Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

Liquid-solid interface control of BFe10-1-1 cupronickel alloy tubes during HCCM horizontal continuous casting and its effect on the microstructure and properties

Based on horizontal continuous casting with a heating-cooling combined mold （HCCM） technology, this article investigated the effects of processing parameters on the liquid-solid interface （LSI） position and the influence of LSI position on the surface quality, microstructure, texture, and mechanical properties of a BFe10-1-1 tube （φ50 mm × 5 mm）. HCCM efficiently improves the temperature gradient in front of the LSI. Through controlling the LSI position, the radial columnar-grained microstructure that is commonly generated by cooling mold casting can be eliminated, and the axial columnar-grained microstructure can be obtained. Under the condition of 1250℃ melting and holding temperature, 1200-1250℃ mold heating temperature, 50-80 mm/min mean drawing speed, and 500-700 L/h cooling water flow rate, the LSI position is located at the middle of the transition zone or near the entrance of the cooling section, and the as-cast tube not only has a strong axial columnar-grained microstructure （{hkl}〈621〉, {hkl}〈221〉） due to strong axial heating conduction during solidification but also has smooth internal and external surfaces without cracks, scratches, and other macroscopic defects due to short solidified shell length and short contact length between the tube and the mold at high temperature. The elongation and tensile strength of the tube are 46.0%-47.2% and 210-221 MPa, respectively, which can be directly used for the subsequent cold-large-strain processing.

Effect of additives on anode passivation in direct electrolysis process of copper–nickel based alloy scraps

Effects of nickel component,thiourea,glue and chloride ions and their interactions on the passivation of copper–nickel based alloy scrap anodes were investigated by combining conventional electrochemical techniques.Results obtained from chronopotentiometry and linear voltammetry curves showed that the Ni component made electrochemical stability of the anode strong and difficult to be corroded,caused by the adsorption of generated Cu2O,NiO or copper powder to the anode surface.The Ni2+reducing Cu2+to Cu+or copper powder aggravated the anode passivation.In a certain range of the glue concentration≤8×10–6 or thiourea concentration≤4×10–6,the increase of glue or thiourea concentration increases the anode passivation time.Over this range,glue and thiourea played an adverse effect.The increase of chloride ions concentration led to the increase in passivation time.

On the Role of Boric Acid in the Copper-Tin Alloy Bath

The role of boric acid in the copper tin alloy bath has been investigated by means of the cathodic polarization curves,cyclic voltammograms,rate of alloy electrodeposition and morphological analysis of deposits.The results indicate that the presence of boric acid in weak acidic solution for electrodeposition of Cu Sn alloy raises the overvoltage of hydrogen discharge and lowers the overvoltage of Cu,Sn and Cu Sn alloy deposition on the Pt,and accelerates the rate of depostion.Boric acid was adsorbed on the surface of cathode and inhibited reduction of hydrogen,then the adsorbed boric acid promoted electrodeposition of metals as a catalyzator.However,as the concentration of boric acid is more than 0.50 mol/L,the above effect was weakened due to the complexation reaction between the excessive boric acid and metallic ions.

Wear Evaluation of Copper-Nickel-Aluminum Alloys under Extreme Conditions

Cu-Ni-Al alloys at different concentrations were obtained using a high frequency induction melting unit, keeping a balance in the nominal compositions. Light alloys are important to be used in industrial applications. Aluminum additions result in a positive hardness increment of the ternary alloys in comparison with the binary Cu-Ni alloys. Generalized wear mechanisms of the alloys with low aluminum content are basically type abrasive, while samples with 5 and 10 at.% Al present an oxidative-adhesive wear mechanism. Wear results have indicated that aluminum addition affects positively the wear resistance, mainly in samples with high aluminum content product of the creation during the test of different oxides corresponding to the elements present in the alloys.

