Precipitation and aging in high-conductivity Cu–Cr alloys with additions of zirconium and magnesium

Abstract

The precipitation reactions responsible for age hardening in a high-conductivity Cu–Cr–Zr–Mg alloy have been investigated by analytical transmission electron microscopy and compared briefly with the processes that occur in simpler Cu–Cr and Cu–Cr–Mg alloys. Aging at low temperatures (400°C) results in the formation of Guinier–Preston zones. Peak hardness, obtained by aging for 24 h at 450°C, is found to be a result of the fine scale precipitation of an ordered compound, possibly of the Heusler type, with the suggested composition CrCu₂(Zr, Mg). Overaging results in the formation of coarse precipitates of Cr and CU₄Zr. The intergranular precipitate which forms in the Cu–Cr–Zr–Mg alloy is Cu₄Zr. This phase precipitates both as discrete particles on the grain boundaries and as thin ( ~ 5 nm) continuous intergranular films.

MST/89     

Effects of Cr,Mn, Si,Cu and Zr on microstructure and mechanical properties of high carbon Fe–16Al alloy

Abstract

Effects of alloying elements Cr, Mn, Si, Cu and Zr on the microstructure and mechanical properties of Fe₃Al (Fe–16Al) based alloy containing ～0·5 wt-%C have been investigated. Six alloys were prepared by a combination of air induction melting with flux cover and electroslag refining (ESR). ESR ingots were hot forged and hot rolled at 1373 K and were further characterised with respect to microstructure and mechanical properties. The base alloy and the alloys containing Cr, Mn, Si and Cu exhibit a two phase microstructure of Fe₃AlC_0·5 precipitates in Fe₃Al matrix whereas the alloy containing Zr exhibits a three phase microstructure, the additional phase being Zr rich carbide precipitates. Cr and Mn have high solubility in Fe₃AlC_0·5 precipitates as compared to Fe₃Al matrix whereas Cu and Si have very high solubility in Fe₃Al matrix compared to Fe₃AlC_0·5 precipitate and Zr has very low solubility in both Fe₃Al matrix and Fe₃AlC_0·5 precipitate. No significant improvement in room and high temperature (at 873 K) strengths was observed by addition of these alloying elements. Furthermore, it was observed that addition of these alloying elements has resulted in poor room and high temperature ductility. Addition of Cr, Mn, Si and Cu has resulted in marginal improvement in creep life, whereas Zr improved the creep life significantly from 22·3 to 117 h.     

Cu-15Cr-0.1Zr原位复合材料中纤维相的组织演变

通过感应熔炼、铸造、锻造和冷拔变形制备了Cu-15Cr-0.1Zr原位复合材料.采用SEM和TEM观察分析纤维相组织形态的演变.在较低的应变量下纤维保持着与铸态树枝晶相同的bcc单晶结构,在较高的应变量下,单根Cr纤维被分隔为一些由亚晶界组成的亚结构,相邻亚晶的偏差角在5～30°之间.     

Microstructure and bond strength of Ni–Cr steel/Al2O3 joints brazed with Ag–Cu–Zr alloys containing Sn or Al

Abstract

Sintered Al₂O₃ was joined to Ni–Cr steel by the active metal brazing route with Ag–Cu–Zr brazing alloys containing Sn or Al. A single ZrO₂ layer with a monoclinic structure was formed at the Al₂O₃ /brazement interface by the migration of Zr in the molten brazing alloy to the Al₂O₃ surface, followed by a redox reaction between the Al₂O₃ and Zr. The remainder of the brazement formed a Cu–Ag eutectic alloy. Precipitates CuZr₂ and Cu–Zr–Al were formed in the brazements of the Ni–Cr steel/ Al₂O₃ joints brazed with Ag–Cu–Zr alloys and Al containing Ag–Cu–Zr alloys, respectively. On the other hand, no precipitates were formed in the brazement of the Ni–Cr steel/Al₂O₃ joints brazed with Sn containing Ag–Cu–Zr alloys. The Ni–Cr steel/ Al₂O₃ joints brazed with Sn containing Ag–Cu–Zr alloys showed much higher fracture shear strengths than those brazed with Ag–Cu–Zr alloys or Al containing Ag–Cu–Zr alloys.     

