Phase selection and performance of Mg–Cu–Y amorphous composite with different Mg/Cu ratios

In this article, Mg–Cu–Y alloys with two different Mg/Cu ratios(in at%) were prepared using a watercooled copper mold. Scanning electron microscopy and X-ray diffraction were applied to analyze the microstructure and phase composition. Moreover, corrosion resistance and wear resistance were studied systematically. The results show that both Mg65 Cu25 Y10 and Mg60 Cu30 Y10 alloys could form a composition of crystalline and amorphous phases. Although the microstructure of Mg65 Cu25 Y10 consists of an amorphous phase and a-Mg, Mg2 Cu, and Cu2 Y crystalline phases, the microstructure of Mg60 Cu30 Y10 alloy mainly consists of the amorphous phase and a-Mg, Mg2 Cu. With reducing Mg/Cu ratio, the alloys have better corrosion resistance and wear resistance. The mechanism has also been discussed in detail.     

Effect of Microstructure on Corrosion Behavior of Mg–Sr Alloy in Hank's Solution

Mg–Sr alloy has been studied as a potential biodegradable material with excellent bioactivity to promote the bone formation. However, its degradation behavior needs to be well controlled to avoid the negative effect, which is important for future application. Therefore in this study, the microstructure and its effect on corrosion behavior of an Mg–1.5 Sr alloy were investigated. The microstructures of the alloy under different processing procedures were characterized by both optical and scanning electron microscopes. The corrosion performance was studied in Hank's solution using immersion,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests. The results showed that the grain size and the amount and distribution of b-Mg_(17)Sr_2 had obvious effects on the corrosion behavior of Mg–Sr alloy. The smaller the grain size was, the more the protective surface layer formed on Mg–Sr alloy, and the higher the corrosion resistance was. For the as-cast Mg–Sr alloy, the network-like second phases precipitated along the grain boundaries could not hinder the corrosion due to their own corrosion cracking accelerating the intergranular corrosion. However, the refinement of second phases increased the corrosion resistance of the as-extruded alloy. After solution treatment at 450 °C for 5 h, the grains in the alloy did not grow much and b-Mg_(17)Sr_2 phases homogenously distributed in the alloy, resulting in the increase in corrosion resistance. However, after aging treatment, large amount of precipitated second phases increased the galvanic corrosion of the alloy, accelerating the development of corrosion.     

Biocorrosion properties of Ti–3Cu alloy in F ion-containing solution and acidic solution and biocompatibility

Ti–3Cu alloy has shown low melting point and strong antibacterial properties against S.aureus and E.coli and thus has potential application as dental materials and orthopedic application.In this paper, the corrosion properties of Ti–3Cu alloy in five kinds of simulated solutions were investigated in comparison with cp-Ti(commercially pure titanium) by electrochemical technology and immersion experiment.Electrochemical results have demonstrated that Ti–3Cu alloy exhibited much nobler corrosion potential, lower corrosion current density and high corrosion resistance than cp-Ti in all solutions, especially in saliva-pH6.8+0.2 F and saliva-pH3.5, indicating that Ti–3Cu alloy has much better anticorrosion properties than cpTi.Immersion results have shown that Ti ion and Cu ion were released from Ti–3Cu, especially in saliva-pH6.8+0.2 F and saliva-pH3.5 solutions.Both electrochemical data and immersion results have indicated that high corrosion rate and high metal ion release rate were detected in F ion-containing solution and low-pH solution, displaying that F~- and low pH had much strong aggressive attack to cp-Ti and Ti–3Cu alloy.The corroded surface morphology was observed by scanning electron microscopy(SEM), and the roughness was tested in the end.The good corrosion resistance of antibacterial Ti–3Cu alloy suggests its great potential as a long-term biomedical application.     

Corrosion and wear behavior of an Mg–2Zn–0.2Mn alloy in simulated body fluid

In this work, the corrosion behavior of the ascast and extrusion and aging treatment Mg–2Zn–0.2Mn alloy in simulated body fluid(SBF) were studied. The wear behavior of Mg–2Zn–0.2Mn alloy was investigated using pin-on-disk technique and stainless steel as counterbody under a constant sliding velocity at different loads ranging from 2 to 5 N with deionized water and SBF as lubrication.The results showed that the extrusion and aging treatment Mg–2Zn–0.2Mn alloy exhibited better corrosion resistance compared with the as-cast alloy due to finer average grain size, more homogeneous phase distribution, and decrease in porosity. The friction coefficient of fractional pair under SBF and deionized water lubrication were obviously lower than that of dry sliding condition. However, the wear rate of Mg–2Zn–0.2Mn alloy under SBF lubrication was higher than that of dry sliding and deionized water lubrication due to the corrosiveness of SBF accelerated the wear of the magnesium alloy. The magnesium alloy exhibited different wear mechanisms with the variety of loads and lubrication conditions.     