Inhibition effects of PMA/SbBr_3 complex inhibitor on copper and copper-nickel alloy in LiBr solutions

The effects of PMA/SbBr3 inhibitor on copper and copper-nickel alloy in 55%LiBr solution were investigated by chemical immersion and electrochemical measurements. The results indicate that in boiling 55%LiBr solution containing PMA/SbBr3 inhibitor, corrosion rates of copper and copper-nickel alloy are 67.48μm/a and 38.14μm/a, respectively. Since both anodic and cathodic electrochemical reactions can be inhibited, PMA/SbBr3 belongs to complex inhibitor. PMA has the effect of inhibiting hydrogen evolution and [PMo<sup>12 O<sup>40 ]3- , the anion of PMA, has a strong oxidizing effect. Sb3+ also shows an oxidizing effect. It may exist in LiBr solutions stably with PMA. Because of the synergistic effect of PMA and Sb3+ , a protective film, comprising CuO, Cu2O and Sb, formed on copper and copper-nickel alloy surface may prevent Br-from diffusing to the surface of metals. As a result, the anticorrosion performance of copper and copper-nickel alloy may be improved.

Effects of Fe content on the microstructure and properties of CuN i10FeM n1 alloy tubes fabricated by HCCM horizontal continuous casting

Heating-cooling combined mold（HCCM） horizontal continuous casting technology developed by our research group was used to produce high axial columnar-grained CuN i10 FeM n1 alloy tubes with different Fe contents. The effects of Fe content（1.08wt%–2.01wt%） on the microstructure, segregation, and flushing corrosion resistance in simulated flowing seawater as well as the mechanical properties of the alloy tubes were investigated. The results show that when the Fe content is increased from 1.08wt% to 2.01wt%, the segregation degree of Ni and Fe elements increases, and the segregation coefficient of Ni and Fe elements falls from 0.92 to 0.70 and from 0.92 to 0.63, respectively. With increasing Fe content, the corrosion rate of the alloy decreases initially and then increases. When the Fe content is 1.83wt%, the corrosion rate approaches the minimum and dense, less-defect corrosion films, which contain rich Ni and Fe elements, form on the surface of the alloy; these films effectively protect the α-matrix and reduce the corrosion rate. When the Fe content is increased from 1.08wt% to 2.01wt%, the tensile strength of the alloy tube increases from 204 MPa to 236 MPa, while the elongation to failure changes slightly about 46%, indicating the excellent workability of the CuNi10FeMn1 alloy tubes.

Kinetics of discontinuous precipitation in Cu–20Ni–20Mn alloy

The morphology and growth kinetics of discontinuous precipitation （DP） in a Cu-20Ni-20Mn alloy were investigated in the tem- perature range of523-573 K by optical microscopy, scanning electron microscopy, and transmission electron microscopy. A lamellar mixed structure consisting of alternating larnellae of a matrix and NiMn phase was observed in DP colonies. The volume fraction of regions formed by a DP reaction was determined by quantitative metallographic measurements. The kinetics of DP was evaluated on the basis of the John- son-MehI-Avrami Kohnogorov equation, which resulted in a time exponent of approximately 1.5. We confirmed that the nucleation of the discontinuous precipitate was confined to grain edges or boundaries at an early stage of the reaction. The activation energy of DP process was determined to be approximately （72.7 ± 7.2） kJ/mol based on the Arrhenius equation; this result suggests that DP is controlled by gn-ain boundary diffusion. The hardness values exhibited good correlation with the volume fraction of DP; this correlation was attributed to the plvsence of the ordered N iMn phase.

Laser cladding of Ni-based alloy on copper substrate

The laser cladding of Ni1015 alloy on Cu substrate was prepared by a high power continuous wave CO2 laser. Its microstructure was analyzed by optical microscope （OM）, scanning electron microscope （SEM）, and X-Ray diffraction （XRD）. The average microhardness of the cladding coating was Hv 280, which was almost three times of that of the Cu substrate （Hv 85）. OM and SEM observations showed that the obtained coating had a smooth and uniform surface, as well as a metallurgical combination with the Cu substrate without cracks and pores at the interface. With the addition of copper into the nickel-based alloy, the differences of thermal expansion coefficient and melting point between the interlayer and cladding were reduced, which resulted in low stresses during rapid cooling. Moreover, large amount of （Cu, Ni） solid solution formed a metallurgical bonding between the cladding coating and the substrate, which also relaxed the stresses, leading to the reduction of interfacial cracks and pores after laser cladding.

