Microstructure study of the hardening mechanism of Cr–Ni alloy deposits after flame heating for a few seconds

Cr–Ni alloy deposits with different chemical compositions could be obtained from a bath with trivalent Cr and divalent Ni ions. With a plating current density above 20 A dm^? 2, amorphous Cr-rich alloy deposits were obtained, and crystalline Ni-rich deposits were achieved with an electroplating current density lower than 15 A dm^? 2. The hardness of the Ni-rich deposit decreased gradually with increasing flame-heating time. On the contrary, the hardness of Cr-rich alloy deposit could be significantly increased from 550 Hv to 1450 Hv after flame heating for 3 s. The results of a microstructure study show that the precipitation of nano-sized carbon-related particles, possibly diamond-like particles, could be the main hardening mechanism of flame-heated Cr-rich alloy deposit. These particles have particularly high hardness values, and they distort the nearby Cr-rich lattice, which leads to obvious strain fields in the flame-hardened Cr-rich alloy deposits.     

Increasing the wear and corrosion resistance of magnesium alloy (AZ91D) with electrodeposition from eco-friendly copper- and trivalent chromium-plating baths

Mg alloy, AZ91D, which has a two-phase structure, was successfully electroplated in an alkaline Cu-plating bath. The Cu-coated Mg alloy specimen was further electroplated in eco-friendly acidic Cu and then trivalent Cr baths to obtain an anti-wear and anti-corrosion Cr/Cu coating. Experimental results show that the wear and corrosion resistance of the Mg alloy specimen was considerably improved by trivalent Cr electrodeposition. The hardness of the as-plated Cr deposit was drastically increased by using reduction-flame heating for 0.5 s. The above-mentioned results were measured via bonding strength, hardness, wear and corrosion tests. A superior wear and corrosion resistance was obtained when a Cu-coated Mg alloy specimen was electroplated with a trivalent Cr deposit, followed by heating with reduction-flame heating for 0.5 s.     

The structure and properties of electroless Ni–Mo–Cr–P coatings on copper alloy

In the present study, the quaternary Ni–Mo–Cr–P alloy coatings were deposited on copper alloy by an electroless deposition process. Crystallization behavior and the effect of heat‐treatment on hardness and corrosion resistance of Ni–Mo–Cr–P deposits were detailedly investigated. X‐ray diffraction (XRD) analysis shows that as‐deposited Ni–Mo–Cr–P coatings are Ni–Mo–Cr–P solid solution and mixed crystal structure; the trend of microcrystallinity increases with the introduction of additional types of metal element; Ni–Mo–Cr–P alloy coatings start to occur in the crystallization with the heat‐treatment temperature increasing. With an increase in the annealing temperature, the hardness improves and reaches the maximum value at 500 °C. Further, it is found that Ni–Mo–Cr–P coatings have superior corrosion resistance than Ni–P and Ni–Mo–P deposits after the analysis of electrochemical measurements. Moreover, corrosion resistance increases before annealed at 400 °C, but heat‐treatment at higher temperatures has a negative effect on the corrosion resistance of Ni–Mo–Cr–P alloy coatings.     

Pulse-reverse electroplating of chromium from Sargent baths: Influence of anodic time on physical and electrochemical properties of electroplated Cr

Herein, chromium film was successfully synthesized by pulse-reverse (PR) electrodeposition using various anodic current time in a Sargent bath which is mainly composed of hexavalent chromium (Cr⁶⁺) and sulfuric acid (H₂SO₄). The correlation between anodic time during electroplating and various physical properties was investigated. The crack density, hardness, and thickness of electrodeposited chromium was decreased with an increase in anodic time for PR electroplating. The chromium prepared by PR electroplating showed higher corrosion resistance than that prepared by direct current (DC) electroplating owing to low crack density. Consequently, the optimal anodic time for PR electroplating was found to be 0.001 s based on the crack density, hardness, current efficiency, and film thickness. The results obtained suggest that this optimized process is a promising route for electroplating chromium film with low crack density and high corrosion resistance.     