Preparation of Ti–Nb–Ta–Zr alloys for load-bearing biomedical applications

Ti–Nb–Ta–Zr alloys for biomedical applications were successfully fabricated by arc melting(AM) and diffusion bonding.The microstructure, mechanical properties and electrochemistry behavior in a simulated body fluid(SBF) were studied.It shows that melted Ti–Nb–Ta–Zr alloy mainly contains β phase although there are a few Ti-rich phases and micropores, the number of which is lower than that in sintered sample with a few Ti-rich and Ta-rich phases.The melted alloys present higher strength(1224 MPa), Young's modulus(15.3 GPa) and corrosion potential(-0.34 V) in SBF, while total recovery strain ratio(67.5%) and pseudoelastic strain ratio(8.4%) of sintered Ti–Nb–Ta–Zr alloy keep higher value than 35.7%and 5.0% for melted Ti–Nb–Ta–Zr.The reasons were discussed based on the microstructure of the Ti–Nb–Ta–Zr alloys.     

Joint Characteristics and Corrosion Properties of Bypass-Current Double-Sided Arc-Welded Aluminum 6061 Alloy with Al–Si Filler Metal

Sheets of aluminum 6061 alloy were welded using bypass-current double-sided arc welding with Al–Si filler wire to investigate the effect of Al–Si intermetallic compounds on the microstructure, microhardness and corrosion behavior of weld joint. Experimental results indicated that the Al_(4.5)FeSi phase in the topside of the weld joint was finer than that in the backside and newly formed phase of Al_(0.5)Fe_3Si_(0.5)was observed in the backside. The formation of reinforcing phases of Al–Fe–Si in the weld improved the microhardness of the weld by about 18%. The corrosion resistance of the weld zone was greater than that of the base metal, while the corrosion current displayed opposite, and the corrosion resistance of the weld region was better than that of the base metal.     

Effect of Phase Transformation During Long-Term Solution Treatment on Microstructure,Mechanical Properties,and Bio-corrosion Behavior of Mg–5Zn–1.5Y Cast Alloy

The influence of long-term solution treatment for various intervals on the microstructure,mechanical properties,and corrosion resistance of the as-cast Mg–5Zn–1.5Y alloy was investigated.Variation of secondary phases was studied during solution treatment through thermal analysis test and thermodynamic calculations.Tensile and hardness tests,as well as polarization and immersion tests,were performed to evaluate the mechanical properties and corrosion behavior of the ascast and heat-treated alloy,respectively.Results show that solution treatment transforms I-phaseinto W-phaseas well as dissolves it into the a-Mg matrix to some extent;therefore,the amount of W-phase increases.Moreover,prolonged solution treatment decreases the volume fraction of the phases.In the first stage of solution treatment for 14 h,the tensile properties significantly increase due to the incomplete phase transformation.Although long-term solution treatment sharply decreases the tensile and hardness properties of the alloy,it improves the corrosion resistance due to the transformation of I-phase into W-phase.In fact,it decreases corrosion potential and simultaneously dissolves intermetallic compounds into the a-Mg matrix,resulting in the reduction in galvanic microcells between the matrix and compounds.It is found that the optimum time for long-term solution treatment is 14 h,which improves both corrosion behavior and mechanical properties.     

Corrosion behavior of three Ag–50Cu alloys prepared by different processes in NaCl solutions

Corrosion behavior of two nanocrystalline bulk Ag–50Cu alloys and one coarse-grained counterpart prepared by liquid-phase reduction(LPR), mechanical alloying(MA) and powder metallurgy(PM) methods,respectively, were investigated in Na Cl solutions. They were finished by means of PARM273 A and M5210 electrochemical apparatus through potentiodynamic polarization method and electrochemical impedance spectroscopy(EIS) technique. The results show that corrosion rates of three Ag–50Cu alloys increase with the increment of Na Cl solution concentrations. Corrosion rates of LPRAg–50Cu alloy are a little higher than those of PMAg–50Cu alloy,but evidently lower than those of MAAg–50Cu alloy. The difference in corrosion rates is attributed to the large reduction in the grain size and homogeneous microstructure of nanocrystalline alloys. Passive current densities decrease and afterward increase for PMAg–50Cu alloy,decrease for MAAg–50Cu alloy, and increase for LPRAg–50Cu alloy with the increment of Na Cl solution concentrations. After the grain sizes are refined, passive current densities become lower.     