Effect of compression direction on the dynamic recrystallization behavior of continuous columnar-grained CuNi10Fe1Mn alloy

The dynamic recrystallization（DRX） behavior of continuous columnar-grained（CCG） Cu Ni10Fe1 Mn alloy was investigated by hot compression along the solidification direction（SD） and perpendicular to the solidification direction（PD）. Specimens were compressed to a true strain of 0.8 at temperatures ranging from 25°C to 900°C and strain rates ranging from 0.01 to 10 s-1. The results indicate that DRX nucleation at grain boundaries（GBs） and DRX nucleation at slip bands（SBs） are the two main nucleation modes. For SD specimens, C-shaped bending and zig-zagging of the GBs occurred during hot compression, which made DRX nucleation at the GBs easier than that at the SBs. When ln Z ≤ 37.4（Z is the Zener–Hollomon parameter）, DRX can occur in SD specimens with a critical temperature for the DRX onset of;50°C and a thermal activated energy（Q） of 313.5 k J·mol-1. In contrast, in PD specimens, the GBs remained straight, and DRX nucleation occurred preferentially at the SBs. For PD specimens, the critical temperature is about 700°C, Q is 351.7 k J·mol-1, and the occurrence condition of DRX is ln Z ≤ 40.1. The zig-zagging of GB morphology can significantly reduce the nucleation energy at the GBs; as a result, DRX nucleation occurs more easily in SD specimens than in PD specimens.

化学镀Ni-Sn-P和磁控溅射TiN对Mn-Cu合金耐腐蚀性能和阻尼性能的影响

分别对Mn-Cu阻尼合金表面化学镀1 h和磁控溅射2 h,获得了5.42μm厚的Ni-Sn-P合金层和1.43μm厚的TiN层。对比了Mn-Cu合金及其表面化学镀Ni-Sn-P合金和磁控溅射TiN后的微观形貌、元素组成、结构、耐蚀性和阻尼性能。结果表明,化学镀和磁控溅射都能提高Mn-Cu合金的耐蚀性,Ni-Sn-P合金镀层的耐蚀性最好。化学镀Ni-Sn-P合金能够在一定程度上改善Mn-Cu合金的阻尼性能,而磁控溅射TiN会使基体的阻尼性能轻微下降。

Surface and transport properties of Cu-Sn-Ti liquid alloys

The lack of experimental data and / or limited experimental information concerning both surface and transport properties of liquid alloys often require the prediction of these quantities. An attempt has been made to link the thermophysical properties of a ternary Cu-Sn-Ti system and its binary Cu-Sn, Cu-Ti and SnoTi subsystems with the bulk through the study of the concentration dependence of various thermodynamic, structural, surface and dynamic properties in the frame of the statistical mechanical theory in conjunction with the quasi-lattice theory （QLT）. This formalism provides valuable qualitative insight into mixing processes that occur in molten alloys.

Electrolytic production of Cu-Ni alloys in CaCl_2-Cu_2S-NiS molten salt

An alternative metal/alloy production method,known as direct electrochemical reduction(DER),was introduced for the fabrication of CuNi alloys from mixed sulfides(Cu2S,NiS)under both galvanostatic and potentiostatic conditions.The influences of the process parameters(e.g.,cell voltage and current)on the compositions of the reduced compounds were investigated to yield industrially desirable alloys,namely,CuNi10,CuNi20,and CuNi30.The electrochemical behaviors of Cu2S and NiS in CaCl2 melt were examined at a temperature of 1200°C via cyclic voltammetry(CV).Based on the CV results,the cathodic reduction of Cu2S occurred in one step and cathodic reductions of NiS occurred in two steps,i.e.,Cu2S?Cu for copper reduction and NiS?Ni3S2?Ni for nickel reduction.Galvanostatic studies revealed that it was possible to fabricate high-purity CuNi10 alloys containing a maximum sulfur content of 320×10-6 via electrolysis at 10 A for 15 min.Scanning electron microscopy along with energy-dispersive X-ray spectrometry and optical emission spectroscopy(OES)examinations showed that it was possible to fabricate CuNi alloys of preferred compositions and with low levels of impurities,i.e.,less than 60×10-6 sulfur,via DER at 2.5 V for 15 min.