Effect of Sc and Zr alloying on microstructure and precipitation evolution of as cast Al–B4C metal matrix composites

Abstract

Additions of Sc and Zr were introduced into Al–15 vol.-%B₄C composites, and eight experimental composites with different Sc and Zr levels were prepared via a conventional cast process. Optical microscopy, SEM and TEM were applied for observing the as cast microstructures, including the interfaces between the Al matrix and the B₄C as well as the evolution of the precipitates. It was found that Sc involved the interfacial reactions with B₄C that partially consumed the Sc. On the other hand, no major Zr reaction products were found in the interfaces, and the major part of Zr remained in the matrix for precipitation strengthening. The Sc addition yielded considerable precipitation strengthening in the as cast and peak aged conditions. The combination of Sc and Zr significantly enhanced the precipitation strengthening. Nanoscale precipitates Al₃Sc and Al₃(Sc,Zr) were found in the as cast microstructure and contributed to the significant increase of matrix hardness.     

Solidification Studies of 3003 Aluminium Alloys with Cu and Zr Additions

The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.     

Mechanical properties and cyto-toxicity of new beta type titanium alloy with low melting points for dental applications

Beta stabilized new alloys such as Ti–29Nb–13Zr–2Cr, Ti–29Nb–15Zr–1.5Fe, Ti–29Nb–10Zr–0.5Si, Ti–29Nb–10Zr–0.5Cr–0.5Fe and Ti–29Nb–18Zr–2Cr–0.5Si have been developed for dental applications. These alloys were designed based on master alloy Ti–29Nb–13Ta–4.6Zr (TNTZ) for biomedical applications. In this research, high melting temperature element Ta was replaced with beta stabilizing elements such as Cr, Fe and Si to lower the melting temperature of the alloy.Their melting points, mechanical properties, surface reaction layers and cyto-toxicity were investigated in this study.Melting points of designed alloys fall by about 50 K to 370 K as compared with that of TNTZ, and Ti–29Nb–13Zr–2Cr has the lowest melting point of around 2050 K. Vickers hardness of the surface of each designed alloy cast into modified magnesia based investment material is in the range of 400 Hv to 500 Hv, which is lower than that of TNTZ (around 560 Hv).Balances of strength and ductility of cast Ti–29Nb–13Zr–2Cr, Ti–29Nb–15Zr–1.5Fe and Ti–29Nb–10Zr–0.5Cr–0.5Fe are nearly equal to that of cast TNTZ.Cell viability of each cast designed alloy is excellent.     

Precipitation characteristics of Cu–15Cr–0·15Zr in situ composite

Abstract

The precipitation characteristics of Cu–15Cr–0·15Zr in situ composite made by cold drawing have been studied using analytical TEM and hardness measurement. It has been observed that the in situcomposite reaches peak hardness at a lower aging temperature than the corresponding alloy which is not subjected to cold working prior to aging treatment. The Cr rich precipitates in the peak aged composite are much smaller than those in the peak aged alloy. Under peak aging conditions, precipitation free zones adjacent to the grain boundaries of the Cu matrix are also observed in both the alloy and the composite. The addition of Zr enhances the precipitation hardening effect in the alloy and the composite. The major mechanism of this enhancement may be through increasing the Cr rich precipitate nucleation rate and precipitate/matrix interfacial energy.     

