Instrumented indentation properties of electrodeposited Ni–W alloys with different microstructures

The microstructures and mechanical properties electrodeposited Ni–W alloys synthesized at two plating bath temperatures of 353 and 348 K were investigated. Whereas the 353 K sample is amorphous, the 348 K sample has a mixed amorphous-nanocrystalline structure. As a result, the strength of the 348 K sample exhibits strong strain rate dependence during nanoindentation.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.     

Numerical modeling of damping capacity of Zn-Al alloys with fully lamellar microstructures

The damping behaviors of Zn-Al alloys with fully lamellar microstructures were simulated with the cell method. The influences of the grain boundary condition, the strain amplitude, the number of the lamellae in the grain （N） and the content ratio of Zn and Al in Zn-Al alloys on the damping capacity were investigated. The results indicate that the grain boundary condition has great influence on the damping capacity of Zn-Al alloys, and also affects the relationship between the damping capacity and the number of lamellae （N）. The variation of damping capacity with the strain amplitude is increasing exponentially with the strain amplitude and the damping capacity increases with the increasing of content of Zn.     

Influence of La on microstructures of hypereutectic Al-Si alloys

1　INTRODUCTIONThemicrostructureofhypereutecticAl Sialloys ,preparedbyconventionalcastingroutines ,usuallyconsistsofcoarseSicrystals[112 ] ,leadingtothepoorextrudability ,machinability ,strengthandductili ty[1315] .Therefore ,structuralmodificationmustbedonethroughtwo generalways :1)alloyingaddi tions ,and /or ;2 )syntheticalternatives .Accordingtothedimensionalconditionofaneffectivemodifier ,theradiusratiooftheagenttoSishouldbeabout1.6 5 [16 ] ,La ,withtheratioof 1.5 9,ispossiblycon sid…     

Effect of Lanthanum and Yttrium on Microstructures of Cu-Cr alloys

Microstructures of Cu-based alloys (including Cu0.8Cr0.05La, Cu0.8Cr0.1La, Cu0.8Cr0.4La, Cu0.8Cr0.05Y,Cu0.8Cr0.1Y and Cu0.8Cr0.4Y) were studied by optical microscope, X-ray diffractometer, Scanning electron microscope and Energy-dispersive X-my spectroscopy. The results show that La and Y refine the grains and change the distribution of microstructures of Cu-Cr alloys. The sizes of Cr particles are smaller in CuCrRE alloys than in CuCr alloy. In CuCrLa and CuCrY alloys, La and Y usually respectively, exist as compounds of Cu6La and Cu5Y. These compounds distribute in the grains with sphere shape and on the grain-boundaries with slice shape.     

Tensile and fracture properties of Ti-62A alloy plate with different microstructures

Ti-62A alloy plates with three different types of microstructure,fully equiaxed,bimodal,and Widmanst(a)tten,were obtained by various heat treatments to investigate the effects of microstructure on the tensile and fracture properties at room temperature.The results reveal that Widmanst(a)tten microstructure exhibits good damage tolerance behavior considering strength,fracture toughness,and fatigue crack growth behavior,while the bimodal microstructure shows good comprehensive properties considering the plasticity synthetically.Optical microscopy (OM) and scanning electron microscopy (SEM) microstructure analyses on fracture and fatigue crack path demonstrate that the dependence of mechanical properties and fatigue crack growth behavior on microstructural feature are attributed to the α lamellae width and the α colony size.     