Behaviour and mechanisms of alkali-sulphate-induced hot corrosion on composite coatings at 900 °C

Three coating systems (one single MCrAlY, two composite coatings with/without the Cr-rich interlayer) have been prepared by the arc ion plating (AIP) and electroplating methods. Hot corrosion of the coatings at 900 °C by alkali sulphates shows that a composite coating with a chromium-rich interlayer exhibits the best corrosion resistance. The MCrAlY coating was severely deteriorated in 100 h since its non-productive (Ni,Co)Al₂O₄ and Cr₂O₃ scales induce internal sulfidation and oxidation. However, the microstructural involutions seldom occur within composite coatings, especially for the one with the Cr-rich interlayer. Mechanisms of hot corrosion of the three coatings are discussed.     

Zn-Ni合金镀层中添加第三种元素和纳米颗粒的研究新进展

介绍了在汽车、航空航天等行业中得到广泛应用的钢铁零件电镀Zn-Ni合金镀层,以及往碱性、氯化物等锌镍合金镀液中加入Fe、Co、Mn、Ce、P等第三种元素所获得的锌镍三元合金镀层,具有更优良的耐腐蚀性、催化性等性能的情况。介绍了往Zn-Ni合金镀液里加入氧化硅、氧化铈、氧化钛、氧化铝、碳化硅等纳米颗粒的进展情况,发现含有纳米颗粒的锌镍复合镀层具有耐腐蚀性、耐磨损性、热稳定性更好,硬度更高等优点。梳理了2016年以来在Zn-Ni合金电镀中添加第三种元素和纳米颗粒的多层镀层研究新进展。从Zn-Ni单一镀液中沉积Ni-P和Zn-Ni合金多层镀层时,在低电流密度下沉积出Ni-P层;在较高电流密度下,沉积出含3.2%P的Zn-Ni-P合金镀层,这种多层镀层可以大幅度提高钢铁零件的防腐蚀性能。介绍了在含12%Ni的Zn-Ni镀层上镀覆Ni-Co-SiC纳米复合镀层的情况,这种多层结构既可以提高镀层的结合力,又可提高其在3.5%NaCl溶液中的耐腐蚀性能。该复合镀层是一种硬度高、磨损量低的新型Zn-Ni合金复合镀层。     

Electrochemical studies on the electrodeposited Zn-Ni-Co ternary alloy in different media

The electroplating of ternary Zn-Ni-Co alloy, surface morphology and corrosion resistance were investigated and contrasted with the characteristics of Zn-Ni electrodeposits. The investigation of electrodeposition was carried out using cyclic voltammetry and galvanostatic techniques, while potentiodynamic polarization resistance and anodic linear sweeping voltammetry techniques were used for corrosion study. Under the examined conditions, the electrodeposition of the alloy was of anomalous type. It was found that the obtained Zn-Ni-Co alloy exhibited more preferred surface appearance and better corrosion resistance compared to Zn-Ni alloy that electrodeposited at similar conditions. During the cathodic scan of cyclic voltammetry, a cathodic peak at − 574 mV is appeared and correlated with the deposition of sulfur liberated from the reduction of sulphate group in the presence of H⁺. Up to four anodic peaks were obtained by cyclic voltammetry technique, two correlated with zinc oxidation from pure deposited Zn and γ-Ni₅Zn₂₁ phases and two correlated with oxidation of cobalt and nickel, were observed. The phase structure, surface morphology and chemical composition of the deposits were characterized by means of X-ray diffraction analysis, scanning electron microscopy and atomic absorption spectroscopy, respectively.     

Annealing effects on the microstructure and properties of bulk high-entropy CoCrFeNiTi0.5 alloy casting ingot

