Al0.8CoCrFeNiTi0.2高熵合金铸态及退火态组织和性能研究

采用真空电弧熔炼法熔炼出Al0.8CoCrFeNiTi0.2高熵合金,并在600 ℃、800 ℃、1000 ℃下进行了真空退火热处理。利用X射线衍射仪（XRD）、光学显微镜（OM）、电子探针（EPMA）、硬度计、万能试验机以及电化学工作站对合金铸态和不同温度退火态的微观组织结构、硬度、压缩机械性能和在3.5wt.%的NaCl溶液、0.5mol/L的H2SO4溶液中的耐蚀性进行了研究。组织分析表明退火处理使合金的相组成和组织形貌都发生了改变,铸态下合金由BCC和FCC两相固溶体组成, 600 ℃、800 ℃和1000 ℃退火态下合金由BCC、FCC和σ相三相组成,800 ℃退火态中σ相析出最多。随着退火过程的进行,铸态下的单相固溶体树枝晶转变为了细小层片状的两相混合组织。在800 ℃及以下温度范围,退火温度越高,混合组织越细小,成分均匀性越好。但1000℃退火态有大块状单相固溶体析出,导致元素偏析重新加剧。硬度试验和压缩试验结果表明合金在铸态和三种温度退火态下都有较高的硬度、屈服强度、断裂强度和塑性变形量,表现出了良好的综合机械性能和抗回火软化能力。800 ℃退火态的硬度、屈服强度和断裂强度最高,铸态的塑性最好。电化学腐蚀试验表明铸态和三种温度退火态下的合金在3.5% NaCl溶液和0.5mol/L H2SO4溶液中都表现出了良好的耐蚀性, 800 ℃退火态的耐蚀性最好。     

铸态和退火态Al_(0.5)CoCrFeNiTi_(0.5)高熵合金的组织与性能

采用真空电弧熔炼法熔炼出Al_(0.5)CoCrFeNiTi_(0.5)高熵合金,并在600、800和1000℃下进行真空退火热处理。利用X射线衍射仪(XRD)、光学显微镜(OM)、电子探针(EPMA)、硬度计、万能试验机以及电化学工作站对合金铸态和不同温度退火态的微观组织、硬度、压缩力学性能以及在3.5%NaCl溶液中的耐蚀性进行研究。组织分析表明:铸态和退火态的Al_(0.5)CoCrFeNiTi_(0.5)合金均由富(Cr,Fe)的FCC、富(Al,Ni,Ti)的BCC和σ三相组成,但退火处理使合金的组织形貌和各相的相对含量发生了改变,铸态下的粗大白色FCC柱状晶转变为细小的FCC+BCC+σ的混合组织;随着退火温度的升高,BCC和σ相含量增加。800℃退火态合金成分均匀性最好,1000℃退火态合金由于退火温度过高,组织粗大,元素偏析重新加剧。硬度试验和压缩试验结果表明:合金在铸态和3种温度退火态下的硬度都较高,表现出良好的抗回火软化能力;800℃退火态合金中由于BCC和σ相的增加,其硬度和屈服强度最高,但塑性最差。1000℃退火态合金由于大量σ相的析出以及组织粗大,其屈服强度、断裂强度和压缩形变率都急剧降低。600℃退火态合金具有理想的FCC、BCC和σ相的组成含量,其综合力学性能最好。电化学腐蚀试验表明:铸态和3种温度退火态的合金在3.5%NaCl溶液中都表现出良好的耐蚀性,800℃退火态合金由于其成分均匀性最好,耐蚀性最好。     

AlCoCrFeNiTi0.5高熵合金的组织控制和腐蚀性能

研究冷坩埚悬浮熔炼AlCoCrFeNiTi0.5多组元高熵合金的微观组织及回火工艺对合金组织、硬度和电化学性能的影响规律。结果发现,冷坩埚悬浮熔炼AlCoCrFeNiTi0.5高熵合金铸锭中晶粒呈树枝晶长大并析出少量ω相。随回火温度的升高,晶粒长大,共晶组织增多,BCC相强度呈先下降后升高趋势。800℃时,合金树枝晶晶粒变得细小,之后随着温度的升高,枝晶间的元素偏析减弱。合金具有较强的抗回火软化能力。在3.5%NaCl溶液中,孔蚀主要集中在树枝晶与共晶组织α相的交接处,回火后合金的耐蚀性均优于铸态合金,700℃回火后合金的耐腐蚀性能比铸态及其它合金更强。     

AlCoCrFeNiTi0.5高熵合金的组织控制和腐蚀性能

研究冷坩埚悬浮熔炼AlCoCrFeNiTi0.5多组元高熵合金的微观组织及回火工艺对合金组织、硬度和电化学性能的影响规律。结果发现,冷坩埚悬浮熔炼AlCoCrFeNiTi0.5高熵合金铸锭中晶粒呈树枝晶长大并析出少量ω相。随回火温度的升高,晶粒长大,共晶组织增多,BCC相强度呈先下降后升高趋势。800 ℃时,合金树枝晶晶粒变得细小,之后随着温度的升高,枝晶间的元素偏析减弱。合金具有较强的抗回火软化能力。在3.5%NaCl溶液中,孔蚀主要集中在树枝晶与共晶组织α相的交接处,回火后合金的耐蚀性均优于铸态合金,700 ℃回火后合金的耐腐蚀性能比铸态及其它合金更强。     