Air oxidation of Cu-50Ni and Cu-70Ni alloys at 800℃

The air oxidation of Cu Ni alloys with 50% and 70% nickel (mole fraction) at 800?℃ was studied. The kinetic curves for the oxidation of the two alloys are complex and deviate from the parabolic rate law. Typical double layered scales are produced, which consist of a CuO outer layer and an inner layer containing a mixture of Cu 2O and NiO with many pores. Cu 50Ni presents a small degree of internal oxidation of nickel, which is observed in many binary double phase systems, but is quite rare in single phase systems.

Metal Dusting-Mechanisms and Preventions

Metal dusting attacks iron,low and high alloy steels and nickel-or cobalt-base alloys by disintegrating bulk metals and alloys into metal particles in a coke deposit.It occurs in strongly carburising gas atmospheres(carbon activity a_C>1) at elevated temperatures(400℃～1000℃).This phenomenon has been studied for decades,but the detailed mechanism is still not well understood.Current methods of protection against metal dusting are either directed to the process conditions-temperature and gas composition-or to the development of a dense adherent oxide layer on the surface of the alloy by selective oxidation.However,metal dusting still occurs by carbon dissolving in the base metal via defects in the oxide scale.The research work at UNSW is aimed at determining the detailed mechanism of metal dusting of both ferritic and austenitic alloys,in particular the microprocesses of graphite deposition,nanoparticle formation and underlying metal destruction.This work was carried out using surface observation,crosssection analysis by focused ion beam and electron microscopic examination of coke deposits at different stages of the reaction.It was found that surface orientation affected carbon deposition and metal dusting at the initial stage of the reaction.Metal dusting occurred only when graphite grew into the metal interior where the volume expansion is responsible for metal disintegration and dusting.It was also found that the metal dusting process could be significantly changed by alterations in alloy chemistry.Germanium was found to affect the iron dusting process by destabilising Fe_3C but increasing the rate of carbon deposition and dusting,which questions the role of cementite in ferritic alloy dusting.Whilst adding copper to iron did not change the carburisation kinetics,cementite formation and coke morphology,copper alloying reduced nickel and nickel-base alloy dusting rates significantly.Application of these fundamental results to the dusting behaviour of engineering alloys is discussed.

Effect of Solution Heat Treatment in α+β Phase Region on Shape Memory Characteristics of Cu-Al-Ni-Mn-Ti Alloys

The effect of aluminium content and solution heat treatment in α+β phase region on the shape memory characteristics and mechanical properties of cold wrought Cu-Al-Ni-Mn-Ti alloy are studied in this paper. Results indicate that the transformation temperature (Tt) of Cu-Al-Ni-Mn-Ti alloy reduces obviously with the increase of the amount of α-phase. During aging at 623 K, Tt increases at first up to a peak value, then decreases with prolongation of aging time. Life time of heat resistance of the alloy at high temperatures is improved with increase of the amount of α-phase, this life time becomes poor with Bainite precipitation. When the amount of α-phase is less than 5%, the ratio of shape recovery brought about by the solution heat treatment in α+β phase region is almost not effected. However, plasticity of the alloy increases obviously as aluminium content decreases. We believe that improving cold workability of Cu-Al-Ni-Mn-Ti alloy and keeping good heat resistant property and shape memory effects are possible by means of reducing the content of aluminium and solulion heat treatment in α+β phase region.