Most previous researches focused on small casting ingots prepared by arc melting, when studying high-entropy alloys. Large sized ingots were also necessary in exploring the existence of volume effects in the multi-principal element alloys. During the experiments, a large sized CoCrFeNiTi_0.5 alloy casting ingot was prepared by a medium frequency induction melting furnace. A slight volume effect occurred, reflecting mainly in the growth of crystalline grains and the increase of alloy hardness in the ingot. To investigate the effect of annealing temperature on microstructure and properties of CoCrFeNiTi_0.5 alloy, several samples taken from the ingot were annealed at 600 °C, 700 °C, 800 °C and 1000 °C respectively for 6 h. Almost no effects were found to the crystalline structure and elemental distribution when the samples were annealed below 1000 °C. The crystalline structure of CoCrFeNiTi_0.5 alloy was composed of one principal face-centered cubic (FCC) solid-solution matrix and a few intermetallic phases in the form of interdentrite. Dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti. When annealed below 1000 °C, the interdendrite stayed in (Ni, Ti)-rich phase, (Fe, Cr)-rich phase and (Co, Ti)-rich phase. After 1000 °C annealing, (Co, Ti)-rich phase disappeared, while (Ni, Ti)-rich phase and (Fe, Cr)-rich phase grew. The microhardness of the as-cast CoCrFeNiTi_0.5 alloy was 616.80 HV and the macrohardness was 52 HRC. The hardness of the samples stayed generally unchanged after annealing. This indicated a high microstructure stability and excellent resistance to temper softening that the CoCrFeNiTi_0.5 alloy exhibited.     

Effect of annealing on microstructure and properties of Cu–30Ni alloy tube

The microstructure, mechanical properties and seawater corrosion resistance of annealed Cu–30Ni alloy tube were investigated using mechanical test, optical microscope, scanning electronic microscope and electrochemical measurement system, respectively. The recrystallizations gradually increased with the increase of annealing temperature and holding time. The hardness and tensile strength, which maintained invariability with annealing temperature at 680–720 °C, dramatically decreased with annealing temperature at 720–770 °C. As annealing temperature and holding time increase, corrosion potential (E_C) increased while corrosion rate (i_C) decreased at the beginning of seawater immersion. But after 15 days’ seawater immersion, as annealing temperature and holding time increase, E_C firstly increased and then decreased, on the contrary, i_C firstly decreased and then increased. The Ni-rich surface film and the Ni-rich sub-grains were responsible for the initial and extended immersion, respectively. It was found that the Cu–30Ni alloy tube annealed at 720 °C for 30 min exhibited favorable comprehensive mechanical properties and seawater corrosion resistance.     

Electrodeposition of B,Ni co-doped diamond-like carbon films on AZ91D magnesium alloy: Corrosion and wear resistance

Diamond-like carbon (DLC) possesses brilliant and excellent properties, including excellent corrosion resistance as well as outstanding wear resistance. Ni and B co-doped DLC films were deposited on AZ91D magnesium alloy by electrodeposition under mild conditions (300 V and 25°C). Uniform and dense morphology of co-doped DLC films were observed, and Ni and B were uniformly incorporated into the carbon-based films. Among all the electrodeposits, the appearance of D and G peaks near 1330 and 1570 cm⁻¹ revealed that the as-deposited films were typical DLC films. As the addition of Ni was increased to 0.05 g, the highest microindentation hardness, the lowest friction coefficient, and wear loss were achieved to be 164.5 HV, 0.3, and 0.6 × 10⁻⁵ kg/m, respectively. The amorphous carbon films fabricated at 0.05 g Ni had the lowest corrosion current density and the most positive corrosion potential, which was mainly due to the small and dense granular structure effectively hindering the penetration of corrosion media.     

Cr含量对CrxMoNbTiZr系高熵合金组织与性能的影响

采用真空电弧熔炼的方法制备了Cr_xMoNbTiZr系高熵合金(x=0, 0.5, 1, 1.5)。利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)、显微硬度计以及电化学工作站研究了Cr含量对该高熵合金结构、组织、硬度和耐蚀性能的影响。结果表明,Cr的添加使合金由单相BCC结构转变为富Zr相与富Mo-Nb相的双相BCC结构,随着Cr含量增加,在富Zr相中还有富Cr的Laves相析出;Cr_1.5MoNbTiZr合金具有最高硬度765.53 HV,这是由于第二相析出强化、固溶强化与高熵合金晶格畸变的共同作用;Cr的加入增加了Cr_xMoNbTiZr系高熵合金在质量分数为3.5%NaCl溶液中发生腐蚀倾向,但降低了该系高熵合金的腐蚀速率,同时发现Cr的添加存在一个临界值来保证合金的抗点蚀能力,超过这个临界值合金就会更容易发生点蚀现象。     