Corrosion Behavior of Selective Laser Melted AISi10Mg Alloy in NaCl Solution and Its Dependence on Heat Treatment

This work investigates the corrosion behavior of AlSilOMg alloy produced by selective laser melting(SLM) and the counterparts heat-treated at 450-550℃in 3.5 wt% NaCl solution.Electrochemical measurements and weight loss tests together with microstructural characterizations were conducted.The SLM-produced alloy displays a microstructure with a continuous network of Si particles,exhibiting superior corrosion behavior.After heat treatment,the Si particles are coarsened and isolated and A1 matrix dissolves into their surrounding area,thereby degrading the corrosion resistance properties.Therefore,the corrosion resistance of AlSilOMg alloy degrades with increasing the heat treatment temperature.     

Microstructure and melting properties of Ag–Cu–In intermediate-temperature brazing alloys

The microstructure and melting properties of ternary Ag–Cu–In intermediate-temperature alloys(400–600 °C) prepared by electric arc melting were investigated in this work. The melting properties, phase compositions, microstructure and hardness were characterized by differential scanning calorimetry(DSC), X-ray diffraction(XRD), scanning electron microscopy(SEM)and micro-hardness tester, respectively. The results show that the melting properties, phase compositions, microstructure and hardness of Ag–Cu–In brazing alloys are substantially different when adding different levels of indium. Indium element could effectively reduce the melting temperatures of(Ag–Cu28)–x In alloys, and the melting temperatures of(Ag–Cu28)–25In alloy are located at 497.86 and 617.48 °C. When the indium content varies from 5 wt% and 10 wt%, the dominant phases in the alloys are Ag-rich and Cu-rich phases, and their granular crystals are smaller than 0.5 lm. When the indium content is higher than 15 wt%, the phase compositions of the alloy are Ag4 In and Cu11In9, and the microstructure exhibits dendritic crystals with a uniform distribution. The hardness of(Ag–Cu28)–x In alloy decreases first and then increases with the content of indium increasing, and the highest hardness of(Ag–Cu28)–25In alloy is HV 266.0.     

Microstructure of a Ti–50wt% Ta alloy produced via laser powder bed fusion

Ti-Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance.In this work,nearly fully dense and in situ alloyed Ti-50 wt% Ta samples were fabricated by the laser powder bed fusion(LPBF) of mechanically mixed powders.With increased exposure time,and thereby increased laser energy density,insoluble Ta particles were almost dissolved,and a Ti-50 wt% Ta alloy was formed.Cellular and dendritic structures were formed due to constitutional undercooling,which was caused by the high cooling rate of LPBF process.Both retained βphases and α " phases were observed in the LPBFed Ti-50 wt% Ta alloy.The α" phase was found at the boundary of the cellular structures,where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the β phase→α' phase transition.     

Typical Microstructural Characteristics of Ti-5Al-5Mo-5V-3Cr-1Fe Metastable βTi Alloy Forged in α+β Region

In this study, typical microstructural characteristics of a metastable β Ti alloy (Ti-5Al-5Mo-5V-3Cr-1Fe) forged in a dual-phase region (strain of 54% at 820 °C) were investigated in detail by the combined use of X-ray diffraction, energy dispersive spectroscopy, electron channeling contrast imaging and electron backscatter diffraction techniques. Results show that the microstructure of the forged alloy is composed of bulk α grains, α plates and β matrix. The bulk α grains correspond to retained primary α phase (α_p, average grain size~2.4 μm), while the α plates are secondary α phase (α_s, width~70 nm) precipitated from the β matrix during air cooling. During forging, the β matrix experiences dynamic recovery with many subgrains and significant orientation gradients formed. Analyses of the orientation relationship between the α and β phases show that the Burgers orientation relationship is not maintained between some α_p and β phases, which should be related to thermal deformation-induced changes of their orientations. In contrast, all of the α_s plates are found to maintain well the Burgers orientation relationship with the β phase.     

