TC4钛合金表面Cr2AlC涂层的制备及高温氧化行为

目的为提高钛合金在高温条件下的服役性能,探索Cr_2AlC MAX相涂层对TC4钛合金高温氧化行为的影响。方法采用低温反应直流磁控溅射技术再经后续退火处理的方法,在TC4钛合金基体表面制备高纯度的Cr_2AlC MAX相涂层。利用X射线衍射仪、拉曼光谱仪、扫描电子显微镜和能谱仪,分析了Cr_2AlC涂层试样和TC4钛合金经750℃静态空气恒温氧化前后的相结构、组织形貌和组分,并采用分析天平测定了TC4钛合金和Cr_2AlC涂层试样在750℃静态空气中氧化后的氧化动力学曲线。结果经750℃空气中氧化10 h后,TC4钛合金表面形成厚度达13μm的疏松团絮状TiO_2和Al_2O_3混合物氧化膜。而Cr_2AlC涂层表面能够形成以α-(Al,Cr)2O3为主的致密氧化膜,可有效阻止氧元素向内扩散。Cr_2AlC涂层试样在750℃空气中氧化90 h后的氧化增重仅为无涂层TC4钛合金在750℃空气中氧化10 h后的6.6%。结论 Cr_2AlC涂层具有优异的抗高温氧化性能,能够明显提高TC4钛合金的使用温度,使其氧化增重速率大幅降低。     

电弧复合磁控溅射结合热退火制备Ti2AlC涂层

利用电弧复合磁控溅射技术制备不同Ti/Al比的Ti-Al-C涂层,结合后续的退火处理制备Ti_2AlC相涂层。利用SEM、EDS、XRD、Raman光谱仪和TEM等研究了Ti/Al比及退火温度对退火后Ti-Al-C涂层的相和微观结构的影响。结果表明,Ti-Al-C沉积态涂层为富Al层和TiCx层交替堆垛的多层结构,涂层表面大颗粒较少且结构致密。Ti/Al比对退火后涂层中的相结构有重要的影响:当Ti/Al比为2.04时,退火后涂层中Ti_2AlC的纯度和结晶度最高;Ti/Al比过高(3.06)时,退火后涂层中形成TiC和Ti_3AlC杂质相,而低Ti/Al比(0.54)则大幅度降低Ti_2AlC相的纯度和结晶度。同时,退火温度很大程度影响Ti_2AlC相的形成,当沉积态涂层中Ti/Al比为2.38时,Ti_2AlC相涂层形成的最佳退火温度为750℃,偏低的退火温度(600℃)下,原子不能充分扩散,难以形成211结构的Ti_2AlC相,而退火温度过高时(900℃)涂层中存在较多的TiC、TiAlx等杂质相。     

氮气流量及后续热处理对多弧离子镀制备Ti2AlN涂层的影响规律

利用电弧离子镀技术在1Cr18Ni9Ti基材上低温沉积Ti-Al-N涂层,研究氮气流量及热处理工艺对涂层微观组织结构的影响。结果表明,沉积态涂层中不含三元层状陶瓷Ti_2AlN MAX相,可能含有Ti_3AlN(反钙钛矿结构)、TiN、α-Ti、fcc-Al及Ti_xAl_y金属间化合物等。涂层经退火后在一定条件下可以形成Ti_2AlN。涂层中的N元素含量及退火温度对Ti_2AlN的形成起到重要作用。N元素含量过多不利于Ti_2AlN的形成;提高退火温度可以促进Ti_2AlN的形成。透射电镜(TEM)分析结果表明,退火过程中Ti_2AlN的形成伴随着涂层微观组织结构的转变,从明显的层状结构转变为细小的等轴晶结构。     

以Cr_3C_2为碳源合成Cr_2AlC陶瓷粉体及其动力学

以Cr、Al、Cr_3C_2为原料,在700~1350℃温度范围内氩气环境下,采用无压烧结法合成Cr_2AlC陶瓷粉体。研究了原料组成、烧结温度对合成Cr_2AlC的影响。结果表明,原料摩尔比为1 Cr_3C_2/2.2Al/1Cr,温度1250℃时,样品中含有少量Cr_7C_3杂质,温度升高到1350℃时,获得高纯的Cr_2AlC陶瓷。温度低于800℃时,Cr_3C_2和Al反应生成Cr_2AlC和Al_4C_3。950℃时Cr2Al和C反应得到Cr_2AlC。1350℃Cr_2Al、Cr_3C_2和Al反应生成目标相Cr_2AlC。用Kissinger方法和Owaza方法计算得到反应的表观活化能分别为362.24 k J/mol和389.01 k J/mol。     

轰击离子能量对V2AlC MAX相涂层结构及力学性能的影响

采用物理气相沉积（PVD）磁控溅射沉积方法,通过改变轰击离子能量制备高密度的V₂AlC涂层,并探究不同轰击离子能量对涂层结构和性能的影响。利用能谱仪测试、X射线衍射、拉曼光谱、扫描电镜、原子力显微镜对涂层的化学组成、相结构、表面与截面形貌进行分析,同时利用纳米压痕测试评价V₂AlC涂层力学性能。结果表明,提高轰击离子能量从15 eV到35 eV可以有效使得V₂AlC涂层致密化,且降低涂层表面粗糙度~50%（从~20.2 nm到~11.9 nm）,同时提高涂层的硬度~50%（从~14 GPa到~21 GPa）,与杨氏模量~20%（从~309 GPa到~363 GPa）。但当轰击离子能量升高到50 eV时,Al元素含量急剧下降,涂层由V₂AlC相转变为V₂C与VC多相混合。轰击离子能量的提高有效改善V₂AlC涂层的结构,提高V₂AlC涂层的硬度,杨氏模量,但需控制轰击离子能量改变范围才可实现结构与性能最优化。     