脉冲电沉积纳米晶铁-镍-铬合金箔工艺与性能研究

采用脉冲电沉积方法从含三价铬镀液中制备出铁-镍-铬合金箔,通过正交试验优化工艺条件,探究了配位剂和温度对合金箔成分的影响。采用扫描电镜(SEM)、能谱(EDS)、X射线衍射(XRD)对合金箔进行表征,并对合金箔的电性能、力学性能和抗腐蚀性进行研究,采用电化学手段对合金电沉积机理进行初探。获得最优工艺为:CrCl3·6H2O50g·L-1,电流密度16A·dm-2,周期100ms,占空比0.3,温度60℃,pH1～1.5,沉积45min可获得厚度为20～30μm的合金箔,此合金箔成分质量分数为:(62～67)%Fe、(30～33)%Ni和(3～5)%Cr。电沉积Fe-Ni-Cr合金箔微观为紧密堆砌的球形,无微裂纹,晶粒尺寸在纳米范围内,主相结构为Cr与α-Fe或γ-Fe形成的固溶体,当Cr含量4%,基体主要为γ-Fe;最佳工艺条件下获得的合金箔电阻率为68.66×10-6A·cm,具有良好的电性能;显微硬度为5819MPa(HV);在3.5%NaCl中腐蚀电流密度仅为1.685×10-6A·cm-2,抗腐蚀性优良;配位剂的加入使得铁、镍、铬的合金沉积电位接近,合金沉积变为可能。     

电沉积非晶态Cr—Fe—C合金镀层结构与性能研究

采用以三价铬为主盐的铬合金电镀工艺,对获得的Ｃｒ－Ｆｅ－Ｃ合金镀层的化学成分、结构、性能及其成因进行研究,结果表明,这种含铁量为２０％,含碳为５％左右的镀层为非晶态结构,含有大量微裂纹,微观上镀层表面呈结瘤状,热处理后可出现极明显的硬化现象,并伴随镀层逐渐向晶态转化。     

Electrochemical Deposition of Ni on an Al-Cu Alloy

Metallic coatings can be used to improve the wear and corrosion resistance of Al alloys. In this study, Ni was used as a candidate material for such a coating which was applied on the surface of Al 2014 alloy using electrodeposition in a standard Watt’s bath. A two-step heat treatment procedure was employed that served to increase the adhesion as well as hardness of Ni. Deposition was undertaken for different durations using both galvanostatic and potentiostatic techniques. The effect of deposition parameters such as surface finish, current, potential, temperature, pH level and duration on the microstructure, adhesion, and surface properties of the Ni deposit was studied. Materials characterization was performed using scanning electron microscopy, atomic force microscopy, and x-ray diffraction. Cross-sectional scanning transmission electron microscope images revealed the fine-grained (10 nm) structure of Ni initially deposited at the Ni-Al alloy substrate. Microhardness, adhesion, and corrosion behavior of the Ni deposit were evaluated. Experimental results indicate that deposition by galvanostatic technique on 1 μm surface finish at 45 °C with a pH level maintained at 3.6 represented the optimum conditions to generate a uniform Ni deposit on Al 2014. It was concluded that Ni deposition can be used to improve the surface properties of Al alloys.     

Corrosion behavior of Cr/Cu-coated Mg alloy (AZ91D) in 0.1 M H2SO4 with different concentrations of NaCl

An electroplating process was proposed for obtaining a protective Cr/Cu deposit on the two-phase Mg alloy AZ91D. The corrosion behavior of Cu-covered and Cr/Cu-covered AZ91D specimens was studied electrochemically in 0.1 M H₂SO₄ with different NaCl concentrations. Experimental results showed that the corrosion resistance of an AZ91D specimen improved significantly after Cr/Cu electrodeposition. The corrosion resistance of Cr/Cu-covered AZ91D decreased with increasing NaCl concentration in 0.1 M H₂SO₄ solution. After immersion in a 0.1 M H₂SO₄ with a NaCl-content above 3.5 wt.%, the surface of Cr/Cu-covered AZ91D suffered a few blisters. Cracks through the Cr deposit provided active pathways for corrosion of the Cu and the AZ91D substrate. Formation of blisters on the Cr/Cu-covered AZ91D surface was confirmed based on the results of an open-circuit potential test, which detected an obvious potential drop from noble to active potentials.     