铸态Ti-20Zr-10Nb-xMo合金的微观组织和耐腐蚀性能

采用X射线衍射仪(XRD)、光学显微镜(OM)、硬度测试、压缩试验和电化学工作站等研究了Mo含量对Ti-20Zr-10Nb-xMo(x=0,3,6,9,wt%)合金相结构、显微组织、力学性能以及电化学腐蚀性能的影响。结果表明,随着Mo含量的增加,Ti-20Zr-10Nb-xMo合金的相结构发生了α′+β→α″+β→β的变化,平均晶粒尺寸亦随着Mo含量的增加而逐渐降低;当Mo含量为9%时,合金的平均晶粒尺寸约为45 μm。通过Mo的添加,合金的抗压强度和屈服强度呈现先降低后升高的趋势,而显微硬度则先增大后降低;当Mo含量为9%时,合金的抗压强度最大,为1610 MPa,压缩应变为50.9%。未添加Mo的试验合金的自腐蚀电流密度最小,为33.19 nA·cm^-2,R_p值最大,为1531.52 kΩ·cm²,其耐腐蚀性最好。     

Hot Deformation Behavior and Microstructural Characteristics of Ti–46Al–8Nb Alloy

Hot deformation behavior,microstructural evolution and flow softening mechanism were investigated in Ti–46Al–8Nb alloy via isothermal compression approach.The true stress–strain curves exhibited typical work hardening and flow softening,in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener–Hollomon(Z)parameter,and the activation energy was calculated to be 446.9 k J/mol.The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation.The Al segregation promoted flow softening mainly arising from the recrystallization of γ phase with low stacking fault energy.The coarse recrystallized γ and several massive γ phase were observed at grain boundaries.While in the case of Nb segregation,β/B2 phase harmonized bending of lamellae,combined with the growth of recrystallized γ grains and α+β+γ→α+γ transition under conditions of temperature and stress,leading to the breakdown of α_2/γ lamellar colony.During the hot compression process,gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism,leading to extensive c twins and cross twins in α/γ lamellae and at grain boundaries.In general,homogeneous microstructure during the hot deformation process can be obtained in Ti Al alloy with high Nb addition and low Al segregation.The deformation substructures intrinsically promote the formability of Ti–46Al–8Nb alloy.     

新型医用Ti-24Nb-4Zr-8Sn合金在Hanks溶液中的电化学腐蚀行为研究

采用极化曲线分析、电化学阻抗谱（EIS）测试和浸泡实验的方法,并结合XPS,XRD和SEM等分析手段对新型医用Ti-24Nb-4Zr-8Sn合金在37℃的Hanks人工模拟体液中的电化学腐蚀行为进行了研究,并与纯Ti和Ti-6Al-4V合金进行了比较.结果表明:在37℃的Hanks溶液中,Ti-24Nb-4Zr-8Sn合金的腐蚀电流密度与纯Ti相等,并且钝化性能优于纯Ti和Ti-6Al-4V,这与其钝化膜中存在大量的Nb₂O₅密切相关;EIS结果显示,Ti-24Nb-4Zr-8Sn合金表面形成内层致密而外层疏松的双层钝化膜结构,致密层特性对材料的耐蚀性能起到决定性作用;随着浸泡时间的延长,致密内层的电阻大幅度提高,Ti-24Nb-4Zr-8Sn合金的耐蚀性能增强,同时疏松外层中的微缺陷发展成为宏观裂纹,造成疏松外层整体脱落.     

选区激光熔化制备Ti-6Al-4V合金的热处理工艺及力学性能

采用选区激光熔化技术(SLM)制备Ti-6Al-4V合金圆棒试样,通过不同的热处理工艺改善材料的拉伸性能,并对SLM制备的Ti-6Al-4V合金试样开展了高周疲劳性能测试。通过微观组织和疲劳试样断口分析,揭示了显微组织结构与拉伸性能的关系,以及Ti-6Al-4V合金的疲劳裂纹起始源和裂纹扩展机理。结果表明,热处理工艺对SLM成型Ti-6Al-4V合金的力学性能有显著的影响,920 ℃×1 h水冷,随后800 ℃×2 h炉冷的固溶时效热处理制度可以获得较好的综合室温拉伸性能。其室温组织为晶界上分布的α相和晶粒内部片层状分布的α+β相。SLM成型Ti-6Al-4V合金显微组织中的晶界形成与扫描路径相关,热处理过程中α相会优先在扫描分区搭接处析出。与手册锻件的疲劳寿命曲线比较,在同样的最大应力水平下,增材试样的疲劳寿命比锻件的疲劳寿命低,这种降低的趋势随着应力水平的降低而逐步增大。在400 MPa的应力水平下(R=-1),锻件的疲劳寿命已经在2×10⁷水平,增材试样的疲劳寿命依然较低,约为锻件的1%。SLM成型Ti-6Al-4V合金的应力疲劳寿命偏低,是由于试样中存在未熔合缺陷造成。扫描分区搭接处易产生未熔合缺陷,而疲劳裂纹也会沿着这些缺陷扩展。     