(FeCoNiCr)100-xMnx高熵合金在NaCl和NaOH溶液中的抗腐蚀性能

研究了放电等离子烧结(FeCoNiCr)_100-xMn_x(x=4,8,12,20)高熵合金的组织结构及在NaCl和NaOH溶液中的耐腐蚀性能。结果表明,(FeCoNiCr)_100-xMn_x合金主要由FCC单相组织和少量BCC相组成。(FeCoNiCr)₈₈Mn₁₂合金在3.5wt%NaCl 溶液中具有最好的耐腐蚀性能。Mn的添加使合金在1 mol NaOH 溶液中耐腐蚀性增强。退火对合金在1 mol NaOH 溶液中抗腐蚀性能影响不大。(FeCoNiCr)_100-xMn_x合金在3.5wt%NaCl溶液和1 mol NaOH溶液中的抗腐蚀性能均优于304S不锈钢。     

退火处理对CoFeNiVTi高熵合金组织和性能的影响

采用真空电弧炉熔炼和铜模吸铸法制备了CoFeNiVTi高熵合金柱状试样，并对其在氩气保护条件下进行了800℃退火20 h的处理。利用X射线衍射仪(XRD)、扫描电镜(SEM)、能谱仪(EDS)和压缩实验等研究了铸态和退火态CoFeNiVTi合金的显微组织和力学性能。结果表明：铸态合金为单相BCC固溶体结构，显微组织呈现典型的柱状晶特征，合金元素均匀分布；退火态合金由BCC基体和金属间化合物Ni₂V₃型的σ析出相构成，σ析出相具有明显的取向特征，呈粗大板条状和细小针状。与铸态合金相比，由于σ析出相的存在，退火后合金的断裂强度有所下降，但仍高达2.5 GPa,硬度则显著提高至800 HV0.2。     

退火处理对AlCoCuFeNi0.2高熵合金组织与性能的影响

利用电弧熔炼技术制备得到AlCoCuFeNi_(0.2)高熵合金,研究了铸态与900℃退火态高熵合金的组织、力学性能、磁学性能之间的差异。研究发现,铸态及900℃退火态合金都是BCC+FCC+有序BCC共存结构,BCC相是主相,组织都是典型的树枝晶组织,都具有优良软磁性能。900℃退火后,BCC相向FCC相转变,合金塑性显著改善,强度和硬度有所下降,饱和磁化强度得到提高。     

铸态及退火态Mg66Al34阳极镁空气电池的性能

制备了铸态及退火态Mg66Al34共晶合金,通过研究该合金的腐蚀及放电行为,考察了该合金作为镁空气电池阳极的放电性能。结果表明:在3.5 mass%NaCl溶液中,铸态合金具有较低的腐蚀速率及放电活性,退火态合金具有高的腐蚀速率及放电活性。在NaCl溶液中加入水溶性石墨烯后,铸态合金具有低的腐蚀速率及较高放电活性。铸态合金低的腐蚀速率是由于在β-Mg17Al12层间形成了黑色富铝氧化物腐蚀产物。     

时效处理对Cr_xCu_1Fe_2Mo_(0.5)Nb_(0.5)Ni_2高熵合金组织与力学性能的影响

采用非自耗真空电弧熔炼炉制备了Cr_xCu_1Fe_2Mo_(0.5)Nb_(0.5)Ni_2(x=0、0.5、1.0、2.0,记为C1~C4合金)高熵合金,在700℃和800℃退火12h后对其微观组织和硬度进行了分析。结果表明,Cr_xCuFe_2Mo_(0.5)Nb_(0.5)Ni_2合金在铸态主要由BCC相、FCC相和HCP相组成、经700℃退火处理后,合金物相均未发生明显改变,表现出良好的热稳定性;经800℃退火后,除C2合金外,其余合金的FCC相转变为BCC相。Cr_xCuFe_2Mo_(0.5)Nb_(0.5)Ni_2合金经700℃和800℃退火后,其微观组织为枝晶和枝晶间组织,并随Cr含量的增加,枝晶间区域扩大。Cr_xCuFe_2Mo_(0.5)Nb_(0.5)Ni_2合金在铸态、700℃和800℃退火态的硬度均随Cr含量的增加而提高,但是增加幅度较小。800℃退火处理后,C4合金的硬度(HV)由441增加至480,增幅仅为8.8%,表现出相对较弱的时效硬化现象。     

退火对FeCoNi2-xMnGax高熵合金微观组织、力学性能和磁性能的影响

利用非自耗真空电弧熔炼炉制备FeCoNi_2-xMnGa_x(x=0, 0.5, 0.75, 1.0, 1.25)高熵合金铸锭,然后在800℃和1000℃退火8 h,研究了退火对高熵合金微观组织、力学性能和磁性能的影响。结果表明,随着Ga含量的增加,铸态合金组织由未添加Ga时(x=0)的FCC单相过渡到FCC+BCC双相,最终在Ga含量为25at%时(即x=1.25)转变为BCC单相。经过800℃和1000℃退火后,在FCC相内产生了棒状的析出物。双相组织的FeCoNi_2-xMnGa_x合金具有较好的磁性能和压缩性能,退火后合金的力学性能和磁性能均有所提高。FeCoNi_1.25MnGa_0.75合金1000℃退火后的力学性能最优,在形变量约为20%时的抗压强度为1852.5 MPa。FeCoNi_1.0MnGa_1.0合金1000℃退火后的饱和磁化强度最大,为121.8 emu/g。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.