Liquid phase separation of Cu-Cr alloys during rapid cooling

1 Introduction Cu-Cr alloys containing 20%- 50%Cr have been widely investigated because they are the most important contact materials used in high voltage vacuum switches. It has been well known that the smaller the Cr particles in Cu-Cr alloys are, the b…     

Effects of electromagnetic stirring on microstructures of solidified aluminum alloys

1　INTRODUCTIONPractically ,mechanicalstirringandelectromag neticstirring (EMS)arewidelyusedtogenerateforcedflowinsolidificationandcastingofmetalsandalloys,resultingin greatchangesofthesolidifiedstructures,segregationsand propertiesofthecast ings .Muchattentionhasbeenpaidtosolidificationofdendriticalloyssuperposedwithforcedflow ,andmanypreviousworkshavebeenfocusedontheeffectsoffluidflowonthestructuraltransitions,suchascolumnar equiaxedtransitions(CET)ormacro segre gationinthealloys[13] .…     

Solidification characteristics of high Nb-containing γ-TiAl-based alloys with different aluminum contents

The effect of Al content on the microstructure and solidification characteristics of Ti–Al–Nb–V–Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction(XRD), scanning electron microscopy(SEM) equipped with energy dispersive spectroscope(EDS), and transmission electron microscopy(TEM). The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47Al7Nb2.5V1.0Cr(at%) alloy solidifying through the peritectic reaction. The b-solidifying Ti46Al7Nb2.5V1.0Cr(at%) alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous finegrained microstructure. However, the crystallization temperature range of Ti48Al7Nb2.5V1.0Cr(at%) alloy is equivalent to that of Ti46Al7Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.     

Succession law of Nd–Fe–B alloys with different coercivities

In order to establish a succession law of every phase in sintered Nd–Fe–B magnets marked as 38/38H/38SH/38 UH, four alloys of Nd33-xDyxAl0.7Nb0.6Cu0.1B1.05 Fe bal.(at%) were investigated after smelting processing, sintering processing, high-temperature tempering processing, and highand low-temperature tempering processing. It is found that the four phases: the Nd2Fe14B matrix phase, Nd-rich phase,B-rich phase, and defect phase can be inherited by means of the subsequent processing. These phases might have the special constitution and appearance in the different states.Magnetic properties also have succession law. In every processing except smelting one, the values of remanence and maximum energy product hardly alter, but the value of coercive force increases gradually.     

粉末冶金Cu-Cr合金在0.1MPa纯氧气中的氧化

研究了具有均匀两相组织的粉末冶金Ｃｕ－２５Ｃｒ和Ｃｕ－５０Ｃｒ合 ０．１ＭＰａ氧气中的氧化。与组织不均的铸态Ｃｕ－Ｃｒ合金相似,氧化后两种成分的粉末冶金Ｃｕ－Ｃｒ合鑫匀形成了复杂的混合氧化膜,但未形成连续的Ｃｒ２Ｏ３层。而经机械合经法获和的铬颗粒大小在１μｍ左右的Ｃｕ－２０Ｃｒ合金,氧化时则形成了连续的Ｃｒ２Ｏ３层。档见,在二元双相合金中,合 氧化行为与合金的组织形态,大小和分布密切相关。     

High temperature oxidation of powder metallurgy two-phase Cu-Cr alloys under low oxygen pressure

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭａｎｙｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓｆｏｒｈｉｇｈｔｅｍｐｅｒａｔｕｒｅａｐｐｌｉｃａｔｉｏｎｓｃｏｎｔａｉｎｔｗｏｏｒｍｏｒｅｍｅｔａｌｌｉｃｐｈａｓｅｓ,ｓｕｃｈａｓＮｉｏｒＣｏｂａｓｅｓｕｐｅｒａｌｌｏｙｓ,ａｎｄｈａｖｅｄｉｆｆｅｒｅｎｔｃｏｒｒｏｓｉｏｎｂｅｈａｖｉｏｒｓｗｉｔｈｒｅｓｐｅｃｔｔｏｔｈｅｃｏｍｍｏｎｓｉｎｇｌｅｐｈａｓｅａｌｌｏｙ[1].ＣｕＣｒａｌｌｏｙｓａｒｅｉｄｅａｌｓｙｓｔｅｍｓｔｏｓｔｕｄｙｈｉｇｈｔｅｍｐｅｒａｔｕｒｅｃｏｒｒ…     