激光功率对TC4合金表面Ni60A/CeO2熔覆层组织及耐腐蚀性能的影响

为了提高TC4合金基体表面的耐腐蚀性能,运用激光熔覆同轴送粉技术,采用1200、1500、1800、2100、2400 W等不同激光功率在TC4合金基体表面上制备Ni60A/CeO₂复合熔覆层,对熔覆层进行了显微组织观察、电化学检测以及电化学腐蚀后的表面观察,探究激光功率对熔覆层耐腐蚀性能的影响。研究表明,随着激光功率的增加,熔覆层的显微组织变得排布均匀且细密,电化学特性呈现出耐腐蚀性先增大后减小的特点。当激光功率为2100 W时,电化学阻抗最大,为25.74 km²,熔覆层表面并未出现明显的腐蚀隧道,大部分为腐蚀产物覆盖在Ni60A/CeO₂熔覆层的表面,耐腐蚀性良好。     

时效时间对Zn-5.5Mg-0.4Ba-0.7Gd合金组织及性能的影响

对真空熔炼制备的Zn-5.5Mg-0.4Ba-0.7Gd合金在150 ℃分别时效2、4、8 h,研究时效时间对合金组织及性能的影响。结果表明,时效可以改善合金的微观结构,时效初期合金中的MgZn₂相逐渐转化为Mg₂Zn₁₁相。电化学测试结果表明,时效4 h后合金耐腐蚀性能最佳,自腐蚀电位为-942.844 mV,自腐蚀电流密度为13.34 μA/cm²,微孔电阻为1894 Ω·cm²,电荷转移电阻为1613 Ω·cm²。时效4 h后合金腐蚀产物主要由具有优良的生物相容性的磷酸锌(钙)、碳酸锌(钙)和氢氧化锌组成。     

Creep-Induced Phase Instability and Microstructure Evolution of a Nearly Lamellar Ti-45Al-8.5Nb-(W,B,Y)Alloy

Microstructure degradation and stress-induced transformation of a high Nb-containing TiAl alloy with nearly lamellar microstructure during creep were investigated. Tensile creep experiments were performed at 800, 850 and 900 °C under 150 MPa in air. Microstructures before and after creep tests were examined using scanning and transmission electron microscopy (SEM and TEM). Dislocations within the lamellar structure and β_o(ω) region and twin intersection in massive γ grains were investigated. Dislocation sliding played a critical role in the deformation of ω_o phase, which preferentially occurred on the (0002)ω_o plane. Possible deformation mechanisms were revealed. A stress-induced γ→α₂ phase transformation took place during the creep test at 850 and 900 °C. α₂ lamella could directly decompose into the ω_o phase at 850 °C. The instability of high-temperature microstructure can weaken the creep resistance and promote the plastic deformation of the lamellar matrix, thus could be detrimental to the creep properties. The correlations between creep properties and microstructure instability were discussed.     

Effect of Metal Cations on Corrosion Behavior and Surface Structure of Carbon Steel in Chloride Ion Atmosphere

In order to better understand why the corrosion behavior of carbon steel exposed in Nansha atmospheric environment is very serious, the effect of sodium, potassium and magnesium chlorides deposited on carbon steel surface has been studied under atmosphere conditions by wet/dry accelerated test. The difference of corrosion behavior and surface structure in Na⁺, K⁺, and Mg²⁺ containing atmosphere has been investigated by thickness loss, scanning electron microscope, X-ray diffraction and electrochemical techniques. The results indicate that the thickness loss of carbon steel exposed in different metal cations containing atmospheric environment increases in the order of Na⁺, K⁺, Mg²⁺. The hard metal cation can promote the dissolution of the steel to a certain extent. In Mg²⁺ containing atmosphere, the relative content of β-FeOOH is rather higher and the protective ability index α*/γ* decreases in the order of Na⁺, K⁺, Mg²⁺. The corrosion current density of both bare carbon steel and the rusted carbon steel increases in the order of Na⁺, K⁺, Mg²⁺. The polarization resistance and the charge transfer resistance decreases in the order of Na⁺, K⁺, Mg²⁺.