丝电爆喷涂过程工艺参数对涂层性质的影响

采用气体放电式丝电爆装置进行丝电爆喷涂试验,利用扫描电镜分析涂层性质特点,认识喷涂距离和能量密度对涂层性质的影响。结果表明,在不同工艺参数下,可获得四类性质的涂层,其中液相喷涂层和气相沉积涂层与基体结合强度较高;沉积在金属丝上能量密度和喷涂距离直接影响涂层性质。     

粉末电热爆炸喷涂方法制备钼涂层的工艺试验

利用粉末电爆喷方法制备涂层的过程中,爆炸产物粒径的大小分布对所形成的涂层质量和均匀性有重要影响。采用自主开发的连续粉末电爆喷涂设备,改变粉末涂敷量和初始充电电压等工艺参数,在304不锈钢基体上进行钼粉电爆炸喷涂试验,得到不同工艺参数下的钼涂层。通过分析其表面和截面的组织,研究了电热爆炸喷涂的工艺参数与爆炸产物粒径的大小分布之间的相关性。结果表明:初始电压和粉末涂敷量对爆炸产物粒径的分布均有影响。初始电压由小升大的过程中,产物粒径大小总体上先减小后增大,初始电压过高还会发生沿面放电现象。粉末涂敷量由少变多,产物粒径大小总体上增大。     

电爆过程中能量密度与爆炸产物变化的关系

电爆应用于材料喷涂有独特优势.电爆过程中爆炸产物的特性及其演变直接影响涂层质量.利用高压电场中金属丝段电爆方法,通过改变初始充电电压和金属丝的直径,调节沉积在金属丝上的能量密度,进行系列电爆试验;同时,利用探针收集电爆过程中的产物并进行显微分析.结果表明,金属丝电爆最初产物中含有液相和气相,随着膨胀距离的增大转变为固相.当基体处在爆炸产物未凝固的膨胀距离内,可得到液相喷涂层或气相喷涂层.提高能量密度可以提高产物中气相的膨胀距离,同时减少产物中液相成分所占比例.当能量密度大于125 J/mm3,爆炸产物中液相成分可达5%,气相膨胀距离约为9.5 mm.     

管内壁的粉末电爆喷涂工艺

开发了小口径管内壁连续送粉电爆喷涂设备,适用于内径最小为Φ50 mm的管内壁涂层的制备。使用多种粒径的Ni60A合金粉末进行了电爆喷涂试验,分析粉末粒径对涂层形成的影响。结果表明:在本试验参数范围内,粉末粒径越小、电压越高,电爆过程中能量沉积越多,获得的涂层结合强度越高。在加热阶段,放电回路中会产生旁路电流,该电流阻碍了能量向粉末上沉积。通过减小粉末粒径或增大初始充电电压可延迟旁路电流的发生,增加粉末上的能量沉积率。     

粉末电爆喷涂方法制备Ti3SiC2涂层

在自制的连续送粉电爆喷涂设备上,以Ti3SiC2粉末为电爆喷涂材料制备了Ti3SiC2涂层.根据所制备涂层的表面形貌和截面特征,分析了充电电压、粉末粒径、石墨掺入量对电爆喷涂过程的影响.结果表明,粉末粒径为28μm,充电电压高于15 kV、掺入的石墨粉为10％时,涂层沉积率较高,均匀性较好.XRD分析表明,涂层由TiC...     

管约束WC粉末电爆喷涂涂层的形成

采用压敏胶载送粉末连续电爆喷涂方法,进行WC粉末电爆喷涂,分析初始电压与喷射腔横截面积对涂层形成的影响。结果表明:在3~7 mm喷涂范围内,可形成表层为液相喷涂层和底层为气相沉积层的复合涂层。在较小的喷射腔横截面积下升高初始电压,能提高爆炸的区域温度和产物速度,增加气相份额。分析认为:气相优先形成气相沉积层,且气相沉积层与基体结合致密;残留的液相滞后喷射,并覆盖在气相沉积层上形成液相喷涂层。     

初始充电电压对电爆产物尺度分布的影响

在丝电爆过程中,初始充电电压对最终的纳米粉尺度分布有重要影响。在气体放电式丝电爆装置上进行系列试验,通过分析爆炸产物尺度分布及其形成原因,认识初始充电电压的影响。结果表明,在初始充电电压较低时,纳米粉中纳米级颗粒的平均粒径、微米级大颗粒比例随初始充电电压升高而逐渐减小,而初始充电电压过高时,纳米级颗粒平均粒径、微米级大颗粒比例反而会随初始充电电压的升高而增大。分析可知,在初始充电电压过高时,丝表面发生沿面放电现象,会阻碍能量向金属丝沉积。     

丝电爆炸喷涂方法用于管内壁钼涂层的制备

开发一种管内壁连续丝电爆炸喷涂装置,在不锈钢管内进行钼丝的电爆炸喷涂试验,分析不同能量密度下涂层的表面形貌以及与基体的结合形态.结果表明,涂层主要是由爆炸产物中熔融液滴直接撞击基体表面形成.随着能量密度的提高,涂层由液相堆积层向液相喷涂层转变;进一步增大能量密度E,当E>350 J/mm3时,熔融金属粒子尺寸减小,温度增高,冲击速度变大,从而获得表面平整喷涂层,该类型涂层与基体结合强度高,但爆炸产物中的气相粒子份额增多,涂层的沉积率降低.     

腔内约束电热爆喷涂涂层的形成

在内径为7 mm的聚乙烯爆炸腔进行钼丝的电热爆喷涂试验,用扫描电镜观察涂层的表面和截面形貌、涂层厚度,分析涂层与基体的结合情况.结果表明,爆炸腔内钼丝的爆炸产物在基体上会形成一个喷涂圆面,由中心涂层区和外围粘结层组成.中心涂层区在喷涂距离5～8 mm时,所得涂层致密、厚度均匀,与基体结合良好,局部界面附近存在元素扩散现象;外围粘结层随喷涂距离的增大而消失.大面积喷涂层可由单个喷涂圆面的合理搭接来形成,通过多次喷涂可增加涂层的厚度.     

用均匀设计法试验研究超音速电弧喷涂Ti-Al合金涂层结合强度与其工艺参数之间的关系

采用SAS－Ⅱ型超音速电弧喷涂设备，在LY12合金基体上制备Ti-Al合金涂层，用均匀设计法对超音速电弧喷涂电压、电流和喷涂距离等工艺参数对涂层结合强度的影响规律进行了试验研究与优化。结果表明，喷涂电压、喷涂电流和喷涂距离对涂层的结合强度均有影响，并且电压和电流之间存在交互作用。其中喷涂距离对结合强度的影响最大，呈二次非线性递减规律；其次是喷涂电压，其对涂层结合强度的影响为线性递增规律；而喷涂电流对涂层结合强度的影响因受喷涂电压的制约呈二次抛物线规律变化。在本试验条件下，获得的最佳喷涂工艺参数为：喷涂电压为38V，喷涂电流100A，喷涂距离为5cm。     

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.