Improve stress corrosion cracking resistance and mechanical properties of Al‐Zn‐Mg‐Cu‐Zr alloy with heterogeneous lamellae structure produced by high pressure torsion

High pressure torsion experiment followed with heat treatment were carried out on as‐cast Al‐Zn‐Mg‐Cu‐Zr alloy at 400 °C under the pressure of 1 GPa. The microstructure, mechanical property and stress corrosion resistance properties for the as‐cast and high pressure torsion processed samples were studied. The results show that high pressure torsion processing can improve the mechanical property by the refinement of grains and grain boundary precipitates, as well as the homogeneous distribution of fine matrix precipitates. On the other side, the grain refinement, broken of coarse grain boundary precipitates and narrowed precipitates free zone caused by the high pressure torsion result in the improvement of stress corrosion cracking resistance. And due to the influence of heterogeneous lamellae structure, the sample after 0.5 high pressure torsion turn shows preferable mechanical property and stress corrosion cracking resistance than the sample after 2 high pressure torsion turns.     

Tensile and fatigue properties of a cast aluminum alloy with Ti, Zr and V additions

The development of aluminum alloys for automotive powertrain applications is in high demand due to the required weight reduction and fuel efficiency. The aim of this study was to evaluate the microstructure and mechanical properties of a newly developed Al-7%Si-1%Cu-0.5%Mg cast alloy with further additions of Ti, Zr and V. The microstructure of the alloys consisted of Al dendrites surrounded by Al-Si eutectic structures with Mg/Cu/Fe-containing Si particles, and contained nano-sized trialuminide precipitates in the Ti/Zr/V added alloys. The alloys had a significantly (60-87%) higher yield strength but lower ductility than A356-T6 and 319-T6 alloys. With the addition of Ti/Zr/V both monotonic and cyclic yield strengths increased, but ductility and hardening capacity decreased due to reduced dislocation storage capacity caused by stronger interactions between dislocations and trialuminide precipitates. The Zr/V-modified alloy had a longer fatigue life, and all the alloys exhibited cyclic stabilization at low strain amplitudes and cyclic hardening at higher strain amplitudes. With increasing strain amplitude, the extent of cyclic hardening increased. Both cyclic yield strength and cyclic strain hardening exponent were higher than the corresponding monotonic yield strength and strain hardening exponent, indicating that a stronger cyclic hardening ability of the alloys developed. Fatigue cracks were observed to initiate at near-surface defects, and crack propagation was mainly characterized by the formation of fatigue striations together with secondary cracks.     

Microstructural investigations on as-cast and annealed Al–Sc and Al–Sc–Zr alloys

Al–Sc and Al–Sc–Zr alloys containing 0.05, 0.1 and 0.5 wt.% Sc and 0.15 wt.% Zr were investigated using optical microscopy, electron microscopy and X-ray diffraction. The phase composition of the alloys and the morphology of precipitates that developed during solidification in the sand casting process and subsequent thermal treatment of the samples were studied. XRD analysis shows that the weight percentage of the Al₃Sc/Al₃(Sc, Zr) precipitates was significantly below 1% in all alloys except for the virgin Al0.5Sc0.15Zr alloy. In this alloy the precipitates were observed as primary dendritic particles. In the binary Al–Sc alloys, ageing at 470 °C for 24 h produced precipitates associated with dislocation networks, whereas the precipitates in the annealed Al–Sc–Zr alloys were free of interfacial dislocations except at the lowest content of Sc. Development of large incoherent precipitates during precipitation heat treatment reduced hardness of all the alloys studied. Growth of the Al₃Sc/Al₃(Sc, Zr) precipitates after heat treatment was less at low Sc content and in the presence of Zr. Increase in hardness was observed after heat treatment at 300 °C in all alloys. There is a small difference in hardness between binary and ternary alloys slow cooled after sand casting.     

Composite precipitates in a commercial Al–Li–Cu–Mg–Zr alloy

Composite precipitates with duplex and triplex association of single precipitates commonly found in commercial Al–Li alloys were observed by transmission electron microscopy (TEM) in a re-solution and quenched AA2090 alloy after aging. These novel precipitates were the duplex association of δ′(Al₃Li) and T₁ (Al₂CuLi) as well as the triplex δ′/β′(Al₃Zr)/T₁ and δ′/β′/θ′(Al₂Cu). The reduction of elastic energy associated with composite precipitate formation is suggested as a basic mechanism with plate-like T₁ and θ′ particles serving as preferential sites for nucleation of either δ′ or δ′/β′ spherical particles, which although in much smaller numbers, represent a volume fraction of 10 to 20% of all precipitates.     