Evolution of microstructure,hardness, and corrosion properties of high-entropy Al0.5CoCrFeNi alloy

In this study, we investigate the microstructure, hardness, and corrosion properties of as-cast Al_0.5CoCrFeNi alloy as well as Al_0.5CoCrFeNi alloys aged at temperatures of 350 °C, 500 °C, 650 °C, 800 °C, and 950 °C for 24 h. The microstructures of the various specimens are investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe X-ray microanalysis (EPMA). The results show that the microstructure of as-cast Al_0.5CoCrFeNi comprises an FCC solid solution matrix and droplet-shaped phases (Al–Ni rich phases). At aging temperatures of between 350 and 950 °C, the alloy microstructure comprises an FCC + BCC solid solution with a matrix, droplet-shaped phases (Al–Ni rich phase), wall-shaped phases, and needle-shaped phases (Al–(Ni, Co, Cr, Fe) phase). The aging process induces a spinodal decomposition reaction which reduces the amount of the Al–Ni rich phase in the aged microstructure and increases the amount of the Al–(Ni, Co, Cr, Fe) phase. The hardness of the Al_0.5CoCrFeNi alloy increases after aging. The optimal hardness is obtained at aging temperatures in the range 350–800 °C, and the hardening effect decreases at higher temperatures. Both the as-cast and aged specimens are considerably corroded when immersed in a 3.5% NaCl solution because of the segregation of the Al–Ni rich phase precipitate formed in the FCC matrix. Cl^? ions preferentially attack the Al–Ni rich phase, which is a sensitive zone exhibiting an appreciable potential difference, with consequent galvanic action.     

Corrosion resistance of duplex stainless steel subjected to long-term annealing in the spinodal decomposition temperature range

The effect of thermal annealing up to 15,000 h between 300 °C and 500 °C on the corrosion resistance of the duplex stainless steel (DSS) 7MoPLUS has been investigated by using the DLEPR test. Spinodal decomposition in 7MoPLUS is unabated even after annealing for 15,000 h and no healing has been observed. The possible healing mechanisms in this temperature range (back diffusion of Cr atoms from the Cr-rich ferrite (α_Cr) and diffusion of Cr atoms from the austenite) and its absence in the present steel have been discussed.     

Co–Cr–Mo-based composite reinforced with bioactive glass

The powder metallurgy (PM) technology was used to produce a porous Co–Cr–Mo-based composite material with the bioactive glass (S2) addition of 5 wt.%, 10 wt.% and 15 wt.%. The results show that the addition of bioglass to the matrix of Co–Cr–Mo alloy, as well as rotary cold repressing and heat treatment of sintered specimens can cause significant changes in the microstructure, mechanical and corrosion properties of composite materials in comparison with the pure porous Co–Cr–Mo alloy. A significant increase in the hardness, yield strength and corrosion resistance of the composites was observed with increasing the bioglass volume fraction. Although all PM samples are in a passive state, the higher corrosion resistances were obtained in the case of the composites with bioglass additions. Superior mechanical properties were achieved in the case of composite with 10 wt.% of bioglass.     

Effect of microstructure on the mechanical and corrosion behaviors of a hot-extruded nickel aluminum bronze

In this paper,the influence of microstructure on the corrosion behavior of a hotextruded nickel aluminum bronze was studied.Three kinds of samples subjected to the hot-extrusion,annealing and quenching conditions were prepared and immersion tests in 3.5% NaCl solution were carried out.Microstructures and corrosion surface morphologies of the samples were observed by SEM.It was found that the retained β martensite and(α+κⅢ) lamella eutectoid in the as hot-extruded material were eliminated after annealing,and...     

退火温度对ZL102组织和性能的影响

利用金相显微镜观察经不同温度退火处理的ZL102合金的显微组织,通过测量硬度得出其随退火温度的变化规律;并通过全浸腐蚀试验比较其耐腐蚀性,观察其在不同温度下的腐蚀形貌.结果表明,经不同温度退火处理的材料其显微组织发生明显的改变,硬度随退火温度呈一个波动趋势;在250℃和300℃退火处理时其腐蚀形貌较好.