemical characteristics can be used to identify such alloys. Knowledge of the in vitro corrosion behaviour of these alloys may lead to better understanding of any biologically adverse effects in vitro.     

Copper-oxide whisker growth on tin–copper alloy coatings caused by the corrosion of Cu6Sn5 intermetallics

This paper reports the effect of corrosion caused by high temperature and humidity on pure tin and tin–copper alloy coatings. A new phenomenon was observed; the development of copper-oxide whiskers on tin–copper alloys plated on copper substrates (1–5 % copper content stored at 105 °C/100 % relative humidity). The copper-oxide whiskers showed similar growth properties to tin whiskers. We have made a model to understand the development of copper-oxide whiskers. Localized corrosion of the tin coating reaches the Cu₆Sn₅ intermetallic layer, and copper oxide accumulates after the corrosion of Cu₆Sn₅. The dilating SnO _x compresses and extrudes out the copper oxide in a whisker form.     

Comportement de l'alliage Cuivre-Nickel 7030 dans une solution de NaCl A 3%

The corrosion behaviour of $\text{70}\text{30}$ copper-nickel alloys in 3% NaCl solution has been investigated through the use of potentiokinetic curves, measure of the $\text{Cu}\text{Ni}$ ratio in the reaction products and surface analysis by E.D.X.The anodic current-potential curves were measured after free corrosion (for up to 10 days) and it was shown that there were one or two Tafel slopes depending on the time of free corrosion. At the corrosion potential, copper was found to exist in a high concentration in solid corrosion film products and nickel in a high concentration in the solution. The percentage of copper in the total reaction products was higher than in the alloy substrate. In the Tafel region, E.D.X analysis has shown that there was a nickel enrichment of the surface of the alloy which could be related to a dealloying of the alloy.     

Corrosion resistance of Al–Li alloys

Abstract

Experiments designed to investigate the corrosion resistance of several lithium-containing aluminium alloys are described. Intergranular corrosion was investigated using the NAWL test, exfoliation corrosion using the EXCO test, and stress corrosion using the C-ring test. It was found that intergranular corrosion varied with extrusion parameters and was more severe in copper-containing alloys. Alloys containing less than 0·4% Cu were not susceptible to stress corrosion. In alloys that failed, susceptibility increased as the aging treatment was extended from the underaged to the peak aged temper and also with increasing copper content. The addition of copper to ternary Al–Mg–Li alloys also increased the exfoliation corrosion attack.

MST/494     

A first report on fracture toughness ofbcc iron alloys as influenced by solutes: opposite effects of silicon and cobalt

The effect of solutes on resistance to fracture of body centred cubic iron single-phase solid-solution alloys has been investigated. TheJ-integral method has been used for the measurement of ductile fracture toughness. TheJ _IC values so determined quantitatively indicate the extent of degradation in fracture toughness due to the addition of hardening solute silicon. Cobalt addition results in alloy softening. The measuredJ _IC values clearly demonstrate the toughening effect of cobalt addition as a solute, which result renders the case of Fe-Co solid-solution alloys interesting.     

Fracture toughness of cast aluminium alloys

An investigation was carried out to evaluate the fracture toughness of cast aluminium alloys of different microstructural complexity, brought about by alloy constitution and cooling rate of castings. In all cases the three-point bend specimens, which had a thickness of 15 mm, did not provide valid plane — strain stress intensity factor values. The fracture susceptibility at a given stress level reckoned in terms of the conditional plane strain stress intensity factor (K _Q) was found to be lowest in aluminium-4.5% copper alloy castings and the susceptibility increased with increase in microstructural complexity. Casting cooling rate in these castings is likely to affect the damage potential of a given defect at yield stress to a greater extent than the fracture susceptibility at a given stress.     

Potentiodynamic behaviour of Ti alloys in physiological solution containing lubricant

Ti based alloys are finding wide spread usage in various biomedical applications including joint replacement. The corrosion behaviour of these alloys in simulated body fluid conditions in the presence of lubricant is not reported so far. Thus, present work is undertaken to understand the influence of the lubricant on potentiodynamic behaviour of three types of Ti alloy, namely commercially pure (C.P.) Ti having α structure, Ti-6Al-4Fe having α + β structure and Ti-13Ta-29Nb-4.6Zr having β structure in Ringer's solution. The results show that lubrication does not alter the corrosion rates of single-phase alloys, which have low corrosion rates. However, it significantly reduces the corrosion rates of alloy Ti-6Al-4Fe having α + ß structure.     

Effect of addition of Al and Cu on the properties of Sn–20Bi solder alloy

This study investigates the effect of the composite addition of Al and Cu on the microstructure, physical properties, wettability, and corrosion properties of Sn–20Bi solder alloy. Scanning electron microscopy and X-ray diffraction were used to identify the microstructure morphology and composition. The spreading area and contact angle of the Sn–20Bi–x (x?=?0, 0.1 wt% Al, 0.5 wt% Cu, and 0.1 wt% Al–0.5 wt% Cu) alloys on Cu substrates were used to measure the wettability of solder alloys. The results indicate that the alloy with 0.1 wt% Al produces the largest dendrite and the composite addition of 0.1 wt% Al and 0.5 wt% Cu formed Cu₆Sn₅ and CuAl₂ intermetallic compounds in the alloy structure. And the electrical conductivity of Sn–20Bi–0.1Al is the best, which reaches 5.32 MS/m. The spread area of the solder alloy is reduced by the addition of 0.1 wt% Al and 0.5 wt% Cu, which is 80.7 mm². The corrosion products of Sn–20Bi–x solder alloys are mainly lamellar Sn₃O(OH)₂Cl₂ and the corrosion resistance of 0.1 wt% Al solder alloy alone is the best. The overall corrosion resistance of Sn–20Bi–0.1Al–0.5Cu is weakened and the corrosion of solder alloy is not uniform.

     

Microstructure and corrosion behaviour of FeCoNiCuSnx high entropy alloys

Abstract

The FeCoNiCuSn_x alloys with different Sn contents are prepared, the microstructure and the corrosion behaviour of the alloys are investigated. When Sn content is lower than 0.09, FeCoNiCuSn_x alloys consist of a single FCC phase. While Sn content of the alloy is 0.09, a small quantity of BCC structure is present. The FeCoNiCuSn_x alloys have a wider passive region in the NaOH solution. FeCoNiCuSn_x alloys exhibit a better corrosion resistance in NaCl solution than 304 stainless steel, the corrosion resistance of FeCoNiCuSn_0.04 alloy is best among all the alloys. The corrosion resistance of FeCoNiCuSn_x alloys in NaOH solution is lower than that of 304 stainless steel, the corrosion resistance of FeCoNiCuSn_0.03 alloy is best among all FeCoNiCuSn_x alloys.