Microstructural effects on the high temperature oxidation of two-phase Cu-Cr alloys in 1 atm O2

The oxidation of a Cu-Cr alloy containing about 60 wt% Cr and of two Cu-Cr alloys containing about 40 wt% Cr was studied at 700 and 800 °C in 1 atm O₂. The 60 wt% Cr alloy was prepared by powder metallurgy (PM) and had a phase particle size of 50-150 μm. One of the two alloys containing about 40 wt% Cr was prepared by mechanical alloying (MA) and had a phase grain size ranging from 10-50 nm to 200-300 nm, depending on the location, while the other was prepared by magnetron sputtering (MS) and had a phase grain size around 5-10 nm. The most important difference between the oxidation behavior of the three alloys is the formation of an exclusive chromia scale on the surface of the Cu-40 wt% Cr alloy prepared by magnetron sputtering and of a continuous chromia layer beneath an outermost layer of copper oxides on the corresponding alloy prepared by mechanical alloying, while the Cu-60 wt% Cr alloy prepared by powder metallurgy formed complex scales composed mostly of CuO, Cu₂O with some Cu₂Cr₂O₄ and Cr₂O₃. Thus, the microstructure of two-phase binary alloys has a strong effect of their oxidation behavior. In particular, a decrease of the alloy grain size favors the exclusive external oxidation of the most reactive component, reducing the corresponding critical content in the alloy. This effect is attributed to the presence of larger concentrations of rapid diffusion paths for the migration of the components in the alloy as well as to a faster dissolution of the particles of the Cr-rich phase in the copper matrix.     

The air oxidation of two-phase Cu-Cr alloys at 700–900°C

The oxidation in air of three two phase Cu-Cr alloys with nominal Cr contents of 25, 50, and 75 wt. % was studied at 700–900°C. The alloys corroded nearly parabolically, except at 900°C, when the corrosion rates decreased with time more rapidly than predicted by the parabolic rate law. The corrosion rate decreased for higher Cr contents in the alloy under constant temperature and generally increased with temperature for the same alloy composition. The scales were complex and consisted in most cases of an outermost copper oxide layer free from chromium and an inner layer composed of a matrix of copper oxide or of the double oxide Cu₂Cr₂O₄, often containing particles of chromium metal surrounded by chromia and then by the double oxide. Metallic copper was also frequently mixed with chromia. Cr-rich regions tended to form continuous chromia layers at the base of the scale, especially at the highest temperature. No chromium depletion was observed in the alloy.     

合金化和形变处理对Cu-Mg-Te-Y合金组织性能的影响

制备具有高强高导性能的铜合金,研究添加Mg和微量的Y对合金的组织和性能的影响。通过变形和退火等工艺处理后,Cu-0.47Mg-0.2Te-0.04Y合金的性能指标可达到：抗拉强度510 MPa,伸长率11%,导电率大于63% IACS。稀土元素Y的熔体净化作用、细晶强化作用和添加适量Mg产生的固溶强化作用能够提高合金的力学性能和导电率。     

Oxidation of molybdenum-tungsten-chromium-silicon alloys

The oxidation kinetics of (50–60) wt.% Mo-(35–47) wt.% Cr-(2–5) wt.% Si and (30–40) wt.% Mo-(30–40) wt.% W-(27–37) wt.% Cr-(0–3) wt.% Si alloys were studied between 1000 and 1200°C in a pure oxygen atmosphere. The oxidation of Mo-W-Cr-Si alloys resembled that of Mo-Cr-Si alloys but was much more oxidation resistant. In general, oxidation resistance increased with increasing Cr and Si content. Alloys with good oxidation behavior had a thin outer Cr₂O₃ layer and an internal oxidation zone (in both Mo and Mo-W alloys). Alloys displaying poor oxidation behavior had a porous Cr₂O₃ layer (in Mo alloys) or layers of oxides of W and Cr (in Mo-W alloys). Although the alloy systems were not truly oxidation resistant, definite improvement in oxidation resistance was achieved.     