HiPIMS复合热处理制备高纯Ti2AlC MAX相涂层

Ti₂AlC MAX相涂层是一类兼具金属和陶瓷特性的具有密排六方结构的高性能陶瓷涂层,在电接触、高温防护、宽温域摩擦等领域具有广阔的应用前景。然而MAX相涂层的成相成分窗口窄,性能受杂质相影响大,实现高纯、致密Ti₂AlC MAX相涂层的制备目前仍存在挑战。考虑沉积气压与溅射等离子体能量密切相关,采用高功率脉冲复合直流磁控溅射技术在钛合金基体上制备了TiAl/Ti-Al-C涂层,经后续热处理退火得到高纯Ti₂AlC MAX相涂层,重点研究不同沉积气压对涂层退火前后的成分、微观结构以及力学性能的影响和作用机制。结果表明,随着气压不断增大,沉积态涂层厚度先增加后减少。其中低沉积气压下沉积态涂层退火后,结构中除了Ti₂AlC MAX相外,还含有一定量杂质相;而在高气压下沉积态涂层退火后几乎全部转变为Ti₂AlC MAX相,呈现高纯、表面光滑致密的MAX相涂层特征。相较于沉积态涂层,退火后的涂层硬度变化不大,但由于生成了Ti₂AlC MAX相,涂层弹性模量有所提高...     

真空退火对多弧离子镀Ti-Al-N涂层的影响

采用多弧离子镀技术和后续的真空退火工艺在06Cr19Ni10不锈钢基体上制备了Ti2AlN涂层;研究了多弧离子镀工艺及退火处理对涂层的成分、相组成以及摩擦系数等性能的影响。结果表明,沉积时氮气通量以及退火温度的选择是Ti2AlN相形成的关键因素,在氮气通量40 nm3/h、负偏压400 V、靶电流75 A、占空比90%的条件下镀制的涂层经700℃真空退火获得了纯度较高的Ti2AlN涂层,其硬度为7.2 GPa,摩擦系数仅为0.18。     

纯铁表面三价镀铬/渗氮复合处理制备CrN/Cr_2N涂层

采用预三价镀铬再穿透气体渗氮的方法,在纯铁表面制备CrN/Cr_2N涂层。研究不同镀铬层厚度、渗氮温度和时间所形成涂层的微观结构和相组成变化规律。随渗氮温度从540℃提高到700℃,镀铬层相结构变化为:Cr→CrN/Cr_2N(具有超点阵结构的Cr_2N)→CrN/Cr_2N。在同一温度(640℃)渗氮,随时间延长,Cr→CrN/Cr_2N,形成大量具有超点阵结构的Cr_2N相。SEM/EPMA测试结果表明,采用该复合处理制备的氮化铬层与基体间可形成互扩散的冶金结合,实现氮化铬层与基体间在组织结构上的平缓过渡,有利于提高涂层性能。     

Cr_2AlC陶瓷粉体的无压烧结及表征

本文以Cr、Al和C粉为原料,采用无压烧结合成了纯相的Cr_2AlC粉体。研究了烧结温度对合成物相的影响,得出最佳烧结温度为1400℃。分析反应路径,发现Al先熔化成Al液,同时引发Cr和Al反应生成Cr2Al及少量Cr_2AlC。Cr-Al金属间化合物再与C和Al发生反应最终合成Cr_2AlC。掺杂Si元素后发现Cr_2AlC晶格常数变化,说明Si固溶到Cr_2AlC当中。     

钛合金表面Cr_2O_3颗粒增强复合搪瓷涂层的抗高温氧化性能研究

通过在TC4钛合金的搪瓷涂层釉料中添加0%～50%的Cr_2O_3陶瓷颗粒,制备出了搪瓷涂层。利用XRD、EDS、SEM和体视显微镜观察搪瓷涂层的微观结构、界面形貌及相组成。结果表明:随着涂层中Cr_2O_3陶瓷颗粒加入量的增加,搪瓷涂层的致密度增加,但添加量超过30%以后,涂层变得疏松,涂层中添加20%～30%的Cr_2O_3陶瓷颗粒,其致密性最好;不含Cr_2O_3陶瓷颗粒的涂层组织主要由玻璃相和少量的点状晶体组成,当添加Cr_2O_3陶瓷颗粒的量小于30%时,晶体呈点状弥散分布;当Cr_2O_3含量大于30%时,晶体呈树枝状分布;搪瓷涂层中主晶相为NaAlSi_3O_8和Ca_2SiO_4,加入的Cr_2O_3陶瓷颗粒部分以独立相存在,部分形成Ca_5Cr_3O_(12)相;添加30%Cr_2O_3陶瓷颗粒的搪瓷涂层抗高温氧化性能最好,这主要是因为NaAlSi_3O_8转变为Na_2Si_2O_5,有利于涂层的自愈合。     

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.