石墨上化学气相沉积SiC组织特征与性能

利用压汞法、SEM和EDS等分析手段对石墨及化学气相沉积SiC组织结构进行了研究.石墨试样的比表面测试显示:经2200℃高温处理石墨试样的比表面积较未处理试样增大了近34%.石墨试样的孔径分布显示:高温处理石墨试样的孔径分布在＜10 nm和＞200 nm有所增加,而界于两者之间的中型孔径分布略有降低,从而证明了热处理中大量原子发生一定范围的重排.SEM和EDS分析表明,高温处理过的石墨沉积SiC具有CVI结构特征;经过高温处理的石墨SiC沉积呈CVI特征,而未经高温处理石墨沉积的SiC呈典型CVD特征.对CVD SiC/graphite再经1600℃处理,对强度影响不大.     

电磁场辅助CVI沉积SiC/PyC复合材料的磨损性能（英文）

采用电磁场辅助CVI沉积在SiC陶瓷基体上沉积热解炭,制得具有自润滑性和耐磨性的SiC/PyC复合材料。利用XRD、SEM和EDS等手段对SiC/PyC材料的成分和显微结构进行表征,研究沉积温度对SiC/PyC材料的截面结构和耐磨性能的影响。结果表明,在较低温度下可将热解炭引入SiC基体,并可降低与自对偶材料在干滑动摩擦条件下的磨损率。磨损试验结果表明,在沉积温度为800℃条件下制得的SiC/PyC材料具有较优的抗磨损性能,其磨损率为未沉积热解炭的SiC材料磨损率的64.6%。     

金刚石表面镀覆碳化硅的研究

采用硅粉与金刚石颗粒混合粉体为原料,通过高温热处理在金刚石表面镀覆SiC晶体,用XRD、SEM和EDS分析产物的物相组成与显微形貌,同时研究金刚石镀钛对金刚石表面涂覆SiC状态的影响。研究结果表明:采用硅粉和金刚石混合粉体为原料,高温1400℃处理后,在金刚石表面上形成了SiC,但并没有形成连续的涂层,同时金刚石发生一定程度的石墨化。选用镀钛金刚石后,在较低温度(1200℃),金刚石表面上会形成TiC和Ti3SiC2;当温度升高到1300℃时,金刚石表面形成TiC、Ti3SiC2和SiC;温度升高到1400℃时,金刚石表面镀覆了较厚的SiC和Ti3SiC2涂层。     

TBCs对DD6单晶高温持久性能的影响研究

利用离子镀技术和电子束物理气相沉积(EB-PVD)技术在DD6单晶基体表面依次制备NiCoCrAlYHf粘结层和YSZ陶瓷面层.研究了TBCs对DD6单晶1100℃/130 MPa高温持久性能的影响.采用SEM、EDS等检测技术对高温持久性能检测后的试样进行分析.结果 表明,DD6单晶沉积TBCs涂层后,1100℃高温...     

SiC 涂层对不同碳基体氧化防护行为的研究

为了提高碳材料的抗氧化性能,采用料浆烧结法在石墨和C/C复合材料上制备了SiC 抗氧化涂层.测试了SiC涂层在1200℃的高温下对不同碳基体的氧化防护能力,利用扫描电子显微镜 (SEM)、X-射线衍射仪(XRD)对涂层结构进行分析.结果表明:SiC涂层对不同碳材料的抗氧化防护行为有很大差异,在1200℃的高温下SiC涂层对石墨具有较好的抗氧化性能,而对C/C复合材料的氧化防护性能较差.     

高温过滤支撑体用SiC基多孔陶瓷的制备与表征

通过以平均粒径300 μm的SiC为骨架材料,特定配比的高岭土、长石和二氧化硅的混合物为粘结剂,制备了可用于高温过滤膜管支撑体的SiC基多孔陶瓷.将粘结剂在1300 ℃烧结并保温1 h,X射线衍射(XRD)分析表明粘结剂中主要为石英相和玻璃相.多孔陶瓷的气孔率随着粘结剂含量从3%增加到15%(质量分数,下同)先升高后降低,其抗弯强度随着粘结剂含量的增加而增加.在粘结剂含量为10%时,多孔陶瓷的气孔率和抗弯强度都取得了较高的值,分别是34.3%和36.6 MPa.压汞法测得其平均孔径为24 μm,孔径分布较窄.用X射线能谱(EDS)测得不同SiC颗粒粘结处的粘结剂的元素组成,并与粘结剂设计组成对比,结果显示粘结剂各组分在多孔陶瓷中分布较均匀.利用扫描电子显微镜(SEM)观察了多孔陶瓷试样条断面的形貌.研究表明此多孔陶瓷可用作高温煤气过滤管的支撑体材料.     