Oxidation of iron-nickel aluminum alloys in oxygen at 600–800° C

The oxidation behavior of iron-nickel-aluminum alloys containing 0–40 wt.% nickel and 0–30 wt.% aluminum has been investigated at 600 and 800° C. Through the construction of oxide maps it can be shown that three possible oxide morphologies may exist: Alloys containing less than approximately 5 wt.% aluminum form scales consisting of predominantly Fe₂O₃ and spinel; alloys with between 5 and 10 wt.% aluminum form Al₂O₃ scales interspersed by Fe₂O₃ nodules, and alloys with greater than 10 wt.% aluminum form predominantly -Al₂O₃ scales.     

Cu-Cr合金在H_2-H_2S混合气中的腐蚀行为

研究了Cu Cr合金及纯铜、纯铬在 5 0 0～ 60 0℃ ,硫分压为 10 -5Pa时的硫化腐蚀。两种Cu Cr合金的腐蚀速度均介于两种纯金属之间 ,并随温度的升高而增大 ,但在两种Cu Cr合金的表面均形成了复杂的腐蚀产物膜 ,外层为Cu2 S层 ,有时不连续甚至剥落 ,中间层为二元Cu Cr硫化物CuCrS2 ,内层为二元Cu Cr硫化物Cu Cr2 S4和CrS的混合物 ,有时也包含未被腐蚀的金属铬颗粒。在腐蚀区以下的合金基体中没有铬的贫化现象发生。这种腐蚀膜结构的形成是合金中存在两相的结果     

Fabrication and characteristics of magnesium alloys produced via powder metallurgy

1　ＩＮＴＲＯＤＵＣＴＩＯＮＭａｇｎｅｓｉｕｍａｌｌｏｙｓ ,ｅｓｐｅｃｉａｌｌｙＭｇｍａｔｒｉｘｃｏｍ ｐｏｓｉｔｅｓ ,ａｒｅｅｘｃｅｌｌｅｎｔｃａｎｄｉｄａｔｅｓｆｏｒｅｎｇｉｎｅｅｒｉｎｇｌｉｇｈｔｓｔｒｕｃｔｕｒａｌｍａｔｅｒｉａｌｓｂｅｃａｕｓｅｏｆｔｈｅｉｒｈｉｇｈｓｐｅｃｉｆｉｃｓｔｉｆｆ ｎｅｓｓａｎｄｓｐｅｃｉｆｉｃｓｔｒｅｎｇｔｈ ,ｇｏｏｄｄｉｍｅｎｓｉｏｎａｌｓｔａｂｉｌｉｔｙａｎｄｈｉｇｈｄａｍｐｉｎｇｃａｐａｃｉｔｙ .Ｔｈｕｓ ,Ｍｇａｌｌｏｙｓａｒｅｅｘ ｐｅｃｔｅｄｉｎａｄ…     

Oxidation of molybdenum-chromium-palladium alloys

Isothermal and cyclic oxidation studies have been carried out on (80–90) wt.% Mo-(8–17) wt.% Cr-(0.5–3) wt.% Pd alloys in atmospheres of both air and pure oxygen at temperatures between 1000 and 1250°C. The Pd additions decreased the oxidation rate with the most pronounced effect being observed for an alloy of 80 wt.% Mo-17 wt.% Cr-3 wt.% Pd. Palladium played a major role in providing the necessary oxidation protection by accelerating the formation of Cr₂O₃ layers at low Cr concentrations. Contrary to the behavior of most metals, an increase in oxidation resistance with increase in temperature was observed. Although the alloy systems were not truly oxidation resistant, definite improvement in oxidation resistance was achieved. The oxidation mechanism of Mo-Cr-Pd alloys is described.