Mechanical properties of Cu–Cr system alloys with and without Zr and Ag

The effects of addition of Zr and Ag on the mechanical properties of a Cu–0.5 wt%Cr alloy have been investigated. The addition of 0.15 wt%Zr enhances the strength and resistance to stress relaxation of the Cu–Cr alloy. The increase in strength is caused by both the decrease in inter-precipitate spacing of Cr precipitates and the precipitation of Cu₅Zr phase. The stress relaxation resistance is improved by the preferentially forming Cu₅Zr precipitates on dislocations, in addition to Cr precipitates on dislocations. The addition of 0.1 wt%Ag to the Cu–Cr and Cu–Cr–Zr alloys improves the strength, stress relaxation resistance and bend formability of these alloys. The increase in strength and stress relaxation resistance is ascribed to the decrease in inter-precipitate spacing of Cr precipitates and the suppression of recovery during aging, and to the Ag-atom-drag effect on dislocation motion. The better bend formability of the Ag-added alloys is explained in terms of the larger post-uniform elongation of the alloys.     

Structure of centrifugally cast austenitic stainless steels: Part 2 Effects of Nb,Ti, and Zr

Abstract

The microstructures of several centrifugally cast stainless steels containing strong carbide formers (Nb, Ti, and Zr) have been examined as cast and after prolonged creep in the range 800–1000°C. These additions refine the eutectic carbide, changing the morphology and composition as illustrated by the behaviour of IN 519 (Fe–Ni–Cr–Nb) and IN 519 TZ (Fe–Ni–Cr–Nb–Ti–Zr). The carbides present have been identified by electron diffraction and by energy-dispersive X-ray analysis. During creep, the precipitation of both MC and M₂₃C₆ carbides was observed, the former being very much finer and very resistant to coarsening. The role of both the grain-boundary carbide networks and the matrix precipitation in determining the creep properties is discussed.

MST/136     

Preparation of Cu-based Bulk Metallic Glass Matrix Composites

Cu47Ti34Zr11Ni8 bulk metallic glass （BMG） matrix composites containing in situ formed TiC particles and 5-TiCu dendrite phase were developed by copper mold cast. The thermal stability and microstructure of the composites are investigated. Room temperature compression tests reveal that the composite samples exhibit higher fracture strength and distinct plastic strain of 0.2%-0.5%, comparing with that of the corresponding Cu47Ti34Zr11Ni8 monolithic BMG.     

Fabrication of Cu rich bulk metallic glass composites via solidification method

Abstract

Cu based bulk metallic glasses and composites with tiny crystalline phases embedded in metallic glass matrix have been successfully fabricated by solidification technique in the present work. The formation of crystalline phases and structure inhomogeneity in bulk metallic glasses was characterised. Al is used as the minor alloying element to partly substitute Cu element in 61Cu–34Zr–5Ti. The results show that quarternary 60Cu–34Zr–5Ti–1Al alloy exhibits monoamorphous feature, and 56Cu–34Zr–5Ti–5Al alloy has a few crystalline peaks superimposed on a broad diffraction peak, suggesting that a composite structure forms in certain solidification conditions. To further identify the microstructure of the as cast rod, all samples were characterised by scanning electron microscopy (SEM). Small size phases are found in 2 mm diameter 56Cu–34Zr–5Ti–5Al rod, which has larger plastic deformation. The composition of those crystalline phases is also investigated. All results indicate that the presence of certain phases in metallic matrix benefits the mechanical properties of the as cast bulk metallic glasses.     