Al4SiC4陶瓷的高温氧化行为

从高温氧化动力学、组织的微观进化及高温氧化机理3部分对Al4SiC4陶瓷在1200℃-1700℃的高温氧化行为进行了系统的研究。研究结果表明，Al4SiC4陶瓷具有优异的高温抗氧化性能。氧化动力学符合抛物线规律，其氧化活化能经计算为220kJ／mol。XRD及SEM研究结果表明：Al4SiC4陶瓷在1200～1500℃的氧化表面物相为Al2O3和铝硅酸盐玻璃；而高温氧化表面（1600℃～1700℃）的物相由Al2O3，莫来石和铝硅酸盐玻璃构成。由氧化试样横截面观察得知氧化层按其特征的不同分为3个部分：具有较多细小尺寸孔洞的反应层；具有较大尺寸孔洞的中间层和致密的外氧化层。在高温抗氧化机理部分中首先从热力学上计算了氧化过程中各反应的生成焓和吉布斯自由能；然后对高温氧化过程进行了推理和分析；最后根据上述试验及推理结果建立了Al4SiC4陶瓷的高温抗氧化模型。     

二硅化钼涂层对碳化硅电热元件高温抗氧化性能的影响

采用MoSi2粉末自烧结方法，在SiC电热元件表面制备一层致密的MoSi2高温抗氧化涂层，并对其高温抗氧化性进行测试。抗氧化试验在空气中1500℃炉温下进行118h和32次热循环，结果表明，带有MoSi2涂层的试样表面致密光洁，且试样抗氧化性能随MoSi2涂层厚度增加。SEM和EPMA显微分析表明，MoSi2涂层与SiC基体结合较好，没有起层和剥落，涂层中Mo分布均匀，损失约为20％。     

Ti对9Cr-3Si-Al铁素体耐热钢微观组织及力学性能的影响

研究了Ti元素对9Cr-3Si-Al系铁素体耐热钢显微组织以及力学性能的影响。研究发现试验钢锻态试样晶粒内分布着大量的碳化物颗粒且细小均匀,经固溶处理后部分碳化物颗粒溶入试样基体。结合XRD以及EDS能谱分析试样表面的碳化物颗粒主要为Ti(C,N)的MX相,而晶界上检测到少量的Cr₂₃C₆相。经600 ℃时效后试样的抗拉强度、屈服强度均明显高于固溶态试样。通过对室温以及650 ℃高温断口形貌观察,发现室温下的断口为脆性断口,呈河流花样状,周围有少量微孔,为准解理断裂;而高温下断口呈微孔聚集型特征,韧窝密度较大,韧性较好。     

超声冲击处理对高合金钢表面高温耐磨损性能的影响

采用超声冲击设备对高合金钢进行冲击加工,并对冲击后的试样进行400℃退火2 h处理。通过扫描电镜(SEM)、显微硬度仪和高温摩擦磨损仪研究了超声冲击处理后试样的显微组织、硬度分布和高温环境下的摩擦磨损性能;采用光学显微镜和SEM观察试样磨损表面和磨痕的微观形貌,使用能谱仪(EDS)分析磨损表面的元素组成,以研究其磨损机理。结果表明,经超声冲击处理的高合金钢,在温度低于500℃时摩擦系数为0.3～0.4,磨损率为0.04%～0.05%,起伏较小。与原始试样相比,超声冲击处理使其表面形成一层梯度细化组织,表面硬度提高了15.8%,在同等高温条件下的摩擦系数降低了45.8%,磨损率降低了35.8%,表明其高温耐磨损性能经超声冲击处理后得到显著提升。     

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.     

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.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

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.