Effect of grain size on high-temperature oxidation behavior of Cu-80Ni alloy

The thermogravimetric analysis of binary Cu 80Ni alloys prepared respectively by conventional casting(CA) and mechanical alloying(MA) techniques and presenting widely different grain sizes was performed at 800 ℃ in air in order to study the effect of grain size change on the oxidation behavior of a solid solution alloy. The results show that the kinetic curves for the oxidation of the two alloys are complex and deviate from the parabolic rate law and usually are not composed of a single stage. Mixed scales were produced on the CACu 80Ni alloy surface, which consists of a mixture of copper and nickel oxides. However, oxide scale for MACu 80Ni alloy is mainly composed of a thick compact and continuous inner layer of nickel oxide. The reduction in the alloy grain size speeds up the diffusion of the more reactive component nickel from the alloy to alloy/oxide scale interface and completes the transition from a mixed scale to continuous scale of nickel oxide.

Strengthening bulk metallic glasses with minor alloying additions

Cu47Ti34Zr11Ni8, (Cu47Ti34Zr11Ni8)99Si and (Cu47Ti34Zr11Ni8)99Al bulk metallic glass were prepared by copper mold casting method, and the thermal stability, mechanical properties and microstrucrures of them were studied. With minor alloying of Si and Al additions, the glass transition temperature (Tg), crystallization temperature (Txl) and temperature interval of supercooled liquid region△Tx (=Txl-Tg) and reduced glass transition temperature (Trg) were proved to be changed from 672 K, 734 K, 62 K, 0.575 to 691 K, 752 K, 61 K, 0.592 and to 681 K, 729 K, 48 K, 0.590, respectively. The results indicate that the glass-forming ability (GFA) are improved with minor alloying additions. And the bulk glasses also exhibits high three point-bending flexural strength. Because of the additions of Si and Al, three point-bending flexural strength and flexural modulus of the bulk glass change from 2 350 MPa, 102 GPa to 3 260 MPa, 102 GPa and 2 970 MPa, 108GPa respectively. The obvious strengthening is due to the appearance of the medium-range ordered regions with a size of 2-5 nm under the high-resolution TEM image. The reason that the mixed amorphous and nanocrystalline phases caused by minor alloying of Si and Al additions, is that Si or Al is the third kind of elements, which are different from other constituting elements, and there are a strong bonding and atoms size effects between constituting elements, which cause the glass-forming ability (GFA) and the bulk metallic glasses strength improving.

海洋平台海水系统新材料适用性研究

海洋平台利用周围取之不尽的海水作为平台的工艺处理介质已成常规做法。因为海水利用的普通性、经济性以及重要性,对于海水系统选材通常涉及到的使用寿命、制造成本、耐腐蚀性能等多个方面研究值得关注。对常用的几种海水管道材料进行了系统的比较和评价,并介绍了一些新型材料应用前景。在综合考虑各种材料的优劣后,提出了一种最适合海洋平台海水系统的选材方案,并阐述了其理由和依据。旨在为海洋平台海水系统设计和施工提供借鉴。

暖通空调给排水管道的表面改性与性能研究

为提升暖通空调铜合金排水管的表面性能,采用化学镀的方法在铜合金排水管表面制备了Ni-P/TiN镀层,研究镀液中TiN质量浓度对化学镀层物相组成、表面及截面形貌、硬度和耐磨性能的影响。结果表明,无镀层的铜合金基体主要物相为CuZn和CuZn5,表面镀层主要由非晶Ni组成;在基础镀液中适当添加TiN会形成镀层质量较好的含有胞状颗粒的镀层,而过量的TiN添加会使得镀层质量恶化。相较铜合金基体,表面镀层的硬度明显更高,且表面镀层硬度会随着镀液中TiN质量浓度的增加而增大;当TiN质量浓度为10 g/L时,表面镀层的硬度和磨损率分别为633 HV0.1和0.93×10^(-8)g/(r·N),具有相对较好的耐磨性,此时的磨损机制主要为氧化磨损。