Effects of Mn and Cu on the Mechanical Properties of a High Strength Low Alloy NiCrMoV Steel

The present study focuses on the effects of Mn and Cu on the mechanical properties, in particular, strength and toughness of a low alloy steel containing Ni, Cr, Mo and V. Specimens with different amounts of Mn (0.23%-0.85%) and Cu (0.15%-0.45%) were cast and forged, and then austenitized at 870℃for 1 h, followed by oil quenching. All specimens were tempered at 650℃for 1 h. The results show that as the amounts of Mn and Cu increase respectively from 0.35% to 0.85% and from 0.15% to 0.45%, the yield and tensile strength increase. The highest impact energies were observed in the specimen with 0.35% Mn and in the specimen with 0.25% Cu. The impact energy decreases with increasing the Mn and Cu from 0.35% to 0.85% and from 0.25% to 0.45%, respectively. Furthermore, the variation of Mn and Cu does not cause a considerable change in the tempered martensite microstructure. The optimum strength and toughness is observed in 0.35% Mn containing steel and in the 0.25% Cu containing steel.     

The influence of Nb,Ti, and Si additions on the liquidus and solidus temperatures and primary microstructure refinement in 0.3C-30Ni-18Cr cast steel

This study explores the effect of niobium, titanium and silicon on the liquidus and solidus temperatures and primary structural refinement in creep-resistant 0.3C-30Ni-18Cr cast steel. Fifteen test alloys were investigated. The concentrations of niobium, titanium and silicon in these alloys ranged from 0.03 to 3.0 wt.%, 0.03 to 1.42 wt.%, and 1.39 to 4.26 wt.%, respectively. It was found that an increase of these elements in 0.3C-30Ni-18Cr cast steel lowered the beginning and ending temperatures of the solidification process, extended the range of solidification temperatures, reduced the density, and refined the microstructure, i.e., reduced the secondary dendrite arm spacing. Alloys with the highest content of the examined elements were reported to contain carbide precipitates, as well as the G phase in an as-cast state.     

Phase transformation in Cu-Cr-Zr-Mg alloy

After solid solution treatment, the effects of aging processes on the microstructure and electrical conductivity of Cu-Cr-Zr-Mg lead frame alloy were investigated in order to determine the phase transformation and the time-temperature-transformation (TTT) behavior. The results show that aged at 470 °C the fine precipitation of an ordered CrCu₂(Zr,Mg) phase is found in copper matrix as well as fine Cr and Cu₄Zr, aged at 550 °C the phase CrCu₂(Zr,Mg) is decomposed into Cu₄Zr and Cr phase, aged at 600 °C the precipitates is bcc Cr only. The phase transformation kinetics equation was deduced from the Avrami empirical formula based on the linear relationship between the electrical conductivity and the volume fraction of the phase transformation.     

合金元素对 Nb2Mo2Si合金相平衡及Nb2 Nb 5Si 3共晶组织形态的影响

采用电弧熔炼法制备了 Nb220Si210Mo、Nb220Si210Mo23M (M = Cr , Al , Ti) (原子分数) 四种 Nb2Mo2Si基超高温合金。利用 SEM、EDS、XRD等实验技术对铸造合金的相组成与组织形态进行了观察和分析。Nb220Si210Mo 合金由铌固溶体 (Nb SS) 与βNb 5Si 3化合物两相构成 , 其铸造组织包含大量片层状共晶 (Nb SS 2βNb 5Si 3) 组织。少量合金元素 Cr (3 at %) 能够改变 Nb220Si210Mo 合金的相平衡关系 , Nb220Si210Mo23Cr 的铸造组织中不仅存在 Nb SS和βNb 5Si 3 , 而且还出现少量 Cr 2Nb相 ; 而添加合金元素 Al、Ti (3 at %) 并不改变 Nb220Si210Mo 合金的相平衡关系。添加 Cr 使 Nb SS 2 βNb 5Si 3共晶组织失去了平直片层特征 ; Al 有利于共晶组织中片层状共晶形成 ; 添加 Ti使共晶组织呈现羽毛状特征。合金化使 Nb与βNb 5Si 3的晶格常数发生变化 : Nb的晶格常数均变小; Nb220Si210Mo23Cr合金中βNb 5Si 3的 c/ a值减小 , 其它 3种合金中βNb 5Si 3的 c/ a值增大。